1 School of Biochemistry and Microbiology, and Antimicrobial Research Centre, The University of Leeds, Leeds LS2 9JT; 2 Division of Genomic Medicine, The University of Sheffield Medical School, Sheffield S10 2RX, UK
Keywords: chlamydiae, antimicrobial susceptibility, ß-lactam antibiotics
Sir,
Chlamydophila pneumoniae (previously known as Chlamydia pneumoniae) was first characterized in 1986 and is now recognized as an important respiratory pathogen.1 The organism can cause pneumonia, bronchitis, sinusitis and pharyngitis as well as community-acquired pneumonia.1 C. pneumoniae is susceptible in vitro to a number of antibiotics including macrolides, tetracyclines, quinolones and penicillins.2,3 Although chlamydiae lack detectable quantities of peptidoglycan, the susceptibility of C. pneumoniae to penicillins is consistent with the presence of penicillin-binding proteins (PBPs) in this organism.4
In a recent study with Chlamydia trachomatis, we observed that mecillinam, a semi-synthetic penicillin, possessed potent in vitro anti-chlamydial activity that was superior to other penicillins, cephalosporins and carbapenems.5 Since the susceptibility of C. pneumoniae to ß-lactam antibiotics has not been extensively studied we decided to examine the activity of a number of these antibiotics, including mecillinam, against a recognized strain of C. pneumoniae. One strain was tested as there are only a few reference isolates and unlike C. trachomatis, there are no biovars or serovars of C. pneumoniae.
C. pneumoniae strain ATCC VR1310 was cultured in HEp2 cells and antibiotic MICs and MBCs determined essentially as described previously.5 We observed that benzylpenicillin, ampicillin and mecillinam were the most active ß-lactam antibiotics with MICs in the range 0.22.0 mg/L and MBCs in the range 0.28.0 mg/L (Table 1). Among these penicillins, mecillinam was the most potent, exhibiting an MIC/MBC of 0.2 mg/L. In contrast, ceftriaxone and meropenem only exhibited moderate activity and cefotaxime and imipenem were essentially inactive. These results with C. pneumoniae are qualitatively similar to those we previously reported for C. trachomatis.5 Consequently, we have now demonstrated that mecillinam has potent in vitro activity against both species.
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ß-Lactam antibiotics are usually considered to lack sufficient activity against C. pneumoniae to have a role in the therapy of infections caused by this organism, but patients with diagnosed C. pneumoniae infections have responded well to therapy with ceftriaxone and/or cefuroxime axetil.6 Whether mecillinam might have a role in the treatment of C. pneumoniae is unknown. Nevertheless, the potent bactericidal activity of this antibiotic suggests that it could be an interesting agent for further study.
Acknowledgements
This work was supported in part by research grants to Ian Chopra from LEO Pharma, Ballerup, Denmark and The Wellcome Trust, UK.
Footnotes
* Corresponding author. Tel: +44-113-343-5604; Fax: +44-113-343-5638; E-mail: i.chopra{at}leeds.ac.uk
References
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Storey, C. & Chopra, I. (2001). Affinities of ß-lactams for penicillin binding proteins of Chlamydia trachomatis and their antichlamydial activities. Antimicrobial Agents and Chemotherapy 45, 3035.
6 . File, T. M., Jr, Segreti, J., Dunbar, L. et al. (1997). A multicenter, randomized study comparing the efficacy and safety of intravenous and/or oral levofloxacin versus ceftriaxone and/or cefuroxime axetil in treatment of adults with community-acquired pneumonia. Antimicrobial Agents and Chemotherapy 41, 196572.[Abstract]
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