Characterization of antibiotic and disinfectant susceptibility in biofilm-forming Acinetobacter baumannii: A focus on environmental isolates

Abstract The clinical role of Acinetobacter baumannii has been highlighted in numerous infectious syndromes with a high mortality rate, due to the high prevalence of multidrug-resistant (MDR) isolates. The treatment and eradication of this pathogen is hindered by biofilm-formation, providing protection from noxious environmental factors and antimicrobials. The aim of this study was to assess the antibiotic susceptibility, antiseptic susceptibility and biofilm-forming capacity using phenotypic methods in environmental A. baumannii isolates. One hundred and fourteen ( n = 114) isolates were collected, originating from various environmental sources and geographical regions. Antimicrobial susceptibility testing was carried out using the disk diffusion method, while antiseptic susceptibility was performed using the agar dilution method. Determination of biofilm-forming capacity was carried out using a microtiter-plate based method. Resistance in environmental A. baumannii isolates were highest for ciprofloxacin (64.03%, n = 73), levofloxacin (62.18%, n = 71) and trimethoprim-sulfamethoxazole (61.40%, n = 70), while lowest for colistin (1.75%, n = 2). Efflux pump overexpression was seen in 48.25% of isolates ( n = 55), 49.12% ( n = 56) were classified as MDR. 6.14% ( n = 7), 9.65% ( n = 11), 24.65% ( n = 28) and 59.65% ( n = 68) of isolates were non-biofilm producers, weak, medium, and strong biofilm producers, respectively. No significant differences were observed between non-MDR vs. MDR isolates regarding their distribution of biofilm-producers ( P = 0.655). The MIC ranges for the tested antiseptics were as follows: benzalkonium chloride 16–128 μg mL −1 , chlorhexidine digluconate 4–128 μg mL −1 , formaldehyde 64–256 μg mL −1 and triclosan 2–16 μg mL −1 , respectively. The conscientious use of antiseptics, together with periodic surveillance, is essential to curb the spread of these bacteria, and to maintain current infection prevention capabilities.