Dept. Microbiology-PIFM School of Medicine-UAG

Dept. Microbiology-PIFMDept. Microbiology-PIFM

School ofSchool of Medicine-UAG Medicine-UAG

A.- General A.- General CharacteristicsCharacteristics

1.- 1.- Skin is relatively resistant to infection.Skin is relatively resistant to infection.

2.- Microflora inhibits harmful organism.2.- Microflora inhibits harmful organism.

3.- Skin infections occur when protective 3.- Skin infections occur when protective

mechanism fall.mechanism fall.


EntryEntry1) Skin (pores, hair follicles).1) Skin (pores, hair follicles).

2) Wounds (scratches, cuts, burns).2) Wounds (scratches, cuts, burns).

3) Insect & animal bites.3) Insect & animal bites.

EntryEntry1) Skin (pores, hair follicles).1) Skin (pores, hair follicles).

2) Wounds (scratches, cuts, burns).2) Wounds (scratches, cuts, burns).

3) Insect & animal bites.3) Insect & animal bites.


DiseasesDiseases– Localized infections with local and/or Localized infections with local and/or

systemic effect.systemic effect.– Systemic infections.Systemic infections.

MultiplicationMultiplication– Extracellular.Extracellular.– Intracellular (??).Intracellular (??).

DamageDamage– Toxin.Toxin.– Host immune response.Host immune response.

DiseasesDiseases– Localized infections with local and/or Localized infections with local and/or

systemic effect.systemic effect.– Systemic infections.Systemic infections.

MultiplicationMultiplication– Extracellular.Extracellular.– Intracellular (??).Intracellular (??).

DamageDamage– Toxin.Toxin.– Host immune response.Host immune response.


DefenseDefense– DryDry

Usual infection sites are wet areas, skin Usual infection sites are wet areas, skin folds, armpit, groinfolds, armpit, groin

– Acidic (pH 5.0)Acidic (pH 5.0)– Temperature less than 37Temperature less than 37ooCC

Some pathogens grow best <37Some pathogens grow best <37ooCC– Lysozyme and toxic lipids (pore, hair follicles, Lysozyme and toxic lipids (pore, hair follicles,

sweat gland)sweat gland)– Resident microflora (mainly Gram positives)Resident microflora (mainly Gram positives)– Skin-associated lymphoid tissue (SALT)Skin-associated lymphoid tissue (SALT)

DefenseDefense– DryDry

Usual infection sites are wet areas, skin Usual infection sites are wet areas, skin folds, armpit, groinfolds, armpit, groin

– Acidic (pH 5.0)Acidic (pH 5.0)– Temperature less than 37Temperature less than 37ooCC

Some pathogens grow best <37Some pathogens grow best <37ooCC– Lysozyme and toxic lipids (pore, hair follicles, Lysozyme and toxic lipids (pore, hair follicles,

sweat gland)sweat gland)– Resident microflora (mainly Gram positives)Resident microflora (mainly Gram positives)– Skin-associated lymphoid tissue (SALT)Skin-associated lymphoid tissue (SALT)

B.- Skin and Soft Tissue InfectionsB.- Skin and Soft Tissue Infections

1.- Impetigo: Initially a vesicular infection 1.- Impetigo: Initially a vesicular infection

that rapidly evolves into pustules that that rapidly evolves into pustules that

rupture, with the dried discharge formingrupture, with the dried discharge forming

honey-colored crust on an erythematous base.honey-colored crust on an erythematous base.

2.- Ecthyma(Pustules): Begin as vesicles2.- Ecthyma(Pustules): Begin as vesicles

that rupture, creating circular erythematous that rupture, creating circular erythematous

lesions with adherent crusts.lesions with adherent crusts. 3.- Folliculitis: Inflammation at the opening3.- Folliculitis: Inflammation at the opening of the hair follicle that causes erythematousof the hair follicle that causes erythematous papules and pustules surrounding papules and pustules surrounding individual hairs.individual hairs. 4.- Furuncle: Deep-seated inflammatory4.- Furuncle: Deep-seated inflammatory nodule with a pustular center that developsnodule with a pustular center that develops around a hair follicle.around a hair follicle. (painful, localized, abscess).(painful, localized, abscess).

