congresos y reuniones científicas
Survival of Escherichia coli O157:H7 in water of animal-drinking troughs in dairy farm
Ciudad de Buenos Aires
Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxin)?producing Escherichia coli infections (VTEC 2009).; 2009
Institución organizadora:
Asociaicón Argentina de Microbiología
Resumen: This study was realized with the aim to observe until what time Escherichia coli O157:H7 can survive in water from animal-drinking troughs from dairy farm. This ability was observed by many authors. E. coli could survive over more than 200 days in water from river and lake at temperature lower than 4° C, overall in countries with cold weather. Recent microbiological studies demonstrated that E. coli O157:H7 and other bacteria may become viable but nonculturable (VBNC) when exposed to sublethal stress, such as changes in temperature, available nutrients, pH or exposure to chlorine. Under simple starvation conditions, E. coli O157:H7 can also enter into a VBNC state. In this state, the bacteria can not be growth in regular enrichment media used in the microbiology laboratory and could become culturable again in the presence of sodium pyruvate.We inoculated steril water from animal-drinking troughs and Luria Bertani broth (LB)  each one with  103 CFU/ml of a strain of E. coli O157:H7 isolated from feedlot cattle resistant to nadilixic acid (characteristic virulence factors of this strain: ehlyA, eae, vt2). The bacteria?s presence was periodically controlled by the colony enumeration in SMAC plates with nadilixic acid added at a concentration of 50 μg/ml (SMAC-Nal), until the 117th day when the enumeration in water was inferior to 1 UFC/ml. At day 0, 50 and 56 we took samples to compare the colony count (CC) with the optic density at 600 nm (OD600). The results at day 0 were almost the same for water and LB cultures (104 CFU/ml by CC and 103 by OD600). At day 50 and 56, the water showed 104 UFC/ml by CC and 107 by OD600 and 103 CFU/ml by CC and 106 by OD600 , respectably; whereas the result for the LB were constant for both times (107 CFU/ml by CC and 109 by OD600 ). One sample was taken at time 92 day and the CC in SMAC-Nal. was 10 CFU/ml. We compared the colony count in LB agar containing 0.1% of sodium pyruvate (LB+ P) and SMAC, without antibiotic to reduce the stress condition, and to observe if the cells could be in VBNC state. The result was an enhanced count in the medium containing pyruvate (>500 CFU/ml in LB+P vs. 150 CFU/ml in SMAC ). We confirm positive result to E. coli O157:H7 in LB+P by using agglutination test with latex particles (OXOID) in 5 random selected colonies, multiplex PCR (ehlyA, eae, vt2) and a new culture in LB+P+Nal from the sample took at 92th day. This last count colony was 110 CFU/ml and positive for OXOID test. These results suggest that it was possible to recover cells of E. coli O157:H7 that could have been in VBNC state due the starvation. The presence of VBNC E. coli cells is a concern regarding in water from animal-drinking troughs in the dairy farm and a potential health human risk.