Bac Chp. 18 Exam 3

What is the Gram stain morphology of Haemophilus?

Gram-negative, pleomorphic coccobacilli/rods

Is Haemophilus motile?

No, nonmotile

What is the oxygen requirement of Haemophilus?

Facultative anaerobe

What is the oxidase result for Haemophilus?

Positive

What is the catalase result for Haemophilus?

Positive

What are the three major pathogenic Haemophilus species?

H. influenzae, H. aegypticus, and H. ducreyi

Why is Haemophilus called the "blood lover"?

It requires growth factors found in lysed red blood cells

What is X factor?

Hemin (hematin)

What is V factor?

NAD (nicotinamide adenine dinucleotide)

Where are X and V factor found?

Inside red blood cells

Why won't Haemophilus grow on blood agar (BAP)?

The RBCs are intact, so the growth factors inside them are not available

Why does Haemophilus grow on chocolate agar?

Chocolate agar is heated blood agar with lysed RBCs, which release X and V factor

What are the incubation conditions for Haemophilus?

35 to 37 C (slides also say 33 to 37 C) with 5 to 10% CO2

What conditions is Haemophilus very sensitive to?

Drying and chilling

What is satellitism?

Haemophilus growing on BAP only around an organism that makes V factor (e.g., S. aureus); on respiratory cultures you see tiny colonies around an S. aureus colony

Where does Haemophilus get X and V factor in satellitism?

X factor from the BAP and V factor from S. aureus

What does satellitism identify?

Haemophilus species that require V factor

How do you set up a satellite test?

Streak a known S. aureus on BAP, then streak the Haemophilus of interest next to it

What are the X and V requirements of H. influenzae?

Requires both X and V

What are the X and V requirements of H. parainfluenzae?

V only (no X needed)

What are the X and V requirements of H. ducreyi?

X only (no V needed)

What are the X and V requirements of H. aegypticus?

Requires both X and V

What are the X and V requirements of H. haemolyticus?

Requires both X and V (per the slide)

What are the X and V requirements of H. parahaemolyticus?

V only (no X needed)

What is a Haemophilus quad plate?

A plate with four zones: X only, V only, X plus V, and a blood zone (growth factors present) as a control

How do you read a quad plate for an organism needing both factors?

Growth only in the X plus V zone (and the blood control), none in the X-only or V-only zones

How else can X and V requirements be tested?

Filter paper discs impregnated with X, V, or both; growth only around the X plus V disc means both are required

What growth pattern points to Haemophilus?

Gram-negative coccobacilli growing on chocolate agar with no growth on BAP or MAC

What does H. influenzae look like on chocolate agar?

Translucent, tannish, moist, smooth, and convex

What odor does H. influenzae produce?

A "mousy" or bleach-like odor

What plate comparison suggests Haemophilus?

Many brown colonies on chocolate but none on blood agar

What does Haemophilus look like on Gram stain?

Ranges from small coccobacilli to long filaments

What does a capsule look like on a Gram stain?

A clear, non-staining halo

What are common specimen sources for Haemophilus?

Blood, CSF, middle ear exudate, joint fluid, respiratory specimens, conjunctival swabs, vaginal swabs, abscess drainage

Why is prompt specimen processing vital for Haemophilus?

Haemophilus dies rapidly in clinical specimens

What is the preferred way to plate Haemophilus specimens?

Direct plating on selective media at the bedside instead of transport media

Why was H. influenzae named, and does it cause influenza?

Named during the 1889 to 1890 flu pandemic because it was isolated from the nasopharynx of flu patients; it is actually a secondary infection to the influenza virus

What is the most significant virulence factor of H. influenzae?

The capsule

How many capsule types does H. influenzae have?

Six antigenically distinct types: a, b, c, d, e, f

Which capsule type caused most infections before the Hib vaccine?

Type b

What are non-encapsulated H. influenzae strains called?

Non-typeable

What are the other H. influenzae virulence factors besides the capsule?

IgA protease, adherence mechanisms, and outer membrane components

What does IgA protease do?

Breaks down IgA to help the organism infect mucosal surfaces

What type of disease do encapsulated H. influenzae strains cause?

Invasive disease

What are the invasive diseases caused by encapsulated H. influenzae?

Septicemia, septic arthritis, meningitis, osteomyelitis, cellulitis, pericarditis, pneumonia, epiglottitis

What type of disease do non-typeable H. influenzae strains cause?

Localized infections

What are the localized infections caused by non-typeable H. influenzae?

Otitis media with effusion, conjunctivitis, sinusitis, and bacteremia

What did the Hib vaccine do to invasive disease?

Greatly decreased invasive disease among children

What is the situation with H. influenzae serotypes today in the US?

Most infections are caused by non-b and non-typeable strains because of vaccination

Where is type b still a major problem?

