Low Dose Amoxicillin Stimulates Biofilm Formation in Methicillin Resistant Staphylococcus aureus

Previous studies showed that sub-MIC levels of beta-lactam antibiotics induce extracellular DNA release and biofilm formation in most MRSA strains, a process that may have relevance in hospitals and on farms. The objective of this study was to gain insight into the mechanism of antibiotic induced MRSA biofilm. We found that low-dose amoxicillin increased the ability of MRSA cells to auto-aggregate and attach to a surface under static and gyratory conditions. By screening a transposon insertion library for mutants deficient in biofilm induction, we identified a novel gene (designated aibA for antibiotic-induced biofilm) that was required for biofilm formation in sub-MIC levels of antibiotics. This gene encodes a small hypothetical protein conserved among Bacilli that may play a role in glucose transport and metabolism. We concluded that low-dose cell wall active antibiotics alter the physical properties of MRSA cells, and that screening for biofilm induction mutants provides a means to identify novel effectors that mediate both the cell wall stress response and biofilm formation in MRSA.