Automated food microbiology: potential for the hydrophobic grid-membrane filter.
Bacterial counts obtained on hydrophobic grid-membrane filters were comparable to conventional plate counts for Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus in homogenates from a range of foods. The wide numerical operating range of the hydrophobic grid-membrane filters allowed sequential diluting to be reduced or even eliminated, making them attractive as components in automated systems of analysis. Food debris could be rinsed completely from the unincubated hydrophobic grid-membrane filter surface without affecting the subsequent count, thus eliminating the possibility of counting food particles, a common source of error in electronic counting systems. (+info)
Salmonella infections in Norway: descriptive epidemiology and a case-control study.
The epidemiological progression of human salmonellosis in Norway is parallel to trends noted elsewhere in Europe. During the past two decades, the number of reported cases has increased steadily, with a special sharp rise in the early 1980s due to the emergence of Salmonella enteritidis, followed by a levelling off in recent years. However, in contrast to the situation in most other European countries, about 90% of the cases from whom a travel history is available, have acquired their infection abroad. The incidence of indigenous salmonella infections as well as the prevalence of the microorganism in the domestic food chain, are both comparatively low. In 1993-4, a national case-control study of sporadic indigenous salmonella infections was conducted to identify preventable risk factors and guide preventive efforts. Ninety-four case patients and 226 matched population controls were enrolled. The study failed to demonstrate any statistically significant association between salmonellosis and consumption of domestically produced red meat, poultry or eggs. The only factor which remained independently associated with an increased risk in conditional logistic regression analysis, was consumption of poultry purchased abroad during holiday visits to neighbouring countries. A separate analysis of Salmonella typhimurium infections incriminated food from catering establishments and foreign travel among household members, in addition to imported poultry. (+info)
An outbreak of viral gastroenteritis associated with consumption of sandwiches: implications for the control of transmission by food handlers.
Although food handlers are often implicated as the source of infection in outbreaks of food-borne viral gastroenteritis, little is known about the timing of infectivity in relation to illness. We investigated a gastroenteritis outbreak among employees of a manufacturing company and found an association (RR = 14.1, 95% CI = 2.0-97.3) between disease and eating sandwiches prepared by 6 food handlers, 1 of whom reported gastroenteritis which had subsided 4 days earlier. Norwalk-like viruses were detected by electron microscopy or reverse transcriptase-polymerase chain reaction (RT-PCR) in stool specimens from several company employees, the sick food handler whose specimen was obtained 10 days after resolution of illness, and an asymptomatic food handler. All RT-PCR product sequences were identical, suggesting a common source of infection. These data support observations from recent volunteer studies that current recommendations to exclude food handlers from work for 48-72 h after recovery from illness may not always prevent transmission of Norwalk-like viruses because virus can be shed up to 10 days after illness or while exhibiting no symptoms. (+info)
A general method for selection of alpha-acetolactate decarboxylase-deficient Lactococcus lactis mutants to improve diacetyl formation.
The enzyme acetolactate decarboxylase (Ald) plays a key role in the regulation of the alpha-acetolactate pool in both pyruvate catabolism and the biosynthesis of the branched-chain amino acids, isoleucine, leucine, and valine (ILV). This dual role of Ald, due to allosteric activation by leucine, was used as a strategy for the isolation of Ald-deficient mutants of Lactococcus lactis subsp. lactis biovar diacetylactis. Such mutants can be selected as leucine-resistant mutants in ILV- or IV-prototrophic strains. Most dairy lactococcus strains are auxotrophic for the three amino acids. Therefore, the plasmid pMC004 containing the ilv genes (encoding the enzymes involved in the biosynthesis of IV) of L. lactis NCDO2118 was constructed. Introduction of pMC004 into ILV-auxotrophic dairy strains resulted in an isoleucine-prototrophic phenotype. By plating the strains on a chemically defined medium supplemented with leucine but not valine and isoleucine, spontaneous leucine-resistant mutants were obtained. These mutants were screened by Western blotting with Ald-specific antibodies for the presence of Ald. Selected mutants lacking Ald were subsequently cured of pMC004. Except for a defect in the expression of Ald, the resulting strain, MC010, was identical to the wild-type strain, as shown by Southern blotting and DNA fingerprinting. The mutation resulting in the lack of Ald in MC010 occurred spontaneously, and the strain does not contain foreign DNA; thus, it can be regarded as food grade. Nevertheless, its application in dairy products depends on the regulation of genetically modified organisms. These results establish a strategy to select spontaneous Ald-deficient mutants from transformable L. lactis strains. (+info)
Pulsed-light inactivation of food-related microorganisms.
