Susceptibility Breakpoints Research Articles

Antimicrobial susceptibility of enterobacterales causing bloodstream infection in United States medical centres: comparison of aztreonam-avibactam with beta-lactams active against carbapenem-resistant enterobacterales

BackgroundBloodstream infection (BSI) is associated with poor outcomes especially when effective antimicrobial therapy and control of infection source are delayed. As the frequency of Enterobacterales producing metallo-β-lactamases (MBL) and/or OXA-48–like carbapenemases is increasing in some United States (US) medical centres, effective antimicrobials to treat the infections caused by these organisms are urgently needed. Aztreonam-avibactam is under clinical development for treatment of infections caused by Gram-negative bacteria, including MBL producers.ObjectivesTo evaluate the antimicrobial susceptibility of Enterobacterales causing BSI in US medical centres and compare the activity of aztreonam-avibactam with ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, cefiderocol, and other antimicrobials used to treat BSI.Methods4,802 Enterobacterales were consecutively collected (1/patient) from 72 US medical centres in 2020–2022 and susceptibility tested by broth microdilution. Aztreonam-avibactam was tested with avibactam at a fixed concentration of 4 mg/L. A pharmacokinetic/pharmacodynamic susceptible breakpoint of ≤ 8 mg/L was applied for aztreonam-avibactam for comparison. Carbapenem-resistant Enterobacterales (CRE) isolates were tested for β-lactamase–encoding genes using Next-generation sequencing.ResultsAztreonam-avibactam was highly active against Enterobacterales; only 2 isolates showed aztreonam-avibactam MICs > 8 mg/L: 1 meropenem-susceptible E. coli and 1 K. aerogenes (CRE). All carbapenemase producers and 98.0% of CRE were inhibited at an aztreonam-avibactam MIC of ≤ 8 mg/L. CRE susceptibility rates were 81.6% for ceftazidime-avibactam, 65.3% for meropenem-vaborbactam, 61.2% for imipenem-relebactam, and 87.8% for cefiderocol. Aztreonam-avibactam retained activity (MIC, ≤ 8 mg/L) against all (100.0%) meropenem-vaborbactam nonsusceptible (n = 17), 99.5% of imipenem-relebactam nonsusceptible (n = 206), and 90.0% of ceftazidime-avibactam nonsusceptible (n = 10) isolates. The most common carbapenemases were KPC-2/3 (57.1% of CREs), OXA-48–like (16.3%), and NDM (14.3%). A carbapenemase gene was not observed in 12.3% of CREs. Ceftazidime-avibactam and meropenem-vaborbactam were active against 100.0% of KPC producers, but ceftazidime-avibactam showed limited activity against MBL producers and meropenem-vaborbactam showed limited activity against OXA-48–like and MBL producers. The most active non–β-lactam comparators against CRE were gentamicin (49.0% susceptible) and amikacin (44.9% susceptible).ConclusionsAztreonam-avibactam demonstrated potent activity against a large collection of Enterobacterales isolated from patients with BSI in US hospitals, including CRE, MBL producers, and isolates resistant to recently approved β-lactamase inhibitor combinations.

Acquired blaCfxA-3 carried by a conjugative transposon or duplicated intrinsic blaCME-3 mediates cefiderocol resistance in Elizabethkingia anophelis clinical isolates

ObjectivesElizabethkingia spp. are resistant to multiple antibiotics. This study aimed to determine in vitro and in vivo activities of cefiderocol against Elizabethkingia spp. and to investigate resistance mechanisms. MethodsBloodstream isolates were collected from four hospitals. In vitro and in vivo activities were determined using broth microdilution and the wax moth model, respectively. Genome comparison and gene editing were used to confirm the contribution of target genes. Conjugation experiments and serial passage were used to determine transferability and stability, respectively. A MIC of ≤ 4 mg/L was designated as the susceptibility breakpoint. ResultsAmong 228 non-duplicated isolates, 226 exhibited a MIC of ≤ 4 mg/L with MIC50/90 of 1/2 mg/L. Two isolates had a MIC of 128 mg/L; both source patients had multiple comorbidities, were ventilator-dependent, and had not received cefiderocol previously. Resistance was attributable to acquisition of blaCfxA-3, carried by a conjugative transposon from Prevotella jejuni, and duplication of intrinsic blaCME-3, which led to its overexpression. tetQ coexisted with blaCfxA-3 in this conjugative transposon and minocycline facilitated its transfer among E. anophelis. Antibiotics prescribed for source patients did not induce blaCME-3 duplication. The stabilities of blaCfxA-3 and double blaCME-3 were 100% and > 90%, respectively, after 10-day serial passage. Cefiderocol failed to rescue moth larvae infected with resistant strains, but removal of resistance mechanisms restored in vivo efficacy. ConclusionsCefiderocol was in vitro and in vivo active against Elizabethkingia spp. but resistance may emerge due to the availability, transferability, and/or stability of resistance mechanisms.

