Download an update on mixed aerobic and anaerobic infections

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AN UPDATE ON MIXED AEROBIC AND ANAEROBIC INFECTIONS*
—
John G. Bartlett, MD
ABSTRACT
In many respects, anaerobic microbiology has
fallen out of the spotlight of infectious diseases, in
part due to the extraordinarily successful effort to
recognize and treat these infections. Today, anaerobic cultures of clinical specimens are rarely performed and the treatment is fairly standardized.
This article reviews the microbiology and pathogenesis of anaerobes, the concept of synergy in
mixed infections, and specific anaerobic infections
such as lung infections, intra-abdominal sepsis, and
female genital tract infections, and a historical
overview of the study of anaerobic infection. The
more recent developments include some disturbing
trends in in vitro sensitivity test results and a continuing controversy about the role of the microbiology
lab in these infections.
(Advanced Studies in Medicine 2002;2(4):104-109)
*This article is based on a presentation given by
Dr Bartlett at a satellite symposium at the 39th Annual
Meeting of the Infectious Diseases Society of America.
Correspondence to: John G. Bartlett, MD, Chief,
Infectious Diseases Division, Johns Hopkins Medical School,
1830 East Monument Street, Suite 439, Baltimore, MD
21287-0003; Tel: 410-955-7634; Fax: 410-955-7889;
E-mail: [email protected].
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naerobes were discovered by Louis
Pasteur in 1862 when he grew
Clostridium butyricum. Veillon and
Zuber in 1893 wrote the first report of
a clinical isolate of an anaerobe,
Bacteroides fragilis. Its name was based on the difficulty of growing it in a laboratory compared with
C butyricum. In fact, B fragilis is quite easy for a laboratory to grow. The Veillon and Zuber publication is
considered a first recognition of anaerobes.1
A variety of clinical studies from 1909 to about 1938
are now considered classical studies of anaerobes.
Schottmueller, in 1910, observed that puerperal sepsis
could be caused by Group A streptococci, but the anaerobes were far more important.2 David Smith conducted
his famous studies at Duke University (1927-1930) on
lung abscesses showing that the bacterium in the gingival crevice matched those at autopsy and postulated aspiration as the mechanism. Altemeier wrote his famous
papers in 1938 on intra-abdominal sepsis finding recovered anaerobes in 99 of 100 people with appendicitis. In
one of his papers, he named the essential diagnostic sign
of anaerobic infection, putrid discharge.3
The period from 1939 to 1964 was a time of gross
neglect in research on anaerobes. Medical schools’ teachings on anaerobes focused on discussions of tetanus, botulism, and gangrene. That was the total menu of
anaerobic bacteria and anaerobic infections. The period
from 1965 to 1980 is therefore a “Renaissance Period” in
anaerobic microbiology. What changed? Three major
advances occurred: 1) the Virginia Polytechnic Institute
established a formal taxonomy, to help remove the confusion that existed until then; 2) the GasPak jar became
an easy way for clinical laboratories to handle oxygen-
A
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sensitive forms (few research laboratories could work
with anaerobes before this); and 3) clinical studies were
spearheaded by Sid Fiengold who devoted his life’s work
to anaerobic bacteria and “put them on the map.” For
this, he is often referred to as the Father of the
Renaissance. As a result, clindamycin became the drug of
choice for anaerobic infections in the United States and
metronidazole was used in the United Kingdom.
Table 1 shows an example of the current nomenclature, which has undergone some major changes. For
example, Prevotella sp are now the former B melaninogenicus, which is a group of black pigmented strains.
A now-famous paper from John Washington II
showed the results of his experience with culturing gramnegative rods in blood. As shown in Table 2, Escherichia
coli was the most common, as it was in most other studies from that period; more than half of the cases were due
to E coli. Bacteroides bacteremia was second to E coli.4
Since 1980, Bacteroides bacteremia is rarely seen, testifying to the success of the campaign in the 1970s to raise
awareness about anaerobes. B fragilis is recovered so
infrequently in blood cultures in the year 2001 that
many laboratories are considering discontinuation of the
anaerobic blood culture bottle as a method of cost reduction for the laboratory. In fact, the clinical laboratory at
Johns Hopkins has an anaerobic chamber plus all of the
appropriate equipment for transporting specimens, but
still seem to infrequently detect anaerobes.
