Genetic diversity of Streptococcus infantarius subsp. infantarius isolated from human stool, raw and fermented milk from Isiolo Central Sub County, Kenya

Abstract

Unlike Streptococcus thermophilus which is classified for food production and human consumption using the “generally recognized as safe” (GRAS, Food and Drug Administration (FDA) or the “qualified presumption of safety” (QPS), European Food Safety Authority (EFSA), Streptococcus infantarius subsp. infantarius (Sii) is associated with various human and animal infections such as endocarditis, bacteremia and colorectal cancer. Sii has been isolated as predominant species from fermented African dairy products in Kenya, with a prevalence rate of being 8.5 percent. Information on microbial load and genetic diversity of Sii isolates from consumers of traditionally fermented dairy products and human stool from consuming population is limited. A total of 121 Sii isolates were obtained from 47 samples from each three sample categories collected from Isiolo Central Sub-County. The Sii isolates were morphologically and biochemically identified and found to have similarity. Sii isolate count were least present in human stool sample with mean log10 Colony forming unit/ml (CFU/ml) of 1.11, whereas raw milk had the second highest Sii isolates count with a mean log10Cfu/ml 2.64. Lastly, fermented milk registered the highest Sii count with a mean log10Cfu/ml of 6.03. The total Sii count across the three samples category differed significantly (p<0.05). Subsequently, Sii isolate molecular identifications were conducted using SBSEC-specific16S rRNA gene PCR assay. 7 out of 121 Sii isolates displayed positive results for 16S rRNA gene, representing a prevalence of 5.8%. Positive control of Sii CJ18 was used to confirm the results, at the same time, negative control was used during the PCR. Genetic diversity determination Sii was achieved by subjecting isolates to rep-PCR and the gel image of the isolates analyzed using UPGMA clustering Algorithm to generate Dendogram. Conclusively, raw and fermented milk are major sources of Sii among consumers of the traditionally fermented milk and its products leading to the faecal carriage of Sii.