CH 18: Haemophilus and other fastidious Gram negative bacilli

Quad Plate - X and V testing

• special plate to identify members of Haemophilus genus

• distinguishes organisms based on whether they require X, V factor, both, and whether or not they hemolyze blood

Haemophilus - general characteristics

• GN, pleomorphic, coccobacilli or rods

• most are non-pathogenic or produce opportunistic infections

• most require some combo or X and V factor

  • dont grow on SBA, but will grow on CHOC

• colony morphology

  • growth ONLY on CHOC

  • wet, tan-colored, convex

  • distinct “moussy” or “bleachy” odor

  • catalase and oxidase (+)

Haemophilus influenzae

• major pathogen of its genus

• six antigenically distinct types

  • types a-f

  • type b, AKA Hib, most virulent

• most known for causing:

  • upper and lower resp. infections

    • pneumonia, otitis media, sinusitis, and conjunctivitis

    • meningitis much less common w/ vaccinations

Haemophilus influenzae - Testing

• Quad plate:

  • requires X and V factors

  • NO hemolysis

• satellitism

  • special characteristic

  • colonies will grow on SBA if a beta hemolytic S. aureus also present

    • S. aureus releases X and V factors

Haemophilus aegyptius

• subgroup of H. influenzae

  • biochemically very similar

• known for causing

  • pediatric conjunctivitis

  • Brazilian Purpuric fever

    • small outbreaks in South America

    • conjunctivitis followed by high fever, septicemia, shock, death

    • mortality rate approaching 70%

Haemophilus decreyi

• causative agent of chancroid

  • highly contagious STI

  • genital ulcer disease

    • causes chancres - open lesions on penis or labia

  • facilitates spread of other STIs

• uncommon in US, but significant in South America, Asia, and Africa

• testing

  • requires X, but not V

HACEK Bacilli

• acronym used to describe group of fastidious GNBs

• oral/respiratory normal flora

• most known and high risk for

  • endocarditis and septicemia after dental procedures

  • pts w/ previous heart conditions/sx most susceptible

HACEK Bacilli Species

• Haemophilus aphrophilus - now called Aggregatibacter aphrophilus

  • most prevalent species in this group

  • lives in oral cavity

• Aggregatibacter actinomycetemcomitans

  • major contributor in periodontitis (severe gum disease)

• Cardiobacterium hominis

• Eikenella corrodens

  • infection after human bites or trauma from human teeth

  • colonies ‘pit’ or ‘corrode’ the agar

• Kingella spp.

  • important pathogen in pediatric population

  • infects heart, joints, and bones

Capnocytophaga

• normal microbiota in oral cavity of mammals

• significant cause of

  • zoonotic infections

  • soft tissue infections and septicemia after cat/dog bites

• morphology: long, banana-shaped, fusiform GNB

Pasteurella multocida

• normal microbiota in oral cavity of birds and mammals

• most known for causing soft tissue infection after cat bites

• morphology: small, ovoid, GN coccobacilli

  • bi-polar staining, ‘safety-pin’ staining

Bioterrorism Agents

• category A

  • highly contagious

    • aerosolized

  • high mortality

• category B

  • moderately contagious

  • moderate damage (morbidity)

Brucella spp.

• GNB zoonotic ifx passed thru pigs, cattle, goats, and sheep

  • ingestion of undercooked/unpasteurized animal products

• category B bioterrorism agent

  • highly contagious (NOT aerosolized)

    • high morbidity, low mortality

• brucellosis

  • recurrent, chronic, undulating fevers

  • chronic fatigue syndrome, arthritis, depression

• testing

  • growth on BAP (no X or V factor)

  • quickly urease (+) (<2 hrs)

Francisella tularensis

• zoonotic infx passed thru rabbits

  • rabbit fever = tularemia

  • ingestion of infected meat, inhalation during meat processing, or tick bites

• category A bioterrorism

• GS looks very similar to Haemophilus

• tularemia

  • severe respiratory infx that affects lymph nodes

  • septecemia common and mortality rate near 30%

• morphology/testing

  • requires L-cysteine to grow

    • CHOC, MTM, or Buffered Charcoal Yeast Extract (BCYE) agars

  • oxidase, satellite, and X/V test negative

Legionella pneumophila

• legionnaire’s disease

  • community acquired atypical pneumonia

  • most often contracted thru inhaled water sources

    • AC, humidifers, misters

  • lead to bacteremia and organ failure

    • mortality near 30%

• morphology

  • requires L-cysteine to grow

  • light growth on CHOC, but grow best on BCYE agar

    • gray to white center w/ blue, green, or pink outer bands

    • ground glass appearance

Legionella pneumophila Testing

• lightly staining GNB

• requires L-cysteine for growth

• direct fluorescent antibody (DFA) test

• urine antigen

Bordetella pertussis

• causative agent of whooping cough

  • highly communicable childhood illness

  • fever and severe cough w/ ‘whoop’ sound

  • mortality rates around 2%, but can cause permanent lung damage

• DTaP vaccine

• culture and testing

  • doesnt grow well outside of host

  • specialized media

    • Bordet-Gengou media

    • Regan-Lowe agar

  • more testing is done thru PCR and molecular methods