Nosocomial outbreak of imipenem-resistant Pseudomonas aeruginosa producing VIM-2 metallo-β-lactamase in a kidney transplantation unit

  • S Hammami1Email author,

    Affiliated with

    • I Boutiba-Ben Boubaker1, 2,

      Affiliated with

      • R Ghozzi1, 2,

        Affiliated with

        • M Saidani1, 2,

          Affiliated with

          • S Amine1, 2 and

            Affiliated with

            • S Ben Redjeb1

              Affiliated with

              Diagnostic Pathology20116:106

              DOI: 10.1186/1746-1596-6-106

              Received: 22 August 2011

              Accepted: 28 October 2011

              Published: 28 October 2011

              Abstract

              Background

              Twenty four non replicate imipenem resistant P. aeruginosa were isolated between January and November 2008, in the kidney transplantation unit of Charles Nicolle Hospital of Tunis (Tunisia). This study was conducted in order to establish epidemiological relationship among them and to identify the enzymatic mechanism involved in imipenem resistance.

              Methods

              Analysis included antimicrobial susceptibility profile, phenotypic (imipenem-EDTA synergy test) and genotypic detection of metallo-β-lactamase (MBL) (PCR), O-serotyping and pulsed-field gel electrophoresis.

              Results

              All strains showed a high level of resistance to all antimicrobials tested except to colistin. The presence of MBL showed concordance between phenotypic and genotypic methods. Sixteen isolates were identified as VIM-2 MBL-producers and 13 of them were serotype O4 and belonged to a single pulsotype (A).

              Conclusions

              This study describes an outbreak of VIM-2-producing P. aeruginosa in a kidney transplantation unit. Clinical spread of bla VIM-2 gene is a matter of great concern for carbapenem resistance in Tunisia.

              Keywords

              pulsed-field gel electrophoresis carbapenem P. aeruginosa epidemiology

              Background

              Pseudomonas aeruginosa is a frequent nosocomial pathogen that causes a wide range of opportunistic infections and nosocomial outbreaks [13]. Its high intrinsic resistance to antibiotics and ability to develop multidrug resistance pose serious therapeutic problems. Four broad-spectrum β-lactams, such as carbapenems, are potential drugs for the therapy of infections caused by P. aeruginosa [4, 5]. However, the increasing use of these compounds has resulted in the emergence of carbapenem-resistant P. aeruginosa isolates, limiting treatment options [6, 7]. Most carbapenem resistance is due to impermeability, which arises via loss of the OprD (D2) porin, but carbapenem hydrolysing metallo-β-lactamases (MBLs) are increasingly reported [8]. Genes encoding MBLs are located as cassettes in integrons that provide them with the potential for expression and dissemination [9, 10]. To date, nine MBL types, namely, IMP-like[9], VIM-like[9], SPM-1[11], GIM-1[12], SIM-1[13], AIM-1[14], KHM-1[15], NDM-1[16] and DIM-1[17], have been identified in Gram negative bacilli. Worldwide, the IMP and VIM types are the most commonly detected MBLs in P. aeruginosa [9, 10]. VIM-type MBLs are predominant in the Mediterranean region [9, 10].

              At Charles Nicolle hospital of Tunisia, since November 2002, VIM-2 producing P. aeruginosa has been isolated, mainly in surgery and intensive care unit [18]. In 2008, an increasing rate of imipenem resistance in P. aeruginosa was observed in the kidney transplantation unit. The aim of the present study was to determine the occurrence of MBL genes among imipenem resistant isolates and to establish epidemiological relationship among them.

              Methods

              Patients, Bacterial strains, Serotyping and susceptibility testing

              Twenty four non duplicate imipenem resistant P. aeruginosa isolates were recovered between January and November 2008 in the kidney transplantation unit of Charles Nicolle hospital of Tunis. They were isolated from urine (n = 20), cutaneous pus (n = 3) and blood (n = 1).

              All samples were taken for microbial diagnosis from 24 different patients [sex ratio 3.8]. The median age of the patients was 51 years [range: 34 to 80 years]. They were admitted in the urology unit (n = 10) and nephrology unit (n = 14).

              A retrospective review was conducted for only 15 patients (6 from urology unit, 9 from the nephrology unit). Date of transplantation was mentioned in Table 1. However, no data concerning kind of transplantation and live donator was collected. All patients presented chronic renal failure associated in 13 cases to at least one underlying co-morbidity [High blood pressure (n = 13), systemic lupus erythematosis (n = 1), diabetes (n = 1), chronic glomerulonephritis (n = 5), nephritic syndrome (n = 1) and renal tuberculosis (n = 1)]. In all patients fever was the major symptom. Ceftazidime combination therapy with colistin accounted for all patients. Attributable mortality was 5% of cases.
              Table 1

              Characteristics of imipenem resistant P. aeruginosa strains

                      

              MICs

               

