Effect of pH, NaCl content, and temperature on growth and survival of Arcobacter spp.

Growth and survival of six human isolates of the pathogenic Arcobacter spp. in the presence of selected environmental factors were studied. Four strains of Arcobacter butzleri and two strains of Arcobacter cryaerophilus were exposed to pH levels of 3.5 to 8.0. Most strains grew between pH 5.5 and 8.0, with optimal growth of most A. butzleri and A. cryaerophilus strains at pH 6.0 to 7.0 and 7.0 to 7.5, respectively. The 24-h optimal growth range in the presence of NaCl was 0.5 to 1.0% for A. cryaerophilus. However, after 96 h, the optimum was between 0.5 and 2.0% NaCl. The optimum range for growth of A. butzleri strains was 0.09 to 0.5% NaCl after 96 h. The upper growth limits were 3.5 and 3.0% NaCl for A. butzleri and A. cry zerophilus, respectively. Survival at 25degreesC in up to 5% NaCl was noted for A. butzleri 3556 and 3539 and A. cryaerophilus 3256. Decimal reduction times (D-values) at pH 7.3 in phosphate-buffered saline for three A. butzleri strains were 0.07 to 0.12 min at 60degreesC, 0.38 to 0.76 min at 55degreesC, and 5.12 to 5.81 min at 50degreesC. At pH 5.5, decreased thermotolerance was observed, with D-values of 0.03 to 0.11 min at 60degreesC, 0.30 to 0.42 min at 55degreesC, and 1.97 to 4.42 min at 50degreesC. Calculated z-values ranged from 5.20 to 6.28degreesC. D-values of a three-strain mixture of A. butzleri in raw around pork were 18.51 min at 50degreesC and 2.18 min at 55degreesC. Mild heat (50degreesC) followed by cold shock (4 or 8degreesC exposure) had a synergistic lethal effect, reducing more cells than with an individual 50degreesC treatment or with cold shock temperatures of 12 or 16degreesC.