Haemophilus and Other Fastidious Gram-Negative Rods

This set of flashcards encapsulates the essential information about Haemophilus and other fastidious Gram-negative rods, covering characteristics, pathogenicity, clinical infections, lab diagnosis, and specific species details.

What are the main species included in the fastidious group of Gram-negative bacilli?

Haemophilus, HACEK, Legionella, Bordetella, Pasteurella, Brucella, Francisella.

What type of bacteria are Haemophilus spp.?

Gram-negative pleomorphic coccobacilli or rods.

Are Haemophilus species motile?

No, they are nonmotile.

What type of respiration do Haemophilus spp. perform?

They are aerobic or facultatively anaerobic.

What test results would you expect for Haemophilus species regarding oxidase and catalase?

They are oxidase and catalase positive.

Which Haemophilus species are major human pathogens?

H. influenzae, H. aegyptius, and H. ducreyi.

What factors classify Haemophilus species related to their growth requirements?

They are classified based on their requirements for V and X factors.

How does Haemophilus species typically appear on chocolate agar?

They appear as small, translucent, moist colonies.

What is the effect of satellitism in identifying Haemophilus species?

It helps to identify Haemophilus species when grown near other bacteria like Staphylococcus aureus.

What diseases are commonly associated with H. influenzae in children under 18 months?

Meningitis and septicemia.

What conditions does H. influenzae cause in older children?

Epiglottitis.

What symptoms can H. influenzae non-typable strains cause?

Bronchitis, sinusitis, pneumonia, and otitis media.

What is a characteristic of H. ducreyi?

It causes chancroid, a sexually transmitted condition.

What is the clinical feature of H. ducreyi infection?

Painful genital ulcers and enlarged inguinal lymph nodes.

What is unique about H. aegyptius?

It is associated with conjunctivitis and Brazilian purpuric fever.

What is Brazilian purpuric fever characterized by?

High fever, vomiting, petechiae, rash, septicemia, and shock.

What type of specimens are appropriate for collecting Haemophilus species?

Blood, CSF, respiratory specimens, conjunctiva swabs, etc.

Which culture media is employed for Haemophilus species due to their growth requirements?

Chocolate agar is used to provide X and V factors.

What type of morphology do Haemophilus species usually exhibit microscopically?

They appear as coccobacilli or small regular bacilli.

What could be seen in cerebrospinal fluid of a patient with H. influenzae meningitis?

Neutrophils and Gram-negative coccobacilli.

In the laboratory, what color and odor do Haemophilus colonies show on chocolate agar?

They appear grayish, moist, and have a ‘mousy’ or ‘bleach-like’ odor.

What are the two specific tests for identifying Haemophilus spp. regarding growth factors?

Testing for X and V factors.

What conditions do Aggregatibacter species often relate to?

Subacute bacterial endocarditis and soft tissue infections.

What is the characteristic setting for growing HACEK group organisms?

An increased CO2 environment (5%-10%).

What does a positive porphyrin test indicate for Haemophilus species?

It indicates heme-producing strains.

Which species of Haemophilus is primarily responsible for invasive diseases in children?

H. influenzae type b (Hib).

What type of test is used to determine the V factor requirement in Haemophilus species?

Traditional X and V factor tests using impregnated strips.

How does Eikenella corrodens appear under the microscope?

As slender, medium-length, straight Gram-negative bacilli.

What type of infections does Eikenella corrodens usually associate with?

Infections from human bites or clenched-fist wounds.

What is a typical ocular infection caused by H. aegyptius?

Conjunctivitis or ‘pinkeye’.

What role does oxidase testing play in the laboratory diagnosis of Eikenella corrodens?

It helps in identification as Eikenella is oxidase positive.

What is the most common species of Pasteurella associated with human infections?

Pasteurella multocida.

What type of infections can occur from P. multocida?

Localized infections after animal bites, respiratory infections, and systemic diseases.

What is a characteristic feature of P. multocida on culture?

Small, smooth, convex colonies with a musty odor.

What is unique about the growth requirements of Aggregatibacter aphrophilus?

It does not grow on MacConkey agar and requires an increased CO2 environment.

