EUCAST Research Articles

Improving Turnaround Times for Routine Antimicrobial Sensitivity Testing Following European Committee on Antimicrobial Susceptibility Testing Methodology in Patients with Bacteraemia

Background/Objectives: Bacteraemia can be fatal without antibiotic intervention. Antibiotic Susceptibility Testing (AST) provides the necessary information for targeted antibiotic therapy; however, the traditional method using disc diffusion can take over two days from a positive blood culture. Inappropriate empiric therapy is associated with increased mortality and increased antibiotic resistance, highlighting the need for more rapid turnaround times for AST. By making changes to an established method, turnaround times can be reduced. Methods: Eighty-two patient positive blood culture samples were collected from January to April 2022, representing the range of common bacteria causing sepsis. This followed the normal methodology in the laboratory of inoculating agar from positive blood cultures in preparation for European Committee on Antimicrobial Susceptibility Testing (EUCAST) disc diffusion AST method. EUCAST methodology outlines that disc diffusion should be performed on isolates from an overnight culture of 16–24 h. This study looked at comparing disc diffusion results from cultures with 6 h of incubation to those with incubation times of 24 h, after organism identification by MALDI-ToF. Results from 6-h and 24-h cultures were compared by disc zone sizes and by interpreted susceptibility reading following EUCAST guidelines of sensitive, resistant, susceptible with increased exposure, or an area of technical uncertainty. Results: A total of 99.65% interpreted susceptibility readings matched across all organisms to all relevant antibiotics, with an average zone size difference of 1.08 mm between results from 6 h versus 24 h cultures. Conclusions: This method offers a non-automated way of using the traditional disc diffusion method, reducing turnaround times while still producing reliable and accurate results. This would mean validated ASTs can be set up in the same day as a blood culture flags positive rather than waiting for a longer culture. As this method is widely used within the laboratory already, it would mean that additional training is not required, as the process is the same, and only incubation time varies. This would positively impact patient outlook due to the shorter use of empiric therapy, and benefit antimicrobial stewardship (AMS).

Microorganisms isolated from thermoplastic masks and storage racks in head and neck cancer patients with radiation dermatitis.

Healthcare-associated infections (HAIs) remain a critical public health issue, as they contribute to prolonged treatment duration, increased healthcare costs, and heightened risks of morbidity and mortality. In head and neck cancer patients undergoing radiotherapy, thermoplastic masks (TMs), which come into direct contact with the skin, represent a potential vector for infection. Additionally, the storage racks where these masks are kept may also facilitate microorganism transmission. Our study aimed to isolate and identify microorganisms from infective skin lesions secondary to radiation dermatitis in head and neck cancer patients, as well as from the TMs and storage racks, and to evaluate the antibiotic resistance profiles of the isolated microorganisms. The study included 71 locally advanced head and neck cancer patients who underwent radiotherapy between August 2022 and November 2023. Patients were monitored daily, and their skin evaluations were made according to Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Grade 2 and 3 radiodermatitis was observed in 29 of these 71 patients. Samples were collected using sterile swabs from the skin lesions on the head and neck area, the inner surfaces of the TM, and the storage rack from 29 patients. Samples were inoculated into enrichment and selective media. After the growing microorganisms were identified, antimicrobial susceptibility was evaluated using conventional methods and automated systems according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. At least one type of microorganism was isolated from the skin samples of infected patients, and double growth was detected in two patients. Among the samples, 2 were methicillin-resistant coagulase-negative Staphylococcus (MRCNS), 1 was methicillin-resistant Staphylococcus aureus (MRSA), 1 was Candida albicans (C. albicans), 15 were methicillin-sensitive coagulase-negative Staphylococcus (MSCNS), 1 was methicillin-sensitive Staphylococcus aureus (MSSA), 1 was Bacillus subspecies (Bacillus spp.) and 3 were Corynebacterium diphtheriae (C. diphtheriae). Coagulase-negative Staphylococcus strains were isolated from the skin of 14 of 19 patients with grade 2 radiation dermatitis, whereas CNS strains were isolated from only 2 of 10 patients with grade 3 radiation dermatitis. Among the gram-negative bacteria, 3 Pseudomonas aeruginosa (P. aeruginosa), 2 Enterobacter cloacae (E. cloacae), 1 Klebsiella pneumoniae (K. pneumoniae) and 1 Moraxella catarrhalis (M. catarrhalis) strain were isolated. Sixteen (55.1%) of the TMs used in 29 patients and 20 (68.9%) of the storage racks harbored microorganisms, including HAI agents and flora bacteria. Bacteria colonize TMs and storage racks where they are risk factors for secondary skin infections in radiation dermatitis lesions that develop on the skin of head and neck cancer patients. Decontamination procedures should be meticulously applied to surfaces such as TMs and their storage racks during the course of radiotherapy.

