Antimicrobial resistanc ein equine Actinobacillus isolates. Actinobacillus

Actinobacillus species are Gram-negative bacteria, causing different disease conditions in several animal species, including swine, cattle, and horses. Even though Actinobacillus equuli (A. equuli) is most frequently associated with disease in horses, also other Actinobacillus species, such as A. suis, A. arthritidis, A. genomospecies 1, and A. genomospecies 2 have been occasionally described in equine samples. The fact that it is very difficult to differentiate some of these species with standard biochemical tests, 16S rDNA sequencing and/or MALDI-TOF mass spectrometry and that nomenclature has changed throughout the years, makes it hard to interpret final identification in previously and currently published reports. Actinobacillus equuli is an important cause of septicemia in foals (sleepy foal disease) and is inflicted as primary or secondary pathogen in lower respiratory tract diseases, peritonitis and meningitis in adult horses. The A. equuli species contains 2 subspecies, ie A. equuli subspecies equuli and A. equuli subspecies haemolyticus. Both subspecies can cause disease in horses, even though A. equuli subspecies haemolyticus has been associated more with severe respiratory disease, possibly because of the A. equuli toxin (Aqx), a member of the RTX toxin family, which is encoded by the aqx gene in A. equuli subspecies haemolyticus strains only and contributes to the haemolytic characteristic of this subspecies (Kuhnert et al., 2003). A. equuli infections are feared by both horse owners and veterinarians for the high mortality rate of such infections.