Physiological peculiarities of vancomycin-resistant staphylococci

L.I. Kononova and V.P. Korobov

Institute of Ecology and Genetics of Microorganisms, UB RAS, 13, Golev str., Perm, 614081, Russia

Marked elevation of heteroresistance to glycopeptides being observed among methycilline-resistant coagulase-negative staphylococci (CNS) determines the necessity in examination the nature of this CNS resistance and searching the ways for its overcoming.

The subject of this study was the analysis of physiological peculiarities of collection strains S. epidermidis 33,   S. aureus 25923 and their Vanr derivatives that were selected in the laboratory with cultivation on media containing increasing antibiotic concentrations and also clinical Vanr CNS strains being detected through their inoculation on agarized media with concentration gradient of this antibiotic (Hanaki et al., 2001).

In was found that obtained Vanr strains of S. epidermidis and S. aureus, and clinical isolates possessed high level of resistance to vancomycin (MPC 250-1000 mkg/ml) and to a number of antibiotics with different mechanisms of action.

Unique feature of all clinical and laboratory Vanr staphylococcal strains appeared to be significant increase in generation time and lesser biomass accumulation as compared with initial strains. The formation of cross-resistance to several antibiotics was found to negatively influence the viability of Vanr staphylococcal strains.

Development of vancomycin resistance in S. epidermidis strain was accompanied by apparent decline in vancomycin binding from the solutions while this ability was observed to significantly increase in Vanr               S. aureus.

All of Vanr strains demonstrated the reduction in cell surface hydrophobicity. The growth of all Vanr strains was suppressed by NaCl concentrations when heavy growth was typical for sensitive strains. The emergence of vancomycin resistance did not result in alteration of strain capacity to biofilm formation both in presence of high vancomycin concentrations in cultivation medium and in antibiotic-free medium.

It was found that all of Vanr staphylococcal strains demonstrated the decrease in lysostaphin sensitivity and change in resistance to cationic peptide warnerin (Korobov et al., 2003). In addition, MPC for all of Vanr CNS strains exceeded more that by 500-fold that for test strain S. epidermidis 33. At the same time, Vanr derivatives of S. aureus strain were found to become more sensitive to warnerin as compared with the parent strain. The analysis of lipid composition in Vanr derivatives of S. aureus revealed significant decrease in lysylphosphatidylglycerol content in their cytoplasm membranes that apparently evoked changes in cell surface charge in those strains.

This work was supported by grant 07-04-01546-a and RAS Presidium Program “Molecular and Cell Biology”.

References

Hanaki, H. et al. // In: Antibiotic resistance / Humana Press, 2001. Vol. 48. P. 8591.

Korobov, V.P. et al. // Docl. Biol. Sci. 2003. Vol. 390, No. 5. P. 2868.

Key words staphylococci, vancomycin, resistance, warnerin