Streptococcus Lec 1 & 2 & Bacterial Structure

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Characteristics of streptococcus
Morphology
Gram Stain
Oxygen

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pairs/chains of cocci
Gram +
Facultative anaerobes

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Examples of alpha hemolysis

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viridans streptococci
Streptococcus pneumoniae

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Examples of b hemolysis

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Groups A, B, C and G streptococci
Streptococcus iniae

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Examples of gamma hemolysis

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Streptococcus gallolyticus
Enterococcus (sexually promiscuous)

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Optochin disk diffusion test

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to test for alpha hemolytic streptococci; S. pneumoniae is susceptible

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Bile salt solubility test

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to test for alpha hemolytic streptococci
S. pneumoniae is lysed by bile salts

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Bacitracin test

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tests for Beta hemolytic streptococci;
Only S. pyogenes is susceptible

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Group D streptococci (S. gallolyticicus) is tested by

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is either alpha or gamma hemolytic; ability to grow in presence of 40% bile, ability to hydrolyze esculin/optochin
very sensitive to penicillin

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Enterococci resistant to

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penicillin

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Streptococcus pyogenes

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Group A, Beta hemolytic streptococci; antigenic, antiphagocytic capsule, 60 dif M proteins, C carbohydrate, peptidoglycan; extracellular products

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Peptidoglycan

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made up of carbohydrate strands cross linked by oligopeptide;
functions as a phage receptor
endotoxin like activity

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extracellular products produced by s. pyogenes

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pyrogenic exotoxins A-J aka erythrogenic toxins AKA SPEA, SPEB, SPEC;
Streptococcal superantigen
streptococcal mitogenic Z

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toxic strep syndrome caused by

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superantigens - pyrogenic exotoxins; causes hypotension, multiple organ impairment

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Scarlet fever rash

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pyrogenic exotoxins A-J produced S. pyogenes

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Pyrogenic exotoxin B

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cysteine protease that degrades ECM proteins like fibronectin and vitronectin ; facilitates spread of infection

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Streptolysin O

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oxygen labile hemolysin neutralized by cholesterol in the skin

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Antistreptolysin O titers (ASO)

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used diagnostically for rheumatic fever

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streptokinase
used by what bacteria?
treats what?

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activates plasminogen to disrupt blood clots, produced by Group C streptococci , treats coronary occlusion

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DNAse

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antigenic; anti DNAse B titers used diagnostically and are more useful than ASO titers bc they are not neutralized by cholesterol during skin infections

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examples of acute suppurative diseases

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pharyngitis/tonsillitis; pyoderma (impetigo); cellulitis

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Erysipelas

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form of cellulitis; diffuse lymphangitis of skin

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examples of toxin associated diseases

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scarlet fever ; toxic strep syndrome "flesh eating bacteria"

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post streptococcal sequelae

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acute rheumatic fever (autoimmune disorder that usually follows strep throat); acute glomerulonephritis (immune complex deposition); caused by dif M types; guttate psoriasis

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Treatment of group A streptococcal infections

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penicillin and cephalosporin
alternatives to penicillin: macrolies (erythromycin, azithromycin, clarithromycin)

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Example of Group B streptococci & patient/victim population

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Streptococcus agalactiae, resistant to bacitracin

Occurs in neonates, postpartum women, and older individuals with other illnesses

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Early onset neonatal infections

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occur within 7 days of birth, presents with bacteremia, pneumonia, meningitis

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Group B streptococci - less common illnesses are....

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endocarditis, meningitis, osteomyelitis, peritonitis, pericarditis, endophthalmitis

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Effect of penicillin on Group B streptococci

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inhibits growth but does not kill it.

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Example of Group D. streptococcus

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S. gallolyticus which causes bacteremia, endocarditis, lesions of GI tract --> COLON CANCER!

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Enterococcus

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E. faecalis (80-90%), E. faecium (5-10%); occur in hospitalized patients; resistance to many antimicrobial agents, must combine gentamicin or streptomycin with these agents to achieve synergy

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Examples of Group C organisms

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S. dysgalactiae, S. zooepidemicus, S. equi

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Examples of Group G

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S. canis & S. anginosis; normal flora of pharynx, skin, intestinal tract, vagina
infection includes abscesses, purpural sepsis, pleuropulmonary, skin and soft tissue infections, endocarditis, bone and joint infections, bacteremia

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Examples of viridans

And what they cause....

