Cultural and Biochemical Characterization of Actinobacillus and Actinobacillus-Like Species from Ram Lambs with Epididymitis

Cellular, colonial, cultural, and biochemical characteristics of 25 field strains of gram-negative pleomorphic bacilli from rams with epididymitis were compared with Actinobacillus actinomycetemcomitans American Type Culture Collection (ATCC) strain 29522 and Actinobacillus seminis ATCC strain 15768. Three field strains were identified as A. actinomycetemcomitans, 15 as A. seminis, and 2 as Haemophilus agni; however, 5 strains (3 in group A and 2 in group B) were not identified as species in the genera Actinobacillus, Haemophilus, or Pasteurella based on the taxonomic criteria in Bergey's manual of systematic bacteriology. The 5 Actinoba- cillus-like organisms in groups A and B were predominantly gram-negative coccobacilli and exhibited less pleomorphism than the 2 Actinobacillus species. The colonial morphologies of groups A and B were similar to the 2 Actinobacillus species but were smaller in diameter and had a pale yellow color. Groups A and B, like the actinobacilli, were facultative anaerobic and capnophilic, did not grow on MacConkey agar, and were catalase- positive and oxidase-positive. Group A reduced nitrate but group B did not. The A. seminis strains utilized ornithine, and group A utilized arginine; but group B did not utilize either omithine or arginine. All strains failed to utilize lysine or tryptophane. All strains produced acid but no gas from glucose, and the utilization of other carbohydrates varied markedly both between and within the 5 groups of bacteria. Based on carbohydrate utilization profiles, the 15 field strains of A. seminis represented 13 biotypes, but with a commercial semi- quantitative enzyme system only 1 biotype was identified. All the A. actinomycetemcomitans, A. seminis, and group B strains produced moderate to high levels of alkaline phosphatase and acid phosphatase, but the group A strains were negative. Groups A and B were negative for beta-glucuronidase, but all the A. actinomycetem- comitans and A. seminis strains produced this enzyme. Actinobacillus seminis, Haemophilus agni, and His- tophilus ovis were first reported as new bacterial species in 1960, 1958, and 1956, respectively. 2,11,19 The A. sem- inis isolate was from a ram with epididymitis, and the H. agni and H. ovis isolates were from sheep with other disease conditions. Subsequently, these bacterial species and a few other species in the genera Actinobacillus and Haemophilus, as well as other gram-negative pleo- morphs that were frequently referred to as Actinoba- cillus-like or Haemophilus-like organisms, were iso- lated from either epididymal lesions or semen from