Comparison of Methods for Enumerating Fluorescent Bacteria

Comparable numbers of fluorescent bacteria may be obtained by either the most-probable-number procedure or by preparing spread plates on modified Henrici agar.     

Comparison of Several Methods for Preserving Bacteriophages

A wide variety of bacteriophages were processed and stored under different conditions to compare methods for long-term preservation. Specimens were stored for 2 years at room temperature (24 to 28 C) and at 4 C as broth lysates in 50% glycerol, dried, and freeze-dried. Titers determined after processing indicated that, of the broth, glycerol, and freeze-dry methods, freeze-drying was most damaging to the phages tested, glycerol less damaging, and the broth method least damaging. After 2 years, titers of broth lysates were generally higher than those of glycerol or freeze-dried preparations. Dried preparations generally did not prove satisfactory. Preparations stored at 4 C showed better titers than those kept at room temperature. All titers declined with time regardless of the conditions of preservation.     

Comparison of Methods for Coccidioidomycosis Complement Fixation

A Laboratory Branch Task Force of the National Communicable Disease Center has proposed a standardized complement fixation procedure (LBCF) and an adaptation of this to microtitration techniques (MT) as uniform methods for performing complement fixation (CF) tests. A common procedure should make CF results from one laboratory more comparable to another. In addition, it would be preferable if the common procedure reproduced the titer levels of a testing procedure which is to be replaced, particularly when valid clinical interpretations have been derived from the latter. Replicated sets of sera were tested by the LBCF, MT, and the standard Smith CF procedure for coccidioidomycosis. Results with all three procedures were highly reproducible within an acceptable one-tube variation of a twofold dilution series, but the frequency of one-tube variations was greater with the MT method than with the other two. There was no statistical difference in the titers obtained with the Smith and LBCF procedures, but there was a significant difference when the MT results were compared to those with the Smith method. The LBCF method should be acceptable as a standardized and uniform CF procedure for coccidioidomycosis, subject to comparative testing between different laboratories.     

The Influence of Methods of Collection and Storage on the Bacteriology of Human Milk

Staphylococcus epidermidis and other organisms from the skin were found to be the commonest contaminants in 21 samples of human milk donated to a milk bank. Only 2 samples contained enterobacteria; no β-haemolytic streptococci were isolated. Data presented show the difference between bacterial numbers in the first 10 ml and subsequent secretions of milk when drawn sequentially. Refrigerated storage led to the growth of some organisms in the milk; no growth occurred in milk stored at −18°C. A miniaturized resazurin dye test was devised but preliminary observations showed that it had a limited value in detecting rapidly milk of poor bacteriological quality.