5.- Carbuncle: Involvement of several adjacent5.- Carbuncle: Involvement of several adjacent

follicles, with pus discharging from multiplefollicles, with pus discharging from multiple

follicular orifices.follicular orifices.

6.- Cutaneous abscesses: Painful, fluctuant, red,6.- Cutaneous abscesses: Painful, fluctuant, red,

tender swelling, on which may rest a pustule.tender swelling, on which may rest a pustule.

7.- Erysipelas: Erythema and swelling of the 7.- Erysipelas: Erythema and swelling of the

cutaneous surface, involves the superficial cutaneous surface, involves the superficial

dermis (redness-lymphangitis).dermis (redness-lymphangitis).

8.- Cellulitis: Erythematous, hot, swollen skin 8.- Cellulitis: Erythematous, hot, swollen skin

with irregular edge.with irregular edge.

(affects the deeper dermis and subcutaneous fat.)(affects the deeper dermis and subcutaneous fat.)

9.- Acne: Infection of sebaceous follicles 9.- Acne: Infection of sebaceous follicles

with plugs of keratin blocking the with plugs of keratin blocking the

sebaceous canal, resulting insebaceous canal, resulting in

“ “blackheads”.blackheads”.

10.- 10.- Necrotizing fasciitis: Rapidly spreading cellulitisNecrotizing fasciitis: Rapidly spreading cellulitis

with necrosis (skin and deeper fascia; may with necrosis (skin and deeper fascia; may

involve muscle).involve muscle).

Begin with fever, systemic toxicity, severe painBegin with fever, systemic toxicity, severe pain

in the development of a painful, red swelling thatin the development of a painful, red swelling that

rapidly progress to necrosis of the subcutaneousrapidly progress to necrosis of the subcutaneous

tissue and overlying skin.tissue and overlying skin.

Dept. Microbiology-PIFMDept. Microbiology-PIFM

School of Medicine-UAGSchool of Medicine-UAG

Family MicrococcaceaeFamily Micrococcaceae

Genera: Genera: MicrococcusMicrococcus

PlanococcusPlanococcus

StomatococcusStomatococcus

StaphylococcusStaphylococcus

SaprophyteSaprophyte

Family MicrococcaceaeFamily Micrococcaceae

Genera: Genera: StaphylococcusStaphylococcus

TheThe name name staphylococcus is derivedstaphylococcus is derived

from the Greek term sthapylé meaning from the Greek term sthapylé meaning

“ “ a bunch of grapes”.a bunch of grapes”.

Family MicrococcaceaeFamily Micrococcaceae Genera: Genera: StaphylococcusStaphylococcus May occur singly, in pairs, or clusters,May occur singly, in pairs, or clusters,this arrangement is due to tendency ofthis arrangement is due to tendency ofthe organism to divide in different the organism to divide in different planesplanes..

Clinically important species of Clinically important species of staphylococcistaphylococci

1.- 1.- Staphylococcus aureusStaphylococcus aureus

2.- 2.- Staphylococcus epidermidisStaphylococcus epidermidis

3.- 3.- Staphylococcus saprophyticusStaphylococcus saprophyticus


1.- 1.- Staphylococcus aureus Staphylococcus aureus (Coagulase +)(Coagulase +)

2.- 2.- Staphylococcus epidermidisStaphylococcus epidermidis

3.- 3.- Staphylococcus saprophyticusStaphylococcus saprophyticus


S. Aureus S. Aureus classically has a golden or classically has a golden or

yellow pigmentation, but many clinical yellow pigmentation, but many clinical

isolates have a creamy or white isolates have a creamy or white pigmentation.pigmentation.

