Abstract
Pseudomonas aeruginosa is an opportunistic pathogen that poses a threat in clinical settings. This study aimed to investigate the molecular characterization and epidemiology of fluoroquinolones (FQs) resistance in P. aeruginosa isolated from South China. A total of 256 P. aeruginosa strains isolated from outpatients, emergency patients and inpatients were collected from January 2010 to December 2010 in the hospital of South China. The resistance profile of all isolated strains was screened by antibiotic-susceptibility testing, and the molecular characteristics of plasmid-mediated quinolone resistance (PMQR) and the quinolone resistance determining region (QRDR) were determined using PCR in combination with DNA sequencing. The result of antibiotic-susceptibility tests showed that most strains were sensitive to polymyxin B, piperacillin, piperacillin/tazobactam, ceftazidime and amikacin. Moreover, 65 isolates were identified as resistant to ciprofloxacin. Further analysis of QRDR revealed that the resistant strains carried at least one mutation in the gyrA (The83Ile), gyrB (Ser467Phe, Gln468His) and parC (Ser87Leu) genes, but no mutation was detected in parE. For the first time, we report here that the qnrA1 gene is associated with low levels of resistance to ciprofloxacin from clinical P. aeruginosa isolates in South China. The mutation of gyrA (at position 83) is clearly linked to the FQs resistance of P. aeruginosa. Moreover, FQs resistance of P. aeruginosa may be due to the chromosome-mediated resistance mechanism rather than PMQR.
Keywords: Fluoroquinolone resistance, PMQR, QRDR, Pseudomonas aeruginosa
Introduction
Pseudomonas aeruginosa is one of the most common and important opportunist gram-negative pathogens causing hospital-acquired infections [1]. The pressure of antibiotics has led to the rapid development of bacterial resistance. Among these antibiotics, Fluoroquinolones (FQs) are some of the most commonly prescribed effective antimicrobials against P. aeruginosa infections. Unfortunately, overuse of FQs in medicine has promoted bacterial resistance to FQs in recent years, which has caused a huge challenge in the anti-infective therapy of P. aeruginosa [2,3]. Therefore, the monitoring of antimicrobial susceptibility is crucial for selecting effective antimicrobial agents in the treatment of this disease.
Substantial evidences have shown that resistance to FQs is mainly due to: (i) the point mutations in the DNA gyrase (gyrA and gyrB) and topoisomerase IV (parC and parE) genes, (ii) the presence of transferable plasmid-mediated quinolone resistance (PMQR) determinants, and (iii) mutations in genes regulating the expression of efflux pumps and decreased expression of outer membrane porins [4]. The aim of this study was to investigate the prevalence and molecular characteristics of P. aeruginosa in South China, including antimicrobial susceptibility, and whether they present transferable PMQR genes or mutations of quinolone resistance determining region (QRDR), in order to assess the resistance mechanisms of P. aeruginosa in the local area.
Materials and methods
Bacterial isolates
A total of 256 isolates of non-duplicated P. aeruginosa from outpatients, emergency patients and inpatients were collected from the Third Affiliated Hospital of Sun Yat-sen University between January 2010 and December 2010. All strains were identified by the MicroScan WalkAway-40 automatic microorganism analyzer.
Susceptibility testing
The antibiotics susceptibility of all P. aeruginosa isolates to 19 common antibiotics was determined by methods of K-B disk diffusion. Nineteen common antibiotics, including Piperacillin (PIP, 100 μg), piperacillin/tazobactam (TZP, 100 μg/10 μg), Amoxycillin/clavulanic acid (AMC, 20 μg/10 μg), Ampicillin/sulbactam (SAM, 10 μg/10 μg), Ticarcillin/clavulanic acid (TIC, 75 μg/10 μg), Aztreonam (ATM, 30 μg), Cefoperazone (CPZ, 75 μg), Cefoperazone/sulbactam (SCF, 75 μg/30 μg), Cefoxitin (FOX, 30 μg), Ceftriaxone (CRO, 30 μg), Ceftazidime (CAZ, 30 μg), Ceftne (FEP, 30 μg), Imipenem (IMP, 10 μg), Ciprofloxacin (CIP, 5 μg), Levofloxacin (LVX, 5 μg), Moxifloxacin (MXF, 5 μg), Gentamycin (GM, 10 μg), Amikacin (AK, 30 μg), and Polymyxin B (PB, 10 μg), were used. Generally, the breakpoints for the antimicrobial agents for P. aeruginosa were according to standards from the Clinical and Laboratory Standards Institute (CLSI). The reference strains Escherichia coli ATCC25922 and P. aeruginosa ATCC 27853 served as quality control strains for MIC determinations.
