J. E. Thomson

Effectiveness of Sampling Methods for Salmonella Detection on Processed Broilers

A total of 240 processed broiler carcasses (water-chilled and unfrozen) were each sampled by three methods (whole-carcass rinse, neck-skin rinse, and macerated neck skin) for detection of Salmonella . In addition to this, various procedures were compared: destructive (incubating the entire carcass with the rinse fluid) versus non-destructive (incubating the rinse water with concentrated lactose or selenite cystine broth added after removal of the carcass) sampling and pre-enrichment versus no pre-enrichment during Salmonella detection procedures. There was no significant difference (p < 0.05) between the percentage of Salmonella -positive carcasses obtained by destructive sampling and the percentage obtained by non-destructive samples of whole carcasses. There was also no significant difference (p < 0.05) in results obtained by rinsing and blending excised neck-skin samples. There was highly significant difference (p = 0.001), however, between whole carcass and neck-skin analyses. With whole-carcass sampling, 45% of the carcasses were positive for the presence of Salmonella while with rinsing or blending the neck skin of these same carcasses, only 11% and 12%, respectively, were positive for the organism. Pre-enrichment of the whole carcass, of the whole-carcass rinse, or of the neck-skin samples did not result in significantly greater percentages of positive results than did direct enrichment of these samples.

Selecting a Miniaturized System for Identification of Enterobacteriaceae

The most commonly used commercial diagnostic kits for identification of Enterobacteriaceae are API, Enteric-Tek, Enterotube II, Micro-ID, Minitek and Spectrum-10. The accuracy of identification by all systems does not vary significantly, and falls within the acceptable range. Therefore, a bacteriologist who is considering the use of these products should evaluate factors other than accuracy when making a choice. Twenty-three professional microbiologists who had previous experience with these systems listed advantages and disadvantages of each system, and evaluated the conventional procedure for identification. The comments were summarized and presented in tabular form. The current cost per isolate of each system and the cost of the identification manual, reagents and incidental costs were also determined. These data provide the potential user with comparative information on price, shelf-life, versatility, time required for inoculation, incubation and manipulation after incubation, possible difficulties in determining positive and negative reactions, and potential safety factors for laboratory personnel.

Identification of Enterobacteriaceae in Foods with the AutoMicrobic System

Stock cultures (136) and fresh isolates (163) of Enterobacteriaceae from ground beef, processed chickens, frozen pot pies and commercial poultry feeds were identified to species with the AutoMicrobic System (AMS). All stock cultures and fresh isolates were also concurrently tested with two other identification systems (Micro-ID and API), previously evaluated and proven accurate for identification of Enterobacteriaceae . The AMS correctly identified to species 135/136 (99.3%) of the stock cultures and 160/163 (98.2%) of the fresh isolates. All Salmonella cultures tested (74) were correctly identified by AMS.

Minimizing Salmonella Contamination on Broiler Carcasses with Poly (Hexamethylenebiguanide Hydrochloride)

Broiler carcasses, each inoculated with 30 cells of marker Salmonella heidelberg , were prechilled and chilled together with uninoculated carcasses in a simulated commercial chilling system. When either 10 or 25 ppm of PHMB [poly(hexamethylenebiguanide hydrochloride)] was added to the prechill water, cross-contamination (uninoculated carcasses showing contamination with marker Salmonella after chilling) was prevented, and no viable Salmonella were found on the inoculated carcasses. When carcasses, each inoculated with 60,000 cells of marker Salmonella , were similarly chilled, and 10 ppm of PHMB was added to the prechill water, cross-contamination was not prevented, and viable Salmonella were found on the inoculated carcasses. With 60,000 cells, and 25 ppm PHMB, cross-contamination was prevented, but viable Salmonella remained on the inoculated carcasses.