Morphology and PhysiologyMorphology and Physiology

1.- Gram positive cocci, usually arranged in1.- Gram positive cocci, usually arranged in

clusters.clusters.

2.- Non-motile, non-sporeforming.2.- Non-motile, non-sporeforming.

3.- Grow over a wide temperature range 3.- Grow over a wide temperature range

(10-42° C), optimum of 37° C(10-42° C), optimum of 37° C

4.- Aerobic and facultatively anaerobic.4.- Aerobic and facultatively anaerobic.

5.- Grow on simple media5.- Grow on simple media

6.- Catalase positive.6.- Catalase positive.


Gram positive cocci which may lose the ability Gram positive cocci which may lose the ability to retain their gram positive staining to retain their gram positive staining characteristics with age.characteristics with age.

CapsuleCapsule: a loose – fitting, polysaccharide : a loose – fitting, polysaccharide layer ( layer ( slime layerslime layer) is only ocasionally found ) is only ocasionally found on staphylococci cultured in vitro.on staphylococci cultured in vitro.

Eleven capsularEleven capsular serotypes have been serotypes have been indentified in indentified in S. aureus, S. aureus, with serotypes 5 and with serotypes 5 and 7 associated with the mayority of infections.7 associated with the mayority of infections.

Half of the cell wall by weight is Half of the cell wall by weight is peptidoglycan, peptidoglycan, a feature common to G+.a feature common to G+.


The peptidoglycanThe peptidoglycan consists of layers of consists of layers of glycan chains built with 10 to 12 alternting glycan chains built with 10 to 12 alternting subunits N- acetylmuramic acid and subunits N- acetylmuramic acid and

N- acetylglucosamine.N- acetylglucosamine.

The peptidoglycanThe peptidoglycan has endotoxin – like has endotoxin – like activity, stimulating the production of activity, stimulating the production of endogenous pyrogens, activation of endogenous pyrogens, activation of complement and the production of IL- 1 from complement and the production of IL- 1 from monocytes. monocytes.


Teichoic AcidsTeichoic Acids are species – specific, ribitol are species – specific, ribitol teichoic acid with N- acetylglucosamine teichoic acid with N- acetylglucosamine residues (polysaccharide A) is present in residues (polysaccharide A) is present in

S. aureus.S. aureus.

Glycerol teichoic acid with glucosyl residues Glycerol teichoic acid with glucosyl residues

(polysaccharide B) is present in (polysaccharide B) is present in S. epidermidisS. epidermidis..

The outer surfaceThe outer surface of most strains of of most strains of S. aureusS. aureus

contains contains clumping factorclumping factor ( bound coagulase) ( bound coagulase)

Characteristics of Characteristics of StaphylococcusStaphylococcusaureusaureus

1.- Colonial morphology: Colonies are grey1.- Colonial morphology: Colonies are grey to golden yellow and produces hemolysinsto golden yellow and produces hemolysins (beta hemolysis on Blood Agar).(beta hemolysis on Blood Agar). 2.- Enzymes: 2.- Enzymes: a) Coagulase, which acts on plasma toa) Coagulase, which acts on plasma to form a clot.form a clot. b) Deoxyribonuclease (DNAase)b) Deoxyribonuclease (DNAase) 3.- Protein A, cell-wall antigen3.- Protein A, cell-wall antigen 4.- Halophilic (tolerate high concentrations of salt) 4.- Halophilic (tolerate high concentrations of salt) and ferments mannitoland ferments mannitol

EpidemiologyEpidemiology 1.- 1.- Reservoir: Nasal carriage (30-50% of healthyReservoir: Nasal carriage (30-50% of healthy

adults), fecal carriage (20%), skin carriage inadults), fecal carriage (20%), skin carriage in

5-20% of healthy individuals.5-20% of healthy individuals.

