Oral tylosin administration is associated with an increase of faecal enterococci and lactic acid bacteria in dogs with tylosin-responsive diarrhoea

• Canine idiopathic and recurrent diarrhoea responds to oral tylosin in a few days.
• Tylosin increases faecal Enterococcus spp. and lactic acid bacteria in dogs.
• Tylosin increases faecal tylosin-resistant enterococci and lactic acid bacteria (LAB).
• Tylosin has a stronger effect on the increase in enterococci in relation to LAB.
• Cessation of diarrhoea may be due to selection of enterococci in the intestine.

The term tylosin-responsive diarrhoea (TRD) is used for canine recurrent diarrhoea cases for which no underlying cause can be found after extensive diagnostic investigations, but which show a response to the antibiotic tylosin in a few days. The objective of this prospective, one-arm longitudinal trial was to assess the effects of oral tylosin administration on the faecal levels of potentially probiotic bacteria, such as Enterococcus spp. and lactic acid bacteria (LAB), in dogs with TRD.This trial included 14 client-owned suspected TRD dogs that were on tylosin treatment and had firm faeces. Treatment was then terminated and dogs were followed up for up to 2 months to determine the recurrence of diarrhoea. Once diarrhoea started, dogs received tylosin (orally, 25 mg/kg, once daily for 7 days). At the end of the treatment period, stools were firm again in 11 dogs (TRD dogs); three dogs continued having diarrhoea and were excluded from the study. Faecal samples were collected at all three time-points for culture of LAB and enterococci. In TRD dogs, the colony counts of Enterococcus spp. (P = 0.003), LAB (P = 0.037), tylosin-resistant Enterococcus spp. (P < 0.001) and LAB (P < 0.001) were significantly higher when the dogs were on tylosin treatment and had normal faecal consistency compared to when they had diarrhoea following discontinuation of tylosin. In conclusion, cessation of diarrhoea in TRD dogs with tylosin treatment could be mediated by selection of a specific lactic acid population, the Enterococcus spp., due to their potential probiotic properties.