MICR 201 Microbiology for Health Related Science

Microbiology- a clinical approach by Anthony Strelkauskas et al. 2010

Chapter 26: Infections of the skin and eyes

Skin and eyes are in contact with potentially pathogenic organisms all the time.

Alterations of skin and eyes can represent a psychological burden.

Infections of the eyes can lead to blindness.

Why is this chapter important?

Map for chapter 26

Largest organ in the body. Barrier between our body and the outside

◦First line of defense against invading microorganisms

Outer layer (epidermis) comes into direct contact with the environment.◦Constant shedding of cells keeps pathogens

from successfully attaching to the skin. Skin gets infected when surface is

disrupted.◦Exceptions: some worm infections;

schistosomiasis, hookworm infection

Anatomy of skin

Close access to blood system Surface penetrated by hairs and glands Site of infections

Anatomy of skin

Four main types of skin lesions:◦ Macules◦ Papules◦ Vesicles◦ Pustules

Skin lesions

Bacterial infections of the skin

in burnpatients

Gram+cocci in clusters

Catalase + Facultative

anaerobe Salt tolerant Coagulase + Leukocidin Exfoliative toxin Protein A (captures

antibodies)8

Staphylococcus aureus

SA PrA

YAntibody (Fc region)

Golden-yellow colonies

Folliculitis◦ Infections of hair

follicles Sty

◦ Folliculitis of an eyelash

Furuncle (boil)◦ Abscess; pus

surrounded by inflamed tissue

Abscess ◦ Inflammation of tissue

under the skin, accumulation of pus, walled off

9

Staphylococcal skin infections

Caused by exotoxin◦ Exfoliatins

Mostly in children < 2 years

Good prognosis and long lasting immunity

10

Staphylococcal scalded skin syndrome (SSSS)

Gram + cocci in pairs and chains

Catalase negative Facultative anaerobe beta-hemolytic streptococci Group A antigen M protein (adherence and anti-

phagocytic) Streptolysin O Hyaluronidase Streptokinase DNAse Erythrogenic toxin (phage

encoded)◦ Responsible for red rash of scarlet

fever! 11

Streptococcus pyogenes

Localized◦ Erysipelas◦ Impetigo

Invasive◦ Cellulitis◦ Necrotizing fasciitis

(flesh eating disease)

12

Streptococcal skin infections

Gram-negative rod Aerobic Oxidase + Non-fermenter Pyocyanin produces

a blue-green pus Pseudomonas

dermatitis◦ Otitis externa

(swimmer’s ear)◦ Post-burn infections

13

Pseudomonas aeruginosa

Comedonal acne◦ Occurs when sebum

channels are blocked by shedded cells

Inflammatory acne◦ Propionibacterium

acnes Gram + rods Anaerobic Skin flora

Nodular cystic acne

14

Acne

Pathogenesis◦ Propionibacterium acnes utilizes

glycerol in sebum and produces fatty acids (fermentation!)

◦ Fatty acids are pro-inflammatory◦ Neutrophils are attracted further

contributing to inflammation Treatment

◦ benzoyl peroxide (antiseptic, dries out acne lesions)

◦ Antibiotics (erythromycin, clindamycin)

◦ Isotretinoin (reduces sebum production, TERATOGENIC, 30% of newborns with severe damage)

15

Acne pathogenesis and treatment

Ischemia Loss of blood supply to tissue

Necrosis Death of tissue

Gangrene Death of soft tissue

Gas gangrene Clostridium perfringens, gram-positive, endospore-

forming anaerobic spore forming rod, grows in necrotic tissue

Produces phospholipase, proteinase, hyaluronidase Produce also hydrogen gas Treatment includes surgical removal of necrotic tissue

and/or hyperbaric chamber In addition antibiotics such as penicillin and

clindamycin

http://medicine.ucsd.edu/clinicalimg/Skin-Gangrene-DIC.jpg

16

Gangrene

Staphylococcus aureus: pus, abscess, SSSS

Streptococcus pyogenes: impetigo, erysipela

Pseudomonas aeruginosa: Otitis externa

Propionibacterium acnes: acne Clostridium perfringens: gangrene

17

Summary of bacterial skin infections

Exanthem◦ Aerosol infection viremia skin manifestation

Skin tumors (warts)

Measles Rubella Smallpox (variola) Chickenpox and shingles Herpes simplex virus type 1 Warts

Viral infections of the skin

Extremely contagious infection Caused by single-stranded RNA

virus Transmitted by respiratory route Cold symptoms and fever Viremia Macular rash, raised spots, Koplik's

spots in oral mucosa Rash begins on face, affects trunk

and extremities 15-25% mortality rate in developing

countries Up to 15% of cases of measles have

complications - Otis media, sinusitis, pneumonia, sepsis, encephalitis

Prevented by vaccination

Measles

Very mild or asymptomatic infection◦ Low-grade fever,

lymphadenopathy, and faint macular rash.

