Staphylococcus aureus Enterotoxin Genes Detected in Milk from various Livestock 2 Species in Northern Pastoral Region of Kenya

Staphylococcus aureus (SA) food poisoning results from consumption of preformed S. aureus 33 enterotoxins in food. The enterotoxins are one of the most important virulence factors of the 34 bacterium. The risk posed by contamination of milk intended for human consumption by 35 pathogenic S. aureus in pastoral areas in Kenya is still generally not well documented yet this 36 information is critical for ensuring safety to consumers who sometimes may take unpasteurized 37 milk. This study, therefore determined the prevalence of S. aureus enterotoxin genes in raw 38 milk from cattle, goats, sheep and camels intended for human consumption in northern Kenya. 39 A total of 603 milk samples from 57 zebu cattle, 346 galla goats, 8 red Maasai and dorper 40 sheep, 4 one-humped camel (Camelus dromedaries) and 188 pooled from all animals were 41 collected from Isiolo and Marsabit counties of Kenya. S. aureus isolates were cultured from 42 milk samples using a selective media, mannitol salt agar (MSA). Suspect colonies of SA were 43 further analyzed using biochemical tests. Polymerase chain reaction and sequencing techniques 44 were used to confirm SA and detect sea, seb, sec, sed and see enterotoxin genes. 45 Overall, potentially pathogenic S. aureus harboring enterotoxic genes were detected in 85 46 (14.09 %, 95 % CI: 11.55-17.1 %) of the total milk samples. Genes encoding enterotoxins were 47 detected in the S. aureus bacteria isolated from the milk samples. At least one type of S. aureus 48 enterotoxin gene (SE) was detected in 74.11% (95 % CI: 63.91-82.24 %) of the 85 isolates. 49 The most frequently encountered gene in the two counties was see (51; 60%, 95 % CI: 49.73- 50 69.76 %) followed by sea (22; 25.88 %, 95 % CI: 17.76 -36.09 %) and sec (19; 22.35 %, 95 % 51 CI: 14.8-32.29 %). None of the isolates tested positive for sed. Overall, 21 of the 85 (24.7%, 52 95 % CI: 16.76-34.83 %) strains harbored more than one enterotoxin gene. More than half of 53 the S. aureus isolates harbored at least one of the enterotoxin coding genes, indicating milk 54 samples contaminated by S. aureus could have a high chance of causing staphylococcal food 55 intoxication. 56 Consumption of raw and sour milk in the region could increase the risk of staphylococcal food 57 poisoning and pastoral communities in the region are therefore advised to consume pasteurized 58 milk.