Bacteriological study of root canals associated with periapical
abscesses
Ezilmara Leonor Rolim de Sousa, DDS, MSc, Caio Cezar Randi Ferraz, DDS, MSc, PhD,
Brenda Paula Figueiredo de Almeida Gomes, DDS, MSc, PhD, Ericka Tavares Pinheiro, DDS,
MSc, Fabrı́cio Batista Teixeira, DDS, MSc, PhD, and Francisco José de Souza-Filho,
DDS, MSc, PhD, Piracicaba, Brazil
UNIVERSITY OF CAMPINAS
Objective. The aim of this study was to identify microorganisms from root canals with periapical abscesses and to
ascertain the susceptibility of Peptostreptococcus prevotii and Fusobacterium necrophorum to antimicrobials.
Study design. Thirty root canals were microbiologically sampled by using sterile paper points. The concomitant
microorganisms were identified through the use of established methods. The susceptibility of P prevotii and F
necrophorum to antimicrobials was evaluated by using the E test method.
Results. A total of 117 different bacterial strains were recovered, including 75 strict anaerobes or microphilic species.
The most frequently isolated strict anaerobes were P prevotii, Peptostreptococcus micros, and F necrophorum.
Facultative bacteria such as Gemella morbillorum and Streptococcus mitis were also found, albeit less frequently. The
data revealed that P prevotii and F necrophorum were susceptible to the tested antibiotics.
Conclusions. Gram-positive anaerobic bacteria predominate in the mixed microbiota of root canals with periapical
abscesses. Moreover, P prevotii and F necrophorum are susceptible to the tested antibiotics.
(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;96:332-9)
Endodontic therapy plays an important role in removing bacteria, their by-products, and their substrates by
disrupting, then destroying, the microbial ecosystem
through chemicals and mechanical methods. If root
canal instrumentation and treatment are not performed,
the infection can reach the periapical tissue, causing
inflammatory alterations in this region.1
Many studies have been performed to identify the
microorganisms present in infected root canals and to
correlate them with clinical signs and symptoms.2-4
Periapical abscesses are characterized clinically by pain
or swelling, or both.5 Such abscesses are a significant
odontogenic infection because of their potential to
progress through the cortical bone and to spread over
the sinuses and other facial spaces of the head and neck,
with possibly lethal consequences. Therefore, early recognition of the etiology of periapical abscesses is essential to the development of appropriate therapies.6
Most periapical abscesses do not require antibiotic
therapy or bacteriologic investigation. Patients who
need antibiotics as an adjunct to root canal therapy—
medically compromised individuals, for example—
usually respond well to empirical treatment that is not
predicated on the results of culture and susceptibility
testing.
Several studies have revealed that the microbiota
associated with periapical abscesses are usually
polymicrobial, with the mean number of species ranging from ⬍3 to 8.5 per specimen.6-11 However, it is
important to periodically obtain culture and susceptibility data to monitor possible changes in the types and
antibiotic resistance of microorganisms responsible for
periapical abscesses.12,13 The E test system (AB BIODISK, Solna, Sweden), a plastic strip with a continuous
gradient of antibiotic with 15 minimum inhibitory concentration (MIC) dilution, is a simple and reliable
method for susceptibility testing of all anaerobic bacteria.14
The aim of this study was to identify microorganisms
in root canals with periapical abscesses and to determine the susceptibility of Peptostreptococcus prevotii
and Fusobacterium necrophorum to benzylpenicillin,
amoxicillin, amoxicillin and clavulanate potassium,
metronidazole, clindamycin, erythromycin, and
azithromycin.
MATERIAL AND METHODS
Supported by FAPESP—Grants 1996/05584-3, 1999/08504-9, and
2000/13683-9 — and CNPq—Grant 520277/99-6.
Received for publication Sep 30, 2002; returned for revision Nov 13,
2002; accepted for publication Mar 21, 2003.
© 2003, Mosby, Inc. All rights reserved.