Screening for PMQR genes
PCR amplification of PMQR genes (qnrA, qnrB, qnrC, qnrD, qnrS, aac (6’)-Ib and qepA) was performed [5,6]. Genomic DNA templates of the 256 P. aeruginosa strains were prepared according to the standard boiling method [7]. Purified PCR products were cloned into pGEM-T (TAKARA, Dalian, China) and then sequenced using the Applied Biosystems ABI3730 Analyser (Applied Biosystems, Inc., USA).
Determination of QRDR of gyrA, gyrB, parC and parE
To identify QRDR mutations in FQs-resistant P. aeruginosa, the gyrA, gyrB, parC and parE genes were amplified and then sequenced as described above [8]. To determine the mutations in these genes, the sequences were aligned with Clustal X.
Results
Bacterial isolates
Overall, 256 clinical isolates of P. aeruginosa were isolated from sputum (80.5%), urine (7.0%) and wound secretions (4.7%). The top three sample sources were the intensive care unit (ICU), respiratory medicine and the neurosurgery department, with proportions of 26.5% (68/256), 25.0% (64/256) and 15.2% (39/256) (Tables 1 and 2).
Table 1.
Distribution of specimens among 256 P. aeruginosa clinical isolates
| Specimens | Isolates | Rate (%) |
|---|---|---|
| Sputum | 206 | 80.5 |
| Urine | 18 | 7.0 |
| Wound secretions | 12 | 4.7 |
| Bile | 7 | 2.7 |
| Blood | 6 | 2.4 |
| Other | 7 | 2.7 |
Table 2.
Distribution of P. aeruginosa isolates in the department
| Department | Isolates | Rate (%) |
|---|---|---|
| ICU | 68 | 26.5 |
| Respiratory Medicine | 64 | 25.0 |
| Neurosurgery | 39 | 15.2 |
| Rehabilitation | 14 | 5.5 |
| Hepatobiliary surgery | 13 | 5.1 |
| Urinary | 10 | 3.9 |
| Infectious disease | 8 | 3.1 |
| Thoracic surgery | 7 | 2.7 |
| Cardiovascular | 6 | 2.3 |
| Emergence | 6 | 2.3 |
| Tumour | 5 | 2.0 |
| Haematology | 5 | 2.0 |
| Gastrointestinal surgery | 4 | 1.6 |
| Dermatology | 4 | 1.6 |
| Rheumatology | 3 | 1.2 |
Antibiotics resistance in P. aeruginosa
The results of the antibiotic-susceptibility tests are shown in Table 3. Polymyxin B had the highest susceptibility rate (98.8%), while the susceptibility of piperacillin, piperacillin/tazobactam, ceftazidime, amikacin and ciprofloxacin were about 70.0%-80.0%. Lower efficacy was observed in isolates when using ticarcillin/clavulanic acid, cefoperazone/sulbactam, cefepime, imipenem, gentamicin, moxifloxacin. The antibiotic-susceptibility of levofloxacin was between 60.0% and 70.0%. There were no more than 30% of isolates with resistance to cefoperazone and aztreonam. In contrast, more strains were found to be resistant to ampicillin/sulbactam, amoxicillin/clavulanic acid, ceftriaxone and cefoxitin, with less than 10% detected.
Table 3.
