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Microbiology > Microbiology of Respiratory Infection > Flashcards

Microbiology of Respiratory Infection Flashcards

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1
Q

URT defences?

A

Nasopharynx:
Nasal hairs
Ciliated epithelia
IgA

Oropharynx:
Saliva
Sloughing
Cough

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2
Q

Bacteria that colonise the URT?

A

Gram +ve:
α-haemolytic inc. Strep. pneumoniae
β-haemolytic inc. Strep. pyogenes
Coagulase +ve inc. Staphylococcus aureus

Gram -ve:
Haemophilus influenzae
Moraxella catharalis

Many others

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3
Q

Infections in the URT, resulting inflammation and causes?

A 
Sinusitis - paranasal sinuses
Rhinitis - nose
Pharyngitis - pharynx, tonsils, uvula
Epiglottitis - epiglottis, superior larynx
Laryngitis - larynx

May be viral/bacterial and are not always confined to a single structure

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4
Q

Describe acute epiglottitis, what it is and characteristics

A

Inflammation of the epiglottis caused by Haemophilus influenzae type B (HiB)

Children (2-7 yrs) - acute onset (within hours), sore throat, drooling (unable to swallow properly), severe croup/stridor, high temp

Adults - onset is gradual, over days

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5
Q

Risk factors for epiglottitis?

A

Immunocompromised/immunosuppressed

Transmission of capsulated strain to UNVACCINATED HOST

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6
Q

Testing for epigottitis and cautions?

A

Blood culture

NOT A THROAT SWAB - can irritate epiglottis causing spasm and asphyxiation

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7
Q

Treatment of epiglottitis?

A

Tend to be admitted to ITU immediately to get endotracheal intubation
Antibiotics given are CEFTRIAXONE

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8
Q

Describe Haemophilus influenzae and the culture

A

Gram negative coccobacilli and the culture appears very distinctive:
Morphology is pure for Haemophilus species (blood-loving)

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9
Q

What are the conducting airways and describe them in relation to infection?

A 
Trachea and bronchi - not normally colonised and resist infection due to:
Mucociliary escalator
Cough
AMPs
Cellular and humoral immunity
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10
Q

When does infection occur?

A

Changes to airway - trauma/intubation
Abnormalities, e.g: COPD, CF
Inhalation/contact with causative organism

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11
Q

Acute COPD exacerbation symptoms?

A

Adults - productive cough/acute chest illness, breathlessness, wheezing, increased sputum purulence
Often follow a viral infection/fall in temp and increase in humidity (winter)

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12
Q

Acute COPD exacerbation common bacteria and importance when sending to lab?

A

Haemophilus influenzae
Moraxella catarrhalis
Streptococcus pneumoniae

GRAM NEGATIVES and others

Must specify that person has COPD, so lab can look for gram -ve organisms (not normally associated with chest infection)

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13
Q

Describe Moraxella catarrhalis

A

Gram negative diplococci

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14
Q

Testing for cause of infection in COPD?

A

Sputum culture can be combined with clinical evidence:
Sputum purulence
Chest X-ray

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15
Q

Treatment of COPD exacerbation?

A

Only treat if increase in sputum purulence/new chest X-ray changes/pneumonia

1st line - Amoxicillin (aim to cover H. influenzae, M. catarrhalis, S. pneumoniae
2nd line - Doxycycline

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16
Q

What is cystic fibrosis?

A

Inherited disease leading to abnormally viscous mucous, causing blockages of many tubular structures in. conducting airways and lungs

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17
Q

Characteristics of CF?

A

Repeated chest infections and chronic colonisation

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18
Q

Bacteria in CF?

A 
Inefficient clearing of mucous and build-up facilitates bacterial colonisation:
Staph aureus
H. influenzae
Strep pneumoniae
Pseudomonas aeruginosa 
Burkholderia cepacia
Many others
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19
Q

Characteristics of whooping cough?

