Microbial Diseases of the Skin Chapter 21

Know the general structure of the skin Normal microbiota of the skinSome major microbial diseases (Bacteria, Viral & fungal)Differentiate staphylococci from streptococci, and name skin infections caused by themKnow some arthropods infestation of the skinObjectives

Fig. 21.1SkinOccupies ~1.9m2 & .05 to 3 mm thicknessTwo major layersEpidermisDermisChemical defensesSalt inhibits microbesLysozyme hydrolyzes peptidoglycanFatty acids inhibit some pathogensDefensins are antimicrobial peptidesStructure and Function of the Skin

Mucous MembranesLine body cavitiesGastrointestinal, respiratory, urinary, and genital tractsOften folded to maximize surface area, ~400 m2Epithelial cells attached to extracellular matrixCells secrete mucusAcidicMay contain lysozyme (tears)Some cells have ciliaCiliary escalator

Normal Microbiota of the SkinGram-positive, salt-tolerant bacteria, group into small clumpsMicrococciM. luteusM. roseusStaphylococciS. epidermidisS. aureusDiphtheroids (pleomorphic rods)Corynebacterium xerosis (aerobic)Propionibacterium acnes (anaerobic)Opportunistic pathogens

Bacterial Diseases of the SkinCause by two major genera StaphylococcusStreptococcusThese bacteria are well adapted to skin physiological environmentThey also produce invasive enzymes and toxins

Staphylococcal Skin InfectionsBroadly divided into two groups, coagulase (-) and coagulase (+) (coagulates fibrin) S. epidermidis: coagulase(-). Describe organism: ______Very common on skin (90%)Opportunistic infection (broken skin or catheter)Produce biofilmS. aureus: coagulase (+) +ve). Describe organism: ______Most pathogenic of staphylococciProblem in hospitals (MRSA)Produce leukocidin - an exfoliative toxinProduces toxins that kills phagocytesResistant to opsonization, Produces superantigen

S. aureus skin infectionsFolliculitis: Infections of the hair follicles (often called pimples)Sty: Folliculitis of an eyelashFuruncle (boil)- localized More serious hair follicle infection A type of abscess (pus surrounded by inflamed tissue).Carbuncle: more extensive damage Inflammation of tissue under the skinUsually accompanied by feverImpetigo: Infectious skin lesions with crusted centers Mostly affects children (2 to 5 yrs)Highly contagiousSometimes both S. aureus and Streptococcus pyogenes are involved

Staphylococcal Scalded Skin Syndrome (SSSS) In babies (problem in nurseries) Due to exfoliative toxinToxins cause a separation of skin layersToxic Shock Syndrome (TSS)Life threateningToxin (with superantigenic properties) enter the bloodstreamCharacterized by high fever, low blood pressure, malaise and confusion, can progress to coma and multi-organ failureTreatment for Staphylococcus infections? Vancomycin, last line of antibiotic defense (polypeptide antibiotic)Figure 21.4S. aureus Skin Infections

Streptococcal Skin InfectionsStreptococci cause a wide range of diseasesMeningitis, pneumonia, sore throats, endocarditis, puerperal fever, otitis, etc.Not a normal flora of the skinProduce hemolysins (a and b)b-hemolytic are often associated with disease and have A to T serological groupsS. pyogenesDescribe the bacteria: ____Group A b-hemolytic streptococci (GAS)Produce several virulent factors:Capsule of hyaluronic acid (poorly immunogenic)M proteins (prevents activation of complement, evade phagocytosis and assist adhesion on mucous membranes); >80 serotypes based on M proteinStreptokinases (dissolve blood clots)Deoxyribonucleases (degrade DNA)Streptolysins (lyse RBC and toxic to neutrophils)

Figs. 11.19 & 21.5Learn TheseVirulentFactors!

Streptococcal Skin InfectionsErysipelasReddish patches with raised margins (more superficial-not very deep)ImpetigoIn older childrenSometime occurs together with S. aureusTreatment for streptococcal infections? (b-lactam-type antibiotics, e.g. cephalosporin )Necrotizing fasciitis (flesh eating disease)

Produces an extra toxinExotoxin A, acting as a superantigen, causing the immune system to contribute to the damageStreptococcal toxic shock syndrome that leads to bacteremiaTreatment (broad spectrum antibiotics and surgery)Figs. 21.7, 21.8

Infections by PseudomonadsPseudomonads The most important is P. aeruginosaDescribe the organisms:Produces pyocyanin, blue-green pus as bacterial pigmentPseudomonas aeruginosaOpportunistic infectionMajor problem in cystic fibrosis patients (accumulation of thick and sticky mucus)Deep burn patients Adhesin for colonizationExotoxins (proteases and hemolysins) for tissue damage, bloodstream invasion and disseminationBiofilms, against complement, phagocytosis, and antibioticsEndotoxinRelative resistance to antibioticsPseudomonas dermatitisSelf limiting rash associated with swimming pools, saunas, and hot tubsOtitis externa (swimmers ears)Treatment: Quinolones and antipseudomonal b-lactam antibiotics