Non-invasive Streptococcus pneumoniae infections are associated with different serotypes than invasive infections, Belgium, 2020 to 2023.

BackgroundDespite widely implemented pneumococcal vaccination programmes, Streptococcus pneumoniae remains a global risk for human health. Streptococcus pneumoniae can cause invasive (IPD) or non-invasive pneumococcal disease (NIPD). Surveillance is mainly focusing on IPD, assessing the full impact of pneumococcal vaccination programmes on pneumococcal disease is challenging.AimWe aimed to prospectively investigate serotype distribution and antimicrobial resistance (AMR) of S. pneumoniae isolates from patients with NIPD and compare with data on IPD isolates and with a 2007-2008 dataset on NIPD.MethodsBetween September 2020 and April 2023, we collected isolates and patient data from patients with NIPD from 23 clinical laboratories in Belgium. Capsular typing was performed by a validated Fourier-Transform Infrared spectroscopic method, and AMR was assessed with broth microdilution, using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) clinical breakpoints.ResultsWe received S. pneumoniae isolates from 1,008 patients with lower respiratory tract infections (n = 760), otitis media (n = 190) and sinusitis (n = 58). Serotype 3 was the most prevalent serotype among the NIPD isolates. Serotypes not included in the 20-valent pneumococcal conjugate vaccine (PCV20) were significantly more common among the NIPD than among the IPD isolates. Antimicrobial resistance levels were significantly higher among the NIPD isolates (n = 539; 2020-2022) compared with the IPD isolates (n = 2,344; 2021-2022). Resistance to several β-lactam antimicrobials had increased significantly compared with 15 years before.ConclusionsThe NIPD isolates were strongly associated with non-vaccine serotypes and with increased AMR levels. This underlines the importance of continued NIPD surveillance for informed policy making on vaccination programmes.

Antibiotic susceptibility testing using minimum inhibitory concentration (MIC) assays

Antimicrobial resistance is due to genetic changes that allow bacteria to evade antibiotic treatment. Antimicrobial susceptibility testing is critical for the detection of antibiotic-resistant strains, the selection of effective therapeutic strategies against bacterial infections, and the evaluation of the efficacy of novel antimicrobials. Among the variety of clinical microbiology methods used for antibiotic susceptibility testing, minimum inhibitory concentration (MIC) assays have become the gold standard in clinical practice. MIC assays determine the lowest concentration of an antimicrobial agent that is required to inhibit visible bacterial growth in vitro. Here, we outline MIC assay protocols, in strict accordance with European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines that aim to assess the susceptibility of non-fastidious organisms to antimicrobial agents. The protocols described in this methods paper are intended to aid the performance of reliable and informative MIC assays for research purposes that are in line with clinical microbiology practices.

Fosfomycin—Overcoming Problematic In Vitro Susceptibility Testing and Tricky Result Interpretation: Comparison of Three Fosfomycin Susceptibility Testing Methods

Background: Fosfomycin (FOS) is an older antimicrobial agent newly rediscovered as a possible treatment for infections with limited therapeutic options (e.g., Gram-negative bacteria with difficult-to-treat resistance, DTR), especially in intravenous form. However, for correct usage of FOS, it is necessary to have a reliable susceptibility testing method suitable for routine practice and robust interpretation criteria. Results: The results were interpreted according to 2023 interpretation criteria provided by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). DTR Gram-negatives were more likely to be resistant to FOS (45% in Enterobacterales and 20% in P. aeruginosa) than non-DTR (10% and 6.7%, resp.). All isolates of S. aureus were susceptible to FOS. In Gram-negatives, all agreement values were unacceptable. Etest® performed better in the DTR cohort (categorical agreement, CA, 80%) than in the non-DTR cohort (CA 45.7%). There were no very major errors (VREs) observed in P. aeruginosa. S. aureus had surprisingly low essential agreement (EA) rates (53% for MRSA and 47% for MSSA) for Etest®, but categorical agreement was 100%. Methods: A total of 130 bacterial isolates were tested and compared using the disc diffusion method (DD) and gradient strip method (Etest®) with the reference method (agar dilution, AD). The spectrum of isolates tested was as follows: 40 Enterobacterales (20 DTR vs. 20 non-DTR), 30 Pseudomonas aeruginosa (15 DTR vs. 15 non-DTR), and 60 Staphylococcus aureus (30 methicillin-susceptible, MSSA, vs. 30 methicillin-resistant, MRSA). Conclusions: Neither one of the tested methods was identified as a suitable alternative to AD. It would be beneficial to define more interpretation criteria, at least in some instances.

