MIC Results Research Articles

Endocarditis due to Gram Positive Anaerobic Cocci: First report of Peptoniphilus indolicus endocarditis and literature review

Abstract Background Gram positive anaerobic cocci (GPAC) are rare causes of Infective Endocarditis (IE). We report the first case of Peptinophilus indolicus endocarditis 2 months after valve replacement. We reviewed all cases of GPAC IE listed in PubMed and identified main characteristics of these infections. Case report A 82-year old man presented a 48H fever with transcatheter valve replacement 2 months earlier. Hyperleukocytosis and high C-Reactive protein level were found. Gram positive cocci grew on anaerobic blood cultures. Peptoniphilus indolicus was identified, susceptible to Penicillin G (MIC Results P. indolicus are Gram Positive Anaerobic Cocci (GPAC) bacteria described in deep infections. In this case, IE occurred early after intervention without any secondary embolic complication. We reviewed 34 cases reports-series of GPAC IE. They are more often observed in male patients with mean age of 52 years and occur mainly on prosthetic valve. GPAC are described as susceptible bacteria towards antibiotics. Penicillin G, amoxicillin are first-choice molecules with 6 weeks duration of treatment. We compared GPAC to streptococcal and anaerobic Gram-Positive Bacilli (GPAB) IE. Anaerobic IE occur more often on prosthetic valves compared with streptococci IE. Surgical treatment was more frequently performed in anaerobic IE than in streptococci IE. Amoxicillin MIC was lower for anaerobic compared with streptococci IE. A lower mortality rate seems to be observed with GPAC than streptococci IE. Conclusion We reported the first case of Peptoniphilus indolicus IE. These GPAC IE occur mostly on prosthetic valves without embolic complications, are susceptible to antibiotics and lead to frequent favorable outcome of the patients.

A rapid MALDI-TOF mass spectrometry-based method for colistin susceptibility testing in Escherichia coli.

SummaryColistin is recognized as a last‐resort treatment option against multi‐drug resistant bacteria including carbapenem‐resistant Enterobacteriaceae (CRE). However, the plasmid‐mediated colistin‐resistance gene mcr‐1 has been reported globally resulting in an increase of colistin‐resistant bacteria. A quick and accurate method for determining the pathogen resistance of colistin is therefore crucial in the clinic. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) is a potential tool forto be applied for antimicrobial susceptibility testing. We compared the growth of Escherichia coli strains in the presence or absence of colistin. Automated analyses of the spectra were performed with a prototype software tool written with package R. Three mcr‐1‐positive and six mcr‐1‐negative E. coli were used for establishing the model to obtain the optimal incubation time, the breakpoint concentration of colistin and cut‐off of the relative growth (RG) value. The distinction between susceptible and resistant strains was already noticeable after 2 h of incubation. The best separation between the susceptible and resistant strains was achieved at a concentration of 4 µg ml‐1 and a relative growth cut‐off value of 0.6. Application of the model for the analysis of 128 E. coli isolates, a sensitivity of 97.4% and a specificity of 88.2% were achieved compared with colistin MIC results. The rapid MALDI‐TOF MS‐based method approach is simple to set‐up, uses a short incubation time, and had excellent outcomes with respect to sensitivity and specificity for colistin sensitivity testing in Escherichia coli.

IMMOBILIZATION AND APPLICATION OF PARTIAL PURIFIED LOVASTATIN PRODUCED FROM LOCAL ISOLATE ASPERGILLUS TERREUS A50 USING SOLID STATE FERMENTATION

This work was designed to study the free and immobilized partial purified lovastatin in various applications. The results of HMG-CoA reductase inhibition showed enzyme inhibition at 10 mM of standard and partial purified lovastatin with specific activity 0.056 and 0.062 U/mg protein respectively, compared with specific activity 0.277 U/mg protein without inhibitor. The results of the thermal stability and storage time on lovastatin for inhibition of HMG-CoA reductase demonstrated that the standard and partial purified lovastatin were stabled in temperatures between 20-40 ᵒC, then the stability begun to decrease at 45 ᵒC, while lovastatin was stable in storage time between 1- 8 hours, then the stability begun to decrease after ten hours at 40 ºC. The results of MIC for lovastatin were demonstrated that most tested concentration were showed antibacterial activity of free and immobilized partial purified lovastatin against Candida albicans, Escherichia coli, and Staphylococcus aureus with MIC values ranging from 15 to 75 µg/ml. Whereas the results of minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) showed that C. albicans, E. coli, and S. aureus had no growth with concentration ranging from 55 to 75, 55 to 75, and 30 to 75 µg/ml, respectively. As well as the results of the cytotoxic impact using MTT experiment indicated that partial purified lovastatin caused a reduction in cells viability (p ≤ 0.05) at a dose-dependent manner on MCF-7 cell lines, with a calculating IC50 of 138.1 µg/ml, compare with normal cell line (WRL 68 Cell Line) at IC50 of 198.7 µg/ml.

Clinically Relevant Concentrations of Polymyxin B and Meropenem Synergistically Kill Multidrug-Resistant Pseudomonas aeruginosa and Minimize Biofilm Formation.

