1 Infection Research Group, Glasgow Dental Hospital, Glasgow, Scotland, UK; 2 Anaerobe Reference Laboratory, NPHS Microbiology Cardiff, University Hospital of Wales, Cardiff, Wales, UK; 3 Bacteriology Department, Glasgow Royal Infirmary, Scotland, UK; 4 Division of Immunology, Infection and Inflammation, Medical School, University of Glasgow, Scotland, UK
Received 6 April 2005; returned 25 April 2005; revised 24 May 2005; accepted 24 May 2005
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Abstract |
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Methods: Human clinical isolates of Actinomyces spp. were collected from stored collections held at the Microbiology Department, Edinburgh University, Anaerobe Reference Laboratory, Cardiff, Glasgow Dental Hospital and Glasgow Royal Infirmary. Each isolate was identified by restriction analysis of amplified 16S ribosomal DNA. MICs of 12 antibiotics comprising benzyl penicillin, amoxicillin, ceftriaxone, linezolid, tetracycline, deoxycycline, clindamycin, erythromycin, clarithromycin, ciprofloxacin, meropenem and piperacillin/tazobactam for 87 strains of Actinomyces species were obtained by Etest methodology.
Results: The Actinomyces species identified for this study comprised: Actinomyces israelii, Actinomyces gerencseriae, Actinomyces turicensis, Actinomyces funkei, Actinomyces graevenitzii and Actinomyces europaeus. All isolates were susceptible to penicillin and amoxicillin. All but one strain of A. turicensis was susceptible to linezolid. A number of A. europaeus and A. graevenitzii isolates were resistant to ceftriaxone and piperacillin/tazobactam. A number of isolates of A. turicensis and A. europaeus also demonstrated resistance to erythromycin. All Actinomyces species tested appeared resistant to ciprofloxacin.
Conclusions: Actinomyces species appear to be susceptible to a wide range of ß-lactam agents and these, when combined with ß-lactamase inhibitors, should be regarded as agents of first choice. Ciprofloxacin performed poorly. Tetracyclines also demonstrated poor performance. This is the first study of antimicrobial susceptibilities for a number of accurately identified clinical isolates of Actinomyces spp. There are a number of species differences in susceptibility profiles to the antimicrobials tested, suggesting that accurate identification and speciation may have an impact on clinical outcome.
Keywords: Actinomyces israelii , Actinomyces gerencseriae , Actinomyces turicensis , Actinomyces funkei , Actinomyces graevenitzii , Actinomyces europaeus , antimicrobial susceptibility
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Introduction |
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The clinical significance of the many recently described Actinomyces spp. has yet to be proven but some, including Actinomyces turicensis and Actinomyces europaeus are clearly associated with mixed infections in superficial soft-tissue abscesses.6
Those Actinomyces spp. that have been tested are susceptible to a wide range of antimicrobial agents.7 However, interpretation of different studies is hampered by difficulties in the accurate identification of members of the Actinomyces genus and taxonomic changes. Susceptibility data on accurately identified Actinomyces will become increasingly important as our knowledge of the infections caused by the Actinomyces genus improves.
The aim of this study was to analyse the antimicrobial susceptibility of a wide range of Actinomyces spp. isolated from clinical infections and identified by restriction analysis of amplified 16S ribosomal DNA.
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Materials and methods |
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Clinical isolates were collected from stored collections held at the Microbiology Department, Edinburgh University, Anaerobe Reference Laboratory, Cardiff, Glasgow Dental Hospital and Glasgow Royal Infirmary.
Identification of isolates
There were 87 isolates available for analysis and each isolate was identified by restriction analysis of amplified 16S ribosomal DNA (ARDRA) as described previously.8
Susceptibility testing
The MICs for 12 antibiotics consisting of benzyl penicillin G, amoxicillin, ceftriaxone, linezolid, tetracycline, deoxycycline, clindamycin, erythromycin, clarithromycin, ciprofloxacin, meropenem and piperacillin/tazobactam were obtained by Etest methodology. All tests were performed on freshly poured WilkensChalgren agar plates and were incubated anaerobically for 4872 h. The plates were inoculated with a bacterial suspension in saline of turbidity equivalent to that of McFarland standard 4.9 Quality assurance was performed using Bacteroides fragilis (ATCC 25285) and Eubacterium lentum ATCC 43055.
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Results |
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Use of the ARDRA technique resulted in the identification of 25 Actinomyces israelii, 23 Actinomyces gerencseriae, 11 A. turicensis, 10 Actinomyces funkei, eight Actinomyces graevenitzii and 10 A. europaeus.
Antimicrobial susceptibility
The susceptibilities of the 87 Actinomyces spp. tested are shown in Table 1. All isolates were susceptible to penicillin and amoxicillin (MIC < 1 mg/L). A number of A. europaeus (2), A. funkei (5) and A. turicensis (9) demonstrated reduced susceptibility (1 mg/L) to piperacillin/tazobactam. For isolates of A. turicensis, two of the 11 isolates and two of the 10 isolates of A. europaeus demonstrated resistance to erythromycin (MIC > 1 mg/L). All isolates were resistant to ciprofloxacin (MIC > 1 mg/L). Of the 87 isolates tested, only three (3%) had an MIC of linezolid >1.0 mg/L. These isolates comprised 1 A. europaeus (MIC 1.5 mg/L) and two isolates of A. turicensis (MIC 4.0 and >256 mg/L).
