microorganisms of the skin and mucous membranes

8/7/2019 Microorganisms of the Skin and Mucous Membranes

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MICROORGANISMS OF THE SKIN AND MUCOUS

MEMBRANES

Microbial flora of the skin and mucous membranes :

1. Resident flora, usually commensal microorganisms

2. Pathogenic microorganisms


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Role of the resident flora

Role of resident flora of the skin and mucous membranes:

To prevent colonization by pathogens and possible disease through

bacterial interference.

The mechanisms of bacterial interference :

1. competition for receptors or binding site on host cells

2. competition for nutrients

3. mutual inhibition by metabolic or toxic products4. mutual inhibition by antibiotic materials or bacteriocins


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Suppression of the normal flora creates a partial local void that tend

to be filled by microorganisms from the environment or from other

part of the body.

Such organisms behaves as opportunists and may be becomepathogen


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Members of the normal flora may themselves produce disease

under certain circumstances

These organisms are adapted to the noninvasive mode of life

defined by the limitations of the environment

If forcefully remove the restrictions of that environment andintroduced into the blood stream or tissues, these organisms may

become pathogenic

Large numbers of Streptococcus viridans (normal flora of the upper

respiratory tract ) introduced into the bloodstream (following tooth

extraction or tonsillectomy), they may settle on deformed heart valveand produce infective endocarditis


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Normal flora of the skin

The skin is particularly apt to contain transient microorganisms,

because of its constant exposure to and contact with the

environment

There is a constant and well-defined resident flora, modified in

different anatomic area by secretions, proximity to mucousmembranes (mouth, nose, perineal areas) , and habitual wearing of

clothing

The factors that may be important in eliminating nonresident

microorganism from the skin are the low pH, the fatty acid in

sebaceous secretions, and the presence of lyzozyme


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Anaerobic and aerobic bacteria often to join to form synergistic

infections ( gangrene, necrotizing fasciitis, cellulitis) of skin and soft

tissues

The bacteria are frequently part of the normal microbial flora

It is usually difficult to pinpoint one specific organisms as beingresponsible for the progressive lesion, since mixtures of organisms

are usually involved


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Staphylococcus epidermidis

Staphylococcus aureus ( in small numbers )

Alpha-hemolytic and nonhemolytic Streptococcus

Micrococcus species

Peptostreptococcus species

Neisseriae species ( nonpathogenic )

Propionibacterium species

Diphtheroids

Candida species ( small numbers ) Acinetobacter species ( small numbers )


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Genus Staphylococcus

Cells spherical, 0,5 1,5 um in diameter, occuring singly, in pair andirregular cluster

Gram positive, nonmotile, nonsporing

Facultative anaerobic, chemoorganotrophic,with both respiratory andfermentative metabolism

Colonies are usually opaque and may be white or cream andsometimes yellow to orange

Usually catalase positive, cytochromes present but usually oxidasenegative

Nitrate often reduce to nitrite, susceptible to lysis by lysostaphin butnot by lyzozyme

Usually grow with 10 % NaCl, the optimum temperature is 300-370C Mainly associated with the skin and mucous membranes of warm-

blooded vertebrates, but are often isolated from food products, dustand water

Some species produce extracellular toxin


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Tabel 1. Laboratory test for differentiation of

Staphylococcal sp.

Test S. aureus S.epidermidis S.saprophyticus

MSA :

-Growth-Fermentation

++

+-

+-

Coagulase + - -

DNase + - -

Hemolysis beta - -Novobiocin

test

S S R

Pigmentation Golden

yellow

white white


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Genus Streptococcus

Cells spherical or ovoid, 0,5 2,0 um in diameter, occurring in pairs

or chains when grown in liquid media; they sometimes elongated in

the axis to a lanceolate shape

Gram positive, nonmotile, nonsporing, some sp are encapsulated

Facultatively anaerobic, chemoorganotrophs, requiring nutrutionallyrich media for growth and sometime 5 % CO2

