Differential effects of temperature on natural transformation to erythromycin and nalidixic acid resistance in Campylobacter coli

Abstract

Campylobacter jejuni and Campylobacter coli are naturally competent, but limited information exists on the impact of environmental conditions on transformation. In this study, we investigated the impact of temperature and microaerobic versus aerobic atmosphere on transformation of C. coli to erythromycin and nalidixic acid resistance. Frequency of transformation was not significantly different between microaerobic (5 to 10% CO(2)) and aerobic conditions. However, C. coli was transformed to erythromycin resistance at a significantly higher frequency at 42 degrees C than at 25 degrees C (P < 0.05), and few or no transformants were obtained at 25 degrees C. In contrast, transformation to nalidixic acid resistance was highly efficient at both 42 degrees C and 25 degrees C and was similar or, at the most, fourfold higher at 42 degrees C than at 25 degrees C. DNase I treatment experiments suggested that steps both prior and subsequent to internalization of DNA were influenced by temperature in the case of transformation of C. coli to erythromycin resistance. However, the moderately increased (fourfold) frequency of transformation to nalidixic acid resistance at 42 degrees C compared to that at 25 degrees C was exclusively associated with steps prior to DNA internalization. These findings suggest that transformation to erythromycin resistance may be significantly more frequent in the gastrointestinal tract of hosts such as poultry (at 42 degrees C) than in other habitats characterized by lower temperatures, whereas transformation to nalidixic acid resistance may be highly efficient both within and outside the animal hosts.

FIG. 1.

Effects of temperature and microaerobic versus aerobic atmosphere on frequency of transformation of C. coli strains 961, 3237, and 1702rnd to erythromycin resistance. Transformation frequency was determined as described in Materials and Methods. Conditions employed: A, 42°C, microaerobic atmosphere; B, 25°C, microaerobic atmosphere; C, 42°C, aerobic atmosphere; D, 25°C, aerobic atmosphere.

FIG. 2.

Effects of temperature and microaerobic versus aerobic atmosphere on frequency of transformation of C. coli strains 3237 and 1702rnd to nalidixic acid resistance. Transformation frequency was determined as described in Materials and Methods. Conditions employed: A, 42°C, microaerobic atmosphere; B, 25°C, microaerobic atmosphere; C, 42°C, aerobic atmosphere; D, 25°C, aerobic atmosphere.

FIG. 3.

Effect of temperature on transformation of C. coli 961 to erythromycin resistance. Temperature shifts (42°C versus 25°C) and DNase I treatments to degrade noninternalized DNA were done as described in Materials and Methods. Transformation frequency was determined as described in Materials and Methods. Treatments: A, standard transformation conditions (42°C for 5 h, without addition of DNase); B, positive-control transformation with DNase added after 1 h of incubation at 42°C and subsequent incubation of the mixture at 42°C for an additional 4 h; C, DNase added after 1 h at 25°C and subsequent incubation of the mixture at 42°C for an additional 4 h; D, DNase added after 1 h at 42°C and subsequent incubation of the mixture at 25°C for an additional 4 h; E, DNase added after 1 h at 25°C and subsequent incubation of the mixture at 25°C for an additional 4 h.

FIG. 4.

Effect of temperature on transformation of C. coli 1702rnd to nalidixic acid resistance. Temperature shifts (42°C versus 25°C) and DNase I treatments to degrade noninternalized DNA were done as described in Materials and Methods. Transformation frequency was determined as described in Materials and Methods. Treatments: A, positive-control transformation with DNase added after the first 30 min of incubation at 42°C and subsequent incubation of the mixture at 42°C for an additional 4.5 h; B, DNase added after 30 min at 25°C and subsequent incubation of the mixture at 42°C for an additional 4.5 h; C, DNase added after 30 min at 42°C and subsequent incubation of the mixture at 25°C for an additional 4.5 h; D, DNase added after 30 min at 25°C and subsequent incubation of the mixture at 25°C for an additional 4.5 h.