Very serious in pregnant women◦ Can cause congenital

abnormalities in fetus (embryoathy)

Infected individual contagious for 8 days before and 8 days after appearance of rash.

Rubella (German measles)

Infection caused by a DNA poxvirus. Two forms of smallpox:

◦ Variola major – mortality rate 20% or higher◦ Variola minor – mortality rate 1%

Vaccinatiom: side effects, 1-2 deaths/million Smallpox has effectively been eradicated from

the entire world; last victim in Somalia in 1977 Only reservoir is humans; should be no more

cases Stocks of smallpox virus mean further infections

are possible Decreased herd immunity to smallpox increases

the possibile potential as bioweapon

Smallpox (Variola)

Smallpox (Variola)

Dominant feature is the appearance of papulovesicular rash and pustules.

Incubation period is usually 12-14 days.◦ Can be 4-5 days◦ Abrupt onset of fever, chills, and muscle aches

Rash appears 3-4 days later.◦ Papulovesicles most prominent on the head

and extremities.◦ Become pustular over 10-12 days.

Death from smallpox results from: ◦ Overwhelming virus infection ◦ Bacterial superinfection

Smallpox: Pathogenesis

Measles (measles virus, Koplik’s spots, subacute panencephalitis)

Rubella (rubella virus, embryopathic) Small pox (variola virus, up to 30%

mortality) Chicken pox and shingles (Varizella Zoster

virus, latency dorsal root ganglion) Herpes simplex virus (HSV 1, latency

trigenimal ganglion and recurrence) Warts (Papilloma virus, cancer)

Summary of viral infections

Candidiasis Dermaphytosis

Fungal infections of the skin

Infections of the eyes

HSV1

River blindness

Contact lenses (Pseudomonas)

Pink eye

Infected by the mother during vaginal birth Neonatal gonorrheal ophthalmia by

Neisseria gonorrhoeae infection Chlamydia trachomatis can also infect the

eyes of newborns. Both infections cause large amounts of pus

to form in the eyes.◦ Causes ulceration and scarring of the cornea if

not treated Common practice to treat eyes of newborn

infants with erythromycin.

Neonatal eye infections

Neonatal gonorrheal ophthalmia

Topical eye drops and ointments containing erythromycin or gentamicin are effective against acute bacterial conjunctivitis.

Fluoroquinolones can be used for eye infections caused by Pseudomonas.

Quinolones such as ciprofloxacin useful for all types of eye infection.

Eye infections treatment

Parasitic worm Loa loa African rain forest Transmitted by bite of

deer fly Migrate from tissue to

eye Grow up to an inch and

easily seen

LOAIASIS

Skin is an impermeable barrier to almost all pathogens.

A wide variety of bacteria can cause infection of the skin, with necrotizing fasciitis being one of the worst infections.

Bacteria can infect hair follicles, sebaceous glands, and sweat glands.

Viral pathogens also require a portal of entry to infect the skin.

Viral infections that cause lesions on the skin include measles, rubella, smallpox, chickenpox, herpes simplex type 1, and human papillomavirus.

Fungi are always present on the skin but rarely cause infection.

Chapter 26 key concepts

The most common fungal infection of the skin is candidiasis.

Dermatophytosis can be seen as ringworm, athlete’s foot, or jock itch.

One of the most common parasitic infections of the skin is leishmaniasis.

Eyes are infected through direct exposure to pathogens.

A common eye infection and leading cause of blindness is trachoma, which is caused by Chlamydia trachomatis.

Parasitic infections of the eye include loaiasis.

Chapter 26 key concepts

Final Examination –Wednesday, June 12, 2013 10:45am – 1:15pm Lecture, Chapter End Self Study Questions 100 Multiple Choice Questions: 2 points

each x 100 = 200 points ~65%: Chapters 14-26 ~35%: Chapters 1-13 Please bring Scantron and No. 2 pencil

CORRECTION – Chapter Question Chapter 22 Infections of the Digestive

System 1. The most common source of

gastrointestinal infection in the developed world is◦ A. Salmonella◦ B. Shigella◦ C. Escherichia◦ D. Campylobacter◦ E. Staphylococcus aureus

Correct answer is D. Campylobacter