Abstract
The Carba NP test has been evaluated to detect carbapenemase-producing Pseudomonas spp. directly from blood cultures. This rapid and cost-effective test permits an early identification of carbapenemase-producing Pseudomonas spp. directly from blood cultures with excellent sensitivity and specificity. Results may be useful in particular for guiding the first-line therapy and epidemiological purposes.
TEXT
Pseudomonas aeruginosa shows a remarkable capacity to resist antibiotics. This pathogen is intrinsically resistant to narrow-spectrum β-lactams due to the constitutive expression of β-lactamases and efflux pumps and the low permeability of the outer membrane (1). In addition, acquired extended-spectrum β-lactamases (ESBLs) of the PER, VEB, and GES types have been reported in P. aeruginosa (2). Consequently, the treatment of P. aeruginosa-related infections is becoming increasingly difficult, and therefore carbapenem-containing treatments are frequently needed to treat those infections.
Carbapenem resistance in Pseudomonas spp. can result from different mechanisms, such as a decreased bacterial outer membrane permeability (e.g., loss or modification of the OprD2 porin or overexpression of efflux pumps), often associated with overexpression of β-lactamases possessing no significant carbapenemase activity (AmpCs) or to expression of true carbapenemases (1, 3). Carbapenemases have been reported in Pseudomonas spp., including the Ambler class A KPC- and GES-type β-lactamases and most commonly the Ambler class B or metallo-β-lactamases (MBLs) of the VIM, IMP, SPM, GIM, AIM, DIM, FIM, and NDM types (1, 3–7).
Spread of carbapenemase-producing P. aeruginosa strains is a critical issue since those strains are resistant to almost all β-lactams. In addition, the early detection of carbapenemases is important because carbapenemase genes are usually located on transferable genetic determinants such as plasmids, leading to their rapid dissemination. Carbapenemase producers are commonly first screened based on susceptibility testing results. Then, specific phenotypical tests may be used to identify carbapenemase production in vitro, such as the modified Hodge test (8). Other detection methods based on the inhibitory properties of EDTA (against MBL) and boronic acid or clavulanic acid (for KPC) allow the discrimination of the different carbapenemase types. Since those techniques are performed on strains grown on agar plates, they do require at least an additional 24- to 48-h period of time after the blood culture is flagged as positive, and significant expertise is needed (9), particularly with P. aeruginosa (10). Molecular methods remain costly and require substantial expertise (11, 12). Overall, both phenotypic and molecular tests are time-consuming and consequently not suited for routine and rapid testing. One of the most recent and reliable techniques for the detection of carbapenemase-producing P. aeruginosa is the biochemically based Carba NP test (11). This test, applied on isolated cultures, detects all types of carbapenemase-producing P. aeruginosa isolates with the exception of several GES-type producers (13). In addition, this test may be used for detecting carbapenemase-producing Enterobacteriaceae from blood (12).
The aim of this study was to determine the ability of the Carba NP test to detect carbapenemase-producing Pseudomonas species directly from blood cultures. Since the successful treatment of bacteremia depends on prompt administration of the appropriate antibiotherapy, the routine use of the Carba NP test directly on blood culture may guide the first-line therapy for patients with sepsis (13).
The Carba NP test was performed on spiked blood cultures from which the positivity was assessed using the BacT/Alert blood culture system (bioMérieux, Marcy l'Etoile, France). Blood cultures (10 ml of sterile human blood) were inoculated with 1 × 103 CFU of each strain (500-μl total volume) (Table 1). The inoculum of 1 × 103 CFU was prepared by diluting a 0.5 McFarland standard suspension (108 CFU/ml) in sterile water. Then, aerobic bottles (BacT/Alert SA standard aerobic bottles without charcoal) were incubated until a positivity of the blood culture was detected by the BacT/Alert system (detection time ranged from 6 to 15 h). As previously described, the final bacterial count at the time of positivity ranged from 5 × 107 to 5 × 109 CFU/ml (14).
TABLE 1.
