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2.2 Microbiology > Celine - Haemophilus > Flashcards

Celine - Haemophilus Flashcards

1
Q

What are the three families of small gram negative rods (coccobacilli)?

A

Pasteurellaceae
Alcaligenaceae
Brucellaceae

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2
Q

What are the two genera of pasteurellaceae

A

Haemophilus
Pasteurella

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3
Q

What is the genera in alcaligenaceae

A

Bordetella

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4
Q

What is the genera in brucellaceae

A

Brucella

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5
Q

How are pasteurellaceae classified
(3)

A

Family is classified into nine genera

Most are regarded as commensals

The two genera of interest are Haemophilus and Pasteurella

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6
Q

Write about Haemophilus

A

10 species found in clinical specimens
Most are non-pathogenic

H. influenzae
H. ducreyi
H. aegyptius
H. parainfluenzae (opportunistic)

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7
Q

What are the two types of H. influenzae

A

Type B
Non-typable

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8
Q

What infections does H. influenzae type b cause
(6)

A

Meningitis type B

Epiglottis type B

Bloodstream infection - type B

Cellulitis
Arthritis
Osteomyelitis

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9
Q

What infections does non-typable H. influenzae cause

A

Otitis - non-typable
Sinusitis - non typable
Pneumoniae - non-typable

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10
Q

What infections does H. aegyptius cause

A

Conjunctivitis

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11
Q

What infections does H. parainfluenzae cause

A

Opportunistic infection
Pneumoniae
Endocarditis

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12
Q

What infections does H. ducreyi cause

A

Chanchroid (genitals and lymph nodes)

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13
Q

Write about H. influenzae infection
(3)

A

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

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14
Q

Write about invasive infections

A

H. influenzae is the primary pathogen
Acute pyogenic invasive infection
Meningitis, epiglottitis, bloodstream infection

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15
Q

Write about the noninvasive infections

A

H. influenzae play secondary role
Induce inflammatory response
Pneumonia, otitis media and sinusitis

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16
Q

What are the virulence factors of H. influenzae
(5)

A

Capsule
IgA protease
Pili
Endotoxin
Outer membrane proteins

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17
Q

Write about the capsule virulence factor of H. influenzae
(4)

A

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

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18
Q

Write about the virulence of Type b strains
(4)

A

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.

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19
Q

What are the significant virulence factors of Hib

A

PRP Capsule

Fimbriae

IgA protease

Lipooligosaccharide

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20
Q

What are the significant virulence factors of NTHI

A

Fimbriae
IgA protease
Especially active lipooligosaccharide

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21
Q

What is the function of fimbriae

A

Successful colonisation of the nasopharynx

22
Q

What is the function of IgA protease

A

Degrades host secretory IgA

23
Q

What is the function of lipooligosaccharide

A

Inhibits mucocilliary clearance

Antigenic diversity

Immune evasion

24
Q

Write about H. influenzae
(5)

A

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

25
Q

Write about H. influenzae epidemiology in children

A

Not developed antibody response to PRP capsule
Hib most common cause of H. influenzae

26
Q

Write about H. influenzae epidemiology in adults

A

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

27
Q

Write about Hib infection

A

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

28
Q

What is epiglottis

A

Epiglottis inflamed may close off upper airway

29
Q

Write about NTHI infections

A

Pneumonia
Otitis media

30
Q

Write about H. influenzae caused meningitis
(5)

A

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

31
Q

Write about the Hib vaccine
(5)

A

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

32
Q

Write about NTHI pathogenesis

A

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

33
Q

Write about non-invasive H. influenzae infections
(5)

A

Most often non-capsulated

NTHI

Otitis media

Pneumonia

But NTHI increasingly implicated in invasive disease - meningitis in elderly

34
Q

Write about invasive H. influenzae infections
(7)

A

Associated with capsulated H. influenzae capsule type B: Hib

Meningitis
Epiglottitis
BSI
Arthritis
Osteomyelitis

Less commonly pneumonia and otitis media

35
Q

What are the clinical specimens of Haemophilus

A

Cerebrospinal fluid
Blood
Sputum
Middle ear aspirates
Nasopharyngeal swabs -> carriage
Eye swabs -> H. aegyptius
Genital swab -> h. ducreyi

36
Q

Write about the day 1 investigation of Haemophilus
(2)

A

Haemophilus fastidious - very prone to drying and chilling

Specimens should be held at room temperature and processed as soon as possble

37
Q

What is done with Haemophilus on day 1

A

Direct specimen microscopy - gram stain

Direct specimen microscopy - CSF white cell count

Direct specimen - antigen detection

Isolation of Haemophilus

38
Q

Write about the gram stain of haemophilus

A

Done directly on CSF, blood, sputum or ear swabs

Small Gram-negative pleomorphic coccobacilli - very difficult to see especially in small numbers

39
Q

Write about the WCC in direct specimen microscopy of Haemophilus

A

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

40
Q

Write about the day 1 direct specimen antigen detection of Haemophilus
(5)

A

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

41
Q

What are the growth characteristics of Haemophilus
(6)

A

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

42
Q

What does capnophilic mean

A

Only grows in 5-10% CO2 at 37 degrees for 24-48 hours

43
Q

Why does Haemophilus need chocolate agar to grow
(4)

A

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

44
Q

Write about day 2 basic characteristics of Haemophilus
(7)

A

No growth on blood agar
Growth on chocolate agar
1mm grey wet colonies
Pungent odour
Gram-negative coccobacilli
Oxidase positive
Catalase positive

45
Q

What tests are carried out on day 2 Haemophilus identification

A

X and V growth factor requirement test - discriminatory test

Automation:
- Maldi TOF
- Vitek-NH-biochemical profile

Molecular detection

46
Q

Write about X and V factor test

A

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

47
Q

What species needs factor X and V

A

H. influenzae
H. aegyptius

48
Q

What species needs factor V

A

H. parainfluenzae

49
Q

What species needs factor X only

A

H. ducreyi

50
Q

Write about the molecular detection of Haemophilus
(3)

A

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

2.2 Microbiology (60 decks)

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