Efficiency of selenite cystine and TT enrichment broths for the detection of Salmonella

Evaluation of a new enrichment broth for the isolation of Salmonella spp. from poultry products

Four selective enrichment broths were compared for the detection of Salmonella spp. in naturally contaminated poultry products and the recovery of atypical Salmonella strains in suspensions of pure cultures. In analysis of 100 poultry samples, the sensitivities observed were 94.0% for Müller-Kauffmann Tetrathionate-Brilliant Green (MKTBG), 97.6% for Rappaport Vassiliadis (RV), 42.2% for Selenite Cystine (SC) and 97.6% for the new broth KIMAN (Whitley Impedance Broth supplemented with 20 mg/l of novobiocin sodium salt, 10 mg/l of malachite green oxalate and 40 g/l of potassium iodide). The two most efficient broths--RV and KIMAN for recovery of atypical Salmonella strains (gallinarum biotypes gallinarum and pullorum, typhi, paratyphi A) were less toxic than MKTBG but more toxic than s.c. broth. According to these results, the use of RV and KIMAN could be a good combination to assure maximal recovery of Salmonella strains.

Efficiency of different enrichment and isolation procedures for the detection of Salmonella serotypes in edible offal

Rapid detection systems for Salmonella in foodstuffs are currently being developed. However, existing standards still call for application of traditional methods employing pre-enrichment followed by selective enrichment and isolation. The efficacy of various methods was tested using 264 chicken and lamb organ meats. Pre-enrichment was carried out in Tryptone Soy Broth (TSB) and enrichment in Tetrathionate Brilliant Green Broth (TTB) at 37 degrees C, Selenite Broth with Brilliant Green and Sulphapyridine at 37 degrees C and 43 degrees C, and Rappaport-Vassiliadis Broth (RV 10) at 42 degrees C. The isolation media were Brilliant Green Agar (BGA), Deoxycholate Citrate Agar, Hektoen Enteric Agar (HEA) and Salmonella-Shigella Agar. Enrichment in RV/42 degrees C followed by isolation on BGA as recommended by ISO standard no. 6579 and enrichment in TTB/37 degrees C followed by isolation in HEA, no longer recommended by that standard, produced the best results. Low percentages of positive samples and difficulties in detecting Salmonella are the result of interference by competing organisms (Enterobacteriaceae) and the number of salmonellas present after enrichment. A total of 528 samples (TSB, eggs, lamb liver and chicken liver) were inoculated with Salm. enteritidis, Salm. kapemba and Salm. virchow, and the preceding experiment was repeated. All the TSB and egg samples tested positive, but the percentage of positive samples from the lamb and chicken liver was only 81-92%. Recovery of the salmonellas did not depend upon the method employed or the serotype inoculated but instead on interference by competing flora and the numbers of Salmonella present in the samples.

Laboratory study of several enrichment broths for the detection of Salmonella spp. particularly in relation to water samples

The selectivity and efficiency of several enrichment broths used for the the detection of salmonellas were comparatively evaluated under laboratory and environmental conditions. Media with selenite were less efficient in their inhibition of the growth of Gram-positive micro-organisms. Salmonellas grew slowly in tetrathionate broth and in media containing brilliant green. These media inhibited the growth of Salmonella typhi, which grew only in media containing selenite. The results obtained in the experiments with stressed salmonellas indicate that the media selenite F, selenite F with novobiocin, selenite cystine and Rappaport-Vassiliadis (RV/43), in conjunction with the double agar layer technique, showed an optimal efficiency for the detection of stressed salmonellas. When natural samples (freshwater and seawater) were used to evaluate the media, however, those containing malachite green, whether or not supplemented with sodium novobiocin, enhanced the recovery of salmonellas.

