The Staphylococcus aureus cidAB Operon: Evaluation of Its Role in Regulation of Murein Hydrolase Activity and Penicillin Tolerance

Abstract

Recent studies have shown that expression of the Staphylococcus aureus lrgAB operon inhibits murein hydrolase activity and decreases sensitivity to penicillin-induced killing. It was proposed that the lrgAB gene products function in a manner analogous to an antiholin, inhibiting a putative holin from transporting murein hydrolases out of the cell. In the present study the cidAB operon was identified and characterized based on the similarity of the cidA and cidB gene products to the products of the lrgAB operon. Zymographic and quantitative analyses of murein hydrolase activity revealed that mutation of the cidA gene results in decreased extracellular murein hydrolase activity compared to that of S. aureus RN6390, the parental strain. Complementation of cidA expression restored the wild-type phenotype, indicating that expression of the cidAB operon has a positive influence on extracellular murein hydrolase activity. The cidA mutant also displayed a significant decrease in sensitivity to the killing effects of penicillin. However, complementation of the cidA defect did not restore penicillin sensitivity to wild-type levels. Reverse transcriptase PCR also revealed that cidAB is maximally expressed during early exponential growth, opposite of what was previously observed for lrgAB expression. Based on these results, we propose that the cidAB operon encodes the holin-like counterpart of the lrgAB operon and acts in a manner opposite from that of lrgAB by increasing extracellular murein hydrolase activity and increasing sensitivity to penicillin-induced killing.

The cidA murein hydrolase regulator contributes to DNA release and biofilm development in Staphylococcus aureus

“…Previous studies of the S. aureus cid and lrg genes have illustrated their importance in mediating cell death and/or lysis in stationary phase (36) and in response to antibiotic treatment (23,24). In this present study, analysis of the clinical S. aureus isolate UAMS-1 and its isogenic cidA mutant (KB1050) in the context of biofilm growth led to the discovery that CidA contributes to biofilm adherence both in vitro and in vivo by affecting cell lysis and the release of genomic DNA.…”

“…Expression of cid and lrg is responsive to physiological signals (24,25) and to genetic regulation by SigB (26), LytSR (27,28), and CidR (29,30). Although their specific functions are unknown, CidA and LrgA share structural similarities to bacteriophage holins, a family of small membrane proteins that control the timing and onset of phage-induced cell lysis (22,23,27,31). Furthermore, the cid and lrg operons have been proposed to encode components of a bacterial programmed cell death and lysis mechanism (32,33).…”

“…The S. aureus cidABC and lrgAB operons regulate cell lysis and antibiotic tolerance in an opposing manner: lrgAB has an inhibitory effect on murein hydrolase activity and promotes antibiotic tolerance (22), whereas cidA has a positive effect on murein hydrolase activity and decreases tolerance to various antibiotics (23,24). Expression of cid and lrg is responsive to physiological signals (24,25) and to genetic regulation by SigB (26), LytSR (27,28), and CidR (29,30).…”

Inflammatory responses and histopathological changes in a mouse model of Staphylococcus aureus-induced bloodstream infections

“…After overnight growth, bacteria were diluted 1:100 (v/v) with fresh LB broth and grew for another 4-6 hours to reach the midlog phase at optical density (OD)600 0.5. The bacteria were harvested by centrifugation (3,000 × g, 5 minutes, at room temperature), washed three times, and resuspended in sterile phosphate-buffered saline (PBS) (BBI, Shanghai, China) at OD600 1, while bacterial colony forming units (CFUs) were calculated as 4.5 × 10 8 /mL [8].…”

Tolerance to the Glycopeptides Vancomycin and Teicoplanin in Coagulase-Negative Staphylococci

“…Tolerance mechanisms remain elusive to this day, even if recent works on Streptococcus pneumoniae and S. aureus have suggested the involvement of impaired autolysin regulation systems (3,18) or modifications in the cell wall composition (7,17). Studies should be undertaken to explore the mechanism of the phenomenon of S. lugdunensis tolerance to glycopeptides observed in the present work and to evaluate its clinical implications.…”