With that in mind, James Dick, PhD, Associate
Professor in the Department of Pathology who also
heads the microbiology lab at Johns Hopkins, was
asked to record positive blood cultures for E coli and
Bacteroides for a period of 1 year. The results were surprising: 22 positive blood cultures for Bacteroides spp
from 13 patients, and 192 positive cultures for E coli
from 196 patients.
The period of gross neglect in the 1940s through
the early 1960s was followed by a period of great
emphasis. Many laboratories were doing extensive
studies of anaerobic bacteria and the annual meetings
of the Infectious Diseases Society of America and the
Interscience Conference on Antimicrobial Agents and
Chemotherapy (ICAAC) were heavily focused on
anaerobes—the bacteria, infections, culturing, clinical
features, etc. By contrast, there was not a single session
at the 40th or 41st ICAAC on anaerobic bacteria or
anaerobic infection.
One of the main reasons behind the current shift in
emphasis is the existing awareness of anaerobes and
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Table 1. Clinically Important Anaerobes Seen
with Greatest Frequency
Gram-negative Bacteria
Bacteroides fragilis group
– B fragilis
– B thetaiotamicron
– B distasonis
– B ovatus
– B vulgatus
Pigmented Prevotella (formerly B melaninogenicus)
– P intermedia
– P melaninogenics
– P corporis
– P denticola
– P loescheii
– P nigrescens
Prevotella (other)
– P bivia (formerly B bivius)
– P disiens (formerly B disiens)
– P oralis (formerly B oralis)
Porphyromonas asaccharolyticus (formerly B asaccharolyticus)
Fusobacterium
– F nucleatum
– F necrophorum
– F varium
Bilophila
– B wadsworthia
Table 2. Gram-negative Bacteremia: Mayo Clinic
(July 1968 to December 1970)
Bacterium
E coli
Bacteroides
Klebsiella
P aeruginosa
Enterobacter
Proteus sp
S marcenscens
No. of Isolates
533
332
245
213
90
88
54
Data from: Washington JA 2nd. Comparison of two commercially available
media for detection of bacteremia. Appl Microbiol. 1971;22:604-607.
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our success in identifying and treating them. Most
infectious disease specialists know that clindamycin
should be used to treat a lung abscess, because it is
most commonly an anaerobic lung infection and that
is the standard treatment. Culturing is not necessary.
Because anaerobic bacteriology is not cost effective,
there is a movement to eliminate anaerobic culturing
in laboratories.
Table 3 outlines how much it costs to identify an
anaerobe and conduct sensitivity tests, based on data
gathered at Johns Hopkins’ laboratories. Included are
the labor, reagents, and overhead. Clearly the costs are
not enormous, but this is to be part of an overall diminishing emphasis on microbiology, which had, until very
recently, become an epidemic in American medicine.
Table 3. Costs of Blood Cultures:
Johns Hopkins Hospital (October 15, 2000 to
October 15, 2001)
Bacteroides sp
E coli
Identification
$12
$5-7
Susceptibility tests
$20
Data from personal communication, J. Dick, PhD. October 18, 2001.
ANAEROBIC MICROBIOLOGY
Anaerobic infections are endogenous; there is only
one anaerobic infection that can be transmitted from
patient to patient—Clostridium difficile. Most anaerobic infections are polymicrobial, and they often produce gas in the soft tissue and a putrid discharge, at
least in the late stages.
Mucosal surfaces such as saliva, teeth, the stomach,
ileum, and vagina usually share a 1:1 ratio of anaerobic to aerobic bacteria, although the vagina may have
as high as 5 times more anaerobes than aerobes. The
gingival crevice and colon have a 1000:1 ratio of
anaerobic to aerobic bacteria. So, dental infections and
colonic perforation are associated with very high rates
of anaerobic infection. Table 4 distinguishes the frequent and rare anaerobic infections. Most anaerobic
infections are endogenous, meaning they originate
from the host’s flora. An exception is urinary tract
infections (UTIs). UTIs are endogenous but rarely
involve anaerobes. UTIs originate from the urethral
flora, which is teeming with anaerobes, but these
organisms cannot replicate in the pO2 of urine. The
same applies to spontaneous bacterial peritonitis.
