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Clinical Micro > RTI's (bacterial) > Flashcards

RTI's (bacterial) Flashcards

1
Q

How are RTIs normally divided?

A

Into lower and upper tract infections

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2
Q

What two types of infections are grouped into lower tract infections?

A
  1. Pneumonia (CA and nosocomial)

2. AECB/AE-COPD

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3
Q

What does AECB/AE-COPD stand for?

A

Acute exacerbations of chronic bronchitis / acute exacerbations of chronic obstructive pulmonary disease

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4
Q

What 3 infections are grouped into upper tract infections?

A

Pharyngitis
Otitis media
Sinusitis

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5
Q

What is the most common type of sample to obtain from someone with a lower tract infection?

A

Sputum

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6
Q

What are 7 types of specimens you can obtain to test for an RTI ?

A 
Sputum
BAL / bronchial washing
Nasopharyngeal aspirates / swabs
Endotracheal aspirates
Sinus aspirates
Tympanocentesis
Throat swabs
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7
Q

What is the pathogen most commonly associated with all RTIs (with the exception of pharyngitis)?

A

Streptococcus pneumoniae

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8
Q

What are the 3 common (not atypical) pathogens responsible for RTIs?

A
  1. Streptococcus pneumoniae
  2. Haemophilus influenzae
  3. Moraxella catarrhalis
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9
Q

What are the 3 atypical pathogens commonly associated with RTIs?

A
  1. Mycoplasma pneumoniae
  2. Chlamydophyla pneumoniae
  3. Legionella pneumophila
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10
Q

What are the 2 major causes (pathogens/types of pathogen) for community acquired pneumonia?

A
  1. Streptococcus pneumoniae (40%)

2. Atypical pathogens (30%)

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11
Q

Why can you not treat CA pneumonia empirically with a a ß-lactam?

A

Because it won’t deal with the atypical pathogens that are the cause in 30% of cases

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12
Q

Define pneumonia

A

an inflammatory condition of the lung primarily affecting the alveoli (microscopic air sacs)

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13
Q

What are the three “types” of pneumonia?

A

CAP: community acquired
HAP: hospital acquired
VAP: ventilator associated pneumonia

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14
Q

What pathogens tend to be the cause of HAP and VAP?

A

gram negatives and anaerobes

- ex: Klebsiella, S. aureus

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15
Q

What are some typical signs and symptoms of pneumonia?

A

fever,cough (productive or dry), chest pain,shortness of breath

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16
Q

Why are throat swabs useless for diagnosing pneumonia?

A

Because 5-10 % of adults and 20-40% of children have their nasopharynx colonizes by streptococcus pneumoniae

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17
Q

What are the main features (atmosphere, shape, testing, susceptibilities) of Strep. pneumoniae?

A
  1. small gram positive diplococci
  2. alpha haemolytic
  3. bile soluble
  4. optochin sensitive
  5. growth often enhanced in CO2 atmosphere
  6. most are encapsulated
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18
Q

Streptococcus pneumoniae being soluble in bile and sensitive to optochin allows it to be separated from…?

A

other viridans group strep

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19
Q

What are 6 factors that can predispose someone to developing a pneumococcal infection?

A
  • defective Ab formation
  • insufficient numbers of neutrophils
  • day-cares, military, prisons, shelters (close quarters)
  • chronic respiratory disease (i.e. COPD)
  • infancy and aging
  • diabetes, alcoholism, liver disease (comorbidities)
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20
Q

What is the most important virulence factor for S. pneumoniae?

A

Capsule formation!

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21
Q

What two jobs does the capsule have for S. pneumoniae?

A
  1. Helping the bacteria escape from phagocytic cells

2. Help form adherence + colonization

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22
Q

What are 2 other virulence factors used by S. pneumoniae?

A
  1. Pneumolysin (hemolysin)

2. Secretory IgA protease

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23
Q

What does pneumolysin do? (3 things)

A
  1. destroys ciliated epithelial cells
  2. suppress oxidative burst by phagocytic cells
  3. activates the classical complement pathway
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24
Q

What two vaccines exist against pneumococcal infections?

