Molecular mechanism of drug resistance of non-fermentative Gram-negative bacteria in hospitals

The development and persistence of antibiotic resistance in non-fermentative Gram-negative (NFGN) bacteria in hospitals has become one of the major causes for clinical infection. This study aimed to investigate the species, source, drug resistance and relevant molecular mechanism of NFGN bacteria in hospitals. NFGN bacteria isolates from samples of blood, sputum, urine, pus, secretion and throat swab in our hospital was cultured and identified using a VITEK 2 Compact automated microbiology system. Drug susceptibility was determined using the conventional KB disk diffusion method. Antibiotic resistance was analyzed with WHONET 8.6 software, and resistance rate was compared by X-2 test using SPSS 16.0. The genotypes of these NFGN bacteria were analyzed by polymerase chain reaction (PCR). The expression of CTX-M type extended spectrum beta-lactamase (ESBL) was measured by Western blot analysis. The correlation between CTX-M ESBL level and antibiotic resistance was analyzed by Spearman rank test using SPSS 16.0. A total of 608 isolates of NFGN bacteria were identified including 198 isolates of Pseudomonas aeruginosa, 152 Acinetobacter baumannii, 96 Pseudomonas spp., 54 Escherichia coli, 58 Staphylococcus aureus and 50 Klebsiella pneumoniae. These NFGN bacteria were isolated from blood (30%), sputum (18%), urine (12%), pus (10%), throat (8%) and secretion (22%). The highest proportion of these bacteria was isolated in ICU (40%), followed by the respiratory department (26%). The remaining (34%) was isolated in other departments. High level of CTX-M ESBL was expressed in these NFGN bacteria and was positively correlated with the antibiotic resistance of these bacteria. The antibiotic resistance of hospital NFGN bacteria is positively correlated with the expression level of CTX-M ESBL. The finding may provide valuable information for infection control in hospital settings.