Table 1

Results of the Carba NP test

Species (n)aCarbapenemase detected (n)aMIC(s) (μg/ml)Test resultb
ImipenemMeropenemErtapenem
Non-carbapenemase producersc
    Citrobacter freundii (3)None2–30.5–31.5–12
    Enterobacter aerogenes (4)None0.5–40.06–1.50.12–16
    Enterobacter cloacae (28)None0.19–60.06 to ≥320.25
    Escherichia coli (20)None0.023–30.023–120.008 to ≥32
    Klebsiella oxytoca (1)None0.250.251
    Klebsiella pneumoniae (18)None0.19–40.016–120.016 to ≥32
    Morganella morganii (1)None20.120.25
    Providencia stuartii (1)None1.50.120.5
    Pantoea spp. (1)None0.380.0470.19
    Serratia fonticola (1)None0.384
    Serratia marcescens (6)None0.38–40.023–0.50.25–2
    Pseudomonas aeruginosa (15)dNone6 to ≥323 to ≥32ND
Carba NP test-positive carbapenemase producerse
    Citrobacter freundii (3)KPC (2)6–122–66–4+
NDM (1)41.56+
    Citrobacter youngae (1)KPC166≥32+
    Enterobacter cloacae (25)KPC (11)0.75 to ≥320.38 to ≥320.75 to ≥32+
NDM (4)2 to ≥320.75 to ≥322 to ≥32+
NMC/IMI (6)≥326 to ≥3216 to ≥32+
VIM (4)6–246–322–24+
    Escherichia coli (33)KPC (5)1–160.25 to ≥320.5 to ≥32+
NDM (10)4 to ≥322 to ≥3212 to ≥32+
OXA-48 (14)0.5–80.25–20.5 to ≥32+
VIM (3)2–120.5–240.125–16+
IMP-27 (1)0.543+
    Klebsiella oxytoca (3)KPC (2)8–323–168–16+
OXA-48 (1)30.753+
    Klebsiella pneumoniae (28)KPC (7)8 to ≥322 to ≥323 to ≥32+
NDM (13)3 to ≥322 to ≥324 to ≥32+
OXA-48 (5)0.75–240.38–81 to ≥32+
OXA-181 (3)12 to ≥32≥32≥32+
    Morganella morganii (3)NDM8 to ≥320.38 to ≥320.38–12+
    Pseudomonas putida (1)IMP and VIM≥32≥32≥32+
    Pantoea spp. (1)KPC12824+
    Raoultella planticola (1)KPC2–160.75 to ≥320.75–16+
    Raoultella terrigena (2)KPC16≥3216+
    Serratia marcescens (5)SME (4)≥3212 to ≥324 to ≥32+
KPC (1)≥3224≥32+
    Pseudomonas aeruginosa (11)dIMP (5)≥32≥32≥32+
VIM (6)≥32≥32ND+
Carba NP test-negative carbapenemase producersc
    Enterobacter cloacae (1)fNMC-A≥3234
    Escherichia coli (4)GES-5 (1)≥32≥32≥32
OXA-48 (3)1.5–30.38–11.5–4
    Klebsiella pneumoniae (13)fOXA-48 (10)0.25–120.094–320.25 to ≥32
OXA-181 (3)1–320.38 to ≥323 to ≥32
    Proteus mirabilis (1)IMP-27444
    Providencia rettgeri (1)fNDM-1≥32≥3216
    Providencia stuartii (1)NDM-1≥32≥32≥32
    Serratia marcescens (6)GES-5 (2)≥32≥32≥32
SME-1 (4)≥32≥32≥32
    Pseudomonas aeruginosa (2)dGES-5≥32≥32ND
  • a n, number of isolates tested.

  • b Carba NP test results: −, negative (red); +, positive (yellow/orange). All the results shown in this table were obtained using 3 to 4 10-μl loopfuls resuspended in 200 μl of the lysis buffer. The same results were obtained using the original protocol (1 10-μl loopful resuspended in 100 μl of the lysis buffer), except for some OXA-48-producing isolates (n = 15) that were detected only by the modified protocol.

  • c Negative by PCR analysis for blaKPC, blaNDM, blaOXA-48-like, blaVIM, blaIMP, and blaGES-type genes (6, 7).

  • d CLSI guidelines do not recommend ertapenem testing for Pseudomonas.

  • e Positive by PCR analysis for at least one of blaKPC, blaNDM, blaOXA-48-like, blaVIM, blaIMP, and blaGES-type genes.

  • f Mucoid strains. Five out of 10 OXA-48-producing K. pneumoniae isolates were mucoid.