A
  1. Pneumovax (pneumococcal vaccine)

2. PREVNAR (conjugate vaccine)

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25
Q

What is Penumovax preventative against? what are the drawbacks?

A

Effective against 23 most common capsular serotypes of invasive disease causing pathogens (getting into the blood)
- these account for 90% of infective strains

Drawbacks are that it is not very immunogenic and doesn’t offer long lasting protection because it’s a carbohydrate vaccine
- also doesn’t work for kids

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26
Q

What is PREVNAR effective against? What are the drawbacks?

A

Conjugative vaccine that can be used for kids under 2 y/o as well as adults

Drawbacks: not as wide a spectrum?

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27
Q

What are the 5 kinds of antibiotics that you can prescribe for an infection with Streptococcus pneumoniae? Which one can you not use empirically?

A

penicillins, cephalosporins, macrolides, fluoroquinolones, vancomycin
- can’t use the penicillins empirically

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28
Q

What 4 factors will influence the choice of antibiotic for S. pneumoniae?

A
  • Site of infection
  • Comorbidities
  • Severity of illness
  • Ambulatory / inpatient
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29
Q

What tend to be the 3 main causes of acute bronchitis?

A
  1. Viral antigens
  2. pollutants/allergens/smoke
  3. atypical pathogens
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30
Q

What are the 3 classifications of chronic bronchitis?

A
  1. Simple
  2. Complicated
  3. Complicated + risks
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31
Q

What 2 pathogens tend to be the cause of Simple chronic bronchitis?

A

H. influenzae and S. pneumoniae

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32
Q

What types of pathogens (4) tend to be the cause of more complicated/risky chronic bronchitis?

A
  1. Enterobacteriaceae
  2. Pseudomonas spp
  3. Gram-negatives
  4. Resistant organisms
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33
Q

What is COPD? (acronym and definition). What types of diseases does it include

A

Chronic obstructive pulmonary disease

umbrella term used to describe progressive lung diseases including emphysema, chronic bronchitis, refractory (non-reversible) asthma, and some forms of bronchiectasis.

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34
Q

What is a common characteristic of all COPD?

A

increasing breathlessness due to narrowing of the bronchiole tree
- hard to breathe in, even harder to breathe out

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35
Q

Which pathogen is the most common cause of AE-COPD?

A

Haemophilus infleunzae

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36
Q

What are 4 ‘facts’ about H. influenzae (growth, morphology, requirements..)

A
  • small gram negative bacilli
  • requires X and V factors for growth
  • will grow on “chocolate” agar with 5% CO2
  • may be encapsulated
37
Q

Why is the infectious encapsulated form of H. infleunzae not an issue currently? What did it used to cause?

A

Because of the effectiveness of the Hib vaccine against the type b form of H. influenzae

Used to cause meningitis (kids) and acute epiglottitis (kids and adults)

38
Q

what does H. influenzae cause most now? In what form?

A

majority of mucosal disease due to non-encapsulated strains

39
Q

What are the other two members of Haemophilus spp that you need to be able to differentiate between?

A

H. parainfluenzae, Aggregatibacter aphrophilus

40
Q

How can you differentiate between H. influenzae, H. parainfluenzae, A. aphrophilus? What 3 tests?

A

Test if they are X, or V factor dependent as well as the catalase test

H. influenzae: positive for all 3

H. parainfluenzae: negative for X factor, positive for V factor and catalase (can be +/-)

A. aphrophilus: negative for all tests

41
Q

What is X factor

A

Porphyrin which is essentially heme

42
Q

What is V factor?

A

NAD

43
Q

Why is H. influenzae X factos dependent?

A

They do not excrete porpho-bilinogen and porphyrins because of deficiencies in the hemin biosynthetic pathway

44
Q

How can you test for X factor dependence (porphyrin test). How do you know if you have H. influenzae or not?