1079-2104/2003/$30.00 ⫹ 0
doi:10.1016/S1079-2104(03)00261-0
332
Patients
In accordance with the protocols of the Ethical Committee at the Piracicaba School of Dentistry (Piracicaba, SP, Brazil), the microbial samples were obtained
from adult patients who presented at the emergency
department at the Piracicaba School of Dentistry. Pa-
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
Volume 96, Number 3
tients who had received antibiotic therapy in the 6
months before presenting at the emergency department
and those in whom it was not possible to reach an
adequate length of the root canal to take the microbiologic sample were excluded from our study. Therefore,
of 70 patients initially examined, samples for this study
were collected from 30 root canals (30 patients). The
patients ranged from 11 to 53 years of age. The population consisted of 13 male patients and 17 female
patients, all of whom had pain and swelling. Furthermore, their symptoms met the criteria for acute periapical abscesses described by Torabinejad and Walton.15
Patient sampling
The microbiologic investigation was performed under strict aseptic conditions. A standardized routine of
root canal therapy was instituted, and in each case a
single root canal was sampled. In multirooted teeth,
only the largest canal was sampled to preserve the
identity of a single endodontic/microbiologic ecosystem. Necrotic pulp tissue was observed in 27 root
canals and previous endodontic treatment in 3.
Before sampling the contents of the root canal, the
restorations and carious lesions were completely removed. Then the tooth was isolated by using a rubber
dam disinfected with 5.25% sodium hypochlorite for 30
seconds applied with a cotton-tipped applicator.16 The
sodium hypochlorite was neutralized with 5% sodium
thiosulfate,17 and sterile saline solution was used as a
final wash. The access cavity was prepared with sterile
burs (Gates-Glidden, Dentsply, Maillefer, Ballaigues,
Switzerland) but without the use of a water spray,
which allowed us to preserve the contents of the radicular pulp tissue. The coronal necrotic pulp tissue was
carefully removed, and subsequent enlargement of the
coronal third of the root canal was performed to prevent
contamination of the sampling paper point by the contents of the coronal pulp. When the tooth had an atresic
root canal that interfered with the penetration of the
paper point, patency was accomplished through minimal instrumentation with a No. 10 file (C⫹ Files,
Dentsply, Maillefer, Ballaigues, Switzerland), without
any irrigant. Pre-existing root fillings were removed by
mechanical means as completely as possible, and, in
these cases, the canal was copiously irrigated with a
sterile saline solution to remove treatment residues
before our microbial investigations were begun. In no
case was the sampling preceded by irrigation with any
chemically active agent. In patients in whom a dry
canal was identified, 0.5 mL of sterile saline solution
was injected before sampling.
Microbiologic samples were then collected by introducing sterile paper points (Tanari-Tariman Ltda, Manaus, AM, Brazil) to the full length of the canal, which
de Sousa et al 333
was determined through standard initial radiographs.
The paper points were held in place for 60 seconds
under a continuous flow of nitrogen to preserve the
anaerobic bacteria.18 The teeth in which it was not
possible to reach the full length of the canal were
excluded from the microbiologic sampling.
The paper points were immediately placed in an
Eppendorf tube containing 1.0 mL of Viability Medium
Göteborg Agar (VMGA) III transport medium17,19 and
were submitted to the endodontic microbiology laboratory within 15 minutes. Inside the anaerobic workstation (Don Whitley Scientific, Bradford, England), the
Eppendorf tube was vortexed for 1 minute. The VMGA
III medium was diluted to 1/10, 1/100, 1/1000, and
1/10,000 by using prereduced suspension medium (fastidious anaerobe broth; Lab M, Bury, England). Fifty
microliters of each dilution were inoculated onto plates
containing 5% defibrinated sheep blood–fastidious
anaerobe agar (FAA; Lab M) and incubated in the
anaerobic workstation at 37°C in an atmosphere of 10%
H2, 10% CO2, and 80% N2 for 2, 5, and 14 days to
differentiate strict anaerobes from facultative anaerobes. Selecting for gram-positive anaerobes and actinomycetes involved the use of a 5% defibrinated sheep
blood–FAA ⫹ nalidixic acid (0.001% wt/vol; Lab M)
agar plate at 37°C anaerobically, for 2, 5, and 14 days.
