Distribution of Arcanobacterium pluranimalium in animals examined in veterinary laboratories in the United Kingdom

The genus Arcanobacterium was originally described for the Gram-positive coryneform organism Arcanobacterium haemolyticum (previously, Corynebacterium haemolyticum), ⁴ and currently contains 9 species, many of which are associated with animal hosts and can be involved in pyogenic and other opportunistic infections. Two of these species, Arcanobacterium pyogenes, affecting ruminants and pigs principally, ¹⁴ but also other species including human beings, ⁸ and Arcanobacterium bernardiae, recovered from clinical specimens, were also transferred from the genus Actinomyces. ¹³ A further 6 newly described species have also been added: Arcanobacterium phocae recovered from seals, ¹³ Arcanobacterium bialowiezense and Arcanobacterium bonasi from European bison (Bison bonasus), ¹² Arcanobacterium hippocoleae from horses, ⁹ Arcanobacterium abortisuis from pigs, ¹ and Arcanobacterium pluranimalium, which was initially described for 2 isolates cultured from a harbor porpoise (Phocoena phocoena) and a fallow deer (synonym: sallow deer; Dama dama), respectively. ¹¹ All of the aforementioned species are typically surrounded by a zone of β-hemolysis with the exception of A. bernardiae, for which hemolysis is variable, ⁷ and A. hippocoleae, which is nonhemolytic. ⁹

Soon after the initial description, phenotypic testing and 16S ribosomal RNA sequencing identified A. pluranimalium as a cause of occasional opportunistic infections in sheep, particularly abortion, in England ⁵ and Scotland. ⁶ In the years that followed, only 1 further report of the isolation of A. pluranimalium was found, for an isolate recovered in mixed culture from a dog with pyoderma. ¹⁵ It has remained unclear to what extent sheep and other host animals are infected by A. pluranimalium or which systems are more susceptible to infection. The present report details the recovery of A. pluranimalium from routine postmortem and diagnostic sample submissions submitted to U.K. Veterinary Disease Surveillance Laboratories during the years following the initial reports (2001) until the end of 2009.

The sample material used in the current study included specimens collected from carcasses following necropsy and diagnostic samples submitted by veterinary practitioners from a broad range of animal species, but predominantly livestock species of cattle, sheep, pigs, and poultry, which were submitted on a regular basis for disease diagnosis and surveillance to the 8 SAC Consulting Veterinary Services Centres in Scotland and 14 Defra Regional Laboratories in England and Wales. Less frequently, other farmed species have been examined including goats, camelids, and deer, as well as wild deer and other terrestrial and avian wildlife. Microbiological investigations of material from companion animals including horses, cats, and dogs, as well as various other species, were also carried out, particularly in Scotland. In the marine environment, a large number of cetaceans and pinnipeds, which had stranded around the coastline of Scotland or been bycaught in fishing nets, were examined under the Scottish Marine Animal Stranding Scheme (http://www.strandings.org/).

All specimens were routinely plated on Columbia agar, supplemented with 5% sheep blood ^a (CSBA) and MacConkey agar, ^a and incubated at 37ºC either aerobically or in a capnophilic atmosphere according to sample site. Arcanobacterium-like isolates, which appeared as tiny β-hemolytic colonies after 24 or 48 hr of incubation, were checked for Gram morphology. Isolates that had a coryneform morphology were further tested for the production of catalase and tested with a commercial kit ^b according to the manufacturer’s instructions. In addition, hemolytic activities were evaluated for selected strains in a Christie, Atkins, Munch-Petersen (CAMP) test ³ by single streaks of the test isolate on CSBA placed perpendicular to single streaks of Staphylococcus aureus National Collection of Type Cultures (NCTC) 8511, Rhodococcus equi NCTC 1621, and Streptococcus agalactiae NCTC 8181.