How does Legionella pneumophila primarily infect humans?

Through inhalation of aerosols.

What disease is commonly caused by Legionella pneumophila?

Legionnaire’s disease.

What is the typical appearance of Legionella colonies on BCYE agar?

They are the smallest visible colonies.

What adverse effects can H. influenzae type b cause if untreated?

Severe invasive diseases like meningitis and bacteremia.

Why are some strains of Eikenella corrodens penicillin resistant?

Due to the production of beta-lactamases.

What is the clinical significance of non-typable strains of H. influenzae?

They can still cause respiratory infections in adults.

What is the role of chocolate agar in the growth of Haemophilus species?

It provides necessary growth factors—X and V factors.

How does H. influenzae typically appear in Gram stains of relevant specimens?

As Gram-negative coccobacilli.

What morphological characteristic does P. multocida have?

It is very small Gram-negative rods with a ‘safety-pin’ appearance.

What must be performed for identifying Haemophilus species in the lab?

Direct microscopic examination and plating to suitable growth media.

What distinguishes H. parainfluenzae from H. influenzae in terms of growth factors?

H. parainfluenzae requires only V factor for growth.

What type of agar is not utilized for the growth of Haemophilus species?

MacConkey agar.

What is an important cause of respiratory tract colonization in adults?

Haemophilus species, including H. parainfluenzae.

What can be concluded if a Haemophilus species grows only on chocolate agar and not on SBA?

It indicates membership in the Haemophilus group.

What is a defining characteristic of HACEK organisms?

They are opportunistic pathogens commonly found in the oral cavity.

What biotypes does H. influenzae exhibit?

Six to seven different biotypes based on capsular features.

What does the term ‘fastidious organisms’ describe in reference to Haemophilus?

Organisms that have complex growth requirements.

Why might H. ducreyi be more prevalent in developing countries?

Due to lower access to health care and higher rates of sexually transmitted infections.

Which Haemophilus species may cause neonatal sepsis?

Nonencapsulated strains of H. influenzae.

How is the diagnosis confirmed for infections caused by H. influenzae?

Through culture and identification of the organism from clinical specimens.

What does satellitism indicate for Haemophilus species when cultured?

The organism's growth is dependent on nearby bacteria for V factor.

What is the typical growth time for Aggregatibacter aphrophilus in culture?

It requires at least 48 hours to grow.

What feature aids in differentiating H. influenzae from other species in the lab?

Using growth factor requirements and biochemical tests.

What is a common condition caused by H. influenzae in adults?

Pneumonia, particularly in those with underlying illnesses.

What is a laboratory visual characteristic of H. influenzae colonies?

Convex appearance with possible mucoid texture.

What infections are associated with Pasteurella multocida?

Localized infections post animal bites leading to bacteremia.

How do Gram stains help identify H. ducreyi?

They show typical Gram-negative coccobacilli morphology.

What is the significance of the capsular polysaccharide in H. influenzae?

It enables the strain to be typed and indicates virulence.

What do laboratory tests for Haemophilus often include?

Testing for hemolysis and growth factors like X and V.

What is the primary role of H. influenzae biogroup aegyptius?

It causes severe conjunctivitis leading to systemic disease.

In addition to specific clinical infections, what role do fastidious Gram-negative rods play?

They contribute to normal flora and can become opportunistic pathogens.

What clinical feature is unique to illnesses caused by capsulated strains of H. influenzae?

Invasive diseases such as meningitis.

What is the indirect indicator of H. influenzae infection when seen in CSF specimens?

Presence of neutrophils alongside Gram-negative bacilli.

Why are certain fastidious species important in a clinical laboratory setting?

Their growth requirements often necessitate special culture techniques.

What might colonies of Eikenella corrodens display on agar?

Pitting or corrosion of the agar surface.

How does passive disease transmission often occur involving Pasteurella species?

Through bites or scratches from infected animals.

In culture, what does a ‘musty’ odor indicate when identifying bacteria?

It may suggest the presence of Pasteurella multocida.

What laboratory processing step is crucial for CSF when diagnosing Haemophilus infections?

Cytocentrifuge recommended for Gram stain.