Small Pleomorphic Gram-Negative Bacilli – Part 1

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Vocabulary flashcards covering key organisms, growth requirements, virulence factors, clinical diseases, and laboratory characteristics from the lecture on small pleomorphic gram-negative bacilli (Part 1).

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50 Terms

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Small Pleomorphic Gram-Negative Bacilli

Group of fastidious, shape-variable, gram-negative rods/coccobacilli that require enriched media and often special growth factors.

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Pleomorphism

Ability of a bacterium to alter its size and shape in response to environmental conditions.

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Fastidious Microorganism

Bacterium that needs complex nutritional or environmental requirements for growth, making it difficult to culture.

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Capnophile

Organism that grows best in an atmosphere with elevated CO₂ levels.

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Haemophilus (genus)

Small, non-motile, pleomorphic, gram-negative coccobacilli that are normal upper-respiratory flora and require X and/or V factors.

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X Factor (Hemin)

Heat-stable iron-porphyrin (hemin) required by some Haemophilus species for growth.

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V Factor (NAD)

Heat-labile cofactor nicotinamide adenine dinucleotide needed by many Haemophilus species.

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Haemophilus influenzae

‘Pfeiffer’s bacillus’; major cause of pediatric meningitis and epiglottitis; commonly tested for β-lactamase production.

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Pfeiffer’s Bacillus

Alternate name for Haemophilus influenzae.

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β-Lactamase

Enzyme that hydrolyzes the β-lactam ring of penicillins/cephalosporins, conferring resistance.

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H. influenzae Polysaccharide Capsule

Type-specific capsule (especially type b) that increases invasiveness and severity of infection.

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IgA Protease

Virulence enzyme of H. influenzae that cleaves secretory IgA, aiding mucosal colonization.

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Encapsulated vs Non-encapsulated H. influenzae

Encapsulated (typeable) strains cause invasive disease; non-encapsulated (non-typeable) strains usually cause local, milder infections.

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Epiglottitis

Life-threatening inflammation of the epiglottis commonly caused by encapsulated H. influenzae.

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Haemophilus ducreyi

Agent of chancroid; not normal flora; produces painful genital ulcers; requires X factor only.

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Chancroid (Soft Chancre)

Painful necrotizing genital ulcer caused by Haemophilus ducreyi; highly communicable STI.

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Haemophilus aegyptius

‘Koch-Weeks bacillus’; genetically related to H. influenzae; causes acute purulent conjunctivitis (pink-eye).

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Pink-Eye Conjunctivitis

Red, swollen eyes with sticky discharge produced by H. aegyptius infection.

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Haemophilus parainfluenzae

V-factor-dependent oral commensal that can cause endocarditis, often affecting the mitral valve.

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Satellite Phenomenon

Growth of V-factor-dependent Haemophilus as tiny colonies around NAD-producing organisms (e.g., S. aureus) on blood agar.

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Blood Agar vs Chocolate Agar

Blood agar supplies X factor; chocolate agar (heated blood) supplies both X and V factors for Haemophilus growth.

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Staphylococcus aureus (V-factor Producer)

Common helper organism used to supply V factor on blood agar for Haemophilus isolation.

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HACEK Group

Oral flora gram-negative bacilli (Haemophilus/ Aggregatibacter, Actinomycetemcomitans, Cardiobacterium, Eikenella, Kingella) causing slow endocarditis.

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Aggregatibacter (Haemophilus) aphrophilus

Most prevalent HACEK member; V-factor-dependent; causes endocarditis; yellow-granular colonies.

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Aggregatibacter actinomycetemcomitans

HACEK species linked to periodontitis; produces collagenase and leukotoxin; star-shaped colonies.

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Star-Shaped Colonies

Colony morphology (4–6 pointed center) characteristic of Aggregatibacter actinomycetemcomitans on agar.

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Cardiobacterium hominis

HACEK member that infects aortic valve; shows rosette cell arrangement and pits agar surface.

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Rosette Formation

Flower-like clustering of gram-negative bacilli seen with Cardiobacterium hominis.

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Eikenella corrodens

Chlorine-bleach-odored, agar-corroding bacillus causing cellulitis in drug users and clenched-fist wounds.

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Clenched-Fist Wound Infection

Soft-tissue infection of the hand following human bite trauma, often involving Eikenella corrodens.

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Kingella kingae

Non-motile HACEK bacillus causing bone and joint infections in children <3 yrs; resists decolorization.

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Brucella species

Intracellular, strict aerobes (B. abortus, B. melitensis) acquired from animals/milk; Category B bioterror agents.

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Brucellosis

Zoonotic infection with fever, malaise, possible chronicity; transmitted via aerosols, contact, or unpasteurized dairy.

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Undulant (Malta) Fever

Characteristic fluctuating fever pattern of sub-chronic brucellosis—normal in morning, spikes later in day.

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Bordetella pertussis

Strictly human pathogen causing whooping cough; fastidious aerobic gram-negative coccobacillus.

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Whooping Cough (Pertussis)

Highly contagious respiratory illness with paroxysmal coughing followed by inspiratory ‘whoop’.

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Mercury Droplet Colonies

Shiny, domed colonies of B. pertussis on Bordet-Gengou or Regan-Lowe agar.

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Regan-Lowe Medium

Charcoal, horse-blood, cephalexin transport/enrichment medium for B. pertussis.

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Paroxysmal Stage (Pertussis)

Second clinical phase marked by severe, repetitive coughing fits that may cause vomiting.

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Francisella tularensis

Tiny, cysteine-requiring gram-negative coccobacillus causing tularemia; Category A bioterror agent.

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Tularemia

Zoonotic disease (often from ticks, rabbits) featuring ulceroglandular lesions and systemic symptoms.

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Eschar (Tularemia)

Black necrotic ulcer at Francisella inoculation site.

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Pasteurella multocida

Mushroom-odor, penicillin-susceptible gram-negative rod from animal bites; oxidase, indole positive.

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Mushroom Odor Colony

Distinct earthy smell produced by Pasteurella multocida on blood agar.

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Legionella pneumophila

Waterborne intracellular bacillus causing Legionnaires’ disease and Pontiac fever; requires L-cysteine and iron.

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BCYE Agar

Buffered charcoal-yeast-extract agar supplying L-cysteine and iron for Legionella isolation.

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L-Cysteine Requirement

Essential amino acid needed for Legionella growth, used diagnostically in specialized media.

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Legionnaires’ Disease

Severe atypical pneumonia with fever, cough, possible multi-organ involvement caused by L. pneumophila.

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Pontiac Fever

Mild, non-pneumonic, flu-like illness linked to Legionella exposure.

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Ground-Glass Colonies

Blue-green, glistening colonies with finely granular center typical of Legionella pneumophila on BCYE.