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Antibiotic sensitivity and synergism of 'penicillin-tolerant' Staphylococcus aureus
Abstract:
15 Staphylococcus aureus strains were isolated from 15 patients with staphylococcal bacteremia. Eight of these strains were shown to be tolerant for cloxacillin. Cloxacillin-tolerant strains were also tolerant for most of the cephalosporins tested except for cephapirin. Strains were not tolerant for clindamycin and gentamicin. Penicillin-tolerant staphylococci showed a high degree of synergism between gentamicin and cloxacillin or cephalothin and gentamicin.
Insights
Cloxacillin tolerance was observed in eight Staphylococcus aureus strains from bacteremia patients. These tolerant strains showed cross-tolerance to cephalosporins but not clindamycin or gentamicin.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Staphylococcus aureus is a common cause of bacteremia.
- Antimicrobial tolerance can complicate treatment of serious infections.
- Understanding resistance patterns is crucial for effective therapy.
Purpose of the Study:
- To investigate the antimicrobial susceptibility and tolerance of Staphylococcus aureus strains isolated from patients with bacteremia.
- To determine the cross-tolerance patterns among different antibiotic classes in tolerant strains.
- To explore potential synergistic antibiotic combinations for penicillin-tolerant staphylococci.
Main Methods:
- Isolation and identification of Staphylococcus aureus from patient blood cultures.
- Antimicrobial susceptibility testing (minimum inhibitory concentration - MIC) for various antibiotics.
- Determination of antibiotic tolerance by comparing growth in the presence of antibiotics at different concentrations.
- Evaluation of synergistic effects of antibiotic combinations using checkerboard assays.
Main Results:
- Fifteen Staphylococcus aureus strains were isolated from patients with staphylococcal bacteremia.
- Eight of the 15 strains exhibited tolerance to cloxacillin.
- Cloxacillin-tolerant strains demonstrated tolerance to most tested cephalosporins, with the exception of cephapirin.
- No tolerance was observed for clindamycin and gentamicin in any of the tested strains.
- Penicillin-tolerant staphylococci displayed significant synergistic activity when combined with gentamicin and either cloxacillin or cephalothin.
Conclusions:
- A significant proportion of Staphylococcus aureus bacteremia strains exhibit cloxacillin tolerance.
- Cloxacillin tolerance in Staphylococcus aureus is associated with cross-tolerance to other beta-lactam antibiotics, except cephapirin.
- Gentamicin and cloxacillin or cephalothin combination therapy may be a promising strategy for treating infections caused by penicillin-tolerant Staphylococcus aureus.