In 1976 two major modifications were introduced in the composition and use of Rappaport's magnesium chloride—malachite green enrichment medium for salmonellas. One modification consisted of the reduction to one‐third of the amount of malachite green contained in the original formulation of Rappaport's medium, and the other in the incubation at 43 instead of 37°C. Since 1980, the modified medium incubated at 43°C is known as RV (Rappaport—Vassiliadis) enrichment medium for salmonellas. From 1977 to 1981, in eleven studies, the RV enrichment broth has been compared to the standardized Muller‐Kauffmann tetrathionate broth (MK broth) recommended as a reference method by the International Standards Organization, for the isolation of salmonellas from meat products, after pre‐enrichment in buffered peptone water. In all these studies the RV broth was superior to the MK broth in the isolation of salmonellas from naturally contaminated meat products (bovine minced meat, pork sausages, mesenteric lymph nodes, chicken carcases), sewage and faeces of healthy pigs, after pre‐enrichment in buffered peptone water. This superiority was statistically significant in seven of the eleven trials. Furthermore, in three more investigations the RV medium was compared with Oxoid selenite broth, with Difco tetrathionate broth and Difco selenite‐cystine broth. In all these three investigations the RV medium was superior for isolation of salmonellas, after pre‐enrichment, from naturally contaminated meat products and animal feeds. The superiority was statistically highly significant. When dealing with meat products, the RV medium in 10 ml volume inoculated with 0.1 ml of the pre‐enrichment medium, proved to be as effective as the RV medium in 100 ml volume, inoculated with 1 ml of pre‐enrichment medium, and clearly superior to the MK broth in 100 ml quantity. In all these studies involving enrichment in RV medium, MK broth, Difco tetrathionate broth, Oxoid selenite broth, incubated at 43°C and Difco selenite‐cystine broth incubated at 37°C, the RV medium proved to be highly specific. This means that the RV medium inhibits much more strongly the competing organisms, (including ‘Proteus hauseri’) which are lactose‐ and sucrose‐negative on the selective media and which may produce salmonella‐like colonies.

Forty samples of sewage on Moore's swabs were examined for the presence of salmonellae. They were first pre‐enriched in buffered peptone water. From each pre‐enrichment, three enrichments were made: (1) in a new, considerably modified, formula of Rappaport medium (R 10) incubated at 43 °C (R 10/43 °C), (2) in the usual formula (R25) of the same medium at 37 °C (R25/37 °C) and (3) in Muller‐Kauffmann's tetrathionate broth at 43 °C (MK/43 °C). Practically the same numbers of swabs were found positive by the first two enrichment procedures, 38 and 39 respectively, while only 17 were found positive by the MK procedure. The R10/43 °C method was superior to the two other procedures; it yielded 103 strains of salmonellae as against 82 with the second Rappaport procedure, and only 25 with the MK/43 °C technique. A similar observation was made concerning the frequency of isolation of different serotypes by the three procedures; the number of the isolated serotypes was 24, 19 and 11, respectively. The new R 10/43 °C method of enrichment had also a much stronger inhibitory effect on the competing bacteria than the two other procedures of enrichment used.

SUMMARYThe prevalence of salmonellas in drain swabs from three abattoirs of Athens was studied with the use of conventional methods of Salmonella isolation as well as with a new procedure which involves secondary enrichment from the usual selenite broth or Muller-Kauffmann's tetrathionate broth in Rappaport's medium slightly modified.In all groups studied the secondary enrichment in Rappaport's medium led to an increase in the number of positive swabs, in the number of Salmonella serotypes, and in the total number of strains isolated.The frequency of Salmonella isolations was higher in samples from abattoirs killing only pigs and lower in samples from abattoirs killing only cattle or only sheep.The predominant serotype in abattoirs dealing with cattle was Salmonella tennessee, and S. typhimurium in abattoirs dealing with sheep. No predominant serotype was found in samples from abattoirs dealing mostly with pigs.S. abony, S. drypool, S. emek, S. Indiana, S. muenchen and S. tennessee were isolated for the first time in Greece.

Summary. The behaviour of 70 strains of salmonellae belonging to 44 serotypes in Rappaport's broth and in Muller‐Kauffmann's tetrathionate broth was examined. With an inoculum of 5–25 cells, 5 strains did not grow in Rappaport's medium, 2 multiplied slowly and 63 grew strongly in 24 h. With an inoculum of 100–500 organisms all but one strain grew readily in 24 h. In Muller–Kauffmann's tetrathionate broth inoculated with pure cultures of salmonellae, growth of many strains was markedly inhibited, in the absence of added faeces, at 37° and 43°. This inhibition was more severe with light inocula at 43°. The addition of 0.05% (w/v) of salmonella‐free human faeces to Muller–Kauffmann's tetrathionate broth, did not stimulate growth of salmonellae. In contrast, the addition of 5% (w/v) of human stools to this medium resulted in a heavy growth of the added salmonellae, especially at 43°.