Metabolism fermentative, producing mainly lactate bu no gas

Catalase negative, commonly attack red blood cells, with either

greenish discolorization ( alpha hemolysis ) or complete clearing

(beta hemolysis ), growth is usually restricted to a temperature of250 450 C (optimum 370C )

Mainly inhabiting the mouth and upper repiratory tract


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Genus Micrococcus

Cells spherical, 0,5 2,0 um in diameter, occurring in pairs, tetrads

or irregular cluster, not in chains

Gram positive, seldom motile, nonsporing

Strictly aerobic; collonies usually pigmented in shades of yellow or

red, usually grow on simple media

Chemoorganotrophs, with a respiratory metabolism, often producing

little or no acid from carbohydrates, catalase positive and often

oxidase positive, usually halotolerant, grow with 5% NaCl

Contain cytochromes and are resistant to lysostaphin

The optimum temperature is 250 370 C, occur primarily onmammalian skin and in soil but commonly are isolated from food

products and the air


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Genus Peptostreptococcus

Cells spherical, 0,5 1,2 um in diameter, and sometimes ovoid;

arrangement is variable; in pair, tetrads, clumps, or chains.

Gram positive, nonmotile, nonsporing

Anaerobic, chemoorganotrophic and fermentative, requiring

nutritionally rich media, metabolize peptone to mainly acetic acid;their attack on carbohydrates is usually weak or absent

Usually catalase negative, but weak or pseudocatalase reactions

may occur; some members produce indole and reduce nitrate

The optimum temperature is 370 C

The genus is differentiated from Peptococcus mainly by its lowermol % G+C content of the DNA ( 27 45 )

Obligate parasites of the mouth, mucous membranes, and intestinal

tract of mammals, and may play a part in purulent infections


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Genus Neisseria

Cocci are 0,6 1,0 um in diameter, occurring singly but more often in

pairs with adjacent sides flattened; one species (N. elongata) is an

exception and consists of short rods 0,5 um wide, often arranged as

diplobacilli or in short chains

Division of the coccal species is in two planes at right angle to eachother, sometimes resulting in tetrads

Capsules and fimbriae (pili) may be present; endospore are not

present

Cells stain gram negative, but there is tendency to resist

decolorization Swimming motility does not occur, and flagella are absent

Aerobic; some species produce a greenish yellow carotenoid

pigment


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Genus Neisseria

Some species are nutritionally fastidious and hemolytic, optimum

temperature is 350 370 C

Oxidase positive, catalase positive, except N. elongata; carbonic

anhydrase is produced by all species; all species reduce nitrite

except N. gonorrhoeae and N. canis. Chemoorganotrophic, some species are saccharolytic

They are inhabitants of the mucous membranes of mammals

Some species are primary pathogens for humans


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Genus Propionibacterium

Pleomorphic rods, 0,5-0,8x1-5 um, are often club shaped with oneend rounded and the other tapered; some cells may be coccoid, bifidor branched, but they are not filamentous; cells occur singly, in pairsor short chains, in V or Y configurations, or in clumps with chinesecharacter arrangement

Gram positive, non motile, nonsporing

Facultative anaerobs but have variable aerotolerance; most growsomewhat in air but better anaerobically, giving on blood agarcolonies that are usually convex, semi opaque, glistening, and oftenpigmented in shades of cream to reddish

Chemoorganotrophic with complex nutritional requirement, have ametabolism fermentative, producing from glucose and some othercarbohydrates large amounts of propionic acid , acetic acid andoften small amounts of gas


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Genus Propionibacterium

The optimum growth temperature is 300 370 C

Usually catalase positive; they are found mainly in cheese and dairy

products and on human skin

Readily confused with some species of Corynebacterium or

Clostridium


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Genus Corynebacterium

Straight or slightly curved, slender rods have tapered or sometimesclubbed ends and are 0,3-0,8 x 1,5-8,8 um

