ISOLATION OF SALMONELLAE BY SELECTIVE MOTILITY SYSTEMS

The isolation of salmonellas from animal feedingstuffs

A technique is described for the routine isolation of salmonellas from meat and bone meal samples used in animal feedingstuffs. The technique more than doubled the number of positives obtained by an orthodox method. Identical samples were used in the trial.

New semisolid agar for the detection of motile salmonellae

A semisolid selective motility agar based on selenite broth and designated semisolid selenite fecal (SSF) agar was developed for recovery of motile salmonellae from large numbers of rodent fecal specimens. The medium is easily prepared and inoculated; results are readily interpreted. When combined with selenite or gram-negative broth enrichment, SSF agar yielded significantly better Salmonella isolation from experimentally infected rodents than a standard battery of media. Only 14 non-Salmonella isolates from 1,002 Salmonella-free rodent fecal specimens migrated on SSF agar.

Semisolid selective-motility enrichment medium for isolation of salmonellae from fecal specimens

A semisolid selective-motility enrichment medium for the isolation of salmonellae from fecal specimens was developed which was based on Rappaport enrichment broth. During a 7-year period more than 30,000 stool samples were tested. The medium showed a high specificity (95.1%) and sensitivity (80.3%) when compared with MacConkey agar, SS agar, and brilliant green agar (after Selenite-F Enrichment [BBL Microbiology Systems]). Furthermore, our isolation rate of Salmonella species from fecal samples showed an increase of 22.3% when this semisolid medium was added to the routine culture media. Growth could easily be interpreted. The medium has a bias toward the isolation of Salmonella paratyphi B, but it is unsatisfactory for detecting the nonmotile strains Salmonella typhi and S. paratyphi A.

Influence of multiple plating from fluid media on salmonella isolation from animal feeding stuffs

The influence of multiple plating of fluid cultures on salmonella isolation from animal feeding stuffs was examined. Four plating were made from broth culture after 24 h at 37 degrees C and four platings from selenite enrichment from 24 h at 43 degrees C. Selenite enrichment followed broth culture which was used as a pre-enrichment stage. Brilliant green MacConkey agar plates were employed for broth subculture and brilliant green MacConkey and desoxycholate citrate agars for selenite subculture. The eight brilliant green plates subcultured from broth and selenite were examined for salmonellas after incubation for 24 h at 37 degrees C. The four desoxycholate citrate agars after 24 h at 37 degrees C were used for motility enrichment. The food sample size was a single 100 g instead of 4 x 25 g cultured in an earlier study. This pooling of samples aimed at technical economy. Quadruple plating played an important part in salmonella isolation from 100 g specimens. The combination of multiple plating with motility enrichment was the most successful technique used.

Secondary selective enrichment of salmonellae from naturally contaminated specimens by using a selective motility system

A selective motility medium was used as a secondary selective enrichment medium to examine specimens naturally contaminated with salmonellae. The medium, incubated at 37 degrees C, was inoculated from either selenite brilliant green sulfa enrichment broth or Müller-Kauffman tetrathionate broth, both of which had been incubated at 42 degrees C. The use of the selective motility medium resulted in an increase in the number of positive specimens from 65 and 74% to 80 and 82%, when inoculated at 24 and 48 h, respectively, from tetrathionate broth. Tetrathionate broth, when used singly, was significantly better than selenite brilliant green sulfa broth, which detected 55% of positive specimens at both 24 and 48 h. The use of the selective motility medium of Harper and Shortridge (J. Hyg. 67: 181--186, 1969) for the further examination of specimens culturally negative on primary selective enrichment is advocated.

Salmonella surveillance with reference to pigs--Cardiff abattoir, 1968-1975

Between 1968 and 1975, well over 3000 samples of pig faeces and 407 samples of pig mesenteric glands were examined for salmonellas. A very wide range of serotypes was isolated. The material from this survey was used to evaluate certain aspects of salmonella isolations. The factors studied were: selective motility enrichment, size of inoculum of faeces, comparison of drain swab with animal sample and comparison of selenite F broth with Muller-Kauffmann tetrathionate broth. The conclusions drawn from these investigations allowed an efficient routine to be developed during the survey.

