Recirculating immunomagnetic separation and optimal enrichment conditions for enhanced detection and recovery of low levels of Escherichia coli O157:H7 from fresh leafy produce and surface water.

The objective of this study was to develop a rapid, simple method for enhanced detection and isolation of low levels of Escherichia coli O157:H7 from leafy produce and surface water using recirculating immunomagnetic separation (RIMS) coupled with real-time PCR and a standard culture method. The optimal enrichment conditions for the method also were determined. Analysis of real-time PCR data (C(T) values) suggested that incubation of lettuce and spinach leaves rather than rinsates provides better enrichment of E. coli O157:H7. Enrichment of lettuce or spinach leaves at 42 degrees C for 5 h provided better detection than enrichment at 37 degrees C. Extended incubation of surface water for 20 h at 42 degrees C did not improve the detection. The optimized enrichment conditions were also employed with modified Moore swabs, which were used to sample flowing water sites. Positive isolation rates and real-time PCR results indicated an increased recovery of E. coli O157:H7 from all samples following the application of RIMS. Under these conditions, the method provided detection and/or isolation of E. coli O157:H7 at levels as low as 0.07 CFU/g of lettuce, 0.1 CFU/g of spinach, 6 CFU/100 ml of surface water, and 9 CFU per modified Moore swab. During a 6-month field study, modified Moore swabs yielded high isolation rates when deployed in natural watershed sites. The method used in this study was effective for monitoring E. coli O157:H7 in the farm environment, during postharvest processing, and in foodborne outbreak investigations.

Teaching the History of Microbiology and the Transformation of the Laboratory: A Study in Miniature.

This article presents a technique for bringing the history of microbiology to life in an exciting way. Eight miniature models were created, based on photographs or drawings, showing scientists at work in their labs. The models chosen represent important discoveries in microbiology, illustrating changes and advances in techniques and tools over the history of the discipline from 1600 through 2000. They serve as a novel and engaging teaching tool. While the instructor still presents the historic facts, the use of models provides the feeling of being there! They can also serve as a record for the future.

Survival of Bacteria in Food Cooked by Microwave Oven, Conventional Oven and Slow Cookers 1.

To assess the destructive effect of different cookery methods on bacteria, strains of Escherichia coli , Clostridium perfringens , Streptococcus faecalis and Staphylococcus aureus were used to inoculate a meatloaf preparation. After inoculation, a sample was withdrawn for bacterial analysis and the remainder of the meatloaf was divided and cooked by microwave oven, conventional oven and slow cooker. The temperature of the meatloaf was recorded at various locations immediately after cooking to obtain minimum, maximum and mean temperatures for each loaf. Also, just after cooking, representative samples were taken and analyzed by conventional means for the specific bacteria and for total bacterial content. Survival percentages were calculated and plotted against temperature for each cooking method. Temperature variation within the loaf was greatest for those cooked with microwaves and smallest for those cooked by the slow method. For each bacterial strain and the total count, the destructive effect of cooking method was not different at the 0.05 level of significance.

Colony Count Accuracy Using Selective Media: Analysts Versus Automatic Colony Counters 1, 2.

Using two different methods of counting, a comparison was made of the ability of five analysts to enumerate colonies on selective bacteriologic media. First, analysts manually counted the colonies aided by a Quebec colony counter and a hand tally. This was followed by the counting of colonies on each of three automated colony counters. In this pilot study, the media used included violet red bile agar. KF streptococcal agar, sulfite-polymyxin-sulfadiazine agar, and Standard Methods agar with 2,3,5 triphenyltetrazolium chloride added. The analysts' ability to count colonies on selective media by the manual method was superior to results obtained with the automatic colony counters.

Mutagenic Potential of Chemicals Associated with Tenebrionid Flour Beetle Secretions as Determined by the Ames Assay.