Cells are usually arranged singly or in pairs, often in a V formation orin palisade of several parallel cells

G

ram positive, though some cells stain unevenly, giving beadedappearance; metachromatic granules of polymethaphosphate arecommonly formed within the cells

Nonmotile, nonsporing,not acid-fast

Facultative anaerobs, commonly requiring nutritionally rich mediasuch serum or blood media, on which colonies are usually convex

and semi opaque, with a mat surface Chemoorganotrophs with fermentative metabolism, most species

produce acid without gas from glucose and some othercarbohydrates


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Genus Corynebacterium

Catalase positive, often reduce nitrate and tellurite; rarely acidify

lactose or raffinose or liquefy gelatin

Primarily obligate parasites of mucous membranes of skin of

mammals; but occasionally they are found in other sources; some

species are pathogenic for mammals


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Normal flora of the mucous membranes

Normal flora of the :

Conjunctiva

Mouth and upper respiratory tract

Intestinal tract

Urethra

Vagina


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Normal flora of the conjuctiva

The predominant organisms of the conjunctiva are :

Diphtherids

Staphylococcus epidermidis

Streptococcus (nonhemolyticus)

Neisseriae

Moraxella sp

The conjunctival flora is normally held in check by the flow of tears;which contain antibacterial lyzozyme


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Normal flora of the mouth and upper respiratory tract

The flora of the nose consist of :

- corynebacteria

- Staphylococcus epidermidis- Staphylococcus aureus

- streptococci


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The mucous membranes of the mouth and pharynx are often sterile

at birth but may be contaminated by passage through birth canal

Within 4 12 hours after birth, viridans streptococci become

established as the most prominent members of the resident flora

and remain so for life. They probably originate in the respiratorytracts of the mother and attendants.

Early in life, aerobic and anaerobic staphylococci, gram negative

diplococci ( Neisseriae, Moraxella catarrhalis ), diphtheroids, and

occasional lactobacilli are added


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When teeth begin to erupt, the anaerobic spirochetes, Prevotella sp

(especially P. melaninogenica ), Fusobacterium sp, Rothia sp, and

Capnocytophaga sp established themselves, along with some

anaerobic vibrios and lactobacilli

Actinomyces sp are normally present in tonsillar tissue and on thegingivae in adults, and various protozoa may also present. Yeast

(Candida sp) occur in the mouth

In the pharynx and trachea, a similar flora established itself,

whereas few bacteria are found in normal bronchi. Small bronchi

and alveoli are normally sterile


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The predominant organisms in the upper respiratory tract,

particularly in the pharynx :

Nonhemolytic streptococcus

Alpha hemolytic streptococcus

Neisseriae

Staphylococci

Diphtheroid

Haeomophili

Pneumococci

Mycoplasma

Prevotella


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Infections of the mouth and respiratory tract are usually caused by

mixed oronasal flora, including anaerobs

Periodontal infections, perioral abscess, sinusitis and mastoiditis

may involved predominantly Prevotella melaninogenica,

Fusobacteria and Peptostreptococci Aspiration of saliva (containing up to 102 of these organisms and

aerobs) may results in necrotizing pneumonia, lung abscess and

empyema


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Normal flora of the intestinal tract

At birth the intestine is sterile, but organisms are soon introduced

with food. In breast-fed children, the intestine contain large numbers

of lactic acid streptococci and lactobacilli. These aerobic and

anaerobic, gram positive, nonmotile organisms (e.g. Bifidobacterium

species) produced acid from carbohydrates and tolerate pH 5.0 In bottle-fed children, a more mixed flora exist in the bowel, and

lactobacilli are less prominent. As food habits develop toward the

adult pattern, the bowel flora changes

Diet has a marked influence on the relative composition of the

intestinal fecal flora

Bowels of newborns in intensive care nurseries tend to be colonized

by Enterobacteriaceae, e.g. Klebsiella, Citrobacter, Enterobacter


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In normal adults, the esophagus contains microorganisms arriving

with saliva and food.