Selecting for gram-negative anaerobes involved the use
of a 5% defibrinated sheep blood–FAA ⫹ nalidixic acid
⫹ vancomycin (0.00025% wt/vol; Lab M) agar plate at
37°C anaerobically, for 2, 5, and 14 days. Selection for
Clostridia and other anaerobes involved the use of a 5%
defibrinated sheep blood–FAA ⫹ neomycin (0.0075%
wt/vol; Lab M) agar plate at 37°C anaerobically, for 2,
5, and 14 days.
Fifty microliters of the dilutions were also inoculated
onto plates containing 5% sheep blood ⫹ brain-heart
infusion agar (Oxoid, Hampshire, England), which
were aerobically incubated at 37°C and examined after
18 hours and 2 days, to differentiate aerobes from
facultative anaerobes.
Identification of bacteria
After the incubation period, a bacterial morphology
analysis was performed with light stereomicroscopy
(Lambda Let 2; Atto Instruments Co, Hong Kong,
China). The different colony types were subcultured
onto fresh prereduced medium (FAA ⫹ 5% sheep
blood) to obtain pure cultures. Different colonies were
selected on the basis of their appearance on the agar
plates. The pure cultures were initially identified in
terms of their Gram morphology, gaseous requirements, and ability to produce catalase.
Each colony obtained by anaerobic incubation was
used to inoculate 2 plates of fresh FAA ⫹ 5% sheep
334 de Sousa et al
blood (Lab M). One plate was incubated aerobically
and the other anaerobically, both for 2 days. The bacterial growth on each plate was compared to determine
the gaseous requirements of the bacterial species.
These procedures allowed us to make the primary
identification of the strain as gram-positive or gramnegative, coccus or bacillus, catalase-positive or
catalase-negative, and aerobic or anaerobic. On the
basis of these primary results, the appropriate kit for
identification was selected.
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
September 2003
Table I. Frequency of the number of bacterial species
per root canal
No. of species per root canal
Frequency (n ⫽ 30)
%
0 (no growth)
1
2
3
4
5
6
7
8
9
10
1
3
3
5
8
3
5
1
0
0
1
3.3
10.0
10.0
16.7
26.7
10.0
16.7
3.3
0
0
3.3
Microbial speciation
The following biochemical identification systems
were used for the primary speciation of individual
isolates: Rapid ID 32 A (bioMérieux, Marcy-l’Etoile,
France) for strict anaerobic gram-negative and grampositive rods; RapID ANA II System (Innovative Diagnostic Systems Inc, Atlanta, Ga) for strict anaerobic
gram-positive cocci; API Staph (bioMérieux) for staphylococci and micrococci (gram-positive cocci; catalasepositive cocci); Rapid ID 32 Strep (bioMérieux) for
streptococci (gram-positive cocci; catalase-negative
cocci); and the Rapid NH System (Innovative Diagnostic Systems Inc) for Eikenella, Haemophilus, Neisseria,
and Actinobacillus.
Additional tests were performed for the blackpigmented gram-negative anaerobes, including fluorescence testing under long-wave (366-nm) ultraviolet
light; hemagglutination of 3% sheep erythrocytes, lactose fermentation by application of the fluorogenic substrate 4-methylumbelliferyl-␤-galactosidase (Sigma
Chemical Co, St Louis, Mo), as described by Aicoforado et al20; and the determination of trypsinlike activity by application of the synthetic fluorogenic peptide,
as described by Aicoforado et al,20 Nakamura et al,21
and Slots.22
mycin, erythromycin, and azithromycin and then applied to each plate, in duplicate. Plates were incubated
in an anaerobic workstation (Don Whitley Scientific) at
37°C for 48 hours. After incubation, an elliptical zone
of growth inhibition was seen around the strip. The
MIC was read from the scale at the intersection of the
zone with the strip. In this study, the susceptibility
breakpoints against anaerobes were determined by using the National Committee for Clinical Laboratory
Standards (NCCLS) criteria.23 The breakpoints (in micrograms/milliliters) used to determine the susceptibility were as follows: benzylpenicillin, ⱕ0.5; amoxicillin, ⱕ4; amoxicillin combined with clavulanic acid,
ⱕ2; metronidazole, ⱕ8; and clindamycin, ⱕ2. The
breakpoints of erythromycin and azithromycin against
anaerobes have not been determined by the NCCLS23;
therefore, for this study, we used ⱕ4 ␮g/mL, as did
Spangler and Appelbaum24 and Kuriyama et al.11 In all
species, the tests were read after 24 and 48 hours of
incubation.
