Comparative evaluation of desoxycholate citrate medium and xylose lysine desoxycholate medium in the isolation of shigellae

External Quality Assessment in the Evaluation of Laboratory Performance of Faecal Culture

In Finland, all laboratories carrying out diagnostics of infectious diseases in humans are approved by the Regional State Administrative Agencies and are obligated to participate in External Quality Assurance rounds. Performance in these rounds is thought to reflect the quality of laboratory work. In the 6-year study period, 17 Finnish laboratories received 48 simulated faecal specimens for the culturing of diarrhoeal pathogens, yielding altogether 586 faecal culture External Quality Control specimens and 581 reports. The results were correct in 92% of all reports and in 67% of all specimens. False-negative Salmonella results were given for 2 of the 18 specimens, one with biochemically atypical Salmonella strain and the other with a low count of Salmonella cells. False-negative Shigella report was given for 6 of the 7 specimens in some participating laboratory. Detection of all common faecal pathogens is especially relevant to patient safety, public health, and epidemiological surveillance.

Shigellaas 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.

Assessment of the effects of Nurmi-type cultures and a defined probiotic preparation on a Salmonella typhimurium 29E challenge in vivo

The effects of treatment with an undefined commercial Nurmi-type culture (NTC), cultured cecal contents, and a dual-strain probiotic, containing Enterococcus faecalis and Pediococcus pentosaceus, on Salmonella Typhimurium colonization were evaluated in a specific-pathogen-free bird model. Two sets of trials were performed, and each study was arranged as a randomized complete block design with three treatments. Treatments consisted of (i) control, (ii) commercial NTC, and (iii) cultured cecal contents in the first set of trials and (i) control, (ii) defined probiotic, and (iii) cultured cecal contents in the second set. On day 1, birds were administered 1.2 x 10(7) CFU of the appropriate treatment by oral gavage. On day 3, all birds were challenged with 1 x 10(6) CFU of Salmonella Typhimurium 29E (nalidixic acid resistant). Chicks were asphyxiated with argon gas on day 10, and ceca were aseptically removed. Salmonella Typhimurium counts (CFU per milliliter of cecal contents) were determined on brilliant green agar containing 30 mg of nalidixic acid per liter, and CFU counts were log transformed prior to analysis. Cecal pH and volatile fatty acid concentrations were also determined. Data were analyzed by one-way analysis of variance, and means were compared by Tukey's pairwise analysis. Commercial NTC and cultured cecal contents treatments resulted in a significant decrease (P < or = 0.05) in Salmonella Typhimurium 29E colonization, with the NTC offering a higher level of protection. In the second set of trials, the defined probiotic tended to reduce colonization by Salmonella Typhimurium (P = 0.07), while chicks treated with cultured cecal contents displayed a significant decrease (P = 0.03) when compared to the negative control. No significant change was observed in cecal pH or in acetate and propionate concentrations; however, a significant increase in butyrate concentrations in both the cultured cecal contents and defined probiotic treatment groups was observed when compared to the control birds. These observations suggest that defined cultures are less effective Salmonella control agents than are preparations generated from the complete cecal microflora.

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.