Isolation of stx1 and stx2 genes from clinical and environmental samples of Escherichia coli

Abstract

E. coli O157:H7, a Shiga toxin producing microbe was first acknowledged as a virulent organism in 1982 during an analysis of an outbreak of hemorrhagic colitis associated with consumption of hamburgers from a fast food chain restaurant. Ability of E. coli O157:H7 to induce injury in humans is a result of its ability to produce numerous virulence factors, most notably Shiga toxins Stx1 and Stx2, both of which constitute one of the most potent toxins known to man. Besides, Shiga toxin, E. coli O157:H7 produces several other virulence factors, which include proteins which aid in the attachment and colonization of the bacteria in the intestinal wall and which can break down red blood cells and release iron to help support metabolism in E. coli . Virulence factors facilitate this organism’s ability to cause intestinal and extra-intestinal diseases such as diarrhea, hemorrhagic colitis (HC), hemolytic uremic syndrome (HUS), urinary tract infections (UTI), septicemia and neonatal meningitis. In this study r, 7 samples from Dhaka city was collected, cultured in various media for enumeration, isolation and screening of E. coli colonies which were further analyzed to check for the presence of stx genes using PCR and gel electrophoresis. The seven samples collected were: Door knob swab, tea water, bhel puri, kitchen pipe swab, vegetable water, Lake water and Rectal swab. The samples collected initially were enriched in enrichment media overnight, followed by a dilution series which were then used for spread plating on nutrient agar and MacConkey agar and EMB for confirmation with the observation of pink colonies and metallic sheen. The confirmed E. coli isolates were later subjected to DNA extraction and amplification after which the bands for stx genes were observed and recorded. Out of the seven samples tested for stx1 and stx2 genes, two showed the presence of stx1 genes and one showed the presence of stx2 gene. The presence of the stx1 and stx2 genes in regular food and in our surrounding signifies how close we are to a large outbreak. Knowledge of processing such food or avoiding such environmental contacts or taking precautions when possible may prevent occurrence of diseases.