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Microbiology 2 > M5 Lower Respiratory Tract Infections > Flashcards

M5 Lower Respiratory Tract Infections Flashcards

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1
Q

What are the four possible routes that organisms cause LRT infections?

A

Organisms cause infection by four possible routes:
1. Upper airway colonization or infection that extends into the lung
2. Aspiration of organisms
3. Inhalation of airborne droplets containing the organism
4. Seeding of the lung via the blood from a distant site of infection

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2
Q

What in general plays a role in whether a LRT infection is caused or not?

A

Organism cause infection due to specific host and virulence
factors. Immune response, normal flora and general health play a role in infection.

Infections can be community acquired or nosocomial

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3
Q

In what population is Streptococcus pneumoniae infection common in and what is its virulence factor?

A

Streptococcus pneumoniae: most common cause in geriatric population; agent of
community-acquired pneumonias; the presence of a capsule facilitates attachment and resistance to phagocytosis.

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4
Q

What bacteria is known to produce “current jelly” sputum and is an “old man’s friend”?

A

Klebsiella pneumoniae (tends to live with a person after infection)

Virulence factor is that it is encapsulated.

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5
Q

What bacteria causes LRT infection by being aspirated and destroys cells?

A

Staphylococcus aureus: agent in community acquired and nosocomial pneumonias; Strains have enzymes capable of destroying host cells.

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6
Q

What kind of strains of bacteria are associated with severe pneumonia in patients with cystic fibrosis?

A

Pseudomonas aeruginosa: agent in nosocomial pneumonias; acquired through aspiration and non-aspiration routes; mucoid strains are the ones associated with the severe pneumonia in CF.

Also Burkholderia cepacia and Stenotrophomonas maltophilia.

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7
Q

What population is mostly affected by Haemophilus influenzae to cause LRT in and what is its virulence factor?

A

Haemophilus influenzae: agent of infections in non-immunized infants and children and immunosuppressed adults; presence of capsule facilitates infection.

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8
Q

What is pneumonia
and its symptoms?

A

Inflammation involves the lung’s airways and supporting structures.

Symptoms include cough, chest pain, fever, and difficulty breathing, varies with the pathogen involved.

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9
Q

What is bronchitis and what other infection may proceed it?

A

Bronchitis: Is an inflammation of the tracheobronchial tree mucous membrane.

May be preceded by an upper respiratory tract infection (influenza).

Acute infections are often the result of viral agents or bacterial pathogens

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10
Q

What is a pleural infection (pleuritis) and what is made really painful because of it?

A

Pleural Infections (pleuritis)
Organisms infect the lungs and gain access to the pleural space.
The condition can make breathing extremely
painful, and sometimes it is associated with another condition called pleural effusion where excess fluid fills the area between the membrane’s layers.

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11
Q

What is the most non-invasive way to get a micro lab sample to study for a LRT?

A

Expectorated sputum are
the most easily obtained and
common specimen of the LRT

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12
Q

What are the volume, transport and storage requirements for a sputum specimen?

A

Minimum volume- > 1 ml.
Transport- < 2 hr., RT
Storage- < 24 hr., 4º C

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13
Q

What is an endotracheal secretion? Where is it most used? How does it affect analyzing in the micro lab?

A

Invasive method where sputum is aspirated or suctioned out with a ‘Lukens Trap’.

Used in Intensive care units (ICU) where patients are unable to collect sputum.

Specimen treated like sputum for culture and reporting.

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14
Q

What are the three methods to get LRT samples by bronchoscopy?

A
  1. BRONCHIAL BRUSH
  2. BRONCHIAL WASH

Small amount of saline in and out of bronchial tree. They can get contaminated with upper respiratory flora.

  1. BAL: Broncho-alveolar lavage - more sterile. Higher volume of saline is infused deeper into a section of the lung (100-300 mL) up to the alveoli.
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15
Q

How is bronchial brush and/or wash treated in the micro lab?

A

Specimen treated like sputum for culture and reporting.

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16
Q

How is broncho-alveolar lavage (BAL) treated in the micro lab?

A

Culture is quantitative and reported in CFU/L (similar to urine). There is a correlation between acute bacterial pneumonia and ≥10^6-10^7 CFU/L in BAL’s.

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17
Q

What specimens are unacceptable for sputum’s?

A
  1. ‘Sputum’ for anaerobic culture
  2. Sputa collected over a 24 hr. period
  3. Sputum > 24 hrs. without refrigeration
  4. Sputum in preservative
  5. Specimen leaking
  6. Specimen not labeled or mislabeled
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18
Q

What specimens are screened for suitability with a direct slide stained with gram stain?

