Induction of MRSA Biofilm by Low-Dose β-Lactam Antibiotics: Specificity, Prevalence and Dose-Response Effects

Abstract

ᮀ Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of hospital-and community-associated infections. The formation of adherent clusters of cells known as biofilms is an important virulence factor in MRSA pathogenesis. Previous studies showed that subminimal inhibitory (sub-MIC) concentrations of methicillin induce biofilm formation in the community-associated MRSA strain LAC. In this study we measured the ability sub-MIC concentrations of eight other β-lactam antibiotics and six non-β-lactam antibiotics to induce LAC biofilm. All eight β-lactam antibiotics, but none of the non-β-lactam antibiotics, induced LAC biofilm. The dose-response effects of the eight β-lactam antibiotics on LAC biofilm varied from biphasic and bimodal to near-linear. We also found that sub-MIC methicillin induced biofilm in 33 out of 39 additional MRSA clinical isolates, which also exhibited biphasic, bimodal and linear dose-response curves. The amount of biofilm formation induced by sub-MIC methicillin was inversely proportional to the susceptibility of each strain to methicillin. Our results demonstrate that induction of biofilm by sub-MIC antibiotics is a common phenotype among MRSA clinical strains and is specific for β-lactam antibiotics. These findings may have relevance to the use of β-lactam antibiotics in clinical and agricultural settings.

Effects of Low-Dose Amoxicillin on Staphylococcus aureus USA300 Biofilms

“…6C). These findings are consistent with those of Ng et al (28), who showed that the methicillin concentration that induced maximum biofilm formation in 39 different MRSA clinical isolates was inversely proportional to the susceptibility of each strain to methicillin. These observations help further validate the biofilm induction phenotype and the Nebraska Transposon Mutant Library screen.…”

“…Previous studies showed that sub-MIC amoxicillin induces eDNA-dependent biofilm formation in the MRSA strain LAC (26,28), a well-characterized community-associated USA300 isolate (15,16). Strain JE2, the parent strain of the Nebraska Transposon Mutant Library, is a derivative of strain LAC that has been cured of two plasmids, p01 and p03 (17).…”

“…Taken together, these findings suggest that biofilm formation may be a general response to cell wall stress. In one study, however, sublethal doses of several non-cell wall-active antibiotics, including linezolid, daptomycin, tigecycline, trimethoprimsulfamethoxazole, and rifampin, failed to induce biofilm in strain LAC (28), which suggests that biofilm formation may not be a response to all cell stressors. A screen of the Nebraska Transposon Mutant Library identified 16 mutants deficient in biofilm formation in low-dose amoxicillin (Table 2 and Fig.…”

“…Previous studies showed that sub-MIC levels of ␤-lactam antibiotics induce biofilm formation in genetically diverse MRSA strains in vitro (16,28,(44)(45)(46). This process is of interest because it can provide information about biofilm regulation and the signaling pathways involved in global gene regulation in response to cell wall stress (16).…”

Sodium Lactate Negatively Regulates Shewanella putrefaciens CN32 Biofilm Formation via a Three-Component Regulatory System (LrbS-LrbA-LrbR)

“…For example, aminoglycoside antibiotics inhibit the inner membrane phosphodiesterase Arr and increase intracellular bis-(3=-5=)-cyclic dimeric GMP (c-di-GMP), which induce biofilm formation in Pseudomonas aeruginosa (6). ␤-Lactam antibiotics promote biofilm formation by inducing autolysin-dependent extracellular DNA release in Staphylococcus aureus (7,8). Then two-component regulatory systems (TCSs), the predominant way by which bacteria sense and respond to environment signals, play an important role in the regulation of biofilm development (9).…”