AcneNames:Pimples, spots, zits, or acne.Most common skin disease in humansComedonal acne (blackhead)- mildSebum channels are blocked by shed cellsInflammatory acne- moderateCaused by Propionibacterium acnesCharacteristics of organism: Gm (+) rods, aerotolerant anaerobesBreakdown sebum inflammatory reactionNodular cystic acne- severeForm nodules or cysts (inflamed pus filled lesions in skin)Leave scars on face and upper body (psychological scars?)http://en.wikipedia.org/wiki/Acne_vulgaris

Mild Acne Topical applications: salicylic acid and vitamin A derivative (tretinoin, tazarotene)Moderate and Severe AcneAccutane (Isotretinoin)reduces sebum formationHowever, it is teratogenic (not for pregnant women) Antibiotics to target P. acnes; ErythromycinBenzoyl peroxideEffective against P. acnes Also loosen clogged folliclesVisible (blue or red) light (kills P. acnes)

Infection in the GymJason, a 21-yr-old college football player, goes to a health center with a redness on his right leg. It was swollen, warm & tender when touched. His temp was normal and is given sulfamethoxazole-trimethoprimAfter 2 days, he returned. Examination revealed a broader area of redness and was diagnosed as cellulitisThe pus was sent to a lab for Gram stain & coagulase test Antibiotics sensitivity testing was done with penicillin, methicillin, erythromycin, vancomycin & trimethoprim-sulfamethoxazoleTreatment: vancomycin

Viral Skin InfectionsWarts Caused by papillomavirusesCharacteristics of virus: dsDNA, nonenvelopedSpread by direct contact (see genital warts later)TreatmentPhysical removal: extreme cold, dry or burn themChemical Salicylic acid, Imiquimod (stimulates interferon production)Interferon

Smallpox Figure 21.9During the Middle Ages, ~80% of the population of Europe contracted this diseaseCaused by an orthopoxvirusTwo basic forms: variola major (> 20% mortality and variola minor (< 1% mortality)Transmitted by the respiratory routeFirst infect internal organs before they move into bloodstream and eventually infect the skinEradicated by vaccinationFirst disease to which immunity was artificially induced and to be eradicatedVaccination in US ended in 70s due to no animal host reservoirs for the diseaseCandidate for bioterrorism

Chickenpox (varicella-zoster virus)Figure 21.11Human Herpes virus (HHV-3) What are the viral characteristics: _________Transmitted by respiratory routeCauses pus-filled vesicles (face, throat, lower back, chest & shoulders)Virus may remain latent (enters the peripheral nerves and moves to a central ganglion)Adaptive immunity cannot get rid of latent virusLower immune competence activates the viruses in the form of shinglesTreatment: AcyclovirLive & attenuated vaccine

Cold Sores (Fever Blisters)Human herpes virus 1, HSV-1 Also Herpes simplex virus (Genital herpes mostly caused by HHV-2)What are the viral characteristics? ______________________________Transmitted direct contact (also oral or respiratory routes)Infection rates range from 70% to 100% (90% of US population infected)Virus remains latent in nerve cellsCauses cold sores (fever blisters) and can cause encephalitis when reactivatedTreatment: Acyclovir (encephalitis)No vaccine available

Measles (Rubeola)Measles virusViral characteristics; ________________Highly contagious (extremely dangerous disease in infants & very old people)Characterized by macular rashSymptoms similar to smallpox & chickenpox, resembling those of common coldFrequently complicated by middle ear infection & pneumoniaTransmitted by respiratory routePrevented by vaccinationType of vaccine?Live attenuated virusesAdministered as MMR (measles, mumps, rubella)Figure 21.14

Rubella (German Measles)Figure 21.15Rubella virusViral characteristics:A milder viral disease than measlesMacular rash and light fever, complications are rareCongenital rubella syndrome causes severe fetal damage (35% of serious fetal damage)Prevented by vaccinationType of vaccine?

Cutaneous MycosesDermatomycoses Tineas or ringwormAthletes footMetabolize keratinkeratinase Trichophyton hair, skin, & nailsEpidermophytonskin & nailsMicrosporum hair & skinTreatmentOral griseofulvinTopical miconazole

CandidiasisCaused by Candida albicans (yeast)Candidiasis Can result from suppression of competing bacteria due to antibiotics useOccurs in skinOn mucous membranes of genitourinary tract and mouthThrush is an infection of mucous membranes of mouthTopical treatment:Antifungal agentsMiconazole or nystatin.

Scabies Also known as the itchCharacterized by intense itching, a generalized rash and can lead to secondary infectionCaused by mites (Sarcoptes scabiei) Burrows in the skin to lay eggsTreatment with topical insecticidesFigure 21.18http://en.wikipedia.org/wiki/File:Sarcoptes_scabei_2.jpg

PediculosisFigure 21.19PediculosisContagiousFeed on blood Lay eggs (nits) on hairCause itching Treated with topical insecticides

Two major types:Pediculus humanus capitis (head louse)Do not spread diseaseP. h. corporis (body louse)Can spread disease (epidemic typhus)

*KING OF BACTERIAL INFECTIONS*