Infestation of flour and other stored products by the tenebrionid (flour beetles) has been proven a health hazard to the public. Secretions from these insects have been found to be harmful toxicologically. These secretions also possess characteristics typical of mutagens. Therefore the mutagenic potential of 2-methyl-1, 4-benzoquinone (MBQ), 2-ethyl-1, 4 benzoquinone (EBQ) and 1-pentadecene (P-dec) was assessed by using the Ames Salmonella/Mammalian Microsome Mutagenicity Assay, a screening test for detection of mutagens. Tester strains TA 98, TA 100, TA 1535, TA 1537, and TA 1538 were exposed to doses of 10-1 mg/plate to 3.2 × 10-5 mg of MBQ/plate, 10-2 mg/plate to 3.2 × 10-6 mg of EBQ/plate and 1 mg/plate to 3.2 × 10-4 mg of P-dec/plate. No evidence of mutagenic potential was observed at the levels tested.

Microbial Flora of Preseasoned Comminuted Turkey Meat.

Preseasoned comminuted turkey meat, prepared at the retail level, was examined and revealed the following levels of microbial contamination per gram: mean standard plate count 2.2 × 108, mean coliform plate count 2.0 × 105, Escherichia coli count 8.7. Gram-positive and gram-negative microbial flora were isolated and identified.

Comparison of Bacterial Species Isolated from Ground Beef, Textured Soy Protein and Ground Beef Extended with Textured Soy Protein 1, 2.

A survey of the bacterial species of public health importance which could be isolated from ground beef (GB), textured soy protein (TSP) and ground beef extended with TSP (SGB) after 3 and 10 days of storage at 4 C was conducted. Escherichia coli was the most frequent gram-negative isolate from GB and SGB. Few gram-negative organisms were found in TSP. Clostridium perfringens was the most frequent gram-positive isolate from GB and SGB while Bacillus sp. was isolated most frequently from TSP. Salmonella enteriditis ser. worthington was isolated from GB and TSP. These products contained a wide variety of microorganisms, some of which might result in a food-associated infection or intoxication. However, if properly handled and cooked before consumption, these products should present few public health hazards.

Bacterial Populations of Ground Beef, Textured Soy Protein and Ground Beef Extended With Soy Protein After 3 and 10 Days of Refrigerated Storage 1, 2.

A survey of the microbial populations of 31 samples of ground beef (GB), textured soy protein (TSP), and ground beef extended with TSP (SGB) after 3 and 10 days of storage at 4 C was done. Analyses included aerobic plate count (APC), psychrotrophic plate count (PPC), coliform Most Probable Number (CMPN) and plate determinations (CPC), Escherichia coli MPN (EMPN) and plate determinations (EPC), Staphylococcus aureus MPN, and fecal streptococcus plate count. Statistical analyses of data from the enumeration procedures showed significant increases in the total microbial flora after 10 days of storage. PPCs were significantly higher than APCs. CMPNs were significantly higher than CPCs for GB and SGB. The EMPNs were significantly higher than EPCs in SGB only. These products contained a variety of microorganisms many in large numbers; however if properly handled and cooked before consumption, these products should present no public health problems.

Accuracy and Speed in Counting Agar Plates 1.

To determine the accuracy of colony counts made by analysts, agar plates were photographed. The agar plates and photographs were compared to obtain a true count (photocount) which was used to determine analyst accuracy over selected count ranges. Analyst accuracy was also determined by comparing analyst's counts to the mean of the counts obtained by several analysts ("established standard"). The "established standard" compared favorably with the photocount. Analysts' counts were within 5% of the photocount and "established standard" on 60 and 68% of plates having 30-300 colonies and 60 and 67% on plates having 20-200 colonies, respectively. Average counting time for plates in the 10-100, 20-200, 30-300, and 40-400 colony count ranges was 18, 30, 41, and 52 sec, respectively. Plates having 20-200 colonies were as suitable for counting as plates having 30-300 colonies and were counted with a time-saving of 27%.