Minimum Inhibitory Concentration Breakpoints Research Articles

Isolation of Multidrug-Resistant Bacteria from Raw Hides, Salted Hides, and Tannery Wastewater and Their Heavy Metal (Cr) Tolerance

Numerous leather products are created from cattle hides and skins. However, the processing of these products can release toxic heavy metals, including chromium into the environment, leading to health hazards and environmental pollution. This study aims to isolate and identify multidrug-resistant bacteria from rawhide, salted hides, and tanneries in different areas of the Savar region in Dhaka City, Bangladesh. The secondary objective is to determine the heavy metal tolerance and Minimum Inhibitory Concentration (MIC) of Cr against all isolated bacteria. The study found 206 bacterial isolates from three areas: Polashbari Kathaltola, Polashbari Bazar, and Savar Hemaythpur. Rawhide yielded 100 (48.54%) bacterial isolates, salted hide yielded 80(38.83%) isolates, and tannery wastewater yielded only 26 (12.62%) isolates. Further, Bacillus spp. (60) was the most common isolated bacteria. The other identified bacteria were Pseudomonas spp. (46), Staphylococcus spp. (40), Proteus spp. (40), and Escherichia coli (20). The isolated strains showed multidrug resistance, with Staphylococcus spp. Being highly resistant to Erythromycin (100%), followed by Trimethoprim (95%) and Tetracycline (88%). Pseudomonas spp. Were highly resistant to Azithromycin (100%) and Gentamycin (100%). The MIC and the MIC breakpoint determined the screening and evaluation of Cr tolerance against bacteria, and among the isolated bacterial isolates, Bacillus spp. showed a MIC breakpoint of 600 ppm (11.52mM) for Cr tolerance. The isolated heavy metal-resistant bacteria are useful in the bioremediation process and can aid in recovering and removing heavy metals from environmental effluents, thus preventing adverse effects on humans and animals. The government and leather companies should take legal responsibility for proper leather processing to ensure a preventative approach for safe public health. Otherwise, carcinogenic heavy metals can cause cancer in humans.

Tensor modeling of MRSA bacteremia cytokine and transcriptional patterns reveals coordinated, outcome-associated immunological programs

Abstract Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is a common and life-threatening infection that imposes up to 30% mortality even when appropriate therapy is used. Despite in vitro efficacy determined by minimum inhibitory concentration (MIC) breakpoints, antibiotics often fail to resolve these infections in vivo, resulting in persistent MRSA bacteremia. Recently, several genetic, epigenetic, and proteomic correlates of persistent outcomes have been identified. However, the extent to which single variables or their composite patterns operate as independent predictors of outcome or reflect shared underlying mechanisms of persistence is unknown. To explore this question, we employed a tensor-based integration of host transcriptional and cytokine datasets across a well-characterized cohort of patients with persistent or resolving MRSA bacteremia outcomes. This method yielded high correlative accuracy with outcomes and immunologic signatures united by transcriptomic and cytokine datasets. Results reveal that patients with persistent MRSA bacteremia exhibit signals of granulocyte dysfunction, suppressed antigen presentation, and deviated lymphocyte polarization. In contrast, patients with resolving bacteremia heterogeneously exhibit correlates of robust antigen-presenting cell trafficking and enhanced neutrophil maturation corresponding to appropriate T lymphocyte polarization and B lymphocyte response. These results suggest that transcriptional and cytokine correlates of persistent versus resolving bacteremia outcomes are complex and may not be disclosed by conventional modeling. In this respect, a tensor-based integration approach may help to reveal consensus molecular and cellular mechanisms and their biological interpretation.

Evaluation of Antibiotics by Disk Diffusion and Minimum Inhibitory Concentration Breakpoints in Urinary Tract Infections

Antibiotic resistance (ABR) has made it more challenging to treat uropathogenic organisms. It is impossible to compromise antimicrobial susceptibility testing (AST), which is essential and has a significant impact on infection treatment strategies. Although labor-intensive and technically challenging for everyday laboratory use, the agar dilution technique is appropriate for monitoring and assessing novel antimicrobials. Objective: To determine the minimum inhibitory concentration (MIC), Agar dilution technique and disk diffusion as susceptibility test methodologies. Methods: This study was carried out at Khyber Girls Medical College (KGMC) Peshawar. Keeping in view the Clinical and Laboratory Standards Institute (CLSI) guidelines AST was executed. BIOMÉRIEUX® API® kits and gram staining were utilized for identification of bacteria. The disk diffusion was performed using Thermo ScientificTM OxoidTM antibiotic discs of Co-trimoxazole, Levofloxacin, Nitrofurantoin and Fosfomycin. The MIC and zone of inhibitions for disk diffusion were noted according to the CLSI protocol. Results: 158 culture positive samples were isolated out of 680 total received. Esherechia Coli (E. coli) (74.1%) being the most isolated organism. In comparison of disk diffusion and agar dilution, categorical agreement for Levofloxacin, Cotrimoxazole, Nitrofurantoin and Fosfomycin were (82.28%, 72.15 %, 87.97% and 82.28%) respectively. Kappa coefficients of (0.64, 0.43, 0.57 and 0.37) (p < 0.0001) were calculated for Levofloxacin, Co-trimoxazole, Nitrofurantoin, and Fosfomycin respectively, revealing considerable level of agreement for these antibiotics. Conclusions: It was concluded that Agar dilution is more precise than disk diffusion but being more labor intensive and technical. Disk diffusion can still produce significantly accurate results with less resource consumption.

