Taxonomical classification of 20 newly isolated Listeria bacteriophages by electron microscopy and protein analysis.

A set of 20 newly isolated temperate bacteriophages for phage typing of the pathogen Listeria monocytogenes has been investigated by means of electron microscopy and electrophoretic analysis of phage structural proteins. All phages had isometric capsids (60-64 nm diameter), and long contractile or non-contractile tails of 170-320 nm length. They could be classified into 2 morphotypes (A1 and B1) and were assigned to 3 listeriaphage species (4211, 2671, and 2389). Individual protein profiles were generated by SDS-PAGE of viral polypeptides, as well as isoelectric focusing of solubilized phage proteins in immobilized pH gradient gels. The major structural proteins ranged in size from approximately 15 to 38 kD, and showed isoelectric points from pI 4.3 to 6.2. Protein compositions permitted the differentiation of individual phages as well as the recognition and grouping of similar viruses.

Comparison of conventional and reversed phage typing procedures for identification of Listeria spp.

Of 225 Listeria isolates evaluated, 199 had the same bacteriophage patterns by both the conventional (A. Audurier, A.G. Taylor, B. Carbonelle, and J. McLaughlin, Clin. Invest. Med. 7:229-232, 1984) and the new, easier to apply, "reversed" (M. J. Loessner, Appl. Environ. Microbiol. 57:882-884, 1991) phage typing procedures, 5 had different phage reactions, and the remaining 21 isolates were untypeable. Thus, the overall typeability rate was 90.7%, and 97.6% of the typeable isolates had the same phage patterns by both procedures.

Recovery of Salmonella species from nonfat dry milk rehydrated under rapid and reduced pre-enrichment conditions: collaborative study.

A collaborative study was conducted to compare the relative efficiency of the AOAC rapid rehydration method with the reduced rehydration soak method for the recovery of Salmonella species from nonfat dry milk (NFDM). In the AOAC method, a 25 g sample of NFDM is rapidly rehydrated at a 1:9 sample/water ratio and mixed by swirling. After 60 min, the flask contents are adjusted to a pH of 6.8, and 0.45 mL of 1% aqueous brilliant green dye solution is added. The flasks are then incubated at 35 degrees C. In the soak method, a 25 g sample of NFDM is gently added to the sterile brilliant green (BG) water at a 1:9 sample/BG water ratio and allowed to soak undisturbed for 60 min at room temperature before incubation. Twelve collaborators analyzed 3 shipments of samples with the following results for the AOAC and soak methods: shipment 1-31 and 46 positive samples, respectively, with a 48% increase in detection by the soak method; shipment 3-45 and 66 positive samples, respectively, with a 47% increase in detection by the soak method; shipment 2--no significant difference in recovery of Salmonella species by the 2 methods. It is recommended that the official final action method for the detection of Salmonella species, 46.054-46.067, be revised to use the soak method for the analysis of nonfat dry milk.

Evaluation of the counterimmunoelectrophoretic (CIE) procedure in a clinical laboratory setting.

The counterimmunoelectrophoretic (CIE) procedure was evaluated under clinical laboratory conditions to determine its validity and comparability with culture methods. The procedure was further evaluated to determine applicability to a variety of clinical samples. An inexpensive set-up was developed to utilize the CIE procedure at bench level. Results indicated the procedure to be sensitive in detecting Haemophilus influenzae, type b, and Neisseria meningitidis (meningococcus), group B. The procedure was more sensitive for detection of H. influenzae, type b, than for meningococcus, group B. The authors have confirmed the usefulness of the CIE procedure in the detection of group B streptococci, pneumococci and teichoic acid antibody to Staphylococcus aureus. Detection of Escherichia coli K 1 antigen was also accomplished by CIE. In the authors' laboratory the CIE procedure was superior to culture methods when used for the detection of H. influenzae, type b, and meningococcus group B.