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Discussion |
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A number of early studies have indicated that many patients respond insufficiently or not at all to penicillin G and have led to the suggestion of prolonged high-dose therapy.10 However, this may reflect the mixed flora found in the infections from which Actinomyces species may be isolated. Furthermore, antimicrobial agents will poorly penetrate the chronically indurated tissue of actinomycotic lesions and the dense co-aggregations of Actinomyces known as sulphur granules, implying the importance of surgical curettage as adjunctive treatment. Current treatment schemes therefore include drugs effective against actinomycetes and potential ß-lactamase producers such as Staphylococcus aureus, Gram-negative anaerobes, and, in cases of abdominal actinomycoses, members of the Enterobacteriaceae.
A possible scheme for the antibiotic treatment of cervicofacial actinomycoses may consist of amoxicillin plus clavulanic acid or possibly ampicillin plus sulbactam. The initial dose is 3x2 g amoxicillin plus 3 x 0.2 g clavulanic acid per day for 1 week, and 3 x 1 g amoxicillin plus 3 x 0.1 g clavulanic acid per day for another week. Rarely, chronic cervicofacial infections may require up to 4 weeks of treatment. This regimen may suffice for thoracic actinomycoses, but the high dose continued for 34 weeks is recommended. In advanced chronic pulmonary cases, an increased dose of ampicillin may be necessary to increase tissue levels and, depending on the concomitant flora, an aminoglycoside may be necessary if resistant Enterobacteriaceae such as Klebsiella spp. or Enterobacter spp. are present. The latter is generally the case in abdominal actinomycosis. The treatment of choice for these infections is a combination of amoxicillin and clavulanic acid with metronidazole (or clindamycin) for strict anaerobes plus tobramycin or gentamicin. Imipenem and piperacillin/tazobactam may be a suitable alternative, but they have rarely been used for actinomycotic infections. Interestingly, a number of isolates of A. turicensis, A. funkei and A. europaeus displayed elevated MICs of piperacillin/tazobactam.
It should be noted that metronidazole should not be used to treat actinomycotic infections without added antimicrobial agents, since metronidazole is not active against the pathogenic actinomycetes. Patients allergic to penicillin may be treated with tetracyclines or cephalosporins instead of aminopenicillins, but the clinical efficacy of these drugs is much less than that of aminopenicillins or the combination of aminopenicillins with ß-lactamase inhibitors.
In conclusion, our data suggest that Actinomyces spp. appear susceptible to a wide range of ß-lactam agents and these should be regarded as agents of first choice when combined with ß-lactamase inhibitors. Since linezolid, a new agent, has been tested against this group of organisms, it is of interest that apart from one strain of A. turicensis all Actinomyces spp. were susceptible (<4 mg/L) to this antibiotic. Ciprofloxacin and tetracycline performed poorly. This is the first study of antimicrobial susceptibilities for a range of clinical isolates of Actinomyces spp. that have been accurately identified. There are a number of species differences in response to the antibiotics tested, suggesting that accurate identification and speciation may have an impact on clinical outcome. Further clinical studies are required to elucidate the potential role of the antibiotics tested in this study.
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Acknowledgements |
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References |
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2. Benhoff DF. Actinomycosis: diagnostic and therapeutic considerations and a review of 32 cases. Laryngo 1984; 94: 11981217.[ISI]
3. Samuels RHA, Martin MV. A clinical and microbiological study of actinomycetes in oral and cervicofacial lesions. Br J Oral Maxillo Surg 1988; 26: 45863.[CrossRef][ISI]
4. Cintron JR, Del Pino A, Duarte B et al. Abdominal actinomycosis. Report of 2 cases and review of the literature. Dis Col Rect 1996; 39: 1038.[ISI][Medline]
5. Fiorino AS. Intrauterine contraceptive device-associated actinomycotic abscess and Actinomyces detection on cervical smear. Obst Gyn 1996; 87: 1429.[CrossRef][ISI]
6.
Sabbe LJM, Van de Merwe D, Schouls L et al. Clinical spectrum of infections due to the newly described Actinomyces species A. turicensis, A. radingae and A. europaeus. J Clin Micro 1999; 37: 813.
7. Schaal KP, Pulverer G. Epidemiologic, etiologic, diagnostic, and therapeutic aspects of endogenous actinomycete infections. In: Ortiz-Ortiz L, Bojalil LF, Yakoleff V, eds. Biological, Biochemical, and Biomedical Aspects of Actinomycetes. Orlando, New York, London: Academic Press, 1984; 1332.
8.
Hall V, Talbot PR, Stubbs SL et al. Identification of clinical isolates of Actinomyces species by Amplified 16S Ribosomal DNA Restriction Analysis. J Clin Micro 2001; 39: 355562.
9. Hall V, Talbot P. Evaluation of the E-test for susceptibility testing of Actinomyces species. Rev Med Microbiol 1997; 8 (Suppl 1): S83.
10. Prather JR, Eastridge CE, Hughes FA et al. Actinomycosis of the thorax. diagnosis and treatment. Annals Thoracic Surg 1970; 9: 30712.
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