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HMS116: Microbiology & Immunology > Introduction to Diagnostic Microbiology > Flashcards

Introduction to Diagnostic Microbiology Flashcards

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2
Q

How differentiate Staphyloccocus aureus from other Staphylococcus species?

A
  • -* coagulase positive, other species are coagulase negative
  • beta-hemolytic, other species are non-hemolytic
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3
Q

What does catalase do?

A
  • prevents bacteria oxidative damage by reactive oxygen species, by catalysing H2O2 to water and oxygen
  • all Staphyloccus species are catalase-positive
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4
Q

What does coagulase do?

A
  • leads to fibrin formation around bacteria, protecting it from phagocytosis
  • found within Staphylococcus aureus
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5
Q

Where is Staphylococci found?

A
  • ubiquitous (found everywhere)
  • Coagulase-negative staphylocci are part of skin normal flora

: ~30% of normal healthy adults are persistant nasopharyngeal carriers of S. aureus

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6
Q

How is Staphylococci spread?

A
  • person-to-person spread through direct contact or exposure to contaminated fomites (e.g. bed linens, clothing, etc.)
  • among the most common causes of community and/or hospital acquired infections

(some strains are resistant to different antibiotics)

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7
Q

How do you differentiate Staphylococcus epidermidis from Staphylococcus aureus?

A
  • S. epidermidis is coagulase-negative
  • considered less virulent than S. aureus
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8
Q

Where is S. epidermidis usually associated with and what is its pathogenesis associated with?

A
  • most commonly found associated with prosthetic devices
  • pathogenesis associated with slime layer and biofilm
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9
Q

What causes hemolytic patterns?

A
  • bacteria secrete proteins / metabolites that lyse red blood cells
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10
Q

What are the different hemolytic patterns and their characteristics?

A

alpha: incomplete lysis; green

beta: complete lysis; clear

gamma: no lysis

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11
Q

Mannitol-salt agar

A
  • contains mannitol sugar and pH indicator (phenol red)
  • if an organism can ferment mannitol, an acidic byproduct is formed that will cause the pheno red in the agar to turn yellow
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12
Q

Which is (are) the catalse-negative species?

a) enterococci
b) staphylococci
c) streptococci
d) micrococci

A
  • a) enterococci
  • c) streptococci
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13
Q

Description of Streptococcus

A
  • gram-positive cocci in chains
  • catalase-negative
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14
Q

What classifications can be used for Streptococcus?

A

1) Lancefield grouping

: based on cell wall carbohydrate antigens

  • Group A-W (Strep test RAPID)
    2) Hemolytic pattern
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15
Q

How can you differentiate the following in a lab:

  • S. pyogenes*
  • S. pneumoniae*
  • S. agalactiae*

Viridans streptococcus

A

1) hemolytic pattern

  • S. pneumoniae & Viridans strep are alpha-hemolytic
  • S. pyogenes & S. agalactiae are beta-hemolytic

2) Optochin test & capsule presence

  • S. pneumoniae is optochin sensitive & has a capsule
  • Viridans strep is optochin resistant & does not have a capsule

3) Bacitracin test

  • S. pyogenes is bacitracin sensitive
  • S. agalactiae is bacitracin resistant
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16
Q

S. agalactiae

: Group?

: virulence factors?

: epidemiology?

: transmission?

A
  • Group B streptococcus
  • virulence factors: polysaccharide capsule
  • epidemiology: colonise lower GIT & UGT

: commonly associated with infections of newborns (Meningitis, pneumonia)

  • transmission: increased risk if mother is vaginally colonised
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17
Q

Viridins streptococci

A
  • heterogenous collection of alpha-hemolytic and non-hemolytic streptococci
  • colonises the oropharynx, GIT and UGT
  • avirulent

: can cause dental carries (S. mutans)

