Chapter 21

Bacterial Disease of Skin and Eyes


I. Skin structure - 2 layers (Fig.21.1)


A. Epidermis (outer, thin layer)- several epithelial layers- outermost is stratum corneum- dead cells with much keratin incorporated (waterproofing protein).

B. Dermis (inner, thick layer)- contains hair follicles with oil gland ducts (sebum contains lipids/proteins/salts, and sweat glands (perspiration contains salt and lysozyme)

C.     Mucous membranes (epithelial cells lining passageways & body cavities)- -secrete mucous (often acidic & may have lysozyme, ex. tears, sweat), may have cilia to move mucous & anything trapped.


II. Skin normal flora


A. Diptheroids- pleomorphic G+ rods, ex. Propionibactrium acnes (anaerobic, live in hair follicles & grow on sebum), Corynebacterium xerosis (aerobic)

B. Yeast- Pitosporum ovale (also grow on sebum, may cause dandruff)

C. Staphylococci- S. epidermidis & other coagulase negative species,(Staphylococcus aureus- in some individuals)


III. Streptococcus Skin Infections (Streptococcus pyogenes- Lancefield GroupA, B-hemolytic)- G+ cocci in chains, more than 80 types based on M protein on end of cell wall fibrils (Fig.21.3, similar to fimbria)- important in specific attachment (colonization) and resistance to phagocytosis by WBCs. Other Streptococcal virulence factors include steptokinases, streplolysins, hyaluronidase, proteases, deoxyribonucleases, erythrogenic toxin (scarlet fever).


A. Ensipelas- infection of dermal layer, reddish patches, raised margins, often occurs after a strep throat infection, may cause local tissue destruction or progress to septicemia.

B. Impetigo- highly contagious (spread by contact- children scratching inset bites, rug burns, rubbing runny noses, gives an opening for infection), bacterial penetrate skin through minor abrasion most often toddlers/grade school children, thin-walled vesicles that ooze liquid, rupture and form yellowish-brown crust (Fig.21.7). Also caused (less often) by Staphylococcus aureus.

C. Necrotizing fascitis (Fig. 21.8, muscle fascia) and other invasive Group A Streptococcal infections (solid tissue-cellulitis, muscle tissue- myositis)- associated with exotorin A production (superantigen- causes immune system to contribute to damage).


IV. Staphylococcus skin disease


A.     Staphylococcus aureus- G+ coccus arranged in clusters, coagulase +, normal flora in nasal passages, minor part of skin flora (gets deeper through hair follicles) in some. Other (coagulase -, ex. S. epidermidis) Staphylococcus species typically make up 90% of normal skin flora, but can be opportunistic pathogens (catheters, cannulas, Fig.21.3).


B. Skin lesions- Staphylococcus aureus is the most common cause of abscesses (circumscribed pus-filled lesion). It is important to use antiseptics (ex. Betadine) and topical antibiotics (Bactroban- Mupirocin) before a tiny skin infection becomes larger or progresses to a devastating systemic condition (below).

1. Folliculitis- small pimple from an infected hair follicle (if an eyelash- sty).

2. Furuncle (boil)- a larger skin abscess that can develop from folliculitis.

3. Carbuncle- a larger & deeper skin abscess (multiple heads) caused by failure of body to wall off infection in furuncle.

4. Impetigo- especially of newborns in nurseries.

C. Systemic Complications from Staphylococcus Skin infections- generally due to toxin production.

1. Scalded skin syndrome (Ritters disease, Fig.)- especially common in infants, skin gets red, wrinkled, tender & peels off due to toxin (prophage) production by staphylococci in other parts of the body, high mortality rate.

2. Toxic shock syndrome (TSS)- First major outbreak (1980) associated with very absorbent tampons (now making less absorbent tampons and advising frequent changes). Now ~1/2 of cases are associated with nasal surgery (absorptive packing) and childbirth. Due to TSST -1 (Toxic Shock Syndrome Toxin #1) produced in dry anaerobic environment, organism can get into bloodstream through abrasions. Symptoms include sudden fever, vomiting, diarrhea, sore throat, muscle aches, sunburn-like rash (especially on palms of hands and soles of feet), and finally circulatory collapse(shock-sudden drop in blood pressure due to massive vasodilation/obstruction).


