Frontline Antibiotics Research Articles

Alkoxyphenylthiazoles with broad-spectrum activity against multidrug-resistant gram-positive bacterial pathogens

With the continued rise of antibiotic resistance and reduced susceptibility to almost all front-line antibiotics, multidrug-resistant Gram-positive bacterial infections represent an incessant threat to healthcare providers. This study presents a new series of phenylthiazole compounds where two active moieties were combined into one scaffold. The antibacterial activity of the hybrid structures extended to include several clinically-relevant multi-drug resistant pathogens including methicillin-resistant and vancomycin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis, vancomycin-resistant enterococci, cephalosporin-resistant and methicillin-resistant Streptococcus pneumoniae, and Listeria monocytogenes. In addition, the most potent compounds, 16a and 17a, exhibited a fast bactericidal mode of action in vitro with low susceptibility to induce bacterial resistance. In addition to its potent spectrum of activity against Gram-positive bacterial pathogens, compound 17a was found to be metabolically stable in rats, with a half-life of 4 h.

Novel aromatic polyketides from soil Streptomyces spp.: purification, characterization and bioactivity studies

Aromatic polyketides are important therapeutic compounds which include front line antibiotics and anticancer drugs. Since most of the aromatic polyketides are known to be produced by soil dwelling Streptomyces, 54 Streptomyces strains were isolated from the soil samples. Five isolates, R1, B1, R3, R5 and Y8 were found to be potent aromatic polyketide producers and were identified by 16S rRNA gene sequencing as Streptomyces spectabilis, Streptomyces olivaceus, Streptomyces purpurascens, Streptomyces coeruleorubidus and Streptomyces lavendofoliae respectively. Their sequences have been deposited in the GenBank under the accession numbers KF468818, KF681280, KF395224, KF527511 and KF681281 respectively. The Streptomyces strains were cultivated in the media following critically optimised culture conditions. The resulting broth extracts were fractionated on a silica gel column and preparative TLC to obtain pure compounds. The pure compounds were tested for bioactivity and the most potent compound from each isolate was identified by UV-Vis, IR and NMR spectroscopic methods. Isolated S. spectabilis (R1), yielded one potent compound identified as dihydrodaunomycin with an MIC of 4µg/ml against Bacillus cereus and an IC50 value of 24µM against HeLa. S. olivaceus (B1), yielded a comparatively less potent compound, elloramycin. S. purpurascens (R3) yielded three compounds, rhodomycin, epelmycin and obelmycin. The most potent compound was rhodomycin with an MIC of 2µg/ml against B. cereus and IC50 of 15µM against HeLa. S. coeruleorubidus (R5), yielded daunomycin showing an IC50 of 10µM and also exhibiting antimetastatic properties against HeLa. S. lavendofoliae (Y8), yielded a novel aclacinomycin analogue with IC50 value of 2.9µM and potent antimetastatic properties at 1µM concentration against HeLa. The study focuses on the characterization of aromatic polyketides from soil Streptomyces spp., which can serve as potential candidates for development of chemotherapeutic drugs in future.

Dominant serotype distribution and antimicrobial resistance profile of Shigella spp. in Xinjiang, China.