Carbapenemase-producing strains included in this study and found positive using the Carba NP test
| Ambler class | Carbapenemase type | Pseudomonas organism | Carbapenemase | MIC (μg/ml)a |
|
|---|---|---|---|---|---|
| IMP | MER | ||||
| A | KPC | P. aeruginosa COL | KPC-2 | >32 | >32 |
| KPC | P. aeruginosa P13 | KPC-2 | >32 | >32 | |
| KPC | P. aeruginosa PA-2 | KPC-2 | >32 | >32 | |
| KPC | P. aeruginosa PA-3 | KPC-2 | >32 | >32 | |
| GES | P. aeruginosa GW-1 | GES-2 | 3 | 1 | |
| GES | P. aeruginosa P-35 | GES-5 | >32 | >32 | |
| B | VIM | P. aeruginosa P0510 | VIM-1 | >32 | >32 |
| VIM | P. fluorescens COU | VIM-1 | >32 | >32 | |
| VIM | P. aeruginosa JOU | VIM-1 | >32 | >32 | |
| VIM | P. aeruginosa ABA | VIM-1 | >32 | >32 | |
| VIM | P. aeruginosa REZ | VIM-2 | >32 | >32 | |
| VIM | P. putida 9335 | VIM-2 | >32 | >32 | |
| VIM | P. stutzeri P511503100 | VIM-2 | >32 | >32 | |
| VIM | P. aeruginosa BY25753 | VIM-2 | >32 | >32 | |
| VIM | P. aeruginosa V919005 | VIM-2 | >32 | >32 | |
| VIM | P. aeruginosa AK5493 | VIM-2 | >32 | >32 | |
| VIM | P. aeruginosa KA-209 | VIM-2 | >32 | >32 | |
| VIM | P. putida NTU 91/99 | VIM-2 | >32 | >32 | |
| VIM | P. aeruginosa COL-1 | VIM-2 | >32 | >32 | |
| VIM | P. aeruginosa CAS | VIM-2 | >32 | >32 | |
| VIM | P. aeruginosa JAC | VIM-4 | >32 | >32 | |
| VIM | P. aeruginosa MED | VIM-5 | >32 | >32 | |
| IMP | P. aeruginosa 12870 | IMP-1 | 12 | >32 | |
| IMP | P. stutzeri PB207 | IMP-1 | 2 | 4 | |
| IMP | P. putida NTU 92/99 | IMP-1 | 1 | 0.19 | |
| IMP | P. aeruginosa | IMP-1 | >32 | >32 | |
| IMP | P. aeruginosa MKA | IMP-1 | 16 | >32 | |
| IMP | P. aeruginosa 0607097 | IMP-2 | >32 | >32 | |
| IMP | P. aeruginosa ITA | IMP-13 | >32 | >32 | |
| IMP | P. aeruginosa PADI | IMP-13 | 4 | 3 | |
| IMP | P. aeruginosa TSE | IMP-13 | >32 | >32 | |
| NDM | P. aeruginosa 453 | NDM-1 | >32 | >32 | |
| NDM | P. aeruginosa 353 | NDM-1 | >32 | >32 | |
| GIM | P. aeruginosa 73-15574 | GIM-1 | >32 | >32 | |
| GIM | P. aeruginosa 73-15553A | GIM-1 | >32 | >32 | |
| GIM | P. aeruginosa 73-5674 | GIM-1 | >32 | >32 | |
| AIM | P. aeruginosa WCH2677 | AIM-1 | >32 | >32 | |
| AIM | P. aeruginosa WCH2813 | AIM-1 | >32 | >32 | |
| AIM | P. aeruginosa WCH2837 | AIM-1 | >32 | >32 | |
| SPM | P. aeruginosa 16 | SPM-1 | >32 | >32 | |
| DIM | P. stutzeri13 | DIM-1 | >32 | >32 | |
| FIM | P. aeruginosa | FIM-1 | >32 | >32 | |
IMP, imipenem; MER, meropenem.
