Fluoroquinolone resistant Streptococcus pneumoniae.
To the Editor: In pneumococci, resistance to fluoroquinolones is associated with chromosomal mutations in the quinolone-resistance-determining regions (QRDR QRDR Quinolone Resistance-Determining Regions ) of type II topoisomerase Type II topoisomerases cut both strands of the DNA helix simultaneously in order to change the linking number of the molecule. Function
Once cut, the ends of the DNA are separated, and a second DNA duplex is passed through the break. enzymes, predominantly gyrA and parC. Several mutations have been described in these enzymes, but only a few have been shown by in vitro studies to confer resistance: S81F or Y, C, or I and E85K in gyrA; E474K in gyrB; A63T, $79F or Y or L and D83G or N in parC; and E474K and D435N or H in parE (1-5). Other frequently described mutations are K137N in parC and I460V in parE, which appear to not contribute to fluoroquinolone fluoroquinolone /flu·o·ro·quin·o·lone/ (-kwin´o-lon) any of a subgroup of fluorine-substituted quinolones, having a broader spectrum of activity than nalidixic acid.
n. resistance because they are commonly found in susceptible strains, and no evidence exists for their conferring fluoroquinolone resistance in vitro. We describe here a pneumococcal pneumococcal /pneu·mo·coc·cal/ (-kok´al) pertaining to or caused by pneumococci. strain that was isolated from a 66-year-old white man with chronic obstructive pulmonary disease chronic obstructive pulmonary disease
n. Abbr. COPD
A chronic lung disease, such as asthma or emphysema, in which breathing becomes slowed or forced. (COPD COPD chronic obstructive pulmonary disease.
chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD) ).
The patient was admitted to the hospital with a presumed exacerbation of COPD. He had been discharged from the hospital 2 days earlier, having recovered from a similar manifestation of this disease. His treatment history was 250 mg/day oral levofloxacin for 7 days while in the hospital and levofloxacin for 10 days as an outpatient for a similar lower respiratory tract infection While often used as a synonym for pneumonia, the rubric of lower respiratory tract infection can also be applied to other types of infection including lung abscess, acute bronchitis, and emphysema. 3 months earlier.
On this second admission he was given levofloxacin, 250 mg intravenously, once a day. He was treated with a low dosage because he was in renal failure. The patient continued to worsen and was transferred to the intensive care unit, where ceftriaxone ceftriaxone /cef·tri·ax·one/ (cef?tri-ak´son) a semisynthetic, ß–resistant, third-generation cephalosporin effective against a wide range of gram-positive and gram-negative bacteria, used as the sodium salt. , 1 g intravenously once a day, was given along with levofloxacin. He improved on the combination therapy and was discharged without sequelae sequelae Clinical medicine The consequences of a particular condition or therapeutic intervention .
Cultures of the patient's blood and sputum grew Streptococcus pneumoniae. The isolate from blood was resistant to levofloxacin (MIC 8 mg/L) and ciprofloxacin (MIC 8 mg/L), yet susceptible to gatifloxacin (MIC 1 mg/L) and ceftriaxone (MIC 0.38 mg/L), with intermediate resistance to penicillin (MIC 1.5 mg/L). The resistant isolate was of serotype 6A and of multilocus sequence type 376, which is the North [Carolina.sup.6A]-23 clone (http://www.sph.emory.edu/PMEN/index.html).
Efflux efflux Medtalk That which flows outward testing that compared the ciprofloxacin MICs in the presence and absence of reserpine reserpine (rĕsûr`pēn), alkaloid isolated from the root of the snakeroot plant (Rauwolfia serpentina), a small evergreen climbing shrub of the dogbane family native to the Indian subcontinent. (10mg/L) showed no evidence of an overexpressed efflux pump. We sequenced the QRDRs (gyrA, gyrB, parC, parE) and the entire gyrA and parC genes of the resistant strain isolated from blood by using previously described primers (2). Sequencing showed a $79Y mutation in parC and a Q118K (CAA Caa
See CCC. [right arrow] AAA AAA: see American Automobile Association.
(Triple A) A common single-cell battery used in a myriad of electronic devices of all variety. Like its double A (AA) cousin, it provides 1.5 volts of DC power. When used in series, the voltage is multiplied. ) mutation in gyrA. Sequencing of the entire gyrA and parC genes confirmed that no additional amino acid substitutions were outside the QRDRs. The entire gyrA gene PCR PCR polymerase chain reaction.
polymerase chain reaction
Polymerase chain reaction (PCR) product was transformed directly into the susceptible pneumococcal reference strain R6 by a standard transformation protocol (4). Transformants were selected on plates containing increasing concentrations of ciprofloxacin and, in a second step, were transformed with the entire parC gene of the resistant strain.