Role of MIC levels and 23S rRNA mutation sites to clarithromycin in 14-day clarithromycin bismuth quadruple therapy for Helicobacter pylori eradication: A prospective trial in Beijing

BackgroundRising clarithromycin resistance undermines Helicobacter pylori (H. pylori) treatment efficacy. We aimed to determine clarithromycin's minimum inhibitory concentration (MIC) levels and identify specific mutation sites in the 23S ribosomal subunit (23S rRNA) that predict treatment outcomes in a 14-day regimen of clarithromycin bismuth quadruple therapy (amoxicillin 1g, clarithromycin 500 mg, rabeprazole 10 mg, and colloidal bismuth pectin 200 mg). Materials and methodsWe included adult H. pylori patients who hadn't previously undergone clarithromycin-based treatment, either as initial or rescue therapy. Exclusions were made for penicillin allergy, recent use of related medications, severe illnesses, or inability to cooperate. Patients underwent a 14-day clarithromycin bismuth quadruple therapy. Gastric mucosa specimens were obtained during endoscopy before eradication. MIC against amoxicillin and clarithromycin was determined using the E-test method. The receiver operating characteristic (ROC) curve helped to find the optimal clarithromycin resistance MIC breakpoint. Genetic sequences of H. pylori 23S rRNA were identified through Sanger Sequencing. (ChiCTR2200061476) ResultsOut of 196 patients recruited, 92 met the inclusion criteria for the per-protocol (PP) population. The overall intention-to-treat (ITT) eradication rate was 80.00 % (84/105), while the modified intention-to-treat (MITT) and PP eradication rates were 90.32 % (84/93) and 91.30 % (84/92) respectively. No amoxicillin resistance was observed, but clarithromycin resistance rates were 36.19 % (38/105), 35.48 % (33/93), and 34.78 % (33/92) in the ITT, MITT, and PP populations respectively. Compared with the traditional clarithromycin resistance breakpoint of 0.25 μg/mL, a MIC threshold of 12 μg/mL predicted better eradication. Among 173 mutations on 152 sites in the 23S rRNA gene, only the 2143A > G mutation could predict eradication outcomes (p < 0.000). ConclusionsInterpretation of elevated MIC values is crucial in susceptibility testing, rather than a binary "susceptible" or "resistant" classification. The 2143A > G mutation has limited specificity in predicting eradication outcomes, necessitating further investigation into additional mutation sites associated with clarithromycin resistance.

DEVELOPMENT OF THE PHARMACEUTIC CRYSTALLIZATION PROCESS USING PLASMODIUM FALCIPARUM, A DERIVATIVE OF THIOSEMICARBAZONE

Objective: The current study was designed with the goal of analyzing novel derivatives of organic and semi-organic NLO molecules that are just entering this field as the foundation for future therapeutic development. Methods: Thiosemicarbazones (TSC) are semicarbazide analogs that have sulfur atoms in place of oxygen atoms. The greatest number of therapeutic treatments for various disorders are also being used carbonyl compounds. These two types of organic compounds were combined, and their replacement with crystal growth procedures using solution growth was tested as an antibiotic for a few fastidious and nonfastidious species. The preparation of meta-substituted benzaldehydes using TSC. Tests were conducted with this single component. The following experimental technique was used to determine the antibacterial activity of Plasmodium falciparum. Half-inhibitory maximum (IC50) by calculation technique, cell viability % calculation method, and MTT assay by colorimetric method. Results: Method using agar discs. Using the agar disc diffusion method to measure the inhibition zone width and comparing the minimal inhibitory concentration (MIC) and inhibition zone width of available antibiotics against the aforementioned organism using data from the EUCAST and NCCLS databases, The absolute, relative, and mound slope values of an antibiotic that is currently on the market may be determined using the GraphPad Prism software; the epidemiological cutoff value can be determined using the ECOF Finder software; and the nature of the antibiotic can be determined using the WHONET 5.6 software. The newly developed antibiotics’ size and structure are contrasted with the structures of commercially available antibiotics and living organisms. Conclusion: The design of new drugs using novel derivatives of organic and semiorganic NLO molecules is based on the in vitro method of analysis, which has recently been introduced to this field. P. falciparum has an extremely low MIC value (0.625 μg/mL) against TSCMNB. The MIC break points are always larger than, not equal to, the MIC values and fall within the range of 110 μg/mL–130 μg/mL. We concluded that all of the novel compounds exhibit a susceptible form of inhibition.

