Limiting Conditions of Temperature and pH for Growth of “Thermophilic” Campylobacters on Solid Media

Abstract

Strains of Campylobacter previously used for studies with meat, included strains distinguishable as Campylobacter jejuni and nalidixic acid-resistant thermophilic campylobacters (NARTC). The pH and temperature minima for growth on agar plates were determined for 12 strains: six strains used in the meat studies (four C. jejuni, two NARTC), three type strains (C. jejuni, Campylobacter coli, NARTC) and three strains of C. jejuni whose pH and temperature ranges in liquid culture had been determined by other workers. Heavy, visible inocula of most strains grew at temperatures 2°C lower and pH values 0.2 or 0.3 unit lower than the minima observed with light inocula. For all strains of C. jejuni, values for temperature and pH minima from heavy inocula, 32°C and pH 5.1, were comparable with those reported for growth of three strains in liquid media. The pH minima for NARTC strains (pH 5.8) were higher than those for C. jejuni, but temperature minima were similar.