Purpose: To study the distribution of pathogenic bacteria in ventilator-associated pneumonia (VAP), and epidemiological characteristics of extended-spectrum β lactamase (ESBL)-producing bacteria.
Patients and methods: Lower respiratory tract secretions from 156 patients with mechanical ventilation were collected using a protective specimen brush (PSB), with quantitative bacterial culture carried out and antibiotic sensitivity measured. ESBLs produced by Gram-negative bacilli were detected using the double disk diffusion method and monitored by plasmid profiles.
Results: Gram-negative bacilli accounted for 78.9% of VAP pathogens, with Acinetobacter baumannii  (25%), Pseudomonas aeruginosa  (19.7%), and Klebsiella pneumoniae  (14.5%) as the most common strains. There were 12 Gram-positive strains detected (15.8%); mostly methicillin-resistant. Staphylococcus aureus  and methicillin-resistant coagulase-negative Staphylococcus . There were also four strains of Candida albicans  detected (5.26%). Most Gram-negative bacilli are sensitive to imipenem, but A. baumannii  is serious resistant. ESBLs were detected in nine strains of Gram-negative bacilli; mainly produced by K. pneumoniae  and Escherichia coli , to different degrees of multidrug resistance. Five strains of K. pneumoniae -producing ESBLs were from the same clonal origin, as confirmed by plasmid restriction endonuclease analysis.
Conclusion: VAP was mainly caused by Gram-negative bacteria, with high antibiotic resistance rates. Plasmids played an important role in the spread of antibiotic resistance among bacteria.
Keywords: ventilator-associated pneumonia, pathogenic bacteria, extended-spectrum β lactamases, drug resistance plasmid