Aims: The aim of this study was to evaluate the performance of chromogenic agars, Agar Listeria according to Ottaviani and Agosti (ALOA) and Rapid L. mono agar, compared with Oxford agar for the enumeration and detection of Listeria species in food. Methods and Results: A total of 170 food samples were examined using the three plating media. Listeria species were isolated from 63 samples. In contrast to Oxford agar, detection of Listeria colonies on chromogenic media was as good after 24 h of incubation of plates as after 48 h. While there was no significant difference in recovery of Listeria monocytogenes on the three media, recovery of other Listeria species was significantly poorer on Rapid L. mono agar compared with Oxford and ALOA agars. Recovery of species other than L. monocytogenes was significantly improved by including a secondary enrichment stage in the detection method. Conclusions: Using chromogenic agars, presumptive identification of L. monocytogenes is possible after 24 h, compared with 3-4 days using Oxford agar. However, the poor detection of species other than L. monocytogenes on Rapid L. mono agar is a disadvantage of this medium. Significance and Impact of the Study: This study provides new information regarding the isolation of Listeria species other than L. monocytogenes from food using chromogenic plating media. This is important, as nonpathogenic Listeria species act as markers for the likelihood of presence of L. monocytogenes and allow preventive action to be taken to avoid its presence.

A microbiological survey was performed on 4 selected imported spices: black peppercorns, white peppercorns, coriander, and fennel seed. Aerobic plate count values ranged from 104 to 107 colonyforming units (CFU)/g for black and white peppercorns and from 103 to 105 CFU/g for coriander and fennel seed. Combined results of the 3-tube most probable number procedure and the API 20E kit indicated the presence of Escherichia coli in 4 test samples of black peppercorns, 1 test sample of white peppercorns, and 1 test sample of coriander. Two test samples of black peppercorns were positive for Salmonella contamination. Among the various Enterobacteriaceae isolated from the spices, Enterobacter cloacae and Klebsiella pneumoniae were found most frequently in all spice types. Of 18 mammalian and avian fecal pellets removed from the spices and analyzed microbiologically, E. coli was found in only 2 pellet specimens. There was no apparent relationship between the enteric microflora found in spices and those found in the fecal pellets.

During September and October 2002, 3,662 prepackaged raw meat samples were collected to evaluate the extent and nature of microbiological contamination on external surfaces of the packaging, which could potentially cross-contaminate ready-to-eat foods during and after purchase. Salmonella was detected on two (<1%) samples of external packaging (both from raw chicken), and Campylobacter was detected on 41 (1.1%) samples of external packaging. The external packaging of game fowl exhibited the highest Campylobacter contamination (3.6%), followed by raw chicken (3.0%), lamb (1.6%), turkey (0.8%), pork (0.2%), and beef (0.1%); Campylobacter jejuni and Campylobacter coli accounted for 59% (24 of 41) and 24% (10 of 41) of the contaminating Campylobacter species, respectively. C. coli isolates from the external packaging were more multiresistant to antimicrobial drugs, including quinolones such as ciprofloxacin, than was C. jejuni. Escherichia coli (an indicator of fecal contamination) was isolated from the external packaging on 4% of the raw meat samples at levels of 40 to 10(5) CFU per swab. The external packaging of raw meats is a vehicle for potential cross-contamination by Campylobacter, Salmonella, and E. coli in retail premises and consumers' homes. The external surface of heat-sealed packaging was less frequently contaminated with Campylobacter and E. coli compared with other types of packaging (e.g., overwrapping, bag, and tie tape) (P < 0.0001 to 0.01). In addition, external packaging of raw meats was contaminated less frequently with Campylobacter and E. coli when packaging was intact, packaging and display areas were visually clean, display temperatures were below 8 degrees C, and hazard analysis systems were in place.

Commercially shredded cabbage distributed at the retail level is usually packaged under vacuum or in a modified atmosphere of nitrogen and carbon dioxide to suppress proliferation of aerobic spoilage microorganisms. The ability of Shigella sonnei to survive and grow in shredded cabbage packaged under these conditions was determined by the 3-tube most probable number procedure. After artificial inoculation with S. sonnei at one of three different levels, the shredded cabbage was packaged aerobically, under vacuum, or under modified atmosphere (30% nitrogen and 70% carbon dioxide) and stored at room temperature (24 ± 2°C) or under refrigeration (0–6°C). For most levels of inoculation, S. sonnei tended to increase or remain relatively high for 1–3 d in cabbage packaged under all three conditions and stored at room temperature. However, after 3 d of storage at this temperature, S. sonnei approached indeterminately low levels. The steady decrease of pH values of shredded cabbage over the storage period may have contributed to the decrease of S. sonnei. Under refrigeration, however, both the S. sonnei levels and the pH values remained relatively constant. The results indicate that S. sonnei can survive and even proliferate in shredded cabbage packaged and stored under a vacuum or modified atmosphere as well as aerobic conditions, thereby posing a potential hazard to the consumer.

A study of retail modified-atmosphere-packed and vacuum-packed cooked ready-to-eat meats was undertaken from September through mid-November 2003 to determine the microbiological quality at the end of shelf life and to establish any risk factors in the production, storage, and display of this product. Examination of 2,981 samples using Microbiological Guidelines criteria revealed that 66% were of satisfactory or acceptable microbiology quality, 33% were of unsatisfactory quality mainly due to high aerobic colony counts and Enterobacteriaceae concentrations, and 1% were of unacceptable quality due to the presence of Listeria monocytogenes at 100 CFU/g or higher (27 samples; range of 10(2) to 106 CFU/g) and Campylobacter jejuni (1 sample), indicating a risk to health. All samples at the end of the shelf life had satisfactory (<20 CFU/g) and/or acceptable (<102 CFU/g) levels of Staphylococcus aureus and Clostridium perfringens, four samples (<1%) had unsatisfactory levels of Escherichia coli (range of 102 to 106 CFU/g) and 5.5% of the samples contained L. monocytogenes at <20 CFU/g (4.8%) or between 20 and 100 CFU/g (0.7%). More samples of chicken (45%; 224 of 495 samples), beef (43%; 160 of 371 samples), and turkey (41%; 219 of 523 samples) were of unsatisfactory or unacceptable quality compared with ham (23%; 317 of 1,351 samples) or pork (32%; 67 of 206 samples). Twelve different L. monocytogenes typing characters (serotype-amplified fragment length polymorphism type-phage type) were evaluated for isolates recovered from samples of unacceptable quality, and the 1/2-IX-NT type was recovered from almost half (48%) of these samples. Salmonella was not detected in any samples examined. Risk factors identified for cooked meats that were microbiologically contaminated more frequently included vacuum packaging, packaging on retail premises, slicing, temperature not monitored in display units, and no hazard analysis system in place. Results from this study also suggest that the shelf life assigned to some modified-atmosphere-packed and vacuum-packed meats may not be appropriate.