Celine - Haemophilus Flashcards
What are the three families of small gram negative rods (coccobacilli)?
Pasteurellaceae
Alcaligenaceae
Brucellaceae
What are the two genera of pasteurellaceae
Haemophilus
Pasteurella
What is the genera in alcaligenaceae
Bordetella
What is the genera in brucellaceae
Brucella
How are pasteurellaceae classified
(3)
Family is classified into nine genera
Most are regarded as commensals
The two genera of interest are Haemophilus and Pasteurella
Write about Haemophilus
10 species found in clinical specimens
Most are non-pathogenic
H. influenzae
H. ducreyi
H. aegyptius
H. parainfluenzae (opportunistic)
What are the two types of H. influenzae
Type B
Non-typable
What infections does H. influenzae type b cause
(6)
Meningitis type B
Epiglottis type B
Bloodstream infection - type B
Cellulitis
Arthritis
Osteomyelitis
What infections does non-typable H. influenzae cause
Otitis - non-typable
Sinusitis - non typable
Pneumoniae - non-typable
What infections does H. aegyptius cause
Conjunctivitis
What infections does H. parainfluenzae cause
Opportunistic infection
Pneumoniae
Endocarditis
What infections does H. ducreyi cause
Chanchroid (genitals and lymph nodes)
Write about H. influenzae infection
(3)
Range from those associated with local conditions to those that cause invasive disease
2 groups: Invasive and noninvasive
Type of infection depends on Capsule production
Write about invasive infections
H. influenzae is the primary pathogen
Acute pyogenic invasive infection
Meningitis, epiglottitis, bloodstream infection
Write about the noninvasive infections
H. influenzae play secondary role
Induce inflammatory response
Pneumonia, otitis media and sinusitis
What are the virulence factors of H. influenzae
(5)
Capsule
IgA protease
Pili
Endotoxin
Outer membrane proteins
Write about the capsule virulence factor of H. influenzae
(4)
Virulence is directly related to capsule formation
Six capsular types - serotypes a -f
Serotype b most virulent -> causes 95% of blood stream and meningeal Haemophilus infections
Noncapsulated strains known as non-typable strains (NTHI) were primarily associated with noninvasive infection
Write about the virulence of Type b strains
(4)
Type b strains have a polyribosyl ribitol phosphate (PRP) capsule renders them:
Resistant to phagocytosis by PMN leukocytes
Non-inducers of alternative complement pathway
Hib can invade the blood or CSF without attracting phagocytes or provoking an inflammatory response.
What are the significant virulence factors of Hib
PRP Capsule
Fimbriae
IgA protease
Lipooligosaccharide
What are the significant virulence factors of NTHI
Fimbriae
IgA protease
Especially active lipooligosaccharide
What is the function of fimbriae
Successful colonisation of the nasopharynx
What is the function of IgA protease
Degrades host secretory IgA
What is the function of lipooligosaccharide
Inhibits mucocilliary clearance
Antigenic diversity
Immune evasion
Write about H. influenzae
(5)
Human host reservoir for infection
H. influenzae present in the nasopharynx of 75% of healthy children and in a lower percentage of adults
Usually NTHI strains harboured as normal flora
But a minority of healthy individuals (3-7%) intermittently harbour Hib
H. influenzae is spread by droplet transmission through secretions and/or aerosols
Write about H. influenzae epidemiology in children
Not developed antibody response to PRP capsule
Hib most common cause of H. influenzae
Write about H. influenzae epidemiology in adults
Acquired antibody to PRP
NTHI most common cause of Haemophilus infection
NTHI strains have tended to be less invasive, but induce an inflammatory response that cause disease
Write about Hib infection
Hib may penetrate the epithelium, evade IR causing invasive infection:
- epiglottis
- meningitis in children <3
- bloodstream infection
- spread to other areas - cellulitis, arthritis and osteomyelitis
Less frequently Hib causes:
- pneumonia in 15% of Haemophilus infection
- otitis media in 5-10% of Haemophilus infection
What is epiglottis
Epiglottis inflamed may close off upper airway
Write about NTHI infections
Pneumonia
Otitis media
Write about H. influenzae caused meningitis
(5)
Hib used to be the most common cause of meningitis in children between the ages of 6 months and 2 years
Accounted for 50-65% of meningitis cases
5% fatality
15-30% of cases caused hearing impairment or neurological sequelae
