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FMS 3 > Microbiology: Gram Positive Cocci > Flashcards

Microbiology: Gram Positive Cocci Flashcards

1
Q

GP Cocci (GPC)

A
  • Staphylococcus
  • Streptococcus
  • Enterococcus
  • Appear as dark purple clusters (strep as chains)
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2
Q

Lab tests to differentiate GPC

A
  • Catalase test: separates staph from strep and entero (only staph is catalase positive)
  • Coagulase test: separates staph aureus from other staph (only staph aureus clots plasma)
  • Hemolysis on blood agar: distinguishes various types of bacteria
  • Alpha: partial hemolysis leaving green area (S penumoniae, Viridans)
  • Beta: complete hemolysis leaving clear area (S pyogenes)
  • Gamma: no hemolysis
  • Lancefield grouping: group-specific cell wall Ags (groups A, B, D. Refers to polymorphic immunogen on well wall. Primarily beta/alpha hemolytic strep)
  • Enterococci differ from strep in ability to grow in presence of high salt, bile, and hydrolyze esculin
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3
Q

Characteristics of Staphylococcus

A
  • Non-motile, non-spore forming
  • Facultative anaerobes, grow on non-selective media
  • Have polysaccharide capsule can also made of fibrin (due to coagulase)
  • Techoic acid binds to fibronectin to facilitate adhesion
  • Peptidoglycan has endotoxin effects (not an actual endotoxin)
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4
Q

Characteristics of Streptococcus

A
  • Facultative anaerobes
  • Grow on 5% sheep blood or nutrient broths
  • Secrete toxins
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5
Q

Characteristics of Enterococcus

A
  • Group D lancefield Ag

- Hemolysis patter variable

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6
Q

3 most common disease causing GPC

A
  • Staph Aureus
  • Strep Pyogenes
  • Enterococci (E faecalis, and E faecium)
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7
Q

Staph Aureus

A
  • Found in nose, epithelial and mucosal surfaces
  • Spreads to sterile sites via trauma, person contact, fomites
  • Grows on 5% sheep blood agar, selective media is mannitol salt agar
  • Changes the color of sheep blood from red to gold via hemolysis (Au=gold)
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8
Q

Virulence factors of Staph Aures

A
  • Protein A: binds Fc component of Ig (prevents opsonization)
  • Coagulase: builds insoluble fibrin capsule around bacteria (prevents immune cell access)
  • Hemolysins (cytotoxins): directly toxic to hematopoietic cells
  • Leukocidin: toxin specific to PMNs
  • Catalase: prevents toxic action of PMN-derived hydrogen peroxide
  • Penicillinase (B-lactamase): destroys B-lactam ring of penicillins and renders them inactive
  • Capsule and techoic acid
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9
Q

Penetration of Staph Aureus

A
  • Hyaluronidase: hydrolyzes hyaluronic acid in CT
  • Fibrinolysin: dissolves fibrin clots
  • Lipases: allows survival and spread in fat-containing areas
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10
Q

Secreted toxins of staph aureus

A
  • Exfoliative toxins: causes scalded skin syndrome
  • Enterotoxins
  • Toxic Shock Syndrome Toxins (TSST): super antigen that cross-links MHCII on APCs causing non-specific T cell response
  • Cytotoxins (alpha, beta, delta, gamma): panton valentine leukocidin (PVL, gamma toxin) found in methicillin resistant staph aureus (MRSA). Causes lysis of leukocytes via pore formation, tissue necrosis (acquired virulence factor)
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11
Q

Medical syndromes of staph aureus

A
  • Skin and soft tissue (impetigo, cellulitis, abscess, wounds)
  • Bone and joint infections (osteomyelitis, septic arthritis)
  • Pneumonia (infection of lung, empyema)
  • Bacteremia and endocarditis (infection of blood, infection of heart valves, respectively)
  • Food poisoning (enterotoxin B)
  • Scalded skin syndrome (exfoliative toxin): blisters and peeling of skin
  • TSS: localized growth of staph aureus w/ release of TSST into blood (fever, hypotension, rash, multi-organ failure)
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12
Q

Therapy to staph aureus

A
  • Have resistance to penicillin due to B-lactamase
  • Alteration of PBP (to PBP2) causes MRSA (methicillin resistance), coded by mecA gene
  • B-lactamase resistant penicillins (anti-staph penicillins) are not effective against MRSA, but are against some staph aureus
  • Can use 1st generation cephalosporins
  • Vancomycin very effective (especially against MRSA)
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13
Q

Coagulase-negative staph

A
  • Most common is S Epidermidis
  • Colonizes surface of skin, mucous membranes
  • Can spread during implantation of devices, form person contact
  • Contains capsule
  • Often resistant to B-lactamase penicillins, cephalosporins
  • Sensitive to novobiocin
  • Not very virulent, infect patients w/ indwelling medical devices and immunocompromised
  • S Saprophyticus is 2nd most common cause of UTI (resistant to novobiocin, used bactrim or ciprofloxacin)
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14
Q

