Background/Objectives: Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections present a significant clinical challenge due to limited therapeutic options and high transmission potential. This study aimed to identify the resistance genes associated with carbapenemase production in CRKP isolates and evaluate the in vitro activity of ceftazidime/avibactam (CZA) and meropenem/vaborbactam (MEV), among other β-lactam/β-lactamase inhibitor combinations. Methods: Between October 2021 and June 2022, a total of 504 CRKP isolates were grown from patient samples in intensive care units. When duplicate patient samples were removed, the remaining 89 isolates were included in the study. Bacterial identification and antimicrobial susceptibility testing were per-formed using MALDI-TOF, Phoenix M50, and disk diffusion methods, following EUCAST guidelines. PCR analyses identified carbapenemase genes such as OXA-48, NDM, and KPC. Results: The most prevalent carbapenemase gene was OXA-48 (79.8%), followed by NDM (21.4%) and KPC (17.9%). The susceptibility rate to CZA was 82.0%, significantly higher than MEV (10.1%). All isolates were resistant to piperacillin/tazobactam and ceftolozane/tazobactam. Among MEV-resistant isolates, most carried the OXA-48 gene, while NDM was common in CZA-resistant isolates. Conclusions: CZA demonstrates high efficacy against OXA-48-producing CRKP, making it a viable treatment option in settings where OXA-48 predominates. The limited activity of MEV in this study underscores the need for molecular surveillance of resistance mechanisms to guide empirical therapy.

Objective: Invasive candidiasis is defined as an important infection that increases the duration of patients’ hospital stay, costs, mortality and morbidity. In this study, we aimed to investigate the frequency of candidiasis in blood cultures of pediatric hematology patients, Candida species, antifungal susceptibilities, and their effects on mortality. Materials and Methods: Patients with Candida growth in their blood cultures at follow-up in the pediatric hematology clinic of our hospital between 2020 and 2024 were included in the study. Age, gender, primary diseases and risk levels, subtypes and antifungal susceptibilities of Candida grown in blood cultures, the presence of neutropenia in patients, the antifungals used for prophylaxis and treatment, the duration of infection, other bacteria grown additionally during the fungal infection period, the local infection source and the patients’ discharge status were obtained from medical records. These constituted the study data. Results: Blood cultures were requested for 594 patients from the Pediatric hematology Clinic, and Candida was grown in only 37 (6.7%) of them. A total of 43.2% of them were the Candida parapsilosis complex, 29.7% were Candida albicans and 8.1% were the Candida haemulonii complex. Antifungal susceptibilities were over 90% for anidulafungin, micafungin, caspofungin, posaconazole, itraconazole and amphotericin B, followed by 86.7% for fluconazole and 84.4% for voriconazole. The mean age of the patient group was 6.8 years, 50.5% of whom were female and 40.5% of whom were male. The Candida infections developed on the 12.1th day of the neutropenia process on average. The mean invasive Candida infection period was 7 days. A total of 18.9% had a second bacterial infection and 13.5% had a local infection. A total of 51.4% had a single antifungal, 18.9% had two antifungals and 2.1% had more than two antifungals. A total of 35.1% of the patients with invasive candidiasis died. The primary diagnosis of the disease, Patient risk level, and the female gender were important factors affetting mortality. Conclusions: In a pediatric hematology clinic, the non-albicans group in invasive candidiasis infections was notable, with the C. parapsilosis complex occurring most frequently. There was still a high sensitivity to echinocandin antifungals and a decreased sensitivity to triazoles. It was found that the factor of the clinical diagnosis, being in the high-risk group and being female had significant effects on the survival rate of patients with candidiasis infections.

