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S1B5: Micro > Streptococcus > Flashcards

Streptococcus Flashcards

1
Q

What are the general characteristics of the Streptococcus genus?

What tests would you run to detemin species level?

A
  • gram positive cocci in pairs or chains
  • facultative and capnophilic (like CO2)
  • Fastidious species – complex nutritional needs
  • Species level tests
    1. Serology (Lancefield A-W)
    2. Hemolysis
    3. Biochemical/physiological properties
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2
Q

Where are colonies of S. pyogenes found?

What diseases are caused by S. pyogene?

A
  • Colonies
    • asymptomatic URT and transient skin colonization
    • person to person spread by respiratory droplets
    • crowded facilities
  • Diseases
    • Superficiel
      • pharyngitis (5-5 yr olds)– winer
        • lasts 1-4 days (comp. = rheumatic fever/glomerulonephritis)
      • pyoderma (2-5 yr olds)– summer
      • erysipelas (St. Anthony’s fire)
    • Deep Tissue
      • cellulitis
      • necrotizing fasciitis
    • Toxin mediated
      • TSS
      • Scarlet fever
    • Immunological
      • rheumatic fever (+RF/AGN) in resource poor countries
      • glomerulonephritis
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3
Q

What are two important aspects of S. pyogenes cell wall?

A
  • Hyalluronic acid capsule
    • antiphagocytic (prevents being recognized by immune system)
  • M protein
    • binds to plasma fibrinogen – prevents complement activation adn opsonization
    • neutralized by M-protein antibody
      • only for that specific serotype
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4
Q

What disease is present in the image?

What is the likely bacterial cause?

How could you distinguish between viral or bacterial cause?

A

Pharyngitis (Strep Throat)

S. pyogenes

  • if viral, would also expect conjunctivitis
  • severe bacterial: swollen pharyngeal mucosa w/ exudate
    • peritonsillar or retropharyngeal abscesses
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5
Q

What disease is shown in the image provide? What is the likely bacterial cause?

Red/furred tongue

Rash initially on upper chest, spreads to extremities

disappears in 5-7 days follwed by desquamation

A
  • Scarlet Fever
  • S. pyogenes
  • caused by 3 toxins: streptococcal pyrogenic exotoxins A, B, C
    • –> spread through blood and localize on skin
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6
Q

What disease is shown in the image provided?

What are the likely bacterial causes?

Usually present on face or legs– introduced from minor trauma (scratch)

Progression is from vesicles –> pustules –> rupture & crust over

not painful and patients don’t feel ill

A

Streptococcal impetigo/pyoderma

S. pyogenes and S. aureus (major b/c antibiotic resistance)

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7
Q

What disease is indicated in the image shown?

Infection involving skin and subcutaneous tissue

What is often the cause of this disease?

A

cellulitis

due to traumatic/surgical wound, insect bite

often no entry site is apparent

S. pyogenes

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8
Q

What disease is indicated in the image shown?

Ususally on the malar areas of the face– “butterfly rash” bright & red appearance of the skin

A

Erysipelas

severe form of cellulitis

S. pyogenes

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9
Q

What disease is shown in the image provided?

Starts like cellulitis –> bulleas, gangrene & systemic signs

obstructed blood supply along fascial planes

What is the treatment?

A

Necrotizing fasciitis (hemolytic streptococcal gangrene)

S. pyogenes (60% cases)

requires extensive debridement and antibiotic treatment

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10
Q

What disease is characterized by fever, malaise, HT and multiple organ failure?

What bacteria is probably responsible for this disease?

A

Streptococcal Toxic Shock Syndrome:

can also cause pharyngitis (rare), cellulitis (some), NF (always)

streptococal pyrogenic exotoxins = super-antigens

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11
Q

How could you differentiate between cellulitis and erysipelas?

