Chapter 21 Microbiology

Define the layers of the epidermis

Top layer= stratum corneum

-Stratified squamous epithelium, dead cells filled with keratin

Bottom layer= connective tissue, glands and hair follicles

Define first line of defense and the physical factors

Keep pathogens on the outside of the body and neutralizes them before infection

Physical factors: barriers with removal properties

Physical barrier, stratum corneum is composed of stratified squamous epithelium. The cells are dead and filled with keratin. Exfoliation of cells and perspiration removes

Dry

What are the chemical factors in the first line of defense

Inhibits growth and destroys microbes

Sebum (fatty acids) creates an acidic environment

Defensins: antimicrobial proteins

Salts create high osmotic environment

Lysozyme

IgA antibodies

What does perspiration and sebum provide to the pathogen?

Perspiration- provides moisture and some nutrients to the pathogen

Sebum: provides nutrients and proteins to the pathogen

Define mucous membranes and eyes in physical and chemical factors

Epithelial linings composed of tightly packed cells to extra cellular basement membrane

1st line of defense: physical factors- mucus traps and cilia removes

chemical factors- lysozyme, IgA antibodies, acidic

Eyes in physical factors- lacrimal apparatus, tears remove

Chemical factors- lysozyme

Normal microbiota of the skin

Gram positive: salt tolerant bacteria and resistant to drying

Species: staphylococci, micrococci, diphtheroids

Bacterial Diseases of the Skin: exanthem, enanthem, vesicle, bullae, macule, papule, pustule

Exanthem- skin rash arising from disease

Enanthem- mucous membrane rash arising from disease

Vesicle- small fluid-filled lesion less than 1cm

Bullae- larger fluid filled lesion larger than 1cm

Macule- flat reddened lesion

Papule- red raised lesion

Pustule- contain pus (dead phagocytes, dead bacterial cells, and fluid)

What are the staphylococcal skin infections: gram positive cocci

1. Staphylococcus epidermidis- 90% of microbiota of skin, coagulase-negative

2. Staphylococcus aureus

What are the characteristics of staphylococcus aureus?

Gram positive cocci, coagulase-positive, can secrete protein-A to block chemotaxis of neutrophils, leukocidin, opsonization resistant, cell wall is lysozyme resistant, neutralizes defensins, exfoliative toxin, nasal passages (transferred to skin)

20% of population are carriers and 60% are occasional carriers

What are the diseases when staphylococcus enters the skin?

Folliculitis, sty, furuncle, carbuncle, impetigo, toxic shock syndrome, scalded skin syndrome, MRSA

Define the diseases when staphylococcus enters the skin: folliculitis, sty, furuncle, carbuncle, impetigo, toxic shock syndrome, scalded skin syndrome

Folliculitis- infections of hair follicles (pimple)

Sty- folliculitis of an eyelash

Furuncle- more serious hair follicle infection, abscess: pus surrounded by inflamed tissue, hard for antibiotics to penetrate

Carbuncle- hard, round deep inflammation of tissue under skin, invasion of surrounding tissue from a furuncle

Impetigo- thin walled vesicles on skin, rupture and crust over

Toxic shock syndrome toxin 1, fever, vomiting, sunburn-like rash, shock, death

Scalded skin syndrome- exfoliative toxin, reddened area that spreads, skin peels off in sheets

Define streptococcus pyogenes (Group A Streptococci) GAS

Group A beta-hemolytic streptococci: lyse RBC and other cells by hemolysis

Transmitted by direct contact, 80 immunological types determined by M proteins

prevents activation of complement system, aid in adherence of mucous membranes, prevents phagocytosis, capsule of hyaluronic acid, streptokinases, hyaluronidase, deoxyribonucleases, streptolysins lyse RBC and is toxic to neutrophils

Erysipelas

Streptococcus pyogenes

Infects dermal layer (cellulitis)→red lesion with raised margins, often hot to touch

Tissue damage which can progress to sepsis

Necrotizing fasciitis: muscle covering

Exotoxin A is a super-antigen which causes the host immune system to contribute to damage

Streptococcal Toxic Shock Syndrome can lead to death

Define the different types of Pseudomonads

Pseudomonas aeruginosa: gram negative, aerobic rod found in soil and water, produce pyocyanin pigment

Pseudomonas dermatitis: superficial rash when bacteria enter hair follicles, swimmers rash/hot tub rash

Otitis externa: superficial infection of ear canal

Post-burn infections

Define the different types of acne

Comedonal acne- does not have a bacterial cause, occurs when sebum channels are blocked with shed cells

Inflammatory acne- propionibacterium acnes (gram positive, anaerobic rod) metabolizes glycerol in sebum→fatty acid causes inflammatory response→pustule

Nodular cystic acne- inflamed lesions filled with pus deep within the skin which leave permanent scars

Define viral disease of the skin

Warts: human papillomaviruses (50 types), benign skin growths transmitted by contact, virus grows in skin cells and causes the cells to grow quickly

Herpes Simplex Virus 1: transmitted by direct oral contact, latent and reactivation (UV, stress, hormonal)

Define chickenpox and shingles

Varicella-zoster virus (human herpes virus 3), transmitted by respiratory route (respiratory route→blood→epidermal rash) vesicular rash, virus may remain latent in dorsal root ganglia

Shingles- reactivation of chickenpox, releases viruses that move along peripheral nerves to skin

Define Measles

Rubeola (Measles Virus), transmitted by respiratory route, respiratory route→blood→epidermal rash

Macular rash (often raised) and Kopliks spots (red with blue-white specks)

Prevented by vaccination-MMR

Define Rubella

Rubella virus, transmitted by respiratory route (respiratory route→blood→epidermal rash)

Macular rash (not raised) and fever, congenital rubella syndrome causes severe fetal damage, prevented by MMR vaccination

Fungal Diseases of the Skin: Cutaneous Mycoses

Dermatomycoses: tineas or ringworm

Caused by dermatophytes

Colonize epidermis, nails, hair

Metabolize keratin

Transmission: direct and indirect

Define Candidiasis

Candida albicans (yeast), candidiasis may result from suppression of competing bacteria by antibiotics, occurs in mucous membranes

Trush: within mouth

Urethritis and vaginitis within genitourinary tract

What are the parasitic infections of the skin

Scabies: Sarcoptes scabiei burrows in the skin to lay eggs, intense local itching, slightly elevated, serpentine lines, transmitted by intimate contact

Pediculosis (lice): Pediculus humans capitis (head louse)

P. h. corporis (body louse): feeds on blood, itching sensation to louse saliva after weeks, lays nits on hair, hatch in a week, transmitted by direct and indirect contact

Define conjunctivitis

Pink eye, haemophilus influenzae most common bacterial cause, various microbes, associated with unsanitary contact lenses

Neonatal gonorrheal ophthalmia

Neisseria gonorrhoeae, transmitted to newborns eyes during passage through the birth canal, conjunctivitis, ulceration of the cornea, blindness, prevented by treatment newborns eyes with antibiotics

Chlamydial conjunctivitis

Chlamydia trachomatis, inclusion conjunctivitis, transmitted to newborns eyes during passage through the birth canal, prevent by treatment newborn eyes with antibiotics, conjunctivitis, scarring of cornea, blindness, spread through swimming pool water, treated with tetracycline

Trachoma

Chlamydia trachomatis, greatest cause of blindness worldwide, transmission through eye/nose secretions with infected individual and flies, conjunctivitis, trichiasis= in turning of eyelashes, abrasion and scarring of cornea, blindness