A 
Acute tracheobronchitis
Cold-like symptoms for 2 weeks
Paroxysmal coughing (2 weeks) 
Repeated, violent exhalations with severe, inspiratory "whoop" (vomiting common) 
Residual cough for 1 month +
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20
Q

Bacteria causing whooping cough?

A

Bordetella pertussis (gram -ve coccobacillus)

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21
Q

Diagnosis of Bordetella pertussis?

A

Not routinely tested for (pernasal swab is unpleasant), so must include clinical signs & symptoms
Bacterial culture - pernasal swab (charcoal), culture (charcoal-blood agar)

PCR - pernasal swab (

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22
Q

Treatment of Bordetella pertussis?

A

Antibiotics:
If less than 1 month - clarythromycin
If older than 1 month - clarithromycin/azithromycin

Pregnancy - erythromycin

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23
Q

Describe the lung defenses

A

Normally “sterile” (URT and conducting airways keep lungs clean)
No ciliary escalator
Alveolar lining fluid - surfactant, Ig, omplement, FFA, AMP
Alveolar macrophages & neutrophils - phagocytosis > inflammatory response

24
Q

Examples of different lung infections?

A

Community Acquired Pneumonia (CAP) - S. pneumoniae, H. influenzae, M. catarrhalis

Atypical pneumonia - Mycoplasma pneumoniae Legionella pneumphilia
Chlamydophila pneumoniae
Chlamydophila psittaci

Others - due to defects in host defense, e.g: hospital acquired pneumonia, immune defects & anatomical abnormalities, like PCP (Pneumocystis pneumonia), fungal and recurrence

TB

25
Q

Characteristics of CAP?

A 
ACQUIRED IN THE COMMUNITY (no recent hospital/healthcare exposure):
Cough
Increased sputum
Chest pain
Dyspnoea
Fever
Chest X-ray with infiltrates
26
Q

Pathology of CAP?

A

Organism reaches lungs
Immune activation and infiltration (systemic response)
Fluid and cellular build up in alveoli - leads to impaired gas exchange

27
Q

Risk factors for CAP?

A

Increasing age
Immunocompormised/immunosuppressed patients
Smoker

28
Q

Diagnosis of CAP?

A

Sputum culture

Viral PCR

29
Q

Treatment of pneumonia?

A

Streptococcus pneumoniae - sensitive to Amoxicillin, Doxycycline, Co-trimoxazole

30
Q

Describe Legionella pneumoniae

A

Causes atypical pneumonia and is a common environmental gram -ve bacteria that is also an obligate intracellualr organism (resides with water amoeba that provide nutrients and protection)

No person-to-person spread; transmitted by inhalation of contaminated water droplets so can get it from unused shower heads, air conditioning

31
Q

Pathogenesis of Legionella pneumonia?

A

Invades alveolar macrophages (mistakes them for amoeba) and replicates, causing a flue-like illness that can progress to severe pneumonia

32
Q

Symptoms of Legionella pneumonia?

A

Mental confusion
Acute renal failure
GI symptoms
Mortality - 5-30%

33
Q

Risk factors for Legionella pneumonia?

A

Exposure to contaminated aerosolised water
Impaired immunity - >55 yrs, diabetic, smoker, malignancy, altered immunity (HIV)

CURB65 -

34
Q

Diagnosis of Legionella pneumonia

A 
Legionella pneumophila:
Legionella urinary antigen - detects serogroup 1 only
Culture - slow on selective media
Paired serology - rise in titres
PCR available from direct sputum
35
Q

Treatment of Legionella pneumonia?

A

Clarythromycin
Erythromycin
Quinolones, e.g: Levofloxacin

36
Q

Describe Hospital Acquired Pneumonia

A

Alterations in the normal URT function

Caused by:
Gram -ve organisms, inc. E. coli, Klebsiella spp. , Pseudomonas spp.
CAP organisms
S. aureus
Anaerobes

Broad spectrum of antibiotics given, as more likely that there are gram -ve organisms

37
Q

Describe Pneumocystis pneumonia

A

AKA PCP
Caused by Pneumocystis jirovecii
One of the most frequent & severe opportunistic infections in people with weakened immune systems (AIDS, immunosuppression)

38
Q

Pathogenesis of Pneumocystis pneumonia

A

Inhalation of fungus
Normal immune system = asymptomatic carriage/eradication
Infections occur in immunocompromised/immunosuppressed

39
Q

Symptoms of Pneumocystis pneumonia?

