Module 10 ~ Book Notes Bordetella

  • respiratory tract pathogens that cause whooping cough or pertussis

  • general characteristics

    • small, gram-negative bacilli or coccobacilli

    • obligate aerobic bacteria; grows best at 35-37oC

    • no fermentation of carbohydrates & inactive biochemical test systems

    • oxidation of amino acids

    • catalase positive

  • B. pertussis characteristics

    • catalase variable

    • fastidious & requires special collection and transport systems and culture media

    • inhibited by fatty acids, metal ions, sulfides, and peroxides

    • media for isolation require protective substances like charcoal, blood, or starch to bind & neutralize inhibitory substances

  • B. pertussis virulence factors

    • filamentous hemagglutinin (FHA) and pertactin

      • facilitate attachment to ciliated epithelial cells

    • pertussis toxin (PT)

      • a protein exotoxin that modifies host proteins by adenosine diphosphate-ribosyl transferase that interferes with signal transduction

    • adenylate cyclase toxin

      • inhibits host epithelial and immune effector cells by inducing supraphysiologic concentrations of cyclic adenosine monophosphate

    • tracheal cytotoxin

      • contributes to pathogenesis by causing ciliostasis, inhibiting DNA synthesis, and promoting cell death

  • clinical manifestations

    • pertussis

      • catarrhal phase — insidious & nonspecific symptoms such as sneezing, mild cough, and runny nose

        • highly communicable

      • paroxysmal phase — onset of coughing which can lead to coughing spells followed by vomiting

      • convalescent phase — begins within 4 weeks of symptoms onset; decrease in frequency and severity of coughing spells

    • spread by respiratory droplets or direct contact with infectious secretions

      • pathogen can adhere and replicate on ciliated respiratory epithelial cells

      • to prevent spread, acellular pertussis (aP) vaccination distributed

    • for specimen collection:

      • nasopharyngeal aspirates or swabs of Dacron polyester with nonwire shaft

    • detection by nucleic acid w/PCR

      • should only be utilized with at least two DNA targets

      • seek confirmation to avoid mischaracterization

  • isolation methods

    • Bordet-Gengou potato infusion agar with glycerol and horse/sheep blood

    • Regan-Lowe medium (contains charcoal, starch, horse blood, cephalexin, and amphotercin B)

    • Stainer-Schtolte medium (contains casamino acids)

  • colony morphology

    • on charcoal-horse blood and Regan-Lowe media, the colonies are smooth, glistening, and silver like mercury droplets

    • on Bordet-Gengou agar, colonies are hemolytic

  • identification methods

    • tiny gram-negative coccobacilli

  • antimicrobial susceptibility

    • B. pertussis and B. parapertussis are generally sensitive to the macrolides, ketolides, penicillins, and tetracylines but are resistant to oral cephalosporins

    • erythromycin can be used for treatment only during the catarrhal phase

    • alternative treatments include azithromycin and trimethoprim-sulfamethoxazole