A

Erysipelas often presents on the face

Also, erysipelas usually has a clear boundary between diseased skin and non-diseased skin that is not present in cellulitis

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12
Q

What disease is characterized by inflammatory changes in the heart, joints, S/C tissue 1-3 weeks after pharyngitis

What bacterial is likely responsible?

What protein is the cause of this specific reaction?

What are the 4 human proteins targeted by this disease?

A

Acute rheumatic fever (ARF) & rheumatic heart disease (RHD)

Streptococcal pyogenes (rich in M proteins)

M protein antibodies cross-react w/ host tissue proteins

Targets: myosin, tropomyosin, laminin, and keratin

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13
Q

What disease is characterized by acute inflammation, hypertension, hematuria and proteinuria seen after pharyngitis or skin infections?

What bacteria is likely responsible?

What is the physiologic cause of this disease?

A

Acute glomerulonephritis (AGN)

Streptococcal pyogenes

Ag-Ab complexes on glomerular basement membrane

glomerular capillaries are filled with monocytes adn PMNs

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14
Q

How can you identify Streptococcal pyogenes?

Hemolytic?

Gram stain shape?

catalase?

A disc?

PYR test?

growth requirement?

A
  • beta-hemolytic,
  • gram positive (purple) chains of cocci
  • catalase negative
  • bacitracin (A disc) sensitive
  • Positive PYR test (turns disk pink) (only streptococci that is positive)
  • requires enriched medium (blood/serum)
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15
Q

What are the following test results for Streptococcus agalactiae?

catalase?

hemolysis?

gram stain shape?

group?

A disk (bacitracin)?

CAMP test?

Hydrolysis of bile esculin?

Hydrolysis of sodium hippurate?

location?

A
  • catalase (-)
  • beta-hemolysis
  • gram positive in cocci chains
  • group B
  • A disk (bacitracin) resistant
  • CAMP test (positive)- causes synergistic hemolysis with S. aureus
  • Hydrolysis of bile esculin (negative)
  • Hydrolysis of sodium hippurate (positive)
  • location
    • native to female urogenital tract & rectum
    • babies acquire from mother or babies in nursery
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16
Q

Why is it dangerous for a pregnant woman to have genital colonization of S. agalacitae?

A
  • genital coonization increases risk of premature birth
  • premature infants are at greater risk of disease
  • Since newborns do not have anticapsular antibodies, they are at risk for contracting a more serious disease
  • major cause neonatal meningitis
17
Q

Aside from pregnant women, what population is most susceptible to infections caused by S. agalactia?

What types of diseases does it cause?

A

immunocompromised

bacteremia, pneumonia, bone,skin & soft tissue infections

18
Q

What bacteria is often responsible for UTI during and after pregnancy as well as chorioamnionitis and puerperal sepsis (serious septicemia after childbirth)?

A

S. agalactiae

19
Q

What bacteria is responsile for bacteremia, pneumonia and meningitis in newblorns?

How is it acquired?

Why are they particularly susceptible?

A

S. agalactiae

major cause of neonatal meningitis

acquired by aspiration of infected amniotic fluid

they have few alveolar macrophages, poor neutrophils chemotaxis and phagocytosis

20
Q

What steps can be taken to prevent S. agalctiae diseases?

A
  • screen anogenital at 35-37 weeks pregnancy
    • chemoprophylaxis culture for positive cases
  • for women w/ history childbirth & GBS disease
    • chemoprophylaxis regardless
21
Q

What are th 5 groups of viridan Streptococci? Why are they named viridan?

Where are they located?

A
  1. Mitis (includes S. peumoniae)
  2. Anginosus
  3. Salivarius
  4. Mutans
  5. Bovis

they are called viridans b/c they produces a green pigment on blood agar (alpha-hemolysis)

Found in oral cavity/URT

22
Q

Which bacteria group are the most common cause of sub-acute endocarditis?

A

Viridan Streptococci

Important: S. mitis, S. mutans, S. salivarius, S. sanguis

23
Q

How can you identify Streptococcal pneumoniae?

