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PART ONE REVISION. > MICROBIOLOGY - Bacterial Infections > Flashcards

MICROBIOLOGY - Bacterial Infections Flashcards

1
Q
  1. Whats the difference between staph and strep in terms of structure and +ve/-ve enzymes?
  2. Whats the difference bewteen staph aureus and staph epidermis?
A
  1. staph - clusters, strep - chains/pairs
  2. staph aureus - clusters and coagulase and catalase +ve
    staph epidermis - clusters catalase +ve and coagulase -ve, urease +ve
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2
Q

What are the main characteristics of staph aureus?

A

POSITIVE AURA.
Gram +ve, Catalase +ve, Coagulase +ve, occurs in CLUSTERS (as people cluster around)

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3
Q

What are the main virulence factors in staph aureus? (5)

A
  1. Protein A - inhibits complement activation
  2. Penicillin binding protein - cross/links and strengthens peptidoglycan cell wall - can be altered in MSRA so becomes methicillin resistance
  3. Superantigen TSST-1 (toxic shock syndrome toxin-1)
  4. Enterotoxin B - heat stable toxin which leads to food poisoning
  5. Exfoliative epidemolytic toxin causing Staphylococcal scalded skin syndrome
  6. Hyaluronidase
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4
Q

What are the main treatments for staph aureus? (3)

A
  1. beta-lactam Abx (penicillin + first/second gen cephalosporins) + Beta-lactamase inhibitor (cluva acid)
  2. Clindamycin
  3. Vancomycin/Linezolid (MRSA resistant)
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5
Q

What are the main characteristics of staph epidermidis?

A

sticky biofilm stuck on your epidermis
COCCI that appears in clusters

  • sticky biofilm which attaches to endogenous/exogenous medical devices
  • usually occurs with hands and feet
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6
Q

What are the difference types of catalase negative bacteria?

A

Alpha - partial breakdown of Hb - S Pneumoniae, strep viridans

Beta - Strep pyogenes, strep agalactiae

Gamma - enteroccocus, Strep bovis

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7
Q

What are the main structure of strep pneumoniae? Where is it found?

A

Gram positive coccus catalase negtative
Encapsulated lancet shaped diplococci in chains. Usually found in the nasopharynx.

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8
Q

What are the main virulence factors of strep pneumoniae?

A

STREP PNEUMOPSIAE

most common pathogen in patients who are asplenic

Has IgA protease which breaks down IgA proteins and
causes MOPS
Meningitis
Otitis Media
Pneumonia
Sinusitis

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9
Q

What are the main bacterial causes for conjunctivitis and blepharitis?

A
  1. Strep pneumoniae
  2. Staph aureus
  3. Moraxella
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10
Q

What are the main bacterial causes of neonatal conjunctivitis?

A
  1. Neisseria gonorrhoeae (most common hyperacute purulent conjunctivitis)
  2. Chlamydia trachomatis
  3. Herpes simplex virus (rare)
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11
Q

What is the difference between strep pyogenes and strep agalactiae?

A

TRACE (Bacitracin) the genes of strep pyogenes
Both beta haemolytic strep (complete breakdown of haemoglobin on blood agar) - difference is bacitracin

  1. bacitracin +ve: strep pyogenes
  2. bacitracin -ve: strep agalactiae
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12
Q

What is the structure of strep pyogenes? Where is the strep pyogenes found?

A

Group A strep -
Chain-like arrangement of cocci.

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13
Q

What are the main pathogens in bacterial keratitis?

A
  1. pseudomonas (CL wearers
  2. streptococcus (corneal injury allows opportunistic infection - most aggresive
  3. staph aureus (peripheral ulcers)
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14
Q

What is the main structure of pseudomonas?

A

Gram negative aerobic, motile, water soluble and produces water soluble green pigment (pyocin).

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15
Q

What are the virulence factors of pseudomonas aeruginosa? (2)

A

1.Exotoxins via type 3 secretion system (T3SS) - creates pore forming complex with host cell membrane to inject exotoxins into cystosol causing rapid cell lysis and severe corneal disease

  1. LPS and flagellin activate TLR4-5 on macrophages produce chemotaxis and proinflammatory response.
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16
Q

What pathogen is the most prevantable microbial cause of blindness worldwide?

A

Trachoma

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17
Q

What is trachoma caused by?

A

Chalymdia tracomatis subgroups:
A, B, Ba, C

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18
Q

What are the clinical features of trachoma? (4)

A
  1. Mixed papillary and follicular conjunctivitis
  2. Tarsal conjunctival scarring
  3. Entropion due to contraction of scar and trichiasis
  4. Blinding corneal opacity due to corneal scratch from lashes
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19
Q

What are the clinical stages/ progression of trachoma? (4)

A

Stage
1: lymphoid hyperplasia and polymporphs in conjunctival stroma

IIA: lymphoid folicular reaction predominates

IIB: fibrosis and papillae indicate secondary bacterial infection: cornea with pannus formation

III: fibrous replacement of inflamed tissue

IV: contraction with entropion and trichiasis. Suppression of tears due to inflammation and fibrosis within lacrimal gland. Pathological stratification and loss of goblet cells in conjunctival epithelium

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20
Q

What are the main gram negative bacili (rods)? (4)

A
  1. pseudomonas
  2. moraxella lacunata
  3. haemophilus
  4. enterobacteria
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21
Q

What are the clinical fatures of moraxella lacunata? (4)

A
  1. Chronic conjunctivitis
  2. Angular blepharitis
  3. Keratitis in frail patients
  4. Angular ulceration of skin at lateral canthal angle
22
Q

What causes syphilis?

