Module 2 Flashcards
What is the most common human pathogen?
H. influenzae
What is the cellular morphology of Haemophilus?
Pleomorphic
Gram negative
Coccobacilli
Pale staining
What due gives a darker stain with Haemophilus?
Carbon fuchsin
What are the growth requirements for Haemophilus?
Facultative (better growth with oxygen)
Increased CO2 enhances growth
35°C
Moist environment required
What growth factors does Haemophilus require?
X factor- synthesis of iron containing respiratory enzymes, hemin or protoporphyrin, heat stable
V factor- NAD, heat labile
What supplies factors X and V?
X- Hb, whole or lysed blood cells
V- lysed RBCs, other bacteria
What media can be used to grow Haemophilus?
Blood agar with Staph streak- clear, wet, glistening, nonhemolytic colonies
Chocolate agar- small, raised, grey, translucent colonies
Why can’t blood agar alone be used for Haemophilus growth?
NADase in RBCs inactivates NAD
Factor V may also be trapped in the cells
Why may you see Haemophilus growth in anaerobic blood cultures first?
Can grow anaerobically without V factor
What is required for Haemophilus genus ID?
Gram stain
BAP with Staph streak
BAP
Chocolate agar
What tests are used for Haemophilus genus ID?
Oxidase- negative with dimethyl reagent
Catalase- positive
No hemolysis (couple exceptions)
Commercial strips with growth factors- growth around required factors
Porphyrin (ALA)- determines whether an organism can synthesize X factor from ALA
Commercial ID kits- biochem and enzymatic test
Serological ID- slide agglutination for different capsular antigens
What is the reagent for the porphryin (ALA)?
Buffered delta-aminolevulenic acid
How is porphryin detected?
UV light- observation under Wood’s UV lamp shows red-pink fluorescence
Kovac’s reagent- added, colour change to red
What is the QC for the porphryin test?
Positive- H. parainfluenzae
Negative- H. influenzae and most other bacteria
What is the most virulent strain of capsulated Haemophilus?
B
What is the antimicrobial susceptibility of H. influenzae?
Ampicillin resistance has increased- due to B-lactamase (plasmid) and PCP alteration
Testing- nitrocefin, acidimetric and iodometric methods for B-lactamase testing (need disc diffusion for PCPs)
Chloramphenicol- rare resistance due to acetyl transferase
B-lactamase resistant penicillins, trimethoprim sulfa (SXT), amoxicillin-clavulanic acid
What growth factors do each Haemophilus species need?
H. influenzae- X and V
H. parainfluenzae- V
H. haemolyticus- X and V
H. parahaemolyticus- V
What species show hemolysis?
H. haemolyticus
H. parahaemolyticus
What is the pathogenicity of H. influenzae?
Major cause of infections in children
Noncapsulated strains- NF in nasopharynx
Meningitis- increased WBC count
Acute epiglottitis
Pneumonia, sinusitis, conjunctivitis, osteomyelitis
What is the pathogenicity of H. aegyptius?
Conjunctivitis
Brazilian purpuric fever
What are the characteristics of H. haemolyticus?
Beta hemolysis
X and V factors
Porphryin test- negative
NF of nasopharynx
Endocarditis and abscesses of internal organs
What are the characteristics of H. parahaemolyticus?
Filamentous
Beta hemolytic
Requires V factor
Porphryin test- positive
NF of respiratory tract
Rarely causes infections
What are the characteristics of H. ducreyi?
STI
Clusters/schools of fish
Within or outside PMNs
Catalase- negative
Oxidase- negative
ALA- negative
Can’t use X, V or X/V discs
Plasmid mediated resistance to most antimicrobials except third gen cephalosporins, fluoroquinolones and macrolides
What genera belong to the family Pasteurellaceae?
Haemophilus
Actinobacillus
Pasteurella
