Transfer of Firmly Attached 32P- Salmonella typhimurium from Raw Poultry Skin to Other Surfaces.

Salmonellae adhere firmly to poultry skin during processing. Loosely attached bacteria cross-contaminate work surfaces. This study was undertaken to determine if firmly attached bacteria present a health hazard through transfer to work surfaces. Attached 32P-labeled S. typhimurium cells were serially rinsed with 2 to 4 L of Salmonella -free potable tap water or with sterile 0.85% NaCl. Rinsing removed 61 to 89% of attached labeled cells. However, after rinsing, 11 to 39% of cells remained attached, and of these, 3 to 10% were able to detach and transfer from skin to stainless steel surfaces. It was concluded that large rinse volumes may not remove all attached salmonellae from poultry skin surfaces and the potential for cross-contamination does exist.

Modified Procedure to Inoculate Micro-ID.

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.

Comparative Study of Micro-ID, Minitek and Conventional Methods with Enterobacteriaceae Freshly Isolated from Foods.

A total of 400 Enterobacteriaceae isolates freshly taken from broiler carcasses, ground beef, pork sausage, raw shrimp, pre-wrapped sandwiches, raw carrots, lettuce and fresh strawberries was inoculated into the 15 biochemical tests of the Micro-ID (4-h) system and into the 15 corresponding tests in the Minitek (24-h) and conventional systems. For each food there were 750 biochemical test comparisons (50 isolates × 15 tests). The overall agreement between Micro-ID and conventional tests was 96.8%, whereas the agreement between Minitek and conventional tests was 93.6%. Three laboratory technicians who independently recorded results of 6000 biochemical tests from each of the three systems were in complete agreement for 99.3%, 98.9% and 99.7% of the Micro-ID. Minitek and conventional tests, respectively. Thus results obtained with the miniaturized systems were as easy to read and interpret as conventional tests in tubes. The most frequently encountered Enterobacteriaceae from these foods were Escherichia coli (broiler carcasses, pork sausage). Enterobacter agglomerans (carrots, lettuce, shrimp, strawberries), Enterobacter cloacae (pre-wrapped sandwiches), and Serratia liquefaciens (ground beef).

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.

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.

Relation of Enterobacteriaceae Counts to Salmonella Contamination of Market Broilers.

We determined the Enterobacteriaceae counts and the Salmonella status (positive or negative) of 20 individual birds in each of 12 groups of broiler carcasses. The overall logarithmic mean Enterobacteriaceae count for the 240 carcasses was 2.7 with group means ranging from 1.8 to 3.6. One hundred and twenty three (51.2%) of the 240 carcasses were Salmonella -positive. The number of Salmonella - positive carcasses within groups ranged from 0 to 18. No relationship was found between Enterobacteriaceae counts and presence of Salmonella in broiler carcasses.