Background: Urinary tract infections (UTIs) are the most common infections after kidney transplantation and significantly affect patient outcomes. In these immunosuppressed patients, antibiotic resistance is of particular concern due to recurrent infections and limited treatment options. The aim of this study was to evaluate the distribution of microorganisms isolated from urine cultures of kidney transplant patients and to assess their antimicrobial susceptibility patterns. Methods: This retrospective study included all adult kidney transplant recipients with positive urine cultures during 2023–2024. Microorganisms were identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and antimicrobial susceptibility testing was performed with the Phoenix System according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. Results: A total of 363 urine samples from 123 patients (85% female) were analyzed. E. coli (49%) and Klebsiella spp. (24%) were the predominant uropathogens. High resistance rates to ciprofloxacin and trimethoprim–sulfamethoxazole (TMP–SMX) were observed in both species, while carbapenem resistance remained low. Elevated resistance to multiple antibiotics was also detected among Pseudomonas aeruginosa and Acinetobacter spp., highlighting the importance of continued microbiological surveillance in this population. Conclusions: Gram-negative bacteria were the predominant pathogens causing UTIs in kidney transplant recipients. The high resistance rates to ciprofloxacin and TMP–SMX emphasize the need for local antimicrobial surveillance and individualized empirical therapy. Systematic and ongoing monitoring of resistance patterns is essential to optimize infection management in this vulnerable patient group.

In the literature, there is a limited number of case reports of Paenibacillus urinalis in adults. However, there is no information available regarding P. urinalis infection in children and infants. Paenibacillus growth in blood and sterile site cultures is generally considered contamination; it is unclear whether P. urinalis is the true cause of the infection. In this retrospective study, we aimed to clinically evaluate P. urinalis growth in the blood cultures of children at a tertiary referral hospital over a 5.5-year period, with identification performed using the MALDI-TOF MS method. A total of 170 hospitalized children showed P. urinalis growth in sterile site cultures (blood: 162; catheter: 7; CSF: 1), with forty percent of all growth occurring in only three wards (neonatal intensive care unit, hematology, oncology). Of 170 cultures, 5 (2.9%) showed further P. urinalis growth in control cultures, which could be considered significant. In cases with a second culture, the average growth time (time to positivity) was relatively short, at 24 + 7 h (mean + SD, min-max: 17–33 h). No mortality was observed in any case. Evaluations were conducted by the Hospital Infection Control Committee to determine the source of P. urinalis contamination. P. urinalis growth was detected in 33% of samples taken from clean, packaged linens before use; 53% of ambient air cultures; and 65% of hospitalized patient skin swabs. In conclusion, P. urinalis blood culture growths are primarily considered contamination; however, these growths should be carefully evaluated in risk groups (especially those admitted in neonatal intensive care units and young infants less than 3 months old). In hospitalized patients, clustered growths may be influenced by environmental (such as clean packaged linens and ambient air) and skin colonization.

Accurate species-level identification of Aspergillus is clinically important because closely related species may differ in virulence and antifungal susceptibility. This study evaluated the discriminatory capacities of the ITS, β-tubulin (benA), and calmodulin (CaM) loci using an in silico multilocus approach. Whole-genome sequences from the NCBI GenBank and RefSeq databases were used to construct an in-house reference library. Barcode regions were extracted in silico using published primer pairs and analyzed for sequence length variation, nucleotide differences, single nucleotide polymorphisms, insertions/deletions, and candidate species reduction patterns. Principal coordinate analysis (PCoA) was performed to visualize genetic relationships among species. Most clinically important species exhibited similar barcode length distributions and clustered according to Aspergillus sections. PCoA results were largely consistent with section classification, with the first two coordinates explaining 20.4% and 18.2% of the total variation. Sequential analysis using a ≥99% sequence identity threshold showed that ITS had the lowest discriminatory capacity, whereas benA achieved the greatest reduction in candidate species and resolved the highest number of taxa. CaM displayed the highest sequence variation in pairwise comparisons of closely related species. Although A. flavus and A. austwickii remained indistinguishable across all three loci, additional differences were detected in the cyp51A region. These findings indicate that section-oriented marker selection and prior in silico evaluation can improve the efficiency and discriminatory performance of sequence-based Aspergillus identification workflows.

Paenibacillus is abundant in nature and environmental samples, and generally does not contain invasion factors. Therefore, Paenibacillus growth in blood is generally considered a contamination. However, it can lead to infection in children and adults, particularly in at-risk groups. In many of these cases, it may not be clear whether Paenibacillus is the true cause of the infection. The literature reports a limited number of cases of Paenibacillus urinalis in adults. However, there is no information available regarding P. urinalis infection in children and infants. This retrospective study aimed to clinically evaluate P. urinalis growth in blood cultures of children in a tertiary referral hospital over a 5.5-year period. A total of 170 hospitalized children showed P. urinalis growth in blood cultures (blood; 162, catheter; 7, CSF; 1). Identification was performed using the MALDI-TOF MS method. Forty percent of all P. urinalis growths occurred in only three wards (neonatal intensive care unit, hematology, oncology). Of 170 cultures, 5 (2.9%) showed P. urinalis growth again in control cultures, which was considered significant. In cases with a second culture, the average culture growth time was 24+7 hours (mean + SD, min-max; 17-33 hours). No mortality was observed in any case. Evaluations were conducted under the responsibility of the Hospital Infection Control Committee to determine the source of P. urinalis contamination. P. urinalis growth was detected in 33% of samples taken from clean, packaged linens before use, 53% of ambient air cultures, and 65% of skin swabs of the hospitalized patients. In conclusion, P. urinalis blood culture growths are primarily considered contamination. However, these growths should be carefully evaluated in risk groups. In hospitalized patients, clustered growths may be influenced by environmental and skin colonization.

This study aimed to evaluate retrospectively the species Haemophilus influenzae (H. influenzae) that was isolated from clinical specimens of patients admitted to our tertiary care hospital January 1, 2014, and December 31, 2024 and to investigate their antimicrobial resistance patterns. H. influenzae was identified using MALDI-TOF MS (Bruker Daltonik GmbH, Bremen, Germany) and serotyped using Difco H. influenzae Type b antiserum (Difco-BD®-USA). Only 21 (1.4%) samples (10 blood, 5 biopsy, 3 CSF, 2 vitreous, 1 pleural) isolated with H. influenzae were from invasive sites, and sputum was the most common sample among non-invasive samples (1179 strains,81%). Ampicillin resistance in H. influenzae isolates was 38.5%. Amoxicillin–Clavulanate (AMC) resistance was 13.5%, cefuroxime resistance was 66.6%, ceftriaxone resistance was 45.7%, chloramphenicol resistance was 12.2%, clarithromycin resistance was 12.7%, erythromycin resistance was 14.3%, levofloxacin resistance was 11.5%, meropenem resistance was 21.2%, rifampicin resistance was 20.2%, tetracycline resistance was 21%, and Trimethoprim–Sulfamethoxazole (TMP-SMX) resistance was 34.3%. Ampicillin and TMP-SMX resistance were statistically more prevalent in non-Type B strains. TMP-SMX resistance was statistically more prevalent in non-invasive samples. Strains from patients in the intensive care unit (ICU) were statistically more resistant to ampicillin and ceftriaxone. As a result, rates of antibiotic resistance for H. influenzae vary over time, depending on the country, and even within regions of the same country. Considering the annual fluctuations in antibiotic resistance, it is important to be aware of the current local drug resistance situation. This study revealed the need to reevaluate treatment options due to high resistance rates of ampicillin, ceftriaxone, cefuroxime, and TMP-SMX for treating infections caused by H. influenzae.