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.

Spectrum-10, a newly developed miniaturized identification system, was analyzed for its ability to accurately and rapidly identify members of the Enterobacteriaceae family. This study, conducted at two separate laboratories, tested freshly isolated organisms from raw and frozen foods (180) and stock cultures (144). For comparison purposes, the Micro-ID and API-20E identification systems were concurrently inoculated with the test organisms. In comparison to the Micro-ID and the API-20E systems, the Spectrum-10 identified 95 to 96% of the stock cultures to genus and species, whereas 93% of the fresh isolates were identified to genus and 82% to species.

Effects of aerobic and anaerobic incubation of selenite-cystine and TT enrichment broth incubated at 37 and 34°C on the growth of Salmonella were determined. Pure cultures of four serotypes of Salmonella were enumerated at 0, 4, 8 and 24 h of incubation and no significant differences related to incubation conditions were found. The effect of microflora other than Salmonella , in pure and mixed cultures and from chicken and feed samples, on the recovery rate of Salmonella after incubation in enrichment media was evaluated and no significant effects were found; however, aerobic incubation usually gave higher Salmonella counts. Greater recovery of Salmonella was obtained by incubating selective plating media aerobically rather than anaerobically. Aerobic incubation of liquid enrichment media and differential plating media is therefore recommended for optimal recovery of Salmonella .

The survival of Salmonella Montevideo and Salmonella heidelberg in dry milk, cocoa powder, poultry feed, and meat and bone meal was studied at three water activities (a w ) in the range of 0.4 to 0.75. S. montevideo was more resistant to the various dry environments than S. heidelberg . Salmonellae were enumerated immediately after inoculation, after 2 d, and after 1, 3, 7 and 14 wk. Survival was greater at a w of 0.43 and 0.52 than at 0.75 a w . Based on these findings and due to the marked differences in survival observed in the different products equilibrated at a specific a w value, it is concluded that the survival of salmonellae in a dry product cannot be predicted on the basis of the a w alone.

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.

The efficacy of four preenrichment media (lactose broth, lactose broth with Tergitol, buffered peptone and M-9) and of direct enrichment in selenite cystine and modified tetrathionate broths for recovering two Salmonella serotypes from dry poultry feed was determined. The salmonellae, artificially inoculated and stored for 7 wk in the dry feed (1.5 to 2.2 cells of salmonellae/g of feed analyzed), were recovered from significantly more samples after preenrichment with M-9 or buffered peptone than with any of the other procedures tested.

Recovery of pathogens from breast meat, thigh meat and skin from scalded, defeathered but uneviscerated broiler carcasses with and without spray washing was compared to recovery from breast meat, thigh meat and skin from fully processed, chilled carcasses (controls). The incidence of coagulase-positive staphylococci was not significantly different on meat and skin from both uneviscerated carcasses with and without a spray washing compared to meat and skin from fully processed carcasses. The incidence of Clostridium perfringens was not significantly different on skin, breast and thigh meat for any of the sampling sources except that incidence on meat from control breasts was lower than on breast meat from uneviscerated carcasses without spray-washing; and incidence on meat from control thighs was lower than on meat from spray-washed, uneviscerated carcasses. Salmonella incidence was higher on both breast and thigh meat from fully processed control carcasses than from uneviscerated unwashed carcasses. When uneviscerated carcasses were spray-washed after defeathering, the incidence of Salmonella was not significantly different on breast meat, and significantly lower on thigh meat than on these meats from fully processed control carcasses. Skin from fully processed control carcasses had a higher incidence of Salmonella than did skin from uneviscerated, unwashed carcasses, but not skin from uneviscerated, spray-washed carcasses. Reducing the number of stages of processing significantly reduced the incidence of Salmonella but not of coagulase-positive staphylococci or Clostridium perfringens .

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.

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.

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.

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.

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.

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 H 2 S/indole disk.

The accuracy of a miniaturized Enterobacteriaceae system (Micro-ID) was evaluated with 10 different genera grown on 11 selective plating media. Whenever growth occurred, the correct identification was made. In addition, 12 serotypes of Salmonella and 22 other strains of Enterobacteriaceae were grown on the two most common selective media used by food microbiologists for isolation of Salmonella [Brilliant Green Sulfa Agar (BGS) and Bismuth Sulfite Agar (BiS)]. The correct identification was made in all instances. The manufacturer of Micro-ID originally recommended that several colonies be picked for inoculation of the system. We modified the inoculation procedure so that only one colony was selected from a plate; this minimized the chances of having a mixed-culture inoculum. With this procedure, all 21 Enterobacteriaceae tested were correctly identified.

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.

Broiler carcasses were packed in low-permeability film bags that were evacuated, injected with CO 2 , then held at 2 C. Broilers were examined microbiologically and for off-odor to determine the shelf-life and types of bacteria. Vacuum level did not significantly affect bacterial counts. Broilers stored in 65% CO 2 had a 1-day longer shelf-life than those held in 20% CO 2 and about a 5-day longer shelf-life than ice-packed broilers. Spoiled carcasses from either 20 or 65% CO 2 packages had an acid-sour off-odor, and more than 90% of the bacteria present were Lactobacillus . Ice-packed broilers had the typical putrid off-odor at spoilage, and more than 95% of the bacteria were non-pigmented Pseudomonas .

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.