2011 07 microbiology skin diseases1

8/6/2019 2011 07 Microbiology Skin Diseases1

1/8

1

STAPHYLOCCOCUS

Gram (+) cocci in grape like cluster Facultative anaerobe Some are capsulated Non-motile Non-sporeforming

CLASSIFICATION OF STAPHYLOCOCCUS

1. S. aureus 4 biotypes (A-D)

o Biotype A mostcommonly found in

humans

Involved :a.) in superficial (local)

infection

b.)deep (systemic)diseases

c.) toxigenic diseases2. S. epidermidis

Nosocomial bacteremia Endocarditis associated with

valvular prosthesis

Intravenous catheter infection Peritonitis in patients

undergoing COPD

Ventricular shunt infections

Antigenic Structures of Staphyloccocus

Capsule Slime layer Protein A Peptidoglycan-techoic acid complex

Virulence Factors of Staphylococcus

Capsuleo Produced by some S. aureus

strains

o antiphagocytic Slime layer

o Produced by S. epidermidiso Involved in adherence,

persistence on foreign body

Protein Ao Surface protein; covalently

bound to peptidoglycan

o Regularly present in humanstrains of S. aureus; not found

in coagulase (-) staph

o Binds non-specifically with Fcportion of IgG

Prevents Fc-mediatedopsonization

Induces complementactivation

Used in antigendetection (co-

agglutination)

Polysaccharide A (ribitol techoic acid)o Peptidoglycan-techoic acid

complex

A. Peptidoglycan Provides rigid exoskeleton Has interpeptide bridge

connecting oligoglycine peptides

S. aureus L-lysine-glycine 5-6

S. epidermidis L-lysine-glycine 3-5 L-serine

Subject: MicrobiologyTopic: Bacteria Associated w/ skin Infections 1Lecturer: Dr. Eleanor PadlaDate of Lecture: July 5, 2011Transcriptionists: Blue Bolt, Aquamarine,

BrokenEditor: Blue BlinkPages: 8

SY

2011-2012


2/8

2

S. saprophyticus LLysine-glycine 5-6 L-

serine

B. Techoic Acid Water soluble polymers of ribitol

glycerol P04

o Ribitol techoic acid(polysaccharide A)

Cell wall techoicacid

Found in S. aureus Antiphagocytic

o Glycerol techoic acid Cell membranes

techoic acid

Found in S.epidermidis andsaprophyticus

Extracellular enzymeso Hyaluronidase

Hydrolyzes hyaluronicacid in connective

tissues

o Lipase Splits fats and oils

o Staphylokinase (fibrinolysin) Dissolves fibrin clots

o Coagulase (free) Lays down fibrin barrier

during abscess

formation

Toxinso Leucocidin

Consists of 2 proteincomponents (F=fast; S =

slow)

Destroyspolymorphonuclear

leucocytes

o Hemolytic toxins

4 major types (alpha,beta, gamma, epsilon)

Damage red cellmembrane

Produce hemolyticzones on BAP

Alpha toxinso Forms

transmembrane

pores

o Has lethal,dermonecrotic and

leucocidal activities

o Formed by majorityof human strains of

S. aureus

o Not formed bycoagulase (-) staph

o Exfoliative toxins Proteins Produces intraepidermal

splitting of tissues and

necrosis seen in SSS;blisters in bullous

impetigo

Associated with S. aureusphage group II


3/8

3

2 types ETA

Gene on

Chromosome

ETBGene on plasmid

Heat-

labile;stable in

EDTA

o Pyrogenic exotoxins Family of secreted

proteins

Act as superantigens1. Entorotoxins

a. Seven antigenictypes (A, B, C1,

C2, D, E F)

b. Enterotoxin Aand D food

posining

c. Enterotoxin B necrotizing

enterocolitis

2. Toxic Shock SyndromeToxin-1 (TSST-1)

a. Synonymouswith Enterotoxin

F

PATHOGENICITY

A. Habitat S. aureus

i. Anterior nares, skin,nasopharynx, perineum

S. epidermidisi. Skin, mucous

membrane, anterior

nares

S. saprophyticusi. Mucosa of GUT, skin

B. Transmission S. aureusi. Spread to normally

sterile sites by

traumatic

ii. Person-to-personspread (e.g. in

nosocomial setting)

S. epidermidisi. Spread to normally

sterile sites as a result

of implantation of

medical devices

ii. Person-to-personspread (e.g in

nosocomial setting)

C. Diseases caused byS. aureus

1. Superficial (local) infection

Impetigoo Honey colored scabs (on

arms, legs, face)

o 90% is caused by S. aureus,10% by GAS

o Bullous is caused staph whilenon bullous can be caused by

staph or strep

o More common in schoolchildren; occur in warm, humid

environments (coz u see

bacteria likes warm, most

areas)

o Highly contagious; spread bydirect contact with lesions or

with nasal carriers

Folliculitiso Follicular-based pustule (in

areas of irritation)

o Can occur through shaving,scratching, or with an injury to

the skin

o Most commonly superficial(affecting upper part of hair

follicle; or deep (affecting the

whole hair follicle)