The emergence of antibiotic resistance has severely impaired the treatment of chronic respiratory infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa. Since the reintroduction of polymyxins as a last-line therapy against MDR Gram-negative bacteria, resistance to its monotherapy and recurrent infections continue to be reported and synergistic antibiotic combinations have been investigated. In this study, comprehensive in vitro microbiological evaluations including synergy panel screening, population analysis profiling, time-kill kinetics, anti-biofilm formation and membrane damage analysis studies were conducted to evaluate the combination of polymyxin B and meropenem against biofilm-producing, polymyxin-resistant MDR P. aeruginosa. Two phylogenetically unrelated MDR P. aeruginosa strains, FADDI-PA060 (MIC of polymyxin B [MICpolymyxin B], 64 mg/L; MICmeropenem, 64 mg/L) and FADDI-PA107 (MICpolymyxin B, 32 mg/L; MICmeropenem, 4 mg/L) were investigated. Genome sequencing identified 57 (FADDI-PA060) and 50 (FADDI-PA107) genes predicted to confer resistance to a variety of antimicrobials, as well as multiple virulence factors in each strain. The presence of resistance genes to a particular antibiotic class generally aligned with MIC results. For both strains, all monotherapies of polymyxin B failed with substantial regrowth and biofilm formation. The combination of polymyxin B (16 mg/L)/meropenem (16 mg/L) was most effective, enhancing initial bacterial killing of FADDI-PA060 by ~3 log10 CFU/mL, followed by a prolonged inhibition of regrowth for up to 24 h with a significant reduction in biofilm formation (* p < 0.05). Membrane integrity studies revealed a substantial increase in membrane depolarization and membrane permeability in the surviving cells. Against FADDI-PA107, planktonic and biofilm bacteria were completely eradicated. In summary, the combination of polymyxin B and meropenem demonstrated synergistic bacterial killing while reinstating the efficacy of two previously ineffective antibiotics against difficult-to-treat polymyxin-resistant MDR P. aeruginosa.

False amoxicillin/clavulanic acid susceptibility in Bacteroides fragilis using gradient strip tests

BackgroundRepeatedly, too low MIC results were obtained in Bacteroides fragilis quality assessment strains, using gradient strip tests with a ratio of amoxicillin:clavulanic acid of 2:1. We aimed to find the most accurate available gradient strip tests for susceptibility testing of amoxicillin/clavulanic acid in B. fragilis in comparison with agar dilution with EUCAST methodology and breakpoints. MethodsTwenty-seven clinical B. fragilis isolates were investigated using gold standard EUCAST amoxicillin/clavulanic acid agar dilution (fixed clavulanic acid concentration at 2 mg/L, with increasing amoxicillin concentrations) as well as three commercial gradient strip tests: XL (ratio), AUG (ratio) or AMC (fixed concentration). ResultsUsing agar dilution (fixed concentration), 19 isolates were susceptible, 1 isolate was susceptible increased exposure (I) and 7 isolates were resistant. Categorical agreement of the gradient strip tests with agar dilution (fixed concentration) was 70% for XL (ratio), 71% for AUG (ratio) and 89% for AMC (fixed concentration). Very major error rates in comparison with agar dilution (fixed concentration) were 100%, 0%, and 0%, respectively. ConclusionsEUCAST breakpoint usage in amoxicillin/clavulanic acid susceptibility tests for B. fragilis should be accompanied by EUCAST methodology. When using alternative methods such as gradient strip tests, a higher degree of alignment with EUCAST methodology, such as using fixed clavulanic acid concentrations, improves precision.

Emergence of two AcrB substitutions conferring multidrug resistance to Salmonella spp.

AcrAB-TolC is a major tripartite multidrug efflux pump conferring resistance to a wide variety of compounds in Gram-negative pathogens. Many AcrB mutants have been constructed through site-directed mutagenesis to probe the mechanism of AcrB function in antibiotic resistance. However, much less is known about the actual drug resistance related mutants that naturally occur in clinically isolated pathogens. Here, we report two novel AcrB substitutions, M78I and P319L, in clinically isolated Salmonella strains with high-level ciprofloxacin resistance. Plasmids expressing the detected acrB mutations were constructed and introduced into SL1344△acrB Antimicrobial susceptibility assay showed that all AcrB M78I, AcrB P319L and AcrB M78I/319L conferred reduced susceptibilities to multiple substrates, including fluoroquinolones, erythromycin, tetracyclines, bile salts and dyes. Site-directed mutagenesis and MIC results revealed that increased hydrophobicity of M78I was one of the reasons why AcrB M78I had lower susceptibility to fluoroquinolones. Fluorescence labeling experiments suggested that the AcrB M78I substitution enhanced the binding of substrates to certain amino acid sites in the efflux pathway (e.g., site Q89, E673 and F617) and weakened the binding to other amino acids (e.g., S134 and N274). Structural modeling disclosed the increased flexibility of Leu was favorable for the functional rotation of AcrB compared to the original Pro. AcrA 319L makes the functional rotation of AcrB more flexible, this enables substrate efflux more efficiently. In order to understand the mechanism of AcrAB-TolC drug efflux well, interaction between AcrA and AcrB in the role of substrate efflux of AcrAB-TolC should be further investigated.