Shigella represents one of the major diarrhea-inducing pathogens threatening public health, but its prevalence and antimicrobial resistance profile in Xinjiang Uygur Autonomous region, China, remains unclear. We conducted comprehensive investigation of Shigella serotype distribution and antimicrobial resistance pattern in Xinjiang, identifying 458 Shigella isolates between 2008 to 2014. Shigella flexneri was identified as predominant species, and several S. flexneri serotypes were isolated, including atypical serotypes 1c, 2c, and 4s. Dominant S. flexneri serotypes were 2a, 1b, 2b, and Xv, different from those generally dominant in China. A hybrid serotype pattern was observed, which included the major Chinese serotypes (2a, Xv) and those predominant in Pakistan (1b, 2b). Shigella sonnei was shown to have a lower frequency compared with that generally observed in China, but an increasing trend of infections associated with this pathogen was observed. Furthermore, a high frequency of drug resistance and different Shigella antimicrobial resistance patterns were demonstrated as well, including very severe resistance phenotypes, such as multidrug resistance and resistance to frontline antibiotics. Seventy-five cephalosporin-resistant Shigella isolates were frequently identified with the resistance determinants that can undergo horizontal transfer, such as blaOXA, blaTEM, blaCTX-M, and integrons, facilitating the development of cephalosporin resistance among Shigella subtypes. Additionally, genetic analyses demonstrated that all 86 quinolone-resistant S. flexneri isolates possess 3–4 mutation sites in quinolone resistance-determining regions, primarily contributing to their resistance to quinolone. However, S. sonnei isolates were not shown to be quinolone resistant. Co-resistance to cephalosporins and quinolones was detected in 17 S. flexneri isolates, and these isolates were additionally multidrug resistant and carried β-lactamase genes and quinolone-resistance determinants. As is demonstrated in this study, dominant serotypes of Shigella were distributed in unique trend with dangerous drug resistance patterns. Novel strategies are urgently required to prevent the development of drug resistance among diarrhea-inducing pathogens.

Epidemiology and impact of bloodstream infections among kidney transplant recipients: A retrospective single-center experience.

Bloodstream infection (BSI) represents an important source of morbidity and mortality, as well as an increasing therapeutic challenge, among solid organ transplant recipients. Understanding the epidemiological and microbiological characteristics of BSI following renal transplantation is paramount to the implementation of appropriate preventative and therapeutic measures. We conducted a retrospective review of all BSI episodes occurring between July 2009 and April 2016 in adult patients, who received a renal transplant at Royal Free London hospital. A total of 116 episodes of BSI occurred in 87 patients, 43 (49.4%) of them men. The mean age at BSI was 54.37±12.81years. Late-onset BSI (>12months post transplant) represented 55.2%, with the median time to BSI being 16.28month. Sixty-seven patients had single BSI and 20 had recurrent episodes. Enterobacteriaceae were responsible for 73.7% of BSI, with Escherichia coli the commonest causative organism (46.6%). The urinary tract was the most frequent source of infection in 56.9%. Among the E.coli infections, 100% of the tested isolates were sensitive to meropenem, ertapenem, tigecycline, and fosfomycin, and >90% were sensitive to piperacillin-tazobactam, amikacin, and colistin. Lower susceptibility rates were encountered for ceftriaxone (70.6%), amoxicillin-clavulanic acid (48.1%), cotrimoxazole (40.4%), trimethoprim (37.3%), and amoxicillin (21.6%). During BSI, the median serum creatinine increased from a reference of 131μmol/L to a peak of 219μmol/L. Acute kidney injury (AKI) complicated 75/116 BSI episodes (64.7%)-stage 1: 34, stage 2: 31, and stage 3 AKI: 10 episodes. After 3months, the median creatinine remained elevated at 146μmol/L. The 3-month mortality rate was 8% (7/87), and the death-censored graft loss was 6.9% (6/87). No significant difference was seen between BSI of urinary and non-urinary sources in the incidence of AKI (χ2 =0.24, P=.6) or the percentage of creatinine change between baseline and peak and 3-month creatinines (P=.2 and .7 respectively). Urinary tract infection remains the commonest source of systemic infection among kidney transplant recipients and resistance to commonly used frontline antibiotics is common; thus, prevention and early detection are paramount. The appropriate choice of initial empirical antibiotic is vital to improve the outcome. Each unit needs to understand the epidemiology of organisms causing BSI in their transplant patients and their antibiotic susceptibilities.