The Carba NP test from blood cultures adapted from the previously published techniques (13, 14) was performed as follows: 2 ml brain heart infusion (BHI) supplemented with 70 μg/ml ZnSO4 (final concentration) without imipenem was inoculated with five drops (75 μl) of the positive blood culture in two Eppendorf tubes (tubes A and B). Inoculated BHI was then incubated under agitation at 37°C for 3 h. Bacteria were recovered by centrifugation at 10,000 × g for 5 min. This optimized protocol of the Carba NP test was directly performed on this bacterial pellet (15). Briefly, the bacterial pellet was resuspended in 100 μl of a Tris-HCl-20 mM lysis buffer (B-PER II, bacterial protein extraction reagent; Pierce, Thermo Scientific, Villebon-sur-Yvette, France) and vortexed for 1 min. The enzymatic bacterial suspension was mixed with 100 μl of a diluted phenol red solution containing 0.1 mM ZnSO4 (Merck Millipore, Guyancourt, France) in the first tube (A) and with a diluted phenol red solution containing 0.1 mM ZnSO4 and supplemented with 6 mg/ml imipenem monohydrate (Sigma, Saint-Quentin-Fallavier, France) in the second tube (B). Mixtures of the phenol red (±imipenem) solutions and the enzymatic suspension being tested were incubated at 37°C for a maximum of 2 h. Results of the Carba NP test were interpreted as follows: (i) both tubes A and B red, non-carbapenemase-producing isolate; (ii) tube A red and tube B yellow/orange, carbapenemase-producing isolate; and (iii) tube A yellow/orange and tube B yellow/orange, noninterpretable result. All experiments were performed in triplicate, and test results were interpreted by technicians who were blinded to the identity of the samples.
A panel of 42 carbapenemase-producing Pseudomonas species was included in the study (Table 1), and 72 non-carbapenemase-producing Pseudomonas species were used as controls (Table 2). All the strains had previously been characterized for their β-lactamase content and carbapenemase resistance mechanisms at the molecular level in previous works (11).
TABLE 2.
Lack of detection of carbapenemase activity using the Carba NP test
| Resistance mechanism | Pseudomonas organism | Resistance determinant(s) | MIC (μg/ml) |
|
|---|---|---|---|---|
| IMP | MER | |||
| Wild type | P. aeruginosa 76110 | Reference strain | 0.75 | 0.19 |
| P. aeruginosa PU21 | Reference strain | 1.5 | 0.75 | |
| P. aeruginosa ATCC 27853 | Reference strain | 2 | 0.25 | |
| P. aeruginosa PA01 | Reference strain | 1 | 0.5 | |
| P. putida CIP 55-5 | Reference strain | 0.5 | 3 | |
| AmpC overproducer | P. aeruginosa 3-12 | Overexpression of chromosomal AmpC | 3 | 0.25 |
| P. aeruginosa Ved | Overexpression of chromosomal AmpC | 0.12 | 0.19 | |
| Overproduced efflux | P. aeruginosa PA01 | Mex C/D-OprJ | >32 | 4 |
| P. aeruginosa PT629 | Mex A/B-OprM | 1.5 | 1.5 | |
| P. aeruginosa PA01 | Mex X/Y-OprM | 1.5 | 0.75 | |
| Porin deficiency | P. aeruginosa PA01 | OprM deficient | 0.75 | 0.5 |
| P. aeruginosa H729 | OprD deficient | >32 | 6 | |
