Microbiology

Skin
Salt inhibits microbes.
Lysozyme hydrolyzes peptidoglycan.
Fatty acids inhibit some pathogens.
Defensins are antimicrobial peptides.
Figure 21.1

Mucous Membranes
Line body cavities.
The epithelial cells are attached to an extracellular matrix.
Cells secrete mucus.
Some cells have cilia.

Normal Microbiota of the Skin
Gram-positive, salt-tolerant bacteria
Staphylococci
Micrococci
Diphtheroids
Figure 14.1a

Microbial Diseases of the Skin
Exanthem: Skin rash arising from another focus
of the infection.
Enanthem: Mucous membrane rash arising from another focus of the infection.

Microbial Diseases of the Skin
Figure 21.2

Staphylococcal Skin Infections
S. epidermidis
Gram-positive cocci and coagulase-negative
Staphylococcus aureus
Gram-positive cocci and coagulase-positive
Leukocidin
Exfoliative toxin

Staphylococcal Biofilms
Figure 21.3

Staphylococcal Skin Infections
Folliculitis: Infections of the hair follicles.
Sty: Folliculitis of an eyelash.
Furuncle: Abscess; pus surrounded by inflamed tissue.
Carbuncle: Inflammation of tissue under the skin.

Staphylococcal Skin Infections
Impetigo of the newborn
Toxemia
Scalded skin syndrome
Toxic shock syndrome
Figure 21.4

Streptococcal Skin Infections
Streptococcus pyogenes
Group A beta-hemolytic streptococci
M proteins
Figure 21.5

Streptococcal Skin Infections
Erysipelas
Impetigo
Figures 21.6, 21.7

Invasive Group A Streptococcal Infections
Streptokinases
Hyaluronidase
Exotoxin A, superantigen
Cellulitis
Necrotizing fasciitis
Figure 21.8

Infections by Pseudomonads
Pseudomonas aeruginosa
Gram-negative, aerobic rod
Pyocyanin produces a blue-green pus
Pseudomonas dermatitis
Otitis externa
Post-burn infections

Acne
Comedonal acne occurs when sebum channels are blocked with shed cells.
Inflammatory acne
Propionibacterium acnes
Gram-positive, anaerobic rod
Treatment
Preventing sebum formation (isotretinoin)
Antibiotics
Benzoyl peroxide to loosen clogged follicles
Visible (blue) light (kills P. acnes)

Acne
Inflammatory acne (continued)
Nodular cystic acne
Treatment: isotretinoin

Warts
Papillomaviruses
Treatment
Removal
Imiquimod (stimulates interferon production)
Interferon

Poxviruses
Smallpox (variola)
Smallpox virus (orthopox virus)
Variola major has 20% mortality
Variola minor has <1% mortality
Monkeypox
Prevention by smallpox vaccination
Figure 21.9

Herpesviruses
Varicella-zoster virus (human herpes virus 3)
Transmitted by the respiratory route
Causes pus-filled vesicles
Virus may remain latent in dorsal root ganglia
Figure 21.10a

Shingles
Reactivation of latent HHV-3 releases viruses that move along peripheral nerves to skin.
Figure 21.10b

Herpes Simplex 1 and Herpes Simplex 2
Human herpes virus 1 and HHV-2
Cold sores or fever blisters (vesicles on lips)
Herpes gladiatorum (vesicles on skin)
Herpes whitlow (vesicles on fingers)
Herpes encephalitis (HHV-2 has up to a 70% fatality rate)
HHV-1 can remain latent in trigeminal nerve ganglia.
HHV-2 can remain latent in sacral nerve ganglia.
Acyclovir may lessen symptoms.

Measles (Rubeola)
Measles virus
Transmitted by respiratory route.
Macular rash and Koplik's spots.
Prevented by vaccination.
Encephalitis in 1 in 1,000 cases.
Subacute sclerosing panencephalitis in 1 in 1,000,000 cases.
Figure 21.14

Measles (Rubeola)
Figure 21.13

Rubella (German Measles)
Rubella virus
Macular rash and fever
Congenital rubella syndrome causes severe fetal damage.
Prevented by vaccination
Figure 21.15

A 1905 list of skin rashes included (1)measles, (2)scarlet fever, (3)rubella, (4)Filatow-Dukes (mild scarlet fever), and
(5)Fifth Disease: Erythema infectiosum
Human parvovirus B19 produces milk flu-like symptoms and facial rash.
Roseola
Human herpesvirus 6 causes a high fever and rash, lasting for 1-2 days.

Cutaneous Mycoses
Dermatomycoses: Tineas or ringworm
Metabolize keratin
Trichophyton: Infects hair, skin, and nails
Epidermophyton: Infects skin and nails
Microsporum: Infects hair and skin
Treatment
Oral griseofulvin
Topical miconazole

Cutaneous Mycoses
Figure 21.16

Subcutaneous Mycoses
Sporotrichosis
Sporothrix schenckii enters puncture wound
Treated with KI

Candidiasis
Candida albicans (yeast)
Candidiasis may result from suppression of competing bacteria by antibiotics.
Occurs in skin; mucous membranes of genitourinary tract and mouth.
Thrush is an infection of mucous membranes of mouth.
Topical treatment with miconazole or nystatin.

Candidiasis
Figure 21.17

Scabies
Sarcoptes scabiei burrows in the skin to lay eggs
Treatment with topical insecticides
Figure 21.18

Pediculosis
Pediculus humanus capitis (head louse)
P. h. corporis (body louse)
Feed on blood.
Lay eggs (nits) on hair.
Treatment with topical insecticides.
Figure 21.19

Macular Rashes
A 9-year-old girl with a history of cough, conjunctivitis, and fever (38°C) has a mcular rash that starts on her face and neck and is spreading to the rest of her body. Can you identify the cause of her symptoms
Measles
Rubella
Fifth disease
Roseola
Candidiasis

Bacterial Diseases of the Eye
Conjunctivitis (pinkeye)
Haemophilus influenzae
Various microbes
Associated with unsanitary contact lenses
Neonatal gonorrheal ophthalmia
Neisseria gonorrhoeae
Transmitted to a newborn's eyes during passage through the birth canal.
Prevented by treatment of a newborn's eyes with antibiotics

Bacterial Diseases of the Eye
Chlamydia trachomatis
Inclusion conjunctivitis
Transmitted to a newborn's eyes during passage through the birth canal
Spread through swimming pool water
Treated with tetracycline
Trachoma
Leading cause of blindness worldwide
Infection causes permanent scarring; scars abrade the cornea leading to blindness

Figure 21.20a
Trachoma

Viral Diseases of the Eye
Conjunctivitis
Adenoviruses
Herpetic keratitis
Herpes simplex virus 1 (HHV-1).
Infects cornea and may cause blindness
Treated with trifluridine