Trueperella pyogenes infections

Trueperella pyogenes infections

M G COLLETT AND G F BATH

Introduction

Trueperella (Actinomyces) pyogenes occurs in a great variety of suppurative or pyogenic conditions in livestock (particularly in cattle, sheep, goats and pigs), either as a primary pathogen, a secondary invader or as part of a mixed infection with obligate anaerobes. It is most commonly incriminated as a cause of abscesses, wound infections, pneumonia, arthritis, mastitis, foot infections, osteomyelitis of vertebral bodies, pituitary abscessation, abortion, perinatal mortalities, and genital infections. It is the bacterium most frequently isolated from suppurative lesions in farm animals in South Africa.42

Originally called Corynebacterium pyogenes, the name was changed to Actinomyces pyogenes in 198217 and recent phylogenetic and 16S rRNA studies have resulted in it being reclassified as Trueperella pyogenes.93

Aetiology

Trueperella pyogenes is a non-motile, non-sporulating, facultatively anaerobic, slender, pleomorphic coccobacillus which shows varying degrees of Gram-positivity.123 There appears to be only a single serovar.105

Trueperella pyogenes is nutritionally fastidious and grows poorly on common laboratory media unless they have been supplemented with blood or serum.83, 102 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.44 A chemically defined medium which supports rapid growth of the organism has been developed.94

Trueperella pyogenes can survive for at least 10 days at room temperature in moist debris.5

Pathogenesis

Little is known about the antigens of T. pyogenes or the local or systemic immune responses that are induced in the host.129 Trueperella pyogenes produces a filterable, oxygen-stable, haemolytic protein exotoxin, named pyolysin, which has been cloned.9, 14, 30, 71 It is an important virulence factor, is fatal to mice and rabbits after intravenous injection and is dermotoxic to guinea pigs.72, 98, 105 The toxic and haemolytic activities of crude cell extracts are neutralized by an antitoxin9, 105 which is found in the sera of infected animals.90 High levels of antitoxin, however, do not protect against pyogenic infection.49 The organism also produces enzymes, such as protease and neuraminidase,65 as well as a leukotoxin30 and possesses lectin-like surface structures and plasma protein-binding and bacteriocin-like properties65 which potentially aid in its pathogenicity and virulence63 and may account for its ability to survive phagocytosis, 67 but they are not efficient as immunogens.21 The bacterium also has an antigen which cross-reacts with Mycobacterium paratuberculosis.123

In the presence of opsonizing antibodies in serum130 or milk-whey,129 T. pyogenes is highly susceptible to the bactericidal activity of neutrophils in vitro. In the female genital tract, local T. pyogenes infection stimulates uterine antibody synthesis (mainly IgG and IgA) in the absence of an increase in serum antibody.131 The bacterium does not elaborate chemotactic substances.130 On the other hand, Bacteroides spp. in vitro inhibit chemotaxis1 and phagocytosis by neutrophils, 50 suggesting that, in mixed infections, the presence of Bacteroides spp. (which are obligate anaerobes) could allow the persistence of T. pyogenes infection through the protection of the latter from neutrophil phagocytosis.130

There is also a synergistic relationship between T. pyogenes and another obligate anaerobe, Fusobacterium necrophorum. The presence of T. pyogenes in the tissues lowers the oxidation-reduction potential in the affected areas while producing a diffusable factor which stimulates the growth of F. necrophorum.96 The latter, in turn, produces a leukotoxin which protects both organisms from phagocytosis.95 In mixed infections, F. necrophorum is probably the primary invasive and necrotizing agent that facilitates the establishment and growth of bacteria such as T. pyogenes and Bacteroides spp.56, 95, 96

Pulmonary intravascular macrophages play a role in the uptake of T. pyogenes from the blood and the initiation of embolic pulmonary abscesses in cattle.68

Epidemiology, clinical signs and pathology

Trueperella pyogenes is a commensal on the mucosal surfaces of healthy animals.105 For example, it occurs on the mucosa of the preputium of rams52 and that of the alimentary, urogenital and respiratory tracts of healthy cattle, and in the udder of normal cows.81, 83, 105

Damage to tissues, such as that resulting from trauma or viral or other bacterial infections, is usually required to establish infection. Abscesses may occur in virtually every organ or tissue in the body, and the clinical signs manifested by affected animals are related to the disturbance of function of the affected part. Abscesses usually develop rapidly and are generally fluctuant when mature. They contain pus which is greenish-yellow or greyish, has a fluid consistency, and is usually malodorous; their capsules are not as well...

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