Document Type : Original Article
Authors
1 Department of Clinical Pharmacy and Pharmacy Practice, Isfahan University of Medical Sciences, Isfahan, Iran
2 Department of Clinical Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
Abstract
Objective: Synergistic effect between commonly used antibiotics against nosocomial
multidrug-resistant strains of Staphylococcus aureus, if present, could provide a viable
option as an alternative therapy for infections due to this pathogen. The aim of this study
was searching for any synergistic effect between several antibiotics against drug-resistant
strains of S. aureus with nosocomial origin using double-disk synergy test and to determine
the applicability of this test for such a purpose.
Methods: Over a 6-month period, strains of S. aureus isolated from clinical specimens
of hospitalized patients with documented nosocomial infection underwent disk diffusion
test using antibiotic disks of oxacillin, cephalothin, clindamycin, ciprofloxacin, vancomycin,
cotrimoxazole, rifampin, erythromycin, gentamicin and meropenem. Double-disk synergy test
was performed for all isolates resistant to at least two of applied antibiotics. Combinations
of all possible pairs of antibiotics (to which the microorganism was resistant) were tested
by placing antibiotic disks at distance of 20 mm from each other (center to center). After
16-20 hours of incubation, if synergistic effect was present among two antibiotics, an inhibition
zone was formed between their disks.
Findings: Among all of possible two-antibiotic combinations tested for 41 resistant isolates,
only two cases of synergistic effect were detected; both effects were among rifampin and
cotrimoxazole.
Conclusion: The combination of rifampin and cotrimoxazole could provide a viable option
for treatment of infections due to resistant strains of S. aureus; however, clinical trials are
needed before any new recommendation. Also, double-disk synergy test seems to be capable
of detecting the synergistic effect between antibiotics at in vitro level.
Keywords
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