Salmonella on Broiler Carcasses as Affected by Fresh Water Input Rate and Chlorination of Chiller Water

Broiler carcasses, each inoculated with about 1000 cells of a marker strain of Salmonella typhimurium , and uninoculated carcasses were prechilled and chilled in a simulated commercial chilling process. For each experiment, fresh water input was either 1.90 liters (0.50 gal) or 0.95 liters (0.25 gal) per carcass, and the chlorine level was 0, 20 or 50 ppm. The rate of fresh water input had no significant effect on either cross-contamination (uninoculated carcasses showing contamination with marker organisms after chilling) or elimination of Salmonella from the inoculated carcasses. Fewer uninoculated carcasses showed marker Salmonella contamination after chilling with 50 ppm of chlorine than 0 ppm, but cross-contamination was not eliminated. Chlorine in the chilling water decreased rapidly due to the effect of organic matter.

Evaluation of Five Miniaturized Systems for Identifying Enterobacteriaceae from Stock Cultures and Raw Foods

Five miniaturized systems (API, Enteric-Tek, Enterotube II, Micro-ID and Minitek) were compared to conventional procedures for identification of Enterobacteriaceae from stock cultures and freshly isolated from food sources, The accuracy of identification to genus was 98% for Micro-ID; 95%, Minitek; 94%, Enteric-Tek; 93%, API; and 86%, Enterotube II, Accuracy of identification to species was 97% for Micro-ID; 94%, Minitek; 93%, Enteric-Tek; 91 %, API; and 79%, Enterotube II, The 124 organisms tested in this study were from 11 genera of the Enterobacteriaceae family. All systems accurately identified to species the most pathogenic members of the family ( Arizona hinshawii , Salmonella typhi , Salmonella typhimurium and Shigella flexneri ). Most of the inaccuracies in identification occurred with Enterobacter and Serratia species.

Comparison of Brands of Media for Isolating Bacteria from Poultry, Beef and Shrimp

Five brands of media (BBL, Difco, Gibco, Oxoid and Scott) were evaluated for enumerating microorganisms by the aerobic plate count and by Enterobacteriaceae , Escherichia coli , and coliform counts, and for determining Salmonella incidence. Microbiological evaluations were done on raw chickens, raw beef and raw shrimp, except that Salmonella incidence was not determined on shrimp samples. There were statistically significant differences in total plate counts (with chicken, beef and shrimp), Enterobacteriaceae counts (with shrimp) coliforms (with chicken) and E. coli counts (with chicken) by the five brands of media, but these differences were too small to be of practical significance. It was concluded that no differences of practical significance were found among the five brands of media.

Rapid Procedure for Biochemical Characterization and Serological Confirmation of Suspect Salmonella Isolates

Fifty-two freshly processed broiler carcasses were examined for the presence of Salmonella by using a rinse method. Three selective plating media (bismuth sulfite, brilliant green sulfa and Hektoen enteric) were compared. After 24 h of incubation, typical colonies were picked from each selective plate. An 8-h procedure to biochemically characterize (Micro ID) and serologically (poly O and poly H) confirm Salmonella was then compared with a conventional procedure. Suspect Salmonella isolates were correctly classified from 63% of the carcasses with both the 8-h and conventional procedures. Of the 244 isolates confirmed to be Salmonella by conventional testing, 236 (97%) were also confirmed by the 8-h procedure. Brilliant green sulfa and Hektoen enteric agar were superior to bismuth sulfite agar for Salmonella recovery. The 8-h procedure required less incubation time (8 h vs. 48 h) after colony formation, less incubation space, and less media preparation and cleanup than the conventional procedure.

Comparison of Micro-ID and Minitek-Serology Systems for Rapid Identification of Salmonella

A 4-h biochemical identification system (Micro-ID) and a rapid confirmation 24-h biochemical and serological procedure (RC) involving the Minitek system were compared for accuracy of Salmonella identification. Of 144 known Salmonella stock cultures, RC correctly classified all, and Micro-ID correctly classified 141. Both systems correctly classified all the Salmonella isolates obtained from four artificially inoculated broiler carcasses. When 113 suspect- Salmonella isolates from naturally contaminated samples were examined, RC correctly classified all, and Micro-ID correctly classified all except one.

Minitek Inoculum Broth for Testing Indole Production by Enterobacteriaceae

With 73 members of the Enterobacteriaceae family, detection of indole production with Minitek inoculum broth (MIB) correlated more closely with the results of the conventional method than did detection with the Minitek H2S/indole disk.