A

Heavy suspension in amino-levulinic acid, incubated 4 hr illuminated with UV light and examined for red fluorescence

Positive test = Fluorescence under UV = indicates enzymatic conversion of amino-levulinic acid to porphyrins and therefore X-factor independence = not H. influenzae

45
Q

What is the best approach to treating an infection with H. influenzae? what kinds of drugs are they resistant to?

A
  1. Want to test for ß-lactamase activity (present in 18%) with a nitrocephin disk test
  2. If no ß-lactamase produced, you can treat with amoxicillin
  3. If there is a ß-lactamase produced, treat with amoxicillin clavulanate
    - can also treat with 2nd / 3rd generation cephalosporins, newer macrolides (ok), and fluroquinolones (not in kids)
46
Q

What % of H. influenzae infections have altered PBPs?

A

~1%

47
Q

What is the morphology of Moraxella catarrhalis?

A

small gram negative cocco-bacilli

48
Q

What 3 infections is M. catarrhalis associated with?

A

otitis media, sinusitis, AECB

49
Q

What is the approximate carriage rate of M. catarrhalis?

A

about 50 %

50
Q

What % of M. catarrhalis stains are resistant to ß-lactams? why?

A

about 90% produce a ß-lactamase

51
Q

What is M. catarrhalis predictably susceptible to?

A

Most oral antibiotics with the exception of ampicillin / amoxicillin
- susceptible to TMP/SMX?

52
Q

What 2 tests is M. catarrhalis positive for?

A

DNase +, asacchrolytic

53
Q

What type of bacteria is Legionella pneumophila? Where does it live?

A

Intracellular gram negative bacilli

54
Q

Where does Legionella penumophila tend to be found?

A

widespread in the environment, found in the soil, water, taps, and showers

55
Q

Why is Legionella sometimes missed on a gram stain

A

because it stains very faintly

56
Q

What type of agar does Legionella require for growth? Why? what other condition makes growth favourable?

A

Buffer charcoal, yeast extract with the addition of L-cysteine (BYCE)
- Need blood or charcoal to mop up toxins or it won’t grow

stimulated by 5% CO2

57
Q

What are 2 other growth features of Legionella (ie movement and sugar…)

A

Motile and asaccharolytic

58
Q

What is the best (of 4 possible) diagnostic lab tests to detect Legionella? Which is the worst?

A
  1. Urine sample (for antigen detection)
  2. Culture

the worst is DFA testing but serology is also useless unless the disease presentation is acute

59
Q

Is susceptibility testing done for Legionella typically? Why?

A

No because you can get in vitro macrolide resistance but it works fine clinically

60
Q

What two drugs are Legionella predictably susceptible to?

A
  1. Fluoroquinolones

2. Macrolides

61
Q

What are 3 morphological and genomic features of mycoplasma?

A
  1. smallest free living bacteria
  2. small genome size
  3. lack a cell wall
62
Q

What are 2 growth condition preferences/requirements for mycoplasma?

A

Facultative anaerobes and require complex media for growth

63
Q

Which two diseases is Mycoplasma pneumoniae often the cause of? what %?

A
  1. 70-80% of tracheobronchitis cases

2. 20-30% of pneumonia cases

64
Q

What is a common symptom of M. pneumoniae caused tracheobronchitis?

A

prolonged post infectious cough

65
Q

What is a common symptom of M. pneumoniae caused pneumonia?

A

mild disease but long duration

66
Q

What are 2 atypical pathogens that cause RTIs ?

A
  1. Mycoplasma pneumoniae

2. Chlamydophyla pneumoniae

67
Q

What drugs (3) are the atypical pathogens typically susceptible to?

A
  1. doxycycline
  2. macrolides
  3. fluoroquinolones
68
Q

What type of bacteria is Bordella pertussis?

A

small gram negative cocco-bacilli

69
Q

What type of growth conditions does B. pertussis require? What is the name of the media?

A
  1. strict anaerobe
  2. media containing charcoal, blood, or starch
    - Bordet-Gengou(BG) or RL medium
70
Q

What are the 3 stages of disease progression of pertussis? Which is the most contagious stage?

