Shigella as a foodborne pathogen and current methods for detection in food.

Shigella, the causative agent of shigellosis or "bacillary dysentery," has been increasingly involved in foodborne outbreaks. According to the Centers for Disease Control and Prevention's Emerging Infections Program, Foodborne Diseases Active Surveillance Network (FoodNet), Shigella was the third most reported foodborne bacterial pathogen in 2002. Foods are most commonly contaminated with Shigella by an infected food handler who practices poor personal hygiene. Shigella is acid resistant, salt tolerant, and can survive at infective levels in many types of foods such as fruits and vegetables, low pH foods, prepared foods, and foods held in modified atmosphere or vacuum packaging. Survival is often increased when food is held at refrigerated temperatures. Detection methods for Shigella include conventional culture methods, immunological methods, and molecular microbiological methods. Conventional culture of Shigella in foods is often problematic due to the lack of appropriate selective media. Immunological methods for Shigella have been researched, yet there is only one commercially available test kit. Molecular microbiological methods such as PCR, oligonucleotide microarrays, and rep-PCR have also been developed for the detection and identification of Shigella. This manuscript reviews the general characteristics, prevalence, growth and survival, and methods for detection of Shigella in food.

Comparison of chromogenic Shigella spp. plating medium with standard media for the recovery of Shigella boydii and Shigella sonnei from tomato surfaces.

Isolation of Shigella spp. from food is difficult because of a lack of appropriate selective media and the presence of low numbers of shigellae relative to competitive microorganisms. Chromogenic Shigella spp. plating medium (CSPM) was evaluated for use with the U.S. Food and Drug Administration Bacteriological Analytical Manual (BAM) enrichment procedure for isolation of artificially contaminated Shigella boydii UI02 and Shigella sonnei UI05 from tomato surfaces. Tomatoes were inoculated with various concentrations of S. boydii UI02 or S. sonnei UI05 and rinsed using a shake-rub-shake procedure. Tomato rinses were enriched overnight according to the BAM procedure and streaked for isolation on CSPM, Salmonella-Shigella agar (SSA), and MacConkey agar (MAC). To access the isolation of S. boydii UI02 and S. sonnei UI05 without competition from natural tomato microflora, experiments were repeated using rifampin-adapted inocula and enrichments supplemented with 50 microg/ml rifampin. Isolation of S. boydii UI02 and S. sonnei UI05 with or without natural tomato microflora was not significantly different (P > 0.05) on CSPM, MAC, or SSA. Colony color enhancements created by CSPM may ease differentiation of Shigella colonies from those of closely related competitors.

Comparison of conventional culture methods and FTA filtration-nested PCR for the detection of Shigella boydii and Shigella sonnei on tomato surfaces.

Detection of Shigella boydii UI02 and Shigella sonnei UI05 artificially inoculated onto tomatoes was evaluated using enrichment protocols of the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) and the American Public Health Association's Compendium of Methods for the Microbiological Examination of Food (CMMEF), enrichment in Enterobacteriaceae enrichment (EE) broth supplemented with 1.0 microg/ml novobiocin and incubated at 42 degrees C, and FTA filtration-nested PCR. To assess the effect of natural tomato microflora on recovery, conventional culture enrichments were repeated using rifampin-adapted inocula and enrichment medium supplemented with 50 microg/ml rifampin. The lowest detection levels for S. boydii UI02 were > 5.3 x 10(5) (BAM, CMMEF, and EE broth) and 6.2 CFU per tomato (FTA filtration-nested PCR). For S. sonnei UI05, the lowest detection levels were 1.9 x 10(1) (BAM), 1.5 x 10(3) (CMMEF), 1.1 x 10(1) (EE broth), and 7.4 CFU per tomato (FTA filtration-nested PCR). Natural tomato microflora had a large impact on recovery of S. sonnei UI05 and completely inhibited recovery of S. boydii UI02. EE broth was inhibitory to S. boydii UI02. FTA filtration-nested PCR provided superior detection (P < 0.05) compared with the conventional culture enrichment protocols.

Standardization of a method to determine the efficacy of sanitizers in inactivating human pathogenic microorganisms on raw fruits and vegetables.