Clinical Practice: Estimating the Breakpoints for EUCAST Fast Antimicrobial Susceptibility Testing Using Flagged BacT/Alert Blood Culture Bottles

<i>Introduction</i>: The escalating prevalence of multidrug resistance is a global threat to human health particularly in critically ill patients with bloodstream infections (BSIs). Delay in the administration of the appropriate antimicrobial treatment is associated with higher mortality rates and adverse consequences. This study attempted to estimate the rapid antimicrobial susceptibility testing (RAST) breakpoints directly from flagged BacT/Alert blood culture bottles in clinical practice. <i>Material & Methods</i>: A descriptive, cross-sectional study conducted at a tertiary care hospital in Delhi over a period of two months. The RAST was performed directly from the clinical samples for blood cultures received in our laboratory in parallel with the routine antimicrobial testing as per standard CLSI guidelines. Blood cultures were routinely incubated in BacT/Alert 3D. The inhibition zones were read at 4, 6, 8 and 16-20 hour of incubation as per European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. The identification of the isolates was confirmed by Vitek-2 compact system. <i>Results</i>: In our study, the area of technical uncertainty (ATU) percentage was initially high at 4 hours but decreased significantly in later incubation periods. At 4 hours, none of the <i>S. aureus</i> isolates showed >90% categorical agreement (CA) for any antimicrobial tested. However, clindamycin achieved the highest CA (100%) at 6 hours and 90% thereafter, with no very major errors (VME) or major error (ME). Cefoxitin required 8 hours to reach >90% CA, with no VME observed at any time point, but up to 75% ME at 8 hours. At 4 hours, most antimicrobials had high (>1.5%) rates of VME among <i>Enterobacteriales</i>. By 6 hours, only Meropenem and Gentamicin had >90% CA, with no VME observed for other antibiotics. <i>Conclusion</i>: The RAST method is relatively easy to implement in clinical microbiology labs, offering cost-effectiveness, simplicity, and rapid results, especially in resource-limited settings. However, reporting RAST results can be complex due to potential challenges with CA, VME, and ME, particularly in the initial hours of incubation and within the ATU.

Validation of EUCAST rapid antimicrobial susceptibility testing directly from positive blood cultures in a non-automated lab setting

ABSTRACT Introduction To speed up antimicrobial susceptibility testing (AST), the European Committee on Antimicrobial Susceptibility Testing (EUCAST) proposed rapid AST (RAST), a disk diffusion method to be read after 4, 6 and 8 hours of incubation. We investigated the feasibility of implementation of RAST in a non-automated lab setting. Materials & methods To this end, reference strains as well as a variety of clinical and resistant strains were used to spike sterile hemocultures (BioMérieux BACT/ALERT 3D® and Becton Dickinson BACTEC FX® systems), followed by RAST in comparison to classical long-incubation AST. Results & conclusion Our results with reference strains show that reading RAST after 4 hours is frequently too soon to obtain clinical results, and that Streptococcus pneumoniae reference strain did yield readable inhibition zones in RAST when harvested from BioMérieux BACT/ALERT 3D® bottle cultures. In a wider panel of strains, Gram positives RAST results were very similar to standard AST, while with Gram negative species errors were more frequently observed, limiting clinical implementation.

Ten Years Later: Still Unchanged Susceptibility to Antibiotics of Listeria monocytogenes from Poultry Processing Environments.