Antimicrobial and antibiofilm potential of Curcuma longa Linn. Rhizome extract against biofilm producing Staphylococcus aureus and Pseudomonas aeruginosa isolates.

More than 65% of all human bacterial infection are associated with biofilm. Bacteria in such biofilms are 10 to 1000-fold more resistant to antibiotics than free living bacteria cells. Organisms such as S. aureus and P. aeruginosa are responsible for a significant number of biofilm related infections. In this study, we investigated the antimicrobial and anti-biofilm activity of C. longa L. rhizome extract against biofilm producing S. aureus and P. aeruginosa isolates. The results of MIC and MBC demonstrated promising antibacterial activity of the rhizome extract. TLC and column chromatography detected various curcuminoids while phytochemical analysis also reveals presence of number of bioactive compounds such as alkaloids, flavonoids, phenolics, terpenoids, etc. Micro titer plate assay indicated significant inhibition of biofilm formation in clinical isolates treated with turmeric extract. Thus, on basis of our results turmeric extracts can be considered as natural antibiofilm and antibacterial agent.

Evaluation of a Commercial Broth Microdilution Panel for Colistin Susceptibility Testing of Clinical Isolates of Escherichia coli and Klebsiella pneumoniae.

Colistin is among the last resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative pathogens. Antimicrobial susceptibility testing of colistin is challenging due to its physicochemical properties. Broth microdilution (BMD) is the recommended method for colistin susceptibility testing. However BMD is not practical for clinical microbiology laboratories as manual preparation of BMD plates is time-consuming and labor intensive. Recently, some more user-friendly BMD products with commercial panels have become available. Our objective was to evaluate the performance of a commercial broth microdilution (BMD) product [Sensititre (Thermo Fisher Scientific)] for colistin MIC determination by comparison with reference BMD method using a collection of E. coli and K. pneumoniae isolates. A total of 323 unique patient isolates (102 E. coli, 221 K. pneumoniae) were included in the study. Isolates were stored at -70°C and subcultured twice on sheep blood agar before testing. Colistin MICs of the isolates were determined using Sensititre (a premade BMD product with dried antibiotics) and an 'in-house prepared BMD panel prepared in accordance with CLSI guidelines' (reference method). MIC determination with Sensititre was performed according to manufacturer's instructions. The reference method was performed using untreated 96-well sterile polystyrene plates. Colistin MIC results were interpreted according to EUCAST breakpoints (susceptible, ≤ 2 mg/L; resistant, > 2 mg/L). Overall susceptibility rate of isolates to colistin by reference BMD was 75.9%. Overall categorical agreement (CA), essential agreement (EA), very major error (VME), and major error (ME) rates for Sensititre were 98.5%, 72.5%, 3.8%, and 0.8%, respectively. The CA and EA between Sensititre and reference BMD for the isolates with reference colistin MICs close to the susceptibility breakpoint (2 - 8 mg/L) was 94.2% and 48.1%, respectively. Sensititre yielded a VME rate of 15% and ME rate of 0%, respectively, for this subset of isolates. In conclusion, Sensititre showed high CA but low EA with reference BMD for entire collection of isolates. The VME rate was just slightly above 3% and ME rate was acceptable. The rates of CA and EA were decreased and the rate of VME was increased when a subset consisting of more challenging isolates was used.

1258. Activity of a Series of Investigational Compounds Tested Against Invasive Fungal Isolates

BackgroundFox Chase Chemical Diversity Center (FCC) is developing non-peptide analogs of host defense proteins for the treatment of invasive fungal infections mainly caused by Candida (CAN) and Aspergillus (ASP). We evaluated the activity of 6 novel compounds and 2 comparators against 150 isolates from 15 fungal groups.MethodsSusceptibility testing was performed per CLSI broth microdilution methods for investigational compounds and comparators against 70 CAN and 40 ASP isolates in addition to 10 Cryptococcus spp. (CRYP), 10 Fusarium spp. (FUS), 10 Mucorales, and 10 Scedosporium spp. (SCED) isolates from recent (2017-2019) clinical infections. MIC results were determined as ≥ 50% reduction at 24 and 72 hours for CAN and CRYP respectively, and 100% reduction at 24, 72, and 48 hours for Mucorales, SCED, and other moulds, respectively. CLSI clinical breakpoint (CBP) and epidemiological cutoff value (ECV) interpretive criteria were applied for comparators.ResultsCompounds FC10790, FC11083, FC11212, and FC11275 had MIC50 results at ≤ 0.015 mg/L and MIC90 results at ≤ 0.015 to 0.12 mg/L against CRYP, ASP, and FUS isolates. Compounds FC5096 and FC11022 were 2- to 4-fold less active while demonstrating MIC50 and MIC90 results of 0.03 to 0.5 mg/L against CAN, CRYP, ASP, and FUS isolates. The Mucorales isolate set showed the widest range of MIC results for FC compounds. FC10790 exhibited the greatest potency with a MIC50/90 at 0.5/2 mg/L. FC compounds showed potent activity against SCED with MIC90 results of 0.03 to 0.25 mg/L. Fluconazole showed a wide range of MIC results, from 0.06 to >64 mg/L, but the highest results observed were for Candida auris (MIC50/90, 64/ > 64 mg/L) and Candida krusei (MIC50/90; 16/32 mg/L). Itraconazole was active against all ASP (MIC50/90, 1/1 mg/L), but showed poor activity against FUS (MIC50/90, > 8/ > 8 mg/L). Amphotericin B showed a narrow range of MIC results (0.5 to 2 mg/L) for all isolates except 1 ASP and most SCED.ConclusionNovel FCC compounds showed equal or greater activity than comparators against most CAN, ASP, SCED, and FUS. FC10790, FC11212, and FC11275 showed the greatest activity against all tested fungal isolates. development of this series of compounds for clinical studies.Table 1 DisclosuresPaul R. Rhomberg, n/a, Cidara Therapeutics (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Merck (Research Grant or Support) Shawn A. Messer, PhD, Amplyx Pharmaceuticals (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support) Richard W. Scott, PhD, Fox Chase Chemical Diversity Center (Employee) Simon DP Baugh, PhD, Fox Chase Chemical Diversity Center (Employee) Michael A. Pfaller, MD, Amplyx Pharmaceuticals (Research Grant or Support)Basilea Pharmaceutica International, Ltd (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Department of Health and Human Services (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support) Mariana Castanheira, PhD, 1928 Diagnostics (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Amplyx Pharmaceuticals (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Cecilia G. Carvalhaes, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Pfizer (Research Grant or Support)

