Survival of Pseudomonas pseudomallei strains at 5 degrees C

The ability of 15 Pseudomonas pseudomallei strains of different origin to survive at 5 degrees C was tested, in comparison with the type strains of Pseudomonas aeruginosa and Pseudomonas cepacia. Viable cells of each strain were suspended in tryptic soy broth (diluted 1:10) at a concentration of about 10(6) CFU/ml. The suspensions were kept at 5 degrees C, and the number of viable cells was determined by counting colonies every 10 days. Four strains of P. pseudomallei, including the type strain for the species, died within 90-100 days at 5 degrees C. Ten other P. pseudomallei strains together with the type strain of P. cepacia survived 160 days or more, although viable counts of these strains decreased to 10(1-2) CFU/ml. The Oklahoma strain of P. pseudomallei and the type strain of P. aeruginosa maintained 10(5) CFU/ml after 170-190 days. It was concluded that resistance of P. pseudomallei to low temperature differs from strain to strain. From the results of our experiments and those reported in the literature of nation-wide soil contamination by P. pseudomallei in France, prejudice regarding the organism as a tropical inhabitant must be corrected.