              Strains

              Date of transplantation

              Date of Isolation

              Age/Gender

              Speciman

              EDTA test

              PCR VIM-2

              Serotype

              TIC

              TCC

              IMP

              MEM

              CAZ

              AZT

              FEP

              PFGE

              1

              27/11/2007

              04/01/2008

              45/F

              Cu Pus

              -

              -

              O11

              > 2048

              > 1024

              256

              512

              2048

              > 512

              > 256

              ND

              2

              -

              23/01/2008

              54/M

              Urine

              +

              +

              O11

              > 2048

              > 1024

              > 512

              > 512

              64

              > 512

              > 256

              C

              3

              NT

              06/02/2008

              61/M

              Urine

              -

              -

              O4

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              ND

              4

              -

              10/04/2008

              47/M

              Urine

              +

              +

              O11

              > 2048

              > 1024

              > 512

              > 512

              64

              > 512

              > 256

              C

              5

              7/12/2007

              12/05/2008

              45/F

              Cu Pus

              -

              -

              NA

              > 2048

              > 1024

              > 512

              512

              1024

              > 512

              > 256

              ND

              6

              -

              20/05/2008

              61/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              A

              7

              -

              20/05/2008

              52/M

              Urine

              -

              -

              O12

              > 2048

              > 1024

              > 512

              512

              512

              > 512

              > 256

              ND

              8

              20/12/2007

              18/06/2008

              45/F

              Cu Pus

              -

              -

              O11

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              ND

              9

              -

              24/06/2008

              75/M

              Urine

              -

              -

              O4

              > 2048

              > 1024

              512

              > 512

              1024

              > 512

              > 256

              ND

              10

              NT

              04/07/2008

              63/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              1024

              > 512

              > 256

              A

              11

              08/07/2008

              09/07/2008

              34/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              1024

              > 512

              > 256

              A

              12

              -

              21/07/2008

              52/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              1024

              > 512

              > 256

              A

              13

              -

              26/07/2008

              54/M

              Urine

              -

              -

              O4

              > 2048

              > 1024

              > 512

              512

              1024

              > 512

              > 256

              ND

              14

              -

              02/08/2008

              76/M

              Urine

              +

              +

              NA

              > 2048

              > 1024

              > 512

              512

              64

              > 512

              256

              D

              15

              16/07/2008

              02/08/2008

              42/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              256

              > 512

              > 256

              A

              16

              10/08/2008

              21/08/2008

              52/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              512

              512

              > 512

              > 256

              A

              17

              18/08/2008

              26/08/2008

              52/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              A

              18

              -

              03/10/2008

              20/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              32

              64

              > 512

              > 256

              A

              19

              28/08/2008

              06/10/2008

              80/M

              Urine

              -

              -

              NA

              > 2048

              > 1024

              > 512

              > 512

              4

              > 512

              > 256

              ND

              20

              -

              01/11/2008

              54/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              A

              21

              17/10/2008

              05/11/2008

              31/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              A

              22

              05/11/2008

              17/11/2008

              34/F

              Blood

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              A

              23

              15/11/2008

              17/11/2008

              34/F

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              512

              > 512

              > 256

              A

              24

              10/09/2008

              22/11/2008

              52/M

              Urine

              +

              +

              O4

              > 2048

              > 1024

              > 512

              > 512

              1024

              > 512

              > 256

              A

              TIC: Ticarcillin; TCC: Ticarcillin-clavulanic acid; IMP: Imipenem; MEM: Meropenem; CAZ: Ceftazidim; AZT: Aztreonam; FEP: Cefepime; -: clinical data Not found; NT: No Tranplantation; Cu Pus: Cutaneous Pus; NA: Non Agglutinable; ND: Not determined.

              Bacterial identification was performed using ApiNE (bio-Mérieux, Marcy-l'Etoile, France). O-serotyping was determined by slide agglutination test using polyvalent antisera and 16 monovalent antisera numbered O1-O16 according to the manufacturer's instructions (Bio-Rad, Marnes-La-Coquette, France).

              Antimicrobial susceptibility was tested with the agar disk diffusion method according to the CLSI guidelines [19]. The MICs of ticarcillin, ticarcillin + clavulanic acid, ceftazidime, aztreonam, cefepime, imipenem and meropenem were determined using the dilution method in Mueller Hinton agar according to the CLSI guidelines [19]. E. coli ATCC 25922 and P. aeruginosa ATCC 27853 were used as control strains.

              To detect MBL production, the imipenem-EDTA synergy test was used [20]. An enlargement of the inhibition zone of imipenem facing the disc of EDTA was considered as a positive test.

              PCR amplification

              For the detection of bla VIM and bla IMP genes PCR experiments were performed using consensus primers as described previously [21]. Primers specific for bla VIM-2 were also used [22].

              Clonal relationship by Pulsed-Field Gel Electrophoresis (PFGE)

              Molecular typing of MBL producing isolates was carried out, as described previously by Pulsed-Field Gel Electrophoresis (PFGE) using SpeI restriction endonuclease [23]. Clonal relationships based on PFGE patterns were interpreted according to the criteria proposed by Tenover et al [24].

