Comparison of classical isolation protocols with a 24 h screen to detect viable salmonellas in faeces

Abstract

A 24 h screen which detects three viable salmonella cells per g of faeces was compared with classical isolation procedures for their ability to identify salmonella-positive samples from a pig rearing unit. The screen involved an overnight enrichment in Muller-Kauffmann tetrathionate (MK) broth, subculture for 4 h in M broth containing 10 micrograms ml-1 novobiocin, followed by detection of the presence of salmonellas by BacTrace and Salmonella-tek ELISAs. The classical protocols were: (1) an overnight and 48 h incubation in MK or selenite cysteine broth; or (2) overnight incubation in buffered peptone water and 24 h subculture in Rappaport-Vassiliadis broth (BPW-RV). Salmonellas were isolated from the broth cultures on xylose lysine deoxycholate and brilliant green agars. Thirty four of 100 samples were positive for salmonellas but no single isolation protocol identified all of them. The best of the classical isolation protocols, 48 h incubation in MK broth, identified 27 (79%) of the 34 positive samples whilst the screen identified 26 (76%) of the 34 positive samples. False-positive results were obtained from all isolation protocols except BPW-RV.

Comparison of methods for isolating Salmonella bacteria from faeces of naturally infected pigs

“…This observation is consistent with some previously published work ( Skovgaard et al . 1985 ; Cherrington and Huis in't Veld 1993) and it is suggested that the apparent contradictions in other previous studies are attributable to the use of BPW pre‐enrichment prior to enrichment in tetrathionate broths ( Bager and Petersen 1991; Cherrington and Huis in't Veld 1993). Recently, Kim et al .…”

“…1985 ; Vassiliadis et al . 1987 ; Bager and Petersen 1991; Cherrington and Huis in't Veld 1993). All these studies compared RV broth with Muller–Kaufmann tetrathionate broth (MKTB), and some also included selenite broth (SB).…”

“…A relatively small number of previous studies comparing enrichment broths with swine faecal (or caecal) samples has reported con¯icting ®ndings (Skovgaard et al 1985;Vassiliadis et al 1987;Bager and Petersen 1991;Cherrington and Huis in't Veld 1993). All these studies compared RV broth with Muller±Kaufmann tetrathionate broth (MKTB), and some also included selenite broth (SB).…”

“…All these studies compared RV broth with Muller±Kaufmann tetrathionate broth (MKTB), and some also included selenite broth (SB). Interestingly, the two studies that found RV broth to give inferior results used direct inoculation of faeces into MKTB and selenite broth, and BPW pre-enrichment for RV samples (Skovgaard et al 1985;Cherrington and Huis in't Veld 1993). In contrast, the two studies reporting superior results with RV broth used pre-enrichment in BPW for all samples (Vassiliadis et al 1987;Bager and Petersen 1991).…”

Characterization of Salmonella isolates from beef cattle, broiler chickens and human sources on Prince Edward Island

“…The detection of Salmonella in faecal sarnple can be complicated because the organism may be greatly outnumbered by other competing microflora (1 9). As a consequence, isolation and detection of Salmonella either by conventional or rapid methods involves a seledive enrichment step (20). A selective enrichment medium contains inhibitory reagents that allow Salmonella to grow while restricting the growth of other microflora.…”