Miscellaneous Gram-Negative Rods Overview

Overview of Miscellaneous Gram-Negative Rods

Bordetella pertussis

  • Characteristics:

  • Very small (0.2 to 0.5 × 1 µm) gram-negative (GN) coccobacilli, can be found singly or in pairs

  • Strictly aerobic; capable of oxidizing amino acids

  • Optimal growth temperature: 35°C with high humidity

  • Slow-growing; may take up to 12 days to form colonies which are shiny and resemble mercury droplets

  • Requires enriched media such as charcoal, starch, blood, or albumin for growth

  • Pathogen and Disease:

  • The primary pathogenic species is Bordetella pertussis, which causes whooping cough. It can also include:

    • B. parapertussis - mild pertussis
    • B. bronchiseptica - respiratory disease in animals (dogs, pigs) and sometimes humans
    • B. holmesii - rare cause of sepsis

  • Clinical Features of Whooping Cough:

  • Incubation Period: 7-10 days

  • Phases of Disease:

    • Catarrhal Phase: mild cold-like symptoms (sneezing, fever, malaise)
    • Paroxysmal Phase: severe, violent coughing episodes that may lead to vomiting
    • Convalescent Phase: complications may arise such as pneumonia and seizures

  • Duration of paroxysmal cough: possible 3-4 weeks or longer

  • Virulence Factors:

  • Adhesins such as pertactin, filamentous hemagglutinin, and fimbria that bind to ciliated epithelial cells

  • Various toxins:

    • Dermonecrotic toxin: causes local tissue damage during colonization
    • Tracheal cytotoxin: inflammatory effects which inhibit ciliary movement
    • Pertussis toxin: A-B toxin affecting cellular immunity and leading to leukocytosis
    • CyaA toxin: promotes mucus production by raising cAMP levels
    • Siderophores: enhance iron acquisition

  • Epidemiology:

  • Endemic worldwide, with humans being the only reservoir for the pathogen

  • Transmission primarily occurs through inhalation of infectious respiratory droplets

  • Epidemiological factors affecting infection:

    • Age (infants <1 year at high risk)
    • History of immunization or prior infection
    • Antibiotic treatment

  • Vaccination:

  • Vaccines include DTaP and Tdap, which contain inactivated components of the bacteria

  • Vaccination has significantly reduced incidence rates, though cases still occur in inadequately vaccinated populations

Bartonella

  • Characteristics:

  • Short GN rods, optimal growth at 37°C with 5% CO2 and high humidity

  • Facultatively intracellular and fastidious; slow growth on enriched media requiring weeks

  • Notable species causing human disease:

    • B. bacilliformis: causes Oroya fever
    • B. quintana: leads to trench fever
    • B. henselae: linked to cat scratch disease

  • Diseases Caused:

  • Oroya Fever: Zoonotic transmission via vector contact, prevalent in the Andes

  • Trench Fever: characterized by recurrent fever, often observed in immunocompromised (IC) individuals

  • Cat-Scratch Disease:

    • Symptoms include chronic lymphadenopathy
    • Diagnosis requires satisfying specific criteria including known animal contact and histopathological evidence

Legionella pneumophila

  • Characteristics:

  • Thin, faint GN pleomorphic bacilli, notable for being motile

  • Mesophilic; requires iron and L-Cys for growth, fastidious concerning pH conditions

  • Primarily associated with L. pneumophila, responsible for most infections; grows in aquatic habitats and biofilms

  • Transmission & Pathogenesis:

  • Exists both in a transmissive and a replicative intracellular form within host macrophages

  • Inhaled bacteria are phagocytized by alveolar macrophages and replicate within specialized vacuoles

  • Highly virulent due to its ability to evade host immune responses

  • Diseases caused:

  • Legionnaires' Disease: pneumonia often linked with other systemic effects

    • Symptoms include high fever, cough, and gastrointestinal distress
    • Mortality rates are particularly high in IC patients

  • Pontiac Fever: self-limiting illness without pneumonia

  • Epidemiology:

  • Outbreaks are sporadic, usually in water systems, not person-to-person spread

  • Control measures include reducing microbial counts in water supplies

  • Vaccination and Prevention:

  • No effective vaccine currently exists for general use