EPIDEMIOLOGY OF ESCHERICHIA COLI O157:H7 IN SOUTH WEST, NIGERIA AND ROLE OF LIPOPOLYSACCHARIDE IN PROPHYLAXIS

Abstract

The epidemiology of Escherichia coli O157:H7 as the cause of diarrhoea in Southwest, Nigeria and the role of lipopolysaccharide (LPS) of the organism in prophylaxis were investigated between the year, 2012 and 2014. A total of 5400 diarrhoeic patients were recruited for the study. Their stool was collected and subjected to standard microbiological assays for the isolation of the organism. The serological property of the isolates was determined by agglutination technique using Wellcolex serological kit (TSMX782). The molecular properties of the isolates were evaluated by amplifying rfbO157 and flicH7 genes while the level of divergence of the isolates was determined using polymerase chain reaction (PCR) and Randomly Amplify Polymorphic PCR assays respectively. The lipopolysaccharide (LPS) of the organism was extracted using conventional method. This LPS was used for the immunization of the experimental animals: New Zealand white rabbits and Wistar albino rats that were used in this investigation for raising of corresponding antibody. The titre of anti LPS antibody raised was quantified using standard serological assays and the raised antibody was used in passive protection assay against E. coli O157:H7 infection in Wistar albino rats. Active protection using the LPS was also carried out in another set of Wistar albino rats. The data obtained was subjected to one way ANOVA and means separated using Duncan`s New Multiple Range Test using SPSS window software. A 3.6% infection rate was recorded out of 5400 diarrhoeic individuals sampled during the cause of this research work. Sixty five (3.3%) out of the male gender sampled were positive for the organism, while 130 (3.8%) of the female gender sampled were positive. In relation to age group, the highest incidence was observed in the age group 81-90 years in which 13% were positive. The lowest occurrence however was found in the age group, 1-10 years (0.1%). For the factors affecting the distribution among the infected individuals, the rate of occurrence was highest among the farmers (33.3%), followed by elders, 81-90 years (13%), then the unmarried or single individuals (9%), children using diaper (8%), well water (4%) and the lowest occurrence was recorded in the areas with temperature/rainfall of 15-31oC / 4000mm (2.3%). Concerning clonal diversity of E. coli O157:H7 isolated in this research work, 40% were genotypically divergent from the standard molecular weight marker used in the assay (Thermo Scientific, USA) using OPC04 primer. Three strains of EHEC were isolated in this study; those with both fliC and rfbE genes, those with only the fliC gene and those with only the rfbE gene. Active immunization with the LPS of E. coli O157:H7 offered 70% protection on the rats while passive immunization offered only 50% protection despite the high antibody titres of 1:2048 and 1:512 produced by the rabbits and rats immunized with the LPS of the organism. In conclusion, the rate of occurrence of E. coli O157:H7 as the cause of diarrhoea in Southwest, Nigeria is 3.6% and farmers were the most susceptible to the infection. Moreover, since the LPS of the organism has been found to mediate 70% protection against the infection in albino rats, it is conceivable that it can confer protection against the infection, prevent the carriage and shedding of this organism in humans.