Infections Of Skin & Eyes Flashcards
(35 cards)
S. Epidermidis
Generally non-pathogenic, normal inhabitant of skin, nasal and oral cavity of human body. Does not ferment mannitol or produce enzyme coagulase. Usually produces a white colony on culture media.
S. Aureus
Pathogenic and normal inhabitant of nasal and oral cavity on 50-75% of human adults. Ferments mannitol and produces enzyme catalase. Is normally beta hemolytic and produces golden, yellow, or white colony depending on culture medium. Produces several enzymes that contribute to its virulence and pathogenicity: hemolysin, leukocydin, coagulase, fibrinolysin (staphylokinase), hyaluronidase and DNAse. Some strains produce enterotoxin (food intoxication) and exfoliating toxin (TSS and Scalded Skin Syndrome)
How do you isolate and diagnose Staph
- Isolation of bacterium from an infected area in pure culture
- Gram stain indicating gram pos cocci in grape like clusters.
- Inoculation on mannitol salt agar to confirm salt-tolerance and mannitol fermentation
If above three tests are pos, additional tests can be performed to determine pathogenicity:
Coagulase test- use rabbit coagulase plasma (ant-coagulase antibodies) in tubes or slides. 97% of all pathogenic S. Aureus are coagulase positive.
DNAse test- indicates presence of DNAse. Samples streaked on agar containing DNA, confirmed by clear zones after incubating.
Statins of S. Aureus are determined by phage typing. Plate of culture is seeding with organism and known staph phages are placed on lawn of growth. Lysis on the bacterium (plaques) indicate the phage type in question.
Folliculitis
Infection of hair follicles
Cause by S. Aureus.
Reoccurring disease
Boils, furuncles (pimples), and carbuncles
Boils and furuncles are usually from blockage of hair follicles or sebaceous glands, generally eradicated by body defense.
Styes are infections of eyelash follicles.
Carbuncles may spread and lead to extensive abscess, fever and pain. May require surgical drainage and aggressive chemotherapy.
Impetigo
Referred to as purulent dermatitis.
Caused by S. Aureus, often occurs in conjunction with B-hemolytic streptococcal infection.
Occurs primarily in children from scratching and insect bite or direct contact with infected individual. Often epidemic in school/day care.
Can lead to septicemia unless vigorously tx with topical antimicrobics.
TSS & SS
Due to release of exfoliating toxin and exotoxins that causes the blistering and peeling of skin.
Toxin is result of lysogenic conversion (prophage) genes are being expressed.
Nonmenstrual TSS occurs in about 45% of TSS cases, from absorbent packing used in nasal surgery, after surgical incisions, and in women who have just given birth.
Streptococcal infections
Due to Strept. Pyogenes.
Gram pod, non-spore forming, facultatively anaerobic cocci in chains.
Probably responsible for more illnesses and diseases than any other group of microbes. Can attack any part of body, remain alive in pus and sputum and other body secretions for months. Rapidly squire antimicrobic resistance, penicillin and cephalosporin analogs are still effective.
Specified by action on blood agar.
Erysipelas
Dermis is effected due to exotoxins and skin erupts into reddish patches as new areas are infected. Occurs predominately in very old and very young. Usually preceded by strept infections like a sore throat.
Caused by strept pyogenes
Impetigo
Caused by Strept pyogenes and S. Aureus
Puerperal fever
Childbed fever. Infection of uterus following childbirth. Transmission involves streptococci from carriers or contaminated instruments. Was major cause of death prior to aseptic technique in childbirth.
Strept pyogenes
Acute necrotizing fasciitis
Flesh eating Strept. Pyogenes due to a prophage.
Acne
Probably most common disease in humans, cause by sebum accumulation, forming whiteheads and later blackheads. Some bacteria such as staphylococci and propionobacterium acne metabolize sebum forming free fatty acids which causes inflammation. This ruptures the hair follicles lining leading to scarring.
Tx: benzoyl peroxide can be used as well as tetracyclines. Isotreinoin (acutane) inhibits sebum formation, can be dangerous. Used only to treat severe cases of acne, but is teratogenic.
Anthrax
Cause by bacillus anthracis, gram pos, spore forming rod.
First disease for which causative agent was determined. Transmission involves direct contact or inhalation of spores/cells.
It was an occupational disease of sheep herders and workers in animal industries, symptoms include lesions or malignant pustule at site of infection. May localize or spread to circulatory system, causing fatal septicemia within a few days.
Dx: by ascoli test, a serological test
Pseudomonas dermatitis
Caused by P. Aeruginosa, gram neg, no fermentative, aerobic rods.
One of the most important pathogens among compromised patients like burn victims.
Resistant to many antimicrobics and is capable of surviving in many environments.
Gives off grape like odor.
Can be kind of identified on triple sugar iron agar but other biochemical tests are required. Pyocin typing is used for epidemic studies.
Tx: must be preceded by antimicrobic sensitive typing, carenicillin, gentamycin, tobramycin, tricaricikkin and new cephalosporins. Experimental vaccine for burn victims.
Two pigments: pyocyanin(blue green) and fluorescing (yellow)
Burn contamination, nosocomial infections, swimmers ear, toe web infections, green nail syndrome, hot tub dermatitis, UTIs
Staphylococcal infections
Due to S. Aureus, gram Los, non-spore forming, facultatively anaerobic, strongly catalase positive cocci.
Most resistant of all non-spore forming microbes to heat, drying and chemicals. Can live for weeks in dried pus and many are resistant to wide variety of microbes
Two major species can be distinguished by mannitol fermentation and coagulate production. A third species (S. saprophyticus) can be identified by comparing to other two.
Is an opportunist normally in infants and elderly. Spread by person to person contact.
Dermatomycoses
Fungal infections or mycotoxins parasitism of the skin.
Cause infections in skin, hair, and nails, all utilize the protein keratin for growth.
Skin lesions usually present as circular with raised borders (at one time were thought to be caused by worms, so called ringworm)
Three main causative agents: trichophyton, microsporum, and epidermophytin.
Dg: symptomatic, characterized lesions, or cultivation of spores or conidia from lesions on Sabouraud dextrose agar and microscopic examination of lesions and cultures.
Tx: oral administration of Griseofuvulin, topical fungal ointments (clotrimazole, miconazole, tolnaftate) and corticosteroid to relieve itching.
Tinea pedis
Athletes foot
Prevalent mycotic disease.
Sx: burning or itching between toes, small vesicles containing fluid eventually rupture leaving small red ulcers. Lesions may extend to soles and heels of feet, and in severe cases up the legs and thighs.
Tinea ungum
Onchomycosis
Mycotic lesion of the nails.
Sx: nails lose luster and increase in thickness. Shape may become distorted.
Tx: may require prolonged therapy to eradicte organism and arrest growth.
Tinea cruris
Jock itch: ringworm of inguinal region.
Excessive perspiration and rubbing of clothing can cause infection.
Sx: deeply reddened areas of inflammation accompanied by small vesicles around genitalia and thighs.
Tinea corporis
Ringworm of smooth and hairless skin
Times barbae
Barbers itch
Mycotic infection of bearded region of face and neck. Used to be caused by infected shaving brushes and razors. May occur frequently in men and animal industries where spores in animal fur and dust my lodge in bearded areas
Tinea capitis
Ringworm of the scalp.
Occurs frequently in children. May be transmitted by pets.
Sx: can involve epithelium of the scalp and hair itself. Hair may become brittle, lose luster and fall out leaving hairless areas grayish and inflamed.
Tinea veriscolor
Scaly discolorations of skin caused primarily by Pityrosporium obiculare.