P. aeruginosa isolates antimicrobial resistance profiles from South China isolates
| Antimicrobials | Resistant (R) | Intermediate (I) | Sensitive (S) | |||
|---|---|---|---|---|---|---|
|
| ||||||
| Isolates | Rate (%) | Isolates | Rate (%) | Isolates | Rate (%) | |
| Piperacillin | 75 | 29.3 | 0 | 0.0 | 181 | 70.7 |
| Piperacillin/tazobactam | 58 | 22.7 | 0 | 0.0 | 198 | 77.3 |
| Amoxycillin/clavulanic acid | 248 | 96.9 | 0 | 0.0 | 8 | 3.1 |
| Ampicillin/sulbactam | 250 | 97.7 | 0 | 0.0 | 6 | 2.3 |
| Ticarcillin/clavulanic acid | 93 | 36.3 | 0 | 0.0 | 163 | 63.7 |
| Cefoperazone | 69 | 27.0 | 41 | 16.0 | 146 | 57.0 |
| Cefoperazone/sulbactam | 48 | 18.7 | 46 | 18.0 | 162 | 63.3 |
| Ceftriaxone | 195 | 76.2 | 46 | 18.0 | 15 | 5.8 |
| Ceftazidime | 54 | 21.1 | 16 | 6.3 | 186 | 72.6 |
| Cefepime | 48 | 18.8 | 42 | 16.4 | 166 | 64.8 |
| Cefoxitin | 251 | 98.0 | 0 | 0.0 | 5 | 2.0 |
| Aztreonam | 78 | 30.5 | 38 | 14.8 | 140 | 54.7 |
| Imipenem | 70 | 27.4 | 18 | 7.0 | 168 | 65.6 |
| Ciprofloxacin | 65 | 25.4 | 11 | 4.3 | 180 | 70.3 |
| Levofloxacin | 73 | 28.5 | 21 | 8.2 | 162 | 63.3 |
| Moxifloxacin | 71 | 27.7 | 22 | 8.6 | 163 | 63.7 |
| Gentamycin | 56 | 21.9 | 28 | 10.9 | 172 | 67.2 |
| Amikacin | 42 | 16.4 | 11 | 4.3 | 203 | 79.3 |
| Polymyxin B | 3 | 1.2 | 0 | 0.0 | 253 | 98.8 |
Identification of PMQR genes
PCR screening and sequence analysis showed that only one isolate presented the PMQR determinants (qnrA1) in 256 P. aeruginosa, and the ciprofloxacin MIC was 2 μg/ml. However, other PMQR genes, qnrB, qnrC, qnrD, qnrS, aac (6’)-Ib-cr and qepA, were not found in all of the detected strains.
Analysis of the mutations in QRDR
Mutations in the QRDR of gyrA, gyrB, parC and parE were identified; the results are presented in Table 4. Among the 65 ciprofloxacin-resistant P. aeruginosa clinical isolates, 49 strains (75.4%) showed a missense mutation of Thr (ACC)→Ile (ATC) at the 83rd codon of the gyrA gene. Two strains (3.1%) reported the presence of an independent missense mutation in the gyrB gene of Ser467 (TCC)→Phe (TTC) and Gln468 (CAG)→His (CAT). Fifteen strains (23.1%) presented a missense mutation from Ser (TCG)→Leu (TTG) at the 87th codon of the parC gene. Moreover, strains carrying either gyrB or parC gene missense mutations were all accompanied by a gyrA gene missense mutation as well. However, none of the mutations mentioned above in were found in the 10 strains of ciprofloxacin-sensitive P. aeruginosa that were randomly drawn from 180 clinical isolates. The MIC values of ciprofloxacin were significantly higher in the strains with double mutations of either gyrA plus gyrB or gyrA plus parC than in those with only a gyrA gene mutation. In contrast, no missense mutation was found in the parE gene.
Table 4.
Mutations in the QRDRs and the MIC of CIP in P. aeruginosa isolates
| Mutations in QRDRs | Number of strains | MIC (μg/ml) | |||
|---|---|---|---|---|---|
|
| |||||
| gyrA | gyrBa | parC | parEb | ||
| Thr83Ile | — | — | — | 32 | 4~256 |
| Thr83Ile | Ser467Phe | — | 1 | 128 | |
| Thr83Ile | Gln468His | — | 1 | 256 | |
| Thr83Ile | — | Ser-87→Leu | — | 15 | 32~256 |
Other mutations in gyr B: GAA-457→GAG, GCG-459→GCA, GGC-482→GGT, ACG-472→ACT, GAA-485→GAG, ACC-475→ACT.