Pharmacokinetics of Locally Applied Antibiotic Prophylaxis for Implant-Based Breast Reconstruction

Antibiotic irrigation of breast implants is widely used internationally, but no clinical study has investigated the pharmacokinetics of antibiotic prophylaxis in the breast implant pocket. To evaluate how long locally applied gentamicin, cefazolin, and vancomycin concentrations in the implant pocket remain above the minimum inhibitory concentration (MIC) for the most common bacterial infections and to measure systemic uptake. This prospective cohort study was performed at the Department of Plastic Surgery and Burns Treatment, Rigshospitalet, Copenhagen, Denmark, between October 25, 2021, and September 22, 2022, among 40 patients undergoing implant-based breast reconstruction who were part of the ongoing BREAST-AB trial (Prophylactic Treatment of Breast Implants With a Solution of Gentamicin, Vancomycin and Cefazolin Antibiotics for Women Undergoing Breast Reconstructive Surgery: a Randomized Controlled Trial). Patients were randomized to receive locally applied gentamicin, cefazolin, and vancomycin or placebo. Samples were obtained from the surgical breast drain and blood up to 10 days postoperatively. The breast implant and the implant pocket were irrigated with 160 μg/mL of gentamicin, 2000 μg/mL of cefazolin, and 2000 μg/mL of vancomycin in a 200-mL saline solution. The primary outcome was the duration of antibiotic concentrations above the MIC breakpoint for Staphylococcus aureus according to the Clinical and Laboratory Standards Institute: gentamicin, 4 μg/mL; cefazolin, 2 μg/mL; and vancomycin, 2 μg/mL. Secondary outcomes included the time above the MIC for Pseudomonas aeruginosa and other relevant bacteria, as well as systemic uptake. The study included 40 patients (median age, 44.6 years [IQR, 38.3-51.4 years]; median body mass index, 23.9 [IQR, 21.7-25.9]) with a median number of 3 drain samples (range, 1-10 drain samples) and 2 blood samples (range, 0-6 blood samples). Vancomycin and cefazolin remained above the MIC for S aureus significantly longer than gentamicin (gentamicin, 0.9 days [95% CI, 0.5-1.2 days] for blood samples vs 6.9 days [95% CI, 2.9 to 10.9 days] for vancomycin [P = .02] vs 3.7 days [95% CI, 2.2-5.2 days] for cefazolin [P = .002]). The gentamicin level remained above the MIC for P aeruginosa for 1.3 days (95% CI, 1.0-1.5 days). Only cefazolin was detectable in blood samples, albeit in very low concentrations (median concentration, 0.04 μg/mL [range, 0.007-0.1 μg/mL]). This study suggests that patients treated with triple-antibiotic implant irrigation during breast reconstruction receive adequate prophylaxis for S aureus and other common implant-associated, gram-positive bacteria. However, the protection against P aeruginosa may be inadequate.

Antimicrobial Susceptibility Patterns Among a Large, Nationwide Cohort of Chryseobacterium Species Clinical Isolates

Abstract Background Chryseobacterium species are ubiquitous in nature that can be found in soil, water, sinks, and medical devices. They have been implicated in various infections including ventilator-associated pneumonia, catheter-related bloodstream infections (CRBSI), skin and soft tissue infections, and meningitis. C. indologenes has been shown to possess an extended-spectrum beta-lactamase (ESBL) and metallo-β-lactamase (MBL) that render it resistant to most antibiotics. Antimicrobial susceptibility testing (AST) data are required to help clinicians choose effective empiric antibiotics and to investigate potential resistance mechanisms. Methods Chryseobacterium spp. identification was determined prior to submission by client laboratories or performed in our laboratory by MALDI-TOF (Bruker Biotyper) or 16S rRNA gene sequencing. AST was performed on Chryseobacterium species isolates received from across the United States between April 2004 and December 2018. AST was performed using custom-made broth microdilution panels, and minimal inhibitory concentrations (MICs) were interpreted using CLSI M100 MIC breakpoints for non-Enterobacterales organisms. Isolates from a range of clinical specimens including blood, respiratory, wound, tissue, bone, and body fluids were included. Quality control was performed using Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. Results were included only if the QC values were within range. The MIC50, MIC90, and MIC ranges for antimicrobials for frequently tested Chryseobacterium species were determined. Results AST was completed for 245 Chryseobacterium species clinical isolates, and the most frequently tested species were C. gleum/ indologenes (n = 78), C. hominis (n = 25), C. taklimakanense (n = 14), C. anthropi/ haifense (n = 12), C. arthrospharae (n = 12), C. bernardetii/jejuense (n = 3), C. pallidum (n = 3), and C. solincola/treverense (n = 3). 84 isolates were unable to be identified to species level, and were grouped as “Chryseobacterium spp.” Regarding susceptibility, across all Chryseobacterium species, the antibiotics with the most activity included minocycline (97.8%), trimethoprim-sulfamethoxazole (TMP-SMX; 95.5%), levofloxacin (92.3%), and ciprofloxacin (82.8%). Comparing the β-lactams, piperacillin-tazobactam had the most activity (59.7%), whereas ceftazidime (42.2%), cefepime (44.3%), meropenem (41.2%), and imipenem (46.3%) had similar low activity. The highest resistance rates were found for tobramycin (96%), aztreonam (94.6%), and gentamicin (62.7%). Among the Chryseobacterium isolates, certain species were found to be largely pan-susceptible, including C. anthropic/haifense, C. hominis, and C. taklimakanense. Conclusions Chryseobacterium species display significant resistance against β-lactam antibiotics, which are often used for empiric therapy. Minocycline, TMP-SMX, and fluoroquinolones have the most activity against Chryseobacterium species clinical isolates.

