Bacteria Associated With Skin Infections 1 Flashcards by asdfg hjkl

Some bacteria associated with skin infections

Staphylococcus
Streptococcus
Erysipelothrix
Bacillus
Clostridium
Mycobacterium

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Some general Characteristics of Staphylococcus

Gram positive cocci in grape-like cluster
Facultative anaerobe
Some are capsulated
Non-motile
Non-spore forming

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Classification of Staphylococcus

S. aureus
S. epidermidis
S. saprophyticus

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Biotypes of S. aureus

Biotypes A, B, C, D

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Most commonly found biotype in humans

Biotype A

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S. aureus is involved the pathogenesis of

Superficial (Localized) Infection
Deep (Systemic) Infection
`Toxigenic diseases

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Nosocomial Staphylococcus bacteria found in medical instruments or devices (including catheters, CSF shunts, prosthetic heart valve implants)

S. epidermidis

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S. epidermidis is involved the pathogenesis of

Endocarditis associated with valvular prosthesis
Intravenous catheter infection
Peritonitis in patients undergoing CAPD
Ventricular shunt infections

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S. saprophyticus is involved the pathogenesis of

Urinary tract infection in young sexually active women

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Antigenic structures of Staphylococcus

Capsule
Slime layer
Protein A
Peptidoglycan-teichoic acid complex

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True or False.

Antigenic structures are not always associated with the virulence factors.

True

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Virulence Factor of Staphylococcus

Capsule
Slime layer
Protein A
Polysaccharide A (Ribitol Teiochoic Acid)
Extracellular enzymes
Toxins

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This is a virulence factor that is produced by some S. aureus strains (≥ 8 capsular types identified) and anti- phagocytic

Capsule

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This is a virulence factor that is only produced by S. epidermidis

Slime layer

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This is a virulence factor that is involved in adherence and persistence on foreign body; main factor contributing to biofilm formation

Slime layer

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This is a virulence factor that is a surface protein convalently bound to peptidoglycan

Protein A

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This is a virulence factor that is regularly present in human strains of S. aureus but not found in (coagulase-negative Staphylocccus or CONS)

Protein A

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This is a virulence factor that is binds non-specifically with Fc portion of IgG

Protein A

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When protein A binds to the Fc portion of IgG, it

Prevents Fc-mediated opsonization
Induces complement activation by generating chemotactic factors
Used in antigen detection (co-agglutination test)

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This is the part of Polysaccharide A that provides rigid exoskeleton and has interpeptide bridge connecting oligoglycine peptides

Peptidoglycan

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This is the part of Polysaccharide A that is composed of water soluble polymers of ribitol or glycerol phosphate

Teichoic acid

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An extracellular enzyme that hydrolyzes hyaluronic acid in connective tissues

Hyaluronidase

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Also known as spreading factor

Hyaluronidase

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An extracellular enzyme that enhances invasion and survival in tissues by binding cells together and rendering the intercellular spaces passable to pathogen

Hyaluronidase

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Also known as fat-splitting enzyme

Lipase

An extracellular enzyme that splits fats and oils

Lipase

An extracellular enzyme that is essential for survival of Staphyloccoccus in sebaceous areas of the body and in the formation of furuncles and carbuncles

Lipase

Also known as fibrinolysin

Staphylokinase

An extracellular enzyme that dissolves fibrin clots

Staphylokinase

An extracellular enzyme that lays down fibrin barrier during abscess formation to prevent the spread of organism that is bound in the center of the abscess

Free coagulase

True or False. Hyaluronidase, lipase and staphylokinase are used for the spreas of the organism in the body while coagulase is for the localization of the organism.