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S. mitis
S. sanguis.
S. salivarius
S. mutans;

Responsible for dental caries and infective endocarditis

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Microaerophilic streptococci

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S. angionosus group AKA "milleri" group that includes
S. morbillorum
S. constellatus
S. intermedius ; normal constituents of bowel, pyogenic (pus-filled) foci, brain abscesses, hepatic abscesses, empyema, unusual cause of endocarditis

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Streptococcus iniae

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fish pathogen , causes subcutaneous abscesses; causes cellulitis within 12-24 hours

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Anaerobic streptococci

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Peptococcus, Peptostreptococcus
normal constituents of flora of GI and female GU tract; diabetic foot ulcers are more common in Peptococcus

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Properties of Gram + bacteria

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thick peptidoglycan, teichoic acid, lipoteichoic acid; cell wall has pentaglycine bridge to allow extensive cross linking in 3 d

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Properties of Gram - bacteria

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y thin peptidoglycan (PGN)

outer membrane (OM), made of lipopolysaccharide (LPS),

can only cross link directly;
can survive in our gut bc they are protected from bile acids

Periplasmic space - space that contains peptidoglycan layer, degradative enzymes (amylases, nucleases) and detoxifying enzymes (beta lactamase)

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Beta lactam antibiotics block

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peptidoglycan formation

ex. penicillin, cephalosporins

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Gram neg bacteria that cannot survive in gut

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Haemophilus, neisseria ; bc they have LOS instead of LPS

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Lipopolysaccharide componenets

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saturated lipid A fatty acids whose tight packing decrease membrane permeability; endotoxin

Core polysaccharide (KDO),

O antigen - hydrophilic polysaccharide chain, basis of serological differences ; protects against phagocytosis

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features of cytoplasmic membrane

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site of metabolic pathways
sensing the environment, nutrient transport, efflux (multidrug efflux and macromolecules)

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Examples of obligate anaerobes (1), obligate aerobes (2), and facultative anaerobes (3)

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1) clostridium perfringens, prevotella, bacteroides, fusobacterium
2)Mycobacterium tuberculosis
3) E. coli

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genus characterized by sporulation

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Clostridium, bacillus anthracis

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Catalase present in....

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staphylococcus is catalase +
Streptococcus is catalase -

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Toxin production for SPEA and SPEC depends

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infection of the bacteria by a phage

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pyrogenic exotoxins A-J aka erythrogenic toxins aka

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stroptococcal superantigen, streptococcal mitogenic exotoxin Z

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Streptolysin S

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extracellular product of streptococci, oxygen stable; causes surface hemolysis on blood agar plates

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exSuperantigen

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bind directly with Class II MHC molecules, binds only to the Vbeta variable elements of the TCR

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Scarlet fever caused by:
clinical presentation:

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caused s. pyogenes
strawberry tongue, sandpaper rash

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Pyoderma (impetigo)

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superficial skin infection due s. pyogenes and s. aureus,
think fomites

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cellulitis

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diffuse inflammation of both skin and subcutaneous tissues with red and tissue edema

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Lymphangitis clinical manifestation

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lymph node tenderness
soft tissue - streak that comes up their leg, groin hurts

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Causes of cellulitis/erysipelas

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coronary artery bypass (saphenous vein), axillary lymph node dissection, women with lymphedema

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Toxic shock syndrome and clinical signs

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From s. pyogenes; hypotension,renal impairment, coagulopathy, liver involvement, acute respiratory distress syndrome, erythematous rash, soft tissue necrosis etc....know that it is multiple organ involvement

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Jones criteria for diagnosing acute rheumatic fever; major manifestations; most common feature

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subcutaneous nodules, polyarthritis, erythema, carditis, chorea
most common feature: arthritis

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post streptococcal glomerulonephritis manifestations

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edema, hematuria, hypertension, decreased complement levels, abnormal urinary sediment, chronic renal disease

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guttate psoriasis

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increased frequency of Vbeta2 and involves streptococcal pyrogenic exotoxin C; keratinocyte proliferation

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Enterococci resistant to

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aminoglycoside, alters penicillin binding proteins, becta lactam resistance, produces beta lactamase (resistance to penicillin and ampicillin), resistant to vancomycin