2279. Appropriateness of Antibiotic Prescribing Before vs. After Minimum Inhibitory Concentration (MIC) Suppression in Culture Reports: A Quasi-experimental Study

Abstract Background Culture and susceptibility results are essential to identify the offending organism and optimize antibiotic treatment; hence, decrease the emergence of antibiotic resistance and achieve better clinical outcomes. Antibiotic prescribers should learn how to interpret MIC breakpoints to prescribe a suitable antibiotic as different antibiotics have different MIC breakpoints against different microorganisms. No study to date has evaluated the impact of MIC suppression in culture reports while keeping interpretation results on the appropriateness of antibiotics choice by non-infectious diseases prescribers. We assessed the impact of MIC suppression on the appropriateness of antibiotic prescriptions. Methods This was a quasi-experimental study (pre-post intervention) that was conducted over 14 months on hospitalized patients in the medical floor who had a symptomatic infection with a positive culture and were prescribed a full course of definitive antibiotics by prescribers not specialized in infectious diseases pre and post MIC suppression in culture reports. The primary outcome was appropriateness of antibiotic selection (the de-escalation to the narrowest spectrum antibiotic to which the organism is susceptible with appropriate dose). Secondary outcomes were clinical cure (resolution of signs and symptoms, including defervescence and normalization of white blood cells count), length of stay (LOS), and antibiotics expenditure as defined daily dose (DDD) per 1,000 patient days and days of therapy (DOT) per 1,000 patient days. Results 100 patients were included, 50 in each phase. No difference was observed in the baseline characteristics, including age, sex, infection site, isolated organism, and prescribers’ departments. Appropriate antibiotic selection was significantly higher in the post-intervention phase compared to the pre-intervention phase (62% vs. 40%; P=0.028). LOS was shorter in the post-intervention phase compared to the pre-intervention phase (5 vs. 9.5 days; P=0.011). No difference was reported in the other outcomes. Conclusion Our study showed that suppressing MIC values from cultures reports was helpful in choosing the appropriate antibiotic and minimizing the LOS. Future research is needed to confirm these findings. Disclosures All Authors: No reported disclosures

Determining the prevalence and genetic diversity of plasmid-mediated sulfonamide resistance in Escherichia coli from commercial broiler samples

Sulfonamides are commonly used antibacterials in commercial poultry, contributing toward the development of multidrug-resistant (MDR) phenotypes among Escherichia coli and that has emerged as global concern. The current study aimed to assess the sulfonamide resistance among isolated E. coli strains among commercial broilers. The bacterial strains were identified from fecal samples (n = 100) using selective media, followed by initial identification based on biochemical profiles. The susceptibility was determined by measuring the minimum inhibitory concentration (MIC) against sulfamethoxazole. The study also evaluated mobile genetic elements (MGEs), the mediators of antibiotic resistance, by amplification of plasmid DNA using specific primer PCR. Additionally, the isolates were subjected to multilocus sequence typing (MLST) analysis to investigate the genetic diversity among E. coli carrying sulfonamide resistance genes. The results revealed that 58% (58/100) E. coli strains were resistant to sulfonamides, with 36.20% (21/58) of the strains exhibiting an MIC breakpoint ≥512 µg/mL. PCR analysis showed that 42.85% (9/21) of the strains harbored the sul-1 gene, while 38.09% (8/21) carried the sul-2 gene, and 19.04% (4/21) had both genes. No isolate showed the presence of the sul-3 gene. Furthermore, class 1 and class 2 integrons were identified among 80.95% (17/21) and 19.04% (4/21) of the strains, respectively. MLST analysis confirmed that the strains belonged to sequence types (STs) including ST1638, ST155, ST48, ST350, ST23, ST156, and ST746. These findings underscore the diversity among E. coli strains in commercial poultry, which poses a significant risk.

Determination of Minimum Inhibitory Concentration of Different Antibiotics against Pseudomonas aeruginosa by E- test at a Tertiary Care Hospital

