Trueperella pyogenes infections

Previous authors: M G COLLETT AND G F BATH

Current authors:
M G COLLETT - Senior Lecturer, BVSc, MMedVet (Path), Med (CAI), School of Veterinary Science, Massey University, Private Bag 112222, Palmerston North, Manawatu, 4442, New Zealand
R O GILBERT - Associate Dean of Academic Affairs, BVSc, MMedVet, DipACT, FRCVS, Ross University School of Veterinary Medicine, Cornell University, Island Main Road, West Farm, St. Kitts, Federation of St. Kitts and Nevis

GENERAL INTRODUCTION: IRREGULAR, NON-SPORING, GRAM-POSITIVE RODS

Introduction

Trueperella (Arcanobacterium) pyogenes occurs in a great variety of suppurative or pyogenic conditions in economically important livestock (particularly cattle, sheep, goats and pigs), either as a primary pathogen, a secondary invader or as part of a mixed infection with obligate anaerobes. Depending on the animal species, the organism can be a commensal of the mammary gland, urogenital and upper respiratory tracts, and alimentary tract, in particular the oropharynx, rumen and stomach wall.^{91, 134, 148} It is most commonly incriminated as a cause of wound infections and abscesses, genital infections such as post-parturient metritis and endometritis in cows, as well as abortion and perinatal mortalities, mastitis, liver abscesses, endocarditis, lymphadenitis, pneumonia, foot infections, arthritis, osteomyelitis of vertebral bodies, discospondylitis, and bulbar empyema or pituitary abscessation.^{154, 156} Trueperella pyogenes infections such as mastitis, abscesses, polyarthritis, and metritis are important economic reasons for the culling of animals.⁸⁷

This pus-producing bacterium was originally described by Glage in 1903 and called Corynebacterium pyogenes.²¹⁰ The name was changed to Actinomyces pyogenes in 1982³⁰ and phylogenetic and 16S rRNA studies resulted in it being reclassified as Arcanobacterium pyogenes¹⁵¹ in 1997. In 2011, chemotaxonomic and further 16S rRNA gene sequence analysis studies resulted in an emended description of the genus Arcanobacterium (Christie-Atkins-Munch-Petersen [CAMP] test positive) and the creation of a new Trueperella genus (CAMP-test negative), named after the German microbiologist Hans Trüper,²¹⁰ with T. pyogenes as the type species.

Aetiology

Trueperella pyogenes is a Gram-positive, non-motile, non-sporulating, facultatively anaerobic, slender, pleomorphic coccobacillus.^{91, 193} The genome sequences of two isolates from cases of metritis in cows have been published.^{63, 116}

Trueperella pyogenes is nutritionally fastidious and grows poorly on common laboratory media unless they have been supplemented with blood or serum.^{136, 164} On blood agar, colonies are small, translucent and usually dense after 24 hours’ incubation when isolated from pus. After 48 hours, single colonies are approximately 0,5 to 1,0 mm in diameter and light grey in colour. A narrow zone of pale β-haemolysis is usually visible by 36 hours and most isolates typically liquefy inspissated serum. To improve the isolation rate, neomycin (0,6 to 0,7 units/ml), polymyxin B sulphate (25 units/ml) or 0,1 per cent Tween 80 can be added to the medium.⁷⁶ A chemically defined medium which supports rapid growth of the organism has been developed.¹⁵³

In addition to conventional phenotypic (e.g. biochemical markers such as sugar fermentation and haemolysis) as well as genotypic (e.g. detecting virulence factor encoding genes) properties, Fourier transform infrared spectroscopy has been shown to be rapid and reliable in identifying T. pyogenes in routine diagnosis.¹³¹ A loop-mediated isothermal amplification assay has also shown promise as a sensitive, reliable and cost-effective way for the molecular identification of T. pyogenes.^{1, 215} A fluorescent in situ hybridization technique is able to rapidly identify pathogens in mastitis milk samples provided the organisms are present in high numbers.⁵⁸ Fluorescent in situ hybridization has also been used to investigate bacteria present in the pregnant uterus of cows.⁹⁶ The microbial DNA diversity of mastitic milk can also be investigated using metagenomic pyrosequencing of bacterial 16S rRNA genes.¹³⁷ Trueperella pyogenes strain differences can be characterized using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry.^{126, 203}

Pathogenesis

Although T. pyogenes expresses several virulence factors that are believed to be required for cell adherence, colonisation and host tissue damage, many aspects of the pathogenesis of infection are poorly understood.^{91, 156} the most important virulence factor is a filterable, oxygen-stable, cholesterol-dependent, haemolytic protein exotoxin, named pyolysin (PLO), which has been cloned.^{14, 22, 55, 114} Pyolysin is cytolytic for a number of cells including neutrophils and macrophages.⁹¹ It is fatal to mice and rabbits after intravenous injection and is dermotoxic to guinea pigs.^{115, 159, 170} Pyolysin is produced by all T. pyogenes strains so far examined^{14, 73, 91} and is unique in many ways; expression of this cholesterol-dependent cytolysin (CDC) is required for virulence and it is probably the most promising vaccine candidate identified thus far.^{14, 91} Cytolysins produced by other Gram-positive organisms include listeriolysin O, perfringolysin O and streptolysin O, and these toxins all exert their cytolytic effects by targeting cholesterol to form pores in host cell membranes.^{14, 91} The toxic and...