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Investigation of susceptibility of Staphylococcus species to some antibacterial drugs by disk diffusion and broth microdilution

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Author(s): Ašanin Jelena | Aksentijević Ksenija | Žutić Milenko | Katić Vera | Krnjaić Dejan | Milić Nenad | Ašanin Ružica | Mišić Dušan

Journal: Veterinarski Glasnik
ISSN 0350-2457

Volume: 66;
Issue: 3-4;
Start page: 199;
Date: 2012;
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Keywords: mastitis | Staphylococcus | antibacterial drugs | resistance

ABSTRACT
The objective of this work was to identify isolated Staphylococcus species and to investigate their sensitivity to some antibacterial drugs. The material used for these investigations were Staphylococcus isolates originating from milk samples. A total of 25 strains of Staphylococcus isolates were examined, including 24 from milk samples from cows with mastitis, and one strain was isolated from a milk sample from a cow following treatment for mastitis. For primary identification, catalase and oxidase tests were used, as well as the free coagulase test. Following the preliminary tests, the isolated strains were identified using commercial systems ID32 STAPH (bioMérieux, France) and the BBL Crystal Gram-Positive ID Kit (Becton Dickinson, USA) according to the enclosed instructions. The Staphylococcus isolates were examined for sensitivity to the following: oxacillin, penicillin, cefoxitin, gentamicin, erythromycin, chloramphenicol, tetracycline, ciprofloxacin, sulfametoxazol/trimetoprim, and vacomycin using the disk diffusion method and the broth microdilution method as recommended by the Clinical and Laboratory Strandards Institute - CLSI(2003), and the results were interpreted according to CLSI recommendations from 2008 and 2010. Antibiogram disks manufactured by Becton Dickinson (USA) were used, and the broth microdilution method was applied using pure antibiotic substances from different manufacturers: erythromycin, chloramphenicol, cefoxitin, gentamicin, oxacillin, tetracycline (Sigma Aldrich, USA), sulfametoxazol (Fluka, USA), penicillin (Calbiochem, Germany), vancomycin (Abbott laboratories, USA), ciprofloxacin and trimetoprim (Zdravlje A.D., Serbia). All 25 strains were catalase positive and oxidase negative. Of the 25 strains, 19 were coagulase positive and 6 were coagulase negative.With the implementation of the disk diffusion method on 19 strains of S. aureus, 17 were established to be resistant to penicillin (89.5%), and 2 strains to gentamicin (10.5%). The investigation of 3 strains of S. xylosus using the disk diffusion method showed that one strain was resistant to tetracycline (33.3%) and to oxacillin (33.3%), while another strain was found to be resistant to penicillin (33.3%). The third strain of S. xylosus was sensitive to all the examined antibiotics. Two strains of S. simulans and one strain of S. haemolyticus were not found to be resistant to any of the examined antibiotics using the disk diffusion method. The implementation of the broth microdilution method yielded in 13 strains of S. aureus resistance to penicillin (68.4%) with MIC values from 0.5 to 4 μg/m, in 2 strains to gentamicin (10.5%) with MIC values of 32 μg/ml, and intermediary sensitivity to chloramphenicol was established in 9 strains of S. aureus (47.4%) with MIC values of 16 μg/ml and to vancomycin in 1 strain of S. aureus (5.3%) with MIC values of 4 μg/ml. [Projekat Ministarstva nauke Republike Srbije, br. br 31079]
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