A one-day selective migration procedure for detecting salmonellae in faeces

A one-day procedure for detecting salmonellae was developed and evaluated with clinical faecal specimens. The procedure was based on the selective retardation of enterobacteria in their migration through a semi-solid enrichment medium. It was shown that a pure or almost pure growth of salmonella could often be obtained within 16 to 24 hours by this method. The culture thus obtained could then be used directly for serological confirmation. The method was rapid, economical, and efficient. Clinical trials indicated an increase of 28% in the frequency of positive isolations of salmonella with this procedure as compared with the conventional multistep cultural procedures with no false-positive results. However, the method was unsatisfactory for detecting Salmonella typhi due to its slow migration through the semi-solid medium.

Comparison of the rates of motility of Salmonella with those of other enteric bacteria

Comparison of the rates of motility through a semisolid medium of 16 common Salmonella sp., 14 Escherichia coli serotypes, 4 Arizona strains, 2 Escherichia freundii (Citrobacter) isolates, 2 Proteus sp., and 2 Pseudomonas sp. revealed the following. (i) Very closely related bacteria could demonstrate markedly different rates of progression. (ii) All of the salmonellae tested advanced faster than the Proteus and Pseudomonas test cultures but some Salmonella sp., notably S. choleraesuis and S. typhi, progressed relatively slowly compared to many other test cultures. (iii) The mean rate of motility for the fastest 14 Salmonella sp. (1.49 cm/hr) was not statistically greater than the mean value for the 14 E. coli serotypes (1.31 cm/hr) at the 1% level of significance. Selective motility procedures may not be a reliable means of isolating all Salmonella sp. from materials contaminated with other bacteria.

Rapid determination of Salmonella in samples of egg noodles, cake mixes, and candies

A glass apparatus system was compared with a standard enrichment broth-selective agar method to test samples of egg noodles, cake mixes, and candy for the presence or absence of salmonellae. The glass apparatus system used fermentation of mannitol, production of H(2)S, or motility, in conjunction with a serological test of flagellar antigens, to detect salmonellae. No salmonellae were detected in 173 samples of food products. Of these samples, 171 were found to be Salmonella-negative after 48 hr with the glass apparatus system. After 72 hr, the standard Salmonella procedure yielded 38 samples which produced Salmonella false-positive results on selective agars. Inoculation of samples with cultures of Salmonella showed that approximately one inoculated cell could be detected after 48 hr of incubation with the glass apparatus. The standard Salmonella test requires a minimum of 72 hr for completion. Compared with the standard Salmonella test, the glass apparatus system is a more rapid and simple system that can be used to determine the presence or absence of Salmonella in these food products.

A selective motility medium for routine isolation of Salmonella

A modified Shigella—Salmonella medium in semi-solid agar was shown to inhibit the spread of most faecal organisms through a Craigie tube, while selectively allowing the passage ofSalmonella.

A medium for routine use is described.

Over a period of 3 years, in this laboratory, 90% of specimens from which salmonellas were isolated gave positive results with this medium. Over 40% of these specimens would have been reported as negative if the method had not been in use. However, 10% would have been missed if this method alone had been used. It should therefore be used in conjunction with other culture methods, of which direct plating on SS agar was the most successful in this series.

Detection of Salmonella by a single-culture technique

Dulcitol-selenite enrichment medium in a motility flask was used for the detection of Salmonella in food. A drop in pH of the dulcitol-selenite enrichment motility broth indicated the presence of Salmonella; this phenomenon was confirmed by fluorescent-antibody staining. A complete correlation was found between fluorescent-antibody staining and recovery on Brilliant Green agar. Testing of 332 samples of 8 different kinds of foods and feeds indicated no significant difference in sensitivity between the new technique and a conventional Salmonella detection technique. The new technique permitted detection of even small numbers of Salmonella in 1 to 2 days.

Establishment of a salmonella-free Guinea pig colony

Salmonellosis due to Salmonella typhimurium was enzootic in a guinea pig breeding colony for over 25 years. A Salmonella-free auxiliary colony was established by removing weanlings from the infected colony to a clean area, and preventing infection. Examination of agglutinin titers and necropsy specimens indicated that the auxiliary colony was still free from Salmonella 18 months after its establishment while 24% of the guinea pigs dying in the infected colony yielded Salmonella typhimurium.