A
  1. Catarrhal stage (highly contagious)
  2. Paroxysmal stage
  3. Convalescent stage
71
Q

What is the general incubation period for pertussis?

A

7-10 days (can range from 4-21)

72
Q

How long does the catarrhal stage of infection last? what are the symptoms?

A

1-2 weeks

Sneezing, runny nose, mild cough, low grade fever
- fairly non-specific resp. tract infection

73
Q

How long does the paroxysmal stage of infection last? what are the symptoms?

A

1-6 weeks

paroxysmal cough, inspiratory whoop, posttussive vomiting, cyanosis, exhaustion leukocytosis, lymphocytosis

74
Q

How long does the convalescent stage of infection last? what are the symptoms?

A

2-3 weeks

Symptoms should be clearing unless the patient acquires a secondary infection

75
Q

What is the best sample collection method to use to diagnose a respiratory tract infection? What tests should be done after this? what is the best course of antibiotics to put a patient on?

A
  1. Naso-pharyngeal specimens (either by swab or aspirate)
  2. PCR is test of choice (can also culture on Bordet-Genou agar)
  3. Macrolides are the best choice antibiotics
76
Q

What are the stats on S. pyogenes? (type of bacteria, what tests is it positive for, grouping, hemolysis…)

A
  • gram positive, catalase -ve, β-haemolytic
  • Lancefield Group A
  • Pyr +, Taxo A (bacitracin) S
77
Q

What 2 drugs are commonly used to treat bacterial pharyngitis caused by S. pyogenes?

A

Penicillin/Amoxicillin

78
Q

Why do we treat S. pyogenes?

A

Not to resolve symptoms but to:

  1. reduce risk of transmission
  2. reduce risk of post-strep complications
79
Q

what are two complications that can arise after an infection with S. pyogenes?

A
  1. Rheumatic heart disease

2. Post streptococcal glomerulonephritis

80
Q

What is a test that can be used to diagnose S. pyogenes? what population is is not used for and why?

A

Rapid Group A Ag test

Not used for people 16+ because you’re more likely to get a false positive

81
Q

What bacteria causes pharyngitis in teens/YA between 16-24 that also presents with a rash and occasionally more invasive disease?

A

Arcanobacterium hemolyticum

82
Q

If you’re going to treat Arcanobacterium hemolyticum, what should you use?

A

Macrolide is the first choice

- may respond poorly to penicillin

83
Q

What culture conditions are required for Arcanobacterium hemolyticum?

A

Best on rabbit blood with CO2 for 48 hours

84
Q

What is the hemolysis patten for Arcanobacterium hemolyticum ?

A

weakly ß-hemolytic

85
Q

do we treat bacterial pharyngitis empirically? why or why not?

A

No because you aren’t trying to ameliorate symptoms, just prevent spread and complications

86
Q

An otherwise healthy, non-smoking 41 yr male presents to your office complaining of pleuritic chest pain and SOB.
He is mildly febrile and crackles are heard on exam. Chest x-ray confirms the diagnosis of CAP
How would you manage this patient? - Specimens? Antibiotics?

A

No need for a sample

treat empirically with a macrolide

87
Q

12 year old female presents to your office complaining of a sore throat. She is febrile, has evidence of cervical lymphadenopathy.

How would you manage this patient?-Specimens / tests, antibiotics?

A

Take a swab and treat with antibiotic if you get a positive result (that its not viral…)

88
Q

78 year old female presents to the ER complaining of SOB and increased sputum production and purulence. She is afebrile.

Her history indicates she was treated for some unspecified respiratory tract infection 2 months ago with ciprofloxacin (fluoroquinolone)

How would you manage this patient? - Specimens? Antibiotics?

What does she have?

A

want to take a sample (because she’s been treated recently)

Also want to treat empirically but not with cipro

likely has AE-COPD
- don’t always see fever with bronchitis

Clinical Micro (28 decks)

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