Recent increase in Candida auris frequency in the SENTRY surveillance program: antifungal activity and genotypic characterization.

We observed an increase in the frequency of Candida auris among invasive candidiasis isolates in the 2022 SENTRY Antifungal Surveillance Program compared to prior years: ≤0.1% before 2018, 0.4%-0.6% from 2018 to 2021, and 1.6% in 2022. C. auris isolates were collected in seven countries, but 28 (35.9%) isolates were recovered in the USA (five states; more common in New York, Texas, and New Jersey) and 26 (33.3%) in Panama. Greece and Turkey had 12 and 9 isolates, respectively. Overall, 82.1% of the isolates were resistant to fluconazole; 17.9% were resistant to amphotericin B; and 1.3% were resistant to caspofungin, anidulafungin, or micafungin (Centers for Disease Control and Prevention tentative resistance breakpoints). Rezafungin inhibited 96.2% of the isolates (Clinical and Laboratory Standards Institute susceptibility breakpoint). Pandrug resistance was not observed, but 17.9% of the isolates were resistant to fluconazole and amphotericin B. South Asian (Clade I) isolates were most common (n = 40, 51.3%); of these, 97.5% were resistant to fluconazole and 30.0% were resistant to amphotericin B. Thirty (38.5%) isolates belonged to the South American region (Clade IV), and 56.7% of those were resistant to fluconazole and 6.7% to amphotericin B. Seven isolates belonged to the South African Clade III and one to East Asian Clade II. Erg11 (Y132F, K143R, and F126L) and MRR1 (N647T) alterations were detected. One isolate that was resistant to all echinocandins carried an FKS R1354G alteration. Two isolates displayed elevated rezafungin minimum inhibitory concentration (MIC) values but low MIC values against other echinocandins and no FKS alterations. As C. auris is spreading globally, monitoring this species is prudent.

Geographic differences in susceptibility profiles of potential non-class B carbapenemase-producing Enterobacterales isolates against ceftazidime-avibactam, meropenem-vaborbactam, colistin, amikacin, gentamicin, and tigecycline: Data from the Antimicrobial Testing Leadership and Surveillance, 2018–2022

To evaluate the susceptibility profiles of regional meropenem-resistant (MEM-R) potential non-class B carbapenemase-producing Enterobacterales (CPE) isolates (without confirmation by phenotypic tests) against important antibiotics, we extracted data from the 2018-2022 Antimicrobial Testing Leadership and Surveillance. This data included susceptibility information of MEM-R potential non-class B CPE isolates against indicated antibiotics - amikacin [AMK], gentamicin [GM], ceftazidime-avibactam [CZA], colistin [CST], meropenem-vaborbactam [MVB], and tigecycline [TGC] - from sepsis patients hospitalized in ICUs across six major regions. Carbapenemase-encoding genes of the tested CPE isolates, determined by multiplex PCR and Sanger sequencing, were also analyzed. Susceptibility breakpoints recommended by CLSI 2024 and US FDA criteria (for TGC only) against Enterobacterales were employed. A total of 1,500 potential non-class B CPE isolates (89% of which were Klebsiella pneumoniae) were tested globally. Resistance rates to AMK and GM against the evaluated isolates were statistically higher in Africa/the Middle East, Europe, and India compared to other regions. A similar pattern was observed in the susceptibility of these potential CPE isolates to CZA and MVB. High CST resistance rates were noted in Asia, Latin America, and Europe (29%-35%). Furthermore, the proportions of potential CPE isolates carrying genes encoding blaOXA variants were notably higher among the tested CPE isolates in India, Europe, and Africa/the Middle East regions (99.2%, 53.3%, and 96.7%, respectively) compared to other regions. Trends in resistance to important antibiotics among potential non-class B CPE isolates warrant close monitoring.