: common cause of subacute endocarditis

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18
Q

Differentiation of S. pneumoniae and Viridans streps

A

optochin test

S. pneumoniae: sensitive

Viridans streps**: resistant

bile solubility test

S. pneumoniae: sensitive

Viridans streps**: resistant

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19
Q

Biology of Bacillus anthracis

A
  • gram-positive rods; single or paired
  • aerobic
  • spore-forming
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20
Q

Virulence factors of B. anthracis

A
  • polypeptide capsule

: consists of poly-D-glutamic acid

  • toxins

: Protecting Antigen (PA)

: Lethal factor (LF)

: Edema factor (EF)

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21
Q

Epidemiology & Transmission of B. anthracis

  • reservoir
  • transmission
A

reservoir

  • animals, skins, soil
  • human infections via exposure to reservoirs

transmission

  • innoculation (most common form of transmission)
  • ingestion
  • inhalation (i.e. Wool sorter’s disease)

potential for bioterrorism- anthrax

22
Q

Diseases caused by B. anthracis

: cutaneous anthrax

A
  • painless swelling
  • progresses to ulcer surrounded by vesicles
  • necrotic eschar, central, with erythematous border often with painful regional lymphadenopathy
23
Q

Diseases caused by B. anthracis

: gastrointestinal anthrax

A
  • rare
  • symptoms are based on site of infection
  • swelling
  • vomiting, bloody diarrhea
24
Q

Diseases caused by B. anthracis

: pulmonary anthrax

A
  • life-threatening
  • leads to shock if without treatment
  • macrophages ingest bacteria and transport to lymph nodes
  • fever, malaise, swelling, dyspnea
25
Q

Diagnosis of B. anthracis

A
  • gram-stain: gram-positive rods
  • culture: non-hemolytic
  • serology
  • PCR
  • public health reference lab (CDC select agent)
26
Q

Treatment for B. anthracis

A
  • Ciprofloxacin
  • doxycycline
  • vaccine: toxoid, AVA, high risk only
27
Q

Bacillus cereus epidemiology & transmission

A
  • ubiquitous (found in nearly all environments)
  • transmission: foodbourne

: associated with fried rice

: food kept warm (not hot)

: buffets

28
Q

Pathogenesis & Disease of B. cereus

A

eye infections

gastroenteritis (most severe form)

  • heat-stable form
  • heat-labile form
29
Q

Heat-stable form of B. cereus

A
  • emetic (vomitting) form associated with enterotoxins

: ingestion of enterotoxins, not bacteria

: incubation period short (1-6 hours)

: illness duration short (~24 hours)

: vomitting, nausea, abdominal cramps

30
Q

Heat-labile form of B. cereus

A
  • diarrheal form

: stimulates adenylate cylate-cAMP system in intestinal epithelial cells

: profuse watery diarrhea

: true infection with bacteria

: contaminated meat and sauces

31
Q

Diagnosis of B. cereus

A

culture and gram-stain

  • clinical specimens
  • implicated foods
32
Q

Treatment of B. cereus

A
  • vancomycin (glycopeptide)
  • ciprofloxacin (quinolone)
  • gentamicin (amino glycoside)
33
Q

Biology of Corynebacterium

A
  • Gram-positive; irregular, “club-shaped” rods
  • aerobic
  • catalase-positive
  • non-spore forming
34
Q

Virulence factors of Corynebacterium diphtheriae

A

diphtheria toxin

  • lysogenic bacteriophage
  • beta-phage
  • introduces exotoxin encoded on tox gene
  • toxin inhibits protein synthesis by inactivating elongating factor 2 (EF-2)
35
Q

Epidemiology & Transmission of C. diphtheriae

A
  • found worldwide
  • maintained in population by asymptomatic carriage in oropharynx & skin
  • transmission via respiratory droplets
  • immunisation program in US controls disease
36
Q

Pathogenesis & Disease of C. diphtheriae

A
  • respiratory

: sudden onset, malaise, sore throat

: exudative pharyngitis progresses into psuedomembrane (whitish plaque)- bacteria, dead cells, fibrin: firmly adheres to underlying tissue