673. Updated CLSI Ciprofloxacin Breakpoints from a Multicenter Assessment for Enterobacterales, Salmonella spp. and Pseudomonas aeruginosa Using MicroScan Dried Gram Negative MIC Panels

BackgroundUpdated US FDA/CLSI ciprofloxacin breakpoints were evaluated against data from a multicenter clinical study with Enterobacterales, Salmonella spp. and P. aeruginosa on a MicroScan Dried Gram-negative MIC (MSDGN) Panel. MIC results were compared to results obtained with frozen broth microdilution panels prepared according to CLSI methodology.MethodsMSDGN panels were evaluated at three clinical sites by comparing MIC values obtained using the MSDGN panels to MICs utilizing a CLSI broth microdilution reference panel. Data from the combined phases of efficacy and challenge included 803 Enterobacterales, Salmonella spp. and P. aeruginosa clinical isolates tested using the turbidity and Prompt® methods of inoculation. To demonstrate reproducibility, a subset of 12 organisms were tested on MSDGN panels at each site during reproducibility. MSDGN panels were incubated at 35 ± 1ºC and read on the WalkAway System, the autoSCAN-4 instrument, and visually. Read times for the MSDGN panels were at 16-20 hours. Frozen reference panels were prepared and read according to CLSI methodology. FDA and CLSI breakpoints (µg/mL) used for interpretation of MIC results were: Enterobacterales ≤ 0.25 S, 0.5 I, ≥ 1 R; Salmonella spp. ≤ 0.06 S, 0.12-0.5 I, ≥ 1 R; P. aeruginosa ≤ 0.5 S, 1 I, ≥ 2 R.ResultsEssential and categorical agreement was calculated compared to frozen reference panel results. Results for isolates tested during efficacy and challenge with Prompt inoculation and manual read are as follows: Read Method Essential Agreement (EA) % Categorical Agreement (CA) % Very Major Error (VMJ) % Major Error (MAJ) % Enterobacterales 93.8(646/689)97.7(673/689)0.0(0/146)0.0(0/535) Salmonella spp. 100(21/21)95.2(20/21)0.0(0/1)0.0(0/18) P. aeruginosa 94.6(88/93)91.4(85/93)0.0(0/29)1.7(1/58)ConclusionCiprofloxacin MIC results for Enterobacterales, Salmonella spp., and P. aeruginosa obtained with the MSDGN panel correlate well with MICs obtained using frozen reference panels using updated FDA/CLSI interpretive criteria in this multicenter study.* PROMPT® is a registered trademark of 3M Company, St. Paul, MN USA.BEC, the stylized logo and the BEC product and service marks mentioned herein are trademarks or registered trademarks of Beckman Coulter, Inc. in the US and other countries.Disclosures Maria M. Traczewski, BS MT (ASCP), Beckman Coulter (Scientific Research Study Investigator) Denise Beasley, BS, Beckman Coulter (Other Financial or Material Support, Research personnel) Amanda Harrington, PhD, Beckman Coulter (Scientific Research Study Investigator) Sharon DesJarlais, BS, Beckman Coulter (Other Financial or Material Support, Research personnel) Omai Garner, PhD, D(ABMM), Beckman Coulter (Scientific Research Study Investigator) Christine Hastey, PhD, Beckman Coulter (Employee) Regina Brookman, BS, Beckman Coulter (Employee) Zabrina Lockett, MS, Beckman Coulter (Employee) Jennifer Chau, PhD, Beckman Coulter (Employee)

667. Multicenter Assessment of Enterobacterales, Salmonella spp. and Pseudomonas aeruginosa Using Updated CLSI Levofloxacin Breakpoints on MicroScan Dried Gram Negative MIC Panels

