Objective: To study the biofilm-forming ability and the distribution of biofilm-related genes in Acinetobacter baumannii clinical isolates as well as antimicrobial resistance, to analyze their relationships with the bacterial resistance phenotype.
Methods: A prospective study was conducted. Biofilm models of 70 strains Acinetobacter baumannii collected in Chengwu County People's Hospital from October 2012 to October 2013 were constructed using 96-well polystyrene plate. In order to analyze the biofilm-forming ability, a qualitative and quantitative analysis was conduct by crystal violet staining assay. And the antimicrobial resistance of different biofilm-forming ability strains was compared including imipenem, amikacin, meropenem, cefepime, sulbactam cefoperazone, trimethoprim, levofloxacin, gentamicin, ciprofloxacin, cefotaxime, ceftizoxime, aztreonam, piperacillin, ceftriaxone, cefuroxime. In addition, the expressions of biofilm-related gene Bap, bfs and intI1 were tested with polymerase chain reaction (PCR) assay.
Results: Among 70 strains Acinetobacter baumannii, 40 strains were multi-drug resistant (57.14%) and 6 strains were pan-drug resistant (8.57%); 68 strains had biofilm-forming ability (97.14%), 14 of which were weakly positive, 20 were positive and 34 were strongly positive. The antimicrobial resistant rate of Acinetobacter baumannii to imipenem, amikacin, meropenem and cefepime was decreased, it was 30.00%, 32.86%, 38.57% and 41.43%, respectively. However, the antimicrobial resistant rates to other commonly used antibiotics were all higher than 50%. The drug resistance of Acinetobacter baumannii to levofloxacin (85.71%, 45.00%, 38.24%, χ² = 9.225, P=0.010), cefepime (71.43%, 45.00%, 29.41%, χ² = 7.222, P=0.027), gentamicin (78.57%, 55.00%, 38.24%, χ² = 6.601, P=0.037) was significantly decreased when biofilm-forming ability reinforced (weakly positive, positive, hadropositive). Bap gene positive rate of weakly positive, positive and strong positive biofilm-forming strains Acinetobacter baumannii was 50.00%, 65.00% and 79.41% (χ² = 4.244, P=0.120), respectively. Bfs gene positive rate was 35.71%, 65.00% and 88.24% , respectively (χ² = 13.602, P=0.001) and intI1 gene positive rate was 42.86%, 75.00% and 91.18%, respectively (χ² = 12.902, P=0.002). Moreover, the antimicrobial resistances of biofilm-related gene positive strains were higher than the negative, of which the drug resistance of intI1 positive group to amikacin was significantly higher than the negative group (40.38% vs. 11.11%, χ² = 5.194, P=0.023).
Conclusions: The Acinetobacter baumannii collected from the hospital had strong multi-drug resistance as well as strong biofilm-forming ability. The drug resistance of Acinetobacter baumannii decreased when biofilm-forming ability reinforced. In addition, genes, such as Bap, bfs, and intI1, contributed to biofilm formation.