A

Sputum and ETT specimens are assessed for their suitability upon receipt in the laboratory.

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19
Q

What are the different descriptions used to describe sputa microscopically?

A
  1. Purulent
  2. Mucopurulent
  3. Bloody
  4. Mucoid
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20
Q

What is the procedure for screening a direct sputum gram stained slide?

A
  1. Examine stained and dried slide using 10x magnification, examine 20-40 fields.
  2. Average the number of squamous epithelial cells (SEC) per low power field (LPF) – 10x.
  3. Reject sputum if ≥ 10 epithelial cells/low power field (LPF) (10X objective). If not accept.
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21
Q

What are the exceptions to the rejection criteria for direct gram stain screening?

A

Limitations/exceptions:
1. 10X more PMN’s than epi cells + one morph bacteria at 3-4 +
2. Cystic fibrosis and pediatric patients
3. Special culture (Legionella- fungus-TB)

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22
Q

If the sputum sample is rejected, what is reported?

A

‘Sample contaminated with oropharyngeal flora. Please
resubmit.’

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23
Q

What plates are the specimens planted to?

A

Sputum deemed acceptable by microscopic evaluation are planted onto BA, CA, Mac (BA-CA in CO2)

24
Q

If the direct smear of the sputum is accepted what are the next things counted on the microscope?

A

The direct smear is read under 1,000x magnification and reported quantitatively according to specific criteria (PMN, bacteria, yeast)

Usually, the infecting organism is present in higher numbers on direct smear and correlates with the growth in culture.

25
Q

If the BA, CA, and MAC plates are not growing what is done?

A

If culture plates are not growing
they are incubated for another 24 hours before calling negative.

26
Q

You have successful growing plates from your sputum specimen how do go about deciding what to do next (in general)?

A
  1. Cultures are described and quantitated
  2. What to do next depends upon:
    a) the organism itself (some are pathogenic no matter what)
    b) amount of organism (important for the ones that can be normal flora)
    c) amount of this organism in relation to the amount of normal flora present (generally, significant pathogens grow in greater numbers than contaminating normal flora)
    d) correlation with direct smear result and culture growth
27
Q

if you suspect you have Strep. pneumoniae, what would be the test you do to confirm it?

A

Confirm with bile solubility (Sodium deoxycholate 10%)

Optochin Susceptibility (refresher but optional to perform)

[After doing Catalase]

28
Q

What specific considerations are taken for doing AST for Strep. pneumoniae?

A
  1. Several drugs are tested by KB: Use MH-blood in CO2
    oxacillin disk screening used to predict susceptibility to penicillin
  2. If sensitive to oxacillin (≥20mm) report penicillin “S”
    If resistant to oxacillin –> MIC should be done (E-test) and report. S-I-R based on MIC result.
29
Q

Different AST interpretation ranges are used depending on the type of specimen
(sputum-blood-CSF). Why?

A

Antibiotics reach different parts of the body with different concentrations.

30
Q

How may you suspect you have H. influenzae?

A

Grows on CA, not on BA

Pleomorphic GNB (cb)

31
Q

What tests would you do on H. influenzae?

A
  1. XV factors
  2. Satellitism
  3. Porphyrin
32
Q

What specific considerations are taken for doing AST for H. influenzae?

A

Use HTM in CO2 (as per CLSI)
beta lactamase has traditionally been used as a predictor of susceptibility to beta-lactam drugs.

HTM = Haemophilus Testing Media

Note: Standard protocol is to perform AST on most bacterial isolates from the lower respiratory tract

33
Q

Isolates of Haemophilus influenzae are setup to for AST regardless of Beta-lactamase results. Why?

A

H. influenzae may have other resistance mechanism’s. Beta-lactamase only tests for one possible one related to that enzyme.

Note: See slide 47

34
Q

What should you see in the gram stain and test for S. aureus?

A

GPC-clusters
Catalase +
Coagulase +

35
Q

What should you see in the gram stain and test for Pseudomonas aeruginosa?

A

Pseudomonas aeruginosa:

Typical morph: lg gy metallic grape odor, sheen, beta-hem
Gram stain: g-b
oxidase +
complete ID/AST

CF patients: mucoid strain

36
Q

What should do if you suspect Klebsiella pneumoniae on the sputum planted plates?

A

Klebsiella pneumoniae (or other enteric GNB)

Especially important in inpatients

Full ID and AST

37
Q

What is the morphology you would expect if the pathogen was Moraxella catarrhalis in the sputum specimen?

