[A study of outer membrane protein and molecular epidemiology of carbapenem-resistant Acinetobacter baumannii]

To study the characteristics of the distribution and drug resistance of Acinetobacter baumannii, and the epidemiology of the main strains among wards and hospitals, and to investigate the role of outer membrane protein in producing resistance against carbapenems.

145 Acinetobacter baumannii strains were collected from July 2013 to July 2014 from Huangdao Hospital Affiliated to Qingdao University and 401st Army Hospital. Antimicrobial susceptibility test was carried out with K-B disk diffusion method. Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) was used for DNA typing and test of homology. The carO gene of outer membrane protein was amplified by PCR, and the outer membrane proteins were extracted by ultrasonication and ultracentrifuge method from 30 randomly selected carbapenem-resistant Acinetobacter baumannii and 17 carbapenem-sensitive strains. Sodium dodecyl sulfate-polyacrylamide gel electropheresis (SDS-PAGE) was used to analyze the expressions of outer membrane proteins.

145 Acinetobacter baumannii strains were generally resistant to 16 common antimicrobial agents, with the highest susceptibility rate of 79.3% for minocycline, followed by susceptibility rate of 40.7% for amikacin. There were 128 carbapenem-resistant strains (resistance rate of 88.3%), 137 multidrug-resistant strains and 126 extensively drug-resistant strains. The detection rates of carO gene were 97.7% (125/128) and 17.6% (3/17) in carbapenem-resistant and sensitive strains respectively. Around position of relative molecular mass 47,000, 16 of 17 sensitive isolates were expressed this protein, while 20 of 30 resistant ones were detected nothing or fade; 13 of 17 sensitive isolates were expressed around position of relative molecular mass 37,000 and 29,000 while 25 were detected nothing or fade around position of relative molecular mass 37,000 and 23 were detected nothing or fade around position of relative molecular mass 29,000 in 30 resistant ones. 145 Acinetobacter baumannii were classified into 8 types based on ERIC-PCR electrophoresis patterns, and the major prevalence types were type A (71 strains) and type E (37 strains).

Drug resistance of clinically isolated Acinetobacter baumannii is a serious problem in two hospitals; drug-resistant strains are spread and epidemic among wards and hospitals. The carO gene of outer membrane protein is widespread in carbapenem-resistant Acinetobacter baumannii. The loss or fading of outer membrane protein may play an important role in Acinetobacter baumannii resistance to carbapenems drugs.