True

Type of toxin that is expressed by about 2-4% of S. aureus and is a pore-forming cytotoxin causing leukocyte destruction and tissue necrosis

Leukocidin (e.g. Panton Valentine)

Type of toxin that is phage-encoded

Leukocidin

Two protein components of Leukocidin

LukS-PV (Slow) | LukF-PV (Fast)

Difference of LukS-PV from LukF-PV

Electrophoretic mobility

Type of toxin associated with recurrent skin and soft tissue infections and necrotizing pneumonia

Leukocidin

Four major types of hemolytic toxins

Alpha Beta Gamma Delta

Toxin responsible for causing damage to red cell membrane and produce hemolytic zones on BAP

Hemolytic toxins

Major hemolytic toxin

Alpha

Hemolytic toxin that forms transmembrane pores and has lethal, dermonecrotic, and leucocidal activities

Alpha

Hemolytic toxin formed by majority of human strains of S. aureus but not CONS

Alpha

Hemolytic toxin that lipid binding domain that inserts directly into the lipid bilayer of the cell membrane → pores → cell death

Alpha

Toxin that produces intraepidermal splitting of tissues, blister formation and sssociated with S. aureus phage group II

Exfoliative (epidermolytic) toxins

Exfoliative toxin that recognize, hydrolyze desmosomes in the skin and cleave Desmoglein 1

Serine proteases

Four types of exfoliative toxins

Type A, B C, D

Major types of exfoliative toxins

ETA and ETB

Toxin that is a family of secreted proteins acting as superantigens which stimulate and enhance the lymphocyte response

Pyrogenic exotoxins

Two major types of pyrogenic toxins

Enterotoxins | Toxic Shock Syndrome Toxin-1

Seven antigen types of enterotoxins

A, B, C1, C2, D, E, F

Antigenic types of enterotoxins that cause food poisoning

A and D

Antigenic type of enterotoxins that cause necrotizing enterocolitis

Pyrogenic exotoxin that is synonymous with Enterotoxin F and associated with menstrual infections in women

Toxic Shock Syndrome Toxin-1 (TSST-1)

Superficial (localized) infections caused by S. aureus

Impetigo Folliculitis Furuncles Carbuncles

Deep (systemic) diseases caused by S. aureus

Acute osteomyelitis Acute endocarditis Pneumonia

Toxigenic diseases caused by S. aureus

Staphylococcal Scalded Skin Syndrome (SSSS/ Ritter’s Disease) Staphylococcal food poisoning Toxic Shock Syndrome

True or False. | 90% of impetigo cases are caused by S. aureus while the remaining 10% are caused by Group A Streptococci (GAS).

True

Type types of impetigo

``` Bullous impetigo (exclusively by S. aureus) Non-bullous impetigo (by Staph, Strep or both) ```

More common in children Occur in warm, humid environments Highly contagious Spread by direct contact with lesions or with nasal carriers

Impetigo

Toxin mediated (exfoliative toxin) and accounts for 30% of impetigo cases

Bullous impetigo

Type of impetigo that is characterized by vesicles and bullae, when ruptured leaves ligth brown/yellow crusts with oozingn exudates

Bullous impetigo

True or False. | Bullous impetigo has fewer lesions than non-bullous impetigo.

True

Type of impetigo that represents host response to infection, no toxin is needed to produce clinical manifestations

Non-bullous impetigo

True or False. | Non-bullous impetigo is more contagious than the bullous impetigo.

True

Type of impetigo that accounts for >70% of impetigo cases

Non-bullous impetigo

Formation of the stiking characteristic of non-bullous impetigo

Macule/ papule → vesicles/ pustules → rupture leaving honey- colored crusts which discharge pus when pressured

Superficial infection that can occur through shaving, scratching or with any injury to the skin

Folliculitis

Follicular-based pustule, most commonly superficial or deep

Folliculitis

Most characteristic pustular lesion produced by Staph

Furuncles (boils)

Development of furuncles

Start as hard, tender, red nodule surrounding a hair follicle → abscess → pus discharged from center → resolve

True or False. | Furuncles does not need surgery and no antibiotic treatment.

True

True or False. | No manipulations should be done because it will disrupt the fibrin barrier that will be the start of dissemination.

True

Superficial inflammation that arise in hair-bearing areas where there is friction, occlusion, perspiration and may be isolated or multiple

Furuncles

Development of carbuncles

Start as smooth, dome-shaped, acutely tender, painful lesion → develop into swollen, painful area discharging pus from several sites

Clustered boils but is deeper, more sever, develop and heal more slowly

Carbuncles

Frequent areas where carbuncles are found

Nape of the neck, back or thighs

Reason why carbuncles are more severe than furuncles

It can be disseminated to vital organs like cavernous sinus or the subarachnoid space

Toxigenic disease that is characterized by stripping of superficial layers of the skin from the underlying tissue (involves exfoliative toxin)

SSSS/Ritter’s Disease

Most frequently involved age group

Infants and children <5 yrs

Major cause

S. aureus phage group II (most commonly, type 71)

Laboratory diagnosis of Staphylococcus