The ciprofloxacin and levofloxacin MICs of R6 transformed with the gyrA gene of the resistant isolate containing the new Q 118K mutation were 4 and 2 mg/L, respectively. After additional transformation of these transformants with parC of the resistant isolate containing the $79Y mutation, the selected double transformants exhibited the same MICs as the original clinical isolate (8 mg/L for ciprofloxacin and levofloxacin). The transformation of parC alone conferred an intermediate increase in the MICs (ciprofloxacin 2 mg/L, levofloxacin 4 mg/L). All transformants were confirmed by sequencing.
To determine the biologic cost associated with the different resistance mutations in vitro, each fluoroquinolone-resistant mutant was competed against the fluoroquinolone-susceptible parent strain R6 (with an independent streptomycin resistance marker) as described by Johnson et al. (6). The outcome was evaluated as the change in the ratios of the competing strains as a function of the number of generations. Each competition was performed in triplicate by using independent starting cultures of each competing strain. Compared with the wild-type R6 strain, the relative fitness values for the gyrA, parC, and double mutants were 1.06, 1.03, and 0.93, respectively.
These data indicate that a single mutation in either parC or gyrA does not impose a substantial fitness burden. In contrast, the double-mutation parC $79Y and gyrA Qll8K was associated with a slower growth rate. Similar results of relative fitness for single (parC $79Y and gyrA S81F) and double mutations were observed by Gillespie et al. (7).
Development of resistance to fluoroquinolones is a stepwise process, involving spontaneous mutations in the genes encoding the target enzymes DNA gyrase and the topoisomerase IV. Mutants with mutations in 1 of the enzymes are estimated to arise at a frequency of 1 to [10.sup.-7] (1). Therefore, fluoroquinolone resistance due to selection of spontaneous mutants during treatment may be related to the number of bacterial cells in the population under selective pressure. Patients with COPD are frequently colonized Colonized
This occurs when a microorganism is found on or in a person without causing a disease.
Mentioned in: Isolation by high bacterial loads. COPD has been identified in several recent studies as an independent risk factor for fluoroquinolone resistance (8,9). Low doses of fluoroquinolones may also lead to an increased risk for resistance selection (10). Because the Q118K mutation has not been previously described, this new mutation was probably selected by the current or antecedent treatments rather than by an infection with a resistant widely disseminated clone.
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Mathias W.R. Pletz, * ([dagger]), (1) Randolph V. Fugit, ([double dagger]), (1) Lesley McGee, * Jeffery J. Glasheen, ([section]) Darcie L. Keller, ([paragraph]) Tobias Welte, ([dagger]) and Keith P. Klugman * (#)
(1) These authors contributed equally to this paper.
* Emory University Rollins School of Public Health The Rollins School of Public Health (RSPH) is the public health school of Emory University. Founded in 1990, RSPH has more than 850 students pursuing master's degrees (MPH/MSPH) and over 100 students pursuing doctorate degrees (PhD). , Atlanta, Georgia, USA; ([dagger]) Hannover Medical School The Hannover Medical School (abbreviated MHH in German), founded in 1965, is one of the world's leading university medical centres in Germany. The research and patient care set national and international standards. , Hannover, Germany; ([double dagger]) Denver Veterans Affairs Medical Center, Denver, Colorado, USA; ([section]) University of Colorado Health Sciences Center The University of Colorado Health Sciences Center (UCHSC) is part of the University of Colorado System. It has recently been merged with the University of Colorado at Denver (UCD) to form the University of Colorado at Denver and Health Sciences Center. , Denver, Colorado, USA; [paragraph] University of Missouri-Kansas City School of Medicine, Kansas City, Missouri Kansas City is the largest city in the state of Missouri. It encompasses parts of Jackson, Clay, Cass, and Platte counties and is the anchor city of the Kansas City Metropolitan Area, the second largest in Missouri, which includes counties in both Missouri and Kansas. , USA; and (#)Emory University School of Medicine, Atlanta, Georgia, USA
Mathias W. R. Pletz's work was supported by a scholarship from the German Research Foundation Deutsche Forschungsgemeinschaft) and CAPNETZ.
Address for correspondence: Mathias W.R. Pletz, Department of Respiratory Medicine, Hannover Medical School, Carl-Neuberg-Str. 1, Hannover, 30625, Germany; email: pletz. email@example.com