New Plasmid-Mediated Quinolone Resistance Gene, qnrC , Found in a Clinical Isolate of Proteus mirabilis

Abstract

Since the discovery of qnrA in 1998, two additional qnr genes, qnrB and qnrS, have been described. These three plasmid-mediated genes contribute to quinolone resistance in gram-negative pathogens worldwide. A clinical strain of Proteus mirabilis was isolated from an outpatient with a urinary tract infection and was susceptible to most antimicrobials but resistant to ampicillin, sulfamethoxazole, and trimethoprim. Plasmid pHS10, harbored by this strain, was transferred to azide-resistant Escherichia coli J53 by conjugation. A transconjugant with pHS10 had low-level quinolone resistance but was negative by PCR for the known qnr genes, aac(6)-Ib-cr and qepA. The ciprofloxacin MIC for the clinical strain and a J53/pHS10 transconjugant was 0.25 g/ml, representing an increase of 32-fold relative to that for the recipient, J53. The plasmid was digested with HindIII, and a 4.4-kb DNA fragment containing the new gene was cloned into pUC18 and transformed into E. coli TOP10. Sequencing showed that the responsible 666-bp gene, designated qnrC, encoded a 221-amino-acid protein, QnrC, which shared 64%, 42%, 59%, and 43% amino acid identity with QnrA1, QnrB1, QnrS1, and QnrD, respectively. Upstream of qnrC there existed a new IS3 family insertion sequence, ISPmi1, which encoded a frameshifted transposase. qnrC could not be detected by PCR, however, in 2,020 strains of Enterobacteriaceae. A new quinolone resistance gene, qnrC, was thus characterized from plasmid pHS10 carried by a clinical isolate of P. mirabilis.Plasmid-mediated quinolone resistance was first described for a ciprofloxacin-resistant strain of Klebsiella pneumoniae in 1998 (15). The responsible gene, qnr (later named qnrA), was located on plasmid pMG252, which encodes multidrug resistance proteins. qnrB and qnrS were discovered in 2005 and 2006, respectively, and mediated similar levels of ciprofloxacin resistance (9, 11). Qnr proteins belong to the pentapeptide repeat protein (PRP) family and protect DNA gyrase and topoisomerase IV from quinolone inhibition (26,27,28). qnr genes show a high level of diversity; there are at least 6 qnrA, 20 qnrB, and 3 qnrS alleles reported, with one or more amino acid alterations within each family (12; http://www.lahey.org /qnrStudies). More recently, qnrD was found in Salmonella isolates (3). qnr genes are widely distributed in clinical Enterobacteriaceae isolates around the world and are usually associated with mobile elements (21). There were also qnr-like genes found on the chromosomes of Vibrio vulnificus, Vibrio parahaemolyticus, Photobacterium profundum, Stenotrophomonas maltophilia, and gram-positive genera such as Enterococcus, Listeria, Clostridium, and Bacillus (1,17,22,24). The wide distribution of qnr genes in different species of Enterobacteriaceae and their high degree of diversity raise the concern that there might be more qnr genes that have not yet been discovered. In this study, a new plasmid-mediated quinolone resistance gene, qnrC, was found on and cloned from a transferable plasmid, pHS10, in a clinical ...

Antibiotic resistance and resistance genes in Escherichia coli from poultry farms, southwest Nigeria

“…and tet(39) in tetracycline resistant isolates, cmlA, catA1 and floR (primers for floR: Flor-1, 5'-ATGGCAGGCGATATTCATTA-3'; flor-2: 5'-AAACGGGTTGTCACGATCAT-3') in chloramphenicol resistant isolates, acc(3)-IV in gentamicin resistant isolates, qnrA, qnrB, qnrC, qnrD, qnrS, aac(6')Ib and qepA in isolates resistant to ciprofloxacin (≥ 0.125mg/L) but sensitive to nalidxic acid with MIC ≤ 32 mg/L [20,[22][23][24][25]. The variable regions of Class 1 and Class 2 integrons were amplified and representatives of the different sized amplicons sequenced to characterise their gene contents as described by Peirano et al [21].…”

Prevalence of plasmid-mediated quinolone-resistance determinants in Shigella flexneri isolates from Anhui Province, China

“…Screening of qnr, qepA, aac(6¢)-Ib-cr, gyrA, gyrB, parC, parE and bla genes Amplification of qnr, qepA and aac(6¢)-Ib-cr was performed using the methods described previously; 8,9,11,12 different primers (shown in Table 1) were used for the amplification of qnrB and qnrA subtypes in this study. Amplification of bla genes (b-lactamase genes) was also performed with the methods described previously for bla TEM , bla SHV and bla CTXÀM .…”

“…[6][7][8] Several families of qnr (qnrA, qnrB, qnrS, qnrC, qnrD) have been reported and each family has different subtypes. 6,9 qnr encoded a protein of the pentapeptide family, protecting DNA gyrase directly from quinolone inhibition. 10 AAC(6¢)-Ib-cr is a variant of aminoglycoside acetyltransferase AAC(6¢)-Ib with enzymatic modification of ciprofloxacin or norfloxacin.…”

Prevalence of plasmid-mediated quinolone resistance determinants among oxyiminocephalosporin-resistant Enterobacteriaceae in Argentina

“…Molecular detection of qnrA , qnrB, qnrC , qnrD and qnrS was carried out by polymerase chain reaction (PCR) amplification using total heat-extracted DNA as a template and primers previously described (Cattoir et al 2007, Cavaco et al 2009, Wang et al 2009). For further characterisation of qnrB alleles, the following primers were designed (5'-3'): QnrBcF: GTTRGCGAAAAAATTRACAG, QnrBlF: ATGWYGYCATTATGTATA and QnrBcR: CCMATHAYMGCGATRCCAAG.…”