4/8

4

FURUNCLES (boils)o Starts as hard, tender red

nodule surrounding a hair

follicle -> abscess -> pus

discharged from center ->

resolve

o Arise in hair- bearing areaswhere there is friction,

occlusion, perspiration

o Lesions may be isolated , ormultiple

CARBUNCLESo Start as smooth, dome-

shaped, acutely tender,

painful lesion -> develop

into swollen, painful area

discharging pus from

several sites (individual

boils clustered together)

o Often occur at the nape ofthe neck, the back or thighs

o Deeper, more severe,develop and heal more

slowly

2. Deep (Systemic) Diseases

Acute osteomyelitis Acute endocartitis Pneumonia

3. Toxigenic Diseases Staphylococcal scaled skin

syndrome

Staphylococcal foodpoisoning

Toxic shock syndromeSTAPHYLOCOCCAL SCALDED SKIN

SYNDROME (SSSS / RITTERS DISEASE)

Stripping of superficiallayers of the skin from the

underlying tissue

Mostly frequently involvesinfants and children < 5

years

Majority caused by S.aureus phage group II

(mostly commonly, type

71)

LABORATORY DIAGNOSIS

1. GRAM STAIN Gram (+) cocci in

clusters

0.5- 1.5 micrometer Gram-variable within

neutrophils, in

resolving lesions, in the

presence of antibiotics;

in old cultures

2. CULTURE Grows well on unenriched

media

Grows in 7.5% - 10% NaCl;in 40% bile

Media : BAP, selectivemedia (MSA, PEA)

Figure 1. Media: Mannitol

Salt Agar

Figure 2. Colonies on blood Agar Plate


5/8

5

Form smooth, raisedcolonies; mucoid if

capsulate

Colonial pigment variableo s. aureus golden

yellow to white

o s. saprophyticuswhite to pale grey

o s. epidermis white

Hemolytic reactionvariable

o S. aureus- usuallybeta-hemolytic

o S. epidermis and s.saprophyticus

usually non-hemolytic

3. DIFFERENTIAL TESTSA. Catalase Test

Staphylococci (+) Streptococci (-)

B. Coagulase Test Slide Test (bound

coagulase / clumping

factor)

Produced exclusively byS. aureus forming free

coagulase

Tube Test (freecoagulase)

Clotting of citratedplasma in the presence of

coagulase reacting factor(CFR)

For suspected S. aureusthat fail to produce

bound coagulase

4. Susceptibility

Aids in choice ofsystemic drugs

Epidemiologic tool5. Serology (antigen detection)Phage Typing

For epidemiologic tracing ofinfection

Depends on differingsusceptibilities to lysis by

phages

Control and Prevention:

Suppurative Infections:o Cleanliness, hygiene,

and meticulous

handwashing

o Aseptic management oflesions

o Isolation of personswith open lesions

o Suppression/cure ofnasal carriage

STREPTOCOCCI

General Properties:

Gram (+) cocci in chains Facultative anaerobe Some are encapsulated Some are flagellated Non-sporeforming

Classification:

A. Hemolytic Patterns Alpha hemolytic

Incomplete hemolysis

Greening reaction

Beta hemolyticComplete hemolysis

Enhanced by AnO2 conditions

Gamma hemolyticNo hemolysis

B. Lancefield System Based on group-specific CHO antigen

(C-CHO)


6/8

6

Amino sugar determines serologicspecificity

GAS = rhamnose-N-acetylglucosamine

GBS = rhamnose-glucosamine GDS = glycerol teichoic acid

Streptococci groups: A-H, K-V Human pathogens belong to Grps

A to G

Group A

- possess Lancefield group Bantigen

- synonymous with S. pyogenesGroup B

- possess Lancefield group Bantigen

- Synonymous with S. agalactiaeGroup D

- possess Lancefield group Dantigen

- includes Enterococcus spp.Viridans streptococci

- lacks group-specific cell wallantigen

- referred to as oralstreptococci

Streptococcus pneumonia

- lacks group-specific cell wallantigen

- referred to as pneumococcus-

Figure 3. Lancefield Test

C. Biochemical Reactions For untypable species Used to speciateviridans streptococci

Figure 4. Biochemical reaction

Clinical Diseases

Group A streptococci (GAS)

Pharyngitis (sore throat/tonsillitis) Impetigo (pyoderma) Erysipelas Cellulitis Necrotizing fascilitis Scarlet fever Puerperal fever (childbed fever) TSSL (toxic shock syndrome-like) Acute bacterial endocarditis