Epsilometer test
The Epsilometer test (E test) was performed by using
brucella agar medium (Oxoid), supplemented with 5%
sterile defibrinated sheep blood, added to 600 ␮L of
vitamin K1 and 600 ␮L of bovine hemin (Sigma Chemical Co) in 90-mm (diameter) plates. The microorganisms Peptostreptococcus prevotii (Gram-positive) and
Fusobacterium necrophorum, (Gram-negative) were
selected for this test. The inocula of P prevotii and F
necrophorum were prepared in an anaerobic workstation (Don Whitley Scientific) by suspending pure colonies of each microorganism in brucella broth to
achieve the visual turbidity of 1 McFarland standard
3⫻108). An inoculum was applied to each plate with a
fresh sterile cotton swab. The E test strips containing
benzylpenicillin, amoxicillin, and amoxicillin were
combined with clavulanic acid, metronidazole, clinda-
RESULTS
In 30 root canals sampled, 19 teeth had restorations,
8 teeth were decayed, 2 were without coronal sealing,
and 2 were intact. One tooth had both restoration and
decay. In addition, 27 teeth had necrotic pulps and 3
had received previous endodontic treatments. The dental groups involved were incisors (12/30), premolars
(9/30), molars (8/30), and canines (1/30); 15 upper and
15 lower teeth were used.
A total of 117 cultivable isolates were recovered
from the 30 root canals examined, indicating a mean
incidence of 3.9 bacteria per root canal (Table I). Of
these 117 isolates, 75 were identified as strict anaerobes
and 42 as facultative anaerobes, with 29 gram-negative
and 88 gram-positive species (Table II).
Eighty percent of the root canals (n ⫽ 24) had strict
anaerobe bacteria, and 76.6% had facultative anaerobe
de Sousa et al 335
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
Volume 96, Number 3
Table II. Prevalence of the bacterial species identified
Species
Peptostreptococcus prevotii
Peptostreptococcus micros
Gemella morbillorum
Fusobacterium necrophorum
Streptococcus constellatus
Streptococcus mitis
Gemella haemolysans
Prevotella intermedia/Prevotella nigrescens
Prevotella corporis
Veillonella spp
Staphylococcus saccharolyticus
Cardiobacterium hominis
Staphylococcus epidermidis
Prevotella loescheii
Eubacterium lentum
Bacteroides gracilis
Peptostreptococcus anaerobius
Peptostreptococcus spp
Clostridium subterminale
Tissierella praeacuta
Streptococcus oralis
Streptococcus sanguis
Streptococcus anginosus
Lactobacillus acidophilus
Root canals
Gram positive
or negative
Gaseous
requirement
No.
%
⫹
⫹
⫹
⫺
⫹
⫹
⫹
⫺
⫺
⫺
⫹
⫺
⫹
⫺
⫹
⫺
⫹
⫹
⫹
⫺
⫹
⫹
⫹
⫹
Anaerobic
Anaerobic
Facultative
Anaerobic
Anaerobic
Facultative
Facultative
Anaerobic
Anaerobic
Anaerobic
Anaerobic
Facultative
Facultative
Anaerobic
Anaerobic
Anaerobic
Anaerobic
Anaerobic
Anaerobic
Anaerobic
Facultative
Facultative
Facultative
Facultative
13
9
9
7
6
6
4
3
3
3
3
3
3
2
2
2
2
2
2
2
2
2
2
2
43.3
30.0
30.0
23.3
20.0
20.0
13.3
10.0
10.0
10.0
10.0
10.0
10.0
6.6
6.6
6.6
6.6
6.6
6.6
6.6
6.6
6.6
6.6
6.6
The following were isolated from single root canals: Actinomyces naeslundii, Actinomyces viscosus, Aerococcus viridans, Bacteroides spp, Capnocytophaga spp,
Clostridium acetobutylicum, Clostridium butyricum, Clostridium hastiforme, Enterococcus sp, Enterococcus faecium, Eubacterium aerofaciens, Eubacterium
limosum, Lactobacillus lactis, Lactobacillus minute, Lactobacillus acidophilus, Lactobacillus Neisseria spp, Peptostreptococcus asaccharolyticus,
Peptostreptococcus magnus, Peptostreptococcus tetradius, Prevotella buccae, Prevotella oris, Streptococcus acidominimus, Streptococcus intermedius, and
Streptococcus mutans.
bacteria (n ⫽ 23). Gram-negative bacteria were recovered from 56.6% of the root canals (n ⫽ 17), and
gram-positive bacteria were found in 96.6% (n ⫽ 29)
(Table II).