The inhibitory effects of eighteen front-line antibiotics on the substrate uptake mediated by human Organic anion/cation transporters, Organic anion transporting polypeptides and Oligopeptide transporters in in vitro models

Human Organic anion/cation transporters (OATs/OCTs), Organic anion transporting polypeptides (OATPs) and proton-coupled Oligopeptide transporters (PepTs) are important membrane transporters responsible of the cellular influx of drugs in many human key tissues. Inhibitor(s) impacting on the cellular uptake of transporter drug substrates is one of the primary causes of drug-drug interactions that lead to unsatisfied therapeutic outcomes and/or unwanted side effects. In the current study, we selected eighteen antibiotic agents used in infectious disease treatment and comprehensively evaluated their inhibitory effects on the substrate uptake mediated through the essential OATs/OCTs, OATPs and PepTs isoforms. Transport functional assay, dose-response curve and kinetic analysis were performed on the HEK293 cells over-expressing each of these transporter genes. Our data revealed that nitrofurantoin, sulfadiazine and metronidazole significantly inhibited the transport activity of OAT3 (IC50 values of 6.23±1.33μM, 6.65±1.30μM and 6.51±0.99μM; Ki values of 5.86μM, 3.98μM and 6.48μM, respectively). Trimethoprim and ciprofloxacin potently decreased the substrate uptake mediated via OATP1A2 (IC50 values of 9.35±1.10μM and 9.25±1.18μM; Ki values of 8.19μM and 7.64μM, respectively). In addition, these antibiotic agents consistently decreased methotrexate influx via OAT3 and OATP1A2. In summary, our study is the first to show that nitrofurantoin, sulfadiazine and metronidazole are potent inhibitors of OAT3 and trimethoprim is a novel inhibitor of OATP1A2. Our study also provides new evidence for the drug-drug interactions of ciprofloxacin with OATP1A2 drug substrates like methotrexate. Therefore, precautions are required when co-administering these antibiotics with OAT3 or OATP1A2 drug substrates.

An Antibacterial β-Lactone Kills Mycobacterium tuberculosis by Disrupting Mycolic Acid Biosynthesis.

The spread of antibiotic resistance is a major challenge for the treatment of Mycobacterium tuberculosis infections. In addition, the efficacy of drugs is often limited by the restricted permeability of the mycomembrane. Frontline antibiotics inhibit mycomembrane biosynthesis, leading to rapid cell death. Inspired by this mechanism, we exploited β-lactones as putative mycolic acid mimics to block serine hydrolases involved in their biosynthesis. Among a collection of β-lactones, we found one hit with potent anti-mycobacterial and bactericidal activity. Chemical proteomics using an alkynylated probe identified Pks13 and Ag85 serine hydrolases as major targets. Validation through enzyme assays and customized 13 C metabolite profiling showed that both targets are functionally impaired by the β-lactone. Co-administration with front-line antibiotics enhanced the potency against M. tuberculosis by more than 100-fold, thus demonstrating the therapeutic potential of targeting mycomembrane biosynthesis serine hydrolases.

Trends in the Genetic Background of Methicillin-Resistant Staphylococcus Aureus Clinical Isolates in a South African Hospital: An Institutional-Based Observational Study.

Background:This study sought to understand the epidemio-ecological dynamics of MRSA isolates associated with a South African hospital over a period spanning year 2007-8 (a previous study reported in 2009) and year 2010-11 (this study).Methods:One hundred and ninety three isolates were characterised by molecular fingerprinting methods including pulsed field gel electrophoresis (PFGE), spa typing, agr-typing, SCCmec-typing, and multilocus sequence typing (MLST). The Vitek-2 automated antibiogram of representative isolates was also performed.Results:Our data shows that the distribution of MRSA strains among the different clinical conditions was rarely dependent on the genetic backbone or genotype. Compared to the previous survey in 2009, CA-MRSA isolates increased by 31% while HA-MRSA isolates decreased by 17%. An increase in genetic diversity was also revealed including the detection of three pandemic clonal complexes (spa type t012-ST36/CC30, spa type t037-ST239/CC8, spa type t891-ST22/CC22 and spa type t1257-ST612/CC8). Majority of the genotypes were classified as Spa Cluster B-SCCmec I-agr I 19.2%; (37/193) Spa Cluster A-SCCmercury-agr I 14.5%; (28/193)Conclusion:This study reveals that increased diversity in MRSA genetic background was associated with resistance to frontline antibiotics. Also, an increase was recorded in the CA-MRSA/HA-MRSA ratio within a 5-year period despite the continuous dominance of the HA-MRSA genotype.

