The Effect Of Subinhibitory Concentrations Of β-lactam Drugs On α-hemolysin Expression In Staphylococcus Aureus

ObjectiveTo investigate the effect of subinhibitory concentrations of β-lactam drugs on α-hemolysin(Hla)expression in Staphylococcus aureus, and its related mechanism in the expression. Methods ①The Staphylococcus aureus(S. aureus) separated from the clinic were used to collected from the First Affiliated Hospital of Anhui Medical University, and the strain ATCC29213 was chosen as the control. The broth dilution was used to detected the minimal inhibitory concentration(MIC) of β-lactam drugs(penicillin, cefoxitin, organism, cefazolin).②After 8 hours of incubation, the expression of Hla mRNA and the protein in supernatant were evaluated by quantitative PCR and immuocytochemistry, respectively. The haemolytic activity of supernatant was evaluated by Erythrocyte hemolysis assay. ③Furthermore, the S. aureus strain, which was the maximum, was grown with sub-MICs(1/8,1/4 and 1/2MIC) of four antibiotics. After 4, 8, 12 and 24h of incubation, the bacteria titers were evaluated by plaque forming unit assay. The expression of Hla and the haemolytic activity of supernatant were detected and compared with the stain that did not used antibiotics. ④The expression of regulatory factor AgrA was evaluated by quantitative PCR in subinhibitory concentrations of β-lactam drugs. Resultsts ① The levels of Hla mRNA, protein and the haemolytic activity of supernatant were different in the strains. ② 1/8 and 1/4MIC sub-MICs β-lactam drug could significantly increased the expression of Hla and the haemolytic activity since 8 hours after incubation,which compared with the control group and had no change in the bacteria titers. ③ The sub-MICs β-lactam drug could markedly increased the expression of regulatory factor AgrA, which may associate with the up-regulation of the expression of Hla mRNA. ConclusionsThe subinhibitory concentrations of β-lactam drugs could up-regulate the expression of α-hemolysin, the mechanism was possible through the the expression of regulatory factor AgrA.