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MICROBIOLOGY > LECTURE 4 (Gram +ve bacteria) > Flashcards

LECTURE 4 (Gram +ve bacteria) Flashcards

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1
Q

What are the properties of Viridans group of Streptococci?

A
  • Can cause opportunistic infections -> can cause disease when they are protected from host defences
  • Virulence is very low
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2
Q

Describe Enterococcus identification

A

Pin point colony -> Gram stain: Gram +ve cocci in chains -> Catalase test: -ve -> Streptococci -> Bile Esculin Test: +ve -> Growth in 6.5% NaCl -> Enterococcus -> Pyruvate Fermentation Test -> POSITIVE: Enterococcus Faecalis, NEGATIVE: Enterococcus faecium

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3
Q

What are the properties of Enterococcus?

A
  • Facultative anaerobic, catalase -ve, gram +ve cocci
  • Arranged individually, in pairs or short chains
  • Has the group D antigen
  • Normal inhabitants of the intestinal tract, female genital tract and oral cavity
  • Intestinal inhabitants resist action of bile salts
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4
Q

Diseases in humans are associated with which Enterococcus?

A

Enterococcus faecalis & Enterococcus faecium

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5
Q

What is the clinical significance of Enterococcus?

A
  • Upper and lower urinary tract infections
  • Native valve and prosthetic valve endocarditis
  • Intra-abdominal and pelvic infections
  • Wound infections
  • Septicemia and meningitis in neonates
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6
Q

Which is more antibiotic resistant? (E faecium/E faecalis)

A

E faecium

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7
Q

Describe Enterococcus

A
  • ENVIRONMENTAL PERSISTENCE (capsule, biofilm, stress response)
  • COLONISATION OF GI TRACT (stress response, aggregation substance, cytolysin, bile acid hydrolase, antibiotic resistance)
  • TISSUE DAMAGE (cytolysin, gelatinase, extracellular superoxide production)
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8
Q

What is the mechanism of Enterococcus spread?

A
  • Translocation through/breach of intestinal epithelium (cytolysin, extracellular superoxide production)
  • External infection by shed organism (capsule, biofilm, stress response)
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9
Q

Describe the preliminary grouping of Gram +ve cocci

A

CATALASE: -ve = streptococcus group, +ve = salt tolerant? -> YES: staphylococcus/Micrococcus

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10
Q

What is Staphylococcus aureus?

A

A gram +ve bacterial infection that causes abscesses, various pyogenic infections (e.g endocarditis, osteomyelitis), food poisoning, scalded skin syndrome and toxic shock syndrome

  • most common cause of hospital acquired pneumonia, septicaemia and surgical-wound infections
  • most important cause of skin infections (cellulitis, impetigo etc)
  • most common cause of bacterial conjunctivitis
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11
Q

What are the properties of Staphylococci?

A
  • Gram +ve spherical cells
  • Arranged in grape like irregular clusters
  • Non-motile
  • Do not form spores
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12
Q

What are the growth characteristics of Staphylococci?

A
  • Grow readily under aerobic/microaerophilic conditions
  • Grow rapidly at 37 degrees but form pigment best at room temp
  • Colonies on solid media are round, smooth, raised and glistening
  • S aureus = forms gray to deep golden yellow colonies
  • S epidermidis = gray to white
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13
Q

What is the importance of Protein A?

A

Protein A is the major protein in the cell wall which binds to the Fc portion of IgG at the complement-binding site -> prevents activation of COMPLEMENT CASCADE -> no C3b is produced -> opsonisation and phagocytosis is greatly reduced

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14
Q

Do Coagulase-negative staphylococci produce protein A? (YES/NO)

A

YES

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15
Q

Describe the Staphylococci structure

A
  • Protein A
  • Teichoic acids = mediate adherence of staphylococci to mucosal cells
  • Lipoteichoic acids = induce septic shock by inducing cytokines like IL-1 and TNF from macrophages
  • Polysaccharide capsule = type 5 and 8 cause most infections, capsule is immunogenic -> makes producing an effective vaccine difficult
  • Peptidoglycan = has endotoxin-like properties -> can stimulate macrophages to produce cytokines, activate the complement and coagulation cascades
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16
Q

What is important about bacteria that can produce catalase?

A

They can survive the killing effect of H2O2 within neutrophils

17
Q

How is S. aureus distinguished from the others?

A

By coagulase production

Explanation: Coagulase is an enzyme that causes plasma to clot by activating prothrombin to form thrombin. Thrombin catalyses the activation of fibrinogen to form the fibrin clot.

18
Q

What is the importance of Staphyloxanthin?

