Functional verification of computationally predicted qnr genes
© Flach et al.; licensee BioMed Central Ltd. 2013
Received: 10 September 2013
Accepted: 14 November 2013
Published: 21 November 2013
The quinolone resistance (qnr) genes are widely distributed among bacteria. We recently developed and applied probabilistic models to identify tentative novel qnr genes in large public collections of DNA sequence data including fragmented metagenomes.
By using inducible recombinant expressions systems the functionality of four identified qnr candidates were evaluated in Escherichia coli. Expression of several known qnr genes as well as two novel candidates provided fluoroquinolone resistance that increased with elevated inducer concentrations. The two novel, functionally verified qnr genes are termed Vfuqnr and assembled qnr 1. Co-expression of two qnr genes suggested non-synergistic action.
The combination of a computational model and recombinant expression systems provides opportunities to explore and identify novel antibiotic resistance genes in both genomic and metagenomic datasets.
Expression of qnr genes protects type II topoisomerases from quinolone inhibition, and facilitates the selection of mutants with higher level of resistance [1, 2]. Six families of plasmid-borne qnr genes have been identified; qnrA, B, C, D, S and VC[1, 3–7]. In addition, chromosomal qnr alleles have been found in several bacterial species, alleles that may serve as progenitors of plasmid-borne qnr genes [8–10].
Identifications of the first representative of each qnr family relied on screening of clinical isolates and resistance transfer assays [1, 3–5, 7, 11], whereas subsequent studies have identified related qnr genes mainly by using PCR-based strategies [5, 9, 10, 12]. Lately, several qnr genes have been discovered based on sequence homology by use of alignment tools [11, 13]. However, this approach does not efficiently take into account the conserved pentapeptide repeat pattern of qnr genes, neither is it suitable for identifying qnr genes in short-read metagenomic datasets. The lack of optimized methods suggests that there very well could be many qnr genes waiting to be discovered. We have recently developed a computational method based on probabilistic Hidden Markov models with a potential to overcome these hurdles. By using this method a number of putative qnr genes were identified from a large collection of genomes and metagenomes .
In this study we have experimentally evaluated four of these novel candidates (NC), nc1 – nc4 (Additional file 1), in recombinant Escherichia coli expression systems, an approach that has been used with success to characterize qnr genes previously [3–5, 7, 8, 13, 15]. The candidates and the first members of the six described families of mobile qnr genes were synthesized (Eurofins MWG Operon, Ebersberg, Germany) and subcloned into two expression vectors, pZE21 and pZA14 (Expressys, Ruelzheim, Germany), under the control of two different inducible promoters, PLtetO-1 and Plac/ara-1 respectively. The vectors carry either the ColE1 (pZE21) or the p15A (pZA14) origin of replication, and thus belong to different plasmid compatibility groups . Although several cloning procedures were tested, both by us and a contract lab, nc4 could not be subcloned into the pZA14 vector and was thus not evaluated under the control of the Plac/ara-1 promoter. However, this was not likely due to toxicity of the gene product, as has been reported for EfsQnr previously , since nc4 could be evaluated in the E. coli host using the pZE21 vector. The recombinant plasmids were electroporated into E. coli C600Z1 (Expressys), which expresses repressors for the two inducible promoters used . Conceivably, these kinds of expression systems allow the evaluation of gene candidates without knowledge of the intrinsic promoter, information that is often difficult to capture when genes are reconstructed from fragmented metagenomes. In addition, the approach does not depend on the functionality of an intrinsic promoter in a heterologous expression host.
We suggest that the two identified and experimentally verified qnr genes nc2 and nc4, which provide resistance to the E.coli host at the same level as previously reported qnr genes, should be termed Vfuqnr and assembled qnr 1, respectively (Figure 2). The name Vfuqnr reflects the host of the gene, whereas the latter name is chosen to reflect that the gene is assembled from metagenomic DNA, and that the host is not known. The nucleotide sequences of Vfuqnr and assembled qnr 1 have been submitted to GenBank (accession number BK008765 and KF278752, respectively).
To conclude, we have identified two novel, functional quinolone resistance genes. The development of a probabilistic Hidden Markov model and inducible recombinant expression systems together provided an efficient approach for exploring bacterial genomes and fragmented metagenomic datasets for the presence of novel qnr genes. We propose that a similar concept could be developed and used to identify resistance genes for other classes of antibiotics as well.
Availability of supporting data
The data sets supporting the results of this article are included within the article and its additional files.