Background: Antimicrobial drug resistance is a matter of worldwide concern. Different microorganisms, including bacteria, are becoming more resistant day by day. So it is of utmost importance to know the antimicrobial susceptibility pattern not only for initiation of treatment but also for prevention of drug resistance. By determining minimum inhibitory concentration (MIC) by Epsilometer-test (E-test), we can determine the exact dose of a particular drug.&#x0D; Aims: The study is aimed to determine the MIC of different antibiotics against intermediate isolates of P. aeruginosa isolated from clinically suspected patients of chronic suppurative otitis media (CSOM).&#x0D; Materials and Methods: A cross-sectional type of descriptive study was conducted in the Department of Microbiology, Rajshahi Medical College, Rajshahi, during the period of January 2019 to December 2019 to identify the causative bacteria of CSOM with their antibiotic susceptibility pattern. A total of 96 aural swabs were collected from clinically suspected cases of CSOM, irrespective of age and sex, in the ENT department of Rajshahi Medical College Hospital, Rajshahi. Isolation and identification of bacteria were made as per standard procedure, and then antimicrobial susceptibility testing was performed by the disc diffusion method. At last, E-test was performed on different antibiotics against intermediate isolates of P. aeruginosa.&#x0D; Results: Among 73 isolates, 37 showed intermediate susceptibility towards selected antibiotics such as beta-lactams (Ceftazidime, Ceftriaxone), aminoglycosides (Gentamicin), and quinolones (Ciprofloxacin) by disc diffusion method. Among 37 intermediate isolates, P. aeruginosa was 14 in number. Regarding MIC breakpoints in terms of susceptibility, out of 14 intermediate isolates of P. aeruginosa, 09(64.28%) isolates were susceptible, 03(21.43%) intermediate, and 2(14.28%) were resistant to different antibiotics by E-test.&#x0D; Conclusion: In this study, higher susceptibility of different antibiotics against intermediate isolates of P. aeruginosa was observed by E-test than the disc diffusion method.&#x0D; TAJ 2022; 36: No-1: 47-54

Pharmacokinetics and Safety of Sulfamethoxazole-Trimethoprim After Oral Administration of Single and Multiple Doses to Rhode Island Red Chickens (Gallus gallus domesticus).

Sulfamethoxazole-trimethoprim (SMZ-TMP), a commonly prescribed antibiotic for backyard hens, is neither Food and Drug Administration approved nor prohibited in laying hens in the United States. The aim of this study was to determine whether plasma concentrations above targeted minimum inhibitory concentration breakpoint values for Enterobacteriaceae could be achieved with oral dosing. Five Rhode Island red hens (Gallus gallus domesticus) were administered a single dose of 96 mg/kg SMZ-TMP (80 mg/kg SMZ and 16 mg/kg TMP) IV followed by the same dose orally after a washout period. Following oral dosing, mean SMZ concentrations exceeded the target breakpoint for approximately 12 hours; however, TMP only briefly exceeded the target breakpoint. Bioavailability was 60.5% for SMZ and 82.0% for TMP. Ten naïve birds were allocated into control (n = 4) and treatment (n = 6) groups for a 7-day multi-dose study. Treatment birds received an oral suspension dosed at 16 mg/kg TMP and 80 mg/kg SMZ every 48 hours (on days 1, 3, 5, and 7); TMP tablets were additionally dosed at 25 mg/bird on days 1, 3, 5, and 7, and 50 mg/bird on days 2, 4, and 6. Plasma SMZ-TMP concentrations were measured on a multiple time interval by ultraperformance liquid chromatography-mass spectrometry, and pharmacokinetic analyses were performed using a noncompartmental model. No accumulation for either drug was noted following repeated dosing, and no statistical differences in biochemical values, packed cell volumes, or weight were found between pre- and posttreatment in either the treatment or control groups. Sulfamethoxazole (80 mg/kg q48h PO) and TMP (24.1-28.0 mg/kg q24h PO) maintained therapeutic plasma concentrations at or exceeding the minimum inhibitory concentration breakpoint of Enterobacteriaceae for 72 and 24 hours for TMP and SMZ, respectively, without evidence of adverse effects or drug accumulation. Further studies are needed to refine this dosage regimen and evaluate adverse effects in ill birds.

Comparison of clinical antibiotic susceptibility testing interpretations to CLSI standard interpretations

Background: Clinical antibiotic susceptibility testing (AST) interpretations based on minimum inhibitory concentrations (MIC) breakpoints are important for both clinical decision making and some reportable condition criteria. Standardization of MIC breakpoints across clinical laboratories is lacking; AST instruments are often validated for outdated Clinical and Laboratory Standards Institute (CLSI) MIC breakpoint guidelines. In this study, we analyzed the agreement between the reported clinical laboratory AST interpretations and the guideline CLSI interpretation. Methods: Clinical laboratory AST data collected from the Multisite Gram-Negative Surveillance Initiative (MuGSI) carbapenem-resistant Enterobacterales (CRE) surveillance program in Tennessee between 2019 and 2021 were utilized. MIC values from the clinical instrument were used to calculate CLSI standard interpretations following the 2019–2021 CLSI M100 guidelines. Agreement between the clinical laboratory and CLSI interpretations of the reported MIC values were measured using a weighted Cohen κ calculated in SAS version 9.4 software. Total matches were isolates with identical CLSI and clinical laboratory interpretations. Results: In total, 14 antibiotics were assessed. Of those, 9 antibiotics had at least moderate agreement (κ &gt; 0.41) between interpretations. Agreement between the clinical laboratory and the CLSI interpretations were near perfect (κ &gt; 0.81) for 3 antibiotics. Agreement between the clinical laboratory and the CLSI interpretations were poor for cefazolin (0.06) and ertapenem (0.14). Cefotaxime (−0.07) was the only antibiotic that suggested no agreement. Conclusions: Of the antibiotics included in the analysis, 36% had less than moderate agreement between clinical laboratory and CLSI AST interpretations. Given the increases in antimicrobial resistance globally and the emphasis placed on antibiotic stewardship, standardization across clinical AST panels should be prioritized. Inconsistencies have the potential to contribute to inappropriate antibiotic use in addition to under- or overidentification of reportable conditions, including CRE.Disclosures: None