Identification and characterization of potential druggable targets among hypothetical proteins of extensively drug resistant Mycobacterium tuberculosis (XDR KZN 605) through subtractive genomics approach

Among the resistant isolates of tuberculosis (TB), the multidrug resistance tuberculosis (MDR-TB) and extensively drug resistant tuberculosis (XDR-TB) are the areas of growing concern for which the front-line antibiotics are no more effective. As a result, the search of new therapeutic targets against TB is an imperative need of time. On the other hand, the target identification is an a priori step in drug discovery based research. Furthermore, the availability of the complete proteomic data of extensively drug resistant Mycobacterium tuberculosis (XDR-MTB) made it possible to carry out in silico analysis for the discovery of new drug targets. In the current study, we aimed to prioritize the potential drug targets among the hypothetical proteins of XDR-TB via subtractive genomics approach. In the subtractive genomics, we stepwise reduced the complete proteome of XDR-MTB to only two hypothetical proteins and evidently proposed them as new therapeutic targets. The 3D structure of one of the two target proteins was predicted via homology modeling and later on, validated by various analysis tools. Our study suggested that the domains identified and the motif hits found in the sequences of the shortlisted drug targets are crucial for the survival of the XDR-MTB. To the best of our knowledge, the current study is the first attempt in which the complete proteomic data of XDR-MTB was subjected to the computational subtractive genomics approach and therefore, would provide an opportunity to identify the unique therapeutic targets against deadly XDR-MTB.

Antagonism between Front-Line Antibiotics Clarithromycin and Amikacin in the Treatment of Mycobacterium abscessus Infections Is Mediated by the whiB7 Gene.

ABSTRACTCombinations of antibiotics, each individually effective against Mycobacterium abscessus, are routinely coadministered based on the concept that this minimizes the spread of antibiotic resistance. However, our in vitro data contradict this assumption and instead document antagonistic interactions between two antibiotics (clarithromycin and amikacin) used to treat M. abscessus infections. Clinically relevant concentrations of clarithromycin induced increased resistance to both amikacin and itself. The induction of resistance was dependent on whiB7, a transcriptional activator of intrinsic antibiotic resistance that is induced by exposure to many different antibiotics. In M. abscessus, the deletion of whiB7 (MAB_3508c) resulted in increased sensitivity to a broad range of antibiotics. WhiB7 was required for transcriptional activation of genes that confer resistance to three commonly used anti-M. abscessus drugs: clarithromycin, amikacin, and tigecycline. The whiB7-dependent gene that conferred macrolide resistance was identified as erm(41) (MAB_2297), which encodes a ribosomal methyltransferase. The whiB7-dependent gene contributing to amikacin resistance was eis2 (MAB_4532c), which encodes a Gcn5-related N-acetyltransferase (GNAT). Transcription of whiB7 and the resistance genes in its regulon was inducible by subinhibitory concentrations of clarithromycin but not by amikacin. Thus, exposure to clarithromycin, or likely any whiB7-inducing antibiotic, may antagonize the activities of amikacin and other drugs. This has important implications for the management of M. abscessus infections, both in cystic fibrosis (CF) and non-CF patients.