Developing countries without vaccination (bacterial pneumonia deaths and meningitis in children)

What is H. aegypticus related to?

Genetically related to H. influenzae and difficult to differentiate from it

What disease does H. aegypticus cause?

Conjunctivitis ("pinkeye"), common in children

Who first observed H. aegypticus, and when?

Robert Koch in 1883, in Egyptians with conjunctivitis

What is H. ducreyi a strict pathogen of?

Humans only

What disease does H. ducreyi cause?

Chancroid, a highly communicable sexually transmitted disease

What is chancroid also called?

"Soft chancre"

Why is it called a soft chancre?

The sore has no hard, firm base, which is typical of primary syphilis

What are the lesions of chancroid like?

Painful lesions on the genitalia or perianal areas

What lymph node finding is common in chancroid?

Pus-forming, enlarged, draining inguinal lymph nodes

Who is usually asymptomatic with H. ducreyi?

Most women

What does HACEK stand for?

Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella

What infection do all HACEK organisms cause?

Endocarditis

How do HACEK organisms cause endocarditis?

They are opportunists that attach to damaged or prosthetic heart valves and form vegetations

What are the shared characteristics of the HACEK group?

Gram-negative bacilli, fastidious, slow-growing, grow best in increased CO2, and opportunists that often need a compromised host

Why does poor dental hygiene raise endocarditis risk?

Many HACEK organisms live in dental plaque and can spread to the heart, especially after dental procedures

Which primary plate will Haemophilus and Aggregatibacter not grow on?

MacConkey agar

Which HACEK species is most prevalent in endocarditis?

Aggregatibacter aphrophilus

What else is Aggregatibacter aphrophilus linked to?

Bone and joint infections

Where is Aggregatibacter aphrophilus found?

Dental plaque and gingival scrapings

What does Aggregatibacter aphrophilus look like on chocolate agar?

Convex, granular, yellow colonies with an opaque zone near the center

What factor does Aggregatibacter aphrophilus depend on?

V factor

What disease is Aggregatibacter actinomycetemcomitans a major contributor to?

Periodontitis (destroys the alveolar bone supporting teeth)

Where is Aggregatibacter actinomycetemcomitans found?

Normal oral flora in humans

How are tissue infections with Aggregatibacter actinomycetemcomitans acquired?

Bites from cattle, sheep, pigs, and horses

What is the colony appearance of Aggregatibacter actinomycetemcomitans?

Star-shaped with four to six points

What are the X and V requirements of Aggregatibacter actinomycetemcomitans?

Negative for both X and V factor requirements

Where is Cardiobacterium hominis normal flora?

Nose, mouth, and throat

What is the usual manifestation of Cardiobacterium hominis, and what precedes it?

Endocarditis, usually preceded by oral infections or dental procedures

How does Cardiobacterium hominis look in yeast extract?

Rosettes, swellings, long filaments, or stick-like structures

What media does Cardiobacterium hominis grow on?

Sheep blood agar and chocolate agar

Where is Eikenella corrodens normal flora?

Oral and bowel cavities

Which HACEK member is the least common cause of endocarditis?

Eikenella corrodens

Which HACEK member is most often seen as normal flora in respiratory cultures?

Eikenella corrodens

What is Eikenella corrodens associated with?

Human bites, poor dental hygiene, and oral surgery

What is the Gram stain morphology of Eikenella corrodens?

Fastidious gram-negative coccobacilli

What pigment does Eikenella corrodens often produce?

Yellow

What colony feature of Eikenella corrodens is an ASCP favorite?

Colonies often have a pit or depression in the center of the agar surface

What odor does Eikenella corrodens give?

A chlorine/bleach-like odor

Which HACEK organisms are important pediatric pathogens?

Kingella (K. kingae, K. denitrificans, K. oralis, K. potus)

What is Kingella kingae the most common cause of?

Osteoarthritis in children under 4 years old

When is Kingella associated with endocarditis?

Especially in immunocompromised patients

What does Kingella look like on Gram stain?

Coccobacilli/short bacilli with squared ends, in pairs or short chains

What Gram stain problem occurs with Kingella?

It often resists decolorization and appears gram positive although it is gram negative

What family does Capnocytophaga belong to?

Flavobacteriaceae

Where is Capnocytophaga normal flora?

The human oral cavity (and some species in cats and dogs)

Is Capnocytophaga commonly involved in endocarditis?

No, unlike the HACEK organisms

What is the most common clinical isolate of Capnocytophaga?

C. ochracea

What infections does Capnocytophaga cause?

Septicemia in neutropenic patients with oral ulcers, soft tissue infections, and peritonitis

What exposure should you look for in the chart with Capnocytophaga?

A cat or dog bite

What is the shape of Capnocytophaga?

Thin and often fusiform (pointed ends) gram-negative bacilli