Comparison of membrane filtration and multiple-tube fermentation by the colilert and enterolert methods for detection of waterborne coliform bacteria, Escherichia coli, and enterococci used in drinking and bathing water quality monitoring in southern sweden.

A total of 338 water samples, 261 drinking water samples and 77 bathing water samples, obtained for routine testing were analyzed in duplicate by Swedish standard methods using multiple-tube fermentation or membrane filtration and by the Colilert and/or Enterolert methods. Water samples came from a wide variety of sources in southern Sweden (Skåne). The Colilert method was found to be more sensitive than Swedish standard methods for detecting coliform bacteria and of equal sensitivity for detecting Escherichia coli when all drinking water samples were grouped together. Based on these results, Swedac, the Swedish laboratory accreditation body, approved for the first time in Sweden use of the Colilert method at this laboratory for the analysis of all water sources not falling under public water regulations (A-krav). The coliform detection study of bathing water yielded anomalous results due to confirmation difficulties. E. coli detection in bathing water was similar by both the Colilert and Swedish standard methods as was fecal streptococcus and enterococcus detection by both the Enterolert and Swedish standard methods.

Elevated-temperature, colorimetric, monoclonal, enzyme-linked immunosorbent assay for rapid screening of Salmonella in foods: collaborative study.

A collaborative study was performed by 30 laboratories in 3 sets of trials to validate a modified colorimetric monoclonal enzyme-linked immunosorbent assay (ELISA) method for Salmonella detection. The modifications to the current methodology included incubation of enrichments and post-enrichments at an elevated temperature, addition of novobiocin to the M-broth post-enrichment, and elimination of the centrifugation and agitation steps. Five artificially contaminated foods (nonfat dry milk, milk chocolate, dried egg, ground black pepper, and soy flour) and 1 naturally contaminated food (raw ground turkey) were analyzed. The artificially contaminated foods were inoculated with individual Salmonella serotypes at a high (10-50 cells/25 g) and low (1-5 cells/25 g) contamination level. Results from the modified ELISA method were compared to the Bacteriological Analytical Manual (BAM)/AOAC culture method. In 2 of the food products, milk chocolate and pepper, a number of laboratories isolated Salmonella from un-inoculated control samples, thus invalidating their data. As a result, there were too few laboratories remaining with valid data, and these foods were repeated. In the completed study, there were 11 false negative results obtained by the modified ELISA method, while there were 28 false negatives produced by the BAM/AOAC procedure. There were 11 ELISA positive assays which could not be confirmed by culture methods. Statistically, there were no differences between the modified, colorimetric, monoclonal ELISA and the reference culture method in all foods except raw turkey, where the ELISA method was more productive. The colorimetric monoclonal enzyme immunoassay (Salmonella-Tek) method for detecting Salmonella in all foods has been adopted first action by AOAC INTERNATIONAL.

Use of an Elevated Temperature and Novobiocin in a Modified Enzyme-linked Immunosorbant Assay for the Improved Recovery of Salmonella from Foods.

A modified colorimetric enzyme-linked immunosorbant assay (ELISA) for Salmonella detection was compared to the standard culture method of the Bacteriological Analytical Manual/Association of Official Analytical Chemists (BAM/AOAC) using 20 artificially contaminated foods (1,200 test samples). The modifications to the current methodology consisted of an elevated incubation temperature of 42°C for the tetrathionate selective broth and M-broth postenrichments, as well as addition of 10 µg/ml novobiocin to the M-broth. The microtiter plate as not agitated during assay incubation, and centrifugation steps were eliminated from the protocol. This modified ELISA method was at least as productive as the standard AOAC culture method for the food samples tested. No false-positive reactions were encountered. The false-negative incidence was 1.5% for the immunoassay and 5.3% by the AOAC cultural method. The incidence of agreement between the methods was 96.7%.

The behavior of selected microorganisms during the manufacture of high moisture Jack cheeses from ultrafiltered milk.

Whole milk was pasteurized and concentrated two times by ultrafiltration. Starter cultures, Lactococcus lactis ssp. cremoris and Lactococcus lactis ssp. lactis, were propagated in either reconstituted skim milk, two times UF retentate, or UF permeate, or a direct vat system was used for the starter culture. The cheese milk was simultaneously inoculated with starter culture and Pseudomonas fragi 4973, Staphylococcus aureus 196E, and Salmonella typhimurium var. Hillfarm. Control whole milk, UF control milk, inoculated whole milk, and inoculated UF milk were made into Monterey Jack cheese using traditional procedures. The process of cheese manufacture was followed by determination of pH, titratable acidity, and microbial population levels. The cheeses were stored for 6 mo and analyzed every month for percentage solids and microbial population levels. Generally, numbers of contaminant microbes increased at a similar rate during manufacture in all cheeses. During the 6-mo ripening period, bacterial starter culture population levels remained high, psychrotrophs declined slowly, Staphylococcus levels remained stable, and Salmonella populations decreased. No Staphylococcus enterotoxin was detected by reverse passive latex agglutination assay.

Characterization and Behavior of Salmonella javiana During Manufacture of Mozzarella-type Cheese 1.

A patient isolate of Salmonella javiana implicated in an outbreak of salmonellosis in Minnesota was characterized and used to examine its response to Mozzarella manufacturing conditions. The strain possessed biochemical-metabolic activities typical of Salmonella species. Growth was observed in 6.5% NaCl Trypticase Soy Broth (TSB) but not in 12% NaCl TSB. This S. javiana strain was resistant to two antibiotics, penicillin G and erythromycin. Pasteurization trials indicated the strain did not survive pasteurization and that pasteurization affected a log reduction of greater than 9 cycles. Mozzarella-type cheese was manufactured from milk inoculated with S. javiana at levels of 1 × 104 and 1 × 106 per ml milk. Manufacturing process was monitored by following pH, titratable acidity, and temperature. Survival of S. javiana was monitored using traditional enrichment procedures and direct plating procedures. S. javiana survived and grew through the acid-ripening phase, but temperatures attained in cheese mass during stretching and molding (60°C, 140°F) killed all Salmonella present. No subsequent process steps were found positive for Salmonella .