``` Gram stain Culture Differential test Susceptibility test Serology Serotyping Phage typing ```

Gram stain findings of Staphylococcus

Gram positive cocci in clusters 0.5 – 1.5 micrometer in diameter Gram variable within neutrophils, in resolving lesions, in the presence of antibiotics, and in old cultures

Type of culture needed by Staphylococcus

Unenriched media | 7.5%-10% NaCl and in 40% bile

True or False. High concentration of NaCl is a selective medium for Staphylococcus allow growth of S. aureus but inhibit growth for other species.

True

Media used for diagnosing Staphylococcus

Blood Agar Plate Mannitol Salt Agar Phenyl Ethyl Alcohol Agar

Type of media that form smooth, raised colonies and mucoid, if encapsulated

BAP

Selective and differential media for S. aureus

MSA

True or False. | S. aureus is mannitol fermenting.

True

True or False. | Pathogenic staphylococci ferment mannitol and produce acid.

True

MSA contains

1% mannitol 7.5% NaCl Phenol Red as pH as indicator

Results of MSA

Yellow: (+) acid producing mannitol fermenter | Pink or red: (-) non-mannitol fermenters

Staphylococcus species that are mannitol fermenters

S. aureus | S. saprophyticus

Two types of differential test used for Staphulococcus

Catalase test | Coagulase test

Test that differentiates staphylococci from streptococci

Catalase test

Reagent used in Catalase test

3% H2O2

Positive catalase test is seen as

Bubble formation/effervescence of gas (Immediate)

Results of catalase test

Streptococcus (-) | Staphylococcus (+)

Test that distinguishes the different species of Staphylococcus

Coagulase

Two types of coagulases secreted by S. aureus

Staphylocoagulase | von Willebrand factor binding protein

Coagulase that activates human prothrombin

Staphylocoagulase

Coagulase that activates human, rabbit, mouse prothrombin

von Willebrand factor binding protein

Coagulase test that detects bound coagulase/clumping factor produced exclusively by S. aureus

Slide test

Results of slide coagulase test

If the Slide test is positive no need to do the tube test; confirmed S. aureus If negative proceed to tube test

Coagulase test that detects free coagulase and causes clotting of citrated plasma in the presence of coagulase reacting factor (CRF)

Tube test

Coagulase test that is for suspected S. aureus that fail to produce bound coagulase

Tube test

True or False. | Coagulase test is specific in detecting Staphylococcus aureus.

True

Test that is used for complete workup culture and sensitivity test after identification

Susceptibility test

Test that aids in choice of systemic drugs and an epidemiologic tool

Susceptibility test

Type of test that shows that antibody detection has no value

Serology

Test that is adjunct or supplementary to phage typing

Serotyping

Test for epidemiologic tracing of infection and depends on differing susceptibilities to lysis by phages, particularly Phage II

Phage typing

Suppurative infections are prevented and controlled by

Cleanliness, hygiene, and meticulous hand washing Aseptic management of lesions Isolation of persons with open lesions Suppression/cure of nasal carriage

