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Infection & disease

In vitro survival characteristics of koala Chlamydiae

Rush, CM & Timms, P 1996, Wildlife Research, vol. 23, no. 1, pp. 213-219.

Type I and II koala Chlamydia strains were compared to an avian C. psittaci strain. All three strains survived 4 hours of exposure to solutions ranging from pH 4 to 10, with Type I surviving best at pH 7.2-7.5 and Type II surviving optimally at pH 7.0-7.2. Type 1 elementary bodies remained viable for 28 days at temperatures of 18-23°C, but were inactivated within 5 minutes at 56°C. Avian chlamydiae survived 4-6 days after drying, whereas koala Type I only survived 2-4 days. Type I was also still infective after three days exposure on Eucalyptus tereticornis leaves. Overall, these results demonstrated that koala Type I Chlamydia is able to survive significant time periods under extreme conditions, meaning that non-sexual transmission is a possible transmission mechanism for the strain.

  Testing of pH tolerance showed that the koala Type I Chlamydia strain decreased in viability over 4 hours at all pH values tested, but decreased least at pH 7.2-7.5, at which viability only dropped to 54-58% after 15 minutes. The koala Type II isolate and the avian strain preferred the pH range of 7.0-7.2. All strains had increased sensitivity to higher pH values, with no activity present after 4 hours at pH 10. Both koala Type I and avian isolates were completely inactivated at 56°C within 5 minutes. At 4°C, the Type I strain was still 75% viable after 4 hours, but declined to 0% after 10 days, compared to the avian isolate at 14% viability after 10 days. Ambient temperature (18-23°C) resulted in 7% of the Type I strain still viable after 28 days, with 0% remaining of the avian isolate. After desiccation, both strains remained viable for 2-4 days but had 0% viability after 7 days. Type I elementary bodies were infective after surviving on E. tereticornis leaves, with 50% viable after 4 hours, 1.5% after 24 hours, and 1% after 3 days. The same experiment was attempted on E. maculata, but was unsuccessful with only 24% of chlamydiae recovered with immediate swabbing due to the rough leaf surface of the species.

  The comparison of koala chlamydiae to avian Chlamydia was included in this study as previous studies have shown that birds acquire Chlamydia through inhalation of contaminated faeces. Chlamydia bacteria have been isolated from the koala rectum, demonstrating that they can survive digestion, and suggesting that faeces as a possible transmission mechanism for the pathogen. This study also demonstrated that the bacteria can survive at a pH of 6.0 for greater than 4 hours, which another study showed was the pH of koala urine, suggesting urine as another possible transmission mechanism.

  This study has shed light on the possible transmission mechanisms of Chlamydia, with important implications. A notable finding of this study was that koala chlamydiae may be able to survive harsh environmental conditions on a leaf for up to three days. In dense koala populations or captive environments that harvest wild Eucalyptus branches for captive koalas, this represents a possible mechanism for Chlamydia transmission between animals. By better understanding the methods of transmission, interventions can be better designed to reduce transmission rates.

 

Summarised by Laura Wait

 

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