| P. aeruginosa Paeβ-02 | OprD deficient | 4 | 4 | |
| P. aeruginosa Paeβ-05 | OprD deficient | 16 | 8 | |
| P. aeruginosa Paeβ-30 | OprD deficient | 8 | 8 | |
| P. aeruginosa Paeβ-31 | OprD deficient | 16 | 8 | |
| Porin deficiency and overproduced efflux | P. aeruginosa Paeβ-19 | OprD deficient, MexA/B-OprM | 4 | 4 |
| P. aeruginosa Paeβ-29 | OprD deficient, MexA/B-OprM, MexX/Y-OprM | 16 | 32 | |
| P. aeruginosa Paeβ-01 | OprD deficient, MexX/Y-OprM, MexC/D-OprJ | 4 | 8 | |
| Porin deficiency and AmpC overproduction | P. aeruginosa Paeβ-03 | OprD deficient, AmpC | 16 | 8 |
| P. aeruginosa Paeβ-12 | OprD deficient, AmpC | 16 | 8 | |
| P. aeruginosa Paeβ-13 | OprD deficient, AmpC | 16 | 8 | |
| P. aeruginosa Paeβ-14 | OprD deficient, AmpC | 16 | 4 | |
| P. aeruginosa Paeβ-16 | OprD deficient, AmpC | 32 | 4 | |
| P. aeruginosa Paeβ-23 | OprD deficient, AmpC | 32 | 16 | |
| P. aeruginosa Paeβ-25 | OprD deficient, AmpC | 8 | 8 | |
| P. aeruginosa Paeβ-26 | OprD deficient, AmpC | 4 | 4 | |
| P. aeruginosa Paeβ-32 | OprD deficient, AmpC | 64 | 16 | |
| Porin deficiency, overproduced AmpC, and overproduced efflux | P. aeruginosa Paeβ-04 | OprD deficient, AmpC, MexA/B-OprM | 16 | 16 |
| P. aeruginosa Paeβ-24 | OprD deficient, AmpC, MexA/B-OprM | 32 | 32 | |
| P. aeruginosa Paeβ-28 | OprD deficient, AmpC, MexA/B-OprM | 16 | 4 | |
| P. aeruginosa Paeβ-15 | OprD deficient, AmpC, MexX/Y-OprM | 16 | 8 | |
| P. aeruginosa Paeβ-21 | OprD deficient, AmpC, MexX/Y-OprM | 16 | 32 | |
| P. aeruginosa Paeβ-22 | OprD deficient, AmpC, MexC/D-OprJ | 8 | 4 | |
| P. aeruginosa Paeβ-06 | OprD deficient, AmpC, MexX/Y-OprM, MexC/D-OprJ | 16 | 8 | |
| P. aeruginosa Paeβ-07 | OprD deficient, AmpC, MexX/Y-OprM, MexC/D-OprJ | 16 | 8 | |
| P. aeruginosa Paeβ-08 | OprD deficient, AmpC, MexX/Y-OprM, MexC/D-OprJ | 16 | 8 | |
| P. aeruginosa Paeβ-09 | OprD deficient, AmpC, MexX/Y-OprM, MexC/D-OprJ | 16 | 8 | |
| P. aeruginosa Paeβ-11 | OprD deficient, AmpC, MexX/Y-OprM, MexC/D-OprJ | 16 | 8 | |
| P. aeruginosa Paeβ-17 | OprD deficient, AmpC, MexX/Y-OprM, MexC/D-OprJ | 32 | 8 | |
| P. aeruginosa Paeβ-18 | OprD deficient, AmpC, MexA/B-OprM, MexX/Y-OprM | 64 | 64 | |
| P. aeruginosa Paeβ-27 | OprD deficient, AmpC, MexA/B-OprM, MexX/Y-OprM | 32 | 64 | |
| P. aeruginosa Paeβ-10 | OprD deficient, AmpC, MexA/B-OprM, MexC/D-OprJ | 16 | 8 | |
| P. aeruginosa Paeβ-20 | OprD deficient, AmpC, MexA/B-OprM, MexC/D-OprJ | 16 | 8 | |
| ESBL | P. aeruginosa | GES-1 | 1 | 0.75 |
| P. aeruginosa DEJ | GES-9 | 2 | 1 | |
| P. aeruginosa RNL-1 | PER-1 | 6 | 6 | |
| P. aeruginosa | PER-1 | 13 | 3 | |
| P. aeruginosa | PER-1 | 1.5 | 0.38 | |
| P. aeruginosa | PER-1 | 6 | 1 | |
| P. aeruginosa | PER-1 | 3 | 1.5 | |
| P. aeruginosa | PER-1 | >32 | 12 | |
| P. aeruginosa | PER-1 | 12 | 3 | |
| P. aeruginosa | PER-1 | >32 | 12 | |
| P. aeruginosa | PER-1 | 0.25 | 0.016 | |
| P. aeruginosa | PER-1 | >32 | 8 | |
| P. aeruginosa | PER-1 | >32 | >32 | |
| P. aeruginosa 15 | VEB-1 | 2 | 1.5 | |