Genetic relatedness among Neisseria gonorrhoeae isolates in southeastern Michigan

Background: Antimicrobial resistance (AMR) in Neisseria gonorrhoeae (NG) is an emerging public health crisis. Whole-genome sequencing (WGS) is an efficient way of predicting AMR determinants and their spread in the population. In a previous study, genotype–phenotype correlation analyses among NG isolates to determine antimicrobial resistance revealed discordance for azithromycin (AZM) and ceftriaxone (CRO) compared to other antibiotics. We investigated the evolutionary relatedness of NG isolated from patients with sexually transmitted infection (STI) using WGS in southeastern Michigan. Methods: Isolates, corresponding demographic data, and minimum inhibitory concentrations (MIC) via E-test (CRO) and broth microdilution (AZM) were obtained from the Michigan Department of Health and Human Services. Whole-genome libraries were prepared using the QIAseq FX kit followed by sequencing on a NovaSeq6000 (&gt;200X Coverage); samples were aligned to NG reference strain TUM19854 (NZ_AP023069.1) using Snippy before phylogenetic tree generation using Neighbor-joining clustering on the core.aln files. Phylogenetic trees were visualized using ATGC:PRESTO. Results: In total, 38 isolates were analyzed. Demographic data and susceptibility testing results are noted in Table 1. Most isolates were from males (63%), Blacks (44.7%), individuals living in Detroit City proper (47.3%), and those with unknown HIV status (55.2%). More than one-third had prior STI, including NG. All isolates were susceptible to CRO (CLSI susceptible breakpoint MIC, 1). Within the phylogenetic tree, 8 main branches were identified (Fig. 1). Moreover, 1 branch contained a cluster with 12 closely related isolates, which included the 9 isolates with nonsusceptible AZM. Nearly all isolates in that cluster had been collected from Detroit City proper and Wayne County, suggesting epidemiological overlap and potential spread of resistant strains in those counties.Conclusions: Comparative whole-genome and phylogenetic analyses among a subset of NG isolates revealed clustering of AZM resistance strains, suggesting a genomic component to AMR. Further studies are needed to determine the utility of WGS in diagnosis, outbreak investigations, and management of NG infections.Disclosures: None

Using bacterial pan-genome-based feature selection approach to improve the prediction of minimum inhibitory concentration (MIC).

Background: Predicting the resistance profiles of antimicrobial resistance (AMR) pathogens is becoming more and more important in treating infectious diseases. Various attempts have been made to build machine learning models to classify resistant or susceptible pathogens based on either known antimicrobial resistance genes or the entire gene set. However, the phenotypic annotations are translated from minimum inhibitory concentration (MIC), which is the lowest concentration of antibiotic drugs in inhibiting certain pathogenic strains. Since the MIC breakpoints that classify a strain to be resistant or susceptible to specific antibiotic drug may be revised by governing institutes, we refrained from translating these MIC values into the categories "susceptible" or "resistant" but instead attempted to predict the MIC values using machine learning approaches. Results: By applying a machine learning feature selection approach on a Salmonella enterica pan-genome, in which the protein sequences were clustered to identify highly similar gene families, we showed that the selected features (genes) performed better than known AMR genes, and that models built on the selected genes achieved very accurate MIC prediction. Functional analysis revealed that about half of the selected genes were annotated as hypothetical proteins (i.e., with unknown functional roles), and that only a small portion of known AMR genes were among the selected genes, indicating that applying feature selection on the entire gene set has the potential of uncovering novel genes that may be associated with and may contribute to pathogenic antimicrobial resistances. Conclusion: The application of the pan-genome-based machine learning approach was indeed capable of predicting MIC values with very high accuracy. The feature selection process may also identify novel AMR genes for inferring bacterial antimicrobial resistance phenotypes.

Assessment of accredited veterinary diagnostic laboratory use of breakpoints for canine and feline Escherichia coli infections in the United States and Canada.

The objective of this study was to assess the use of breakpoints in antibiotic susceptibility testing among veterinary diagnostic laboratories in the United States and Canada. An eight-question survey was conducted via phone and email to determine how often laboratories use breakpoints consistent with published guidelines in wounds, lower urinary tract infections and upper urinary tract infections (pyelonephritis) involving Escherichia coli, both in dogs and cats, for a total of 6 different hypothetical clinical scenarios. Nineteen veterinary diagnostic laboratories that perform antibiotic susceptibility testing on samples from dogs and cats in the United States or Canada and were accredited by the American Association of Veterinary Laboratory Diagnosticians (AAVLD) responded to the survey between January 15th and September 15th, 2022. The overall response rate of laboratories that were not excluded for known lack of dog and cat antibiotic susceptibility testing was 19 of 44 laboratories. Of the 17 respondent laboratories that reported using minimal inhibitory concentration breakpoints, only four laboratories used breakpoints consistent with published guidelines in all six clinical scenarios included in the survey. Our results suggest that there is clinically important variation in what breakpoints laboratories use to determine antibiotic susceptibility, which is of antibiotic stewardship and clinical relevance. Using breakpoints that are too high, too low, or inappropriately reporting "not interpreted" as the interpretive category may result in inappropriate use of antibiotics.

