Bacteriology exam prep: Klebsiella, Campylobacter, Yersinia, Helicobacter

Genus Klebsiella

• Non-haemolytic, facultative anaerobe, and opportunistic pathogen
• Naturally found in the intestinal tract of animals, producing capsules similar to other Enterobacteriaceae
• Produces endotoxins, adhesins, enterotoxins, and siderophores

Diseases Caused by Klebsiella

• Cervicitis, metritis in mares
• Urinary tract infections in dogs
• Pneumonia and suppurative conditions in foals
• Coliform mastitis in cattle, a serious condition with case-fatality rates ranging from 10-80%
• Mammary gland infections with septicemia and endotoxic shock in cattle

Contributing Factors to Pathogenesis

• Contamination of surgical equipment, cleaning devices, and surfaces
• Acquisition of beta-lactamase resistance

Genus Citrobacter

• Opportunistic pathogen causing wound infections and urogenital tract infections
• Resistant to cephalosporins and penicillin

Pathogenic Species

• Klebsiella pneumoniae: urogenital tract infections, bronchopneumonia, mastitis, and metritis in different animal species
• Klebsiella oxytoca: urinary tract infections and septicaemia in different animal species
• Klebsiella aerogenes: mastitis in cattle, urogenital infections in mares, and mastitis-metritis-agalactiae syndrome in sows
• Citrobacter freundii: meningitis and abscesses in newborn babies, mastitis in cattle, wound infections, and infections of the urogenital tract

Genus Yersinia

• The genus Yersinia was previously included in the family Enterobacteriaceae, but it was reclassified into a new family, Yersiniaceae, in 2016.
• Yersinia species are gram-negative coccobacilli that exhibit bipolar staining, especially in smears from affected tissues and stained with Giemsa stain.
• Most species are flagellated at ambient temperatures, making them motile at 18-20°C.

Pathogenic Species

• Yersinia pestis: causes bubonic plague in humans, rodents, and occasionally in domestic animals.
• Yersinia pseudotuberculosis: mainly affects birds and rodents, causing food and water-borne illnesses, mesenteric lymphadenitis, terminal ileitis, acute gastroenteritis, and septicemia.
• Yersinia enterocolitica: mainly causes disease in domestic animals and primates, and is the most prevalent species in humans, causing food and water-borne illnesses, mesenteric lymphadenitis, terminal ileitis, acute gastroenteritis, and septicemia.

Features of Pathogenic Species

• Tropism for lymphoid tissues
• Resistance to non-specific immune responses and phagocytosis of macrophages
• Facultative intracellular pathogens
• Formation of extracellular colonies in tissues
• Production of Yersinia outer proteins
• Transmission to humans directly or indirectly via animal reservoirs

Yersinia pestis

• Natural habitat: concentrated in certain endemic areas in southern and southeastern Asia, southern and west central Africa, western North America, and north central South America.
• Tolerant rodents (mice, rats) in endemic areas constitute the primary plague reservoir.
• In the urban cycle, the rat is the main intermittent host, and the main vector is the oriental rat flea.
• Transmission: primarily through bite wounds of infected rodent fleas, and through droplet inhalation after close contact with infected mammals.
• Pathogenesis: involves the formation of hemorrhagic inflammatory lesions, local lymph node involvement, septicemia, and endotoxemia, leading to death if untreated.

Yersinia pseudotuberculosis

• Causes mesenteric lymphadenitis, terminal ileitis, acute gastroenteritis, and septicemia in birds and rodents.
• Transmission: fecal-oral, with exposure primarily through ingestion of contaminated food and water.
• Pathogenesis: involves the internalization of bacteria by M cells, phagocytosis, apoptosis, and the induction of inflammation, leading to diarrhea, vomiting, weight loss, and depression.

Yersinia enterocolitica

• Causes mesenteric lymphadenitis, terminal ileitis, acute gastroenteritis, and septicemia in domestic animals and primates.
• Transmission: fecal-oral, through ingestion of food and water contaminated with animal feces, or by direct contact with animal feces.
• Pathogenesis: similar to Y. pseudotuberculosis, involving the internalization of bacteria by M cells, phagocytosis, apoptosis, and the induction of inflammation, leading to diarrhea, vomiting, weight loss, and depression.

Yersinia ruckeri

• Causes enteric red mouth disease in freshwater fish, particularly rainbow trout.
• Transmission: through contaminated water or food.
• Pathogenesis: involves the formation of hemorrhagic inflammation of the perioral subcutaneous tissue, leading to systemic disease and mortality in fish.