The predominant strict anaerobe bacteria recovered
were P prevotii (43.3%), Peptostreptococcus micros
(30.0%), F necrophorum (23.3%), Streptococcus constellatus (20.0%), and Prevotella intermedia/Prevotella
nigrescens (10.0%) (Table II).
Although less frequent, facultative anaerobic bacteria such as Gemella morbillorum (30.0%), Streptococcus mitis (20.0%), and Gemella haemolysans (13.3%)
were also found (Table II).
Two or more (with a maximum of 10) bacterial
species were recovered from 86.7% (26/30) of the root
canals, indicating the polymicrobial component of dental infections (Table I).
All P prevotii and F necrophorum strains had susceptibility to benzylpenicillin, amoxicillin, amoxicillin
combined with clavulanic acid, metronidazole, and
clindamycin. Erythromycin was ineffective against
80% of the F necrophorum strains tested, and azithromycin was ineffective against 60% of these species.
However, these antibiotics had antimicrobial activity
against 80% of P prevotii.
Tables III and IV show the MICs of the antibiotics to
both bacteria and the antimicrobial susceptibility data
based on the NCCLS22 criteria.
DISCUSSION
Culture procedures have traditionally been used in
the assessment of the microbiota associated with various infectious diseases, including infections of endodontic origin.5 The culturing techniques have a reasonable degree of agreement in terms of the
identification of oral microorganisms compared with
that of the “checkerboard” DNA-DNA hybridization
method. The major advantage of the culture procedure
is its ability to enable the detection of unexpectedly
viable cells (molecular procedures enable the detection
of only target microbial species25). Many molecular
techniques assist in the identification of cultivable microorganisms.
The strict anaerobes P prevotii, P micros, F necrophorum, and S constellatus and the facultative anaerobes G morbillorum and S mitis were the most fre-
336 de Sousa et al
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
September 2003
Table III. MIC of the antibiotics to P. prevotii
Peptostreptococcus prevotii (n ⫽ 5)
MIC (␮g/mL)*
Antimicrobial agents
50%
90%
Range of MIC
Susceptibility rate
(%)
Benzylpenicillin
Amoxicillin
Amoxicillin ⫹ clavulanic acid
Metronidazole
Clindamycin
Erythromycin
Azythromycin
0.016
0.19
0.125
0.016
0.38
1.0
1.5
0.38
0.25
0.19
0.38
0.125
1.0
8.0
⬍0.016–0.38
0.032–0.25
0.064–0.19
⬍0.016–0.38
⬍0.016–0.125
0.016–1.0
0.016–8.0
100%
100%
100%
100%
100%
80%
80%
*Fifty percent and 90%, at which 50% and 90% of the isolates are inhibited, respectively.
MIC, Minimum inhibitory concentration.
quently isolated bacteria, a result that is in agreement
with those of Oguntebi et al,26 Sabiston and Gold,27
Sabiston et al,28 Williams et al,6 Lewis et al,7 and
Wasfy et al.10 However, some of these authors obtained
samples by aspirating the abscesses.
The presence of black-pigmented bacteria was also
evaluated in the current study. These microorganisms
were found in 8 of 30 root canals (26.7%). P intermedia/P nigrescens and Prevotella corporis were both
isolated in 10% of the cases, whereas Prevotella loescheii was found in 6.6%. These findings are similar to
those reported by Sundqvist et al8 and Baumgartner et
al.29 In contrast, in the studies by Oguntebi et al26 and
Williams et al,6 the black-pigmented bacteria were less
frequently isolated. Porphyromonas endodontalis was
not isolated in the present study, a finding in accord
with those of Khemaleelakul et al.30 Gomes et al31
reported that a minimum concentration of Porphyromonas species is necessary for their isolation and, consequently, for their clinical recognition. Gomes4 suggested that the presence of Porphyromonas species at a
low concentration is difficult to detect through the use
of culture methods; therefore, the inadequate growth of
such microorganisms does not necessarily signal a lack
of anaerobic conditions. van Winkelhoff et al32 have
already described the difficulties in isolating these bacterial species through the use of culture methods. Moreover, Dymock et al33 and Baumgartner et al34 have
reported that different populations have correspondingly different compositions of microbiota— or it may
be that these species consist of both culturable and
nonculturable biotypes.