              Results and discussion

              Carbapenems are potent agents against multiresistant Gram negative bacilli, including P. aeruginosa, but their efficacy is increasingly compromised by the emergence and the worldwide dissemination of carbapenem resistance strains, which are implicated in large outbreaks as described in many countries [1, 25]. In Tunisia, frequencies of imipenem resistant P. aeruginosa varies between 16% and 37.6% [2628]. At Charles Nicolle Hospital of Tunis, their frequency was stable until 2004 (1%), but increased dramatically from 2005 (25%). They were mainly isolated in surgery and intensive care unit [18], but in 2008, an increasing rate of multidrug-resistant P. aeruginosa was observed in the kidney transplantation unit. All strains exhibited a multidrug-resistant phenotype; they were resistant to antipseudomonal β-lactams (including aztreonam), aminoglycosides and fluoroquinolones. They remained susceptible only to colistin which is used for the treatment of our kidney transplanted patients despite its renal toxicity [29]. MICs results are shown in table 1. All strains showed a high level of resistance to all β-lactams, particularly to carbapenems (> 512 μg/ml). Only 16 strains (67%) were positive according to the imipenem-EDTA synergy test, suggesting the presence of MBLs. The acquisition of a MBL gene alone does not necessarily confer elevated level of resistance to carbapenems. Indeed, secondary changes in regulatory system of MBL gene expression, outer membrane permeability, active efflux systems in bacterial membrane, and/or multiplication of structure gene might well be implicated in acquisition of high-level carbapenem resistance [30, 31]. Aztreonam is the only β-lactam that may remain fully active against MBL producers [8], however all our strains were resistant to this β-lactam, suggesting the occurrence of other mechanisms of β-lactam resistance [32]. The eight MBL negative strains were also resistant to all antibiotic tested (Table 1), but the mechanism involved in the resistance has not been further examined.

              The 16 MBLs-producer strains were positive for bla VIM-2 gene and none strain harboured the bla IMP gene (Table 1). In Tunisia, the most common MBL identified VIM-2 in accordance with the actual situation worldwide [9, 33, 34]. Historically, the first reports of MBLs genes were VIM-2 and VIM-4 types in P. aeruginosa [18, 35] and K. pneumoniae [36] respectively.

              Serotyping identified 3 serotypes: O4 (n = 16), O11 (n = 4) and O12 (n = 1) (table 1). Only 2 strains were nontypeable with monovalent antisera. In Tunisia [37] as well as in many European countries [38], it has been repeatedly demonstrated over the past 20 years that serotypes O11 and O12 dominate among multiresistant P. aeruginosa isolates. The 16 MBL-positive strains were divided into 3 pulsotypes designed A (n = 13), B (n = 2) and C (n = 1) (Table 1). The 13 strains of pulsotype A were of serotype O4. These results imply that the dissemination of VIM-2 in our kidney transplantation unit was mainly due to the of spread clonal strains, however, unrelated VIM-2-harboring strains occurred. Outbreaks of VIM β-lactamase-producing P. aeruginosa have been also reported in Greece [3], Italy [2] and Kenya [39], but there is still very limited knowledge on the epidemiology of MBLs in Africa.

              The emergence of acquired MBLs among P. aeruginosa represents an epidemiological risk for at least two reasons: firstly, MBLs confer resistance not only to carbapenems but to virtually all β-lactams and are frequently associated with resistance to aminoglycosides; and secondly, genes encoding for MBL enzymes are most commonly carried on mobile genetic elements (integrons, plasmids, transposons) that can spread horizontally among unrelated strains [9, 18].

              Indeed, the bla VIM-2 gene was found in strains of different genotypes (A, B and C), reflecting its ability to transfer from one bacterium to another.

              Conclusion

              In conclusion, we found an outbreak of VIM-2-producing P. aeruginosa in a kidney transplantation unit. Thus, bla VIM-2 gene may have been spreading in Gram negative rod in Tunisia. This emphasizes the necessity of early recognition of MBL producing isolates, rigorous infection control, and restricted clinical use of broad-spectrum β-lactams including carbapenems.

              List of abbreviations

              MBL: 

              metallo-beta-lactamase

              PFGE: 

              Pulsed-Field Gel Electrophoresis.

              Declarations

              Acknowledgements

              This work was financed by grants from the Ministry of Scientific Research, Technology and Competence Development of Tunisia.

              Authors’ Affiliations

              (1)
              Laboratoire «Résistance aux Antimicrobiens », Faculté de Médecine de Tunis Université Elmanar
              (2)
              Laboratoire de Microbiologie, Hôpital Charles Nicolle

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              Copyright

              © Hammami et al; licensee BioMed Central Ltd. 2011

              This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://​creativecommons.​org/​licenses/​by/​2.​0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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