Micafungin pharmacodynamics predict clinical outcomes in hospitalized patients with candidemia caused by certain Candida species.

Echinocandins are guideline-preferred therapies for invasive candidiasis (IC). Fixed dosing of echinocandins is commonly used despite variations in body mass index and echinocandin susceptibility. The purpose of this study was to evaluate clinical outcomes of micafungin based on population-predicted pharmacokinetic/pharmacodynamic (PK/PD) factors and susceptibility. Candida isolate results were screened from bloodstream or intraabdominal cultures of hospitalized patients admitted to a quaternary-care teaching hospital. Patients with a first episode of IC who received micafungin for at least 48 h were included. Patients with mixed cultures or Candida species with no minimum inhibitory concentration (MIC) differences were excluded. Breakpoints for micafungin MIC and area under the curve (AUC)/MIC ratio were calculated using classification and regression tree (CART) analysis and related to clinical outcomes. Primary efficacy outcome was candida-contributable mortality, defined as mortality within 28 days of positive culture with concomitant micafungin treatment failure; secondary outcome was micafungin treatment failure within 28 days, MAIN RESULTS: Seventy-two patients were included of whom 15 (21%) had Candida-contributable mortality and 34 (47%) experienced micafungin treatment failure. C. albicans and C. tropicalis did not have differing MICs and these patients were excluded from the study. Mortality using a CART-derived MIC breakpoint of ≥1.0 mg/L was 38% compared to 9% in patients infected with lower MIC strains (p = 0.003). Patients with a CART-derived AUC/MIC value >138.5 had a mortality rate of 9% compared to 41% for patients with AUC/MIC values below the breakpoint (p = 0.0013). Results were similar for treatment failure rates, and both were confirmed using multivariable models. CART-derived micafungin MIC and AUC/MIC breakpoints predicted patient mortality and treatment failure for certain Candida species. These results support the need for further PK/PD studies to optimize echinocandin dosing and improve patient outcomes.

In vitro activity of imipenem/relebactam, meropenem/vaborbactam and comparators against Enterobacterales causing urinary tract infection in Taiwan: results from the Study for Monitoring Antimicrobial Resistance Trends (SMART), 2020

ObjectivesAntimicrobial resistance due to β-lactamase production is a worldwide issue, and β-lactamase inhibitors have been developed to overcome the growing problem. This study aimed to evaluate the in vitro activities of two recently introduced carbapenem/β-lactamase inhibitor combinations – imipenem/relebactam and meropenem/vaborbactam – and their comparators against Enterobacterales from patients with urinary tract infections (UTIs). MethodsEnterobacterales isolates from patients with UTIs in Taiwan and participating in the Study for Monitoring Antimicrobial Resistance Trends (SMART) in 2020 were included. Minimum inhibitory concentrations (MICs) for various antibiotics were determined using the broth microdilution method. Susceptibility was interpreted based on the MIC breakpoints of the Clinical and Laboratory Standards Institute 2022. Genes encoding common β-lactamases, including extended-spectrum β-lactamases, AmpC β-lactamases and carbapenemases, were detected using multiplex polymerase chain reaction. ResultsA total of 309 Enterobacterales isolates were included, against which both imipenem/relebactam and meropenem/vaborbactam exerted excellent efficacy (275 of 309, 95% and 288 of 309, 99.3%, respectively). Among imipenem non-susceptible isolates, 17 of 43 (39.5%) and 39 of 43 (90.7%) were susceptible to imipenem/relebactam and meropenem/vaborbactam, respectively. ConclusionImipenem/relebactam and meropenem/vaborbactam may be appropriate choices for treating UTIs due to Enterobacterales resistant to commonly used antibiotics. Continuous monitoring of antimicrobial resistance is crucial.

Impact of renal replacement therapy strategy on beta-lactam plasma concentrations: the BETAKIKI study—an ancillary study of a randomized controlled trial