Listeria monocytogenes is still recognized as being commonly susceptible to antibiotics; however, there have been reports of reduced susceptibility in recent years. The significance of this resistance is not clear, in part due to the disparity in the antimicrobial susceptibility testing methods used. EUCAST (European Committee on Antimicrobial Susceptibility Testing) has recently proposed a standardized method for antibiotic susceptibility testing of L. monocytogenes. The aim of this work was to evaluate the susceptibility to 11 antibiotics in clinical use of 50 pulsed-field gel electrophoresis types of L. monocytogenes representing 347 isolates from a poultry industry setting using the EUCAST method and to compare the results with those obtained 10 years before. All poultry strains were sensitive to all the antibiotics tested but one strain was resistant to benzylpenicillin according to the EUCAST criteria. The current findings supported the previous study and confirmed that in certain food-associated L. monocytogenes populations, antibiotic sensitivity has remained stable.

Comparison of two commercial broth microdilution panels for multidrug-resistant Gram-negative bacteria: Thermo Scientific™ Sensititre DKMGN vs. Beckman Coulter MicroScan NMDRM1.

Antimicrobial susceptibility testing (AST) using broth microdilution (BMD) is usually the reference method to obtain accurate minimum inhibitory concentrations and optimally manage infections with resistant organisms. Several commercial dry BMD are available for AST in clinical laboratories. Two commercial BMD panels for testing of multidrug-resistant Gram-negative bacteria were compared: the Thermo Scientific™ Sensititre DKMGN and the Beckman Coulter NMDRM1, for 17 antimicrobial agents. A total of 207 isolates were tested: three ATCC strains and one NCTC strain, six quality control strains from the Belgian National Antimicrobial Committee, and 197 clinical isolates, including carbapenem-resistant Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) 2023 breakpoints version 13.1 were used to assign susceptibility categories. Overall, the categorical agreement (CA) and essential agreement (EA) were both above 90%, but several useful antibiotics for the treatment of multi-resistant organisms showed CA and EA under 90%, that is, meropenem, imipenem, and colistin for Enterobacterales and meropenem and colistin for P. aeruginosa. For Enterobacterales, the NMDRM1 panel showed a significantly higher resistance rate for meropenem, imipenem, amikacin, and colistin. For carbapenems, the minimal inhibitory concentrations (MICs) were underestimated by the DKMGN panel, as already pointed out by a warning on the EUCAST website. To better assess carbapenem susceptibility in carbapenem-resistant organisms, the DKMGN panel now requires the use of a higher inoculum in the insert kit. However, for a given isolate whose susceptibility to carbapenems is not known, there is a risk of underestimating the MIC values. Our results show that colistin testing remains a challenge, highlighting the urgent need for the development of more accurate commercial methods. The use of a single commercial method cannot guarantee good precision in the determination of the MIC value for colistin.

In vitro activity assessment of cefiderocol against Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter spp., including β-lactam nonsusceptible molecularly characterized isolates, collected from 2020 to 2021 in the United States and European hospitals.

This study reports the activity of cefiderocol against Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter spp. isolates collected from the United States and Europe, including Israel and Turkey, from 2020 to 2021. Among Enterobacterales, 2.8% were carbapenem nonsusceptible (CNSE); cefiderocol inhibited 96.6%/85.1% [Clinical Laboratory Standards Institute (CLSI)/European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints] of these isolates. Imipenem-relebactam, meropenem-vaborbactam, and ceftazidime-avibactam displayed susceptibilities lower than cefiderocol against CNSE isolates (67.4-84.6% susceptible, CLSI). Cefiderocol was the only agent active against CNSE isolates carrying metallo-β-lactamase (MBL) carbapenemase or multiple carbapenemase genes (84.6%-92.3% susceptible, CLSI). Approximately 18% of carbapenem-susceptible Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis carried extended-spectrum-β-lactamases and/or plasmid-borne AmpC-encoding genes; cefiderocol inhibited 99.8%-100.0% (CLSI) of these genotypic groups. Multi-drug resistance (MDR) phenotypes were observed in 16.9% and 52.5% of P. aeruginosa and A. baumannii-calcoaceticus isolates, respectively. Carbapenemase genes were rare (4.9%) among cephalosporin and/or carbapenem nonsusceptible P. aeruginosa, compared to 87.6% carriage in A. baumannii-calcoaceticus, respectively. Against the MDR and carbapenemase-carrying P. aeruginosa and A. baumannii-calcoaceticus subsets, cefiderocol was active against 98.6%/98.7% and 97.1%/97.4% (CLSI), respectively. Only 69 isolates (0.3%) across all species groups were identified as cefiderocol nonsusceptible per CLSI criteria (>4 mg/L). Cefiderocol was the most active agent in vitro against Enterobacterales, P. aeruginosa, and Acinetobacter spp., with uniform activity against all phenotypic- and genotypic-resistant subsets. Coupled with the low incidence of nonsusceptibility observed across species groups, these results demonstrate cefiderocol as an important option for treating infections caused by pathogens with diverse mechanisms of resistance in US and European hospitals.IMPORTANCEThe worldwide spread of multi-drug-resistant Pseudomonas aeruginosa and carbapenem-resistant Enterobacterales and Acinetobacter spp. poses a serious challenge in healthcare settings as infections caused by these organisms are commonly refractory to many frontline therapeutic agents. Multiple global health organizations highlighted these pathogens as critical priorities for new antibiotic development, thus necessitating continued surveillance of the activities of currently available antimicrobial agents and circulating mechanisms of resistance. To meet this need, this study phenotypically and genotypically characterized priority Gram-negative pathogens collected from patients in US and European hospitals to examine the activity of cefiderocol and other currently available treatment options, including carbapenems and β-lactam-β-lactamase inhibitor combinations. The results presented here provide a detailed perspective to healthcare practitioners of cefiderocol's broad applicability, manifested in high activity and low nonsusceptibility rates, across phenotypic and genotypic organism groups relative to other agents and further support its use against the most intransigent infections.

