Induction of In Vitro Resistance to Penicillin in Viridans Group Streptococci and Its Effect on Susceptibility Pattern of Other Antimicrobial Agents

Background: The development of resistance to penicillin in Viridans Group Streptococci (VGS) during therapy has been reported. However, the in vitro development of resistance to penicillin or other antimicrobial agents in VGS is mostly overlooked and rarely reported. Aim & Objectives: To induce in vitro resistance to penicillin in VGS and to study its effect on susceptibility pattern of other structurally related (Beta–lactams) and unrelated antimicrobial agents. Material and Methods: Four isolates of VGS susceptible to all antimicrobial agents were manipulated in vitro to induce resistance to penicillin by sequential exposure to increasing concentrations of penicillin. Results: Increase in MIC values of penicillin from 0.06-0.12 µg/ml to 2-32 µg/ml was observed indicating development of resistance to penicillin. A significant increase in Minimum Inhibitory Concentration (MIC) values of ampicillin and slight increase in MIC values of other antimicrobial agents in some isolates was also noted. Conclusions: Exposure to increasing concentrations of penicillin can promote the development of resistance to penicillin and cross-resistance to other antimicrobial agents suggesting its mutagenic role

Susceptibility, Resistance and Treatment Strategy for Infections Caused by Viridans Group Streptococci - A Review

Viridans Group Streptococci (VGS) were considered to be commensal organisms of low virulence. Their major disease associations were formerly limited to dental caries and infective endocarditis. Over the last several years, these bacteria have emerged as significant pathogens associated with gingivitis, periodontitis, bacteremia, meningitis, pneumonia and a variety of infections in neonates. Although penicillin remains the drug of choice in the treatment of infections caused by VGS, drug tolerance and clinical therapeutic failures have been reported. Different studies in recent past show that there is an alarming increase in resistance in VGS to various antimicrobial agents. Increase in the incidence of VGS with multiple drug resistance to penicillin and other agents suggest for periodic surveillance of antimicrobial susceptibility among VGS in order to guide appropriate antimicrobial therapy and to develop an appropriate treatment strategy for various infections caused by VGS. The development of appropriate treatment strategy not only helps in effective management but also helps to monitor further spread of resistant pathogens