Mecillinam has potent in vitro activity against Chlamydophila pneumoniae ATCC VR1310

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 communityacquired 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 β-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 β-lactam antibiotics with MICs in the range 0.2–2.0 mg/L and MBCs in the range 0.2–8.0 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