A

Moraxella catarrhalis

Hockey puck morph
GNDC.

38
Q

What tests would you do for Moraxella catarrhalis?

A

oxidase +
MUB + or API NH to
Confirm ID

AST NOT necessary

39
Q

What would expect to see on the gram stain and plates if the pathogen was Burkholderia cepacia? What tests?

A

seen in CF patients.
GNB, non-fermenter, NLF, oxidase weak+

40
Q

What would expect to see on the gram stain and plates if the pathogen was Stenotrophomonas maltophilia? What tests?

A

Stenotrophomonas maltophilia:
GNB, non-fermenter, NLF, oxidase NEG

41
Q

What would expect to see on the gram stain and plates if the pathogen was Acinetobacter spp.? What tests?

A

Acinetobacter spp.:
GNB or GNDC, non-fermenter, NLF, oxidase NEG

42
Q

What are some atypical agents that cause LRT infections that we studied?

A
  1. Legionella pneumophila
  2. Mycoplasma pneumoniae
  3. Chlamydia pneumoniae
  4. Chlamydia psittaci
43
Q

How is Legionnaires disease typically acquired and with who?

A

Agent of Legionnaires’ disease (and milder Pontiac fever); acquired through inhalation of contaminated water aerosols; most often found in middle-aged males with an underlying medical problems;

44
Q

What is Legionnaires virulence factor?

A

ability to survive in macrophages

45
Q

What atypical pneumoniae is most common in young adults? What is its virulence factor?

A

Mycoplasma pneumoniae

Agent of primary atypical pneumoniae; most common in young adults.

Specialized adhesion factors lead to host cell invasion and injury.

46
Q

What population does Chlamydia pneumoniae (an atypical pneumonia) affect?

A

Most common in school aged children and young adults, via droplets, passed in crowded situations (home, schools, barracks, nursing homes, prisons). Starts mild as an upper resp. infection

47
Q

What bacteria causes atypical pneumonia in people who work with birds a lot?

A

Chlamydia psittaci

The bacteria can infect people exposed to infected birds.Bird owners, aviary and pet shop employees, poultry workers, veterinarians

48
Q

What is typically characteristic of sputum for Legionella pneumophila?

A

Specimen Processing
Sputum usually watery
Bronchial wash, brushes, tracheal preferred

49
Q

What media is best for planting a suspected Legionella pneumophila specimen?

A

Buffered Charcoal Yeast Extract
- alpha ketoglutarate
- cysteine
- iron compounds
- may have vancomycin, polymyxin, anisomycin

50
Q

What atmosphere does Legionella pneumophila like to be incubated in?

A

mesophilic, humid environment required

51
Q

What type of antibody test may be done directly from cultures or specimens for Legionella pneumophila? How?

A

A. Direct Fluorescent Antibody test
1. Specimen chemically fixed onto slide
2. Stained with flourescent dye conjugated with an anti-Legionella conjugate (antibodies to several serogroups including serogroup 1)
3. Slides are viewed under fluorescent microscope for green fluorescence; negative as gold due to counterstain

Not good from sputum as it is non-specific.

B. Legionella Antigen Detection (rapid) (like a covid test, me)

52
Q

Why is the atypical pneumonia bacteria Mycoplasma pneumoniae hard to culture in the lab?

A
  1. Lacks a cell wall therefore susceptible to drying
  2. Slow growing organism with complex nutritional requirements
53
Q

What special plate is used for Mycoplasma spp.? Its colonial morphology?

A

SP (sucrose-phosphate) media specific for Mycoplasma spp.
characteristic “grainy “
colonial morphology
(fried egg)

54
Q

Is Mycoplasma spp. easy to see if it grows on a plate?

A

These are colonies, so tiny that
The plate needs to be observed
under a microscope (10X)

55
Q

What is the typical method to diagnose Mycoplasma spp. LRT infection?

A

Serology

56
Q

What tests detect acute or convalescent stages of atypical pneumoniae caused by Mycoplasma pneumoniae by testing for IgM and/or IgG?

A
  1. ELISA (Enzyme Linked Immunosorbent Assay) - gold standard
  2. Complement Fixation
  3. Immunocard
  4. Cold agglutinins
57
Q

What does mucous look like on grams of sputum samples and what else do you need to be aware of?

A

Mucous looks like threads and you need to be aware of general artifacts that are not anything.
(because people can breath stuff in).

Microbiology 2 (22 decks)

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