Norris, JM* and Love, DN.
Department of Veterinary Anatomy & Pathology, Sydney University, NSW 2006 Australia

This study was undertaken to:

• provide current information on antimicrobial susceptibility of recently isolated feline Porphyromonas species by in vitro methods and
• to dose cats with antimicrobials to which feline Porphyromonas species are known to be sensitive in vitro and monitor response by clinical assessment and isolation and enumeration of cfu of each feline Porphyromonas species -

MICs were measured by agar dilution method (NCCLS) and E-test against doxycycline, metronidazole, amoxycillin and amoxycillin/clavulanate. The cfu of each Porphyromonas species was made using digoxygenin labelled species specific DNA probes from samples taken from the canine gingival margin site pre-antimicrobial administration and 24 hours post a five day course of one of four different antimicrobial preparations given at dose rates recommended by the manufacturer.

All Porphyromonas were susceptible to all drugs tested by E-test and agar dilution Mic although the MIC ranges to each antimicrobial varied amongst species. There was a strong association between MIC ranges determined by agar dilution and E-test with few discrepant results. The in vivo responses varied markedly amongst preparations and in some cases between cats given the same antimicrobial. Two preparations only were able to reduce numbers of Porphyromonas below detectable levels in all cats tested and in these cats, all three Porphyromonas species were similarly affected. Of those cats where a response to treatment was variable, PgF was the species more likely to be refractory to treatment.

This microbiological data supported clinical assessment of response to antimicrobial treatment in that those animals where Porphyromonas were cleared post-treatment showed a marked response at the canine site while those sites from which PgF could be isolated post-treatment, no clinical improvement was seen.