Page 118 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 14 Overview of the Major Pathogens & Introduction to Anaerobic Bacteria
TABLE 14–3 Optimal Oxygen Requirements of Representative Bacteria
Growth Under Following Conditions

Representative Organism
Aerobic
Bacterial Type
3+
0
Pseudomonas aeruginosa
Obligate aerobes
3+
Facultative anaerobes
1+
4+
Clostridium histolyticum
Aerotolerant organisms
Campylobacter jejuni
Microaerophiles Escherichia coli 4+ 1+ 1
0
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0
Obligate anaerobes
4+
Bacteroides fragilis
1
C. jejuni grows best (3+) in 5% O 2 plus 10% CO 2 . It is also called capnophilic in view of its need for CO 2 for optimal growth.
are divided into the spore formers (e.g., Clostridium) and
the nonspore formers (e.g., Bacteroides). In this book,
or a mixture of anaerobes plus facultative anaerobes. It is
thought that the facultative anaerobes consume sufficient
three genera of anaerobes are described as major bacterial
pathogens, namely, Clostridium, Actinomyces, and Bacte-
oxygen to allow the anaerobes to flourish.
roides. Streptococcus is a genus of major pathogens consist-
Three important findings on physical examination that
ing of both anaerobic and facultative organisms. The
arouse suspicion of an anaerobic infection are a foul-smell-
ing discharge, gas in the tissue, and necrotic tissue. In addi-
remaining anaerobes are less important and are discussed
in Chapter 27.
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mebooksfree.com mebooksfree.com mebooksfree.com tion, infections in the setting of pulmonary aspiration, mebooksfree.com
bowel surgery, abortion, cancer, or human and animal bites
frequently involve anaerobes.
Clinical Infections
Many of the medically important anaerobes are part of the
Laboratory Diagnosis
normal human flora. As such, they are nonpathogens in
Two aspects of microbiologic diagnosis of an anaerobic
their normal habitat and cause disease only when they leave
infection are important even before the specimen is cul-
those sites. The two prominent exceptions to this are Clos-
tured: (1) obtaining the appropriate specimen and (2) rap-
tridium botulinum and Clostridium tetani, the agents of
idly transporting the specimen under anaerobic conditions
botulism and tetanus, respectively, which are soil organ-
isms. Clostridium perfringens, another important human
not contain members of the normal flora to confuse the
pathogen, is found in the colon and in the soil.
interpretation. For example, such specimens as blood, pleu-
Diseases caused by members of the anaerobic normal
ral fluid, pus, and transtracheal aspirates are appropriate,
flora are characterized by abscesses, which are most fre- to the laboratory. An appropriate specimen is one that does
but sputum and feces are not.
quently located in the brain, lungs, female genital tract, bili-
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In the laboratory, the cultures are handled and incu-
ary tract, and other intra-abdominal sites. Most abscesses
bated under anaerobic conditions. In addition to the usual
chemical reactions, the special technique of gas chromatog-
raphy is important. In this procedure, organic acids such as
TABLE 14–4 Anaerobic Bacteria of Medical Interest
formic, acetic, and propionic acids are measured.
Morphology
Treatment
Spore-forming
+
Clostridium
rods

tion of antimicrobial drugs are indicated. Drugs commonly
Non–spore-form-
Actinomyces, Bifidobacterium,
used to treat anaerobic infections are penicillin G, cefoxitin,
Eubacterium, Lactobacillus,
ing rods + – None In general, surgical drainage of the abscess plus administra-
chloramphenicol, clindamycin, and metronidazole. Note,
Propionibacterium however, that many isolates of the important pathogen B.
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–
Bacteroides, Fusobacterium

fragilis produce α-lactamase and are thus resistant to peni-
+
Peptococcus, Peptostreptococ-
Non–spore-form-
cillin. Note also, that aminoglycosides such as gentamicin
ing cocci
cus, Streptococcus

Veillonella
oxygen-dependent process for uptake into the bacterial cell.
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