E. coli and Salmonella Contamination of Tomato Marketed and Consumed in Nairobi Metropolis

Abstract

Tomato, a worldwide consumed commodity for its nutritive values can harbour Salmonella and E.coli. Tomato can contribute to diarrheal illnesses; and associated burden in households. Seasonal bacterial analyses to detect enterobacteria were conducted from January to June 2017 in Nairobi. The study shows that, the vegetable during the study period is 94% contaminated with E. coli and 28% with Salmonella. February had the highest contamination during the dry season (2.37 log₁₀cfu.ml^-1 >2; p≤ 0.05) and May (2.8 log₁₀cfu.ml^-1 >2; p≤ 0.05) the highest in wet season. Thus, seasons have influence on microbial contamination in tomato. Bacteria multiplication slows in dry period and increases in wet season. Increase of bacteria from March (end of dry season or beginning of rains) to high presence in May (end of rains) might come with more health concerns if attention is not paid to ready-to-eat vegetables. Consumers purchasing from open air markets seem more at risk of bacterial infection (Kangemi 1.84±0.159; Githurai 2.02±0.1815; Wakulima 1.97±0.24 of E. coli contamination) compared to those who use supermarkets (Nakumatt W. 1.54±0.134; Uchumi Sarit C. 1.27±0.105). Although most tomatoes were washed and cleaned, bacteria levels were still a threat to health. Surfactants from pesticides might contribute to tomatoes infection as they are able to wound skins of crops and open ways to bacterial contamination. With sudden bacterial increase in wet seasons (Kangemi 2.98±0.225^kl; Githurai 2.75±0.157^efghi; Wakulima 2.69±0.067^ghijk; Nakumatt 1.78±0.092^bcd; Uchumi 1.54±0.215^cde), consumers might experience more symptoms of enteric bacteria. Special attention should be paid in wet times as best quality of tomato at sight is not necessarily safe for direct consumption without further processing. These findings might help in understanding why consumers of salad might be exposed to symptoms of enteric bacteria in wet times. Food handlers, health workers, consumers and policy designers should be informed of this risk.

Keywords: E. coli, Salmonella spp, bacteria, season, contamination