Role of consumption of spontaneously fermented dairy products and streptococcus infantarius in colorectal carcinoma in Kenya

Abstract

Consumers of traditionally spontaneously fermented dairy products are frequently exposed to high titres of Streptococcus infantarius subsp. infantarius (Sii), that belongs to Streptococcus bovis/Streptococcus equinus complex (SBSEC) - potential pathogens implicated in colonic and non-colonic carcinoma and extraintestinal infections. Study objectives were to determine the association between consumption of fermented dairy products, selected six environmental risk factors of CRC and isolated human faecal strains of Sii/SBSEC with colorectal cancer; and to estimate the safety and pathogenicity associated with the strains obtained in this PhD study by comparing their gene sequence types with a global pool of Sii/SBSEC strains. A case-control study was conducted from June 2013 to June 2015 at the Endoscopy Unit of Kenyatta National Hospital, Nairobi (Kenya). Study participants were 413 adults waiting for colonoscopic examination who gave written consent after they were informed about the study. Overall, 92 out of 413 (22%) participants consumed fermented dairy products (FDP); 20.6% and 24.2% in urban and rural areas, respectively. Faecal carriage of Sii was higher in rural areas than urban areas (16.5% vs 13.0%, p-value (p) 0.46). Prevalence of colorectal adenocarcinoma was higher among persons originating from rural areas (16% vs 23%; p 0.05). Consumption of FDP was not associated with CRC (odds ratio (OR) 1.4; 95% Confidence interval (CI) 0.7- 2.7; P=0.34). Age being above 40 years and consumption of processed meat and alcohol emerged as risk factors of CRC. Although persons with colon tumors and polyps (16.7%: n: 36; CI 6.4%-32.8%) compared to controls (10.6%, n: 94; CI: 5.2%-18.7%), had higher faecal carriage of Sii, the difference was not statistically significant. MLST characterization confirmed the identity of 40 SBSEC which comprised 33 Sii, five Streptococcus lutetiensis, four Streptococcus gallolyticus subsp. pasteurianus, and one Streptococcus gallolyticus subsp. macedonicus previously identified with groEL gene sequence. One out of 33 Sii was confirmed to harbour lacS and lacZ while none of the other SBSEC isolates were detected positive for this dairy adaptation. One out of 33 Sii clustered with the pathogenic strains sourced from Spain. Sgp and S. lutetiensis have unique thrS alleles and Sii D1266 has a regular thrS allele which groups that isolate with blood isolates. The remaining Sii clustered with dairy isolates and have resemblance to Streptococcus thermophilus. In conclusion, Consumption of FDP is not associated with CRC but elevates faecal carriage of Sii/SBSEC. Sii-D1266 isolate is a health hazard and the remaining 32 Sii isolates are potentially harmless to humans. Further elucidation of safety of Sii isolates are proposed to determine their potential role as candidates for development of a novel starter culture for fermented milk products.