Microbiology Lecture 25-26

wounds, pores, circulation

points of entry :

epidermis → dermis → subcutaneous layer

layers of the skin :

keratin (keratinocytes) & cell sloughing (desquamation)

skin defenses; physical blockages : 

low pH (difficult for microbes), high salt, oils (sebum, sweat)

skin defenses; unfavorable environment :

lysozomes & AMPs (antimicrobial peptides)

skin defenses; antimicrobial :

lesions

changes to skin caused by infection

diagnostic indicators

diseases may have specific signs, which we call :

macule

flat and discolored (vitiligo)

papule

raised and solid (warts)

pus

dead WBCs; dead bacterial / fungal cells

purulent

when a fluid contains pus, we describe it as :

vesicle

filled with a clear fluid (blister)

pustule

filled with pus (acne)

abscess

• deep tissue pustule (in dermis or subcutaneous layer)

• swollen and hard (full of pus)

• decreased blood flow, must drain to improve blood flow

• antibiotics don’t penetrate well

serious

the deeper in the skin the infection goes, the more ___ it is.

“itis”

infection or inflammation of

“-emia”

in the blood

for bacterial skin specimens

1. culture on appropriate media (observe characteristics); TSA, MacConkey, blood

2. gram stain

3. virulence factor tests

4. identify via flowchart (gram + cocci or Gram - rod)

acne

propionibacterium ___; opportunistic pathogen; producing more oils during pubery because of hormones

dermatistis

pseudomonas aeruginosa; in the environment (soil), should not be exposed to our skin for a long time; gram-negative

P. aeruginosa

• antibiotic resistant

• opportunistic : only in the right circumstances

P. Aeruginosa Diagnosis

• non-lactose fermenting on MacConkey agar (pale pink)

• oxidase +

• Fruity / corn / new nike odor

• green pigment

Staphylcoccus aureus

gram + cocci

S. aureus diagnosis

• golden colonies

• beta-hemolysis

• catalase + 

• coagulase + 

S. aureus Virulence Factors

• capsule (protects microbes from antigens)

• coagulase (allows bacteria to clot plasma)

• protein A (prevents Abs from binding to bacteria)

• causes : exfoliative skin and TSST-1 (TSS)

MRSA

methicillin resistant S. Aureus

(HA-MRSA) Hospital-Associated

• MecA

• resistant to all antibiotics except VANCOMYCIN (treat w vancomycin)

CA-MRSA (Community-associated MRSA)

• MecA

• resistant to methicillin, sensitive to many others

• PVL (leukocyte) gene as an extra virulence factor

toxemia

• toxin enters bloodstream to cause disease

• bacteria not present at the site of symptoms

• bacteria are not in the blood

Scalded Skin Syndrome (SSS)

oxfoliative toxin; intestine; toxin enters bloodstream; skin peels off in sheets.

Toxic Shock Syndrome (TSS)

TSST-1; fever, rash, skin shedding

Group A Streptococcus (GAS)

causes various skin infections; gram + cocci

S. pyogenes diagnosis

• catalase

• beta-hemolysis

• Group A typing

GAS virulence factors

• capsule

• M protein : fuzzy layer

• SPE A and SLO

SPE A and SLO

toxemia associated with (GAS Necrotizing Fasciitis) : 

SPE A superantigen

Toxemia associated with (GAS TSS) :

treatment for GAS

antibiotic treatment is a MUST; rheumatic fever

exanthems

measles, rubella, roseola, chickenpox, fifth disease

rubeola

• caused by measles

• macular rash, fever, cough

• koplik spots

• most contagious human virus

koplik spots

red patches with white centers; diagnostic indicator

outcomes of measles

pneumonia, immune amnesia, subacute sclerosing pancencephalitis (SSPE)

MMR Vaccine

• measles, mumps, and rubella (MMR)

• live attenuated vaccine

Rubella (german measles)

• caused by rubella virus

• macular rash

• congenital rubella syndrome

congenital rubella syndrome

• infected in 1st trimester of pregnancy

• causes miscarriage, still birth, or birth defects

Roseola

• common and mild disease

• only a few days

Chickenpox (Varicella) & Shingles (Zoster)

• caused by varicella - zoster virus (VZV)

• vesicles

• latent in nerve cells

• live-attenuated vaccine

• respiratory route

shingles (zoster)

• virus is reactivated

• vesicles

• adults over 50

• shingles-specific, subunit vaccine

fifth disease

• parvovirus B19

• “slapped cheek” rash

cold sores (cutaneous herpes)

cold sores (sores near mouth) : HSV - 1; vesicular rash

herpesviruses

direct contact; latent in nerve ganglion

Hand, Foot, and Mouth disease (HFMD)

caused by coxsackievirus 16; vesicular rash; direct contact; enterovirus

enterovirus

infects gut

warts

rough papules; direct contact

mycoses

fungal diseases are called

ringeworm (tinea) & candidiasis

types of mycoses

ringworm (tinea)

caused by various fungi that grow on skin, called dermatophytes

candidiasis

caused by candida albicans; prevalent after antibiotic use (superinfection) and in immunocompromised people (AIDS pts)

leishmaniasis

Caused my Leishmania species; protozoan; vector : sand fly; “volcanic” ulcers form

hookworm

caused by helminth Anclyostoma duodenale; Southern U.S.; stepping barefoot on contaminated soil

scabies

caused by mites; burrows under skin to lay eggs; itchy, maculopapular rash

lice (pediculosis)

caused by Pediculus humanus capitis; children; very itchy scalp; insecticides