Quantifying aminoglycoside resistance in extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales clinical isolates: a retrospective cohort study.

Aminoglycoside resistance is frequently detected in extended-spectrum-beta-lactamase (ESBL)-producing Enterobacterales (ESBL-PE), questioning the appropriateness of aminoglycosides as empiric therapy in patients with suspected ESBL-PE infections. Therefore, we aimed to evaluate the frequency of aminoglycoside resistance in patients harbouring ESBL-PE and identify patient-related risk factors associated with aminoglycoside resistance to facilitate early detection of at-risk patients. This retrospective single-centre cohort study included hospitalised patients aged ≥18 years with an ESBL-PE-positive sample between January 2016 and December 2018. Aminoglycoside resistance was defined according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) clinical breakpoints for Enterobacterales for the current year of testing. Five hundred forty-four patients met the eligibility criteria, of which 240 (44.1%) harboured aminoglycoside-resistant ESBL strains. Identification of ESBL-Klebsiella pneumoniaewas significantly associated with aminoglycoside resistance (odds ratio [OR] = 2.64, 95% confidence interval [CI] = 1.65-4.21, p <0.001) and an international travel history within the past 12 months was marginally associated with aminoglycoside resistance (OR = 1.51, 95% CI = 0.95-2.42, p = 0.084). In a low ESBL endemicity setting, aminoglycoside resistance in patients harbouring ESBL-PE is common, especially ESBL-K. pneumoniae, and needs to be considered in clinicians' decision-making regarding empiric therapy regimens.

Investigations of Antibiotic Susceptibilities of S. aureus Strains Isolated from Various Clinical Samples

Objective: Staphylococcus aureus (S. aureus) is a critical microorganism that causes a range of infections with high morbidity and mortality rates, including skin and soft tissue infections, urinary tract infections, endocarditis, pneumonia, septic arthritis, osteomyelitis, and sepsis in both community and healthcare settings. The objective of this study was to ascertain the antimicrobial resistance rates of methicillin-resistant S. aureus (MRSA) and Methicillin-susceptible S. aureus (MSSA) isolates derived from a range of clinical samples submitted to the Medical Microbiology Laboratory of our hospital and to examine the resistance profile specific to our hospital. Methodology: The study included 229 S. aureus isolates collected between 2022 and 2023. The isolates were identified through the application of conventional methods and the MALDI-TOF-MS system (VITEK MS, bioMerieux France). The antimicrobial susceptibility of the isolates was determined by the BD Phoenix automated system (Becton Dickinson, USA) in accordance with the criteria set forth by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Results: The MRSA rate in the one-year period was 25.77%. When the distribution of S. aureus isolates was analyzed, it was determined that blood cultures were the most common clinical specimens from which S. aureus was isolated. Resistance to glycopeptides and linezolid was determined in MRSA isolates, albeit at a low rate. No resistance to glycopeptide and linezolid was detected in MSSA isolates. MSSA isolates were found to have a more sensitive profile to other antibiotics than MRSA isolates. The highest resistance rate was detected against penicillin with 100% and 87.06% in MRSA and MSSA isolates, respectively. In addition, the most sensitive antibiotics were determined to be glycopeptide, linezolid, daptomycin, and aminoglycoside. Conclusion: In conclusion, knowing the resistance profiles of S. aureus isolates in our hospital, will guide empirical treatment. Furthermore, the implementation of effective infection control measures and a cautious approach to antibiotic use will contribute to the management of MRSA infections.

