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Gentamicin- and methicillin-resistant Staphylococcus aureus: in vitro susceptibility to antimicrobial drugs
1Institut für Medizinische Mikrobiologie und Hygiene, Universität des Saarlandes, Homburg a.d. Saar, BRD.
Abstract:
Thirteen nosocomially significant, gentamicin- and methicillin-resistant (GRMR) Staphylococcus aureus isolates, all of phage group III/M (lysotype 42E/47/53/54/75/77/83A/84/85/94/96), were uniformly resistant against augmentin, erythromycin, fosfomycin, gentamicin, methicillin, oxacillin, penicillin G, tetracycline, and tobramycin, but differed in susceptibility to cefamandole, ciprofloxacin, clindamycin, imipenem, josamycin, the synthetic chinolone Ro 23-6240, and ofloxacin. All isolates were susceptible to chloramphenicol, coumermycin, fusidic acid, novobiocin, rifampin, teicoplanin, trimethoprim-sulfamethoxazole (cotrimoxazole), and vancomycin. One isolate was of intermediate susceptibility to netilmicin. On a weight-for-weight basis, the 7 most active drugs were rifampin, coumermycin, cotrimoxazole, novobiocin, teicoplanin, fusidic acid, and vancomycin (in decreasing order) in terms of minimal inhibitory concentrations. With regard to minimal bactericidal concentrations, coumermycin, rifampin, vancomycin, teicoplanin, cotrimoxazole, ofloxacin, and ciprofloxacin (in decreasing order) were the 7 most potent antimicrobial drugs. Freshly defibrinated human blood [65% (v/v)] combined with chloramphenicol and rifampin, respectively, resulted in a weak additive effect (time kill curves). Indifferent effects were observed following combination of blood with ciprofloxacin, cotrimoxazole, coumermycin, fusidic acid, imipenem, netilmicin, novobiocin, ofloxacin, compound Ro 23-6240, teicoplanin, and vancomycin. Rifampin combined with novobiocin, teicoplanin, and vancomycin, respectively, in the presence of 65% (v/v) human blood, resulted in an additive effect. Combinations of rifampin with 9 other antimicrobial drugs in blood yielded essentially indifferent effects.
Insights
This study investigated gentamicin- and methicillin-resistant Staphylococcus aureus (GRMR S. aureus). Rifampin, coumermycin, and vancomycin showed high activity, with some synergistic effects observed in combination therapies.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Nosocomial infections pose a significant threat, with antibiotic-resistant bacteria like gentamicin- and methicillin-resistant Staphylococcus aureus (GRMR S. aureus) being a major concern.
- Understanding the susceptibility patterns and synergistic potential of antimicrobial agents against these resistant strains is crucial for effective treatment strategies.
Purpose of the Study:
- To evaluate the in vitro antimicrobial activity and synergistic potential of various drugs against clinically significant GRMR S. aureus isolates.
- To identify potent antimicrobial agents and effective drug combinations for treating infections caused by these multi-drug resistant pathogens.
Main Methods:
- Phenotypic characterization of thirteen GRMR S. aureus isolates, including antibiotic susceptibility testing against a panel of antimicrobials.
- Determination of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) for active agents.
- Evaluation of drug-drug interactions in the presence of human blood using time-kill assays.
Main Results:
- All GRMR S. aureus isolates exhibited uniform resistance to multiple antibiotics, including gentamicin and methicillin.
- Rifampin, coumermycin, trimethoprim-sulfamethoxazole (cotrimoxazole), novobiocin, teicoplanin, fusidic acid, and vancomycin demonstrated significant antimicrobial activity.
- Combinations of rifampin with novobiocin, teicoplanin, or vancomycin showed additive effects in human blood, while other combinations were largely indifferent.
Conclusions:
- Several antibiotics remain effective against GRMR S. aureus, with rifampin, coumermycin, and vancomycin being particularly potent.
- Combination therapy, especially involving rifampin with certain other agents, may offer enhanced efficacy in treating GRMR S. aureus infections, warranting further investigation.