Isolation and Antibiogram of Staphylococcus aureus from Powdered Milk Sold in Samaru Market, Zaria

Abstract

Milk is a nutritive food that serves as an excellent growth medium for wide variety of microbes. This study was conducted to determine the occurrence of Staphylococcus aureus in powdered milk sold in Samaru market, Zaria, and their antibiotic susceptibility patterns. Fifty (50) powdered milk samples were collected from different shop vendors. The samples were used for isolation of Staphylococcus aureus by cultural method. Staphylococcal count was determined and the colonies observed were identified based on colonial morphology, microscopic and biochemical characterization. The antibiogram of the isolates were also determined using Kirby-Bauer disc diffusion method. The highest Staphylococcal mean count of 1.47x104 CFU/g was observed in powdered milk samples displayed outside the shop in sacks and the lowest count of 1.22x104 CFU/g was observed for samples displayed inside the shop in sacks. Fifteen (15) samples were positive for Staphylococcus aureus giving a percentage occurrence of 30%, with samples displayed outside the shop in sacks having the highest occurrence (42.9%) while the least (16.67%) occurrence was observed in those displayed inside the shop in sacks. The antibiogram revealed a high susceptibility to Ciprofloxacin (100%), Gentamicin (93.33%), Erythromycin and Chloramphenicol (73.33%). While other isolates showed high resistance to Norfloxacin (66.67%) and Ampicillin-cloxacillin (26.67%). Five (5) isolates were resistant to multiple antibiotics with multiple antibiotic resistance index (MARI) ranging from 0.3-0.4. The study revealed high occurrence of Staphylococcus aureus in powdered milk and its resistance to commonly used antibiotics possess a public health risk to consumers of these products