Understanding the rationale and clinical impact of the revised CLSI 2024 minocycline susceptibility breakpoints against Stenotrophomonas maltophilia

Understanding the rationale and clinical impact of the revised CLSI 2024 minocycline susceptibility breakpoints against Stenotrophomonas maltophilia

Discovery of anti-infective compounds against Mycobacterium marinum after biotransformation of simple natural stilbenes by a fungal secretome.

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, remains a serious threat to human health worldwide and the quest for new anti-tubercular drugs is an enduring and demanding journey. Natural products (NPs) have played a significant role in advancing drug therapy of infectious diseases. This study evaluated the suitability of a high-throughput infection system composed of the host amoeba Dictyostelium discoideum (Dd) and Mycobacterium marinum (Mm), a close relative of Mtb, to identify anti-infective compounds. Growth of Dd and intracellular Mm were quantified by using luminescence and fluorescence readouts in phenotypic assays. The system was first benchmarked with a set of therapeutic anti-Mtb antibiotics and then used to screen a library of biotransformed stilbenes. The study confirmed both efficacy of established antibiotics such as rifampicin and bedaquiline, with activities below defined anti-mycobacterium susceptibility breakpoints, and the lack of activity of pyrazinamide against Mm. The screening revealed the promising anti-infective activities of trans-δ-viniferins and in particular of two compounds 17 and 19 with an IC50 of 18.1 μM, 9 μM, respectively. Both compounds had no activity on Mm in broth. Subsequent exploration via halogenation and structure-activity relationship studies led to the identification of derivatives with improved selectivity and potency. The modes of action of the anti-infective compounds may involve inhibition of mycobacterial virulence factors or boosting of host defense. The study highlights the potential of biotransformation and NP-inspired derivatization approaches for drug discovery and underscores the utility of the Dd-Mm infection system in identifying novel anti-infective compounds.

Pharmacokinetics, Safety and Tolerability of Single-dose or Multiple-dose Cefiderocol in Hospitalized Pediatric Patients Three Months to Less Than Eighteen Years Old With Infections Treated With Standard-of-care Antibiotics in the PEDI-CEFI Phase 2 Study.

Multidrug-resistant Gram-negative bacterial infections are increasing globally in neonates, infants and children; antibiotic options are limited. This international, multicenter, open-label phase 2 study, investigated the pharmacokinetics, safety and tolerability of single-dose and multiple-dose cefiderocol [as a 3-hour infusion (every 8 hours) dosed at 2000 mg for body weight ≥34 kg and at 60 mg/kg for body weight <34 kg], over a range of renal function, in hospitalized pediatric patients with aerobic Gram-negative bacterial infection; multiple-dose patients required standard-of-care systemic antibiotics for 5-14 days. Four cohorts of pediatric patients were enrolled (cohort 1: 12 to <18 years, cohort 2: 6 to <12 years, cohort 3: 2 to <6 years and cohort 4: 3 months to <2 years). A total of 53 patients (median age: 73.5 months) were enrolled. Plasma concentration profiles were similar with single-dose (n = 24) and multiple-dose (n = 29) cefiderocol, irrespective of age and body weight in those with normal renal function or mild renal impairment. Geometric mean concentrations at the end of infusion ranged between 72.7 and 97.1 μg/mL for single-dose cefiderocol and between 88.8 and 106.0 μg/mL after multiple doses. At 8 hours, corresponding trough concentrations ranged from 7.86 to 10.8 μg/mL with single-dose cefiderocol and from 9.64 to 18.1 μg/mL with multiple doses. There were no deaths, no cefiderocol-related serious adverse events, significant related laboratory abnormalities or discontinuations. Multiple-dose cefiderocol, administered for 5-14 days and according to body weight, achieved steady-state plasma concentrations that remained above the susceptibility breakpoints of Gram-negative bacteria throughout the dosing period. Cefiderocol was well tolerated.

Pharmacokinetic Factors Associated With Early Meropenem Target Attainment in Pediatric Severe Sepsis.

