Increase in cell size and acid tolerance response in a stepwise-adapted methicillin resistant Staphylococcus aureus mutant

Abstract

A methicillin-susceptible strain of Staphylococcus aureus (MSSA) showed stepwise adaptation when grown in increasing concentrations of oxacillin, eventually reaching a maximum of 35 lg/ml. The resultant oxacillin resistant mutant strain was stable and did not revert to susceptibility on frequent subculturing. The response of the cells to different concentrations of oxacillin was examined by scanning electron microscopy, which showed that the size of the bacterium increased with increasing concentrations of oxacillin. These changes in cell size were dependent on the concentration of oxacillin and occurred only after addition of non-lethal concentrations. In the presence of lethal concentrations ( ‡35 lg/ml) that completely inhibited cell growth, the cell sizes were smaller than those of wild-type cells and irregular in shape. This stepwise-adapted methicillin (oxacillin) resistant S. aureus (MRSA) mutant showed a greater acid tolerance response (ATR) to lactic and citric acids than the parent susceptible strain. These data indicates that methicillin resistance alters the morphology and ATR in stepwise-adapted MRSA mutant cells.

Prevalence of Methicillin Resistant and Virulence Determinants in Clinical Isolates of Staphylococcus aureus

“…The changes in S. aureus cell morphology are possibly owing to the adaptive response to overcome the adverse environmental conditions mainly occurring due to antibiotic stress in this study and this response has already been reported with several bacterial species [19]. The change in the morphology may be due to antibiotic stress; with an increase in the cell size, the relative contact surface reduces and consequently the attachable surface for organic (antibiotic) compounds.…”

“…The mecA gene is associated with low affinity of penicillin-binding protein, PBP2a and is highly conserved in Staphylococcus species, so it is possible to detect methicillin-resistant S. aureus by detection of these genes. The reason for selecting mecA gene is considered as gold standard and hallmark for the identification of MRSA strains [19]and it is associated with drug resistance determinant [14], while femA gene is associated with the high-level expression of methicillin resistance and involved in the metabolism of cell wall synthesis.…”

In VitroEvaluations andIn VivoToxicity and Efficacy Studies of MFM501 against MRSA

“…The slight increment of treated cells diameter as compared to the untreated cells has been observed in previous studies [ 25 – 27 ] by which MRSA isolates have been subjected to 10% NaCl, manuka honey, and oxacillin. The increased cell sizes indicated disruption of cell divisions and slower growth rate in the treated cells [ 25 – 27 ].…”

The biological mechanisms of butanol tolerance and the application of solvent‐tolerant bacteria for environmental protection

“…They also reduce cell membrane fluidity and cell surface hydrophobicity to adapt to short‐term organic solvent stress . Moreover, microorganisms reduce the specific surface area of cells to decrease contact points with toxic organic solvents to adapt to the pressure of the organic solvent environment . They might also secrete organic solvents from the cell through energy‐coupled efflux pumps such as the resistance‐nodulation‐division (RND) superfamily efflux pump and the ATP‐binding cassette (ABC) transporter efflux pump (characteristic of many Gram‐negative bacteria) .…”