Okemo, P. O.Wahome, Caroline NyawiraNyamache, A. K.2014-08-222014-08-222014-028(1): 134-143, February 20141997-342X1991-8631http://www.ajol.info/index.php/ijbcs/article/viewFile/104044/94153http://ir-library.ku.ac.ke/handle/123456789/11002DOI : http://dx.doi.org/10.4314/ijbcs.v8i1.13Groundwater represents an important source of drinking water and its quality is currently threatened by a combination of over-abstraction and microbiological and chemical contamination. Nairobi, Kenya and its environs is plagued with un-planned dwelling residential settlements, with limited potable water sources which are often contaminated by bacterial pathogens. This coupled with increased incidences of antibiotic resistance among the pathogens is alarming. This study used the MPN technique to determine indicator organisms, and the agar diffusion method to determine resistance in isolated pathogenic bacteria. The total coliforms values recorded were as high as 1.12x102 (±8.8x101) MPN/100 ml, fecal coliform loads were 8.63(±7.01) MPN/100 ml for the shopping centre. Total bacterial counts values recorded were as high as 5.64x104 (±1.77x104) CFU/ml at the shopping centre. Numerous organisms that are potential enteric pathogens such as Vibrio sp, Salmonella sp., Shigella sp., P. aeruginosa and E. coli were isolated from the water samples. There was high resistance to many antibiotics particularly sulphamoxazole (98.5%), kanamycin (95.3%) and ampicillin (87.5%). The most active antibiotics were chloramphenicol with resistance level of 45.4% and streptomycin (59.4%). The study indicates that water from the studied boreholes was not suitable for human consumption and therefore calls for urgent intervention. There is a high likelihood that congestion and lack of proper waste and waste water management is responsible for contamination of aquifers in this region.engroundwatercontaminationcoliformspotable waterantibiotic resistanceArticle