To determine the frequency of early meropenem concentration target attainment (TA) in critically ill children with severe sepsis; to explore clinical, therapeutic, and pharmacokinetic factors associated with TA; and to assess how fluid resuscitation and volume status relate to early TA. Retrospective analysis of prospective observational cohort study. PICU in a single academic quaternary care children's hospital. Twenty-nine patients starting meropenem for severe sepsis (characterized as need for positive pressure ventilation, vasopressors, or ≥ 40 mL/kg bolused fluid), of which 17 were newly escalated to PICU level care. None. Concentration-time profiles were analyzed using modeling software employing opportunistic sampling, Bayesian estimation, and a population pharmacokinetic model. Time above four times minimum inhibitory concentration (T > 4×MIC), using the susceptibility breakpoint of 1 µg/mL, was determined for each patient over the first 24 hours of meropenem therapy, as well as individual clearance and volume of distribution (Vd) estimates. Twenty-one of 29 patients met a target of 40%T > MIC 4 μg/mL. Reaching TA, vs. not, was associated with lower meropenem clearance. We failed to identify a difference in Vd or an association between the TA group and age, weight, creatinine-based estimated glomerular filtration rate (eGFR), or the amount of fluid administered. eGFR was, however, negatively correlated with overall T > MIC. Eight of 29 pediatric patients with early severe sepsis did not meet the selected TA threshold within the first 24 hours of meropenem therapy. Higher clearance was associated with failure to meet targets. Identifying patients likely to have higher meropenem clearance could help with dosing regimens.

Antibacterial action of penicillin against Mycobacterium avium complex.

β-lactam antibiotics are promising treatments for Mycobacterium avium complex (MAC) lung disease. We hypothesized that benzylpenicillin has efficacy against MAC. Benzylpenicillin lung concentration-time profiles of seven doses in three dosing schedules were administered for 28 days using the hollow fiber system model of intracellular MAC (HFS-MAC). Data were analyzed using the inhibitory sigmoid maximal effect (Emax) model for each sampling day, while two ordinary differential equations (ODEs) were used for the wild-type and penicillin-resistant mutants. Benzylpenicillin killed >2.1 log10 colony-forming unit (CFU)/mL below Day 0, better than azithromycin, ethambutol, and rifabutin. Efficacy was terminated by acquired resistance. Sigmoid Emax parameter estimates significantly differed between sampling days and were a poor fit. However, ODE model parameter estimates vs. exposure were a better fit. The exposure mediating Emax was 84.6% (95% CI 76.91-82.98) of time concentration exceeded the minimum inhibitory concentration (MIC). In Monte Carlo experiments, 24 million international units of benzylpenicillin continuous infusion achieved the target exposure in lungs of >90% of 10,000 subjects until an MIC of 64 mg/L, designated the susceptibility breakpoint. Benzylpenicillin demonstrated a better bactericidal effect against MAC than guideline-recommended drugs before the development of resistance. Its role in combination therapy with other drugs with better efficacy than guideline-recommended drugs should be explored.

Assessment of pharmacokinetics-pharmacodynamics to support omadacycline dosing regimens for the treatment of patients with acute bacterial skin and skin structure infections.

Pharmacokinetic-pharmacodynamic (PK-PD) relationships for efficacy were evaluated using data from omadacycline-treated patients with acute bacterial skin and skin structure infections (ABSSSI) enrolled in two phase 3 studies. Patients received omadacycline 100 mg intravenously (IV) every 12 hours for two doses, followed by 100 mg IV every 24 hours (q24h), with the option to switch to 300 mg oral (PO) q24h after 3 days or 450 mg PO q24h for two doses, followed by 300 mg PO q24h for a total duration of 7-14 days. Clinical response was evaluated at 48-72 hours [early clinical response (ECR)], end of treatment (EOT), and 7-14 days after EOT. Using a population pharmacokinetic (PK) model and PK data from patients with Staphylococcus aureus at baseline, omadacycline free-drug plasma area under the concentration-time curve (AUC) values were determined, and the relationships between free-drug plasma AUC:MIC ratio and dichotomous efficacy endpoints were evaluated. Using these relationships, the population PK model, simulation, and an omadacycline MIC distribution for S. aureus, mean percent probabilities of response were evaluated. Statistically significant PK--PD relationships were identified for ECR (P = 0.016 and 0.013 for optimized two- and three-group free-drug plasma AUC:MIC ratios, respectively). At an MIC value of 0.5 µg/mL, percent probabilities of model-predicted success for ECR based on the univariable PK-PD relationships using continuous and two-group free-drug plasma AUC:MIC ratio variables were 91.9 and 95.6%, respectively, for the IV-to-PO dosing regimen and 89.3 and 88.4%, respectively, for the PO-only dosing regimen. These data support for omadacycline IV-to-PO and PO-only dosing regimens for ABSSSI and an omadacycline susceptibility breakpoint of 0.5 µg/mL for S. aureus.