Mutations in parE: AAC-374→AAT, GTG-465→GTA, GGT-472→GGC, AGT-474→AGC, GCC-477→GCT, GGG-494→GGC, CGC-507→CGT.
Discussion
P. aeruginosa has been recognized as a major pathogen that can caused healthcare-associated infection (HCAI), especially ventilator-associated pneumonia. However, increasing antimicrobial resistance among P. aeruginosa has become a major concern when managing its associated infections [9]. It has been reported that most of the P. aeruginosa samples were isolated from lower respiratory tract secretions [10]. Similarly, in this study, isolates were mainly isolated from the sputum, urine and puriform secretions, supporting the suggestion that P. aeruginosa has held a nearly unchanged position in the rank order of pathogens causing ICU-related infections [11,12].
Due to the presence of several drug efflux systems and porins, P. aeruginosa is intrinsically resistant to a wide range of antimicrobials. Our results also confirmed the low occurrence of cefoperazone/sulbactam, ceftazidime, amikacin and ciprofloxacin resistance among P. aeruginosa in South China, and showed a relatively high susceptibility to beta-lactam, aminoglycosides and polymyxin. With increasing utilization of fluoroquinolones in both human and veterinary medicine, emerging resistance has become a significant concern. However, in this study, more than 60% of P. aeruginosa showed susceptibility to ciprofloxacin, levofloxacin and moxifloxacin. Moreover, 70.3% of isolates were susceptible to ciprofloxacin. Other reports showed that FQs resistance of P. aeruginosa was related to the widespread use of levofloxacin rather than ciprofloxacin [13]. Therefore, ciprofloxacin should be preferred when treating P. aeruginosa infections in clinical scenarios.
To date, PMQR genes (qnrA, qnrB, qnrS, qnrD and qepA) have been reported in veterinary clinical isolates in China [14]. In 2008, Libisch et al. found that the aac (6’)-Ib-cr gene was present in the PER-1 and ESBLs-positive P. aeruginosa clinical isolates [15]. However, for the first time, we isolated one P. aeruginosa strain with qnrA1 gene, and the MIC of CIP was 2 μg/ml, suggesting that qnrA1 may mediate the low-level resistance to CIP.
The presence of mutations is associated with resistance; for example, mutations in gyrA (Thr83→Ile, Asp87→Asn), gyrB (Ser464→Phe), and parC (Ser87→Leu) were related to the FQs resistance of P. aeruginosa [9]. It is worth noting that gyrA (at codon 83) was present in 75.4% strains, and 15 (23.1%) of isolates had mutations in parC (at codon 87), suggesting that gyrA mutations are closely correlated with FQs resistance in P. aeruginosa. Moreover, some other mutations, including those in gyrA, gyrB and parC, were found in these strains, which need further verification.
In summary, our work provided novel data on the molecular epidemiology of antimicrobial resistance in P. aeruginosa. Moreover, for the first time, we described P. aeruginosa containing qnrA1 gene in South China. Our study revealed that multiple target gene mutations play an important role in the FQs resistance of P. aeruginosa, not only providing a scientific basis for further studying the mechanism of FQs resistance, but also highlighting its usefulness in the treatment and control of this infection.
Acknowledgements
This work was supported by grants from the Scientific Technologic Research Fund of Guangdong Province, China (NO. 2011B021800075).
Disclosure of conflict of interest
None.