V. Pseudomonas Skin/Eye Infections- P. aeruginosa (pportunistic), resistant to many antibiotics/disinfectants, grows well as biofilm (water and dilute carbon sources, ex. soap, adhesives (caps)


A. Pseudomonas dermatitis- hot tubs, swimming pools with high use chlorine concentration down and pH up and nutrients up (skin, oils, etc.)

B. Otitis externa (swimmers' ear)

C. Second and third degree burn infections blue-green pus (pyocyanin pigment), common because

P. aeruginosa is all over hospital (flower vases, mop water, dilute disinfectants).

D.     Respiratory infections- mainly in immuno-compromised patients or those with chronic pulmonary disease (ex. cystic fibrosis).


VI. Acne- most common human skin disease, affects 17 million Americans, 85% teens. Cystic acne- inflamed cysts, subsequent scarring, blockage of sebaceous ducts - buildup (whiteheads), blockage breaks through skin (blackheads).

A. Caused by Propionibacterium acnes - a diptheroid G+ pleomorphic rod, metabolizes sebrum to form free fatty acids, which causes a body inflammatory response (pustule and scar formation). Oil-based cosmetics worsen the condition.

B.     Treatment:

1. topical benzoyl, peroxide (5- 10%)- antibacterial, dries/loosens plugged follicles

2.        tretinoin (topical Retin-A)- must be applied separately from benzoyl peroxide (inactivates it)

3.        Oral isotretinoin (Accutane) decreased sebrum formation, can't be taken by

pregnant women (teratogenic - damages fetus).


VII. Yaws- tropical skin disease caused by Treponama pertenue, a spirochete related to syphylis agent, spread by skin contact, red "raspberry" skin lesions disappear and recur later.


Eye Diseases

I. Conjunctivitis (pinkeye)- common in children in daycare and with extended wear soft contact lenses. Membranes of the eyes become inflamed (red), eyes swell and itch, discharge from eyes during the day that crusts over at night, develop photophobia (light sensitive), spread by contact and airborne droplets.

A. Haemophilus influenzae, biotype III- small, gram-negative rod (H. aegyptius- old name). Organism can be cultured on chocolate agar - needs CO2, hemin and NAD. blood or chocolate agar usually incubated in CO2. Therapy may or may not be required. - Usually last ~ 2 weeks, may develop into Brazilian purperic fever.


B. Moraxella lacunata- A G- diplococcus (elliptical coccus or coccobacillus)


C. Pseudomonads (Pseudomanas or related bacteria)- may be most common agent, often associated with contact lenses.

II. Neonatal Gornorrheal opthalmia- conjunctivitis caused by the STD agent Neisseria gonorrhoeae (G- diplococcus), transmitted to child at birth in the birth canal. From 1906 (24%) decreased to 1959 (0.3%) of

all children admitted to schools for blind. Easily prevented with 1% silver nitrate opthalmic

solution, now use antibiotic drops (due to high rate of co-infection with Chlamydia). Use dilute providone iodine in 3rd world countries.


III. Trachoma- leading world cause of blindness, seen in hot, dry regions such as Africa, Asia, SW US (native Americans). Caused by Chlamydia trachomatis (another STD agent), infant acquires in birth canal from infected mother. Inclusion conjunctivitis (Fig.21.19, nodular lesions on eyelids and turned in eyelashes can lead to corneal abrasion & scarring of cornea. Easily treated with tetracycline ointment


Nosocomial Infections Review


A disease/infection acquired during hospitalization.


Occurs in up to 10% of all patients resulting in billions of health care dollars, and extensive use of antibiotics, which leads to resistant strain (health care workers become carriers of these resistant strains). Many would be prevented with proper handwashing and good aseptic technique.


Most common infection sites: All may progress to septicemia (bloodstream infection).

Urinary tract- catheters E. coli and other G- rods

Pneumonia from intubation

Surgical sites - blood steam infections


Most common organisms (generally opportunistic pathogens):

1. E. coli- G- rod

2. Staphylococcus aureus- G+ coccus

3. coagulase negative Staphylococci, G+ cocci

4. Pseudomonas aeruguiosa G- rod, burn victims