A

Treponema pallidum (spirochaete)

23
Q

What are the main tests for syphilis? (2)

A
  1. VDRL - detects anti-cardiolipin
  2. FTA-ABS - more sensitive
24
Q

What are the main bacterial causes for endophthalmitis?

A

Usually G+ve from lid flora.

  1. Coagulase negative staphylococci (staph epidermidis)
  2. Staph aureus
  3. beta-haemolytic streptococci
  4. enterococcus faecalis

Gram -ve
1. haemophilus influenzae
2. pseudomonas aeruginosa

25
Q

What are the 3 main cocci?

A

G+ - staphylococus
G+ - streptococcus
G- Neisseria

25
Q

What is the most common anaerobe in normal ocular flora?

A

propionbacterium acne - causes chronic endophthalmitis by inhabiting the lens capsule

26
Q

What are the G+ bacilli?
What are the G- bacilli?

A

G+ - bacilus genus, clostridius, propionbacterium acnes, actinomyces

G- : haemophilus influenza, moraxella, pseudomonas.

27
Q

What is actinomyces? What does it contain? What can it cause?

A

Actinomyces israeli is gram positive, non acid-fast and anaerobic bacteria.
Forms concretions and obstructs the lacrimal sac and sulphur granules are expressed from the canaliculi –> causes canaliculitis/dacrocystitis.

28
Q

What is the sutructure of chlamydia? How many forms does it have? How does it reproduce?

A

Obligate intracellular parasite of mucosal epithelial cells and has 2 forms:
1. Infectious form (elementary body - outside host)
2. Reproducing form (reticulate body - inside host) and replicates through binary fission

29
Q

What are the serotypes of chlamydia causing conjunctivitis syndromes?

A

A-C : Trachoma
D - K - adult/neonatal inclusion conjunctivitis
L1-L3: lymphogranuloma venerum - genital ulcer disease

30
Q

What diseases can chlamydia cause in newborns during delivery?

A
  1. Pneumonitis
  2. Conjunctivitis
31
Q

Which culture medium is used for chlamydia?

A

McCoy

32
Q

What are the differences between neonatal conjunctivtis and adult conjunctivitis? (3)

A
  1. Membrane formation
  2. No follicles
  3. Greater discharge
33
Q

What is the difference between gram positive and gram negative?
1. Cell wall
2. Cell wall Thickness
3. Peptidoglycan layer
4. Teichoic Acids
5. Lipopolysaccharide
6. Outer membrane
7. Lipid content
8. Resistance to Antibiotics

A

See table.

34
Q

What is the difference between endotoxins and exotoxins?

A
35
Q

What is the culture medium for neisseria (gonoccocus and meningococcus)?

A
  1. Blood agar with carbon dioxide
  2. Chocolate medium (Thayer-Martin Gonococcus)
36
Q

What are the main ocular eye flora?

A
  1. staph epidermidis (most common)
  2. staph aureus
  3. diphtheroids (2nd most common)
  4. strep viridans and strep pneumonia
  5. propionibacterium acnes
37
Q

Bacterial / viral conjunctivitis is more prevalent in adults / children?

A

Bacteria is more common than children
Virus is more common in adults

38
Q

What are the physical barriers at the ocular surface from microbes? (4)

A
  1. Blinking
  2. Eyelashes trapping microbes
  3. Sebaceous glands secreting lactic and fatty acid for low pH environment
  4. Tears - contains lacritin, lactoferrin, lipocalin lysozyme, secretory IgA, IgG, complements, B-defensins
39
Q

Which bacteria are capable of transversing INTACT corneal epithelium and establishing bacterial keratitis? (4)

A
  1. Haemophilus (G -ve)
  2. Neisseria (G -ve cocci)
  3. Corynebacterium (G +ve bacili)
  4. Listeria (G+ve bacili)
40
Q

What is the difference between endotoxins and exotoxins?

A

Endotoxins are lipopolysaccharides derived from cell wall of gram negative bacteria. Heat stable, NON-ANTIGENIC, cause septicaemia and activate the complement pathway

Exotoxins are soluble proteins released by both Gram positive and Gram negative. They are ANTIGENIC and readily destroyed by heat. They enter host cells and modify cellular components to alter host cell physiology –> effect sites distal to primary infection site

41
Q

Which organism os most frequently associated with hypersensitivity marginal keratitis?

A

Staph epidermidis

42
Q

Which bacteria has an opsonisation-resistant capsule?

A

Staph aureus

43
Q

What is the structure of mycobacterium?

A

Weak gram positive, acid fast, aerobic and rod shaped.

44
Q

What does pseudomonas secrete?

A

Utilises type 3 secretion system to injection exotoxins into host cells.

45
Q

What is the most likely orgnism to cause orbital cellulitis in a child?

A

Haemophilus influenzae

46
Q

Which bacterial organisms produce IgA proteases?

A
  1. Neisseria
47
Q

Which bacteria produce leukocidins?

A

Group A haemolytic strep - these lyse RBCs and tissue.

48
Q

Gram positive, Gram negative, Anaerobic, Aerobic diagram

A
49
Q

What is the most common pathogen in DELAYED-ONSET post-operative endophthalmitis?

A

Proprionibacterium acnes

PART ONE REVISION. (78 decks)

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