BackgroundData from a multicenter clinical study with Enterobacterales, Salmonella spp. and P. aeruginosa on a MicroScan Dried Gram-negative MIC (MSDGN) Panel was evaluated with updated US FDA/CLSI levofloxacin breakpoints. MIC results were compared to results obtained with frozen broth microdilution panels prepared according to CLSI methodology.MethodsA total of 839 Enterobacterales, Salmonella spp. and P. aeruginosa clinical isolates were tested at three clinical sites in efficacy and challenge combined. MSDGN panels were evaluated with turbidity and Prompt® methods of inoculation. MIC values obtained from the MSDGN panels were compared to MICs utilizing a CLSI broth microdilution reference panel. To assess reproducibility, a subset of 15 organisms were tested on MSDGN panels at each site. MSDGN panels were incubated at 35 ± 1ºC and read on the WalkAway System, the autoSCAN-4 instrument, and visually. Read times for the MSDGN panels were at 16-20 hours. Frozen reference panels were prepared and read according to CLSI methodology. FDA and CLSI breakpoints (µg/mL) used for interpretation of MIC results were: Enterobacterales ≤ 0. 5 S, 1 I, ≥ 2 R; Salmonella spp. ≤ 0.12 S, 0.25-1 I, ≥ 2 R; P. aeruginosa ≤ 1 S, 2 I, ≥ 4 R.ResultsEssential and categorical agreement were calculated compared to frozen reference panel results. Results for isolates tested during efficacy and challenge with Prompt inoculation and manual read are as follows: Read Method Essential Agreement (EA) % Categorical Agreement (CA) % Very Major Error (VMJ) % Major Error (MAJ) % Enterobacterales 96.2(638/663)96.7(641/663)1.5(2/133)0.0(0/515) Salmonella spp. 100(83/83)98.8(82/83)0.0(0/19)0.0(0/38) P. aeruginosa 94.6(88/93)93.6(87/93)0.0(0/34)1.9(1/54)ConclusionLevofloxacin MIC results for Enterobacterales, Salmonella spp., and P. aeruginosa obtained with the MSDGN panel correlate well with MICs obtained using frozen reference panels using updated FDA/CLSI interpretive criteria in this multicenter study.* PROMPT® is a registered trademark of 3M Company, St. Paul, MN USA.BEC, the stylized logo and the BEC product and service marks mentioned herein are trademarks or registered trademarks of Beckman Coulter, Inc. in the US and other countries.Disclosures Omai Garner, PhD, D(ABMM), Beckman Coulter (Scientific Research Study Investigator) Maria M. Traczewski, BS MT (ASCP), Beckman Coulter (Scientific Research Study Investigator) Denise Beasley, BS, Beckman Coulter (Other Financial or Material Support, Research personnel) Amanda Harrington, PhD, Beckman Coulter (Scientific Research Study Investigator) Sharon DesJarlais, BS, Beckman Coulter (Other Financial or Material Support, Research personnel) Christine Hastey, PhD, Beckman Coulter (Employee) Regina Brookman, BS, Beckman Coulter (Employee) Zabrina Lockett, MS, Beckman Coulter (Employee) Jennifer Chau, PhD, Beckman Coulter (Employee)

333. Tedizolid Activity against Gram-Positive Bacterial Isolates Causing Bone and Joint Infections in the United States (2015–2019)

BackgroundProlonged systemic antibiotic courses are frequently used to manage difficult-to-treat bone and joint infections (BJI). Tedizolid has been considered as a therapy candidate for BJI in adults and children. This study assessed the in vitro activity of tedizolid and comparator agents against a contemporary collection of Gram-positive (GP) isolates causing BJI in the US.MethodsA total of 310 Staphylococcus aureus (SA), 79 β-hemolytic streptococci (BHS), 52 coagulase-negative staphylococci (CoNS), and 37 Enterococcus faecalis isolates were included in this study. These isolates were collected from patients with BJI from 30 medical centers in the US between 2015 and 2019 as a part of the Surveillance of Tedizolid Activity and Resistance (STAR) Program. Bacterial identification was confirmed by MALDI-TOF MS. MIC results were obtained by reference CLSI broth microdilution methods and interpretations used CLSI guidelines.ResultsTedizolid (MIC50/90, 0.12/0.25 mg/L) inhibited all SA at the CLSI breakpoint (≤0.5 mg/L) including methicillin-resistant SA (MRSA; 35.8% of SA; MIC50/90, 0.12/0.25 mg/L). Linezolid, vancomycin, and daptomycin had 100% susceptibility rates against SA isolates (Table). All CoNS isolates were inhibited by tedizolid at ≤0.5 mg/L. Tedizolid was active against all BHS (100% susceptible) as follows: S. pyogenes (n=24; MIC50/90, 0.12/0.25 mg/L), S. agalactiae (n=44; MIC50/90, 0.12/0.25 mg/L), and S. dysgalactiae (n= 11; MIC50/90, 0.25/0.25 mg/L). Penicillin, linezolid, vancomycin, and daptomycin also were active against BHS (100% susceptible). Tedizolid (MIC50/90, 0.25/0.25 mg/L; 100% susceptible) was 4- to 8-fold more potent than linezolid (MIC50/90, 1/1 mg/L) and vancomycin (MIC50/90, 1/2 mg/L) against E. faecalis. GP isolates resistant to oxazolidinone were not observed.ConclusionTedizolid demonstrated potent in vitro activity against this collection of contemporary GP isolates causing BJI in US hospitals. Tedizolid and comparator agents showed high susceptibility rates against the most frequent organisms and organism groups, including MRSA. These findings support the clinical development of tedizolid as an additional option for treating BJI caused by GP pathogens.Table 1 DisclosuresCecilia G. Carvalhaes, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Pfizer (Research Grant or Support) Helio S. Sader, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support) Jennifer M. Streit, BS, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support) Mariana Castanheira, PhD, 1928 Diagnostics (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Amplyx Pharmaceuticals (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Rodrigo E. Mendes, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Basilea Pharmaceutica International, Ltd (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Department of Health and Human Services (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Pfizer (Research Grant or Support)