BackgroundSepsis prognosis correlates with antibiotic adequacy at the early phase. This adequacy is dependent on antibacterial spectrum, bacterial resistance profile and antibiotic dosage. Optimal efficacy of beta-lactams mandates concentrations above the minimal inhibitory concentration (MIC) of the targeted bacteria for the longest time possible over the day. Septic acute kidney injury (AKI) is the most common AKI syndrome in ICU and often mandates renal replacement therapy (RRT) initiation. Both severe AKI and RRT may increase outside target antibiotic concentrations and ultimately alter patient’s prognosis.Patients and methodsThis is a secondary analysis of a randomized controlled trial that compared an early RRT initiation strategy with a delayed one in 620 critically ill patients undergoing severe AKI (defined by KDIGO 3). We compared beta-lactam trough concentrations between the two RRT initiation strategies. The primary outcome was the proportion of patients with sufficient trough plasma concentration of beta-lactams defined by trough concentration above 4 times the MIC. We hypothesized that early initiation of RRT could be associated with an insufficient antibiotic plasma trough concentration compared to patients allocated to the delayed strategy.ResultsOne hundred and twelve patients were included: 53 in the early group and 59 in the delayed group. Eighty-three patients (74%) had septic shock on inclusion. Trough beta-lactam plasma concentration was above 4 times the MIC breakpoint in 80.4% (n = 90) of patients of the whole population, without differences between the early and the delayed groups (79.2% vs. 81.4%, respectively, p = 0.78). On multivariate analysis, the presence of septic shock and a higher mean arterial pressure were significantly associated with a greater probability of adequate antibiotic trough concentration [OR 3.95 (1.14;13.64), p = 0.029 and OR 1.05 (1.01;1.10), p = 0.013, respectively). Evolution of procalcitonin level and catecholamine-free days as well as mortality did not differ whether beta-lactam trough concentration was above 4 times the MIC or not.ConclusionsIn this secondary analysis of a randomized controlled trial, renal replacement therapy initiation strategy did not significantly influence plasma trough concentrations of beta-lactams in ICU patients with severe AKI. Presence of septic shock on inclusion was the main variable associated with a sufficient beta-lactam concentration.Trial registration: The AKIKI trial was registered on ClinicalTrials.gov (Identifier: NCT01932190) before the inclusion of the first patient.

Antimicrobial Dilution Susceptibility Testing of Erysipelothrix rhusiopathiae According to CLSI Document VET06 Reveals High Resistance against Penicillin G, Erythromycin and Enrofloxacin

Erysipelas is a re-emerging disease in different poultry species. Antibiotic treatment is crucial to combat outbreaks in poultry flocks, but only very limited data on susceptibility are available. Recently, the Clinical and Laboratory Standard Institute established standardized guidelines and minimal inhibitory concentration breakpoints for E. rhusiopathiae when using the broth microdilution method. In the present investigation, these guidelines were applied to evaluate the antimicrobial susceptibility of 30 E. rhusiopathiae isolates derived from field outbreaks in poultry flocks towards penicillins, macrolides, lincosamides and fluoroquinolones. All isolates were identified by MALDI-TOF MS. The majority of isolates belonged to two serovars, 1b and 5. More than 40% of the isolates proved resistant to penicillin G, with values ranging from 0.25 to 8 µg/mL. Furthermore, the majority of isolates were found resistant to erythromycin (76.7%; MIC 2–4 µg/mL) and enrofloxacin (60.0%; MIC ≥ 2 µg/mL), altogether limiting treatment options. In contrast, most of the isolates proved susceptible to ampicillin and ceftiofur with MICs ≤ 0.25 µg/mL and ≤2 µg/mL, respectively. A great variety of antimicrobial resistance patterns was found, and multidrug resistance was detected in one-third of the isolates. The presented data are helpful to raise awareness for the antimicrobial resistance of a zoonotic pathogen in context of the One Health concept.

Fecal pharmacokinetics/pharmacodynamics characteristics of fidaxomicin and vancomycin against Clostridioides difficile infection elucidated by in vivo feces-based infectious evaluation models

ObjectivesThe pharmacokinetics (PK)/pharmacodynamics (PD; PK/PD) characteristics of fidaxomicin (FDX) and vancomycin (VCM) against Clostridioides difficile infection (CDI) are yet to be elucidated because of the lack of an established PK/PD analysis method for intestinal infections and unabsorbed oral drugs. Here, we developed a feces-based PK/PD analysis method and determined the fecal PK/PD index, with target values of FDX and VCM against CDI. MethodsThe antimicrobial susceptibility, time-kill curves, and post-antibiotic effects (PAEs) of FDX and VCM against C. difficile were determined in vitro. The optimal fecal PK/PD indices, with target values, were determined from the results of PK and PD studies involving 5-week-old female C57BL/6J mice infected with C. difficile ATCC® 43255. The minimum inhibitory concentration (MIC) breakpoints for C. difficile were estimated based on clinical data concerning fecal antibiotic concentrations in patients with CDI. ResultsFDX and VCM inhibited C. difficile growth via time-dependent antibacterial activity and exerted PAEs. In the CDI mouse model experiments, the changes in C. difficile load and clinical cures (72-hour survival rates and clinical sickness score grading) were most highly correlated with the ratio of area under the fecal drug concentration-time curve to MIC (AUC0→∞/MIC). The target AUC0→∞/MIC values of FDX and VCM for 3 log10 reduction in C. difficile load was 13,173 and 8,308, respectively. The MIC breakpoints of FDX and VCM for C. difficile was estimated to be 1.0 and 2.0 μg/mL, respectively. ConclusionsThe developed in vivo feces-based PK/PD analysis method elucidated the optimal fecal PK/PD index, with target values of FDX and VCM against CDI.