Podcast
Questions and Answers
Which species of Haemophilus is most frequently isolated in clinical settings?
Which species of Haemophilus is most frequently isolated in clinical settings?
What is the optimal growth environment for most species of Haemophilus?
What is the optimal growth environment for most species of Haemophilus?
Which factor is required exclusively by Haemophilus species with the prefix 'Para'?
Which factor is required exclusively by Haemophilus species with the prefix 'Para'?
Which media can be utilized to promote the growth of fastidious organisms in combination with Haemophilus species?
Which media can be utilized to promote the growth of fastidious organisms in combination with Haemophilus species?
Signup and view all the answers
What characteristic is true for most Haemophilus species?
What characteristic is true for most Haemophilus species?
Signup and view all the answers
Which of the following is a potential source of V factor needed for the growth of Haemophilus on BAP?
Which of the following is a potential source of V factor needed for the growth of Haemophilus on BAP?
Signup and view all the answers
Which of the following Haemophilus species is primarily associated with the genital tract?
Which of the following Haemophilus species is primarily associated with the genital tract?
Signup and view all the answers
What characteristic of Haemophilus significantly contributes to its virulence?
What characteristic of Haemophilus significantly contributes to its virulence?
Signup and view all the answers
What unique characteristic of C. hominis can lead to misinterpretation in laboratory testing?
What unique characteristic of C. hominis can lead to misinterpretation in laboratory testing?
Signup and view all the answers
Which biochemical reaction is negative in E. corrodens that helps differentiate it from other similar bacteria?
Which biochemical reaction is negative in E. corrodens that helps differentiate it from other similar bacteria?
Signup and view all the answers
Which of the following is considered a common clinical infection associated with E. corrodens?
Which of the following is considered a common clinical infection associated with E. corrodens?
Signup and view all the answers
What environment does E. corrodens require for optimal growth?
What environment does E. corrodens require for optimal growth?
Signup and view all the answers
Which virulence factor is demonstrated by the ability of C. hominis to ferment sucrose?
Which virulence factor is demonstrated by the ability of C. hominis to ferment sucrose?
Signup and view all the answers
Which condition is often associated with K. kingae in pediatric patients?
Which condition is often associated with K. kingae in pediatric patients?
Signup and view all the answers
What is a key nutritional requirement for E. corrodens that distinguishes it from several other bacteria?
What is a key nutritional requirement for E. corrodens that distinguishes it from several other bacteria?
Signup and view all the answers
What morphological feature is associated with the gram stain appearance of Kingella species?
What morphological feature is associated with the gram stain appearance of Kingella species?
Signup and view all the answers
What is the nutritional requirement for organisms within the HACEK group when cultured?
What is the nutritional requirement for organisms within the HACEK group when cultured?
Signup and view all the answers
Which of the following characteristics is NOT true about Aggregatibacter actinomycetemcomitans?
Which of the following characteristics is NOT true about Aggregatibacter actinomycetemcomitans?
Signup and view all the answers
What is a significant clinical relevance of Cardiobacterium hominis?
What is a significant clinical relevance of Cardiobacterium hominis?
Signup and view all the answers
Which species does NOT belong to the HACEK group?
Which species does NOT belong to the HACEK group?
Signup and view all the answers
Which cultural characteristics are most associated with Aggregatibacter actinomycetemcomitans?
Which cultural characteristics are most associated with Aggregatibacter actinomycetemcomitans?
Signup and view all the answers
What aspect of Aggregatibacter aphrophilus is highlighted by its name origin?
What aspect of Aggregatibacter aphrophilus is highlighted by its name origin?
Signup and view all the answers
Which test results would you expect for a typical HACEK organism?
Which test results would you expect for a typical HACEK organism?
Signup and view all the answers
What common misidentification might occur with Aggregatibacter actinomycetemcomitans?
What common misidentification might occur with Aggregatibacter actinomycetemcomitans?
