Toxicity test and bacteriophage typing of Staphylococcus aureus isolates from food contact surfaces and foods prepared by families in Zaria, Nigeria

Abstract

Strains of Staphylococcus aureus isolated from foods prepared in five families in Zaria Local Government Area were screened for enterotoxin production and phage pattern. Toxigenic strains of S. aureus were screened by the cat toxicity (emetic response), coagulase and DNase production tests and later phage typed by group I, II, III and IV phage sets at RTD (routine test dilution). Out of 44 S. aureus strains tested for enterotoxin production, 10 (22.7%) were toxigenic by the cat emetic response, 30 (68.2%) were β-haemolytic, 12 (27.3%)  α-haemolytic while 24 (54.5%) and 20 (45.5%) coagulated human and sheep plasma, respectively. All the 44 strains were DNase positive. Forty two (95.5%) were typable at RTD with 35 (83.3%) and 7 (16.7%) strong and weak lysis, respectively. Most (54.8%) of the typable strains were lysed by group III phages while a small portion 8 (19.1%) were lysed by Group IV phages. About 7 (16.7%) were of mixed phage group. Contamination of foods in the families by toxigenic strains could be said to be low, however, the prevalence of phage group III and  α-haemolytic strains of S. aureus calls for concern since these groups have frequently been implicated in food borne diseases. Effective hazard analysis critical control point (HACCP) evaluation is suggested as a means of preventing contamination of products by toxigenic strains of organisms.

Keywords: Staphylococcus aureus, enterotoxin production, phage typing, haemolysis and food poisoning