Sub-minimum inhibitory concentrations in ceftazidime exacerbate the formation of Acinetobacter baumannii biofilms

Associated with nosocomial infections, the environmental Gram-negative coccobacillus A. baumannii leads to various kinds of high mortality-rate infections among which pneumonias mainly in immune-compromised people from health-care facilities. A critical component of the current antibiotic resistance problem is the presence of antibiotics sub-minimum inhibitory concentrations (sub-MICs) in a variety of natural settings including drinking water, sewage water, rivers, lakes, and natural sludge. In India, third-generation cephalosporins such as ceftazidime (CAZ) count among the most often prescribed β-lactams to treat infections by A. baumannii. In this study, we showed that CAZ sub-MICs 1/reduce adhesion to lung epithelial cells and slow down the growth of the A. baumannii KSK1 strain, which nevertheless quickly resumes its growth; 2/alter the morphology of A. baumannii KSK1 planktonic cells and induce the formation of bacterial aggregates that resemble biofilms; 3/increase the in vitro formation of biofilms by A. baumannii KSK1 bacterial cells. Our findings underscore the importance of considering sub-MICs in antibiotic therapy and environmental contamination as the antibiotics sub-MICs potentially found in wastewater may contribute to the selection causing antibiotic resistance and persistence of antibiotic-resistant strains.