Gram Negative Rod Bacteria with Low Pathogenic Potential

The bacterial species listed in Table 4.10 are typical opportunists that occasionally cause infections in persons with defective specific or nonspecific immune defenses. When they are isolated from infective material, their pathological significance is in most cases difficult to interpret.

Table 4.10 Overview of Gram-Negative Rod Bacteria with Low Pathogenic Potential

Bacterial species

Most important characteristics

HACEK group

- Hemophilus aphrophilus

- Actinobacillus actino-mycetemcomitans

- Cardiobacterium hominis

- Eikenella corrodens

- Kingella kingae

Endocarditis, cerebral abscesses

Part of normal oral cavity flora. Nonmotile, slender rods; microaerophilic; colonies on blood agar with "starfish" appearance. Accompanying bacterium in approx. 25% of oral-cervicofacial actinomycoses. Penicillin G resistance. Also a pathogen in endocarditis.

Nonmotile; pleomorphic. Normal flora of the respiratory tract. Culturing on blood agar in 5% CO2 at 35 °C for 4 days. Endocarditis. Occasionally observed as component of mixed flora in facial purulent infections.

Nonmotile, coccoid. Normal flora of respiratory and intestinal tracts. Cultures, on blood agar, show corrosion of the agar surface.

Abscesses, wound infections, peritonitis, empyemas, septic arthritis, often as part of a mixed flora. Also reports of endocarditis and meningitis.

Normal flora of the upper respiratory tract. Rare cases of endocarditis, arthritis, osteomyelitis.

Table 4.10 Continued: Overview of Other Gram-Negative Rod Bacteria

Bacterial species

Most important characteristics

Calymmatobacterium granulomatis (syn. Donovania granulomatis)

Streptobacillus moniliformis

Chryseobacterium (formerly Flavobacterium) meningo-septicum (and other flavo-bacteria)

Alcaligenes faecalis (and other species of the genus Alcaligenes)

Capnocytophaga spp.

Nonmotile, capsule, culturing on mediums containing egg yolk; facultative anaerobe. Granuloma inguinale. Venereal disease; indolent, ulcerogranulomatous lesions on skin and mucosa. Sporadic occurrence in Europe. Diagnosis involves identification of bacteria in vacuoles of large mononuclear cells using Giemsa staining (Donovan bodies). Antibiotics: aminoglycosides, tetracyclines

Pronounced pleomorphism; frequent production of filaments because of defective cell walls. Culturing in enriched mediums at 35 °C, 5% CO2, 3 days. Component of oral cavity flora in rats, mice, cats Rat bite fever. Incubation period 1-22 days. Fever, arthralgias, myalgias, exanthema. Possible inflammation at site of bite. Polyarthritis in 50% of patients. Therapy with penicillin G.

Strictly aerobic; often with yellow pigment; nonfermen-ter. Natural habitat soil and natural bodies of water. Meningitis. In neonates. Poor prognosis. Sepsis, pneumonia in immunocompromised patients. All infections rare.

Strictly aerobic; nonfermenter. Natural habitat soil and surface water.

Various opportunistic infections in patients with severe primary illnesses; usually isolated as a component in mixed flora; data difficult to interpret.

Component of normal oral cavity flora in humans and dogs. Long, thin, fusiform rods. Proliferation on blood agar in presence of 5-10% CO2. Can contribute to pathogenesis of periodontitis. Sepsis in agranulocytosis, leukemias, malignancys. Wide variety of purulent processes. Often component of mixed flora.

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