Abstract
We determined the prevalence and genetic characteristics of methicillin-resistant Staphylococcus aureus (MRSA) isolated from pigs and humans between September 2013 and February 2015 in Kogi State, a central region in Nigeria. A total of 680 nasal swabs were collected and analyzed from pigs (n = 425) and “pig-contact” humans (n = 55) on 35 farms, and “non-pig-contact” humans (n = 200). MRSA was recovered from 20 (4.7%) pigs on 12 farms and 18 (7.0%) humans. Six (2.4%) of the human isolates were recovered from “pig-contact” humans, of which only three work on farms also harboring MRSA positive pigs. All 38 MRSA were resistant to β-lactams only, belonged to spa type t1603, sequence type (ST) 88, and mecA was associated with a SCCmec IVa element. Four isolates from a pig, a pig-contact human from the same farm, a pig-contact human from a pig farm in a different district, and a non-pig-contact human were subjected to whole genome sequencing (WGS). Core genome SNP analysis revealed high genetic similarity between strains (3–11 SNP differences), despite the temporal (2 year gap) and geographic (165 km) differences between isolates. Furthermore, these Nigerian isolates form a distinct clade when compared to other African MRSA ST88 isolates. All but one porcine strain was positive for scn suggesting a possible human origin and that pigs were either transiently contaminated by humans or result of a very recent human-to-pig transmission event. To our knowledge, this is the first report of genetically confirmed MRSA in pigs in Nigeria, which appear to be a typical CA-MRSA clone present in the human population.
Highlights
Methicillin-resistant Staphylococcus aureus (MRSA) is of great concern in both human and veterinary medicine (Vanderhaeghen et al, 2010)
We describe for the first time the isolation of genetically confirmed MRSA in pigs and pig farm workers in Nigeria
This is only the fifth description of MRSA in healthy pigs on the African continent and appears not to be the typical livestock associated clones found in pigs worldwide namely CC398 and CC9
Summary
Methicillin-resistant Staphylococcus aureus (MRSA) is of great concern in both human and veterinary medicine (Vanderhaeghen et al, 2010). Such concerns are related to difficulty in treating infections, prolonged hospitalization and increased health care costs. In Africa, there are only four reports of MRSA in pigs; two in South Africa (Adegoke and Okoh, 2014; Van Lochem et al, 2018), one in Senegal (Fall et al, 2012), and one in Nigeria (Okunlola and Ayandele, 2015). Pigs have been shown to harbor human-associated MRSA clones e.g., USA300 (Arriola et al, 2011; Baez et al, 2017). In Nigeria, there are no published data regarding colonization of pigs with MRSA and possible transmission of strains between pigs and humans. Our objective was to evaluate the occurrence of MRSA in pigs, and compare the strains to those isolated from pig-contact and non-contact humans
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