2.- Transmission:2.- Transmission:

a) Via droplets (sneezing) and skin scales a) Via droplets (sneezing) and skin scales

(hands)(hands)

b) Direct contamination of surgical woundsb) Direct contamination of surgical wounds

c) Contaminated foods: Ham, canned meats,c) Contaminated foods: Ham, canned meats,

custard pastries, and potato saladcustard pastries, and potato salad..

EpidemiologyEpidemiology

Major Major defenses against defenses against S. aureusS. aureus C3bC3b

– Activated by Staph cell wall fragments.Activated by Staph cell wall fragments.– Opsonizes the bacteria.Opsonizes the bacteria.– Enhances phagocytosis.Enhances phagocytosis.

1) Chemotaxis1) Chemotaxis – attracts neutrophils. – attracts neutrophils. 2)Neutrophils2)Neutrophils – engulf the bacteria. – engulf the bacteria.

3) Intracellular killing by O3) Intracellular killing by O22 radicals. radicals.

EpidemiologyEpidemiologyConditions predispose to Staph infectionsConditions predispose to Staph infections 1) C3 hypercatabolism1) C3 hypercatabolism

2) Chemotherapy–induced neutropenia2) Chemotherapy–induced neutropenia

3) Cyclic neutropenia3) Cyclic neutropenia

4) Chronic granulomatous disease (reduced4) Chronic granulomatous disease (reduced

HH22OO22 production) production)

5) “Lazy leukocyte” (chemotaxis deficiency)5) “Lazy leukocyte” (chemotaxis deficiency)

3.- 3.- Predisposing Factors:Predisposing Factors:

a) Skin trauma: Break or surgery, surgical.a) Skin trauma: Break or surgery, surgical.

packing foreign bodies; e.g. Tampons.packing foreign bodies; e.g. Tampons.

b) Neutropenia: < 500/b) Neutropenia: < 500/μL Cystic fibrosis.μL Cystic fibrosis.

c) IV drug abuse.c) IV drug abuse.

d) Chronic granulomatous disease.d) Chronic granulomatous disease.

E.- Virulence Factors:E.- Virulence Factors:

1) Coagulase: convert fibrinogen to a 1) Coagulase: convert fibrinogen to a

fibrin deposition which interferes withfibrin deposition which interferes with

phagocytosis and increases the invasion of phagocytosis and increases the invasion of

tissue.tissue.

2) Hemolysins and Leucocidin: cytolytic exotoxin2) Hemolysins and Leucocidin: cytolytic exotoxin

a) a) α-Toxin: lyses erythrocytes and damageα-Toxin: lyses erythrocytes and damage

platelets (pore-forming toxin inplatelets (pore-forming toxin in

cell membrane)cell membrane)

b) β-Toxin: degrades sphingomyelin and isb) β-Toxin: degrades sphingomyelin and is

toxic for erythrocytes.toxic for erythrocytes.

c) Leucocidin: lyses WBC.c) Leucocidin: lyses WBC.

3) Protein A: inhibit phagocytosis, binds Fc of3) Protein A: inhibit phagocytosis, binds Fc of

IgG (prevent Complement activation).IgG (prevent Complement activation).

4) Exfoliatins: causes desquamation of the4) Exfoliatins: causes desquamation of the

skin skin (Scalded skin syndrome), formation (Scalded skin syndrome), formation

of bullae.of bullae.

5) Toxic shock syndrome toxin(TSST-1): 5) Toxic shock syndrome toxin(TSST-1):

desquamation of skin, shock.desquamation of skin, shock.

Superantigen: activates large numbers of Superantigen: activates large numbers of

CD4 T cells with induction of cytokinesCD4 T cells with induction of cytokines

production.production.

