Haemophilus Spp. Flashcards
What are the general characteristics of fastidious Gram-negative rods?
- Gram-negative pleomorphic coccobacilli or rods
- Nonmotile
- Aerobic or facultatively anaerobic
- Oxidase and catalase positive
- Obligate parasites of the mucous membranes
These traits are essential for identifying and understanding their pathogenicity.
Which species of Haemophilus are major pathogenic species?
- H. influenzae
- H. aegyptius
- H. ducreyi
Most species of Haemophilus are nonpathogenic or produce opportunistic infections.
What are the growth factor requirements for Haemophilus species?
- X factor (hemin, hematin)
- V factor (NAD)
These factors are preformed growth factors present in blood.
What is the role of chocolate agar in the growth of Haemophilus species?
Chocolate agar provides both X and V factors as heat treatment of the blood inactivates the enzymes that hydrolyze the V factor.
This allows for the effective recovery of Haemophilus species.
What is satellitism in Haemophilus species?
Satellitism is the phenomenon where Haemophilus species grow in proximity to other bacteria such as S. aureus, S. pneumoniae, or Neisseria on SBA.
It helps in identifying these species in clinical specimens.
What is the significance of the capsule in H. influenzae?
The capsule plays the most significant role as a virulence factor, providing antiphagocytic and anticomplement capabilities.
H. influenzae type B is particularly invasive.
What is the primary disease caused by H. ducreyi?
Chancroid, a sexually transmitted disease characterized by painful lesions and enlarged inguinal lymph nodes.
This organism is mostly found in developing countries.
What specimens are collected for laboratory diagnosis of Haemophilus species?
- Blood
- CSF
- Middle ear exudates
- Joint fluids
- Upper and lower respiratory tract specimens
- Swabs from conjunctiva
- Vaginal swabs
- Abscess drainage specimens
Proper collection techniques are essential for accurate diagnosis.
What is the microscopic morphology of Haemophilus species?
Gram-negative coccobacilli or small regular bacilli, often seen as long filaments in pure culture.
This morphology aids in identification during laboratory examinations.
What is the colonial morphology of Haemophilus species on chocolate agar?
Colonies appear translucent, moist, smooth, and convex, with a ‘mousy’ or ‘bleach-like’ odor.
H. influenzae colonies are more grayish and larger if encapsulated.
What traditional tests are used for the identification of Haemophilus isolates?
- Testing for growth factors (X and V factors)
- Traditional biochemicals
- Hemolysis on blood agar
- Oxidase test
- Catalase test
- Porphyrin test
These tests help differentiate between species.
What is the porphyrin test used for?
To differentiate heme-producing strains of Haemophilus species.
The test eliminates the X factor requirement and provides a more straightforward identification process.
What color do porphyrins fluoresce under UV light?
Reddish-orange
This fluorescence is a key characteristic used in tests for porphyrins.
What causes the appearance of red color after the addition of KOVACS reagent?
Presence of porphobilinogen
Porphobilinogen is a compound that indicates certain biochemical activities.
What does the acronym H(A)ACEK stand for?
Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella, Capnocytophaga
These genera are significant in human infections, particularly endocarditis.
What type of bacteria is the HACEK group composed of?
Gram-negative bacilli
Their classification is important for understanding their pathogenicity.
What is required for the growth of HACEK organisms?
Increased CO2 (5%-10%) environment
This is critical for culturing these organisms effectively.
What type of infections are HACEK organisms significant for?
Endocarditis
They are often involved in cases of heart valve infections.
What is the growth requirement for Aggregatibacter aphrophilus?
Slow growing, requiring 48 hours to grow in culture
This slow growth can complicate diagnosis.
What is a notable feature of Aggregatibacter aphrophilus regarding its growth media?
Does not grow on MacConkey agar
This helps in differentiating it from other Gram-negative bacteria.
What are the microscopic characteristics of Aggregatibacter aphrophilus?
Short Gram-negative bacilli; filamentous forms possible
Understanding its morphology aids in identification.
