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A Psychrophilic Strain Relatively Resistant to Hypochlorite-Type Sanitizers¹

Department of Dairy Technology, The Ohio State University, Columbus

ABSTRACT

Hypochlorite-type sanitizers are often used to treat washwater for butter and cottage cheese, as a precaution against bacterial contamination of the so-called psychrophilic type.

Generally, hypochlorites are considered effective against psychrophilic bacteria. However, during a study of sanitizers, a strain of Pseudomonas fluorescens was encountered which proved to be relatively resistant to sanitizers of all types, including hypochlorites.

Figure 1 illustrates the concentration of hypochlorite necessary to get satisfactory destruction of this bacterium in 30 sec. by the Weber and Black method.² For comparison, the figure includes the effective concentration of hypochlorite against an ordinary psychrophilic bacterium represented by Pseudomonas fragi. The resistant species of P. fluorscens was about five times as resistant to hypochlorite as the species of P. fragi.

A survey was conducted to determine the frequency of hypochlorite resistance among psychrophilic bacteria. Twelve additional strains of bacteria of the genera Pseudomonas, Flavobacterium, and Achromobacter were included. All of these bacteria showed a low resistance to hypochlorite similar to that of the strain of P. fragi.

¹ Technical Note 16:57, Department of Dairy Technology, The Ohio State University.