Incubation at raised temperature of enrichment media, combined with secondary enrichment in Rappaport's medium, for the isolation of salmonellas from sewage

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Abstract
A total of 50 duplicate Moore swabs were placed for 2 days, on five different dates, in 9–12 points of the Athens sewage disposal system.Three methods of enrichment were used for the isolation of salmonellas. In the first method, one half of the duplicate swabs was incubated in Muller–Kauffmann's tetrathionate broth at 43° C. for one day. For the second method, a secondary enrichment was carried out in Rappaport's broth, made from the Muller–Kauffmann's broth and for the third method, the other half of the duplicate swab was cultured in Heart Infusion broth at 43° C. for 16–18 hr. after which a secondary enrichment was made in Rappaport's medium.By use of these 3 enrichment procedures, 96% of the swabs were found to be positive for salmonellas. A total of 178 strains were isolated (an average of 3·7 strains per positive swab), belonging to 53 different serotypes (an average of 1·1 different serotypes per positive swab).With the simple enrichment in Muller–Kauffmann's broth, only 72% of the swabs were found positive, and 68 strains of salmonellas belonging to 30 different serotypes were isolated. The secondary enrichment in Rappaport's medium made from the Muller–Kauffmann's broth produced 88% positive samples, and yielded 82 strains belonging to 34 different serotypes. Finally, with the secondary enrichment in Rappaport's broth made from the heart infusion broth, 92% of the swabs were positive and yielded 67 strains of salmonellas belonging to 27 different serotypes.Although the last procedure yielded the greatest number of positive swabs, the method involving secondary enrichment in Rappaport's broth made from Muller–Kauffmann's broth led to the isolation of the greatest number of strains and different serotypes, while the other two procedures were approximately equal in this respect.Of the 178 strains isolated, 110 were recovered only by the procedures involving secondary enrichment in Rappaport's broth. The most frequently isolated serotypes wereSalmonella senftenberg(33 strains),S.typhimuriumincluding var-copenhagen(18 strains),S.poona(11 strains),S.montevideo(10 strains), etc. The following 23 serotypes were isolated for the first time in Greece:S. adelaide, S. alachua, S. allerton, S. binza, S. bobo, S. butantan, S. gnesta, S. goelzau, S. haelsingborg, S. havana, S. hofit, S. ibadan, S. indiana, S. irumu, S. jodhpur, S. nienstedten, S. panama, S. pomona, S. poona, S. reading, S. schwarzengrund, S. stockholm, S. tournai.Moreover, a new serotype,S. athinaiwas described.