Gram stain?

catalase?

Bile soluble?

Growth requirement?

Response to CO2?

hemolysis?

Quellung reactin?

P disk (optochin?)

location?

A
  • Sample
    • pneumonia (sputum/blood)
    • meningitis (CSF)
    • OM (aspirate)
    • urine (pneumonia/meningitis)
  • gram positive coccus diplococci
  • catalase (-)
  • Yes, bile soluble (lysed)
  • Requries blood/serum
  • often capsulated, growth enhanced by CO2
  • alpha-hemolysis on blood agar
  • Quellung reaction (+) appear swollen
  • P disk sensitive
  • Location
    • colonized nasopharynx (5-10% adult) (20-40% children)
    • URT to midle ear, sinuses, meninges, lungs & blood
24
Q

Which proteins are particularly important for Streptococcal pneumoniae pathology?

A
  • IgA protease
  • pneumolysin (Ply)
    • kills ciliated epithelial cells & phagocytic cells
    • helps in penetration through epithelium
    • lysis causes edema, hemorrhage, bacterial growth
25
Q

What is the most important virulent factor of S. pneumoniae?

What are the 3 major diseases it causes?

A
  • capsule
    • inhibits phagocytosis and complement pathway
  • Diseases
    • pneumonia
    • meningitis
    • otitis media
    • Complication–> sub-acute endocarditis
26
Q

What disease is characterized by the image shown and the following symptoms?

  • after a viral URT infection
  • acute onset fever with rigors, productive cough
  • pleural pain, dyspnea, tachypnea, tachycardia, sweats
  • PMNs & lancet shaped diplococci in rusty sputum
  • affects mostly a scton/lobe of the lung

What bacteria is likealy the cause of this disease?

A

Pneumonia

Streptococcal pneumoniea

27
Q

What disease is charcterized by severe & continuous ear-ache often with fever of 39 degrees C or more

Can spread from middle ear to cause meningitis (high protein/low glucose)

What bacteria is the likely cause of this disease?

A

Otitis media

Streptococcal pneuoniae

leading cause of otitis media in young children

28
Q

In what conditions can bacteremia result from a S. pneumoniae infection?

What dissease can result from bactermia?

A

~30% pneumoni and 80% meningitis patients have bactermia

can result in sub-acute endocarditis (common in those with previously damaged heart valve)

29
Q

What are the 2 relevant species of Enterococcus?

What is special about this group?

Where do they often colonize?

A

E. faecalis (predominant) & E. faecium (on the rise)

Can grow in high salt, bile, temperature and confer antibiotic resistance

Enteric pathogen – can also colonize GUT, often after antibiotic use

30
Q

What 3 diseases can be caused by enterococcus?

A
  1. UTI (mainly nosocomial)
    1. hospitals; dysuria & pyruria
    2. commone w/ those w/ indwelling catheter or broad antibiotics
  2. Peritoniitis
    1. abnormal swelling/tenderness after abdominal tauma or surgery
  3. Endocarditis
    1. in patient siwht persistent bactermia
31
Q

How could you identify Enterococcus with relation to the indicated tests?

Growth requirement?

P-disc?

Bile?

Hemolysis?

A
  • High salt, bile, and temperature tolerant
    • Can grow at 45 degrees C, with 6.5% salt of 40% bile
  • P-disc resistant
  • bile resistant (rule out S. pneumoniae)
  • gamma-hemolytic on blood agar
32
Q

Why is it unnecessary to identify anaerobic cocci bacteria to the species level?

General name?

what types of diseases can they cause?

A

They are all sensitive to penicillin, metronidazole, imipenem and chloramphenicol

Peptostreptococcus

URT: sinusitis and pleuropulmonary infections

GIT: intra-abdominal infections

GUT: endometritis, pelvic abscesses, and salpingitis

skin: cellulitis and soft tissue infections

S1B5: Micro (12 decks)

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