This work was supported by the Swedish Research Council, Formas, MISTRA, the Adlerbert Research Foundation, and the Life Science Area of Advance at Chalmers University of Technology.
- Martinez-Martinez L, Pascual A, Jacoby GA: Quinolone resistance from a transferable plasmid. Lancet. 1998, 351 (9105): 797-799. 10.1016/S0140-6736(97)07322-4View ArticlePubMedGoogle Scholar
- Tran JH, Jacoby GA: Mechanism of plasmid-mediated quinolone resistance. Proc Natl Acad Sci USA. 2002, 99 (8): 5638-5642. 10.1073/pnas.082092899View ArticlePubMedPubMed CentralGoogle Scholar
- Cavaco LM, Hasman H, Xia S, Aarestrup FM: qnrD, a novel gene conferring transferable quinolone resistance in Salmonella enterica serovar Kentucky and Bovismorbificans strains of human origin. Antimicrob Agents Chemother. 2009, 53 (2): 603-608. 10.1128/AAC.00997-08View ArticlePubMedPubMed CentralGoogle Scholar
- Hata M, Suzuki M, Matsumoto M, Takahashi M, Sato K, Ibe S, Sakae K: Cloning of a novel gene for quinolone resistance from a transferable plasmid in Shigella flexneri 2b. Antimicrob Agents Chemother. 2005, 49 (2): 801-803. 10.1128/AAC.49.2.801-803.2005View ArticlePubMedPubMed CentralGoogle Scholar
- Jacoby GA, Walsh KE, Mills DM, Walker VJ, Oh H, Robicsek A, Hooper DC: qnrB, another plasmid-mediated gene for quinolone resistance. Antimicrob Agents Chemother. 2006, 50 (4): 1178-1182. 10.1128/AAC.50.4.1178-1182.2006View ArticlePubMedPubMed CentralGoogle Scholar
- Pons MJ, Gomes C, Ruiz J: QnrVC, a new transferable Qnr-like family. Enferm Infecc Microbiol Clin. 2013, 31 (3): 191-192. 10.1016/j.eimc.2012.09.008View ArticlePubMedGoogle Scholar
- Wang M, Guo Q, Xu X, Wang X, Ye X, Wu S, Hooper DC: New plasmid-mediated quinolone resistance gene, qnrC, found in a clinical isolate of Proteus mirabilis. Antimicrob Agents Chemother. 2009, 53 (5): 1892-1897. 10.1128/AAC.01400-08View ArticlePubMedPubMed CentralGoogle Scholar
- Cattoir V, Poirel L, Mazel D, Soussy CJ, Nordmann P: Vibrio splendidus as the source of plasmid-mediated QnrS-like quinolone resistance determinants. Antimicrob Agents Chemother. 2007, 51 (7): 2650-2651. 10.1128/AAC.00070-07View ArticlePubMedPubMed CentralGoogle Scholar
- Jacoby GA, Griffin CM, Hooper DC: Citrobacter spp. as a source of qnrB Alleles. Antimicrob Agents Chemother. 2011, 55 (11): 4979-4984. 10.1128/AAC.05187-11View ArticlePubMedPubMed CentralGoogle Scholar
- Poirel L, Rodriguez-Martinez JM, Mammeri H, Liard A, Nordmann P: Origin of plasmid-mediated quinolone resistance determinant QnrA. Antimicrob Agents Chemother. 2005, 49 (8): 3523-3525. 10.1128/AAC.49.8.3523-3525.2005View ArticlePubMedPubMed CentralGoogle Scholar
- Fonseca EL, Dos Santos FF, Vieira VV, Vicente AC: New qnr gene cassettes associated with superintegron repeats in Vibrio cholerae O1. Emerg Infect Dis. 2008, 14 (7): 1129-1131. 10.3201/eid1407.080132View ArticlePubMedPubMed CentralGoogle Scholar
- Guillard T, de Champs C, Moret H, Bertrand X, Scheftel JM, Cambau E: High-resolution melting analysis for rapid characterization of qnr alleles in clinical isolates and detection of two novel alleles, qnrB25 and qnrB42. J Antimicrob Chemother. 2012, 67 (11): 2635-2639. 10.1093/jac/dks292View ArticlePubMedGoogle Scholar