6) Staphylokinase: fibrinolysis6) Staphylokinase: fibrinolysis

7) Hyaluronidase: dissolves hyaline7) Hyaluronidase: dissolves hyaline

8) Lipase: solubilize lipids8) Lipase: solubilize lipids

9) EnteroToxins: A-E, soluble, heat stable 9) EnteroToxins: A-E, soluble, heat stable

at 60-80 °C for 10min; resistant GI enzymes,at 60-80 °C for 10min; resistant GI enzymes,

acts 2-6 h, vomiting.acts 2-6 h, vomiting.

F.- Clinical Manifestations:F.- Clinical Manifestations:

1)1) Folliculitis, Furuncles, Carbuncles, Folliculitis, Furuncles, Carbuncles,

Abscess.Abscess.

Mechanism: Coagulase, cytolitic exotoxins.Mechanism: Coagulase, cytolitic exotoxins.

Suppuration (pus production) is a hallmark of theseInfections.

2) Impetigo: Erythematous papules to bullae.2) Impetigo: Erythematous papules to bullae.

Mechanism: Coagulase, exfoliatinsMechanism: Coagulase, exfoliatins

3) Staphylococcal Scalded Skin 3) Staphylococcal Scalded Skin

Syndrome(SSSS)Syndrome(SSSS)

Mechanism: ExfoliatinsMechanism: Exfoliatins

*Ritter’s disease: Infants, bullous exfoliative*Ritter’s disease: Infants, bullous exfoliative

dermatitis. From localized perioral erythemadermatitis. From localized perioral erythema

to entire body (2 days).to entire body (2 days).

*Bullous impetigo. *Bullous impetigo.

Negative Nikolsky’s sign. Erythema limited toNegative Nikolsky’s sign. Erythema limited to

localized blisters (contains bacteria).localized blisters (contains bacteria).

4) Staphylococcal Food Poisoning: 4) Staphylococcal Food Poisoning:

Mechanism: Preformed Enterotoxin A-EMechanism: Preformed Enterotoxin A-E

Onset is abrupt and rapid (4 h). Severe vomiting,Onset is abrupt and rapid (4 h). Severe vomiting,

diarrhea, and abdominal pain or nausea.diarrhea, and abdominal pain or nausea.

Sweating and headache may occur, but not fever.Sweating and headache may occur, but not fever.

Watery, non-bloody diarrhea.Watery, non-bloody diarrhea.

5) Toxic Shock Syndrome: Mechanism: TSST-15) Toxic Shock Syndrome: Mechanism: TSST-1

Localized growth of toxigenic strains in vaginaLocalized growth of toxigenic strains in vagina

or wound. Start abruptly, fever, hypotension, or wound. Start abruptly, fever, hypotension,

and diffuse macular erythematous rash. Multipleand diffuse macular erythematous rash. Multiple

organs and systems are involved, entire body skinorgans and systems are involved, entire body skin

desquamates.desquamates.

6) Bacteremia and Endocarditis:6) Bacteremia and Endocarditis:

Mechanism: Cytolytic toxins, Fibrin-platele mesh.Mechanism: Cytolytic toxins, Fibrin-platele mesh.

Nosocomial use of contaminated intravascularNosocomial use of contaminated intravascular

catheter or IV drug abusers.catheter or IV drug abusers.

Nonspecific influenza-like symptoms, disruptionNonspecific influenza-like symptoms, disruption

of cardiac output and septic embolization.of cardiac output and septic embolization.

7) Pneumonia and Empyema:7) Pneumonia and Empyema:

Mechanism: Cytotoxins and enzymesMechanism: Cytotoxins and enzymes

Aspiration or hematogenous pneumonia: Aspiration or hematogenous pneumonia:

Patchy infiltrates with consolidation or abscesses.Patchy infiltrates with consolidation or abscesses.

8) Osteomyelitis and Septic Arthritis:8) Osteomyelitis and Septic Arthritis:

Hematogenous dissemination or secondaryHematogenous dissemination or secondary

infection from trauma.infection from trauma.

In adults: Vertebral. Intense back pain with In adults: Vertebral. Intense back pain with

Fever. Brodie’s abscess.Fever. Brodie’s abscess.

