Page 232 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 27 Minor Bacterial Pathogens
Peptostreptococcus
Rhodococcus equi is a gram-positive bacterium whose shape
Peptostreptococci are anaerobic gram-positive cocci found
varies from a coccus to a club-shaped rod. It is a rare cause
as members of the normal flora of the mouth and colon.
of pneumonia and cavitary lung disease in patients whose
They are also isolated from abscesses of various organs,
usually from mixed anaerobic infections.
cell-mediated immunity is compromised. The diagnosis is
observing salmon-pink colonies that do not ferment most
Plesiomonas
carbohydrates. It may appear acid-fast and, if so, can be
Plesiomonas shigelloides is a gram-negative rod associated made by isolating the organism on laboratory agar and
confused with Mycobacterium tuberculosis. The treatment of
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with water sources. It causes self-limited gastroenteritis,
choice is a combination of rifampin and erythromycin.
primarily in tropical areas, and can cause invasive disease
(Rhodococcus equi used to be called Corynebacterium equi.)
in immunocompromised individuals.
Porphyromonas
Sarcina species are anaerobic gram-positive cocci grouped
in clusters of four or eight. They are minor members of the
Porphyromonas gingivalis and Porphyromonas endodontalis
normal flora of the colon and are rarely pathogens.
are anaerobic gram-negative rods found in the mouth.
They cause periodontal infections, such as gingivitis and
dental abscesses.
Spirillum minor is a gram-negative, spiral-shaped rod that
causes rat-bite fever (“sodoku”). The disease is character-
Propionibacterium Spirillum
ized by a reddish brown rash spreading from the bite,
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Propionibacteria are pleomorphic, anaerobic gram-positive
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accompanied by fever and local lymphadenopathy. The
rods found on the skin and in the gastrointestinal tract.
diagnosis is made by a combination of microscopy and
Propionibacterium acnes is part of the normal flora of the
skin and can cause catheter and shunt infections. It is
involved in mixed infections associated with cat and dog
Streptobacillus
bites and in head and neck abscesses.
Streptobacillus moniliformis is a gram-negative rod that
Propionibacteria acnes is also involved in the pathogen-
causes another type of rat-bite fever (see Spirillum, preced-
esis of acne, a condition that affects more than 85% of
ing paragraph).
teenagers. The pathogenesis of acne involves impaction of
the sebaceous gland followed by inflammation caused by
the presence of P. acnes. The pustules of acne are composed
of sebum, inflammatory cells such as neutrophils and lym-
In August 2005, it was reported that Streptococcus suis
phocytes, and the organism. Antibiotics, such as erythro- Streptococcus suis
caused the death of 37 farmers in China. The illness is char-
mycin, administered either topically or orally, are effective
acterized by the sudden onset of hemorrhagic shock. This
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especially when coupled with other agents such as benzoyl
species is known to cause disease in pigs but only rarely in
peroxide or retinoids.
people prior to this outbreak. Spread of the bacteria from
Pseudomonas pseudomallei
Tropheryma
Pseudomonas pseudomallei (also known as Burkholderia
Tropheryma whipplei is the cause of Whipple’s disease, a
pseudomallei) is a gram-negative rod that causes melioido-
sis, a rare disease found primarily in Southeast Asia. The
rare disease characterized by prolonged weight loss, diar-
organism is found in soil and is transmitted most often
rhea, and polyarthritis. Without antibiotic treatment, it is
when soil contaminates skin abrasions. This disease has
affected tissue, especially in the small intestine, are com-
been seen in the United States, because infections acquired
monly seen. The reservoir of the organism, its mode of
by members of the armed forces during the Vietnam War
transmission, and pathogenesis are unknown.
have reactivated many years later. The acute disease is char- ultimately fatal. Infiltrates of “foamy” macrophages in
The nature of this organism was unknown for many
acterized by high fever and bloody, purulent sputum.
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years. In 1992, it was identified as an actinomycete when
Untreated cases can proceed to sepsis and death. In the
ribosomal RNA taken from bacilli seen in duodenal lesions
chronic form, the disease can appear as pneumonia or lung
abscess or may resemble tuberculosis. Diagnosis is made by
Tropheryma is an intracellular organism that has been
culturing the organism from blood or sputum. The treat-
grown in human cell culture, but that procedure is not used
ment of choice is ceftazidime, which is administered for
several weeks.
to diagnose the disease. Laboratory diagnosis is typically
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