Inactivation of cephalothin and cephaloridine by Staphylococcus aureus

Area of Science:

• Microbiology
• Bacterial resistance mechanisms
• Antibiotic inactivation

Background:

• Penicillinase-producing Staphylococcus aureus exhibits varying susceptibility to cephalosporins.
• Cephalothin and cephaloridine are beta-lactam antibiotics with different resistance profiles in S. aureus.

Purpose of the Study:

• To investigate the differential inactivation of cephalothin and cephaloridine by penicillinase-producing Staphylococcus aureus.
• To elucidate the mechanisms underlying cephaloridine resistance in S. aureus.

Main Methods:

• Testing susceptibility of 100 S. aureus strains to cephalothin and cephaloridine using large inoculums.
• Assessing penicillinase production in susceptible and resistant strains.
• Investigating the effect of acriflavine on antibiotic resistance.
• Analyzing the chemical basis of cephaloridine inactivation.

Main Results:

• Penicillin G-resistant S. aureus showed higher susceptibility to cephalothin (100% at 2 mug/ml) than cephaloridine (50% at 2 mug/ml).
• Staphylococcal penicillinase significantly degraded cephaloridine but not cephalothin.
• Cephaloridine resistance was linked to beta-lactam ring hydrolysis by penicillinase, influenced by the pyridine ring substitution.

Conclusions:

• Cephaloridine resistance in S. aureus is primarily mediated by penicillinase-mediated hydrolysis of the beta-lactam ring.
• The pyridine ring substitution in the cephalosporanic acid nucleus contributes to cephaloridine's susceptibility to penicillinase.
• Cephaloridine resistance mechanisms differ from methicillin resistance in S. aureus.