Legionella antimicrobial sensitivity testing: comparison of microbroth dilution with BCYE and LASARUS solid media.

ObjectivesThere is a lack of international unification for AST methodology for Legionella pneumophila. Current literature contains multiple possible methods and this study compares each of them to determine methodological concordance.MethodsAntibiotic susceptibility of 50 L. pneumophila strains was determined using broth microdilution (BMD), serial antimicrobial dilution in traditional buffered charcoal yeast extract (BCYE) agar (as well as comparison with gradient strip overlay on BCYE) and in a novel charcoal-free agar (LASARUS) for rifampicin, azithromycin, levofloxacin and doxycycline.ResultsThe deviation of tested media relative to BMD highlighted the overall similarity of BMD and LASARUS across all antimicrobials tested (within one serial dilution). BCYE agar dilution showed an increased MIC of up to five serial dilutions relative to BMD, while MICs by gradient strip overlay on BCYE were elevated by two to three serial dilutions, with the exception of doxycycline, which was decreased by three serial dilutions relative to MIC values determined by BMD. The MIC range for azithromycin was wider than for other antimicrobials tested and found to be caused by the presence or absence of the lpeAB gene.ConclusionsBMD-based antimicrobial susceptibility testing (AST) methodology should be the internationally agreed gold standard for Legionella spp. AST, as is common for other bacterial species. Traditional BCYE gave significantly elevated MIC results and its use should be discontinued for Legionella spp., while MIC determination using LASARUS solid medium gave results concordant (within one serial dilution) with BMD for all antimicrobials tested. To the best of our knowledge, this study is the first to identify the lpeAB gene in UK isolates.

Screening of Milk Borne Staphylococcus aureus for Resistance against Beta Lactam Antibiotics

Background: A study was carried out to screen milk borne Staphylococcus aureus for resistance against Beta lactam antibiotics. Methods: A total of 45 milk samples were collected over a period of three months from large animal outpatient unit of Madras Veterinary College Hospital, Chennai. Upon collection of samples, ABST followed by its growth in Mannitol Salt Agar was carried out as part of the phenotypic screening. Genotypic screening for Staphylococcus screening was done with the help of PCR by using nuc and mec A primers. MIC for ceftriaxone and cloxacillin was carried out with the samples that were found positive for Staphylococcus aureus. The antibiotic sensitivity pattern is presented: Fluoroquinolones (87.5% sensitive), aminoglycosides (72.5% sensitive), Amoxicillin-Clavulanic acid (Amoxyclave) (72.5% sensitive). The MSA positive samples were subjected to molecular identification with the help of PCR. Result: The results revealed 10 samples positive for Staphylococcus aureus and 5 among them positive for mecA gene. The MIC results were as follows: MIC50-10.95µg/ml and MIC90- 87.510.95µg/ml for ceftriaxone and MIC50- 43.75 µg/ml and MIC90- 87.5µg/ml for cloxacillin, indicating emergence of resistance. However, further studies are required in a larger sample size that can help us to attain more conclusive results.

Evaluation of Antimicrobial Activity of Buforin I and Nisin and the Synergistic Effect of Their Combination as a Novel Antimicrobial Preservative

One of the most effective methods for increasing the antimicrobial activity of a substance is to combine it with one or more other antimicrobial agents. The aim of the present study was to evaluate the antimicrobial effect of buforin I and nisin alone and investigate the synergistic action of these compounds against the most important food spoilage microorganisms in clouding B. subtilis, S. epidermidis, L. innocua, E. coli, S. Enteritidis, A. oryzae, R. glutinis and G. candidum. The results of MIC and MBC/MFC examinations showed that buforin I had higher antimicrobial activity than nisin on all the microbial strains used in this study (p≤0.5). E.coli was the most resistant to both antimicrobial agents, while Listeria innocua and Staphylococcus epidermidis were the most sensitive to nisin and buforin I, respectively. The results of synergistic interaction between buforin I and nisin indicated that the combination of buforin I and nisin on B. subtilis, S. epidermidis and A. oryzae showed synergistic effect, while it had no effect on S. Enteritidis and Geotrichum candidum. The combination of buforin I and nisin showed partial synergistic effect on Listeria innocua, Escherichia coli, Rhodotorula glutinis. Assessment of viability of the microorganisms under the antimicrobial agents alone and in combination with each other at MICs and FICs indicated that use of these antimicrobial agents in combination enhances antimicrobial activity at lower concentrations of both agents. The present study investigated the antimicrobial properties of buforin I against food spoilage microorganisms for the first time and suggests that its use alone or in combination with nisin may provide a clear horizon for the application of antimicrobial peptides as natural preservatives. Thus, the combination of antimicrobial peptides and traditional antimicrobial food preservative could be a promising option for the prevention of contamination, spoilage, and infestation of food and beverage products.