References
- 1.Solomon S, Horan T, Andrus M. National Nosocomial Infections Surveillance (NNIS) system report, data summary from January 1992 through June 2003, issued August 2003. Am J Infect Control. 2003;31:481–498. doi: 10.1016/j.ajic.2003.09.002. [DOI] [PubMed] [Google Scholar]
- 2.Jones RN, Beach ML, Pfaller MA. Spectrum and activity of three contemporary fluoroquinolones tested against Pseudomonas aeruginosa isolates from urinary tract infections in the SENTRY Antimicrobial Surveillance Program (Europe and the Americas; 2000): More alike than different! Diagn Microbiol Infect Dis. 2001;41:161–163. doi: 10.1016/s0732-8893(01)00287-5. [DOI] [PubMed] [Google Scholar]
- 3.Linder JA, Huang ES, Steinman MA, Gonzales R, Stafford RS. Fluoroquinolone prescribing in the United States: 1995 to 2002. Am J Med. 2005;118:259–268. doi: 10.1016/j.amjmed.2004.09.015. [DOI] [PubMed] [Google Scholar]
- 4.Hall RM. Mobile gene cassettes and integrons: moving antibiotic resistance genes in gram-negative bacteria. Ciba Found Symp. 1997;207:192–202. doi: 10.1002/9780470515358.ch12. [DOI] [PubMed] [Google Scholar]
- 5.Cavaco L, 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;53:603–608. doi: 10.1128/AAC.00997-08. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Kim HB, Park CH, Kim CJ, Kim EC, Jacoby GA, Hooper DC. Prevalence of plasmid-mediated quinolone resistance determinants over a 9-year period. Antimicrob Agents Chemother. 2009;53:639–645. doi: 10.1128/AAC.01051-08. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Sambrook J, Russell D. Molecular cloning: A Laboratory Manual. New York: Cold Spring Harbor Laboratory Press; 2001. [Google Scholar]
- 8.Akasaka T, Tanaka M, Yamaguchi A, Sato K. Type II topoisomerase mutations in fluoroquinolone-resistant clinical strains of Pseudomonas aeruginosa isolated in 1998 and 1999: role of target enzyme in mechanism of fluoroquinolone resistance. Antimicrob Agents Chemother. 2001;45:2263–2268. doi: 10.1128/AAC.45.8.2263-2268.2001. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Hsueh PR, Hoban DJ, Carmeli Y. Consensus review of the epidemiology and appropriate antimicrobial therapy of complicated urinary tract infections in Asia-Pacific region. J Infect. 2011;63:114–123. doi: 10.1016/j.jinf.2011.05.015. [DOI] [PubMed] [Google Scholar]
- 10.Rossolini G, Mantengoli E. Treatment and control of severe infections caused by multiresistant Pseudomonas aeruginosa. Clin Microbiol Infect. 2005;11:17–32. doi: 10.1111/j.1469-0691.2005.01161.x. [DOI] [PubMed] [Google Scholar]
- 11.Grundmann H, Kropec A, Hartung D, Berner R, Daschner F. Pseudomonas aeruginosa in a neonatal intensive care unit: reservoirs and ecology of the nosocomial pathogen. J Infect Dis. 1993;168:943–947. doi: 10.1093/infdis/168.4.943. [DOI] [PubMed] [Google Scholar]
- 12.Trautmann M, Michalsky T, Wiedeck H, Radosavljevic V, Ruhnke M. Tap water colonisation with Pseudomonas aeruginosa in a surgical intensive care unit (ICU) and relation to Pseudomonas infections of ICU patients. Infect Control Hosp Epidemiol. 2001;22:49–52. doi: 10.1086/501828. [DOI] [PubMed] [Google Scholar]
- 13.Lee YJ, Liu HY, Lin YC, Sun KL, Chun CL, Hsueh PR. Fluoroquinolone resistance of Pseudomonas aeruginosa isolates causing nosocomial infection is correlated with levofloxacin but not ciprofloxacin use. Intl J Antimicrob Agents. 2010;35:261–264. doi: 10.1016/j.ijantimicag.2009.11.007. [DOI] [PubMed] [Google Scholar]
- 14.Zhao JJ, Chen ZL, Chen S, Deng YT, Liu YH, Tian W, Huang XH, Wu CM, Sun YX, Sun Y, Zeng ZL, Liu JH. Prevalence and dissemination of oqxAB in Escherichia coli isolates from animals, farmworkers, and the environment. Antimicrob Agents Chemother. 2010;54:4219–4224. doi: 10.1128/AAC.00139-10. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Libisch B, Poirel L, Lepsanovic Z. Identification of PER-1 extended-spectrum β-lactamase producing Pseudomonas aeruginosa clinical isolates of the international clonal complex CC11 from Hungary and Serbia. FEMS Immunol Med Microbiol. 2008;54:330–338. doi: 10.1111/j.1574-695X.2008.00483.x. [DOI] [PubMed] [Google Scholar]