: systemic complications (myocarditis, recurrent laryngeal nerve palsy)

37
Q

Diagnosis of C. diphtheriae

A

- clinical diagnosis

- culture: selective medium- cysteine-tellurite blood agar (CTBA)

: tellurite inhibits growth of most URT bacteria and gram-negative rods

: reduced by C. diphtheriae- produces gray/black colour on agar

- PCR: detect tox gene

- toxigenicity testing: producing of exotoxin

: Elk test

38
Q

Diagnosis of C. diphtheriae with Elk test

A
  • sterile paper with diphtheria antitoxin imbedded into agar medium
  • C. diphtheriae isolates are streaked across plate ar 90 degrees to the antitoxin strip
  • toxigenic C. diphtheriae is detected because secreted toxin diffuses from area of growth and reacts with antitoxin to form lines of precipitin
39
Q

Prevention & treatment of C. diphtheriae

A
  • penicillin or vancomycin
  • antitoxin
  • education on vaccination
  • DPT vaccine (diphtheria, pertussis, tetanus antigens)
40
Q

Myobacterium biology

A
  • aerobic rods
  • cell wall is rich in lipids

: mycolic acids- increases resistance to desiccation and many chemicals

  • acid-fast bacilli
41
Q

Myobacterium tuberculosis biology

A
  • facultative intracellular pathogen (can live/reproduce inside/outisde of cell)
  • aerobic rod
42
Q

virulence factors M. tuberculosis

A
  • dormant in macrophages
  • cord factor

: 2 mycolic acids together with a disaccharide (2 molecules of glucose)

: inhibits neutrophil migration and damages mitochondria

  • sulfatides

: prevent phagosome fusion with lysosome containing bacterocidal enzymes

43
Q

Epidemiology & transmission of M. tuberculosis

A
  • reservoir: human lungs
  • transmission via respiratory droplets

: coughing, sneezing

: ventilation & isoloationi important to prevent transmission

44
Q

pathogenesis & disease of M. tuberculosis

A
  1. enters airways and penetrates alveoli
  2. phagocytosed by alveolar macrophages
  3. bacteria multiply (days-weeks) in macrophages
  4. infected macrophages travel to regional lymph nodes (hilar, mediastinal) and tissues
  5. alveolar macrophages release cytokines (IL-12 and TNF-alpha) that increases local inflammation and recruits T-cells
  6. T-cells are activated and secrete IFN-gamma, which activates macrophages to increase phagosome-lysosome fusion and intracellular killing of bacteria (phagosome has bacteria)
45
Q

granuloma of M. tuberculosis

A
  • prevents further bacteria spread
  • necrotic mass surrounded by dense wall of CD4, CD8 and NK cells and macrophages
  • bacteria can remain dormant in this stage or can be reactivated years later when / if the patient’s immunity decreases
46
Q

clinical manifestations of M. tuberculosis

A
  • initially, non-specific complaints of malaise, weight loss, cough and night sweats

: primary infection with resolution or with progression

  • reactivation
  • disseminated (military) tuberculosis
  • sputum may be scant or bloody and purulent (pus)

: cavitary disease with tissue destruction is associated with sputum production with hemoptysis

47
Q

How is clinical diagnosis of M. tuberculosis supported

A
  1. radiographic evidence of pulmonary disease
  2. positive skin test reactivity
  3. lab dectection
48
Q

Lab Diagnostics of M. tuberculosis

A
  • Auramine-rhondamine staining bacilli (fluroscent apple green)
  • Acid fast stain (Ziehl Neelson method)
  • growth is slow on Lowenstein Jensen medium
49
Q

Acid fast stain for Mycobacterium

A

Ziehl Neelson Method

  • carbolfuschin (primary stain- red colour)
  • acid fast organisms resist decolourization with acid alcohol
  • after decolourisation, methyelene blue (secondary stain) is added to organisms to counterstain any material that is not acid fast
50
Q
A

HMS116: Microbiology & Immunology (16 decks)

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