In vitro studies of plasmid-mediated penicillinase from Streptococcus faecalis suggest a staphylococcal origin

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Plasmid-mediated antimicrobial resistance is a growing concern in clinical settings.
• Streptococcus faecalis (now Enterococcus faecalis) can acquire resistance mechanisms, impacting treatment options.

Purpose of the Study:

• To characterize the penicillinase enzyme produced by a strain of Streptococcus faecalis.
• To investigate the substrate specificity and genetic origin of this penicillinase.
• To understand the implications of this resistance mechanism for antibiotic efficacy.

Main Methods:

• Partially purified penicillinase was isolated from Streptococcus faecalis.
• Enzyme activity was tested against various beta-lactam antibiotics.
• Minimal inhibitory concentrations (MICs) were determined using different inoculum sizes.
• Plasmid DNA hybridization was performed to compare resistance genes with those from Staphylococcus aureus.

Main Results:

• The S. faecalis penicillinase hydrolyzed penicillin, ampicillin, and ureido-penicillins, but not cephalosporins or imipenem.
• Clavulanic acid effectively inhibited enzyme activity.
• Antibiotic hydrolysis correlated with increased MICs at high bacterial inoculums.
• Plasmid DNA hybridization suggested high homology between the streptococcal and staphylococcal penicillinase genes.

Conclusions:

• The characterized penicillinase confers resistance to a range of beta-lactam antibiotics in Streptococcus faecalis.
• The genetic data strongly suggest horizontal gene transfer of the penicillinase determinant from Staphylococcus aureus to Streptococcus faecalis.
• This finding highlights the potential for interspecies transfer of antibiotic resistance genes in Gram-positive bacteria.