Carbapenemase-Producing Enterobacteriaceae (CPE) are known to be on the rise globally and are a major concern. Rapid screening of at-risk patients and implementation of infection control measures can prevent colonization from becoming a source of infection. We investigated the incidence of carbapenem-resistant Enterobacteriaceae (CRE) colonization, CRE-producing Enterobacteriaceae species, carbapenemase gene types and prevalence in patients subjected to CRE screening tests in rectal swab samples using the CHROMAgar culture method and real-time Polymerase Chain Reaction (PCR) method in a tertiary hospital in Istanbul, Turkiye. In addition, we investigated the effectiveness of diagnosis with PCR and CHROMAgar methods by examining whether meropenem-resistant infection foci developed in patients with CRE colonization from hospitalization to discharge. This study was conducted retrospectively in the Microbiology Laboratory of 3953 patients at Başakşehir Çam and Sakura City Hospital in Istanbul between January 2021 and December 2023. All data, including CRE colonization screening test results using CHROMAgar and PCR methods, age, gender, requesting clinic, and meropenem-resistant Enterobacteriaceae culture results in infection foci that developed during hospitalization, were obtained from the hospital automated system. In all 3953 patients included in the study, CRE colonization was screened by CHROMAgar culture method on rectal swab samples and by real-time PCR method in 500 patients. The mean age of the patients was 42.9 ± 30.1 and 58.1% were male. There was no difference in age and gender distribution between the Upon admission to the hospital and during hospitalization groups (p > 0.05). Rectal CRE colonization was detected in 9.7% of all patients with the CROMAgar method and in 9.2% with the PCR method and in 16.2%. The most statistically significant increase was seen in intensive care units with the CHROMAgar method (p < 0.05). Among Enterobacteriaceae species, Klebsiella pneumoniae (69.6%) was most frequently grown, followed by Escherichia coli (13.7%). There was no statistically significant difference between the groups in terms of CRE growth status and microorganism distribution in rectal swab samples of patients during hospitalization and hospital admission (p > 0.05). Among the CRE genes detected by PCR, single genes were the most common. While OXA-48 positivity was detected in 113 (16.40%) of the patients, blaNDM was detected in 31 (4.50%), blaKPC was detected in 5 (0.73%) and bla VIM/IMP gene was detected in 5 (0.73%) of the others. Double gene positivity was observed in a single strain in 6 patients and blaKPC, blaNDM and blaOXA-48 genes were positive together in a single strain in 3 patients. Infection developed in one or more foci resistant to carbapenem in 159 of the patients colonized with CRE during their hospitalization. The rate of infection development was lower in patients colonized by PCR compared to chromogenic agar. The CRE colonization rate is high and should be closely monitored with infection control precautions. Although the detection rate of CRE colonization was higher with PCR, the rate of progression to infection in any focus during hospitalization was found to be lower detected with the CHROMAgar method. This situation showed that rapid detection of CRE colonization with PCR, early diagnosis and isolation are important. Klebsiella pneumoniae colonization was the most common causative agent. Co-production of 3 CRE genes (blaKPC + blaNDM + blaOXA-48) in 3 patients in our hospital highlighted the importance of concerns about multi-resistant Enterobacteriaceae.

Accurate identification of Gram-positive bacteria by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) may be limited by the complex structure of their cell walls. This study evaluated the impact of on-plate formic acid (FA) pretreatment on MALDI-TOF MS identification performance in a routine clinical microbiology laboratory. A total of 148 non-repetitive Gram-positive clinical isolates were analyzed using two preparation methods: direct transfer (DT) and on-plate FA pretreatment. Identification scores were compared with an emphasis on high-confidence species-level identification (log score ≥ 2.0). Statistical analyses were performed using the Wilcoxon signed-rank and McNemar tests. Overall identification rates were significantly higher with FA pretreatment than with DT (99.3% vs. 79.7%). The proportion of isolates achieving species-level identification increased from 27.1% with DT to 76.2% with FA pretreatment. Mean MALDI-TOF MS log scores for all isolates were significantly higher with FA (2.104 ± 0.186) than with DT (1.861 ± 0.265; p < 0.001). Notably, FA pretreatment also resulted in a significant increase in mean log scores among isolates that had already achieved species-level identification using DT (p = 0.001). The most pronounced improvement was observed among Staphylococcus spp., particularly coagulase-negative staphylococci, with complete concordance between DT and FA-assisted species-level identifications. In conclusion, on-plate FA pretreatment significantly enhances identification accuracy and diagnostic confidence for Gram-positive bacteria in routine MALDI-TOF MS workflows. Building on these findings, we propose a pragmatic, score-based, and species-aware diagnostic algorithm in which FA pretreatment is reflexively applied to Gram-positive isolates, yielding a DT log score < 2.0, with primary FA application recommended for staphylococci (particularly coagulase-negative species) and for less commonly encountered Gram-positive organisms.