Fate of Arcobacter spp. upon exposure to environmental stresses and predictive model development
D'Sa, Elaine Marie-Louise
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Growth and survival characteristics of two species of the ‘emerging’ pathogenic genus Arcobacter were determined. The optimal pH growth range of most A. butzleri (4 strains) and A. cryaerophilus (2 strains) was 6.0-7.0 and 7.0-7.5 respectively. The optimal NaCl growth range was 0.09-0.5 % (A. butzleri) and 0.5-1.0% (A. cryaerophilus), while growth limits were 0.09-3.5% and 0.09-3.0% for A. butzleri and A. cryaerophilus, respectively. A. butzleri 3556, 3539 and A. cryaerophilus 1B were able to survive at NaCl concentrations of up to 5% for 48 h at 25°C, but the survival limit dropped to 3.5-4.0% NaCl after 96 h. Thermal tolerance studies on three strains of A. butzleri determined that the D-values at pH 7.3 had a range of 0.07-0.12 min (60°C), 0.38-0.76 min (55°C) and 5.12-5.81 min (50°C). At pH 5.5, thermotolerance decreased under the synergistic effects of heat and acidity. D-values decreased for strains 3556 and 3257 by 26-50% and 21- 66%, respectively, while the reduction for strain 3494 was lower: 0-28%. Actual D-values of the three strains at pH 5.5 had a range of 0.03-0.11 (60°C), 0.30-0.42 (55°C) and 1.97-4.42 (50°C). z-values for the three strains ranged from 5.20-6.11°C and 5.55- 6.28 °C at pHs of 7.3 and 5.5, respectively. D-values for a cocktail of the three strains in raw ground pork were 18.51 min at 50°C and 2.18 min at 55°C. The one strain tested (A. butzleri 3556) was highly sensitive to the combined effects of mild heat (50°C) followed by cold shock, exhibiting a 3.2-4.0 log10 decrease in cell numbers at a cold shock temperature of 4°C, as compared to a 0.33-1.12 log10 decrease at a temperature of 16°C. Predictive mathematical models (quadratic and cubic) were constructed from a dataset of growth curves obtained for a cocktail of three A. butzleri strains. These models described the main and interactive effects of incubation temperature (12-37°C), pH (6.0-7.5), sodium chloride (0.09-3.5%), sodium nitrite (0-180 ppm), and sodium tripolyphosphate (0-0.012%) levels on the growth characteristics of the cells. Predictions for generation time (GT), lag phase duration (LPD) and Gompertz parameters B and M were analyzed from natural logarithm transformed quadratic models.