Clostridium novyi infections

N P J KRIEK AND M W ODENDAAL

GENERAL INTRODUCTION: ENDOSPORE-FORMING GRAM-POSITIVE RODS AND COCCI Malignant oedema/gas gangrene group of Clostridium spp.

Introduction

Infection with Clostridium novyi type A, B, C or D is responsible for a number of distinctive syndromes which are dependent on the respective combinations of exotoxin elaborated by the organism involved. Type C is almost nonpathogenic although it has been isolated from water buffaloes (Bubalus bubalis) suffering from osteomyelitis. In general, type A infections are associated with swollen head in rams, type B with black disease, and type D with bacillary haemoglobinuria.

Rare reports have been published of the association of C. novyi with malignant oedema in cattle in which the lesions at necropsy are indistinguishable from those of blackquarter. ^{31, 36} In these animals it appears that C. novyi, which is often isolated in association with other clostridia from such lesions, may be present as the only cause of the lesions in about 30 per cent of cases. Similar cases are also diagnosed regularly in South Africa at the Veterinary Research Institute, Onderstepoort.¹¹ The type of C. novyi associated with these lesions has, however, not been reported. Some consider such cases of malignant oedema to be the consequence of wound infections, whereas others are of the opinion that the pathogenesis is similar to that of blackquarter. ¹¹ The clinical signs of cattle suffering from malignant oedema caused by C. novyi infection have not been described but are considered to be similar to those of blackquarter. At necropsy the lesions in these animals are characterized by the presence of a very extensive, voluminous, clear, virtually colourless, gelatinous infiltrate which occurs subcutaneously and intermuscularly.³⁶ Occasionally the inflammatory exudate is pinkish to reddish due to haemorrhage. In contrast to blackquarter, muscle lesions in association with the inflammatory infiltrate are generally absent, but if they are present, they are small.¹¹

Clostridium novyi is divided into the types A, B, C and D, based on different combinations of soluble toxic antigens produced by the different biotypes.²⁶

Clostridium novyi used to be referred to as Clostridium oedematiens, a name which still often appears in the literature, while C. novyi type D is also known as Clostridium haemolyticum. Although C. haemolyticum and C. novyi are currently considered to be distinct species,⁶ it has been suggested that they be regarded as the same species, as they have common somatic antigens, and the beta toxin of C. novyi type B is indistinguishable from the lethal toxin produced by C. haemolyticum. They also have similar cultural and morphological characteristics.^{27, 29} They do, however, cause different diseases in domestic animals, and different vaccines are used to protect against them.

Clostridium novyi occurs as part of the microbial flora in soil, marine sediments and intestinal flora of animals. Strains of types A, B and D have been isolated from the liver of normal sheep and cattle.^{28, 29} Toxigenic strains are commonly isolated from the soil.²³

Clostridium novyi type A infections

Synonyms: Swollen head in rams, dikkop by ramme (Afrik.)

Clostridium novyi type A is the aetiology of the swollen head syndrome in rams and is one of the causes of gas gangrene in humans and cattle. Swollen head is an acute, infectious, but non-contagious disease particularly of young rams and is characterized by the development of a pronounced inflammatory oedema of the head and neck which develops after wounds often inflicted to the head during fighting have become infected.

Aetiology

Clostridium novyi type A cells are 1,6 to 17 μm long and 0,6 to 1,4 μm wide, with oval, central or subterminal spores. Type B cells are considerably larger, being more than twice as long and much wider, and measuring 1,1–2,5 × 3,3–22,5 μm. Clostridium haemolyticum (C. novyi type D) cells are 0,6 to 1,6 μm wide and 1,9 to 17,3 μm long. They occur singly or in pairs. All strains are motile by virtue of their peritrichous flagella, the motility causing swarming on blood agar cultures. On wet mounts, however, motility is quite difficult to observe. The optimum temperature for growth is 45 °C, with most strains growing well at 37 °C and moderately at 30 °C, while no growth occurs at 25 °C. Strict anaerobic conditions are required for culturing and the presence of fermentable carbohydrates stimulates growth. Agar plates used for isolation of C. novyi should be stored under anaerobic conditions. No growth occurs when 20 per cent bile or 6,5 per cent sodium chloride is added to the culture medium.⁶

On blood agar, colonies of C. novyi are irregular in outline, round, 3 to 8mm in diameter, translucent and greyish, and have a ground-glass appearance. Spores are formed which are more resistant than those of the other clostridia, as they can resist the effects of boiling water for 30 minutes.⁴

Clostridium novyi type A strains produce alpha toxin (necrotizing, oedematizing and lethal), gamma toxin (necrotizing and haemolytic, and is a lecithinase or phospholipase C), delta toxin (oxygen-labile haemolysin) and epsilon toxin (lipase). Type B produces alpha toxin, beta toxin (necrotizing, haemolytic and lethal, and is a phospholipase C or lecithinase), zeta toxin (haemolytic), eta toxin (tropomyosinase) and a trace of theta toxin (lipase).^{24, 30}...