Double-disk synergy test for detection of synergistic effect between antibiotics against nosocomial strains of staphylococcus aureus

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.

Co-occurrence of Extended-Spectrum Beta-Lactamases in Isolated Enterobacter spp. From Patients Specimens

“…This test was performed for all Enterobacter isolates resistant to at least two of the applied antibiotics. In addition, the effects of inactive agents against the resistant bacteria in combination with each other were determined in this test (12).…”

The genetic background of antibiotic resistance among clinical uropathogenic Escherichia coli strains

“…The 5 genes encoding beta-lactamases ( bla TEM , bla CTX-M-1 , bla SHV , bla OXA-1 , bla CMY ) were detected at first in the reference group of E. coli ESBL strains and next, their presence was defined in the entire collection of clinical E. coli strains. Additionally, the presence of aac(3)-II determines resistance to aminoglycosides and three genes ( sul1, sul2, sul3 ) encoding resistance to sulfonamides were studied.. Further, the strains resistant to quinolones [ 55 ] and the control representative group of strains [ 33 ]—intermediate sensitive and sensitive to quinolones—were analyzed based on the mutations in parC and gyrA genes and based on the presence of qnr genes.…”

“…Resistance to newer generation cephalosporins was also confirmed on chromID® ESBL plates (bioMérieux). Additionally, all isolates were tested for ESBL production by the double-disk synergy test (DDST) with disks containing cefotaxime, ceftazidime, and amoxicillin with clavulanate [ 33 , 34 ].…”

In-Vitro Study the Antibacterial Activity of Bacteriocin against Stenotrophomonas Maltophilia and Evaluation its Synergism with some Antibiotics

“…As well as, efficacious synergistic combinations of antibiotics and bacteriocins can extend the spectra of antibiotics, which may be beneficial in treating bacterial infections of unknown etiology. There are many methods to assessing antibacterial synergy in vitro Examples of such tests include the broth-based checkerboard assay, as well as agar-based screens such as E-tests (bioMérieux) to evaluate synergy (Sopirala et al, 2010;Soltani et al, 2012). However, there is a overall accord that the broth-based methods are more accurate than the agarbased assay.…”

“…There are many methods to assessing antibacterial synergy in vitro. Examples of such tests include the broth-based checkerboard assay, as well as agar-based screens such as E-tests (bioMérieux) to evaluate synergy (Sopirala et al, 2010;Soltani et al, 2012). Therefore, the present study set out to screen the synergism interaction between some antibiotics and bacteriocin producing Lactobacillus acidophilus against isolated S. maltophilia.…”