The stomachs acidity keep the number of microorganisms at

minimum (103 105 /gr content ) unless obstruction at the pylorus

favors the proliferation of gram positive cocci and bacilli. The normalacid pH of the stomach markedly protects against infection with

some enteric pathogens, e.g. cholera

Administration of cimetidine for peptic ulcer leads to great increase

in microbial flora of the stomach, including many organisms usually

prevalent in feces


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As the pH of intestinal content become alkaline, the resident flora

gradually increases. In the adult duodenum, there are 103 -106

bacteria per gram of content; in the jejunum and ileum, 105-108

bacteria/gr; and in the cecum and transverse colon, 108-1010

bacteria/gr In the upper intestine, lactobacilli and enterococci predominate, but

in the lower ileum and cecum, the flora is fecal

In the sigmoid colon and rectum, there are about 1011 bacteria/gr of

content, constituting 10 30% of the fecal mass


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Anaerobs outnumber facultative organisms by 1000-fold. In diarrhea

the bacterial content may diminish greatly, whereas in intestinal

stasis the count rises

In the normal adult colon, 96 99% of the resident bacterial flora

consists of anaerobs : Bacteroides sp, especially B. fragilis

Fusobacterium sp

Anaerobic lactobacilli, e.g. bifidobacteria

Clostridia ( C.perfringens, 103 -105/gr)

Anaerobic gram positive cocci (Peptostreptococcus sp)


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Only 1 4% are facultative aerobs :

Gram negative coliform bacteria

Enterococci

Small number of protei, pseudomonads, lactobacilli, candidae

More than 100 distinct types of organisms, which can be cultured

routinely in the laboratory, occur regularly in the normal fecal flora

There probably are more than 500 sp of bacteria in the colon

including many that are likely unidentified. Minor trauma(e.g.

sigmoidoscopy, barium enema) may induce transient bacteremia in

about 10% of procedures


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Intestinal bacteria are important in :

Synthesis of vitamin K

Conversion of bile pigments and bile acids

Absorption of nutrients and breakdown products

Antagonism to microbial pathogens

The intestinal flora produces ammonia and other breakdown

products that are absorbed and can contribute to hepatic coma

Among aerobic coliform bacteria, only few serotypes persist in the

colon for prolonged periods, and most serotypes of Escherichia coli

are present only over period of a few days


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Antimicrobial drugs taken orally can, in human, temporarily suppress

the drug susceptible component of the fecal flora

This is commonly done by preoperative oral administration of

insoluble drug. For example, neomycin plus erythromycin can in 1

2 days suppress part of the bowel flora, especially aerobs Metronidazole accomplishes that for anaerob. If lower bowel surgery

is performed when the counts are at their lowest, some protection

against infection by accidental spill can be achieved

However, soon thereafter the counts of fecal flora rise again to

normal or higher than normal levels, principally of organismsselected out because to relative resistance to the drug employed


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The drug susceptible microorganisms are replace by drug resistant

ones, particularly staphylococci, enterobacters, enterococci,

protei,pseudomonads, Clostridium difficile and yeast

The feeding of large quantities of Lactobacillus acidophilus may

results in the temporary establishment of this organisms in the gutand the concomitant partial suppression of other gut microflora

The anaerobic flora of the colon, including B. fragilis, clostridia and

peptostreptococci , play a main role in abscess formation originating

in perforation of the bowel.