Non-suppurativeSequelae

acute rheumatic fever acute glomerulonephritis

Group B Streptococci (GBS)

bacteremia, pneumonia, meningitis innewborns

Group D Streptococci (GDS)

bacteremia, endocarditis, nosocomialinfections

Viridans Streptococci

dental plaque/carries subacute bacterial endocarditisStreptococcus Pneumoniae

lobar pneumonia meningitis otitis media

GROUP A STREPTOCOCCI

Group Characteristics:

possess the Lancefield group Aantigen

rhamnose-N-acetylglucosamine synonymous with S. pyogenes

Antigenic Structures:

capsule pili protein antigens (M,F,G,T proteins) C5a peptidase Group-specific polysaccharides (C-

CHO)


7/8

7

Virulence Factors:

1. Capsule- composed of hyaluronic acid- not immunogenic- antiphagocytic

2. Lipoteichoic acid- component of pili- together with M protein,

mediates oral/pharyngeal, skin

epithelial attachment

3. M protein- major virulence factor of GAS- component of pili- anti-phagocytic (prevents

alternative

Cpathwayopsonization)

- dominant in binding toepidermis

- strongly immunogenic- >80 antigenic types

4. F protein- fibronectin-binding protein- together with M protein,

mediates nasopharyngeal

adherence

5. G protein- Fc receptor (prevents Fc-

mediated opsonization)

6. C5a peptidase- surface-bound endopeptidase- anti-polymorphonuclear

leucocyte chemoattractant

(cleaves C5a)

7. Serum opacity factor- an alpha-lipoproteinase- produce opalescence in horse

serum broth

- adjunct to M typing8. Pyrogenic exotoxins

- protein in nature- 4 antigenic types (A-D)EXOTOXIN A

Associated with rash inscaret fever; TSS-L

A superantigen Produced only by

lysogenized strains

Basis ofDick/ Schultz-Charlton tests

EXOTOXIN B

Responsible for tissuedestruction in necrotizing

fascilitis

9. Hemolysins- responsible for beta-hemolysis

on BAP

- cytotoxic- 2 distinct types of hemolysins

a. Streptolysin O- oxygen-labile- hemolytic in reduced form;

responsible for subsurface

hemolysis

- formstransmembrane pores- strongly immunogenic

b.

Streptolysin S- serum soluble, oxygen-stable- responsible for surface

hemolysis

- non-immunogenic10.Spreading factors

Hyaluronidase- splits hyaluronic acids in

connective tissue

Streptokinase(fibrinolysin)

- dissolves fibrin clots DNAse (streptodornase)

- depolymerizes viscous DNA inpus

- strongly immunogenicPathogenicity

A. Habitat Inhabits URT, skin of

humans

B. Transmission Persons to person by direct

contact with mucosa or

secretions

Fomites

C. Clinical Diseases Pharyngitis Impetigo (pyoderma)

- non-bullous Erypselas (St. Anthonys

fire)


8/8

- peripherally spreading, hot,bright-red, edematous, well-

circumscribed, sharply

marginated lesions

- most often affects the face, legs;spreads thru the lymphatic

vessels

- common in infants, children,the elderly

- accompanied by severeconstitutional symptoms

Cellulitis Necrotizing fascilitis Scarlet fever Acute bacterial endocarditis Puerperal fever TSSL (toxic shock

syndrome-like)

Necrotizing fasciitis (flesh- eating

bacteria; streptococcal gangrene)

toxin-mediated, highlydestructive and potentially

lethal infection of soft tissued

(fatty tissues, fascia, muscles)

always follows traumaScarlet fever (scarlatina)

Scarlet-colored (boiled-lobster)body rashes (sandpaper-like);

fever; strawberry-like

appearance of tongue

Exotoxin mediated Evolves from tonsillar /

pharyngeal focus

Laboratory Diagnosis:

1. Gram stain

2. Culture Media BAP chocolate agar selective media (CAN, PEA) greyish white, transparent to

translucent matt or glossy

beta hemolytic

3. Identification4.Antigen Detection

Based on monoclonalantibodies which

react with C-CHO

(e.g. latexagglutination, co-

agglutination, ELISA)

5. Serology

Anti DNAse BDetermination

To demonstrateprevious or recent

streptococcal infection

Significant response inpatients with

pyoderma

Prevention and Control:

Early detection andantimicrobial therapy

DOC: penicillin treating carriers

End of transcription

Do not be anxious about anything, but in every

situation, by prayer and petition, with thanksgiving,

present your requests to God. And the peace of God,

which transcends all understanding, will guard yourhearts and your minds in Christ Jesus. - Philippians 4:6-7

To God be the glory!

2011 07 microbiology skin diseases1

Documents