| P. aeruginosa 51170 | BEL-1 | 1 | 0.5 | |
| P. aeruginosa | SHV2a | 1.5 | 3 | |
| P. aeruginosa 1782 | SHV-5 | 2 | 2 | |
| P. aeruginosa SHAM | TEM-4 | 3 | 0.75 | |
| P. aeruginosa PU21 | OXA-2 | 2 | 1 | |
| P. aeruginosa PAO38 | OXA-4 | 0.016 | 0.19 | |
| P. aeruginosa PU 21 | OXA-10 | 2 | 1.5 | |
| P. aeruginosa PU 21 | OXA-11 | 3 | 1.5 | |
| P. aeruginosa NAJ | OXA-13 | 2 | 1.5 | |
| P. aeruginosa PU 21 | OXA-14 | 2 | 2 | |
| P. aeruginosa MUS | OXA-18, OXA-20 | >32 | >32 | |
| P. aeruginosa ED | OXA-28 | 2 | 0.75 | |
| P. aeruginosa PIC | OXA-31 | >32 | 1.5 | |
| P. aeruginosa PG13 | OXA-32 | >32 | 12 | |
This optimized protocol of Carba NP test (15), performed directly from spiked blood cultures, perfectly differentiated carbapenemase producers from carbapenem-resistant isolates with noncarbapenemase-mediated mechanisms, such as those combining outer membrane permeability defects associated or not with overproduction of cephalosporinase and/or ESBLs. The sensitivity and specificity of the test were 100% under those conditions. Of note, GES-type producers were well detected from blood cultures, whereas they were not from isolated colonies (11). This difference might be explained by (i) the increased inoculum recovered from blood cultures during experiments, as previously observed for ESBL-producing Enterobacteriaceae (14), and (ii) increased β-lactamase production in liquid medium. Furthermore, the test was positive for two strains (IMP-1-producing Pseudomonas stutzeri PB207 and Pseudomonas putida NTU 92/99) that were susceptible to carbapenems (MIC ≤ 2 μg/ml) (16).
The Carba NP test combines multiple advantages. It is inexpensive, rapid, reproducible, and highly sensitive and specific. Use of this test would be helpful for choosing a first-line therapy based on an aminoglycoside associated with a fluoroquinolone rather than β-lactam-containing combinations in case of positivity, in particular when treating pneumonia. It can also be useful for detecting carbapenemase producers in an attempt to control outbreaks and to rapidly differentiate between carbapenemase producers (transferable resistance determinant) and noncarbapenemase producers (nontransferable resistance determinant). Actually, by preventing their spread, and therefore statistically reducing their genetic exchanges with other bacterial species, early identification of carbapenemase-producing P. aeruginosa strains may prevent further dissemination of carbapenemases to Enterobacteriaceae. It corresponds, to the best of our knowledge, to the first easy-to-handle technique allowing rapid identification of carbapenemase producers in P. aeruginosa from blood.
ACKNOWLEDGMENTS
This work was funded by a grant from the INSERM (UMR914) and the University of Fribourg.
We thank T. R. Walsh for the gift of the GIM- and AIM-positive isolates, P. Plésiat for the gift of several efflux and AmpC overproducers, B. Kocic for the gift of the NDM-positive isolates, and G. M. Rossolini for the gift of the FIM-positive isolate.
