Microbiology: Gram Positive Cocci Flashcards Preview

FMS 3 > Microbiology: Gram Positive Cocci > Flashcards

Flashcards in Microbiology: Gram Positive Cocci Deck (23):
1

GP Cocci (GPC)

-Staphylococcus
-Streptococcus
-Enterococcus
-Appear as dark purple clusters (strep as chains)

2

Lab tests to differentiate GPC

-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

3

Characteristics of Staphylococcus

-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)

4

Characteristics of Streptococcus

-Facultative anaerobes
-Grow on 5% sheep blood or nutrient broths
-Secrete toxins

5

Characteristics of Enterococcus

-Group D lancefield Ag
-Hemolysis patter variable

6

3 most common disease causing GPC

-Staph Aureus
-Strep Pyogenes
-Enterococci (E faecalis, and E faecium)

7

Staph Aureus

-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)

8

Virulence factors of Staph Aures

-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

9

Penetration of Staph Aureus

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

10

Secreted toxins of staph aureus

-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)

11

Medical syndromes of staph aureus

-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)

12

Therapy to staph aureus

-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)

13

Coagulase-negative staph

-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)

14

Streptococcus Pyogenes

-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

15

Virulence factors and toxins of strep pyogenes

-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

16

Medical syndromes of strep pyogenes

-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

Toxin complications of strep pyogenes

-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

Non-suppurative (no pus) sequelae

-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

Streptococcus agalactiae (group B)

-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

Viridan streptococci

-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

Streptococcus Pneumoniae

-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

Enterococci

-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

4 key bacteria w/ capsules

-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