In the years from 2001 to 2009, A. pluranimalium was recovered from 22 sheep samples in Scotland and 11 in England and Wales. Twenty of these isolates came from abortion material, 5 from semen samples, 3 from abscesses, 3 from viscera, and 1 case each of navel ill and peritonitis. With respect to all other host species examined, there was only 1 further isolate of A. pluranimalium, which was recovered from a bovine mastitis case.

All ovine A. pluranimalium isolates and the single bovine strain were catalase positive. Biochemical test results gave positive reactions for pyrazinamidase, pyrrolidonyl arylamidase, aesculin, gelatin, and fermentation of glucose and ribose in all cases. Variable results were found for β-glucuronidase and maltose fermentation. All other reactions with the commercial kit ^b were negative. CAMP tests, where performed, gave enhanced hemolytic reactions with S. aureus, no effect with S. agalactiae, and either no effect or weak hemolysis with R. equi. In contrast, all A. pyogenes isolated during the period of the study were consistently catalase negative and provided different profiles with the commercial kit. In particular, negative reactions were obtained for pyrazinamidase and aesculin as opposed to the positive reactions obtained with A. pluranimalium for these tests. The CAMP reactions for A. pyogenes were similar to those of A. pluranimalium.

The predilection of A. pluranimalium for ovine tissues demonstrated for U.K. samples contrasts with that of A. pyogenes, which, although often recovered from sheep specimens, was also a frequent isolate from bovine and porcine hosts as well as an occasional finding from other host species including red deer, reindeer, elk, bison, and rabbit.

Arcanobacterium pyogenes has long been associated with infections of sheep ¹⁴ and has been recovered on numerous occasions during the period of study. In ovine abortion and reproductive material, both A. pyogenes and A. pluranimalium were found on many occasions, whereas in other areas of the body A. pluranimalium was a much less frequent finding.

The predilection of A. pluranimalium for reproductive tissue is also reflected by many of the other recently described Arcanobacterium species for their respective hosts. Arcanobacterium bialowiezense and A. bonasi were first described for isolates from bison bulls with balanoposthitis ¹² ; A. hippocoleae has been recovered from equine reproductive specimens including a case of placentitis and stillbirth in a mare ² ; and A. abortisuis was first described for a strain from the placenta of a sow following abortion. ¹ Furthermore, a recent characterization of 9 further equine A. abortisuis isolates included 6 recovered from vaginal samples, 1 from cervix, 1 from urine, and 1 from a kidney. ¹⁶ While these 9 isolates were mostly cultivated in mixed culture, 7 were associated with clinical signs including vaginitis, vaginal discharge, and fertility problems. ¹⁶

The original description of A. pluranimalium was based on a single isolate recovered from a harbor porpoise from Scotland and another from a fallow deer from Sweden. ¹¹ An appraisal of bacterial isolates recovered from cetaceans over the past 2 decades and stored at −80°C revealed that A. pluranimalium has not been recovered from the tissues of approximately 1,100 other cetaceans from Scottish waters, the majority of which have been porpoises, nor from a large number of seals. A further study of arcanobacterial isolates from marine mammals along the California coast reported a high incidence of A. phocae among several species of pinniped as well as a single isolate from a common dolphin, but A. pluranimalium was not recorded. ¹⁰ The type species of A. pluranimalium ¹¹ therefore remains the only such strain reported from a marine mammal to date. With respect to deer, all further arcanobacteria isolates that were recovered from this host during the years of study have been identified as A. pyogenes.

The current study suggests that ovine animals are the major host of A. pluranimalium, with other host animals rarely affected. Ovine abortion material is the most frequent source of A. pluranimalium in samples submitted to U.K. Veterinary Disease Surveillance Laboratories. It is possible that A. pluranimalium isolates from sheep recovered in diagnostic laboratories prior to 2001 may have been misidentified as A. pyogenes; however, A. pluranimalium and A. pyogenes can be distinguished successfully by pyrazinamidase, aesculin, and catalase tests.