- Sanchez MB, Hernandez A, Rodriguez-Martinez JM, Martinez-Martinez L, Martinez JL: Predictive analysis of transmissible quinolone resistance indicates Stenotrophomonas maltophilia as a potential source of a novel family of Qnr determinants. BMC Microbiol. 2008, 8: 148- 10.1186/1471-2180-8-148View ArticlePubMedPubMed CentralGoogle Scholar
- Boulund F, Johnning A, Pereira MB, Larsson DGJ, Kristiansson E: A novel method to discover fluoroquinolone antibiotic resistance (qnr) genes in fragmented nucleotide sequences. BMC Genomics. 2012, 13: 695- 10.1186/1471-2164-13-695View ArticlePubMedPubMed CentralGoogle Scholar
- Rodriguez-Martinez JM, Velasco C, Briales A, Garcia I, Conejo MC, Pascual A: Qnr-like pentapeptide repeat proteins in gram-positive bacteria. J Antimicrob Chemother. 2008, 61 (6): 1240-1243. 10.1093/jac/dkn115View ArticlePubMedGoogle Scholar
- Lutz R, Bujard H: Independent and tight regulation of transcriptional units in Escherichia coli via the LacR/O, the TetR/O and AraC/I1-I2 regulatory elements. Nucleic Acids Res. 1997, 25 (6): 1203-1210. 10.1093/nar/25.6.1203View ArticlePubMedPubMed CentralGoogle Scholar
- Hegde SS, Vetting MW, Mitchenall LA, Maxwell A, Blanchard JS: Structural and biochemical analysis of the pentapeptide repeat protein EfsQnr, a potent DNA gyrase inhibitor. Antimicrob Agents Chemother. 2011, 55 (1): 110-117. 10.1128/AAC.01158-10View ArticlePubMedPubMed CentralGoogle Scholar
- Lux TM, Lee R, Love J: Complete genome sequence of a free-living Vibrio furnissii sp. nov. strain (NCTC 11218). J Bacteriol. 2011, 193 (6): 1487-1488. 10.1128/JB.01512-10View ArticlePubMedPubMed CentralGoogle Scholar
- Kuo PA, Kuo CH, Lai YK, Graumann PL, Tu J: Phosphate limitation induces the intergeneric inhibition of Pseudomonas aeruginosa by Serratia marcescens isolated from paper machines. FEMS Microbiol Ecol. 2013, 84 (3): 577-587. 10.1111/1574-6941.12086View ArticlePubMedPubMed CentralGoogle Scholar
- Vetting MW, Hegde SS, Wang M, Jacoby GA, Hooper DC, Blanchard JS: Structure of QnrB1, a plasmid-mediated fluoroquinolone resistance factor. J Biol Chem. 2011, 286 (28): 25265-25273. 10.1074/jbc.M111.226936View ArticlePubMedPubMed CentralGoogle Scholar
- Rodriguez-Martinez JM, Briales A, Velasco C, Conejo MC, Martinez-Martinez L, Pascual A: Mutational analysis of quinolone resistance in the plasmid-encoded pentapeptide repeat proteins QnrA. QnrB and QnrS J Antimicrob Chemother. 2009, 63 (6): 1128-1134. 10.1093/jac/dkp111.View ArticlePubMedGoogle Scholar
- Jacoby GA, Corcoran MA, Mills DM, Griffin CM, Hooper DC: Mutational analysis of the Quinolone resistance protein QnrB1. Antimicrob Agents Chemother. 2013, 57 (11): 5733-5736. 10.1128/AAC.01533-13View ArticlePubMedPubMed CentralGoogle Scholar
- Ronquist F, Huelsenbeck JP: MrBayes 3: Bayesian phylogenetic inference under mixed models. Bioinformatics. 2003, 19 (12): 1572-1574. 10.1093/bioinformatics/btg180View ArticlePubMedGoogle Scholar
- Le TM, Baker S, Le TP, Cao TT, Tran TT, Nguyen VM, Campbell JI, Lam MY, Nguyen TH, Nguyen VV, Farrar J, Schultsz C: High prevalence of plasmid-mediated quinolone resistance determinants in commensal members of the Enterobacteriaceae in Ho Chi Minh City. Vietnam J Med Microbiol. 2009, 58 (Pt 12): 1585-1592.PubMedGoogle Scholar
- Zhou TL, Chen XJ, Zhou MM, Zhao YJ, Luo XH, Bao QY: Prevalence of plasmid-mediated quinolone resistance in Escherichia coli isolates in Wenzhou, Southern China, 2002–2008. Jpn J Infect Dis. 2011, 64 (1): 55-57.PubMedGoogle Scholar
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