PATHOGENESIS
Anaerobes are the primary cause of abscess formation at most anatomic sites (Table 5).5-11 The presumed biologic explanation is the capsular
polysaccharide which has been studied with B fragilis and appears to be abscessogenic in animals. That
is, intraperitoneal abscesses can be produced in ani-
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Table 4. Anaerobic Bacterial Infections
Frequent
Head and neck
Rare
Brain abscess
Dental infections
Space infections
(Chronic sinusitis)
Chronic otitis
Meningitis
Pharyngitis
Chest
Aspiration pneumonia
Lung abscess
Empyema
Bronchitis
Abdomen
Peritonitis
Phlegmon/abscess
Cholecystitis
SBP
GU tract
Female genital tract
UTIs
STDs
Acute sinusitis
Acute otitis
GU = genitourinary; UTIs = urinary tract infections; STDs = sexually transmitted diseases; SBP = spontaneous bacterial peritonitis.
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mals with the injection of capsular material from the
B fragilis.12 Further, Tzianobos et al showed in 1993 that
the charge of the B fragilis polysaccharide capsule (ie,
the positively charged amino groups and negatively
charged carboxyl or phosphate groups) is critical for this
biological result; chemical modification has shown that
the oppositely charged groups are an important motif
for abscess formation. In their 1994 study, the
Salmonella capsule, which normally contains only one
carboxyl group, was chemically modified to possess
charges which then gave this organism the property of
producing abscesses.13,14
Most anaerobic bacteria do not have biologically
active endotoxin; the most notable exception is
Fusobacterium necrophorum, which is associated with
Lemierre’s disease and septic shock. B fragilis does not
cause septic shock. One common pathogenic mechanism
of anaerobes focuses on synergy, because they are usually
polymicrobial infections. Synergy is the correlated action
of 2 or more organisms—something that cannot be
achieved by a single organism. Meleney conducted the
sentinel study of anaerobic synergy. He demonstrated
that when a mouse is coinfected with S aureus and an
anaerobic streptococcus, the characteristic lesion forms.
But inoculating with only one or the other organism
alone does not produce Meleney’s gangrene.15
Does synergy have anything to do with this? A
study was conducted in the late 1970s using a Wistar
rat model of intra-abdominal sepsis that, following
intraperitoneal challenge with the mixed flora of stool,
showed that there is an early active peritonitis stage
and a late abscess stage (Figure 1). For peritonitis and
bacteremia, E coli was critical and for abscess formation B fragilis was critical. There was no synergy. E coli
seemed to be totally responsible for the early stage associated with bacteremia and B fragilis was responsible for
the late stage with abscess formation.16 This was supported by studies of antibiotic probes using gentamicin,
showing that gentamicin was active against E coli and
clindamycin was active against anaerobes but not active
against E coli. Gentamicin reduced mortality but had no
effect on abscesses. Clindamycin had no effect on mortality but prevented abscesses (Figure 2).17
Table 5. Anaerobes in Abscesses
Site
Frequent
Source (Ref. No.)
Brain
16/18 (89%)
Dental
Lung
Intra-abdominal
Tubo-ovarian
Cutaneous
Prostatic
29/31 (94%)
53/39 (93%)
67/72 (94%)
32/37 (86%)
81/135 (60%)
16/18 (94%)
Heineman and Braude
19638
Roser et al 19777
Bartlett et al 19746
Onderdonk et al 19745
Golde et al 197711
Meislin et al 19779
Bartlett et al 198110
Data from references 5-11.
Figure 1. Stages of Peritoneal Infection
ANAEROBIC INFECTIONS
LUNG INFECTIONS
The bacteriology of anaerobic pulmonary infections has been studied in more than 300 cases pub-
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Data from reference 16.