Multicentre testing of the EUCAST broth microdilution reference method for MIC determination on Mycobacterium tuberculosis

ObjectivesThe first objective of the European Committee on Antimicrobial Susceptibility Testing (EUCAST) subcommittee for antimycobacterial susceptibility testing (AMST), launched in 2016, was to set a reference method for determining the MICs of antituberculous agents, since many protocols are used worldwide and a consensus one is needed for the determination of microbiological breakpoints. MethodsDuring 2017 and 2018, MIC determination protocols were evaluated prospectively in a multicentre study within the four AMST laboratories. MIC results were obtained for isoniazid, levofloxacin and amikacin on the reference strain Mycobacterium tuberculosis H37Rv ATCC 27294. Broth microdilution (BMD) in Middlebrook 7H9 and solid medium dilution (SMD) in Middlebrook 7H10 were performed using two inoculum concentrations. MICs were interpreted with regard to visual and 99% inhibition after 7, 14 or 21 days of incubation for BMD and 21 days for SMD. ResultsFollowing the EUCAST reference protocol, intra- and inter-assay agreements were within ±1 MIC dilution for >95% of the observations for the three drugs in both methods. MIC values, presented as MIC mode (range) for BMD and SMD respectively, were: 0.03 (0.015–0.06) mg/L and 0.12 (0.06–0.25) mg/L for isoniazid, 0.25 mg/L (0.25–0.5) and 0.5 mg/L (0.12–0.5) for levofloxacin, and 0.5 mg/L (0.5–1.0) and 0.5 mg/L (0.5–1.0) for amikacin. ConclusionsBoth SMD and BMD were reproducible and eligible as a reference method for MIC determination of the Mycobacterium tuberculosis complex (MTBC). BMD was finally selected as the EUCAST reference method. From now on it will be used to set epidemiological cut-off values and clinical breakpoints of new and old antituberculous agents.

In Vitro Activity Analysis of a New Polymyxin, SPR741, Tested in Combination with Antimicrobial Agents against a Challenge Set of Enterobacteriaceae, Including Molecularly Characterized Strains.

The activities of azithromycin, fusidic acid, vancomycin, doxycycline, and minocycline were evaluated alone and in combination with SPR741. A total of 202 Escherichia coli and 221 Klebsiella pneumoniae isolates were selected, and they included a genome-sequenced subset (n = 267), which was screened in silico for β-lactamase, macrolide-lincosamide-streptogramin (MLS), and tetracycline (tet) genes. Azithromycin (>16 mg/liter), fusidic acid (>64 mg/liter), vancomycin (>16 mg/liter), and SPR741 (>8 mg/liter) showed off-scale MICs when each was tested alone against all isolates. MIC50/90 results of 0.5/8 mg/liter, 4/>32 mg/liter, 16/>16 mg/liter, 2/32 mg/liter, and 0.25/4 mg/liter were obtained for azithromycin-SPR741, fusidic acid-SPR741, vancomycin-SPR741, doxycycline-SPR741 and minocycline-SPR741, respectively, against all isolates. Overall, azithromycin-SPR741 (MIC90, 2 to 4 mg/liter) and minocycline-SPR741 (MIC90, 0.5 to 2 mg/liter) showed the lowest MIC90 values against different subsets of E. coli isolates, except for azithromycin-SPR741 (MIC90, 16 mg/liter) against the AmpC and metallo-β-lactamase subsets. In general, minocycline-SPR741 (MIC90, 2 to 8 mg/liter) had the lowest MIC90 against K. pneumoniae isolates producing different groups of β-lactamases. The azithromycin-SPR741 MIC (MIC50/90, 2/32 mg/liter) was affected by MLS genes (MIC50/90 of 0.25/2 mg/liter against isolates without MLS genes), whereas doxycycline-SPR741 (MIC50/90, 0.5/2 versus 8/32 mg/liter) and minocycline-SPR741 (MIC50/90, 0.25/1 versus 1/8 mg/liter) MIC results were affected when tested against isolates carrying tet genes in general. However, minocycline-SPR741 inhibited 88.2 to 92.9% of tet-positive isolates regardless of the tet gene. The azithromycin-SPR741 MIC results (MIC50/90, 1/16 mg/liter) against isolates with enzymatic MLS mechanisms were lower than against those with ribosomal protection (MIC50/90, 16/>32 mg/liter). SPR741 increased the in vitro activity of tested codrugs at different levels and seemed to be dependent on the species and resistance mechanisms of the respective codrug.