General chracteristics of streptococcus

``` Gram positive cocci in chains Evident in broth medium Facultative anaerobe Some are encapsulated Some are flagellated Non- spore forming Capsuled ```

Characterized by a small zone of beta surrounded by alpha hemolysis

Alpha prime hemolysis

This is based on group specific carbohydrate antigen (C-CHO) because amino sugar determines serologic specificity

Lancefield pattern

Components GAS: _____________ GBS: _____________ GDS: _____________

GAS: rhamnose-N-acetylglucosamine GBS: rhamnose-glucosamine GDS: glycerol teichoic acid

Streptococcus groups

A-H, K-V (20 groups)

Groups of Human Streptococcus pathogen

A-G

Human Streptococcus pathogen that is of greater significance

A and B

Nucleotide-based typing scheme

emm classification system

Molecular gold standard for GAS typing for M protein- producing strains

emm classification system

Sequencing of the emm gene that encodes the M protein based on its amino acid sequence variability of the N terminus (5’ end) such as Streptococcus pyogenes

emm classification system

These are used for species which cannot be grouped under the existing ones and to speciate Viridans Streptococci

Biochemical reactions

Antigenic structures of GAS

``` Capsule Pili Protein antigens (M, F, G,T proteins) C5a peptidase Group-specific polysaccharide (C-CHO) ```

Virulence factors for GAS

``` Capsule Lipoteichoic acid M protein F protein G protein C5a peptidase Serum Opacity Factor Pyrogenic (Erythogenic) Exotoxins Hemolysins Spreading Factors ```

Virulence factor composed of hyaluronic acid

Capsule

Virulence factor that is not immunogenic because of its antigenic disguise, and anti-phagocytic

Capsule

Major virulence factor of Streptococcus pneumoniae

Capsule

Virulence factor that is a component of pili and binds with M protein, mediating oral/ pharyngeal and epithelial attachment and subsequent colonization

Lipoteichoic acid

Major virulence factor for GAS

M protein

Virulence factor that is a component of a pili anti- phagocytic and dominantly binds to epidermis

M protein

M protein is anti-phagocytic because

It prevents alternative complement pathway opsonization

True or False. M proteins are strongly immunogenic because specific antibodies are produced against it. Hence, it is difficult to come up with vaccines for M-protein.

True

Virulence factor that is a fibronectin-binding protein

F protein

F protein + M protein

Mediates nasopharyngeal adherence

Surface-bound endopeptidase and cleaves C5a

C5a peptidase

Anti-polymorphonuclear leukocyte chemo-attractant

C5a peptidase

Virulence factor that is an alpha-lipoproteinase and produces opalescence in horse serum broth

Serum Opacity Factor

Adjunct to M typing

Serum Opacity Factor

True or False. | Pyrogenic or Erythrogenic Exotoxins are protein in nature.

True

Four antigenic types of pyrogenic exotoxins

A, B, C, D

Most significant antigenic type of pyrogenic exotoxins

Exotoxin A | Exotoxin B

ETA or ETB. | Associated with rash in scarlet fever and TSSL

ETA

ETA or ETB. | Responsible for tissue destruction in necrotizing fasciitis

ETB

ETA or ETB. | Superantigen - stimulates and enhances a response

ETA

Streptococcal gangrene

ETB

ETA or ETB. | Produced only by lysogenized strains (including bacteriophage)

ETA

Basis of Dick’s tests

Erythrogenic toxin | Presence of erythema or redness of the test site

Basis of Schultz-Charlton test

Anti-erythrogenic toxin Presence of anti-blanching phenomenon Rash fade

Virulence factor responsible for beta-hemolysis on BAP of Streptococcus pyogenes

Hemolysins (Cytotoxic)

2 distinct types of Streptolysin

Streptolysin O | Streptolysin S

``` SO or SS. Oxygen labile (will not produce if not on surface) ```

SO or SS. | Hemolytic in reduced form (to see if there is hemolysis, stab should be performed)

SO or SS. | Oxygen stable

SO or SS. | Responsible for subsurface hemolysis

SO or SS. | Serum soluble

SO or SS. | Forms transmembrane pores

SO or SS. | Strongly immunogenic

SO or SS. | Responsible for surface hemolysis

SO or SS. | Non-immunogenic

SO or SS. | Can be used serologically to titrate

Its titers are determined for the detection of previous or recent streptococcal pharyngeal infection

Anti-streptolysin O (ASO)

Enzymes that act as spreading factors in Streptococcus spp

Hyaluronidase Streptokinase (Fibrinolysin) DNAse (Streptodornase)

Spreading factor that splits hyaluronic acids in connective tissue

Hyaluronidase

Spreading factor that dissolves fibrin clot

Streptokinase (Fibrinolysin)

Spreading factor that depolymerizes viscous DNA in pus and is strongly immunogenic

DNAse (Streptodornase)

True or False. | Streptolysin O is higher following pharyngeal infection while DNAse is higher following skin infection.