Campylobacter Genus

• Belongs to the family Campylobacteraceae
• Characterized as small, slender, curved (S-shaped) rods that are Gram-negative
• Associated with diseases of the reproductive and intestinal tracts

Characteristics of Campylobacter

• Slow-growing, fastidious, and sensitive to oxygen, low pH, osmotic stress, and high temperatures
• Motile with characteristic darting or corkscrew-like motility

Veterinary Importance

• Species of importance include C.fetus, C.jejuni, C.coli, C.upsaliensis, and C.lari
• Species can be pathogenic or non-pathogenic, with non-pathogenic species being commensals of the intestinal tract of humans and animals

Species and Primary Hosts

• C.fetus: ruminants
• C.jejuni: poultry, ruminants, pigs, dogs, cats, and humans
• C.coli: pigs, poultry, ruminants, and humans
• C.upsaliensis: dogs, cats, and poultry
• C.lari: wild birds and dogs

Disease in Animals and Humans

• C.fetus: abortion, diarrhea, and bacteremia in animals; diarrhea and bacteremia in humans
• C.jejuni: abortion, diarrhea, and asymptomatic in animals; diarrhea, bacteremia, and asymptomatic in humans
• C.coli: asymptomatic, abortion in animals; diarrhea, bacteremia, and asymptomatic in humans
• C.upsaliensis: symptomatic, diarrhea in animals; diarrhea, bacteremia in humans
• C.lari: diarrhea, bacteremia in humans

Natural Habitat

• C.fetus: reservoir intestinal tract and gall bladder of infected ruminants
• C.jejuni: intestinal tract and gall bladder of carrier sheep, poultry, and other animals
• C.coli: primary reservoirs in pigs and poultry

Transmission of Campylobacter spp.

• Reproductive disease: C.fetus ssp.venerealis by coitus, artificial insemination, or contaminated semen/equipment
• Enteric disease: ingestion of fecally contaminated feed or water, or by fetal fluids and placental membranes from aborted fetuses

Pathogenesis of Reproductive Disease

• C.fetus ssp.venerealis: multiplier in the vagina, enters the uterus, causes endometritis, and leads to repeated breeding, irregular estrus cycles, and increased calving intervals
• C.fetus ssp.fetus: localize to the placenta, causes placentitis, fetal infection, and abortion

Clinical Signs of Reproductive Disease

• Repeated breeding, irregular estrus cycles, increased calving intervals, and increased non-pregnant cows
• Abortion in cattle and goats

Pathogenesis of Enteric Disease

• C.jejuni adheres to and invades the intestinal epithelium, causing epithelial damage, hemorrhages, and production of cytokines
• Only a small minority of strains are serum resistant and can cause systemic infection

Clinical Signs of Enteric Disease

• Fever, abdominal cramps, and self-limiting watery to bloody diarrhea in both animals and humans

Genus Helicobacter

• Gram-negative, motile bacteria with a range of morphologies from tightly coiled spirals to slightly bent rods
• Belong to the family Helicobacteriaceae
• Originally classified as Campylobacter due to similar morphology

Habitat and Distribution

• Found in the gastrointestinal tract of humans, ferrets, birds, nonhuman primates, dogs, cats, pandas, dolphins, pigs, and other animals
• Can occupy the mucus layer or adhere to gastric epithelium tissue
• Some species are host-specific, while others can infect different animal species

Infection and Transmission

• 50% of humans carry H. pylori and potentially additional species in their GI tract
• ~80-100% of dogs and cats are infected with at least one species (H. felis, bizzozeronii, heilmannii, bilis, and others)
• ~60% of pigs are colonized with H. suis
• ~60% of poultry are infected with H. pylorum
• Transmission occurs through oral-oral and fecal-oral routes
• Can be zoonotically transferred between pets and humans

Pathogenesis and Pathological Changes

• Colonize the stomach, express virulence factors, and induce chronic inflammatory reactions
• Lead to gastric mucosa ulceration, and various changes, including:
  • Mononuclear inflammatory infiltration
  • Gastric intraepithelial lymphocyte infiltration
  • Fibrosis
  • Glandular degeneration
  • Follicular hyperplasia
  • Lymphoma
  • Epithelial injury and ulceration
  • Adenocarcinomas
  • Polyps and other changes

Clinical Signs and Economic Impact

• Possible clinical signs include pallor, melena, chronic vomiting, weight loss, inappetence, and diarrhea
• Enterohepatic helicobacters can cause diarrhea and/or hepatitis
• Majority of infections are asymptomatic
• Chronic gastritis in pigs leads to 10% reduction of daily weight gain, resulting in substantial economic losses