Bactericidal Potentiality of Purified Terpenoid Extracts from the Selected Sea Weeds and its Mode of Action

Terpenoids are hydrocarbons involved in a variety of basic functions in plants such as growth, development and other physiological events. Terpenes and their associated molecules safe guard the organisms from pest, pathogen and herbivores. Similarly, therapeutically terpenoids function as antimicrobial agents against bacteria, fungi and viruses. The mechanism of bactericidal activities may be via inhibiting the synthesis of essential molecules like proteins, nucleic acids, cell-wall components, cell membrane derailment, bacterial DNA replication or inhibition of metabolic pathways. The crude methanolic extracts of the seaweeds were subjected to silica gel column chromatographic purification and eluted with different combinations of ethyl acetate: petroleum ether solvent systems. The eluted fractions were further subjected to thin layer chromatography and fractionated by GC-MS. The fractions obtained from Hypnea musciformis revealed the terpenoids such as eicosane, heneicosane, 2-pentadecnone, hexadecanoic acid methyl ester, n- hexadecanoic acid, hexadecanoic acid ethyl ester, heptadecanoic acid methyl ester, 11-octadecanoic acid metyl ester, whereas Kappapycus alvarezii displayed hexadecane, eicosane, heptadecane, octadecane, heneicosane, tricosane, hexadecanoic acid, methyl ester and beta amyrin. Similarly, Gracillaria dura revealed hexadecanoic acid methyl ester, n- hexadecanoic acid, 11-octadecanoic acid and phytol. Subsequently, the bactericidal activities of the purified terpenoid extracts from the sea weeds were carried. Initially, the extracts were tested for their in vitro antibacterial activity against six bacterial strains such as three Gram-positive ( Staphylococcus aureus , Streptococcus mutans, Enterococcus faecalis ) and three Gram-negative bacteria ( Klebsiella pneumoniae , Escherichia coli, Pseudomonas aeruginosa ) by disc diffusion method. The results revealed that the purified terpenoid extracts of G. dura exhibited significant bactericidal potentiality against S. mutans as compared to other strains. The zone of inhibition, MIC and MBC values narrate the efficacy of the purified terpenoid extract of the species. Remarkable leaching of metabolites like protein and DNA further substantiates the MIC and MBC results. Scanning electron microscopic observations such as clumping, irregularity of cells and ballooned walls reflect the possible membrane damage accounted in the cells by the terpenoid extracts. Further studies are planned to validate the above data by using molecular tools.

Ultra-rapid flow cytometry assay for colistin MIC determination in Enterobacterales, Pseudomonas aeruginosa and Acinetobacter baumannii

ObjectivesBoth EUCAST and CLSI recommend broth microdilution for antimicrobial susceptibility testing of colistin, but this method is cumbersome and takes 16-24 h to give results. Our objective was to evaluate a rapid quantitative colistin MIC susceptibility assay based on flow cytometry analysis (FASTcolistin MIC) in comparison with standard broth microdilution assay. MethodsOne hundred and sixteen Gram-negative bacilli (78 Enterobacterales, 28 Pseudomonas aeruginosa and 10 Acinetobacter baumannii) were studied in parallel using standard broth microdilution following EUCAST recommendations and FASTcolistin MIC kit. In the last one, a bacteria suspension (0.5 MacFarland) was prepared, diluted in Muller-Hinton broth, incubated in the susceptibility panel containing different colistin concentrations (range 0.125-64 mg/L) with a fluorescent probe and incubated 1 h at 35ºC. After that, a flow cytometry analysis using CytoFLEX (Beckmam) was performed. Using a dedicated software (BioFAST) an automated MIC result was obtained after 1.5 h. Performance evaluation was performed according to the ISO standard 20776-2. Reproducibility and repeatability, categorical (CA) and essential agreement (EA), and lot-to-lot variation and operator-to-operator variability, as well as time to results were determined. ResultsOverall, 100% CA (CI 97-100%) and 95.7% EA (CI 90-98%) was obtained with high repeatability (100%; CI 80-100%)and reproducibility (97%; (CI 83-99%)). Absence of lot-to-lot variations or differences in the operators' performance was observed. ConclusionsFASTcolistin MIC is an accurate, reliable and ultra-rapid method (1 h incubation versus 24 h) for susceptibility testing of colistin of common Gram-negative bacilli recovered in clinical laboratories.

Total synthesis and a systematic structure-activity relationship study of WAP-8294A2

WAP-8294A2 is a cyclic peptide antibiotic with novel structure and excellent activity against Gram-positive pathogens. Herein, we report the total synthesis of complex macrocyclic peptide WAP-8294A2 (W1), ent-analogue W2, deoxy analogue W3 and de-methyl analogue W4 using a solid-phase synthetic route followed by a final stage solution-phase cyclization reaction. Exploitation of this process allowed the synthesis of eleven alanine-scanning analogues and eight lysine-scanning analogues. The antimicrobial activity of these analogues was evaluated in vitro against Gram-positive bacteria. Based on the MIC results, a primary systematic structure-activity relationship has been established.