A
  • Imparts a golden colour to its colonies
  • Pigement enhances the pathogenicity of the organism by inactivating the microbicidal effect of superoxide and other reactive oxygen species within neutrophils
19
Q

What are the different Hemolysins?

A
  • α-toxin = pore-forming cytotoxin that lyses the cytoplasmic membranes by direct insertion into the lipid bilayer to form transmembrane pores
  • β-toxin = toxic for many cells
  • delta-toxin = disrupts biological membranes + may have a role in s. aureus diarrhoeal diseases
  • gamma-hemolysin = leukocidin that lyses white blood cells
20
Q

What are the properties of Enterotoxin?

A
  • causes food poisoning characterised by prominent vomiting and watery, non-bloody diarrhoea
  • acts in GI tract to stimulate release of IL-1 and IL-2 from macrophages and T helper cells
  • resistant to heat, stomach acid and stomach and jejunum enzymes
21
Q

What is Exfoliative?

A
  • causes “scalded skin” syndrome in young children
  • “epidermolytic” and acts as a protease that cleaves desmoglein in desmosomes -> leads to separation of epidermis at granular cell layer
22
Q

What is P-V leukocidin?

A

A pore-forming toxin that kills cells (especially WBCs) by damaging cell membranes. The two subunits of the toxin assemble in the cell membrane to form a prom through which cell contents leak out.

23
Q

What is Toxic shock syndrome toxin (TSST)?

A

A toxin that causes Toxic shock and enters the bloodstream causing a toxaemia. TSST is produced locally by S. aureus in the vagina, nose or other infected site.

24
Q

What are the properties of coagulase-negative staphylococci?

A
  • Do not produce exotoxins
  • Do not cause food poisoning or toxic shock syndrome
  • Cause pyogenic infections
25
Q

What is Furuncle?

A

A skin infection that typically develops in a hair follicle, sebaceous gland or sweat gland

[no surgical or antimicrobial treatment is needed]

26
Q

What is Carbuncle?

A

An infection of the hair follicle that extends into the surrounding skin and deep underlying subcutaneous tissue. It is a serious lesion that may result in bloodstream invasion.

27
Q

What is Impetigo?

A

Strains of S aureus that produce exfoliatin cause BULLOUS IMPETIGO characterised by blisters containing many staphylococci in the superficial layers of the skin

28
Q

What is Staphylococcal food poisoning?

A

A gastrointestinal illness caused by eating foods contaminated with toxins produced by the bacterium

  • can contaminate food by people who carry it
  • found in unpasteurised milk, cheese, ham
  • illness cannot be passed to other people + lasts for 1 day

SYMPTOMS
- vomiting (most prominent!)
- nausea
- stomach cramps
- diarrhoea

29
Q

What is Toxic Shock Syndrome?

A

A bacterial infection characterised by fever, hypotension, a diffuse, sunburn-like rash and involvement of 3 or more of the following organs: liver, kidney, GI tract, CNS, muscle, blood

SYMPTOMS:
- high fever
- vomiting
- diarrhoea
- sore throat
- muscle pain

TREATMENT:
- antibiotics
- blood transfusions
- corticosteroids
- electrolyte replacements
- ventilator

30
Q

What is Scalded skin syndrome/Ritter von Ritterschein disease?

A

Results from the production of the toxin exfoliatin. It is characterised by red blistering skin that looks like a burn or scald.

SYMPTOMS:
- Irritability
- Tiredness
- Fever
- Redness of the skin
- Fluid-filled blisters that break easily and leave an area of moist skin that becomes tender and painful
- Large sheets of the top layer of skin may peel away
- Electrolyte imbalance
- Hair and nails can be lost

TREATMENT
- IV antibiotic
- Fluids to prevent dehydration
- NG feeding
- Use of skin creams, ointments or bandages
- Pain medicines

31
Q

What is Staphylococcus epidermidis?

A
  • catalase +ve, coagulase -ve & facultative anaerobe
  • live on skin, anterior nares and ear canals of humans
  • colonise implanted medical devices (e.g can cause catheter related sepsis)
32
Q

What is Staphylococcus saprophyticus?

A
  • catalase +ve, coagulase -ve, facultative anaerobe
  • stays in GI tract & urinary tract
  • causes urinary infections in young women
  • infection process aided by surface adhesins to uroepithelial cells and factors aiding survival in urine (e.g production of urease)
33
Q

How do you conduct the Catalase test?

A

1) Inoculate bacteria onto a microscope slide
2) Add a drop of hydrogen peroxide onto the bacteria
3) If bubbles are formed the organism is catalase positive

MICROBIOLOGY (14 decks)

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