Chapter 14 Miscellaneous Coliforms: The Genera Klebsiella, Enterobacter, and Citrobacter

Members of the family Enterobacteriaceae ferment lactose, producing acid and gas, with the former evidenced in the pink colonies they produce on MacConkey agar (Figure 14-1). Colonies of Klebsiella, Enterobacter, and Citrobacter on blood agar are nonhemolytic, shiny, round, gray with entire margins, and 2 to 3 mm diameter after 24-hour incubation at 37° C. All are facultatively anaerobic, oxidase-negative, gram-negative rods. Infections associated with these organisms are opportunistic.

FIGURE 14-1 Lactose-fermenting colonies on MacConkey agar. Klebsiella, Enterobacter, and Citrobacter spp.

(Courtesy Karen W. Post.)

THE GENUS KLEBSIELLA

The genus Klebsiella contains nonmotile encapsu lated organisms that are Voges-Proskauer positive, hydrolyze urea, ferment inositol, and utilize citrate, but fail to produce ornithine decarboxylase or hydrogen sulfide (Table 14-1). The three species currently in the genus are Klebsiella pneumoniae, Klebsiella oxytoca, and Klebsiella granulomatis. Klebsiella pneumoniae is divided into subspecies ozaenae, pneumoniae, and rhinoscleromatis. The animal pathogenic species are K. pneumoniae ssp. pneumoniae and K. oxytoca.

TABLE 14-1 Biochemical Differentiation Among Genera Klebsiella, Enterobacter, and Citrobacter

Diseases and Epidemiology

Klebsiella spp. are common in nature, where they are found in surface water, sewage, soil, and on plant material. Klebsiellae are commensals of the mammalian intestinal tract. Klebsiella pneumoniae ssp. pneumoniae has been associated with a variety of infectious processes in animals, including bovine mastitis, equine metritis, navel ill/joint ill, and neonatal septicemia in foals, calves, and kids, and is a cause of various infections in dogs, pet birds, poultry, and captive reptiles.

Bovine mastitis attributed to K. pneumoniae ssp. pneumoniae is economically significant, occurring as peracute disease in individual animals or as outbreaks of acute disease. Case fatality rates may be as high as 80%. Sawdust and shavings are major reservoirs of klebsiellae, and disease is most common in dairy cattle housed during the winter months on sawdust bedding. It is also diagnosed in animals kept in confinement on dry lots. Mastitis is associated with gross contamination of udder and teats with feces and bedding, and is frequently seen within a few days of calving. Moist bedding promotes environmental replication of the organism, and trauma induced by improperly functioning milking machines predisposes the udder to infection. Sporadic cases of caprine and porcine mastitis caused by K. pneumoniae have also been reported (Figure 14-2).

FIGURE 14-2 Porcine mastitis caused by Klebsiella pneumoniae.

(Courtesy J. Glenn Songer.)

Klebsiella pneumoniae and K. oxytoca are opportunistic pathogens of the equine reproductive tract. The clitoris, urethra, and vestibule of mares may become colonized, and vaginitis, infertility, metritis, and abortion occur in some of these individuals. Stallions acquire the infection during coitus and transmit it to other mares during natural service. However, stallions are not considered to be important reservoirs of infection, as klebsiellae are usually cleared from the male reproductive tract within 2 weeks. Fomites, such as vaginal speculums and biopsy equipment, can also serve to transmit infection.

The acute neonatal infection known as navel ill can be caused by a variety of bacteria, but coliforms are commonly involved. It is more common in animals with failed passive transfer resulting from ingestion of inadequate amounts of colostrum. Disease manifests as septicemia, often with a purulent focus in umbilicus, joints, lungs, or kidney, resulting in omphalitis, septic arthritis, pneumonia, and pyelonephritis.

Klebsiella pneumoniae has been recovered from a wide range of canine infections. Disease manifestations include pyometra, cystitis, prostatitis, pneumonia, meningoencephalitis, enteritis, mastitis, neonatal septicemia, hepatic abscessation, and otitis externa. The ability of Klebsiella to acquire extended-spectrum β-lactamase resistance and to spread within the hospital environment has resulted in its emergence as an important nosocomial pathogen of hospitalized animals. Canine nosocomial infections are primarily associated with surgical wounds, the urinary tract, and septicemia.

Klebsiella pneumoniae and K. oxytoca are important pathogens of companion birds. These organisms are contaminants of birdseed, fruits, and vegetables. Birds are easily colonized, and the organisms are frequently isolated from the cloaca and choana of clinically normal birds. Respiratory infections, septicemia, and diarrhea are common disease manifestations in compromised hosts.

Klebsiella pneumoniae is occasionally associated with embryo mortality in poultry. Disease is often associated with poor hatchery sanitation. The organism is isolated from various reptiles with pneumonia and hypopyon, and from osteomyelitis in snakes and iguanids.

Klebsiella spp. account for 3% to 7% of all nosocomial bacterial infections of humans in the United States. The urinary tract is the most common site of infection. In pediatric wards, Klebsiella spp. are often associated with neonatal septicemia. K. granulomatis is the etiologic agent of granuloma inguinale, a sexually transmitted disease characterized by anogenital granulomatous lesions.

< div class='tao-gold-member'>

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Join