True

Most dominant DNAse produced following skin infections

Anti-DNAse B

True or False. | Titers of Anti- DNAse B are determined for the detection of previous or recent streptococcal skin infection

True

True or False. | Anti-streptolysin O should be detected in pharyngeal infection.

True

Habitat of GAS

Inhabits URT and skin of humans

Transmission of GAS

Person to person by direct contact with mucosa or secretions (coughing, sneezing) Fomites

Clinical Disease of S. pyogenes

``` Pharyngitis Impetigo (pyoderma) Erysipelas (St. Anthony’s Fire) Cellulitis Acute Bacterial Endocarditis Puerperal Fever Toxic Shock Syndrome-like Necrotizing fascitis Scarlet fever ```

Most important clinical disease cause by S. pyogenes

Pharyngitis

Associated with type A; non-bullous | Most cases begin with strep infection but staph replaces strep over time

Impetigo (pyoderma)

Associated M types are frequently nephritogenic (may cause acute glomerulonephritis) In pharyngeal infection – rheumatogenic

Impetigo (pyoderma)

Peripherally spreading; hot, bright red, edematous, well circumscribed, sharply marginated lesions

Erysipelas

Erysipelas most commonly affects

Face and legs

Pattern of spread of Erysipelas

Spreads thru the lymphatic vessels

Age group most commonly affected by Erysipelas

Common in infants, children and the elderly; accompanied by severe constitutional symptoms

“flesh-eating bacteria”, “streptococcal gangrene” (requirement for aerobic conditions)

Necrotizing fascitis

Highly destructive and potentially lethal infection of soft tissue (fatty tissues, fascia, muscles) and always follows trauma

Necrotizing fascitis

Toxin the mediates necrotizing fascitis

ETB

Toxin that mediates Scarlet Fever

ETA

Scarlet colored (boiled lobster), body rashes (sandpaper-like), strawberry like tongue which evolves from tonsillar/pharyngeal focus

Scarlet Fever

Laboratory diagnosis used for GAS

``` Gram stain Culture Identification tests Antigenic detection Serology ```

General characteristics of GAS in culture

Greyish white, transparent to translucent matte or glossy

Glossy: ____________ Matte: ____________

Glossy: less M protein produced Matte: more M protein produced

Media used to culture GAS

BAP Chocolate Agar Selective media: CNA, PEA

Tests used to identify GAS

Bacitracin disc test (TAXO A) | Pyroglutamic acid arylamidase test (PYR)

Test used to differentiate S. pyogenes from other beta-hemolytic streptococci

Bacitracin Disc Test

Test that is helpful in screening for group A strep in throat swab

Bacitracin disc test

Results of bacitracin disc test

(+) any zone of inhibition (susceptible): Group A

Diameter of zone of inhibition to be classifies as susceptible

10mm

True or False. | S. pyogenes is the only beta-hemolytic streptococcus that is PYR (+)

True

True or False. | Majority of Group A are PYR (+)

True

Result of PYR test

(+): Bright pink/cherry red color in 1 minute

Laboratory diagnostic that is based on reaction with monoclonal antibodies which reacts with group-specific carbohydrate antigen

Antigenic detection

Laboratory diagnostic test that can be used in typing or detection of the organism in clinical specimens or in cultures (Group A-agglutination if it is Group A)

Antigenic detection

Two types of serology testing for GAS

Anti-streptolysin O | Anti-DNAse B

Serology test that is used to demonstrate previous or recent streptococcal infection, significantly following skin infections

Anti-DNAse B serology

Prevention and control of GAS

Early detection and antimicrobial therapy | Treating carriers

Replacing penicillin with other antibiotics is a risk factor for antibiotic resistance

Selection pressure

Drug of choice for GAS

Penicillin