Klebsiella spp. infections

M M HENTON

GENERAL INTRODUCTION: FACULTATIVELY ANAEROBIC GRAM-NEGATIVE RODS

Introduction

Infections with Klebsiella spp. cause a variety of syndromes in livestock, the most important being endometritis, infertility and abortion in mares, mastitis in cows and sows, and neonatal septicaemia, particularly in foals. In southern Africa, the majority of infections are associated with the genital tract of Thoroughbred mares. Antibiotic resistant strains of Klebsiella commonly cause nosocomial infections in humans.²⁸

Klebsiella was first described by Escherich in 1885 as Bakterium lactis aerogenes but as this name was later also used for Enterobacter, it was changed to Klebsiella, after the German bacteriologist, Edwin Klebs.²⁸

The pathogenic capsular types found in South Africa are similar to those in other parts of the world (Table 149.1).^{4, 10, 22, 29}

Aetiology and epidemiology

The genus Klebsiella belongs to the family Enterobacteriaceae. Klebsiella spp. are facultative anaerobes and are large, non-motile, Gram-negative rods (0,3 to 1,0 μm wide and 0,6 to 6,0 μm long) usually containing a thick, mucoid capsule.

In the laboratory they grow well on most growth media, forming large, moist and viscid colonies. Klebsiella spp. are inositol-positive, and most pathogenic strains are rapidly urease-positive. They are classified biochemically into K. pneumoniae, K. oxytoca, K. terrigena, and K. planticola. ²⁸ Klebsiella pneumoniae is subdivided into three subspecies: pneumoniae, ozaenae and rhinoscleromatis. Klebsiella pneumoniae and K. oxytoca are isolated from various pathological processes in humans and animals, while K. terrigena and K. planticola are mainly found in soil and water.²⁸

The biochemically defined species of Klebsiella are serotyped with one set of capsular typing antisera.⁹ Currently, all strains of Klebsiella are serologically classified into 77 currently recognized capsular types,²⁸ and numbered from 1 to 82, as five of them (capsular types 73, 75, 76, 77 and 78) were subsequently found to be invalid.¹² The lipopolysaccharide O-antigens are not usually determined, as the test methods (either unencapsulated mutants have to be selected, or an inhibition enzyme-linked immunosorbent assay performed) are cumbersome, and not as discriminatory, as there are only nine currently recognized O-groups.¹² The serological classification gives a much clearer indication of pathogenicity than does biochemical typing.^{17, 26, 27} Plasmid profiles of isolates from horses and bovine mastitis show promise as indicators of virulence.^{16, 18} Fimbrial adhesins have been described, but their role in the pathogenesis of disease in animals is still unclear.³¹

Serotyping is done by means of the quelling (Neufeld) reaction; ⁹ live bacteria are mixed with capsular antisera, and the reaction indicated by refractile, precipitin patterns which are discernible microscopically on the surface of the bacterial capsule. The O-types of Klebsiella are usually not characterized, as they are few in number, and typing of the O-antigens is hampered by the large capsule.

Table 149.1 Number of common capsular types of Klebsiella spp. isolated from horses at the Veterinary Research Institute, Onderstepoort, from 1972 to 1999

Klebsiella spp. are ubiquitous and occur in soil and water, or are part of the normal flora in the gastrointestinal tract of animals, albeit often in low numbers. They are particularly common in contaminated wood shavings and soil-containing shavings.²⁵ Wood shavings used as bedding are therefore an important source of infection, especially when severely contaminated with faeces.²⁷

Klebsiellae are opportunistic pathogens. The pathogenicity of specific capsular types for livestock species other than horses is largely unknown. In South Africa, capsular types 2, 6, 21, 30 and 33 are most commonly isolated from cattle. The types that are usually associated with mastitis in cows are 2, 19, 21, 30, 33 and 53. Opportunistic infections in pigs are more commonly caused by capsular types 22, 30, 31 and 33, and in sheep and goats types 2, 6, 21 and 33 predominate.¹³

Identification of the capsular types of Klebsiella isolated from the genital tract of horses from 1972 to 1999 at the Veterinary Research Institute, Onderstepoort, showed that certain types are more common than others (Table 149.1). Stallions may be subclinical carriers of these types and may infect mares venereally.^{5, 17, 19} It was found that capsular types 1, 2 and 6 were associated with endometritis in mares. Types such as 3, 31 and 64 occurred only as transient colonists of the uterus, whereas types 6, 7, 21 and 30 that commonly infect the immunocompromised uterus, were also regularly isolated from the cervix of healthy horses.

Endometritis in mares

Flaccid, gaping vulvar lips, a vulva which slants dorso-cranially, or pneumovagina as a result of poor conformation in which the dorsal commissure of the vulva is displaced to a position...