In children: Metaphyseal area of long bones.In children: Metaphyseal area of long bones.

Localized pain, fever.Localized pain, fever.

Septic arthritis: Young children and adultsSeptic arthritis: Young children and adults

who are receiving intraarticular injections orwho are receiving intraarticular injections or

have abnormal joints. Painful, erythematoushave abnormal joints. Painful, erythematous

joints, purulent exudates(shoulder, knee, hip).joints, purulent exudates(shoulder, knee, hip).

Laboratory diagnosisLaboratory diagnosis 1.- 1.- Clinical specimen: Scrapes the base of Clinical specimen: Scrapes the base of

the abscess with a swabs.the abscess with a swabs. Gram stain: Gram (+) cocci in clustersGram stain: Gram (+) cocci in clusters 2.- Culture: Blood Agar, Mannitol Salt Agar2.- Culture: Blood Agar, Mannitol Salt Agar Identification: Coagulase (+), heat-stableIdentification: Coagulase (+), heat-stable nuclease (+), and mannitol fermentationnuclease (+), and mannitol fermentation On blood agar On blood agar S. aureusS. aureus produces beta hemolysis. produces beta hemolysis. Other Staph. species produce alpha or gamma Other Staph. species produce alpha or gamma hemolysis.hemolysis.

Laboratory diagnosisLaboratory diagnosis

2.- Mannitol salts agar (MSA) – high 2.- Mannitol salts agar (MSA) – high salt(7.5) inhibits the grow most ohtrer salt(7.5) inhibits the grow most ohtrer organisms, organisms, S. aureus S. aureus ferments mannitolferments mannitol,,

the acid produce turns the colonies the acid produce turns the colonies yellow and yellow and S. epidermidis does not. S. epidermidis does not.


2.- Coagulase (+).2.- Coagulase (+).

2.- Catalasa (+).2.- Catalasa (+).


2.- Novobiocin2.- Novobiocin

S. epidermidisS. epidermidis is sensitiveis sensitive S. sprophyticus S. sprophyticus is resistantis resistant

2.- Bacitracina (+).2.- Bacitracina (+).

S. Epidermidis S. Epidermidis

1.- Endocarditis.1.- Endocarditis.

2.- Catheter and shunt infections.2.- Catheter and shunt infections.

3.- Prosthetic Joint Infections.3.- Prosthetic Joint Infections.

S. EpidermidisS. Epidermidis

Urinary Tract Infections.Urinary Tract Infections.

TREATMENT:TREATMENT: 1.- Methicillin (Nafcillin), Mupirocin to reduce1.- Methicillin (Nafcillin), Mupirocin to reduce nasal colonization.nasal colonization. 2.- Vancomycin and Fusidic acid.2.- Vancomycin and Fusidic acid.

Streptococcus pyogenesStreptococcus pyogenes

Streptococcal toxic shock-like syndrome.Streptococcal toxic shock-like syndrome. (STSS) (STSS)– Skin or wound infection develop into blood stream Skin or wound infection develop into blood stream

infection, produce Spe which cause fever, rash and infection, produce Spe which cause fever, rash and shock (death rate 30%)shock (death rate 30%)

Scarlet feverScarlet fever– Toxin released from “strep throat” or impetigoToxin released from “strep throat” or impetigo

Streptococcus pyogenesStreptococcus pyogenes

ImpetigoImpetigo - epidermis - epidermis ErysipelasErysipelas - dermal lymphatics - dermal lymphatics CellulitisCellulitis - subcutaneous fat layer - subcutaneous fat layer Necrotizing fasciitis (flesh-eatingNecrotizing fasciitis (flesh-eating bacterium)bacterium)

– Pyogenic exotoxin (Spe) – super AgPyogenic exotoxin (Spe) – super Ag– Dnase A-DDnase A-D

Dept. Microbiology-PIFM School of Medicine-UAG

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