Our results indicate that the microbiota of root canals
with periapical abscesses have polymicrobial characteristics and are predominated by anaerobic grampositive cocci. The role of anaerobic bacteria in periapical abscesses cannot be overstated; in fact, these
bacteria were isolated from 80% of the root canals in
this study.
The root canals with previous endodontic treatment
had an average of 2.6 microorganisms per root canal.
The microbiota of such root canals were represented
mainly by facultative gram-positive species, a finding
in agreement with those of Sundqvist et al.35 Therefore,
the microbiota of root canals in which endodontic therapy failed differed markedly from the microbiota of
untreated teeth, even when the teeth had periapical
abscesses.
These findings play an important role not only in the
identification of the microorganisms present in the root
canals with periapical abscesses, but also in the development of specific antibacterial methods to supplement
conventional emergency treatments. The indiscriminate
use of antibiotics to complement dental treatments
should be avoided because it may result in allergic
reactions, superinfection development instigated by resistant bacterial species, and patients’ unnecessary exposure to both the toxicity and the side effects of the
medication.36
The E test method was used in the present study
because it provides a simple and a rapid method for
quantitative susceptibility testing that is suitable for all
anaerobes. Moreover, the MIC obtained with this test
are generally in very good agreement with those obtained by agar dilution methods, which is the reference
method of the NCCLS.14,37-39
The anaerobic endodontic isolates have shown to be
highly sensitive to benzylpenicillin, amoxicillin,
amoxicillin/clavulanate potassium, metronidazole, and
clindamycin, with MICs substantially below the critical
concentrations.
In this study, the susceptibility breakpoints were
based on NCCLS criteria,23 which are widely used in
various bacterial studies. However, the NCCLS23
breakpoints may be too strict for some test antibiotics
because the breakpoints are below the typical sera or
tissue concentrations of the antibiotics. The bacterial
strains that were determined to be unsusceptible to
de Sousa et al 337
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
Volume 96, Number 3
Table IV. MIC of the antibiotics to F necrophorum.
Fusobacterium necrophorum (n ⫽ 5)
MIC (␮g/mL)*
Antimicrobial agent
Benzylpenicillin
Amoxicillin
Amoxicillin ⫹ clavulanic acid
Metronidazole
Clindamycin
Erythromycin
Azythromycin
50%
90%
Range of MIC
Susceptibility rate
(%)
0.016
0.016
0.016
0.016
0.016
128
0.38
0.016
0.016
0.016
0.047
0.19
⬎256
4.0
⬍0.016–0.016
⬍0.016–0.047
⬍0.016–0.023
⬍0.016–0.047
⬍0.016–0.19
0.047–⬍256
⬍0.016–4
100%
100%
100%
100%
100%
20%
40%
*Fifty percent and 90%, at which 50% and 90% of the isolates are inhibited, respectively.
certain antibiotics according to the present criteria
might actually be clinically susceptible to those antibiotics because they may be affected by other factors
such as infection site or dosage.11 P prevotii and F
necrophorum were used in our study because they were
the predominant species found in the root canals of our
patients.
Benzylpenicillin (penicillin G) and penicillin V are
the most used natural penicillins. Benzylpenicillin is
the parenteral antibiotic of choice when a rapid effect or
a high serum concentration of the drug is required.40
The microorganisms tested had high susceptibility to
benzylpenicillin.
Amoxicillin is extended-spectrum penicillin. It was
developed to provide coverage against certain gramnegative species—particularly Haemophilus influenzae,
Escherichia coli, and Proteus mirabilis.41 Amoxicillin
resistance is well documented in the genera Prevotella,
Porphyromonas, Bacteroides, and Fusobacterium.42
Such resistance has also been documented for anaerobic gram-positive bacteria.42,43 However, the latter data
were from hospital isolates. Our results indicate that the
species isolated from root canals with periapical abscesses remain particularly susceptible to amoxicillin.