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lished in 2 studies.18,19 Of the 865 total anaerobes, the
3 major isolates were pigmented Prevotella (n = 139),
Bacteroides spp (n = 117), and peptostreptococci (n =
165). Others included other spp of Prevotella (n = 40),
Fusobacteria (n = 90), and Clostridia (n = 30).
INTRA-ABDOMINAL SEPSIS
The major anaerobic pathogens are B fragilis, peptostreptococci, and Clostridia. In one study, 808
patients with polymicrobial infection of the peritoneal
cavity or nonvisceral soft tissues were candidates for
treatment with 1 of 2 antibiotic regimens. Of the isolated anaerobic organisms, E coli and Bacteroides sp
were the most common.20
FEMALE GENITAL TRACT INFECTIONS
In pelvic inflammatory disease, the major isolates
are Prevotella bivia, Prevotella disiens, Bacteroides spp,
and peptostreptococcus.21
Figure 2.Antibiotic Probes of Peritoneal Infection
Mortality
Control
Abscess
formation
100%
37%
4%
Gentamicin
98%
Clindamycin
35%
5%
Gentamicin &
Clindamycin
9%
6%
Data from reference 17.
TREATMENT OF ANAEROBIC INFECTIONS
Table 6 lists the classes of antibiotics and their
activity against anaerobes. Of note, 4 antibiotics are
always active against anaerobic bacteria: metronidazole, imipenem, and a β-lactam/β-lactamase inhibitor.
There are only about 6 recorded isolates resistant to
metronidazole, but they are clearly very rare. The
macrolides/ketolides are active against most anaerobes
but not fusobacteria. Tetracycline is quite variable, and
vancomycin and linezolid are active against gram-positive anaerobes.
With regard to resistance, Snydman et al measured
the activity of clinical isolates of B fragilis from 1990
to 1996 for 4000 strains obtained from 8 different
centers. The results showed an increase in resistance to
cefotoxitin, clindamycin, and piperacillin.22,23 A more
recent survey by Aldridge et al shows that 100% of 3
most common pathogens (B fragilis, Prevotella, and
peptostreptococcus) were uniformly sensitive to
piperacillin/tazobactam, imipenem, and metronidazole. Also, 100% of Prevotella and peptostreptococci
but only 93% of B fragilis were sensitive to cefotoxitin.
Lower susceptibility rates were noted for penicillin G,
ciprofloxacin, and clindamycin. The results highlight
the variability in resistance patterns among anaerobes,
which may be both regional and temporal. The results
seem to be sufficiently predictable so that most laboratories do not perform these tests.24
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Table 6. Antibiotics vs Anaerobes
Always Active
Metronidazole
Imipenem
β-lactam/β-lactamase inhibitors
Usually Active
Cefotoxitin/cefotetan
Clindamycin
Piperacillin
Variable Activity
Macrolides/ketolides
Gatifloxacin/moxifloxacin
Tetracycline
Vancomycin/linezolid
Cephalosporins
Never Active
Aminoglycosides
Trimethoprim-sulfamethoxazole
Aztreonam
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CONCLUSION
Anaerobic bacterial microbiology went through a
substantial evolution of change so that diagnosis and
treatment are now standardized to recognize these
microbes and treat them without assistance from the
laboratory.
REFERENCES
1. Veillon A, Zuber A. Sur quelques microbes strictment anaerobies et leur role dans la pathologie humaine. C R Soc
Biol. (Paris) 1897;49:253.
2. Schottmueller H. Allgemeinen krankenhaus hamburg-eppendorf. Mitt Grenzt Med Chir. 1910;21:450.
3. Altemeier WA. Bacterial flora of acute perforated appendicitis with peritonitis: bacteriologic study based upon 100
cases. Ann Surg. 1938;107:517.
4. Washington JA 2nd. Comparison of two commercially
available media for detection of bacteremia. Appl
Microbiol. 1971;22:604-607.
5. Onderdonk AB, Weinstein WM, Sullivan NM, Bartlett JG,
Gorbach SL. Experimental intra-abdominal abscesses in
rats: quantitative bacteriology of infected animals. Infect
Immunol. 1974;10:1256-1259.