Baseline screening for the presence of antimicrobial resistance in E. coli isolated from Kuwait's marine environment

Here we present the findings of a study where 598 isolates of Escherichia coli (351 derived from seawater; 247 derived from the Venus clam, Circenita callipyga) were obtained from Kuwait's marine environment. Isolates were screened for their potential resistance to an array of 23 commonly deployed frontline antibiotics. Results demonstrate the resistant was widespread across all sites with high-levels of resistance (seawater: summer 89–64%; winter 90–57% and biota: summer 77%; winter 88%) observed to at least 1 of the 23 antibiotics tested. Resistance to Ampicillin was by far the most widely observed profile in seawater and biota across both summer and winter seasons, with 55.9 to 70.9% isolates displaying resistance to this antibiotic. This study demonstrates the potential of AMR screening to be used in Kuwait to detect issues related to water quality and the consequences it may pose for human health.

Pharmacokinetic studies of a three-component complex that repurposes the front line antibiotic isoniazid against Mycobacterium tuberculosis

The frontline tuberculosis (Tb) antibiotic isoniazid has been repurposed using a three component complex aimed at increasing the delivery efficiency and adding new avenues to its mechanism of action. This study focuses on pharmacokinetic studies of the isoniazid-sucrose–copper (II)-PEG-3350 complex. The assays include the Plasma Protein Binding Assay (85.8%), Caco-2 Permeability Assay (B→APapp, 0.13 × 10−6 cm/s), Cytochrome P450 Inhibition Assay (i.e. CYP2B6, IC50 = 7.26 μM), In vitro microsomal Stability Assay (t1/2 NADPH-Dependent > 240 min), and HepG2 Cytotoxicity (no toxicity). The National Cancer Institute's 60 cell line panel is used to measure activity against cancer cells. The percent growth values averaged over all 60 cell lines indicates the complex has no anti-cancer activity, which also suggests a lack of general toxicity. It also provides data for the complexes specificity against Mycobacterium tuberculosis.

A morphometric study of human subcarinal angle in different age groups in both sexes and its clinical implications

To evaluate the interactions between the crude extracts of Cocos nucifera (C. nucifera) and six front line antibiotics (ampicillin sodium salt, penicillin G sodium, amoxicillin, chloramphenicol, ciprofloxacin and tetracycline hydrochloride), against some bacterial pathogens linked with human infection.The pulverized husk of C. nucifera was dissolved in 95% n-hexane and extracted using Soxhlet extraction method and sterile distilled water (aqueous). The antibacterial susceptibility of the crude extracts of C. nucifera was tested against environmental and clinical strains (6) obtained from the South African Bureau of Standards (SABS), Vibrio (6) and Listeria pathogens (6). The agar-well diffusion method was used for screening the extracts for their antibacterial activity. The minimum inhibitory concentration and minimum bactericidal concentration of the extracts were determined. Time-kill assay was used to evaluate bactericidal and/or bacteriostatic activity. The synergistic effect of the crude extracts and antibiotics was assessed and evaluated by adopting the checkerboard methods.With the time-kill assay, the highest bactericidal activity was observed on Vibrio fluvialis EL041 with a −5.6 ± 0.2 log10 CFU/mL decrease in cell density as a result of the combination of the extracts and chloramphenicol at two-fold minimum inhibitory concentrations. Synergisms using the time-kill assay constituted about 72%, while indifference constituted about 28%. The checkerboard method revealed synergistic interaction in 67% of the combinations, and indifference in 33%. There was no specificity in the observed synergy to a particular class of antibiotics.This investigation suggests the crude extracts of C. nucifera to be a potential broad spectrum antimicrobial compound. Therefore, further study is needed to isolate the pure compounds from these crude extracts.

