Bacterial Skin Infections
Bacteria are residents of the skin shared with other people in a variety of
ways. Infections may result from skin injury, insect bites, but often arise
spontaneously by bacterial invasion of hair follicles and skin glands. A
golden-crusted surface infection with streptococci is called impetigo that can
be treated with a 10-day course of a topical antibiotic preparation like
bacitracin ointment. Many organisms grow in hairs follicle causing
folliculitis. Hot tubs, pools, or whirlpools may spread bacteria such as
Pseudomonas aeruginosa that causes folliculitis. Loofah sponges support the
growth of bacteria and can be a source of infection. A boil is
a localized abscess created by the growth of staphylococci in a hair follicle.
Spreading infections, described as cellulitis, are commonly caused by group A
streptococci. Rarely, infections with virulent stains of Strep A progress to
cell death in deep tissue (necrotising fasciitis).
Common acne is an example of ecological problems on the skin. The disfiguring
pimples and nodules of acnes are infections of the oil glands (pilosebaceous
ducts) in the skin. The infectious agents are common bacteria, propionibacterium
acnes that grow well in the oily secretions of the glands (sebum).Oil secretion is increased by testosterone, the male sex hormone. Oil
secretion increases in adolescent males and females.
Since acne lesions
appear on the face primarily their negative impact on appearance and social
status is a major concern to teenagers and young adults. Acne persisting or
arising for the first time in adults is the most common cause of cosmetic
Careful skin cleaning with some method of removing the surface
stratum corneum skin layer are essential strategies of controlling acne. The use
of antibiotics and/or antibacterial topical agents is the third method of
Hand cleansing in hospitals is an important method of infection
control. Cleaning skin wounds with warm water and antiseptic detergents
is a primary method of infection control. Topical antibiotics and a protective bandage are secondary infection control measures.
The identification of infecting organisms is not easy. Skin swabs will
grow a mixture of organisms, suggesting the need for an unnecessarily broad
antibiotic coverage. Antibiotics that inhibit the growth of group A streptococci and Staph. aureus
are used when an infection is not controlled by local measures. Bacterial
resistance to many antibiotics has made most penicillins obsolete, so that the choice of antibiotic
requires physicians expertise and knowledge of local bacterial strains.
Fungal Skin Infections
Fungi are found everywhere and yeasts form part of the normal skin flora.
Fungal infections of the skin, hair and nails are common skin diseases. Fungi
can infect the skin of people of all ages. Increased incidence occurs in
immune compromised patients who have AIDS, diabetes, or are being treated with
chemotherapeutic agents and therapy directed at reducing inflammation. People
with diabetes and people who are simply getting older have more skin infections.
Skin infections can divided into the most common superficial group that stays
in the outer layers of the skin and an invasive group that extends beyond the
skin in adjacent tissues and may spread to other organs. Invasive skin
infections such as blastomycosis often develop after a primary lung infection is
established. The infecting yeast travel in the blood from the lung to skin
Fungal infections are probably the most common cause of skin abnormalities in
part because fungi become permanent residents of the skin. Most fungal
infections are superficial but a few a invasive and dangerous. Fungi grow best
where is there is moisture, so that skin inflammation between the finger and
toes, in the groin and around the anus is often caused by fungal growth. The
skin of the scalp is commonly infected with fungi that cause itching and
dandruff. Nail infections cause discoloration and deformity.
Physicians can attempt to identify infecting fungi by scraping scaly lesions
to obtain specimens. Nail samples are obtained scrapings from under the
nail. The specimen is placed on a glass slide; a few drops of potassium
hydroxide are added to digest keratin and the slide is examined under the
microscope for fungal elements. Specimens can be sent for culture on agar
containing Sabouraud medium, combined with antibiotics to eliminate bacteria and
with cycloheximide to inhibit saprophytic fungi. Growth is usually apparent in 3
to 14 days. Dermatophyte test medium culture can be used in the office and is
both accurate and inexpensive. When both KOH preparations and cultures are
negative, a biopsy may be useful in identifying the infecting organism, usually
by special tissue stains such as periodic acid-Schiff or Gomori methenamine-silver