ANTIBACTERIAL-INDUCED DYSBIOSIS

Some antimicrobial drugs may disrupt the normal intesti­nal flora of some Australian marsupials. Such disruption can lead to inappetence, emaciation and death. Chlamydiosis is a significant disease in the koala.

Erythromycin (dosage not documented) (Brown et al. 1984) or oxytetracycline (50 mg/kg SC q 7 d of long-acting formulation for a maximum of four injections) adminis­tered to koalas resulted in emaciation and death (Osawa and Carrick 1990). It is suggested that some antibacterial drugs, especially those with activity against anaerobic bacteria, affect the GIT microbial flora of koalas, result­ing in dysbiosis (Osawa et al. 1993). Osawa and Carrick (1990) prevented fatal inappetence and emaciation during oxytetracycline administration by concurrent adminis­tration of a soya-based supplement PO for 56 d. Griffith (2010) reported inappetence, reduced faecal output, weight loss and depression in five koalas dosed with doxy­cycline at either 0.25 mg/kg bid PO for 5-8 d (one animal); or 2.5-5 mg/kg sid PO (two animals), or 2.5-5 mg/kg sid IM (two animals), and a similar clinical deterioration was observed in one animal treated with chloramphenicol at 50 mg/kg bid PO. The use of doxycycline long-acting injection (doxycycline hydrochloride 50 mg/mL, Psittavet Injection, Vetafarm, Wagga Wagga, NSW, Australia) for the treatment of chlamydiosis in koalas at 5 mg/kg SC (diluted 50:50 with sterile water immediately before injec­tion to reduce reaction at injection site) q 7 d for 2-4 wk has resulted in clinical cure and negative qPCR results in many, but not all, infected koalas (Booth and Nyari 2020). Only a weekly injection is required, which is highly desir­able in wild, anxious or aggressive animals (Booth and Nyari 2020). Despite minimal side effects observed in some koalas, fatal dysbiosis has also been reported in koalas receiving doxycycline (L Vogelnest pers. comm.; J Hanger pers. comm.; A Van Aggelen pers. comm.). A syn­drome of dysbiosis and bloating has also been described in sub-adult eastern ring-tailed possums with the use of certain antimicrobials such as tetracyclines (Johnson and Hemsley 2008) and amoxicillin-clavulanic acid (Scheel- ings et al. 2015). The use of antibiotics in PY and juvenile animals may predispose to candidiasis. The antifungal nystatin (up to 50 000 lU/kg PO, without food) is recom­mended to be administered concurrently with antibiotics to prevent candidiasis, together with administration of probiotics on completion of the course of antibacterial in marsupials (Vogelnest and Woods 2008).

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