Phenotypic and Molecular Characterizations of Staphylococcus Aureus Isolates from Human and Dairy Cows in Mekele, Northern Ethiopia
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Date
2019-03
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Addis Ababa University
Abstract
Introduction: Staphylococcus aureus is one of the common colonizers of human and several animal species with the capacity to cause serious diseases. It is one of the global public health priority pathogens due to its ubiquitous nature, ability to cause life-threatening diseases and continuous evolvement of drug resistance. The emergence and spread of multidrug resistant strains, mainly MRSA, initially in the health care setting, later in the community and recently in the veterinary side with a capacity of transmission to human is of special concern. Several molecular techniques have been used successfully for reliable identification, determination of specific virulence and drug resistance genes and to understand spread and distribution of specific S. aureus strains. In Ethiopia, despite several reports on phenotypic studies of S. aureus isolates from human and animals, data on molecular characterizations is scarce.
Objectives: To isolate S. aureus from human skin and soft tissue infections, milk of dairy cows and nares of dairy farm workers in Mekele, Northern Ethiopia; and then to determine the antimicrobial resistance pattern, virulence genes profile and genotypic diversity and relatedness of the isolates.
Methods: A cross sectional study was conducted during period of March 2016 to August 2017 G.C. A total of 811 non-duplicate specimens (355 wound/pus swabs from human patients with skin and soft tissue infections [SSTIs] attending Ayder referral hospital, 71 nasal swabs from dairy farmers and 384 milk samples from dairy cows) were collected to isolates S. aureus. Culture and identification of S. aureus was performed using standard laboratory procedures. Antimicrobial susceptibility testing was performed following the
CLSI guideline. All phenotypic characterizations of S. aureus were done at the
Microbiology laboratory of Ayder Referral Hospital, Mekele, Ethiopia. AlSaureus isolates were stored at −700C and shipped to USA for Molecular characterizations at the Infectious Diseases Molecular Epidemiology Laboratory (IDEML) of the Ohio State University and the Public Health Research Institute of the State University of New Jersey, USA. Molecular characterizations include confirmation of S. aureus by nuc detection, mecA /mecC detection, toxin genes profiling (pvl, nine se genes and tsst-1), spa typing and SCCmec typing.
Results: From the 811 samples, 193 (23.8%) were positive for S. aureus using phenotypic and molecular methods; where 123 (63.7%) were from human SSTIs, 22 (11.4%) from nares of dairy farmers and 48 (24.9%) from milk of Dairy cows. Overall, high percentage of resistance was observed for Penicillin (92.7%); however, no resistance was found for Vancomycin, Daptomycin and Rifampin. Four (2.1%) of the 193 isolates were MRSA where all were from human and were both cefoxitin resistant and mecA positive. Two of them carried SCCmec type III and the other two SCCmec type IV. Moreover, 26% of S. aureus isolates were multidrug resistant. Regarding toxin genes carriage, 66.8% of the total isolates possessed at least one of the 11 targeted toxin genes. Of the 11 genes, pvl was the most frequently detected (carried by 36.8%) followed by seg and sei (29% each), seb (19.2%), sea(16%) and sec (15%). Interestingly, pvl was found significantly higher (p<0.001) on isolates from SSTI (53.7%) compared to nasal (13.6%) and cows’ milk (4.2%) isolates. In addition,tsst-1 was found in human isolates only. The spa typing yielded 61 different types among the 190 successfully typed isolates. Out of these, five were novel spa types, namely spa typet17828, t17829, t17830, t17831 and t17832. The most dominant spa type among the SSTI isolates was t355 (19%) followed by t306 (8.3%); whereas in milk spa type t042 (61.7%) was the dominant one followed by t2856 (19.1%). The present study also noted that spa type t042, t306, t085, t2856 and t5338 were detected from both human and dairy cows. Based on the spa sequence information, 90.5% of the total S. aureus were assigned in to 12 probable clonal complexes (CCs), namely CC1, CC5, CC8, CC15, CC22, CC25, CC80, CC81, CC88, CC121, CC152 and CC239. The leading CC among the human clinical isolates was CC152 (20.7%) followed by CC15 (19%) and CC5 (16.5%). However, most of the S. aureus isolates from dairy cows (83%) were CC80 followed by CC5 (6.4%).
Conclusion: In the present study, S. aureus was isolated from skin and soft tissue infections, nares of farm workers and milk of dairy cows. Highest resistance was observed against penicillin. No resistance was observed against Vancomycin, Daptomycin and Rifampin. Multidrug resistance was observed in a quarter of the isolates. mecA positive S. aureus (MRSA) strains were of human origin. Majority of S. auresus isolates possessed at least 1 of the 11 toxin genes. The spa typing of S. aureus resulted in 61 different types and showed diversity. Based on the spa sequence information, S. aureus isolates were assigned into 12 probable clonal complexes (CCs). Among these CCs, CC1, CC5, CC15 and CC80 were shared between human and bovine isolates. Findings of the present study indicate that S. aureus is a significant cause of skin and soft tissue infections in human and intramammary infections in dairy cows. Hence, measures to reduce/prevent infection such as improving infection prevention practices in the hospital, keeping hygiene of the dairy cows and educating the community to practice the best possible personal hygiene are recommended. Further study should be conducted in different regions of the country to have conclusive data for policy makers, clinicians and researchers.
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Keywords
Staphylococcus aureus, MRSA, Antimicrobial resistance, toxin genes, spa typing, clonal complex, Ethiopia