6. Bartlett JG, Gorbach SL, Tally FP, Finegold SM.
Bacteriology and treatment of primary lung abscess.
Am Rev Respir Dis. 1974;109:510-518.
7. Roser SM, Chow AW, Brady FA. Necrotizing fasciitis.
J Oral Surg. 1977;35:730-732.
8. Heineman HS, Braude AL. Anerobic infection of the brain:
observations on eighteen consecutive cases of brain
abscess. Am J Med. 1963;35:582.
9. Meislin HW, Lerner SA, Graves MH, et al. Cutaneous
abscesses. Anaerobic and aerobic bacteriology and outpatient management. Ann Intern Med. 1977;87:145-149.
10. Bartlett JG, Gorbach SL. Anaerobic bacteria in suppurative
infections of the male genitourinary system. J Urol.
1981;125:376-378.
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11. Golde SH, Israel R, Ledger WJ. Unilateral tuboovarian
abscess: a distinct entity. Am J Obstet Gynecol.
1977;127:807-810.
12. Kasper DL, Lindberg AA, Weintraub A, Onderdonk AB,
Lonngren J. Capsular polysaccharides and lipopolysaccharides from two strains of Bacteroides fragilis. Rev Infect Dis.
1984;6(suppl 1):S25-S29.
13. Tzianabos AO, Onderdonk AB, Rosner B, Cisneros RL,
Kasper DL. Structural features of polysaccharides that induce
intra-abdominal abscesses. Science. 1993;262:416-419.
14. Tzianabos AO, Onderdonk AB, Zaleznik DF, Smith RS,
Kasper DL. Structural characteristics of polysaccharides that
induce protection against intra-abdominal abscess formation. Infect Immunol. 1994;62:4881-4886.
15. Meleney FL. Clinical Aspects and Treatment of Surgical
Infections. Philadelphia, PA: WB Saunders; 1949.
16. Bartlett JG, Onderdonk AB, Louie T, Kasper DL, Gorbach
SL. A review. Lessons from an animal model of intra-abdominal sepsis. Arch Surg. 1978;113:853-857.
17. Weinstein WM, Onderdonk AB, Bartlett JG, Louie TJ,
Gorbach SL. Antimicrobial therapy of experimental intraabdominal sepsis. J Infect Dis. 1975;132:282-286.
18. Bartlett JG. Anaerobic bacterial infections of the lung and
pleural space. Clin Infect Dis. 1993;16(suppl 4):S248-S255.
19. Marina M, Strong CA, Civen R, Molitoris E, Finegold SM.
Bacteriology of anaerobic pleuropulmonary infections: preliminary report. Clin Infect Dis. 1993;16(suppl 4):S256-S262.
20. Stone HH, Strom PR, Fabian TC, Dunlop WE. Third-generation cephalosporins for polymicrobial surgical sepsis. Arch
Surg. 1983;118:193-200.
21. Sweet RL. Role of bacterial vaginosis in pelvic inflammatory
disease. Clin Infect Dis. 1995;20(suppl 2):S271-S275.
22. Snydman DR, McDermott L, Cuchural GJ Jr, et al. Analysis
of trends in antimicrobial resistance patterns among clinical
isolates of Bacteroides fragilis group species from 1990 to
1994. Clin Infect Dis. 1996;23(suppl 1):S54-S65.
23. Snydman DR, Jacobus NV, McDermott LA, et al. Multicenter
study of in vitro susceptibility of the Bacteroides fragilis
group, 1995 to 1996, with comparison of resistance
trends from 1990 to 1996. Antimicrob Agents Chemother.
1999;43:2417-2422.
24. Aldridge KE, Ashcraft D, Cambre K, Pierson CL, Jenkins
SG, Rosenblatt JE. Multicenter survey of the changing in
vitro antimicrobial susceptibilities of clinical isolates of
Bacteroides fragilis group, Prevotella, Fusobacterium,
Porphyromonas, and Peptostreptococcus species.
Antimicrob Agents Chemother. 2001;45:1238-1243.
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