Configurations of blood supply of brain

To evaluate the interactions between the crude extracts of Cocos nucifera (C. nucifera) and six front line antibiotics (ampicillin sodium salt, penicillin G sodium, amoxicillin, chloramphenicol, ciprofloxacin and tetracycline hydrochloride), against some bacterial pathogens linked with human infection.The pulverized husk of C. nucifera was dissolved in 95% n-hexane and extracted using Soxhlet extraction method and sterile distilled water (aqueous). The antibacterial susceptibility of the crude extracts of C. nucifera was tested against environmental and clinical strains (6) obtained from the South African Bureau of Standards (SABS), Vibrio (6) and Listeria pathogens (6). The agar-well diffusion method was used for screening the extracts for their antibacterial activity. The minimum inhibitory concentration and minimum bactericidal concentration of the extracts were determined. Time-kill assay was used to evaluate bactericidal and/or bacteriostatic activity. The synergistic effect of the crude extracts and antibiotics was assessed and evaluated by adopting the checkerboard methods.With the time-kill assay, the highest bactericidal activity was observed on Vibrio fluvialis EL041 with a −5.6 ± 0.2 log10 CFU/mL decrease in cell density as a result of the combination of the extracts and chloramphenicol at two-fold minimum inhibitory concentrations. Synergisms using the time-kill assay constituted about 72%, while indifference constituted about 28%. The checkerboard method revealed synergistic interaction in 67% of the combinations, and indifference in 33%. There was no specificity in the observed synergy to a particular class of antibiotics.This investigation suggests the crude extracts of C. nucifera to be a potential broad spectrum antimicrobial compound. Therefore, further study is needed to isolate the pure compounds from these crude extracts.

Relation between renal length and height of an individual using computed tomography

To evaluate the interactions between the crude extracts of Cocos nucifera (C. nucifera) and six front line antibiotics (ampicillin sodium salt, penicillin G sodium, amoxicillin, chloramphenicol, ciprofloxacin and tetracycline hydrochloride), against some bacterial pathogens linked with human infection.The pulverized husk of C. nucifera was dissolved in 95% n-hexane and extracted using Soxhlet extraction method and sterile distilled water (aqueous). The antibacterial susceptibility of the crude extracts of C. nucifera was tested against environmental and clinical strains (6) obtained from the South African Bureau of Standards (SABS), Vibrio (6) and Listeria pathogens (6). The agar-well diffusion method was used for screening the extracts for their antibacterial activity. The minimum inhibitory concentration and minimum bactericidal concentration of the extracts were determined. Time-kill assay was used to evaluate bactericidal and/or bacteriostatic activity. The synergistic effect of the crude extracts and antibiotics was assessed and evaluated by adopting the checkerboard methods.With the time-kill assay, the highest bactericidal activity was observed on Vibrio fluvialis EL041 with a −5.6 ± 0.2 log10 CFU/mL decrease in cell density as a result of the combination of the extracts and chloramphenicol at two-fold minimum inhibitory concentrations. Synergisms using the time-kill assay constituted about 72%, while indifference constituted about 28%. The checkerboard method revealed synergistic interaction in 67% of the combinations, and indifference in 33%. There was no specificity in the observed synergy to a particular class of antibiotics.This investigation suggests the crude extracts of C. nucifera to be a potential broad spectrum antimicrobial compound. Therefore, further study is needed to isolate the pure compounds from these crude extracts.

Pseudomonas aeruginosa Alters Staphylococcus aureus Sensitivity to Vancomycin in a Biofilm Model of Cystic Fibrosis Infection.