Prevotella bivia, P. disiens are important in the abscesses of thepelvis originating in the female genital organ

These sp are penicillin-resistant


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Normal flora of the vagina

Soon after birth, aerobic lactobacilli appear in the vagina and persist

as long as the pH remains acids (several weeks)

When pH become neutral (remaining so until puberty), a mixed flora

of cocci and bacilli is present

At puberty, aerobic and anaerobic lactobacilli reappear in largenumbers and contribute to the maintenance of acid pH through the

production of acid from carbohydrates, particularly glycogen

This appears to be an important mechanisms in preventing the

establishment of other, possibly harmful microorganism in the

vagina


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If lactobacilli are suppressed by the administration of antimicrobial

drugs, yeast or various bacteria increase in numbers and cause

irritation and inflammation

After menopause, lactobacilli again diminish in number and mixed

flora returns. The normal vaginal flora includes group B streptococciin as many as 25% of women of childbearing age.

During the birth process, a baby can acquire group B streptococci,

which subsequently may cause neonatal sepsis and meningitis

The normal vaginal vaginal flora often includes also alpha hemolytic

streptococci, anaerobic streptococci( peptostreptococci), Prevotellasp , clostridia, Gardnerella vaginalis, Ureaplasma urealyticum, and

sometimes listeria or Mobiluncus sp


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The cervical mucus has antibacterial activity and contain lyzozyme.

In some women, the vaginal introitus contain a heavy flora

resembling that the perineum and perianal area

This may be a predisposing factor in recurrent urinary tract

infections Vaginal organisms present at time of delivery may infect the

newborn (e.g. group B streptococci )


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Skin and soft tissue infections:

Staphylococcus aureus

Attributes of pathogenicity of S. aureus :

Coagulase enhance fibrin deposition and abscess formation. There

is also clumping factor that coats the cells with fibrin

Cytolytic toxin (alpha, beta, gamma, delta and leukocidin ) are all

hemolytic (except leukosidin) and destroy cellular membranes TSST-1 formerly termed enterotoxin F, is a superantigen and toxin

produced under certain environmental conditions, most commonly

associated with tampon use and surgical packing.

TSST-1 reduces liver clearance of endogenous endotoxin

Exfoliatins produced by phage group II S. aureus cause surfacelayer of the skin to separate (probably through disruption of

intracellular junctions) leading to desquamation


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Attributes pathogenicity of S. aureus

Protein A ( a surface protein ) is anti phagocytic (binding to the Fc

portion of antibody, making it unavailable to attach to phagocytes

Teichoic acids aids in attachment and stimulate the inflamatory

response when complexed with peptidoglycan


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Clinical disease

Skin infections include impetigo (often bullous), folliculitis of the

bearded region, boils (furuncles), carbuncles (more extensive),

styes, and surgical wound, burn, or traumatic-lession infections

Scalded skin syndrome, with its characteristic bullae and

desquamation of body surfaces, occur most commonly in childrenyounger than 5 years old, sometimes with fairly minor infections but

circulating exfoliatins


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Skin and soft tissue infections :

Clostridium perfringens

General characteristic of Cl. perfringens :

Anaerobic, spore-forming, large gram positive rod

Spore can be central or subterminal and relatively heat resistant

Has soil as natural habitat; contamination can occur in home-canned

goods, smoked fish, and honey Has germination of spores and emergence of vegetative cells as

being necessary for toxin production


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Attributes of pathogenicity of Cl. perfringens

Produced alpha toxin, a potent lecithinase that damage cellular

membranes

Produce 11 other toxins or enzymes that damage eukaryotic cells

Produces an enterotoxin associated with food poisoning


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Clinical disease

Cl. perfringens cause two types of infections :

Soft tissue wound infections following severe trauma; organisms

elaborate toxins and enzymes to produce gas, edema, and impaired

of circulation; vascular destruction and lactic acid accumulation

lower the redox potential, with two consequences :1. anaerobic cellulitis, causing destruction of traumatized only

2. myonecrosis (gas gangrene) or destruction of traumatized tissue

and surrounding healthy tissue


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Pseudomonas aeruginosa

General characteristic of P. aeruginosa :