Furthermore, some authors44-46 have recommend
amoxicillin as a first-choice antibiotic for dental infection because of its broader spectrum, longer action, and
ability to compete with food for absorption. However,
amoxicillin can cause gastrointestinal side effects, hypersensitivity, and the development of resistant strains
and it is inactivated by ␤-lactamase.47
The efficacy of ␤-lactamase has been improved by
combining amoxicillin with clavulanate potassium.
This combination has been found to be active against a
range of penicillin-resistant strict anaerobes48,49; in addition, it prevents the destruction of simultaneously
administered ␤-lactamase antibiotics.41 Our results
have shown the good antimicrobial activity of this
formulation, which is in accordance with the findings of
Lewis et al.49
Penicillins are the most frequently used antimicrobial agents because of their historical effectiveness,
minimal toxicity, and relatively low cost.50 The effectiveness of the tested penicillins against P prevotii and
F necrophorum remains positive. One hundred percent
of the species tested were susceptible to these antibiotics (Tables III and IV). Moreover, penicillin has been
the preferred drug for the treatment of odontogenic
infections. However, bacterial resistance to penicillin
has become a problem of great clinical significance
because of its widespread use for many years.51
Erythromycin and clindamycin have been prescribed
for patients who are allergic to penicillin.52-55 However, it has been noted that erythromycin is not effective against Fusobacterium.56 Erythromycin has a spectrum similar to that of penicillins G and V, but it does
not achieve high concontration in blood; in addition, it
is less effective against important anaerobes.41 Our
findings further supported the poor antimicrobial activity of erythromycin against F necrophorum (Table IV).
Fusobacteria are more frequently isolated from severe
odontogenic infections than from milder infections.57
Kuriyama et al11 have suggested that erythromycin may
be effective against mild or moderate infections in
people with penicillin allergies, but it may not be suitable in cases of more severe infection. Our this study,
only 20% of the F necrophorum species were susceptible to erythromycin. However, 80% of the P prevotii
species were susceptible to this antibiotic.
Clindamycin has a bacteriostatic effect— except at
high doses, when it becomes bactericidal. It has excellent activity against strict anaerobes including ␤lactamase–producing bacteria.52-55 Our findings revealed that clindamycin was effective against the strict
anaerobes tested (Tables III and IV). Because of its
propensity to cause antibiotic-associated colitis, it has
not been widely used for more routine mild-to-moderate odontogenic infections. The limited use of clindamycin is probably why it remains effective against a
broad range of microorganisms.41,54
338 de Sousa et al
Metronidazole is a bactericidal antibiotic. Because of
its effectiveness against anaerobic microorganisms, it
has been suggested for the treatment of periapical abscesses, usually combined with penicillin.41,52,54 In this
study, metronidazole worked well against F necrophorum and P prevotii in terms of the recommended MIC
breakpoint. This finding is in accordance with those of
Citron et al.14
Azithromycin achieves higher blood concentration
than erythromycin, without the gastrointestinal side effects.58 Azithromycin was tested as a substitute for
erythromycin and was found to be effective against
80% of the P prevotii and 40% of the F necrophorum
species.
P prevotii and F necrophorum are susceptible to
benzylpenicillin, amoxicillin, and amoxicillin combined with clavulanic acid, metronidazole, and clindamycin antibiotics. Thus, these antibiotics are recommended for use in patients at high risk of bacterial
endocarditis or when antibiotic therapy is indicated
during the treatment of patients with periapical abscesses. Clindamycin can be recommended for the
treatment of severe infection in patients allergic to
penicillin, as was also suggested by Kuriyama et al.11
Penicillin still appears to be the drug of choice for the
treatment of oral infections. In oral infections, clindamycin seems to be a reasonable alternative for patients
who are allergic to penicillin.
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Reprint requests:
Caio Cezar Randi Ferraz, DDS, MSc, PhD
Department of Restorative Dentistry
Piracicaba School of Dentistry
University of Campinas
Av. Limeira, 901
Piracicaba—SP CEP—13414-018, Brazil
[email protected]
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