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In vitro characterisation of koala Chlamydia pneumoniae: Morphology, inclusion development and doubling time

Mitchell, CM, Matthews, SA, Theodoropoulos, C & Timms, P 2009, Veterinary Microbiology, vol. 136, no. 1, pp. 91-99.

The Chlamydia pneumoniae koala nasal isolate termed LPCoLN was compared to the human isolate AR39 and differed significantly from the human isolate in terms of doubling time, size, and morphology.

  The pathogen C. pneumoniae occurs in both humans and animals in which it is commonly associated with respiratory tract infections. An in vitro comparison of the bacteria as it occurs in humans and koalas revealed some key differences in their growth patterns and morphological features. Firstly, the koala isolate multiplied much more rapidly than the human isolate in human epithelial type 2 (HEp-2) cultures, with doubling times of 3.4 – 4.9 hours and 5.9 – 8.7 hours respectively. Bacterial inclusions, which are discrete structures with specific functions within the cell, were heterogeneously shaped and larger in LPCoLN (9-30µm in diameter) than in AR39 (5-9µm in diameter), in which inclusions were uniformly shaped. The LPCoLN elementary body was round with a small or no periplasmic space, whereas the AR39 elementary body was pear-shaped. The level of fusion of chlamydial inclusions was also much higher in LPCoLN at 100%, compared to only 30 – 40% for AR39 inclusions.

  Although the precise reason for the difference in growth between LPCoLN and AR39 is unknown, it is possible that the more rapid multiplication rate of the koala isolate relates to a more efficient attachment and uptake mechanism than that of the human isolate. Similarly, though it has not been confirmed, the observed differences in elementary body morphology may relate to host-specific attachment or adherence functions. A suggested reason for the high fusion level of LPCoLN inclusions is that fusion offers an advantage in terms of growth due to spatial distribution or facilitating the genetic recombination of individual reticulate bodies within the inclusion. The authors also suggest that the differences observed between the isolates reflect the adaptations of each to their unique intracellular environment.

  This study, in combination with future studies of the C. pneumoniae genome, will be beneficial for enhancing our understanding of C. pneumoniae diversity and the genes that facilitate its infection of human and animal hosts, including the koala.


Summarised by Joanna Horsfall


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