Micro Unit 3

Skin

Structure and Function:

Epidermis: Thin, outer portion, several layers of cells

Dermis: inner, relatively thick portion, composed of connective tissue

Perspiration: provides moisture and nutrients for microbial growth

Sebum: Secreted by oil glands, mixture of lipids, proteins, and salts; prevents skin and hair from drying out

Mucous Membranes: an outer protective layer; found in linings of body cavities

• composed of tightly packed epithelial cells which secrete mucus (acidic)

• Eye membranes are washed by tears, lysozyme in tears destroys bacterial cell walls

Normal Skin Flora

• Skin is generally inhospitable to most microorganisms but supports growth of normal flora

• Body area w/ more moisture, such as armpits have higher pop of microbes

Propionibacterium Acnes

• gram +, rod shaped anaerobic

• Grows in hair follicles due to secretion from oil glands

Acne Fulminans

• rare, very severe presentation of acne due to an immunological reaction to Propionibacterium acnes

• Can be triggered by steroid use

Skin Lesions

types:

Vesicles: small fluid filled lesions

Bullae: Larger fluid filled lesions

Macules: Flat, reddish lesions

Papules: raised lesions, called pustule when they contain pus

Comedonal Acne

• mild

• hair follicle blocked by sebum and dead skin cells

• single bump = comedo

• multiple bumps = comdedones

• Blackheads and whiteheads nistead of pimples

• Treated with retnoids

Inflammatory ance

• caused by bacteria that requires sebum for nutrients

  Treated w/ antibiots or benzoyl peroxide

Nodular cystic Acne

• Characterized by nodules or cysts inflammed lesions filled w/ pus deep in skin

• Leaved prominent scars

• treated with accutane, reduced formation of sebum

• Accutane is teratogenic

Staphylococcus

Gram + , sperical bacterial that looks likes grapes

2 groups:

• Coagulase +

• Coagulase -

Staph Epidermis

• gram + Coagulase -

• Pathogenic only when skin barrier broken or invaded by medical procedures

• Produce biofilms on catheters

Staph Aureus:

• yellow gold colonies

• Compromises 20-30% of bacterial pop in our nasal cavities

• Can survive for months on surfaces

• Enters body through natural opening in skin and causes

  • Pimple: Hair follicle

  • Boil: Serious hair follicle infection, has to be drained

  • Sty: infection of eyelash follicle

• Stimulates vigorous inflammatory response

• Most produce toxin to block immune response

Impetigo

Bullous form:

• highly contagious skin infection

• mostly affects children 2-5 years old

• spread by direct contact

• ~70% cases caused by S Aureus

• Toxin causes separation of epidermis and dermis formation of fluid filled blister that breaks easily

• Infection can stay localized or circulate to distant sites

Nonbullous:

• Most common form

• small blisters/pustules

Scalded Skin syndrome (Ritter’s Disease):

• Same toxin

• Children w/ poor immunity/ kidney function

Streptococcal Skin infections

• Gram + spherical bacteria usually grow in chains

• Divided into groups based on their cell wall carbohydrates

• Produce variety of enzymes and other substances that promote rapid spread of infection through tissue by liquefying pus \

Beta-hemolytic Strep:

• associated with human disease

Strep Pyogenes

• Infects dermal Layer of skin causing erysipelas

• Skin erupts in red patches w/ raised margins

• Bacteria can enter bloodstream causing sepsis

Necrozinf Fasciitis

• Invasive strep infection

• Flesh eating bacteria

• Due to endotoxins carried on a lysogenic bacteriophage of S. Pyogenes

• Rapid and progressive infection in Subcutaneous layers of skin

• Destruction of tissue, muscle and fat

• Minor Skin breaks lead to infections

• OFten unrecognized in early stages and treatment have serious sonsequences

• Very rapid

Pseudomonads

• Gram -

• Found in soil and water

• Grow on unusual organic matter such as soap films or cap liner adhesives

• Resistant to disinfectants and antibiotics

• Infections:

  • dermatitis and folliculitis

  • External ear Infections or swimmers ear

TB

• Mycobacterium tuberculosis

  • fairly large non-motile rod shaped obligate aerobe slow grower

• Mycobacterium Bovis

  • in cows

TB pathogenesis

• infected macrophages get walled off into lesion called tubercle

• center of tubercle where macrophages die a release TB

• center gets cut off from air and ends with dormant TB

• if disease is stopped, lesions become calcified and are visible in xray

• mature tubercle can rupture allowing release into bloodstream

TB Symptoms

• spread by coughing in aerosols w/ blood

• weight loss and general loss of vigor

• Cell mediated immune response

• Tuberculin Skin Test

• Delayed hypersensitivity reaction

Tb Treatment

• min 6 month drug therapy

• Resistance common because of patient failure to keep to meds over 6 months

• prolonged treatment because of slow growth and dormant factrs

Multi-drug resistant TB

• Tb exhibiting resistant to 2 or more previously effective drugs

TB Vaccines

• Uses Bovis because the genetics are close enough

• in US vaccine only given to high risk children

• People who have received vaccine test positive via skin test

Rheumatic Fever

• caused by streptococcus pyogenes

• caused by antigens cross reacting with heart valve and joint antigens

• occurs most often after getting strep throat

• can cause inflammation of the heart valve

Lymphatic systems

• Lymph capillaries

  • pick up bacteria and their byproducts easily

• Lymph node

  • oval structures located at various points in lymphatic system

• Buboes: swollen and tender lymph nodes

Tularemia

• zoonotic disease (rabbit fever)

• small gram negative bacillus aerobic and nonmotile no spores

• transmitted by tick and dear fly bite (deer fly fever) via penetration or infection of an abrasion

• lymph nodes become enlarged because of pockets of pus

• requires immediate treatment to avoid sepsis

• inhalation of contaminated feces or urine via dust can cause acute pneumonia (often lethal w/o treatment)

• Min treatment of 10 days

Brucellosis

• undulant fever

• most common form of zoonosis

• small aerobic no spores coccobacilli

• 3 species

  • brucella abortus- in cattle

  • brucella suis - in swine but can infect cattle as well

  • brucella melitensis - most serious strain, causes most diseases mostly found in goats and sheep, imported through unpasturized food products such as soft cheeses made from goats milk

• diagnosis usually done by specialized lab

• is considered a possible bio weapon because of its ability to go airborne

Anthrax

• large gram + anaerobic, endospore forming

• grows in soil with specific moisture conditions

• 3 toxin subunits

  • edema factor: causes edema swelling and interferes with phagocytosis

  • lethal factor: specifically targets and kills macrophages

  • protective antigen: receptor binding protein that forms pore in endosomal membrane enabling EF and LF to cross into cytosol

• 3 types:

  • Cutaneous anthrax:

    • contact with material containing endospores

    • enters through minor skin lesion

    • papule appears then it becomes vesicle

  • Gastrointestinal anthrax

    • ingestion of undercooked contaminated food

  • pulminary anthrax

    • endospores inhaled into lungs and have high probability of entering bloodstream

    • looks like common cold

    • usually kills patient w/in 24-48 hrs

    • mortality approaches 100%

Gangrene

• Ischemia: inadequate blood supply to an organ or part of body that results in necrosis

• Gangrene: soft tissue death due to loss of blood supply

• Clostridium perfringens:

  • most common cause of gangrene

  • anaerobic organism, gram +, spore-forming, rod-shaped, very common in environment

• usually develops at site of trauma or recent surgical wound

• toxins and bacteria enter bloodstream and cause systemic illness

• blisters w/ brown-red fluid, necrosis of flesh

• can be seen in fluid from wound ‘

• treated via antibiotics and surgical removal of necrotic tissue

• When it occurs in abdominal cavity, surgery occurs in oxygen saturated environment

Pasteurella multocida

• most common cause of bite infections

• Small facultative anaerobe, gram -, nonmotile, non spore forming

• treated with combination antibiotics

Cat scratch disease

• bartonella henselea

• aerobic gram - inhabits blood cells of some cats

• 40% of cats carry bacteria some time in their lives

• Multiplies in flea digestive system and passed on through feces

• Treatment is cleaning out wound

The plague

• Yersinia Pestis: gram -, rod shaped bacteria

• Disease of rodents and transmitted rat to rat by flea

• biofilm to block fleas digestive track → regurgitation of blood

• transmission: flea bite, handling infected tissue, or aerosolization

• bubonic plague:

  • multiplication of bacteria in lymph node closest to entry

• Septicemic plague:

  • necrotic death of tissues

  • can be first symptom of plague or can develop from untreated bubonic

• Pneumonic plague:

  • contracted by inhaling infectious droplets or from untreated bubonic or septicemic

  • can spread person to person

  • mortality of 100%

• Treated with IV antibiotics

Lyme Disease

• borrelia burgdorferi

• Field mice most important animal reservoir

• Ticks nymphal stage

• Deer are dead end hosts

• hard to diagnose because it is very easy to confuse with other diseases

meningitis vs septicemia nisseria

• septicemia does not have photophobia

• septicemic has rash