Evaluation of the Disk Diffusion Test for Bacteroides fragilis Group Clinical Isolates.

Bacteroides fragilis group (BFG) isolates are the most frequently isolated gram-negative anaerobic bacteria and exhibit higher levels of antimicrobial resistance than other anaerobic bacteria. Reliable susceptibility testing is needed because of reports of resistance to the most active antibiotics. Recently, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) introduced disk zone diameter breakpoints. We evaluated the disk diffusion test (DDT) for susceptibility testing of BFG isolates compared with the agar dilution method. In total, 150 BFG isolates were collected from three institutes in Korea. The agar dilution method was conducted according to the CLSI guidelines. DDT was performed following the EUCAST guideline. Fastidious anaerobe agar supplemented with 5% defibrinated horse blood was used as the culture medium. Nine antimicrobials were evaluated: penicillin, cefoxitin, cefotetan, imipenem, meropenem, piperacillin-tazobactam, clindamycin, moxifloxacin, and metronidazole. The categorical agreement (CA) between the two methods was >90.0% for imipenem, meropenem, clindamycin, and metronidazole. However, the CA for piperacillintazobactam was low, at 83.2%. Major errors were found: 5.4% for imipenem, 7.4% for meropenem, and 12.8% for piperacillin-tazobactam. All minor errors were <10%. We propose using the area of technical uncertainty (ATU) zone-overlapping area for susceptible and resistant strains to reduce errors in the DDT. Outside the ATU, the CAs of cefoxitin, cefotetan, and piperacillin-tazobactam were >90.0%, whereas that of moxifloxacin was increased to 88.5%. The DDT can be a useful alternative antimicrobial susceptibility test for BFG isolates when using the ATU zone to reduce errors.

Antibiotic resistance in community-acquired urinary tract infections. Did the COVID-19 pandemic cause a change?

This study aimed to evaluate the antimicrobial resistance rates before and during the coronavirus disease 2019 (COVID-19) pandemic. 897 positive urine cultures collected from outpatients of all ages between January 1, 2017, and December 31, 2022, were analyzed. The antibiotic susceptibility tests (AST) were analyzed by using an automated VITEK 2 (Biomerieux, Marcy-l`Étoile, France) compact system. AST results were interpreted according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. The significance of resistance rates was tested with the Pearson's Chi-squared test and risk factors of extended-spectrum beta-lactamases (ESBL) positiveness were identified with binary logistic regression. E. coli (n = 774) and K. pneumoniae (n = 123) were isolated in 86.3% and 13.7% of the patients, respectively. During this period of six years before and during pandemic, the highest resistance rate was found for cefuroxime axetil (49.8%) and the lowest for nitrofuratoin (6.0%). Statistically significant increases in resistance compared to the pre-pandemic period were only determined for cefixime (37.2 vs 46.0%) and ceftriaxone (37.6 vs 46.1%) (p = 0.010). ESBL positivity was the most important factor that statistically increased resistance for all antibiotics (p < 0.001 for all). Being male [OR (95% CI) 1.56 (1.13-2.15)] and presenting to the clinic after the pandemic period [1.4 (1.1-1.8)] were found to increase ESBL positiveness significantly. Ceftriaxone and Cefixime resistance rates and ESBL positivity among the uropathogens E. coli and K. pneumoniae increased during the pandemic compared with the pre-pandemic period. ESBL positivity was higher in males.

The impact of agar depth on antimicrobial susceptibility testing by disc diffusion.

Introduction. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) specifies the agar depth (4±0.5 mm) when performing antimicrobial susceptibility testing (AST). Since the infrastructure to produce standardized agar may be lacking in settings with limited resources, we wanted to examine to what extent variation in agar depth affects the inhibition zone diameters of quality control (QC) strains and AST of clinical isolates.Methods. The inhibition zone diameters on Mueller-Hinton II agar with different depths (2-6 mm) were tested for various QC strain-antimicrobial agent combinations using Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213. The relationship between zone diameters at different agar depths and MICs was investigated for 35 clinical isolates (E. coli, Klebsiella pneumoniae, S. aureus and P. aeruginosa) from Sierra Leone using MICs as the reference.Results. The inhibition zone diameters were within the acceptance ranges as defined by the EUCAST for the majority of QC strains and antimicrobials, independent of the agar depth. At extreme agar depths, inhibition zones were more frequently out of range. The accuracy of AST varied for clinical isolates at different agar depths for categorical agreement (85.8-94.6%), major error rate (0.4-2.1%) and very major error rate (VME: 3.3-12.5%).Conclusions. Even if the QC strains were in the acceptance range at different agar depths, this does not rule out unacceptably high VME rates (>3%) in clinical isolates.