Rapid and Simple Morphological Assay for Determination of Susceptibility/Resistance to Combined Ciprofloxacin and Ampicillin, Independently, in Escherichia coli.

Current antibiograms cannot discern the particular effect of a specific antibiotic when the bacteria are incubated with a mixture of antibiotics. To prove that this task is achievable, Escherichia coli strains were treated with ciprofloxacin for 45 min, immobilized on a slide and stained with SYBR Gold. In susceptible strains, the nucleoid relative surface started to decrease near the MIC, being progressively condensed as the dose increased. The shrinkage level correlated with the DNA fragmentation degree. Ciprofloxacin-resistant bacilli showed no change. Additionally, E. coli strains were incubated with ampicillin for 45 min and processed similarly. The ampicillin-susceptible strain revealed intercellular DNA fragments that increased with dose, unlike the resistant strain. Co-incubation with both antibiotics revealed that ampicillin did not modify the nucleoid condensation effect of ciprofloxacin, whereas the quinolone partially decreased the background of DNA fragments induced by ampicillin. Sixty clinical isolates, with different combinations of susceptibility-resistance to each antibiotic, were co-incubated with the EUCAST breakpoints of susceptibility of ciprofloxacin and ampicillin. The morphological assay correctly categorized all the strains for each antibiotic in 60 min, demonstrating the feasible independent evaluation of a mixture of quinolone and beta-lactam. The rapid phenotypic assay may shorten the incubation times and necessary microbial mass currently required for evaluation.

Ampicillin-sulbactam against Acinetobacter baumannii infections: pharmacokinetic/pharmacodynamic appraisal of current susceptibility breakpoints and dosing recommendations.

Sulbactam dosing for Acinetobacter baumannii infections has not been standardized due to limited available pharmacokinetics/pharmacodynamics (PK/PD) data. Herein, we report a comprehensive PK/PD analysis of ampicillin-sulbactam against A. baumannii pneumonia. Twenty-one A. baumannii clinical isolates were tested in the neutropenic murine pneumonia model. For dose-ranging studies, groups of mice were administered escalating doses of ampicillin-sulbactam. Changes in log10cfu/lungs relative to 0 h were assessed. Dose-fractionation studies were performed. Estimates of the percentage of of time during which the unbound plasma sulbactam concentrations exceeded the MIC (%fT > MIC) required for different efficacy endpoints were calculated. The probabilities of target attainment (PTA) for the 1-log kill plasma targets were estimated following clinically utilized sulbactam regimens. Dose-fractionation studies demonstrated time-dependent kill. Isolates resistant to both sulbactam and meropenem required three times the exposures to achieve 1-log kill; median [IQR] %fT > MIC of 60.37% [51.6-66.8] compared with other phenotypes (21.17 [16.0-32.9] %fT > MIC). Sulbactam standard dose (1 g q6h, 0.5 h infusion) provided >90% PTA up to MIC of 4 mg/L. Sulbactam 3 g q8h, 4 h inf provided greater PTA for isolates with sulbactam-intermediate susceptibility (8 mg/L, 100% versus 86% following the standard dose). Despite the higher exposure following 3 g q8h, 4 h inf, PTA was ≤57% among sulbactam-resistant/meropenem-resistant isolates. Sulbactam standard dose is a valuable regimen across sulbactam-susceptible isolates while the high-dose extended-infusion provides additional benefit against sulbactam-intermediate isolates. Given that most of the sulbactam-resistant A. baumannii isolates are meropenem-resistant, high-dose prolonged-infusion regimens are not expected to be effective as monotherapy against infections due to these isolates.

In Vitro Antibacterial Activities of Fosfomycin against Escherichia coli Isolates from Canine Urinary Tract Infection.