ABSTRACTThe airways of cystic fibrosis (CF) patients have thick mucus, which fosters chronic, polymicrobial infections. Pseudomonas aeruginosa and Staphylococcus aureus are two of the most prevalent respiratory pathogens in CF patients. In this study, we tested whether P. aeruginosa influences the susceptibility of S. aureus to frontline antibiotics used to treat CF lung infections. Using our in vitro coculture model, we observed that addition of P. aeruginosa supernatants to S. aureus biofilms grown either on epithelial cells or on plastic significantly decreased the susceptibility of S. aureus to vancomycin. Mutant analyses showed that 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO), a component of the P. aeruginosa Pseudomonas quinolone signal (PQS) system, protects S. aureus from the antimicrobial activity of vancomycin. Similarly, the siderophores pyoverdine and pyochelin also contribute to the ability of P. aeruginosa to protect S. aureus from vancomycin, as did growth under anoxia. Under our experimental conditions, HQNO, P. aeruginosa supernatant, and growth under anoxia decreased S. aureus growth, likely explaining why this cell wall-targeting antibiotic is less effective. P. aeruginosa supernatant did not confer additional protection to slow-growing S. aureus small colony variants. Importantly, P. aeruginosa supernatant protects S. aureus from other inhibitors of cell wall synthesis as well as protein synthesis-targeting antibiotics in an HQNO- and siderophore-dependent manner. We propose a model whereby P. aeruginosa causes S. aureus to shift to fermentative growth when these organisms are grown in coculture, leading to reduction in S. aureus growth and decreased susceptibility to antibiotics targeting cell wall and protein synthesis.

In vitro assessment of the synergism between extracts of Cocos nucifera husk and some standard antibiotics

ObjectiveTo evaluate the interactions between the crude extracts of Cocos nucifera (C. nucifera) and six front line antibiotics (ampicillin sodium salt, penicillin G sodium, amoxicillin, chloramphenicol, ciprofloxacin and tetracycline hydrochloride), against some bacterial pathogens linked with human infection. MethodsThe pulverized husk of C. nucifera was dissolved in 95% n-hexane and extracted using Soxhlet extraction method and sterile distilled water (aqueous). The antibacterial susceptibility of the crude extracts of C. nucifera was tested against environmental and clinical strains (6) obtained from the South African Bureau of Standards (SABS), Vibrio (6) and Listeria pathogens (6). The agar-well diffusion method was used for screening the extracts for their antibacterial activity. The minimum inhibitory concentration and minimum bactericidal concentration of the extracts were determined. Time-kill assay was used to evaluate bactericidal and/or bacteriostatic activity. The synergistic effect of the crude extracts and antibiotics was assessed and evaluated by adopting the checkerboard methods. ResultsWith the time-kill assay, the highest bactericidal activity was observed on Vibrio fluvialis EL041 with a −5.6 ± 0.2 log10 CFU/mL decrease in cell density as a result of the combination of the extracts and chloramphenicol at two-fold minimum inhibitory concentrations. Synergisms using the time-kill assay constituted about 72%, while indifference constituted about 28%. The checkerboard method revealed synergistic interaction in 67% of the combinations, and indifference in 33%. There was no specificity in the observed synergy to a particular class of antibiotics. ConclusionsThis investigation suggests the crude extracts of C. nucifera to be a potential broad spectrum antimicrobial compound. Therefore, further study is needed to isolate the pure compounds from these crude extracts.

RelA Mutant Enterococcus faecium with Multiantibiotic Tolerance Arising in an Immunocompromised Host.

ABSTRACTSerious bacterial infections in immunocompromised patients require highly effective antibacterial therapy for cure, and thus, this setting may reveal novel mechanisms by which bacteria circumvent antibiotics in the absence of immune pressure. Here, an infant with leukemia developed vancomycin-resistant Enterococcus faecium (VRE) bacteremia that persisted for 26 days despite appropriate antibiotic therapy. Sequencing of 22 consecutive VRE isolates identified the emergence of a single missense mutation (L152F) in relA, which constitutively activated the stringent response, resulting in elevated baseline levels of the alarmone guanosine tetraphosphate (ppGpp). Although the mutant remained susceptible to both linezolid and daptomycin in clinical MIC testing and during planktonic growth, it demonstrated tolerance to high doses of both antibiotics when growing in a biofilm. This biofilm-specific gain in resistance was reflected in the broad shift in transcript levels caused by the mutation. Only an experimental biofilm-targeting ClpP-activating antibiotic was able to kill the mutant strain in an established biofilm. The relA mutation was associated with a fitness trade-off, forming smaller and less-well-populated biofilms on biological surfaces. We conclude that clinically relevant relA mutations can emerge during prolonged VRE infection, causing baseline activation of the stringent response, subsequent antibiotic tolerance, and delayed eradication in an immunocompromised state.