Footnotes
Published ahead of print 5 February 2014
REFERENCES
- 1.Mesaros N, Nordmann P, Plesiat P, Roussel-Delvallez M, Van Eldere J, Glupczynski Y, Van Laethem Y, Jacobs F, Lebecque P, Malfroot A, Tulkens PM, Van Bambeke F. 2007. Pseudomonas aeruginosa: resistance and therapeutic options at the turn of the new millennium. Clin. Microbiol. Infect. 13:560–578. 10.1111/j.1469-0691.2007.01681.x [DOI] [PubMed] [Google Scholar]
- 2.Nordmann P, Naas T. 2010. β-Lactams and Pseudomonas aeruginosa, p 157–174 In Courvalin P, Leclercq R, Rice LB. (ed), Antibiogram. ASM Press, Washington, DC [Google Scholar]
- 3.Rodriguez-Martinez JM, Poirel L, Nordmann P. 2009. Molecular epidemiology and mechanisms of carbapenem resistance in Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 53:4783–4788. 10.1128/AAC.00574-09 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Gupta V. 2008. Metallo-β-lactamases in Pseudomonas aeruginosa and Acinetobacter species. Expert Opin. Invest. Drugs 17:131–143. 10.1517/13543784.17.2.131 [DOI] [PubMed] [Google Scholar]
- 5.Jovcic B, Lepsanovic Z, Suljagic V, Rackov G, Begovic J, Topisirovic L, Kojic M. 2011. Emergence of NDM-1 metallo-β-lactamase in Pseudomonas aeruginosa clinical isolates from Serbia. Antimicrob. Agents Chemother. 55:3929–3931. 10.1128/AAC.00226-11 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Pollini S, Maradei S, Pecile P, Olivo G, Luzzaro F, Docquier JD, Rossolini GM. 2013. FIM-1, a new acquired metallo-β-lactamase from a Pseudomonas aeruginosa clinical isolate from Italy. Antimicrob. Agents Chemother. 57:410–416. 10.1128/AAC.01953-12 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Strateva T, Yordanov D. 2009. Pseudomonas aeruginosa—a phenomenon of bacterial resistance. J. Med. Microbiol. 58:1133–1148. 10.1099/jmm.0.009142-0 [DOI] [PubMed] [Google Scholar]
- 8.Pasteran F, Veliz O, Rapoport M, Guerriero L, Corso A. 2011. Sensitive and specific modified Hodge test for KPC and metallo-β-lactamase detection in Pseudomonas aeruginosa by use of a novel indicator strain, Klebsiella pneumoniae ATCC 700603. J. Clin. Microbiol. 49:4301–4303. 10.1128/JCM.05602-11 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Pasteran F, Veliz O, Faccone D, Guerriero L, Rapoport M, Mendez T, Corso A. 2011. A simple test for the detection of KPC and metallo-β-lactamase carbapenemase-producing Pseudomonas aeruginosa isolates with the use of meropenem disks supplemented with aminophenylboronic acid, dipicolinic acid and cloxacillin. Clin. Microbiol. Infect. 17:1438–1441. 10.1111/j.1469-0691.2011.03585.x [DOI] [PubMed] [Google Scholar]
- 10.Picao RC, Andrade SS, Nicoletti AG, Campana EH, Moraes GC, Mendes RE, Gales AC. 2008. Metallo-β-lactamase detection: comparative evaluation of double-disk synergy versus combined disk tests for IMP-, GIM-, SIM-, SPM-, or VIM-producing isolates. J. Clin. Microbiol. 46:2028–2037. 10.1128/JCM.00818-07 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Dortet L, Poirel L, Nordmann P. 2012. Rapid detection of carbapenemase-producing Pseudomonas spp. J. Clin. Microbiol. 50:3773–3776. 10.1128/JCM.01597-12 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Dortet L, Brechard L, Poirel L, Nordmann P. 2 July 2013. Rapid detection of carbapenemase-producing Enterobacteriaceae from blood cultures. Clin. Microbiol. Infect. 10.1111/1469-0691 [DOI] [PubMed] [Google Scholar]
- 13.Akova M, Daikos GL, Tzouvelekis L, Carmeli Y. 2012. Interventional strategies and current clinical experience with carbapenemase-producing Gram-negative bacteria. Clin. Microbiol. Infect. 18:439–448. 10.1111/j.1469-0691.2012.03823.x [DOI] [PubMed] [Google Scholar]
- 14.Nordmann P, Dortet L, Poirel L. 2012. Rapid detection of extended-spectrum-β-lactamase-producing Enterobacteriaceae. J. Clin. Microbiol. 50:3016–3022. 10.1128/JCM.00859-12 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Dortet L, Bréchard L, Poirel L, Nordmann P. 2013. Comparison of diverse growing media for further detection of carbapenemase production using the Carba NP test. J. Med. Microbiol. [Google Scholar]
- 16.Clinical and Laboratory Standards Institute. 2013. Performance standards for antimicrobial susceptibility testing; 23rd informational supplement. M100-S23 CLSI, Wayne, PA [Google Scholar]