Investigation of Escherichia coli Distribution in Drinking Water Wells Close to Septic Tanks in Densely Populated Areas of Osogbo, Osun State, Nigeria

Groundwater, which serves as the major drinking water source to densely populated areas in Osogbo  metropolis, are usually in close proximity to defective septic tanks. Faecal contamination of such water system  is inevitable. This work investigated the faecal contaminants in eighty wells from five locations. Total coliform  count (TCC) was determined using Most Probable Number (MPN) and membrane filtration; Escherichia coli  was recovered using chromogenic media. Antibiotic susceptibility profile was obtained for E. coli isolates. All  wells were > 15.24m from nearest septic tank; averaging 78m. Depth to water surface ranged between 9ft and  48ft with a mean of 23.8ft while 16.2% were deeper than 30ft to water surface. All samples (100%) had  coliforms. TCC ranged between 1.0 x 102 and 4.0 x 105 cfu/ml (except Kasmo); with a mean 3.8 x 104 cfu/ml.  Mean TCC for wells was highest in Igbona area and lowest for Oke-baale. Escherichia coli was isolated from  48.8% of samples. Five samples had two strains of E. coli as revealed on chromogenic media. The study  recorded 100% resistance to ticarcillin and meropenem; 52.3% to tigecycline. Aztreonam and Colistin inhibited  92.6% and 91.0% of isolates respectively. Multidrug resistance was evident in 79.5% of isolates. The well water  samples analyzed were neither safe for drinking nor put into such uses that may facilitate ingestion by humans.  E. coli was most susceptible in-vitro to aztreonam and colistin, thus suggesting their use in the treatment of  gastrointestinal syndromes resulting from consumption of contaminated groundwater.