The Vehicle of Administration and Prandial State May Reduce the Spectrum of Oral Broad-Spectrum Antibiotics (Oxytetracycline, Fosfomycin and Amoxicillin) Administered to Piglets: A Pharmacokinetic/Pharmacodynamic Approach.

The objective of this study was to assess the impact of the vehicle of administration and the prandial state of post weaning piglets on the indices of therapeutic efficacy for different broad-spectrum antibiotic/pathogen combinations. Pharmacokinetic data were retrieved from previous studies, in which we orally administered oxytetracycline (OTC), fosfomycin (FOS), or amoxicillin (AMX) according to the following treatments: dissolved in soft water to fasted or non-fasted piglets, dissolved in hard water to fasted or non-fasted piglets, and mixed with feed. Minimum inhibitory concentration (MIC) values for susceptible strains of bacteria causing swine diseases were obtained from the database of European Committee on Antimicrobial Susceptibility Testing (EUCAST) for each antibiotic. Pharmacokinetic/pharmacodynamic (PK/PD) indices of therapeutic efficacy-drug exposure over the dosing interval (fAUC/MIC) for OTC and FOS; time that free drug concentration remains above MIC (%fT>MIC) for AMX-were calculated for each antibiotic/pathogen combination under each treatment. After all OTC and in-feed FOS and AMX treatments, the indices of therapeutic efficacy were below the target value for all the study microorganisms. When FOS or AMX were delivered dissolved in soft or hard water, the indices were above the target value over which therapeutic efficacy would be expected for Escherichia coli treated with FOS and, Glaesserella parasuis, Pasteurella multocida, and Actinobacillus pleuropneumoniae treated with AMX. The prandial state of piglets showed no influence on the indices of therapeutic efficacy. Pharmacokinetic profiles of broad-spectrum antibiotics, specifically the ability to achieve target concentrations, may be largely reduced due to drug interactions with components present in feed or water resulting in a discrepancy with PK/PD principles of prudent and responsible use of antibiotics.

Microbiological profile and antimicrobial susceptibility of bacteria associated with urinary tract infections in Ukrainian adults

The aim of the study was to analyse the microbial profile of the urinary tract infections (UTIs) due to urolithiases and to study susceptibility to antibiotics in its causative agents. The main method of the research was bacteriological. Antimicrobial susceptibility testing was conducted by serial microdilution assay in accordance with recommendations of the European committee on antimicrobial susceptibility testing (EUCAST). For present study 128 unique urine samples were collected from patients with UTIs associated with urolithiasis. Among all collected specimens, 78% (n=100) gave clinically signi­ficant growth. Among all examined participants, 88.9% of women (64/72) and 64.3% of men (36/56) had confirmed UTI; in the study, female/male ratio was 1.4 (χ2=9.76; p&lt;0.05). Microorganisms identified in our study predominantly belon­ged to Bacteria (93.4%), and yeasts of Candida genus comprised only 6.6%. Among all, 66.1% were representatives of Enterobacterales (n=80), particularly, Escherichia coli (38.0%), Klebsiella oxytoca (15.7%), Klebsiella pneumoniae (2.5%), Enterobacter cloacae (5.8%), Proteus mirabilis (4.1%). Isolates of Pseudomonas aeruginosa comprised 3.3%. Among gram-positive isolates, Staphylococcus spp. (14.1%) and Enterococcus spp. (9.9%) were identified. Regarding female/male distribution, the biggest proportion of gram-positive bacteria were isolated from women, statistically significant results were obtained for sex distribution of S. saprophyticus (p&lt;0.05). Antimicrobial susceptibility of Enterobacterales was variable, and the best results were obtained for carbapenems, novel antibiotics (cefiderocol, ceftolozane-tazobactam and ceftazidime-avibactam), aminoglycosides and tigecycline. There were 9 isolates with pro­duction of carbapenemases and resistant to all relevant β-lactam antibiotics. All isolated Staphylococcus spp. were β-lactamase producers, one isolate of S. saprophyticus demonstrated methicillin-resistance. To summarise, there is an ongoing outbreak of multidrug-resistant infections in Ukraine and causative agents of UTIs are among the most important contributors. Availability of data on the local antimicrobial susceptibility profile may guide the informed decision making in etiotropic treatment, therefore, contribute to global efforts in rational drug use and fight the resistance escalation.