Signup and view all the answers
Study Notes
Gram-Negative Coccobacilli
- Gram-negative bacteria with a rod-like or slightly oval shape
- Clinically significant microorganisms frequently isolated in the body
- Bacteria do not grow on MacConkey agar (MAC)
- Important examples include Haemophilus influenzae, related organisms, and bacterial virulence
Haemophilus
- Facultative anaerobes ("blood-lovers")
- Most species are part of the normal flora of the upper respiratory tract
- Pathogenic species include:
- Haemophilus influenzae
- H. influenzae biogroup aegyptius
- H. ducreyi (genital tract pathogen)
- Optimal growth for most species is in 5-10% CO2 at 35 +/- 2 degrees Celsius
- H. aphrophilus requires CO2
Haemophilus Nutritional Requirements
- Fastidious bacteria
- Do not grow on routine media (BAP, TSA, MAC)
- Require accessory growth factors found in red blood cells (RBCs):
- X factor (hemin/hematin)
- V factor (nicotine adenine dinucleotide or NAD) or both
- Species with "para" in their name require only V factor
- Media with horse or rabbit blood provides necessary growth factors
- Sheep blood contains X-factor readily available. V factor must be obtained
Haemophilus Growth on BAP
- Additional V factor source can be added to routine BAP
- Fastidious organisms grow as "satellites" surrounding other bacteria releasing the necessary growth factors or toxic products
- S. aureus, S. pneumoniae, and Neisseria species naturally produce V factor
Haemophilus influenzae -- Virulence factors
- Only in typeable strains
- Six types based on polysaccharide capsules—a, b, c, d, e, f
- Type B most common before vaccination
- Implicated in meningitis in children
- Can be typed as needed
- IgA proteases
- Destroys secretory immunoglobulin A (sIgA)
- Adherence via fimbriae and structures
- Damages localized areas in non-typeable strains
- Outer membrane proteins and lipopolysaccharide (LPS)
Haemophilus influenzae -- Infections
- Most common in children
- Organism enters the body through nasopharynx (colonizes) may remain transiently
- May enter bloodstream causing invasive infections
- Two patterns:
- Invasive disease (e.g., bacteremia, septicemia, meningitis, arthritis, epiglottitis*, tracheitis, and pneumonia) caused by encapsulated strains
- Localized infection caused by non-encapsulated strains
Haemophilus influenzae -- Specimens
- Specimens of choice: -Blood -CSF -Sputum -Conjunctival swabs
- Transport specimens at room temperature without delay because organisms die rapidly
Haemophilus influenzae -- Colonial Morphology
- On CHOC agar:
- Colonies are large, translucent, and moist
- Distinct pungent odor (mousey or bleach-like)
- Encapsulated strain colonies appear mucoid
- On BAP:
- No growth with no staph streak
- With staph streak - Satelliting colonies
- Morphology will help in identification
Haemophilus influenzae -- Cellular Morphology
- Pleomorphic appearance (various shapes)
- Tiny gram-negative coccobacilli (Coccobacilli)
- Clear non-staining areas (halos) may be seen (capsules)
- Faint staining; Ensure microscope is clean
Haemophilus influenzae -- ID
- Tiny gram-negative pleomorphic coccobacilli on CHOC agar
- Grows only on CHOC agar, not MAC
- BAP with staph streak – satellite growth
- Oxidase-positive
- X and V Factor Test: -Growth around X + V disk only -No growth around X or V disk
- Porphyrin test (ALA): negative
- Catalase-positive
- Latex Agglutination and Coagglutination kits to detect Hib antigen
- Chromogenic tests – API NH
Haemophilus influenzae -- X and V Factor
- Purpose: Identify growth requirements for the speciation
- Principle: Clear agar missing X and V factor to inoculated with the target organism
- Nutrients (X and V factor) added separately
- Incubate and observe for pattern of growth (growth around X or V indicated positive)
Haemophilus influenzae -- ALA test
- Purpose: Differentiation of Haemophilus spp.
- Principle: determines if isolate requires X-factor
- Organisms needing X factor cannot convert aminolevulinic acid (ALA) to hemin.
- Organisms producing their own hemin can.
