Characterization of the quinolone resistant determining regions in clinical isolates of pneumococci collected in Canada

Abstract

BackgroundThe objective of this study was to examine Streptococcus pneumoniae isolates collected from a longitudinal surveillance program in order to determine their susceptibility to currently used fluoroquinolones and of the frequency and type of mutations in the quinolone-resistant determining regions (QRDRs) of their parC and gyrA genes.MethodsThe Canadian Bacterial Surveillance Network has been collecting clinical isolates of S. pneumoniae from across Canada since 1988. Broth microdilution susceptibility testing was carried out according to the Clinical and Laboratory Standards Institute guidelines. The QRDRs of the parC and gyrA genes were sequenced for all isolates with ciprofloxacin MIC ≥ 4 mg/L, and a large representative sample of isolates (N = 4,243) with MIC ≤ 2 mg/L.ResultsA total of 4,798 out of 30,111 isolates collected from 1988, and 1993 to 2007 were studied. Of those isolates that were successfully sequenced, 184 out of 1,032 with mutations in parC only, 11 out of 30 with mutations in gyrA only, and 292 out of 298 with mutations in parC and gyrA were considered resistant to ciprofloxacin (MIC ≥ 4 mg/L). The most common substitutions in the parC were at positions 137 (n = 722), 79 (n = 209), and 83 (n = 56), of which substitutions at positions 79 and 83 were associated with 4-fold increase in MIC to ciprofloxacin, whereas substitutions at position 137 had minimal effect on the ciprofloxacin MIC. A total of 400 out of 622 isolates with Lys-137 parC mutation belonged to serotypes 1, 12, 31, 7A, 9V, 9N and 9L, whereas only 49 out of 3064 isolates with no mutations belonged to these serotypes. Twenty-one out of 30 isolates with substitutions at position 81 of the gyrA gene had an increased MIC to ciprofloxacin. Finally, we found that isolates with mutations in both parC and gyrA were significantly associated with increased MIC to fluoroquinolones.ConclusionsNot all mutations, most frequently Lys-137, found in the QRDRs of the parC gene of S. pneumoniae is associated with an increased MIC to fluoroquinolones. The high prevalence of Lys-137 appears to be due to its frequent occurrence in common serotypes.

Susceptibility of Streptococcus pneumoniae to Fluoroquinolones in Canada

“…Among these isolates, the most common mutations were at positions 137 (Lys-137) (761 isolates), 79 (Ser-79) (179 isolates), and 83 (Asn-83) (47 isolates). Previous studies and our prior analysis of mutations in these isolates have shown that substitutions at positions 78, 79, 83, 91, 115, and 129 of parC and substitutions at positions 81 and 85 of gyrA are associated with reduced fluoroquinolone susceptibility while other mutations in these QRDRs do not affect fluoroquinolone susceptibility (13,21,23). Therefore, we considered only those isolates with mutations affecting fluoroquinolone susceptibility in our analysis of mutations potentially selected for by the use of fluoroquinolone antibiotics.…”

“…The quinolone resistance-determining regions (QRDRs) of the parC and gyrA genes were amplified and sequenced (23). Multiple nucleotide sequences were performed with the Clustal W2 program (http://www.ebi.ac.uk/Tools/clustalw2 /index.html).…”

Molecular Investigation of Quinolone Resistance of Quinolone Resistance-Determining Region in Streptococcus pneumoniae Strains Isolated from Iran Using Polymerase Chain Reaction–Restriction Fragment Length Polymorphism Method

“…Similar to the findings of Credito et al [17] and Jorgensen et al [18], our findings imply that only mutations in the parC or gyrA gene were resistant to ciprofloxacin, susceptible to ofloxacin, and semisusceptible to levofloxacin. However, the isolates that had simultaneous mutations in both genes were completely resistant to ofloxacin and levofloxacin [9]. However, there are various opinions about the parE gene and its role in the development of resistance to quinolones; according to research by Kawamura et al [19] in Japan and Credito et al [17] in the United States, isolates that had parE gene mutations, along with mutations in the parC or gyrA gene, had higher resistance to ciprofloxacin, ofloxacin, norfloxacin, and lorfloxacin than mutants that did not have mutations in the parE gene.…”

The Use of Systemic and Topical Fluoroquinolones

“…31 Previous concerns that continuing widespread use of respiratory fluoroquinolones would lead to substantial increases in pneumococcal resistance and subsequent lack of usefulness of this class of agents for respiratory tract infections [32][33][34] have, fortunately, not been confirmed by current published surveillance data, particularly for pneumococcal isolates from children. 31,35,36 The Active Bacterial Core Surveillance of the Centers for Disease Control and Prevention documented virtually no levofloxacin resistance in children younger than 2 years between 1999 and 2004. 37 In large-scale pediatric studies of levofloxacin for acute otitis media, emergence of levofloxacinresistant pneumococci was not documented in children with persisting pneumococcal colonization after treatment, which suggests that emergence of resistance during treatment is not a common event.…”