Fosfomycin is a bactericidal drug recommended as an alternative treatment for canine bacterial cystitis, particularly in cases involving multidrug-resistant (MDR) infections when no other options are available. In this study, minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) of fosfomycin were determined against 79 clinical E. coli isolates using the agar dilution method. The susceptibility rate of E. coli to fosfomycin was 86.06%, with MIC50 and MIC90 values of 4 mg/L and 96 mg/L, respectively. MPC50 and MPC90 values were 64 mg/L and 192 mg/L. Using pharmacokinetic (PK) data from dogs given a single 80 mg/kg oral dose of fosfomycin, the area under the curve per MIC50 (AUC0-24/MIC50) was 85.79 with time above MIC50 (T > MIC50) exceeding 50%. In urine, the AUC0-24/MIC50 was 10,694.78, and the AUC0-24/MPC90 was 222.81, with T > MPC90 extending beyond 24 h. Therefore, fosfomycin exhibited significant antibacterial activity against canine uropathogenic E. coli, including MDR strains, at concentrations below the susceptible MIC breakpoint. However, the high MPC values, especially the MPC90, indicate the critical importance of performing susceptibility testing for fosfomycin and maintaining ongoing resistance monitoring.

Piperacillin/tazobactam Susceptibility Test Interpretive Criteria for Enterobacterales: Recommendations from the United States Committee on Antimicrobial Susceptibility Testing.

The in vitro susceptibility testing interpretive criteria (STIC) for TZP against Enterobacterales were recently updated by the Food and Drug Administration (FDA), Clinical & Laboratory Standards Institute (CLSI), and European Committee on Antimicrobial Susceptibility Testing (EUCAST). The United States Committee on Antimicrobial Susceptibility Testing (USCAST) also recently reviewed TZP STIC for Enterobacterales and arrived at different STIC for Enterobacterales and herein we explain our recommendations and rationale behind them. Based on our review of the available data, USCAST does not recommend TZP STIC for certain Enterobacterales species that have a moderate to high likelihood of clinically significant AmpC production (E. cloacae, C. freundii, and K. aerogenes only) or for third-generation cephalosporin-non-susceptible (3GC-NS) Enterobacterales. USCAST recommends a TZP susceptibility breakpoint of ≤ 16/4 mg/L for third-generation cephalosporin-susceptible (3GC-S) Enterobacterales but only endorses the use of extended infusion TZP regimens for patients with infections due to these pathogens.

Evaluation of a simple method for testing aztreonam and ceftazidime-avibactam synergy in New Delhi metallo-beta-lactamase producing Enterobacterales.

NDM-producing carbapenem-resistant bacterial infections became a challenge for clinicians. Combination therapy of aztreonam and ceftazidime-avibactam is a prudent choice for these infections. However, there is still no recommendation of a practically feasible method for testing aztreonam and ceftazidime-avibactam synergy. We proposed a simple method for testing aztreonam and ceftazidime-avibactam synergy and compared it with reference broth micro-dilution and other methods. Carbapenem-resistant Enterobacterales clinical isolates were screened for the presence of the NDM gene by the Carba R test. NDM harbouring isolates were tested for aztreonam and ceftazidime-avibactam synergy by broth microdilution (reference method), E strip-disc diffusion, double disc diffusion, and disc replacement methods. In the newly proposed method, the MHA medium was supplemented with ceftazidime-avibactam (corresponding to an aztreonam concentration of 4μg/ml). The MHA medium was then inoculated with the standard inoculum (0.5 McFarland) of the test organism. An AZT disc (30 μg) was placed on the supplemented MHA medium, and the medium was incubated overnight at 37°C. Aztreonam zone diameter on the supplemented MHA medium (in the presence of ceftazidime-avibactam) was compared with that from a standard disc diffusion plate (without ceftazidime-avibactam), performed in parallel. Interpretation of synergy was based on the restoration of aztreonam zone diameter (in the presence of ceftazidime-avibactam) crossing the CLSI susceptibility breakpoint, i.e., ≥ 21 mm. Of 37 carbapenem-resistant NDM-producing isolates, 35 (94.6%) were resistant to aztreonam and tested synergy positive by the proposed method. Its sensitivity and specificity were 97.14% and 100%, respectively. Cohen's kappa value showed substantial agreement of the reference method with the proposed method (κ = 0.78) but no other methods. The proposed method is simple, easily interpretable, and showed excellent sensitivity, specificity, and agreement with the reference method. Therefore, the new method is feasible and reliable for testing aztreonam synergy with avibactam in NDM-producing Enterobacterales.

