Paul W. Kabler

Application of the “most probable number” method for estimating concentrations of animal viruses by the tissue culture technique

Abstract Justification for use of an MPN (most probable number) method for estimating concentration of Coxsackie B1 virus in monkey kidney tissue culture tubes was demonstrated by comparison of dosage-response data with a theoretical MPN curve based on one-particle infection and by variance analysis of 24 replicate MPN determinations. This method yields units comparable to plaque counts or plaque-forming units and affords unbiased estimates even when data do not bracket the 50% response dilution. It provides a means of testing for conformity to the one-particle infection theory and gives usable results from one dilution if both positive and negative tubes are present. For these reasons it is preferred to conventional LD 50 methods for virus quantitation where the dilution response data are known to follow the one-particle infection curve. A table of 5-tube, 4-fold dilution series and an approximation equation are presented for conversion of data to “most probable number of cytopathogenic units” (MPNCU).

Removal of Coxsackie and Bacterial Viruses in Water by Flocculation: II. Removal of Coxsackie and Bacterial Viruses and the Native Bacteria in Raw Ohio River Water by Flocculation with Aluminum Sulfate and Ferric Chloride

THE ADEQUACY of modern water treatment processes in safeguarding the public from water-borne viral diseases was challenged by the recent outbreak 1 of infectious hepatitis in New Delhi, India, which presented new evidence that this disease can be spread by a water supply treated by flocculation, rapid sand filtration, and chlorination. Quantitative information regarding the destruction of pathogenic viruses in water by chlorination is scant and that regarding their removal by flocculation is almost nonexistent. In a previous study 2 some fundamental principles in removal of bacterial virus from water by flocculation were explored. Two questions arise which require further investigation: (1) is information obtained with bacterial virus applicable to removal of pathogenic viruses?, and (2) is the information obtained with water prepared in the laboratory applicable to the treatment of raw natural waters ? The recent report of Gilcreas and Kelly 3 indicated that about 40 per cent of Coxsackie and Theilers viruses, 85 per cent of Escherichia coli B phage, and about 90 per cent of E. coli were removed from artificially contaminated spring water by alum flocculation. Since no quantitative data were given on the turbidity of the water, the nature and amounts of viral and bacterial inocula, the buffer used, the pH of the treated water, or the amount of floc formed and turbidity removed, it is difficult to judge the removal efficiency of the flocculation process or to apply the results in practice. This series of studies attempts, therefore, to ascertain (1) how certain pathogenic viruses differ from bacterial viruses in their behavior in the flocculation process, and (2) how efficiently current waterworks practices remove vi-

A Delayed Incubation Membrane Filter Test for Coliform Bacteria in Water

+ The ninth edition of Standard Methods for the Examination of Water and Sewage 1 recommends that the bacteriologic examination of relatively pure water be started within 12 hours after collection and that the temperature of the sample be maintained between 6-100 C. Many laboratories serving large geographic areas have found it impractical or impossible to comply with one or both of these recommendations. The exact effects of time and temperature of storage on the coliform densities of water appear to be controversial. Cox and Claiborne 2 found that refrigerated samples showed relatively little change up to 48 hours. Coliform densities in their samples stored at room temperature varied markedly, frequently showing sharp reductions. Hoather 3 found little evidence of large variations of coliform counts in samples stored