Effect of sub-minimal inhibitory concentrations of vancomycin in induction of S. aureus L-forms and study of their stability in blood [in vitro]

ABSTRACT

L - forms of S.aureus are cell wall -defective bacteria that grow and multiply in hypertonic media. Vancomycin is an effective antibiotic for remedy of staphylococcal infections an important inducer of L - froms. The present study investigated whether staphylococcal L - forms induction is related to concentration of vancomycin and whether these forms are stable in blood or not. In this study effect of different concentrations of vancomycin on standard strain of S.aureus [ATCC 25923] were tested; then growth of bacteria in four media [BHI Agar, BHI broth, LPM Agar and LPM broth] were studied. After induction of L - forms in LPM broth, these forms were injected to human complete blood. In bactericidal and minimal inhibitory concentrations of vancomycin, no growth of bacteria in three media was observed, but growth of bacteria in LPM broth after 72 hours was observed. Injection of S.aureus L - forms in to human blood caused changes of these forms to natural bacteria. The results confirm that use of one cell wall affecting Antibiotic alone for remedy of staphylococcal infections, may increase the risk of induction of L - forms and drug resistant bacteria