Gram Positive Cocci Associated Urinary Tract Infections, their Prevalence and Antibiotic Susceptibility Patterns

Background: Urinary tract infections (UTIs) are the third most common type of infection in humans globally. Gram-positive bacteria are said to be responsible for ten percent of urinary tract (UTI) infections. The study's goal was to profile gram-positive cocci-associated UTIs and their antibiogram, as they were observed at LASUTH. Methods: This was a retrospective assessment of the Medical Microbiology Laboratory records of the LASUTH to review the in vitro antibiotic susceptibility patterns of gram-positive urinary bacterial isolates between April 2020 and March 2021. The bacteria were isolated and identified from routine urine samples using standard bacteriological methods and the API. In vitro antibiotic susceptibility test (AST) was routinely performed by the modified Kirby-Bauer disk diffusion test and susceptibility breakpoints were determined using the Clinical and Laboratory Standards Institute (CLSI) guidelines. Results: 2,253 urine samples were processed in the medical microbiology laboratory over the one year and 662 (29.4%) samples yielded Positive cultures. Of the 662 isolates, 494 (74.6%) were gram-negative bacteria. 164 (24.8%) were gram-positive cocci while 4 (0.6%) were gram positive rod. Among the gram-positive cocci’s isolated Enterococcus faecalis had the highest frequency 58 (35.4%). Aminoglycosides (Gentamycin and Amikacin) and Linezolid antibiotics were found to be the most effective drugs against gram-positive cocci bacteria except Enterococcus spp. For empirical treatment of Enterococcus spp in our facility Fosfomycin and Tigecycline are the best options, while for Streptococcus agalactiae associated UTI, Amikacin, Cefuroxime, Linezolid, and levofloxacin can be used for empirical treatment. Conclusion: The prevalence rate of gram-positive cocci associated UTI in this study was 7.3% (164/2253). The emergence of drug resistance in these pathogens to commonly used antibiotics is a thing of concern. Therefore, efficient antimicrobial stewardship programmes must be in place.

Kodamaea ohmeri: A rare yeast causing invasive infections in immunocompromised patients.

Kodamaea ohmeri is a rare, recognized pathogen that has previously been isolated from environmental sources. The patients commonly affected by this yeast include immunocompromised as well as immunocompetent patients having several associated risk factors. We report three cases in which K. ohmeri was isolated from blood using Bact T/ALERT. Identification was carried out by MALDI-TOF MS (Vitek-MS, BioMérieux, Marcy-l'Etoile, France) in addition to color characteristics on chromogenic media. The patients had diminished immune response on account of a multitude of comorbidities. K. ohmeri can be misidentified as Candida tropicalis, Candida albicans, or Candida hemolounii by conventional methods; correct and timely identification can be achieved by MALDI-TOF MS. Antifungal susceptibility breakpoints for K. ohmeri are currently not defined. An Echinocandin was added to the treatment regimen of all three of the cases. Identification of K. ohmeri using conventional methods is difficult and unusual yeasts should be carefully observed, especially upon prolonged incubation.

Pharmacokinetics of intravenous piperacillin/tazobactam among patients with peritoneal dialysis-associated peritonitis.

Currently, pharmacokinetic information on intravenous (IV) piperacillin/tazobactam in patients with peritoneal dialysis-associated peritonitis (PD peritonitis) is limited. This study employed a prospective single-dose pharmacokinetic design to assess the pharmacokinetics of IV piperacillin/tazobactam in these patients. Four patients with PD peritonitis who received an IV loading dose of 4000 mg/500 mg piperacillin/tazobactam were enrolled in this study. The concentrations of piperacillin and tazobactam in plasma, peritoneal dialysis fluid (PDF) and urine were determined by high-performance liquid chromatography. Non-compartmental methods were used for pharmacokinetic analysis. During a 6-h dwell time for chronic ambulatory peritoneal dialysis (CAPD), 9.23 ± 4.01% of the piperacillin was recovered in the PDF. This result is greater than that observed in patients without peritonitis in prior research. Piperacillin's PD clearance (CLPD), steady-state volume of distribution (Vss) and terminal half-life (t 1/2) were 5.79 ± 2.55 mL/min, 24.35 ± 11.26 L and 5.74 ± 1.53 h, respectively. These values are also higher than those of patients without peritonitis in a prior study. Eight hours following the loading dosage, the plasma and PDF piperacillin concentrations of all patients (98.25 ± 26.03 and 52.70 ± 22.99 mg/L, respectively) surpassed the Pseudomonas aeruginosa and Enterobacterales Clinical and Laboratory Standards Institute susceptible breakpoints. In summary, the CLPD, Vss and t 1/2 for piperacillin were found to be greater in patients with PD peritonitis than in CAPD patients without peritonitis when compared with the results of a previous study. The IV loading dose of 4000 mg/500 mg piperacillin/tazobactam is sufficient to treat peritonitis caused by susceptible P. aeruginosa and Enterobacterales. The multiple-dose pharmacokinetics of IV piperacillin and tazobactam in this specific patient group should be further investigated.