The efficacy of sanitizers in killing human pathogenic microorganisms on a wide range of whole and fresh-cut fruits and vegetables has been studied extensively. Numerous challenge studies to determine the effects of storage conditions on survival and growth of pathogens on raw produce have also been reported. Results of these studies are often difficult to assess because of the lack of sufficient reporting of methods or, comparatively, because of variations in procedures for preparing and applying inocula to produce, conditions for treatment and storage, and procedures for enumerating pathogens. There is a need for a standard method to accurately determine the presence and populations of pathogenic microorganisms on produce. The adoption of standard, well-characterized reference strains would benefit a comparative assessment of a basic method among laboratories. A single protocol will not be suitable for all fruits and vegetables. Modifications of a basic method will be necessary to achieve maximum recovery of pathogens on various types of produce subjected to different sanitizer or storage treatments. This article discusses parameters that must be considered in the course of developing a basic standard method against which these modifications could be made.

Microscopic observation and processing validation of fruit sanitizing treatments for the enhanced microbiological safety of fresh orange juice.

Studies were conducted to evaluate the infiltration of dye and bacteria into the interior of orange fruit and the impact of possible infiltration on achieving a 5-log microbial reduction during fresh juice processing. Fresh orange fruit were treated at the stem end area with dye and either Salmonella Rubislaw or Escherichia coli strains expressing green fluorescent protein. Microscopic images showed that bacterial contaminants localized at the surface or near surface areas that may be sanitized by surface treatments. Dye infiltration was not a reliable indicator of bacterial penetration in citrus fruit. To quantify the reduction of bacterial contamination, orange fruit were inoculated with E. coli and processed with and without hot water treatments. Greater than 5-log reductions were achieved in juice extracted from fruit immersed in hot water for 1 or 2 min at 80 degrees C, in comparison to the E. coli level detected in the control juice obtained by homogenization of inoculated fruit.

Coliforms, Escherichia coli and Salmonella serovars associated with a citrus-processing facility implicated in a salmonellosis outbreak.

A salmonellosis outbreak occurred during the summer of 1995 among individuals who consumed nonpasteurized orange juice from a Florida citrus-processing facility. Clinical isolates were identified by the Centers for Disease Control as Salmonella serovars Hartford, Gaminara, and Rubislaw. At the processing facility, 70 samples (equipment swabs, fruit surface swabs, juice, and miscellaneous environmental samples) were collected before, during, and after processing runs on two different dates. Bottled juice samples from eight previous extraction dates were also collected. Total plate counts, fecal coliforms, and Escherichia coli were enumerated from each sample. Analysis for Salmonella cells were conducted on all juice samples, fruit surface swabs, environmental samples, and selected equipment swabs using direct enrichment and pre-enrichment techniques. Salmonella serovars Hartford, Rubislaw, Saintpaul, and Newport were detected from either juice, unwashed fruit surfaces, or amphibians (Hyla cinerea and Bufo terrestris) captured outside the processing building. Salmonella cells in juice were associated with population levels of fecal coliforms and E. coli above the upper most probable number (MPN) limits of detection (> 110/ml).

Public health and nonpasteurized fruit juices.

Well publicized outbreaks of foodborne illness have occurred in recent years due to consumption of commercial, nonpasteurized ("fresh" or "unpasteurized") fruit juices. Nonpasteurized and heat treated juices have been associated with at least 15 foodborne illness outbreaks since the early 1900s. Disease syndromes have included salmonellosis, typhoid fever, cyrptosporidiosis, Escherichia coli-related diarrhea, and hemolytic uremia. Mortality has occasionally occurred during these outbreaks. An increase in the number of reported outbreaks in recent years possibly reflects greater consumption of fresh juices and closer scrutiny of these products by medical and public health authorities. This article reviews the fruit juice borne outbreaks in the 1900s, methods to control pathogens, and regulatory issues related to production of nonpasteurized fruit juices in the U.S.

Investigation of the Microbial Ecology of Commercial Grapefruit Sections 1.

Commercially prepared grapefruit sections were qualitatively surveyed for microorganisms prior to heat processing. The micro flora included 7 genera of yeasts ( Candida , Cryptococcus , Hansenula , Rhodotorula , Saccharomyces , Torulaspora , Trichosporon , Zygosaccharomyces ), 12 genera of molds ( Aspergillus , Aureobasidium pullulans , Byssochlamys , Cladosporium , Fonseceae , Fusarium , Geotrichum , Mucor , Penicillium , Rhizopus , Trichoderma , Trichophyton ), and 2 of bacteria ( Lactobacillus and Leuconostoc ). A quantitative analysis of the native microflora indicated that the overall microbial population was capable of significant growth (p ≥ 0.05) at 25°C within 2 to 4 h in the unprocessed product.