Determination of important bacteria in food and water by FISH and standard microbiological methods

This study has been conducted to investigate the determination and enumeration of E.coli, Salmonella, S.aureus and Legionella sp. in food and water samples by `Fluorescence in situ Hybridization? and FDA approved `Cultural Microbiological Methods?. The food samples were collected from a big supermarket and public bazaars in Aydın city; the water samples were collected from the water tanks which supplies potable water to Aydın city. 100 meat and 100 water samples were studied and 1000 analyses were applied with 2 repetitives. Bacterial counts which were determined by FISH and cultural methods were compared statistically by paired t-test and a significant difference (p<0.01) between the methods is obtained. 12 different hybridization temperature is experimented for 6 different oligonucleotide probes and hybridization temperatures are specified as 43°C for EUB338, NonEUB338 and Sau; 47°C for ECO1167, 37°C for Sal3 and 45°C for Leg705. E.coli cell counts in 84 meat samples have been found higher than Turkish Food Codex limits and 42 of 84 have been observed that were collected from public bazaars. S.aureus counts in 100 meat samples were found below codex limits for all meat samples. On the other hand, 18 of 100 meat samples were found Salmonella positive and it has been observed that only 3 of 18 positive samples were collected from the supermarket. Besides, Salmonella was isolated by FISH from 12 of 82 Salmonella negative samples analysed by culture method. 100 water samples were analysed by FISH and cultural methods and E.coli and Salmonella were not detected by both of the methods. By this study, a FISH method capable of enumerating E.coli, S.aureus, Salmonella and Legionella in food within a single day was developed and the total time for FISH analyse with probe ECO1167 was reduced to 8h.