What is the oxidase reaction of Eikenella corrodens?
Oxidase positive
This biochemical characteristic is crucial for identification.
What infections is Eikenella corrodens commonly associated with?
- Human bites
- Clenched-fist wounds
- Periodontitis
- Osteomyelitis
These infections often arise from the organism’s normal habitat in the oral cavity.
What is the cultural growth characteristic of Eikenella corrodens?
Small colonies with a distinct odor of bleach
The growth characteristics help in its identification in the lab.
What is the most common species of Pasteurella?
Pasteurella multocida
This species is frequently isolated in human infections following animal bites.
What are the clinical manifestations of Pasteurella multocida infections?
- Localized infections
- Respiratory tract infections
- Life-threatening systemic diseases
These manifestations highlight its pathogenic potential.
What is a characteristic of Legionella species in terms of transmission?
Acquired primarily through inhalation of aerosols
This mode of transmission is key to understanding its epidemiology.
What are the general characteristics of Pasteurella and similar organisms?
Small, Gram-negative bacilli
Nonmotile
Oxidase positive
Most will not grow on MacConkey agar
These characteristics help in identifying and differentiating Pasteurella species in clinical settings.
What type of infections do most Pasteurella organisms cause?
Opportunistic infections
These infections usually occur following a disruption of host barriers, such as bites from cats or dogs.
Which antibiotic are most Pasteurella organisms susceptible to?
Penicillin
This susceptibility is crucial for effective treatment of infections caused by these organisms.
What is the Gram stain appearance of Pasteurella species?
Exhibits short, straight bacilli with frequent bipolar staining
This characteristic helps in the identification of Pasteurella under the microscope.
True or False: Pasteurella species are motile.
False
Pasteurella species are characterized as nonmotile.
Fill in the blank: Pasteurella organisms are ______ positive.
Oxidase
Oxidase positivity is a key biochemical characteristic used for identification.
What are the general growth characteristics of Actinobacillus, Kingella, Cardiobacterium, Capnocytophaga, and similar organisms?
Grow slowly or poorly, grow in 48 hours at 35°C to 37°C, capnophilic (5% to 10% CO2), most do not grow on MacConkey agar
Capnophilic organisms require higher carbon dioxide levels for optimal growth.
Where are Actinobacillus, Kingella, Cardiobacterium, and Capnocytophaga typically found?
Normal microbiota of the nasopharynx or oral cavity
These species are usually of low virulence.
How do infections caused by these organisms typically occur?
After introduction into sterile sites via bites, droplet transmission, sharing paraphernalia, manipulations in the oral cavity
Cardiobacterium spp. can also be found in the gastrointestinal and urogenital tracts.
What types of infections can these organisms cause?
Infections vary from periodontitis to endocarditis
Specific organisms include Aggregatibacter actinomycetemcomitans, Cardiobacterium hominis, and Kingella spp.
What diseases are associated with Actinobacillus spp.?
Granulomatous disease in animals and soft-tissue infections
Actinobacillus spp. are also known to cause infections in humans.
What is the primary treatment for infections caused by these organisms?
Most infections are treated with β-lactam antibiotics
β-Lactamase production has been found in Kingella spp.
What is the gram-stain appearance of Actinobacillus spp.?
Short to very short Gram-negative bacilli
This characteristic helps in their identification.
What is the gram-stain appearance of Kingella spp.?
Short, plump Gram-negative coccobacilli with squared-off ends
This morphology assists in their identification.
How does Cardiobacterium hominis appear under gram-staining?
Pleomorphic with one rounded end and one tapered end appearing as a teardrop
This unique shape is significant for identification.
Describe the colonial appearance of Aggregatibacter actinomycetemcomitans.
Rough, sticky, adherent colonies with a greenish tinge, four- to six-pointed star-like colonies (‘crossed-cigars’)
This appearance is important for laboratory identification.
What is a notable characteristic of Kingella spp. colonies?
Small colonies that often pit agar
This pitting can be a helpful diagnostic feature.
