Abstract
Antimicrobial resistance is becoming an extremely serious global problem. The goal of this study was to determine the prevalence and phenotypic and genotypic characteristics of Staphylococcus aureus isolated from milk and milk product samples in Ethiopia and also to determine the presence of methicillin resistant Staphylococcus aureus (MRSA). A total of 577 milk and milk product samples were collected from central Ethiopia and Staphylococcus spp. were isolated using the method described in FDA Bacteriological Analytical Manual (BAM). Resistance of S. aureus isolates to 12 antimicrobials was determined by using the Kirby-Bauer disk diffusion method. PCR detection of mecA and nuc gene was also conducted. To determine the clonal relatedness of S. aureus isolates, DNA fingerprinting of selected isolates was performed by PFGE. Of the 577 milk and milk product samples investigated, S. aureus isolates were recovered from 120 (21%) of the sample. In addition, coagulase negative Staphylococcus species were also isolated from 361/577 (63%) of the samples. The highest frequency of resistance was observed for penicillin (83%) and the lowest was noted for amoxicillin/clavulanic acid (3%) and gentamicin (3%). Fourteen (14) isolates (13%) recovered from raw milk were found to be susceptible to all the tested antimicrobials while 57% of the isolates were resistant to more than one of the antimicrobials. All the isolates were susceptible to vancomycin and none were found to be methicillin resistant S. aureus based on mecA gene carriage. PFGE analysis of 39 S. aureus isolates identified three separate clonal clusters and also several sporadic isolates. S. aureus isolates in this study were found to be resistant to multiple antimicrobials. This warrants a larger representative study to fully understand the extent of the problem and design better strategies for regulation of antimicrobial use in both the medical and veterinary sectors in central Ethiopia. Key words: Bovine milk, Ethiopia, genotypic resistance, Staphylococcus aureus.
Highlights
Different studies conducted in Ethiopia have shown that Staphylococcus aureus is implicated in nearly 40% of mastitic cows (Workineh et al, 2002; Dego and Tarke, 2003; Getahun et al, 2008; Abera et al, 2010)
Isolation of S. aureus isolates from raw bovine milk and milk products
Coagulase Negative staphylococcus (CoNS) species were isolated from 361/577 (63%) milk and milk product samples analyzed
Summary
Different studies conducted in Ethiopia have shown that Staphylococcus aureus is implicated in nearly 40% of mastitic cows (Workineh et al, 2002; Dego and Tarke, 2003; Getahun et al, 2008; Abera et al, 2010). Another study in and around Sebeta, Ethiopia, that looked into the prevalence of mastitis in 180 local and crossbreed dairy cows showed that mastitis (majority of which is subclinical in form) can reach a prevalence rate of 52.78% (Hundurra et al, 2005). The prevalence of S. aureus as a cause of mastitis was 44% and that of Staphylococcus epidermis was 14.93% in the study conducted by Hundurra et al (2005). With such high prevalence of subclinical mastitis in the Ethiopian context, the public health importance of zoonotic pathogens would be of great concern as there is a trend of using raw milk for direct consumption from apparently healthy cows. The liberal use of antimicrobials in hospitals and treatment centers as well as the subtherapeutic use in livestock for growth promotion and prophylaxis has greatly contributed to the emergence and persistence of resistant strains of bacteria (Helmuth, 2000; Ray, 2004)
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