The effects of high-intensity pulsed-light emissions of high or low UV content on the survival of predetermined populations of Listeria monocytogenes, Escherichia coli, Salmonella enteritidis, Pseudomonas aeruginosa, Bacillus cereus, and Staphylococcus aureus were investigated. Bacterial cultures were seeded separately on the surface of tryptone soya-yeast extract agar and were reduced by up to 2 or 6 log10 orders with 200 light pulses (pulse duration, approximately 100 ns) of low or high UV content, respectively (P < 0.001). (+info)
Evaluation of accuracy and repeatability of identification of food-borne pathogens by automated bacterial identification systems.
The performances of five automated microbial identification systems, relative to that of a reference identification system, for their ability to accurately and repeatedly identify six common food-borne pathogens were assessed. The systems assessed were the MicroLog system (Biolog Inc., Hayward, Calif.), the Microbial Identification System (MIS; MIDI Inc., Newark, Del.), the VITEK system (bioMerieux Vitek, Hazelwood, Mo.), the MicroScan WalkAway 40 system (Dade-MicroScan International, West Sacramento, Calif.), and the Replianalyzer system (Oxoid Inc., Nepean, Ontario, Canada). The sensitivities and specificities of these systems for the identification of food-borne isolates of Bacillus cereus, Campylobacter jejuni, Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., and verotoxigenic Escherichia coli were determined with 40 reference positive isolates and 40 reference negative isolates for each pathogen. The sensitivities of these systems for the identification of these pathogens ranged from 42.5 to 100%, and the specificities of these systems for the identification of these pathogens ranged from 32.5 to 100%. Some of the systems had difficulty correctly identifying the reference isolates when the results were compared to those from the reference identification tests. The sensitivity of MIS for the identification of S. aureus, B. cereus, E. coli, and C. jejuni, for example, ranged from 47.5 to 72. 5%. The sensitivity of the Microlog system for the identification of E. coli was 72.5%, and the sensitivity of the VITEK system for the identification of B. cereus was 42.5%. The specificities of four of the five systems for the identification of all of the species tested with the available databases were greater than or equal to 97.5%; the exception was MIS for the identification of C. jejuni, which displayed a specificity of 32.5% when it was tested with reference negative isolates including Campylobacter coli and other Campylobacter species. All systems had >80% sensitivities for the identification of Salmonella species and Listeria species at the genus level. The repeatability of these systems for the identification of test isolates ranged from 30 to 100%. Not all systems included all six pathogens in their databases; thus, some species could not be tested with all systems. The choice of automated microbial identification system for the identification of a food-borne pathogen would depend on the availability of identification libraries within the systems and the performance of the systems for the identification of the pathogen. (+info)
Campylobacter jejuni is the most commonly reported bacterial cause of foodborne infection in the United States. Adding to the human and economic costs are chronic sequelae associated with C. jejuni infection--Guillian-Barre syndrome and reactive arthritis. In addition, an increasing proportion of human infections caused by C. jejuni are resistant to antimicrobial therapy. Mishandling of raw poultry and consumption of undercooked poultry are the major risk factors for human campylobacteriosis. Efforts to prevent human illness are needed throughout each link in the food chain. (+info)
Cyclospora: an enigma worth unraveling.
In part, Cyclospora cayetanensis owes its recognition as an emerging pathogen to the increased use of staining methods for detecting enteric parasites such as Cryptosporidium. First reported in patients in New Guinea in 1977 but thought to be a coccidian parasite of the genus Isospora, C. cayetanensis received little attention until it was again described in 1985 in New York and Peru. In the early 1990s, human infection associated with waterborne transmission of C. cayetanensis was suspected; foodborne transmission was likewise suggested in early studies. The parasite was associated with several disease outbreaks in the United States during 1996 and 1997. This article reviews current knowledge about C. cayetanensis (including its association with waterborne and foodborne transmission), unresolved issues, and research needs. (+info)