Phenotypic and genotypic characteristics of Acinetobacter baumannii enrolled in the relationship among antibiotic resistance, biofilm formation and motility

Acinetobacter baumannii is an important pathogen in clinical. The factors of biofilm formation, antibiotic resistance and motility contribute great to A. baumannii in persisting in stressed environment, and further leads to nosocomial infections. 70 A. baumannii clinical isolates were investigated for their clinical characteristics of infection. Among the tested strains, 54 (77.1%) isolates were obtained from ICUs, with the frequency of multidrug-resistance (MDR) at 55.7%, and that of extensively drug-resistance (XDR) at 31.4%. 97.1% of the clinical isolates could form biofilms, in which 4.3% possessed weak biofilm formation ability, while 41.4% and 51.4% were moderate and strong biofilm producers, respectively. A strong correlation between antibiotic resistance and biofilm formation ability was found that all the resistant strains could form biofilms, with the majority in moderate and strong levels, but 2.9% sensitive isolates had no such ability. However, the sensitive strains that could produce biofilms showed stronger biofilm formation capacity in the early stage before 24 h compared to the resistant isolates, though they became weaker afterwards. 24 biofilm-related genes and two bla_OXA genes were found in both biofilm-forming and non-biofilm-forming strains, but with higher prevalence in the strains that could produce biofilms. No correlation was detected between twitching motility with antibiotic susceptibility or biofilm formation. These results raised a viewpoint that examining timepoint is a key factor for determining the biofilm formation ability, and further highlighted the importance of the appropriate surveillance and control measures in preventing the emergence and transmission of MDR and XDR A. baumannii.