- Tube of ALA or a disk inoculated with organism
- View under UV light to observe for fluorescence for positive result
- Use the appropriate quality controls
Haemophilus influenzae -- Treatment
- More than 35% of strains produce Beta-lactamases (resistance to ampicillin) - common in meningitis and bacteremia
- Testing for Beta-lactamase activity
- Recommended treatment (beta-lactamase positive):
- Cefotaxime, ceftriaxone, and cefuroxime
- Alternate treatment:
- Trimethoprim/Sulfamethoxazole (SXT), imipenem, ciprofloxacin (with ampicillin).
Haemophilus influenzae -- Vaccination
- Hib vaccination recommended for children under 5 years
- Children given multiple shots
- Pre-Vaccination Era -Leading cause of invasive disease in children -Common cause of acute bacterial meningitis in children until mid-1980s
Haemophilus influenzae biogroup aegyptus
- Subgroup of H. influenzae, closely related
- Very difficult to differentiate
- Infections: Acute, contagious conjunctivitis (pink eye)
- Brazilian purpuric fever
- Sudden onset high fever, rash, septicemia, shock, vascular damage
- Mortality rate as high as 70% within 48 hours
- Small outbreaks in South America
Haemophilus ducreyi -- Infection
- NOT normal flora, genital ulcer disease, chancroid
- Highly contagious sexually transmitted disease
- Painful, purulent ulcers, or buboes (swollen lymph nodes)
- Men have more symptoms related to inguinal tenderness and genital lesions
Haemophilus ducreyi -- Cellular Morphology
- Tiny GNCB (gram-negative coccobacilli)
- Arranged as "school of fish"
Haemophilus ducreyi -- Culture and ID
- Requires enriched CHOC
- Specimens inoculated immediately
Haemophilus species (other than H. influenza, and H. ducreyi)
- Typically non-pathogenic but associated with infections like (endo)carditis, Respiratory tract infections, brain abscesses, bacteremia, urethritis, and pneumonia
HACEK Group
- Gram-negative bacilli
- Do not grow on MacConkey agar
- Fastidious nutritional requirements
- Require an increased CO2 (5%-10%) environment
- Significant cause of endocarditis
- Usual oral cavity flora
- Opportunistic in immunocompromised hosts
Capnocytophaga
- Group of fastidious, facultatively anaerobic, gram-negative bacilli
- Normal flora in oral cavity
- Infections in neutropenic patients -Oral ulcers -Soft tissue infections, peritonitis, and endocarditis
Pasteurella -- General Characteristics
- Many species, most clinically relevant: Pasteurella multocida
- Has similar characteristics to Haemophilus
- Infections: Causes pasteurellosis
- Disease acquired from infected animals or products
- Zoonotic disease
- Animal bites, often cat bites
Pasteurella -- Infections
- Common presentation: soft tissue infection
- Injury can be aggressive, with skin manifestations typically appearing within 24 hours
- Wounds exhibit rapidly progressive soft tissue inflammation
- Soft tissue infections can progress to deep-tissue infections (Septic arthritis, osteomyelitis, tenosynovitis)
- Rarer presentation: -Systemic infections (endocarditis, septicemia, meningitis, pneumonia)
Pasteurella -- Cellular Morphology
- Can easily be mistaken with Haemophilus
- Gram-negative coccobacilli
- Ovoid, filamentous, or bacilli
- Bipolar staining (looks like safety pins)
- End of bacillus retains more stain
Pasteurella -- Colonial Morphology
- Not fastidious - Grows on BAP and CHOC
- Growth on BAP helps differentiates from Haemophilus
- Tends to exhibit a "musty" odor similar to wet dog smell
- Nonhemolytic, grey colonies
- Older colonies—mucoid and green/brown halo.
Pasteurella -- Diagnosis
- Nonmotile
- Catalase positive, Oxidase positive (most isolates)
- Nitrate positive, Indole Positive
- Ornithine Positive
- Glucose fermentation -Weak acid production
- Urease negative
Other Knowledge Checks
- Specific characteristics to distinguish between Haemophilus and Pasteurella
- Organisms causing diseases like soft chancres, or brazilian purpuric fever
- Identification of organisms not in the HACEK group
- Organism commonly associated with animal bites causing soft tissue infections
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