Streptococcus Pyogenes

A
  • Group A strep
  • Infects skin and upper respiratory tract
  • Not normal flora but may be carried on mucous
  • Spread by person contact w/ mucous or respiratory droplets
  • Beta hemolysis on blood agar, lancefield A group
  • Different from other beta hemolytic strep by: bacitracin sensitive, and positive PYR test (has nz that forms red product)
  • Tx is penicillin
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15
Q

Virulence factors and toxins of strep pyogenes

A
  • Capsule
  • Lipotechoic acid, F proteins both bind to epithelial cells
  • M proteins (used in epidemiological studies): antiphagocytic protein w/ over 100 serotypes
  • Secretes many toxins: pyogenic (pus-forming) exotoxins, streptolysin S and O, streptokinase, hyaluronidase
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16
Q

Medical syndromes of strep pyogenes

A
  • Skin, soft tissue infections: erysipelas (superficial), cellulitis (deeper), necrotizing fasciitis (deep subcutaneous necrosis w/ high mortality), wounds
  • Streptococcal pharyngitis (strep throat): pain, swelling, fever, white exudate on tonsils. Can be complicated by rheumatic fever, post-streptococcal glomerulonephritis, scarlet fever
  • Pneumonia, bacteremia
  • Puerperal fever (post-partum endomyometritis)
17
Q

Toxin complications of strep pyogenes

A
  • Scarlet fever: pyogenes must be lysogenized by bacteriophage (stimulates to produce pyrogenic exotoxin or erythrogenic toxin). Both toxins are superantigens
  • Is a complication of strep pharyngitis, onset of rash, fever, strawberry tongue. Tx w/ penicillin
  • Streptococcal TSS
18
Q

Non-suppurative (no pus) sequelae

A
  • Acute rheumatic fever (ARF) follows strep throat: cross-rxn of Abs to strep (M1 and M3) w/ Ags in heart
  • Causes acute inflammation of joints, heart, subcutaneous tissue, CNS, chronic damage of heart valved
  • Acute Glomerulonephritis (AGN) follows strep throat or skin infection: acute inflammation of glomeruli due to Ab-Ag (M12, M49) complexes in basement membrane of glomerulus
  • Results in hematuria, proteinuria, hypertension, edema
  • Tx for both is penicillin
19
Q

Streptococcus agalactiae (group B)

A
  • Normal in female genital tract and lower GI, can colonize upper resp tract
  • Mother to infant in utero transmission (10-30% of pregnant women asymptomatic)
  • Looks same as group A strep under microscope and blood agar (both beta hemolysis), use CAMP test (extracellular protein acts synergistically w/ beta-lysin of S aureus to enhance hemolysis, found in GBS but not GAS)
  • Causes UTI in pregnant women; neonatal septicemia, meningitis, penumonia; infections in immunocompromised
  • PCR screening of pregnant women, with vaginal culture
  • Tx is penicillin
20
Q

Viridan streptococci

A
  • Alpha hemolytic (thus green)
  • All resistant to antibio opticin
  • Normal in GI, female genital, transmission is getting access to sterile sites
  • Causes localized infections (abscesses) and systematic infections (endocarditis)
21
Q

Streptococcus Pneumoniae

A
  • Nontypable, usually alpha hemolytic diplococci
  • Identified by quellung rxn: adding anti-capsular Abs to cause swelling of capsule (also: optician sensitive; other viridans are resistant, and bile solubility test; bile lyses colonies)
  • Colonizes nasopharynx, transmitted via respiratory secretions
  • Virulence factors: capsule (what vaccines are directed against), pneumolysin (cholesterol dependent chymolysin (damages both alveolar epithelial and pulmonary endothelial cells, up regulate IL6)
  • Diseases: penumonia, otitis media (ear), sinusitis, meningitis, bacteremia
  • Tx: cephalosporin and vancomycin (resistant to penicillin)
  • Prevention: adult vaccine w/ 23 capsular types, child one w/ 13
22
Q

Enterococci

A
  • Most common are E faecalis, E faecium (group D strep)
  • E faecium more likely to be drug resistant
  • Both normal flora of human GI tract and female genital tract
  • Transmission: access to normally sterile sites, person contact, fomites
  • Most diseases in immunocompromised, healthy people can develop UTI
  • Possible for endocarditis, peritonitis (infection of lining of abdomen due to bowel perforation), bacteremia
  • Tx: inherently resistant to many antibios. Can use ampicillin + gentamicin (aminoglycoside), or vancomycin (effective against any GP)
23
Q

4 key bacteria w/ capsules

A
  • S pneumo
  • H influenzae
  • N meningitidis
  • Pseudomonas Aeruginosa
  • Klebsiella pneumoniae
  • All encapsulated bacteria have resistance to phagocytosis
  • Removing spleen (asplenia) increases risk of infection to encapsulated bacteria

FMS 3 (20 decks)

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