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In vitro activity of chloramphenicol, florfenicol and enrofloxacin against Chlamydia pecorum isolated from koalas (Phascolarctos cinereus)

Black, LA, Higgins, DP & Govendir, M 2015, Australian Veterinary Journal, vol. 93, no. 11, pp. 420-423.

Chloramphenicol and florfenicol were more effective treatments for chlamydiosis in koalas during in vitro experiments than enrofloxacin. The minimum inhibitory concentrations (MICs) were 0.25-0.50 μg/mL for enrofloxacin and 1-2 μg/mL for chloramphenicol and florfenicol. Minimum bactericidal concentration (MBC) values were also calculated to be within one two-fold dilution of the MICs.

  Seven clinical swabs were collected from koalas and confirmed to be positive for Chlamydia pecorum, while negative for Chlamydia pneumoniae and Mycoplasma spp. Three additional frozen isolates were used, and all ten MIC values were within a two-fold dilution of each, as were the MBC values in relation to both each other and the MIC values. The isolates used varied by 23 years and included several different states, but were still all within the two-fold dilution of each other. Enrofloxacin displayed the greatest activity, followed by chloramphenicol and florfenicol. C. pecorum isolates had previously been tested against several antimicrobials, but not against enrofloxacin or chloramphenicol. The dosages of the drugs had therefore been extrapolated from dog and cat dosages or trial and error, hence the need for data indicating the susceptibility of the pathogen to these antimicrobials. The drug susceptibilities were found to be similar to studies done on other cell lines, as well as various Chlamydia strains in other species, including bandicoots and humans. Florfenicol was investigated due to its close similarity to chloramphenicol, which had distribution difficulties, and was found to have almost identical susceptibility. Previous studies’ MIC values were close to the values calculated in this study. The conclusion reached in this study that enrofloxacin is unsafe for koala Chlamydia treatments was based on the calculated MIC combined with previous pharmacokinetic studies, as the dosages required to be effective against Chlamydia may be at toxic levels.

  Studies on the relative effectiveness of different antimicrobial drugs informs better drug choices for treating koala Chlamydia infections, with more accurate dosages and lower risks of toxicity and death.


Summarised by Laura Wait


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