A

Fever
Dry cough
SOB
Fatigue

HIV- sub-acute, low grade fever > severe pneumonia
Non-HIV - more acute, higher fever

40
Q

Diagnosis of Pneumocystic pneumonia?

A

Microscopy with immunofluorescence
PCR
BAL (bronchoalveolar) fluid in sputum - can gargle with oral washes

41
Q

Treatment of Pneumocystic pneumonia?

A

Co-trimoxazole
Pentamidine
Can be given prophalactically

42
Q

What is aspergillus, what is it caused by and in who?

A

Fungal chest infection usually caused by Aspergillus fumigatus (common environmental fungus) and inhalation of fungal spores

In immunocompromised/suppressed patients - severe pneumonia and invasive disease
In immunocompetent patients - localiased pulmonary infection with Aspergilloma (fungus ball) in pre-existing chest cavities (may have previously TB)

43
Q

Diagnosis of Aspergillus?

A

BAL ideally with fungal culture or PCR

Histopathology of tissue

44
Q

Treatment of Aspergillus?

A

Amphotericin B
Voriconazole
Surgery

45
Q

Cause of tuberculosis?

A

Mycobacterium tuberculosis

Acid/Alcohol Fast Bacilli (thick, waxy coat)

46
Q

Pathogenesis of TB?

A

Engulfed by alveolar macrophages in alveoli

Resist killing and multiply

47
Q

Characteristics of TB?

A

90% asymptomatic and develop “LATENT” TB
Then, alterations in immune function REACTIVATE TB (active TB)

10% develop immediate active TB

48
Q

Symptoms of TB?

A 
Long-term cough
Chest pain
Sputum +/- haemoptysis
Weakness or fatigue
Weight loss
Fever & chills
Night sweats
49
Q

Diagnosis of TB?

A

Microscopy of sputum/tissue
Culture on selective media
PCR - more expensive but faster than culture
(Immune reaction)

50
Q

Describe microscopy for TB

A

Mycobacterium tuberculosis:
Acid Alcohol Fast Bacilli
Thick waxy coat

Ziehl-Neelsen (ZN) stain:
Red-dye (charcoal-fuschin) added to smear and is heated to allow dye to penetrate waxy coat
Acid/alcohol added - waxy coat of Mycobacteria retain dye even after exposure to acid/alcohol (non-waxy bacteria, others, do not); usually, means TB
Counter stain is added and the mycobacteria appear red

51
Q

Advantages and disadvantages of ZN stain?

A

Cheap and rapid

No indication of species or sensitivity

52
Q

Describe mycobacterial PCR, dis/advantages?

A

Directly from sample
Results available in 1-2 hours

Advantages:
Potential for “field testing” (Point of Care testing)

Disadvantages:
Provides limited species info
Provides limited sensitivty results
Expensive

53
Q

Describe Mycobacterial culture

A

Comparatively slow-growing organisms that require specialised media

Lowenstein-Jensen (LJ) medium >3 months:
Growth characteristics are used to identify the organism (colour, speed, texture, biochemical characteristics)

Liquid media >2 months:
Faster
Further ID by molecular methods

54
Q

Dis/advantages of Mycobacterial culture?

A

Advantages:
High sensitivity and specificity
Info on sensitivity

Disadvantages - slow

55
Q

Three main routes of transmission?

A

Contact (touch) - direct (person-to-person: secretion-hand to hand-mucous membrance)/indirect (secretion-hand-object-hand-mucous membrane) thus hand hygiene is important and single rooms are ideal

Airborne - small particles (5 microns) fall to floor within 2m and so spread by direct contact with mucous membrane/RT or by indirect contact; single room is ideal

Microbiology (13 decks)

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