Isolation of ciprofloxacin-resistant Legionella pneumophila in a patient with severe pneumonia

Sir, Legionella species are responsible for 1%– 5% of cases of community-acquired pneumonia. Legionella pneumophila serogroup 1 (SG1) accounts for .90% of Legionnaires’ disease (LD) in North America and Europe and is the cause of significant mortality. The mortality rate among patients with L. pneumophila infections continues to be high, up to 26%. The antimicrobial agents most commonly used for treatment of LD are fluoroquinolones (e.g. ciprofloxacin or levofloxacin) and macrolides. In recent studies, we established wild-type distributions and determined the epidemiological cut-off values (ECOFFs) in clinical L. pneumophila SG1 isolates for 10 antimicrobials commonly used for the treatment of Legionella infections. A patient sought care at his general practitioner after several days of falling and body pains. On examination, the patient appeared ill and was sent to the emergency department of a nearby hospital. The initial chest radiograph demonstrated an infiltrate of the left lower lung field. The patient was admitted to the intensive care unit. Blood cultures were taken and antibiotic treatment was started with cefazolin and gentamicin. Urine was examined for the presence of Legionella antigens and when this test was reported positive, treatment was switched to 400 mg of ciprofloxacin intravenously twice daily. After initial improvement the clinical condition of the patient deteriorated, leading to intubation and mechanical ventilation. A new chest radiograph revealed a diffuse interstitial pneumonia. Bronchoalveolar lavage (BAL) was performed 4 days after treatment with ciprofloxacin was started and the patient slowly recovered. Eventually, culture of the BAL grew L. pneumophila SG1 after 4 days of ciprofloxacin treatment. After 10 days, the patient could be transferred to the ward. Therapy was then switched to 500 mg of clarithromycin orally twice daily. The patient’s further recovery was uncomplicated. The L. pneumophila SG1 strain was sent, as part of a national Legionella outbreak detection programme, to the reference laboratory for Legionella in Haarlem, The Netherlands. Susceptibility testing for ciprofloxacin was performed with Etest and an MIC value of ciprofloxacin of 2 mg/L was found. This value is outside the wild-type distribution range ECOFF1⁄41 mg/L as previously described and therefore potentially resistant. For sequencing of gyrA and gyrB (DNA gyrase) and parC and parE (topoisomerase IV) genes, extraction of L. pneumophila DNA was performed. The DNA extraction was performed by use of Qiagen’s BioRobot EZ1 (Hilden, Germany) according to the manufacturer’s instructions. The sequencing reaction was performed twice by using primer systems previously described for the L. pneumophila SG1 strain Paris. A comparative analysis of the obtained sequences was done using the published L. pneumophila genomes and data from the literature describing mutations in the quinolone resistance-determining region (QRDR) of type II topoisomerase of L. pneumophila by using DNAStar (WI, USA) software and the NCBI database. For control experiments, the wild-type strain MTZ OLDA and a spontaneous quinolone-resistant mutant of this strain were used. MTZ OLDA is an environmental isolate (L. pneumophila SG1), isolated from the water supply of a large building. A point mutation in the QRDR of the gyrA gene was identified and this mutation led to an amino acid exchange at position 83 (Escherichia coli numbering system). The result of this amino acid exchange is a change in ciprofloxacin susceptibility. Mutation at the same position (amino acid 83) has also been reported for other spontaneous quinolone-resistant mutants (Table 1). It is known that, in general, pathogens can become resistant during the course of a patient’s therapy and also induction of resistance upon exposure to antibiotics has been described. The origin of resistance in the clinical isolate is as yet unclear. There are two possibilities. The first is that the patient contracted an L. pneumophila SG1 strain with this point mutation from the environment. Alternatively, the mutation occurred during the Research letters