IntroductionRespiratory diseases account for the highest number of clinical problems in horses compared with other body systems. While microbiological culture and sensitivity testing is essential for certain cases, knowledge of the most likely bacterial agents and their susceptibilities is necessary to inform empirical antibiotic choices.MethodsA retrospective study of microbiological and cytological results from upper and lower respiratory samples (n=615) processed in a commercial laboratory between 2002 and 2012 was carried out. A further study of lower respiratory samples from horses with clinical signs of lower respiratory disease from May to June 2012 was undertaken.ResultsBoth studies revealed Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa, Pasteurella species, Escherichia coli and Bordetella bronchiseptica as the most frequently isolated species. S equi subspecies zooepidemicus and subspecies equi were susceptible to ceftiofur (100 per cent) and erythromycin (99 per cent). Resistance to penicillin (12.5 per cent of S equi subspecies equi from upper respiratory tract samples) and tetracycline (62.7 per cent) was also detected. Gram-negative isolates showed resistance to gentamicin, trimethoprim-sulfamethoxazole and tetracycline but susceptibility to enrofloxacin (except Pseudomonas species, where 46.2 per cent were resistant). Multiple drug resistance was detected in 1 per cent of isolates.ConclusionResistance to first-choice antibiotics in common equine respiratory tract bacteria was noted and warrants continued monitoring of their susceptibility profiles. This can provide information to clinicians about the best empirical antimicrobial choices against certain pathogenic bacteria and help guide antibiotic stewardship efforts to converse their efficacy.

Background: Bacterial lower respiratory tract infections (bLRTIs) are common and potentially life threatening in cats and dogs. Antibiotic treatment is often initiated before the diagnosis of bLRTI; therefore improved knowledge of the aetiology and antibiotic susceptibility patterns of these infections is essential to inform empiric antibiotic choices. Methods: A retrospective study of microbiological, cytological results and their drug susceptibilities from lower respiratory samples (n = 1989) processed in a UK commercial laboratory between 2002 and 2012 was carried out. Results: Thirty-nine per cent of feline samples and 50% of canine samples were positive for bacterial growth with most yielding a single organism (72 % and 69%, respectively). Bordetella bronchiseptica (20.2% from dogs and 2.3% from cats), Pasteurella spp. (23.2%, 31.8%), E. coli (16.2%, 13.6%) and Pseudomonas spp. (11.1%, 11.4%) were most frequently isolated from cytologically positive samples which contained intracellular bacteria (10%, 14%). Amoxycillin-clavulanate, cephalothin, cefovecin, oxytetracycline and trimethoprim/sulfamethoxazole showed modest in vitro activity against E. coli from dogs (approximately 70% susceptibility). Pseudomonas spp. were resistant to enrofloxacin (50%), ticarcillin (25%) and marbofloxacin (13%) but showed lower or zero resistance to aminoglycosides (approximately 7%) and ciprofloxacin (0%). Multi drug resistance (acquired resistance to three or more antimicrobial drug classes) was particularly common among E. coli isolates, with 23% from feline samples and 43% from canine samples. Conclusion:Resistance to certain first-choice antibiotics was detected in bLRTIs highlighting the need for continued monitoring and sound evidence to inform decision-making in the management of these infections.