Investigation of the Antibacterial Synergistic Activity of Fosfomycin-Teicoplanin Combination in Methicillin-Resistant Staphylococcus aureus Strains Isolated from Various Clinical Sample

The aim of this study was to investigate the detection of teicoplanin and fosfomycin antibiotic susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) strains by different methods and to evaluate the antibacterial synergistic effect of teicoplanin-fosfomycin combination by using checkerboard assay and time kill curve assay. Forty-five MRSA strains isolated from clinical samples in routine medical microbiology laboratory of Göztepe Prof. Dr. Süleyman Yalçın City Hospital were included in the study. In the first stage of the combination study, minimum inhibitory concentrations (MIC) were investigated by broth microdilution for teicoplanin and by both broth microdilution and agar dilution methods for fosfomycin. The combination of teicoplanin and fosfomycin was tested by the checkerboard method in 45 MRSA strains and combination effect was determined according to fractional inhibitory concentration index (ΣFIC) calculation. The synergistic effect and bactericidal activity of antibiotic combination were studied against a randomly selected strain from the strains used in the study by using time-kill method for 24 hours. As a result of teicoplanin and fosfomycin antibiotic susceptibility studies, all isolates were found to be susceptible to both antibiotics according to the susceptibility breakpoints determined by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). A synergistic effect was found in 22 (49%), additive effect in 22 (49%) and indifferent effect in one (2%) of the 45 strains studied with the checkerboard method. The mean ΣFIC of 45 isolates was found to be 0.5. In the combination study of the antibiotics of the isolate that was studied with time-kill method, synergism was detected for 1/8 MIC concentrations at 12th hour and 24th hour and synergism at 1/4 MIC concentration at sixth hour, 12th hour and 24th hour. In the combination study of 1/4 MIC concentrations of antibiotics, bactericidal effect was detected at sixth hour and this effect was observed to disappear at 12th and 24th hours. High rate of synergistic antibacterial effect of teicoplanin-fosfomycin combination on MRSA isolates was demonstrated as a result of in vitro tests. Such studies conducted on antibiotic-resistant bacterial infections will provide clinicians different treatment options and will contribute to increasing survival. As a result of this study, provided that it is supported by future clinical studies, it can be stated that the teicoplanin-fosfomycin combination may be an effective treatment option in community and hospital-acquired infections caused by MRSA.

Population pharmacokinetic/pharmacodynamic target attainment analysis of IV fosfomycin for the treatment of MDR Gram-negative bacterial infections.

IV fosfomycin is used against MDR Gram-negative bacilli (GNB) but has dose-limiting side effects, especially in patients with impaired kidney function. To determine the optimal dosage of IV fosfomycin for patients with varying degrees of kidney function. Adult patients receiving IV fosfomycin for treatment of GNB were eligible. Five serial blood samples were collected after at least three doses of fosfomycin; plasma was assayed by LC-MS/MS and modelled by population pharmacokinetic analysis. The PTA for AUC24/MIC of 98.9 for Escherichia coli and Klebsiella pneumoniae, and 40.8 for Pseudomonas aeruginosa were computed by Monte Carlo simulations. Cumulative fractions of response (CFR) were analysed for each pathogen using EUCAST MIC distributions. A total of 24 patients were included. Creatinine clearance (CLCR) and gender significantly influenced fosfomycin clearance. The kidney function-adjusted dosing regimens are proposed by using the lowest dose that can achieve ≥90% PTA for AUC24/MIC of 98.9 at an MIC of ≤32 mg/L (EUCAST v.13 susceptibility breakpoint for Enterobacterales). For patients with normal kidney function (CLCR 91-120 mL/min), a dosage of 15 g/day is suggested. This regimen achieved 97.1% CFR against E. coli, whereas CFR was 72.9% for K. pneumoniae and 76.7% for P. aeruginosa. A fosfomycin dosage of 15 g/day with adjustment according to kidney function provided high PTA and CFR when treating E. coli. This dosage is lower than that used in current practice and may improve tolerability. Higher dosages may be needed for P. aeruginosa; however, safety data are limited.