Incidence of Hib invasive disease has declined by 98% since introduction to Hib vaccine
Write about the Hib vaccine
(5)
Introduced in Ireland 1992
The Hib vaccine offered to all children as part of the routine immunisation programme
Hib began to increase in recent years
The Hib booster was introduced in 2006
Hib reducing again
NTHI invasive infections increased
There was only 1 case of Hib invasive infection in 2022
Write about NTHI pathogenesis
IgA protease facilitates colonisation of the upper respiratory tract mucosa
Infection arises from spread from site of colonisation
In babies and young children common cause of middle ear infection - otitis media, which manifests as an earache with fever (90% cases NTHI)
In adults may infect mucosa damaged by viral disease or cigarette smoking may lead to pneumonia, (85% cases NTHI) particularly in COAD
But in past 10 years, a steady but constant increase has occurred in invasive NTHI worldwide, with elderly most at risk- change in epidemiology
Patients with underlying co-morbidities are most susceptible
Write about non-invasive H. influenzae infections
(5)
Most often non-capsulated
NTHI
Otitis media
Pneumonia
But NTHI increasingly implicated in invasive disease - meningitis in elderly
Write about invasive H. influenzae infections
(7)
Associated with capsulated H. influenzae capsule type B: Hib
Meningitis
Epiglottitis
BSI
Arthritis
Osteomyelitis
Less commonly pneumonia and otitis media
What are the clinical specimens of Haemophilus
Cerebrospinal fluid
Blood
Sputum
Middle ear aspirates
Nasopharyngeal swabs -> carriage
Eye swabs -> H. aegyptius
Genital swab -> h. ducreyi
Write about the day 1 investigation of Haemophilus
(2)
Haemophilus fastidious - very prone to drying and chilling
Specimens should be held at room temperature and processed as soon as possble
What is done with Haemophilus on day 1
Direct specimen microscopy - gram stain
Direct specimen microscopy - CSF white cell count
Direct specimen - antigen detection
Isolation of Haemophilus
Write about the gram stain of haemophilus
Done directly on CSF, blood, sputum or ear swabs
Small Gram-negative pleomorphic coccobacilli - very difficult to see especially in small numbers
Write about the WCC in direct specimen microscopy of Haemophilus
CSF - count number of white and red cells
White cell differential - polymorphs (bacterial) vs mononuclear (viral/TB)
Biochemical - increase in protein and decrease in glucose
Write about the day 1 direct specimen antigen detection of Haemophilus
(5)
Latex agglutination for Hib antigens
Latex beads coated with antisera for serotype b
Detect antigens direct in CSF
Rapid, sensitive and specific
Result available before culture
What are the growth characteristics of Haemophilus
(6)
In vitro growth requires accessory growth factors including
Heat stable X factor (haemin)
Heat labile V factor (nicotinamide adenine dinucleotide, NAD)
Capnophilic
Must be cultured on chocolate agar
Incubated for 24-48 hours in 5-10% CO2
What does capnophilic mean
Only grows in 5-10% CO2 at 37 degrees for 24-48 hours
Why does Haemophilus need chocolate agar to grow
(4)
Haemophilus needs X and V factors
Blood agar contains X factor (haemin) but also NADase which inactivates V factor (NAD)
Therefore chocolate agar must be used
Chocolate agar is made by heating blood cells to 80 degrees Celsius which releases V factor and destroys NADase
Write about day 2 basic characteristics of Haemophilus
(7)
No growth on blood agar
Growth on chocolate agar
1mm grey wet colonies
Pungent odour
Gram-negative coccobacilli
Oxidase positive
Catalase positive
What tests are carried out on day 2 Haemophilus identification
X and V growth factor requirement test - discriminatory test
Automation:
- Maldi TOF
- Vitek-NH-biochemical profile
Molecular detection
Write about X and V factor test
Test organism is lawned onto DST agar (free of X and V)
Apply X, V and XV discs on agar
Incubate in 5-10% CO2
What species needs factor X and V
H. influenzae
H. aegyptius
What species needs factor V
H. parainfluenzae
What species needs factor X only
H. ducreyi
Write about the molecular detection of Haemophilus
(3)
CSF sent to Irish Meningitis and Sepsis Reference Laboratory, Temple Street
Confirm by PCR - performed in addition to culture diagnostic lab
50% of meningitis cases in Ireland confirmed by PCR alone - culture negative
