Phenotypic detection and molecular identification of Methicillin-resistant Staphylococcus aureus from dairy products in pastoral communities in Niger State, Nigeria

Abstract

Staphylococcus aureus is an emerging zoonotic infectious agent of public health 
concern, especially in pastoral settings. However, major surveillance gaps exist for 
community-acquired MRSA infections in developing countries. In view of this, 2760 
samples, comprising 360 samples each of ghee (Maishanu), cheese (Awara), local 
yoghurt (Kindirmo), raw milk (Madara), and fermented milk (Nono), and 240 each 
of potential contamination sources (handler’s hands, containers, udders, and 
water), were randomly obtained from various pastoral communities in Niger State, 
Nigeria. Isolation was carried out using the spread-plate method on Mannitol Salt 
Agar. Cefoxitin was used for the phenotypic identification of a methicillin-resistant 
S. aureus isolate via the disc diffusion method. Whereas, a polymerase chain 
reaction was used for the confirmation of S. aureus and the detection of methicillin
resistant genes in the 10 isolates that exhibited phenotypic resistance to oxacillin, 
cefoxitin, and vancomycin. Overall, 204 (7.4%) S. aureus strains were isolated and 
out of the 64 MRSA isolates recovered, 35(54.7%) was from dairy products while 
29(46.5%) was isolated from possible contaminating sources. Raw milk had the 
highest percentage of MRSA (28.6%) followed by fermented milk (25.7%) and the 
least was cheese (5.7%). Similarly, handler’s hands sampled yielded the high MRSA 
(44.8%) compared to other possible contamination sources although water had the 
least. Isolates presumptively classified as S. aureus, revealed the presence of the nuc 
gene by the amplification of the 270-bp product of the species-specific nuc gene.  
Only 4/10 (40%) of the isolates produced a single band of 680 bp specific for the coa 
gene. Similarly, only 3 of the 10 MRSA produced the 533 bp band of the mecA gene 
specific amplicon. The presence of MRSA in dairy products and potential dairy 
products contamination sources suggest that appropriate measures should be in 
place to curtail the spread and menace of this infectious disease agent.