Microbiology- a clinical approach by Anthony
Strelkauskas et al. 2010
Chapter 26: Infections of the skin and eyes
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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.
Largest organ in the body.
 Barrier between our body and the outside
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◦ First line of defense against invading
microorganisms
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Outer layer (epidermis) comes into direct
contact with the environment.
◦ Constant shedding of cells keeps pathogens
from successfully attaching to the skin.
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Skin gets infected when surface is
disrupted.
◦ Exceptions: some worm infections;
schistosomiasis, hookworm infection
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Close access to blood system
Surface penetrated by hairs and glands
Site of infections
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Four main types of
skin lesions:
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Macules
Papules
Vesicles
Pustules
in burn
patients
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Gram+cocci in
clusters
Catalase +
Facultative anaerobe
Salt tolerant
Coagulase +
Leukocidin
Exfoliative toxin
Protein A (captures
antibodies)
Golden-yellow colonies
Antibody (Fc region)
SA
PrA
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Folliculitis
◦ Infections of hair
follicles
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Sty
◦ Folliculitis of an eyelash
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Furuncle (boil)
◦ Abscess; pus
surrounded by inflamed
tissue
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Abscess
◦ Inflammation of tissue
under the skin,
accumulation of pus,
walled off
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Caused by
exotoxin
◦ Exfoliatins
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Mostly in
children < 2
years
Good prognosis
and long lasting
immunity
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Gram + cocci in pairs and chains
Catalase negative
Facultative anaerobe
beta-hemolytic streptococci
Group A antigen
M protein (adherence and antiphagocytic)
Streptolysin O
Hyaluronidase
Streptokinase
DNAse
Erythrogenic toxin (phage encoded)
◦ Responsible for red rash of scarlet
fever!
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Localized
◦ Erysipelas
◦ Impetigo
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Invasive
◦ Cellulitis
◦ Necrotizing fasciitis
(flesh eating
disease)
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Gram-negative rod
Aerobic
Oxidase +
Non-fermenter
Pyocyanin produces a
blue-green pus
Pseudomonas
dermatitis
◦ Otitis externa
(swimmer’s ear)
◦ Post-burn infections
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Comedonal acne
◦ Occurs when sebum
channels are blocked
by shedded cells
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Inflammatory acne
◦ Propionibacterium
acnes
 Gram + rods
 Anaerobic
 Skin flora
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Nodular cystic acne
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Pathogenesis
◦ Propionibacterium acnes utilizes
glycerol in sebum and produces
fatty acids (fermentation!)
◦ Fatty acids are pro-inflammatory
◦ Neutrophils are attracted further
contributing to inflammation
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Treatment
◦ benzoyl peroxide (antiseptic, dries
out acne lesions)
◦ Antibiotics (erythromycin,
clindamycin)
◦ Isotretinoin (reduces sebum
production, TERATOGENIC, 30%
of newborns with severe damage)
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Ischemia
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Necrosis
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Death of tissue
Gangrene
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Loss of blood supply to tissue
Death of soft tissue
Gas gangrene
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Clostridium perfringens, gram-positive, endospore-forming
anaerobic spore forming rod, grows in necrotic tissue
http://medicine.ucsd.edu/clinicalimg/Skin-Gangrene-DIC.jpg
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
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Staphylococcus aureus: pus, abscess,
SSSS
Streptococcus pyogenes: impetigo,
erysipela
Pseudomonas aeruginosa: Otitis externa
Propionibacterium acnes: acne
Clostridium perfringens: gangrene
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Exanthem
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Skin tumors (warts)
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◦ Aerosol infection  viremia skin manifestation
Measles
Rubella
Smallpox (variola)
Chickenpox and shingles
Herpes simplex virus type 1
Warts
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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
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Very mild or
asymptomatic infection
◦ Low-grade fever,
lymphadenopathy, and
faint macular rash.
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Very serious in pregnant
women
◦ Can cause congenital
abnormalities in fetus
(embryoathy)
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Infected individual
contagious for 8 days
before and 8 days after
appearance of rash.
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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
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Dominant feature is the appearance of
papulovesicular rash and pustules.
Incubation period is usually 12-14 days.
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Rash appears 3-4 days later.
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Death from smallpox results from:
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◦ Can be 4-5 days
◦ Abrupt onset of fever, chills, and muscle aches
◦ Papulovesicles most prominent on the head and
extremities.
◦ Become pustular over 10-12 days.
◦ Overwhelming virus infection
◦ Bacterial superinfection
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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)
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Candidiasis
Dermaphytosis
Pink eye
HSV1
River blindness
Contact lenses (Pseudomonas)
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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
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Common practice to treat eyes of newborn
infants with erythromycin.
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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.
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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
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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.
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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.
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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
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Chapter 22 Infections of the Digestive System
1. The most common source of gastrointestinal
infection in the developed world is
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A. Salmonella
B. Shigella
C. Escherichia
D. Campylobacter
E. Staphylococcus aureus
Correct answer is D. Campylobacter