A small, polarly flagellated, gram negative rod with pili

A non fermentative, oxidase positive bacterium

A ubiquitous environmental organism found in water and soil and

widely distributed on plants It can grow in both distilled water or tap water overnight to large

number

Often produces pigments that may be clinically useful, such as

fluorescein ( pyoverdin ) , a greenish fluorecent pigment, and

pyocyanin, a blue-green pigment Blue-green pus is a classic sign of P. aeruginosa infection


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Attributes pathogenicity of P. aeruginosa

Invasive factor includes :

Pili, which adhere

A polysaccharide slime layer, which increases adherence totissue,making them less susceptible to phagocytosis

Virulence factor includes : Exotoxin A, an ADP ribose transferase similar to diphtheria toxin,which inactivates the tRNA elongation factor (EF 2), halt proteinsynthesis, and causes liver necrosis

Exoenzyme S , an ADP ribose transferase capable of inhibitingeukaryotic protein synthesis

Lipopolysaccharide Phospolipase C, which damages membranes causing tissue

damage

Elastase and other proteolytic enzyme


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Clinical disease

Cellulitis :

Occur in patient with burns, wound, or neutropenia; may be highly

necrotic; indicated by blue-green pus and grape-like sweet odor

Septicemia :

Results from hematogenous spread of infection from local lesion orgastrointestinal tract and causes gram negative shock

May result in a distinctive lesion, ecthyma gangrenosum, when

dermal veins and tissue are invaded. These lesions become

necrotic


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Most commonly made by clinical suspicion (grape-like odor,blue-

green pus,or ecthyma gangrenosum) and confirm by culture

Shows beta hemolysis on blood agar, with pigment production

Shows nonfermentation on macConkey agar, blue-green pigment,

grape like odor, and oxidase positivity

Diagnosis


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Streptococcus pyogenes

General characteristic of S. pyogenes :

Occur as single,paired, or chained gram positive cocci, depending

on the environment, facultative anaerobe, attaches to epithelial

surface via lipoteichoic acid portion of fimbriae (pili)

Classification : Classified as group A of the 21 Lancefield group of streptococci,

which are distinguished serologically by slight differences in specific

cell wall carbohydrates

Contains group A- specific carbohydrate and several antigenic

protein (M,T and R antigen) in the cell wall Subdivided into more than 80 types base on antigenic differences in

the M protein


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Streptococcus pyogenes

General characteristics of S. pyogenes :

Sensitive to bacitracin, catalase negative, rarely become resistant to

penicillin


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Classification

Classified into hemolytic group of the three types of enzymatic

hemolysis of red blood cells produced by streptococci on blood agar

plate :

Alpha-hemolytic group; is characterized by incomplete lysis, with

green pigment surrounding the colony Beta-hemolytic group, is characterized by total lysis and release of

hemoglobin and clear area around the colony

Gamma-hemolytic group, is characterized by absence of lysis


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Attributes of pathogenicity of S. pyogenes

Possesses M protein, a potent virulence factor found on fimbriae

that interferes with phagocytosis

Has a nonantigenic, antiphagocytic hyaluronic acid capsule that

promote invasiveness

Produce two hemolysin : streptolysin S ( a leukocidal proteinreponsible for beta hemolysis on blood agar plate) and Streptolysin

O (an oxygen sensitive leukosidal protein )

Possesses multiple other enzyme systems (e.g. hyaluronidase,

streptokinase, streptodornase, nicotinamide adenine dinucleotidase)


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Clinical disease

Impetigo :

An easily spread exudative infection of the epidermis occurringprimarily in children; may results in nephritis as complications

Should be treated with penicillin and scratching should be prevented

Cellulitis and erysipelas :

Initiated by infection through a small break in the skin

The term cellulitis applies if the lesion is defined

Erysipelas applies if the lesion spreads, primarily through thelymphaticFasciitis :

A rapidly spreading infection of the fascia; tends to occur in diabeticpatients; needs surgical debridements of necrotic tissue and therapy

with antibiotics

microorganisms of the skin and mucous membranes

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