The effect of variations in temperature, ultraviolet (UV) radiation, and sunlight intensity on generic Escherichia coli , E. coli O157:H7, Salmonella Newport and antibiotic resistant (ABR) variants of E. coli O157:H7 and S . Newport exposed to sunlight was evaluated. Bacterial strains suspended in sterile deionized water at a concentration of 8 log CFU/ml were exposed to sunlight on three different days for 180 min; control treatments were stored in the dark. The mean temperature of 30.08 and 26.57℃ on day 1 and 3 were significantly different (p<0.05). The UV intensity was significantly different on all three days and sunlight intensity significantly differed on day 3 (p<0.05). Bacterial population decline positively correlated with temperature, sunlight and UV intensity. Differences in bacterial population declines differed among specie, antibiotic resistance (ABR) profile and day of exposure. (p<0.05). On days 1 and 2, the populations of generic E. coli dropped below the limit of detection (1 log CFU/ml) while the % of live cells was 67% and 6.6% respectively. The artificial neural network model developed to predict bacterial survival under different environmental conditions suggested that Salmonella cells were more resistant than E. coli . The ABR strains had significantly higher viable cells after sunlight exposure (p<0.05). Sunlight exposed cells resuscitated in TSB varied in maximum population density and maximum growth rate based on bacterial species and presence of antibiotic resistance. Morphological changes such as viable but non-culturable (VBNC) state transition and filament formation was detected in sub-populations of sunlight exposed bacteria. Daily fluctuations in UV and sunlight intensity can result in significant variations in bacterial decline and recovery.
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