Sensitivity and specificity of different methods for the isolation of Salmonella from pigs

Three different selective enrichment media, Rappaport-Vassiliadis broth (RV), selenite broth (SB) and Müller-Kauffmann tetrathionate broth (MKTB), in combination with plating on modified brilliant green agar (BGA), were compared for the isolation of Salmonella from samples of pig feces. These conventional methods were also compared with a new ELISA kit in conjunction with RV and SB enrichment. Of the conventional methods, enrichment in RV had a higher sensitivity and selectivity than SB and MKTB. Recovery of S. typhimurium from MKTB was significantly poorer than recovery of other serotypes. The combination of RV enrichment and ELISA was as good as the conventional method involving RV enrichment, with a similar high sensitivity and specificity.

Efficacy of prolonged (48 h) selective enrichment for the detection of foodborne Salmonella

The effect of prolonged (48 h) incubation on the productivity of five enrichment-temperature conditions (tetrathionate brilliant green, 35 and 43 degrees C; Muller-Kauffman tetrathionate brilliant green, 43 degrees C; Rappaport-Vassiliadis, 43 degrees C; selenite cystine, 35 degrees C) was compared to homologous results obtained under standard (24 h) conditions of selective enrichment. Of 797 high moisture and 166 low moisture foods tested, 171 (21.5%) and 80 (48.2%), respectively, were found to contain salmonellae by one or more analytical condition. Combined results of the five enrichment conditions after 24 and 48 h of incubation identified 247 (98.4%) and 250 (99.6%) of the 251 contaminated samples identified in this study. Our results are at variance with earlier reports on the greater method sensitivity with extended (greater than or equal to 48 h) periods of selective enrichment. The productivities of individual enrichment conditions after each period of incubation varied markedly where recovery rates with TBG43 and MKTBG43 exceeded that obtained with SC35 and TBG35. Our findings also underline the determinant role of enrichment at an elevated temperature (43 degrees C), and use of multiple enrichment and plating media for the optimal recovery of foodborne Salmonella.

The frequency of salmonellae on duck eggs

Total plate counts on washed duck eggs from a breeder farm on Long Island were less than 30/shell during the winter (January to February) of 1982. Clean unwashed eggs had counts less than 9 X 10(1)/shell, whereas dirty unwashed eggs had counts as high as 9 X 10(5)/shell. Our results showed that washing with a chlorine sanitizer (under commercial conditions) was highly effective in reducing surface bacterial counts on egg shells. Prolonged storage reduced bacterial counts on clean eggs, but it did not significantly affect loads on dirty eggs. No salmonellae could be detected on shells or in the magma of all eggs examined. In a second trial (March 1982) bacterial loads on washed and clean duck eggs from six different breeder farms were low, ranging from too few to count to 10(2)/shell. A higher proportion of dirty eggs were heavily contaminated with counts ranging from 10(5) to 10(6)/shell, but no salmonellae were detected either on shells or in magma. In the third trial (May 1982) bacterial determinations on eggs from breeder ducks that were not confined followed the pattern of the second trial. However, in this trial Salmonella enteritidis was detected on dirty egg shells in four of six farms. In a fourth trial (May 1983), bacterial loads on washed and nest-clean eggs from the same breeder farms (not confined) ranged between 10(2) to 10(3)/shell and 10(2) to 10(4)/shell, respectively. S. enteritidis and S. badar were recovered from washed, nest clean, and dirty eggs in two of six farms. We conclude that proper egg washing and confinement of duck breeders should minimize the problem of salmonellosis in ducklings.

Salmonella and other Enterobacteriaceae found in commercial poultry feed

Poultry feed (mash and pelleted) and meat and bone meal samples were collected from commercial mills. All samples were analyzed for Enterobacteriaceae count (ENT) and Salmonella. The genus and species of the various Enterobacteriaceae present were also determined. The average ENT for mash, pelleted, and meal samples was log 4.1, .8, and 1.8/g, respectively. Enterobacteriaceae were present in 100, 60, and 92% and Salmonella in 58, 0, and 92% of the mash, pelleted, and meal samples, respectively. Overall, the Enterobacteriaceae most frequently isolated from all samples were Enterobacter agglomerans, Enterobacter cloacae, and Klebsiella pneumoniae. Although no Salmonella were found in the pelleted samples, the presence of other Enterobacteriaceae suggests that commercial pelleting may not totally destroy Salmonella since their heat resistance is similar to the other organisms found.