Multistate shigellosis outbreak and commercially prepared food, United States.

In 2000, shigellosis traced to a commercially prepared dip developed in 406 persons nationwide. An ill employee may have inadvertently contaminated processing equipment. This outbreak demonstrates the vulnerability of the food supply and how infectious organisms can rapidly disseminate through point-source contamination of a widely distributed food item.

Industry practices and compliance with U.S. Food and Drug Administration guidelines among California sprout firms.

Since 1995, raw vegetable sprouts have been implicated as the vehicle of infection in 15 foodborne outbreaks involving Salmonella and 2 foodborne outbreaks involving Escherichia coli O157:H7. To reduce the numbers of sprout-related outbreaks, the U.S. Food and Drug Administration (FDA) published Guidance for Industry: Reducing Microbial Food Safety Hazards for Sprouting Seeds in 1999. Between October 2000 and April 2001, 61.5% (16 of 26) of the known commercial sprout firms in California were enrolled in a survey to evaluate the industry practices of California sprouting operations and to determine compliance with FDA guidelines. A standardized questionnaire was used to collect data on firm demographics and seed disinfection practices. Additionally, free chlorine levels in seed disinfection solutions were measured, and 48-h spent irrigation water samples were collected from each firm. The irrigation water was screened for Salmonella and E. coli O157:H7 with FDA-recommended test kits. Free chlorine levels in the treatment solutions ranged from 50 to 35,000 mg/liter (ppm), with a median of 14,000 mg/liter (ppm). Free chlorine levels were higher for firms producing alfalfa sprouts than for those producing only mung bean or soybean sprouts (P=0.03). Levels of free chlorine tended to be higher for firms using a calcium hypochlorite treatment solution than for firms using a sodium hypochlorite treatment solution (P=0.067). All 32 irrigation water samples screened for Salmonella tested negative. Of the irrigation water samples tested for E. coil O157:H7, 75% (24 of 32) tested negative, and 25% (8 of 32) tested presumptive positive. The eight presumptive positive samples were found to be negative after further testing. These results indicate that producers of alfalfa sprouts are generally achieving the FDA-recommended calcium hypochlorite level of 20,000 mg/liter (ppm), whereas mung bean sprout producers are not.

Thermal Resistance of Salmonella spp. and Listeria monocytogenes in Liquid Egg Yolk and Egg Yolk Products †.

The effectiveness of various pasteurization procedures in destroying Listeria monocytogenes and Salmonella enteritidis in liquid egg products was evaluated. Survivor studies were perfonned on individual strains of L. monocytogenes and L. innocua in commercially broken raw egg yolk samples after heating at 61.1, 63.3, and 64.4°C using submerged vials, and on Salmonella spp. at 60.0, 61.1, and 62.2°C. Surviving bacteria were enumerated on TSA and results expressed as D-values. The influence of aw -lowering ingredients such as salt and sugar on thermal resistance in yolk was investigated using a five-strain mixture of L. monocytogenes or a mixture of Salmonella spp. (four strains of S. enteritidis , one stain each of S. senftenberg and S. typhimurium ) at 61.1°C to 66.7°C. At 61.1°C (present minimum temperature for pasteurization of plain egg yolk), a 7-log-unit reduction of Salmonella took 1.4 to 2.4 min, whereas a 7-log-unit reduction of L. monocytogenes took 4.9 to 16.1 min. The D-value for L. monocytogenes at 64.4°C increased from 0.44 min in plain yolk to 8.26 min after a 21.5-min lag (total time to achieve 1-log-unit reduction was 30.7 min) in yolk with 10% salt and 5% sugar, and 27.3 min after a 10.5-min lag (total time 37.8 min for 1-log-unit reduction) in yolk with 20% salt. The D-value for Salmonella in egg yolk at 64.4°C was < 0.2 min, but when 10% salt was added, the D-value was 6.4 min. Aw -lowering solutes in liquid egg yolk increased the thermal resistance of Salmonella and L. monocytogenes .

Evaluation of Commercial Immunochemical Assays for Detection of Sulfamethazine in Milk.

Sulfamethazine (SMZ) is effective in the treatment of bacterial infections in food producing animals but its use is prohibited in dairy cows. Nevertheless, a 1988 survey of milk in ten cities conducted by the Food and Drug Administration revealed the presence of SMZ. Therefore, it was apparent that there was a need for rapid screening methods for SMZ. We evaluated commercial immunochemical test kits for SMZ with detectabilities of 1-10 parts per billion (ppb). Manipulations are suggested to effectively optimize immunochemical detection of SMZ in raw and processed fluid milk. The performances of the enzyme immunochemical test kits were evaluated by studying the effects of sample preparation, sample matrix, calibration and detection range of the kits using raw and processed milk samples. Immunochemical results were compared to quantitative high performance thin layer chromatography and high performance liquid chromatography with electrochemical detection. Both chromatographic methods had detectabilities in the low parts per billion range.