Epidemiology and Antibiotic Resistance of Combat Wound Infection in Surgical Patients

The aim. To analyze the microbiological spectrum of pathogens causing surgical site infections and their antibiotic resistance in surgical patients injured during the military conflict between Ukraine and Russia. Materials and methods. This study was based on 137 bacteriological examinations of biological samples from patients treated in the surgical department of the Kyiv City Oleksandrivska Clinical Hospital in 2022. The samples included 81cultures isolated from postoperative wounds and 56 cultures from the abdominal cavity. Susceptibility to antibacter drugs was determined according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) standards. Statistical analysis was performed using IBM SPSS Statistics. Results. Among the 137 analyzed samples, the most common pathogens were Klebsiella pneumoniae (22.6%), Enterococcus faecalis (13.1%), Staphylococcus epidermidis (13.1%), Pseudomonas aeruginosa (11.6%), and Escherichia coli (10.2%). In the abdominal cavity samples (n = 56), E. coli was predominant (17.9%), followed by K. pneumoniae (16.1%), E. faecalis (16.1%), S. epidermidis (10.7%), Candida (8.9%), and P. aeruginosa (7.1%). In postoperative wound samples (n = 81), K. pneumoniae was found in 27.2%, P. aeruginosa in 14.8%, S. epidermidis in 14.8%, S. aureus in 12.3%, and E. faecalis in 11.1%. K. pneumoniae showed high resistance to amikacin (86.6%), meropenem (74.2%), piperacillin-tazobactam (82.8%), and ceftriaxone (86.2%). E. faecalis exhibited resistance to imipenem (58.8%), levofloxacin (47.1%), and vancomycin (12.5%). S. epidermidis had resistance to gentamicin (13.3%), meropenem (50%), and oxacillin (35.7%). P. aeruginosa demonstrated resistance to ciprofloxacin (45.6%), meropenem (67.4%), ceftazidime (52.3%), and piperacillin-tazobactam (48.7%). Conclusion. The primary pathogens causing surgical site infections in military surgical patients are K. pneumoniae, E. faecalis, S. epidermidis, P. aeruginosa, and E. coli. The pathogen spectrum varies between abdominal cavity infections and postoperative wound infections. There is a clear trend towards increased detection of antibiotic-resistant pathogens, particularly among military personnel. Colonization with resistant microorganisms increases during medical evacuation through different levels of the evacuation chain.

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.

Optimizing Antibiotic Therapy for Stenotrophomonas maltophilia Infections in Critically Ill Patients: A Pharmacokinetic/Pharmacodynamic Approach.

Stenotrophomonas maltophilia is an opportunistic, multidrug-resistant non-fermentative Gram-negative bacillus, posing a significant challenge in clinical treatment due to its numerous intrinsic and acquired resistance mechanisms. This study aimed to evaluate the adequacy of antibiotics used for the treatment of S. maltophilia infections in critically ill patients using a pharmacokinetic/pharmacodynamic (PK/PD) approach. The antibiotics studied included cotrimoxazole, levofloxacin, minocycline, tigecycline, cefiderocol, and the new combination aztreonam/avibactam, which is not yet approved. By Monte Carlo simulations, the probability of target attainment (PTA), the PK/PD breakpoints, and the cumulative fraction of response (CFR) were estimated. PK parameters and MIC distributions were sourced from the literature, the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and the SENTRY Antimicrobial Surveillance Program collection. Cefiderocol 2 g q8h, minocycline 200 mg q12h, tigecycline 100 mg q12h, and aztreonam/avibactam 1500/500 mg q6h were the best options to treat empirically infections due to S. maltophilia. Cotrimoxazole provided a higher probability of treatment success for the U.S. isolates than for European isolates. For all antibiotics, discrepancies between the PK/PD breakpoints and the clinical breakpoints defined by EUCAST (or the ECOFF) and CLSI were detected.