Efficacy of frontline antibiotics therapy in the treatment of Helicobacter pylori-negative gastric low-grade mucosa-associated lymphoid tissue lymphoma.

e19024Background: Previous series reports revealed that certain proportions of Helicobacter pylori (HP)-negative gastric mucosa-associated lymphoid tissue (MALT) lymphoma may respond to antibiotics...

Influence of Minimum Inhibitory Concentration in Clinical Outcomes of Enterococcus faecium Bacteremia Treated With Daptomycin: Is it Time to Change the Breakpoint?

Daptomycin has become a front-line antibiotic for multidrug-resistant Enterococcus faecium bloodstream infections (BSIs). We previously showed that E. faecium strains with daptomycin minimum inhibitory concentrations (MICs) in the higher end of susceptibility frequently harbor mutations associated with daptomycin resistance. We postulate that patients with E. faecium BSIs exhibiting daptomycin MICs of 3-4 µg/mL treated with daptomycin are more likely to have worse clinical outcomes than those exhibiting daptomycin MICs ≤2 µg/mL. We conducted a multicenter retrospective cohort study that included adult patients with E. faecium BSI for whom initial isolates, follow-up blood culture data, and daptomycin administration data were available. A central laboratory performed standardized daptomycin MIC testing for all isolates. The primary outcome was microbiologic failure, defined as clearance of bacteremia ≥4 days after the index blood culture. The secondary outcome was all-cause in-hospital mortality. A total of 62 patients were included. Thirty-one patients were infected with isolates that exhibited daptomycin MICs of 3-4 µg/mL. Overall, 34 patients had microbiologic failure and 25 died during hospitalization. In a multivariate logistic regression model, daptomycin MICs of 3-4 µg/mL (odds ratio [OR], 4.7 [1.37-16.12]; P = .014) and immunosuppression (OR, 5.32 [1.20-23.54]; P = .028) were significantly associated with microbiologic failure. Initial daptomycin dose of ≥8 mg/kg was not significantly associated with evaluated outcomes. Daptomycin MICs of 3-4 µg/mL in the initial E. faecium blood isolate predicted microbiological failure of daptomycin therapy, suggesting that modification in the daptomycin breakpoint for enterococci should be considered.

Genomic islands 1 and 2 play key roles in the evolution of extensively drug-resistant ST235 isolates of Pseudomonas aeruginosa.

Pseudomonas aeruginosa are noscomially acquired, opportunistic pathogens that pose a major threat to the health of burns patients and the immunocompromised. We sequenced the genomes of P. aeruginosa isolates RNS_PA1, RNS_PA46 and RNS_PAE05, which displayed resistance to almost all frontline antibiotics, including gentamicin, piperacillin, timentin, meropenem, ceftazidime and colistin. We provide evidence that the isolates are representatives of P. aeruginosa sequence type (ST) 235 and carry Tn6162 and Tn6163 in genomic islands 1 (GI1) and 2 (GI2), respectively. GI1 disrupts the endA gene at precisely the same chromosomal location as in P. aeruginosa strain VR-143/97, of unknown ST, creating an identical CA direct repeat. The class 1 integron associated with Tn6163 in GI2 carries a blaGES-5–aacA4–gcuE15–aphA15 cassette array conferring resistance to carbapenems and aminoglycosides. GI2 is flanked by a 12 nt direct repeat motif, abuts a tRNA-gly gene, and encodes proteins with putative roles in integration, conjugative transfer as well as integrative conjugative element-specific proteins. This suggests that GI2 may have evolved from a novel integrative conjugative element. Our data provide further support to the hypothesis that genomic islands play an important role in de novo evolution of multiple antibiotic resistance phenotypes in P. aeruginosa.