G.W. Reinbold

The most suitable number of colonies on plates for counting.

Major events that led to acceptance of 30 to 300 as the most suitable number of colonies on plates for counting were reviewed. Three new sets of data were collected, involving triplicate plates of fifteen 1: 1.4 serial dilutions of 65 samples of raw milk. Statistical methods were developed to analyze bias (variability introduced primarily by crowding and analyst counting errors) and variance (sampling and dilution errors). Bias and variance were combined as mean-squared error, which was expresed as a function of the number of colonies per plate, The counting range that minimized the mean squared error could then be determined for selected dilution series. For two-fold, five-fold and ten-fold dilution series, respectively, the most suitable limits on plates for counting were 70 to 140, 40 to 200 and 25 to 250 colonies/plate. A range of 25 to 250 colonies/plate was suggested for the analysis of dairy products. Limitations in application of the data to other systems are discussed.

Media and methods for isolation and enumeration of the Enterococci.

Publisher Summary In this chapter, an overview on the media and methods for isolation and enumeration of the enterococci is illustrated. A comprehensive comparison of media and methods representative of all of those presently available is urgently needed. These media and methods should be utilized simultaneously, using the same samples or subsamples. Subsamples would probably be necessary because the study should include interlaboratory or, preferably, intercontinental collaboration. Isolation and quantification of the fecal streptococci in natural materials of all types should be examined. Only when such experiments are completed, optimum procedures can be selected for specific applications with a reasonable degree of confidence. This chapter briefly explains the types of media available, and also the comparative studies of media and methods.

Indicator organisms—A review. I. Taxonomy of the fecal streptococci1

ABSTRACT The terms “enterococci,” “fecal streptococci” and “group D streptococci” are discussed and defined. Development of the taxonomy of the fecal streptococci is described. Physiological differences, serology, the chemical basis of serological specificity and some other possible taxonomic approaches are elaborated upon.

Ultrastructures of Bacteriophages Active Against Streptococcus thermophilus, Lactobacillus bulgaricus, Lactobacillus lactis and Lactobacillus helveticus1

Several strains of phages active against Streptococcus thermophilus and species of Lactobacillus were examined with an electron microscope after negative staining with phospho-tungstic acid or uranyl acetate. S. thermophilus bacteriophage exhibited exceptionally long tails (polytails). The width and structure of the polytail was the same as a normal phage tail, 10 nm, but was 2 to 4 times longer, 480-960 nm. Preparations revealed extensive adsorption of S. thermophilus bacteriophage to broken bacterial cell walls. One strain of S. thermophilus phage had a spherical structure at the posterior end of its tail. The bacteriophages of Lactobacillus bulgaricus and Lactobacillus helveticus had a distinct contractile tail sheath, whereas Lactobacillus lactis phage did not.

Simplified, Rapid Method to Measure Diameter of Bacteriophage Plaques1

A procedure is described for accurately determining the diameter of bacteriophage plaques down to .05 mm in diameter.