Bacterial pathogens in ventilator-associated pneumonia; molecular assessment of resistance profiles

Ventilator-Associated Pneumonia (VAP) is the most commonly encountered infection in intensive care units and is directly associated with increased mortality, morbidity, and healthcare costs. The most frequently observed bacterial pathogens in VAP cases are multidrug-resistant (MDR) Gram-negative bacteria such as Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli. This study aims to determine the antibiotic resistance profiles of bacteria isolated from hospital-acquired VAP cases at the molecular level. The study was conducted in the Intensive Care Units of Kırşehir Training and Research Hospital between November 30, 2022, and November 30, 2023. The presence of resistance genes in bacterial isolates was identified using Polymerase Chain Reaction (PCR), while clonal similarity and genetic typing analyses were performed using Repetitive Extragenic Palindromic-PCR (rep-PCR) and Multi-Locus Sequence Typing (MLST) methods. A total of 56 culture-positive VAP patients were identified in the study. Of these, 30 (53.6%) were male, with a mean age of 63.3±19.2 years. Among the isolated microorganisms, A. baumannii was the most common pathogen (45.1%), followed by K. pneumoniae (43.1%) and P. aeruginosa (7.8%). Antibiotic susceptibility testing revealed that A. baumannii strains were 100% resistant to ciprofloxacin and meropenem, and 69.6% resistant to colistin. Similarly, K. pneumoniae strains showed 94.73% resistance to carbapenems, and 100% resistance to both piperacillin-tazobactam and colistin. Molecular analyses showed that the following resistance genes were present in A. baumannii isolates: blaTEM, blaCTX-M1, blaOXA-51, blaOXA-23, and blaOXA-40. In K. pneumoniae isolates, blaTEM, blaSHV, blaCTX-M1, blaOXA-1, blaOXA-48, and blaNDM-1 genes were detected. Conjugation experiments identified 9 (17.6%) isolates as transconjugants. Clonal analysis revealed that the ST2096 clone was predominant among K. pneumoniae isolates, while ST2 was the most prevalent among A. baumannii isolates, both of which are known to exhibit hypervirulent characteristics. Notably, clones not previously reported in Turkey were identified, including ST78 in A. baumannii and ST45, ST437, and ST1128 in K. pneumoniae. The findings demonstrate that A. baumannii and K. pneumoniae are the most frequently isolated pathogens in VAP cases, and clonal analysis indicates their spread within the hospital environment. The widespread presence of carbapenem and β-lactamase resistance genes explains the high level of resistance to β-lactam antibiotics. This resistance complicates the treatment of hospital-acquired infections, emphasizing the urgent need for alternative therapeutic strategies and strict adherence to infection control measures. May 2025, 107 Page Keywords: Ventilator Associated Pneumonia, Antimicrobial resistance, Resistance genes, Acinetobacter baumannii, Klebsiella pneumoniae