Cell wall-deficiency in Staphylococcus aureus and its role in antibiotic resistance

Abstract

Cell Wall-Deficiency in Staphylococcus aureus and its Role in Antibiotic Resistance. Elizabeth R. Fuller. Cell wall-deficient bacteria (CWDB) induced from Staphylococcus aureus ATCC 9144 (Oxford strain) were generated on medium with elevated osmolality in the presence of sublethal levels of penicillin G. On removal of antibiotic pressure the cell wall-competent (CWC) revertants along with these CWDB exhibited high-level penicillin and methicillin resistance, which was stable in the revertants. The revertants looked visually different, had an altered Gram stain and growth rate. Their matrixassisted laser desorption/ionisation time-of-flight (MALDI-TOF) `fingerprint' was also altered and they were more resistant to lysis by lysostaphin in comparison to the wild-type. Reversed-phaseh igh-performance liquid chromatography( RP-HPLC) showed that the revertants' cell walls had shorter glycan chains and more pentaglycine cross-bridges. A rapid,r eproduciblem ethodu sing liquid mediaw ase stablishedu singt he same medium and sublethal levels of penicillin G. The revertants produced using this method had the same characteristics as those cells produced from the original method. The high-level resistance seen in the revertants was homogenous and confirmed to be due to the transient CWD state, along with not being strain-specific. Transmission electron microscopy showed that the CWD cells and the revertant cells, when grown in penicillin, had a very disordered cell wall with areas where the cell wall appeared absent and were indistinguishable. The revertant cells were mecA-negative,ß -lactamase-negativea nd did not contain any mutations in the coding regions of pbp genes. The CWD cells and revertant cells, when grown in penicillin, were resistant to lysis by lysostaphin but were very sensitive to lysis with Triton X- 100. These data indicate that the resistant cells are not dependent upon an intact cell wall for osmotic stability and they are able to switch readily to this mode of growth in the presence of penicillin G.