TABLE 1

Results of the comparison of the combined disk method and the MALDI-TOF MS method with specific A and B class inhibitors for detecting Enterobacteriaceae suspected of carbapenemase production

β-Lactamase classNo. of isolates per β-lactamaseaMALDI-TOF MS (% [no.]) assaybMALDI-TOF MS avg time of ERTf hydrolysis detection (min)TEMc analysisInterpreted as class D carbapenemase positive by MALDI-TOF MS (no.)
PBAd analysis: interpreted as class A carbapenemase positiveDPAe analysis: interpreted as class B carbapenemase positiveResistanceg (<12 mm)TEM sensitivity by MALDI-TOF MShAverage time of TEM hydrolysis detection (min)
None5
SHV5
EBC5
K-15
FOX1
CMY-24
DHA5
TEM1
CTX-M137 (1/13)1/130
KPC20100 (20/20)5050
VIM30100 (30/30)3070 (19/30)100 (19/19)35
NDM7100 (7/7)5514(1/7)1/160
IMP1587 (13/15)8027 (4/15)100 (4/4)45
OXA4560100 (45/45)100 (45/45)15100 (45/45)
  • a A total of 161 isolates (44 noncarbapenemase producers and 117 carbapenemase isolates), distributed as indicated, were studied.

  • b Number of strains that yielded a positive result in the carbapenemase group classification by MALDI-TOF.

  • c TEM, temocillin.

  • d PBA, phenylboronic acid.

  • e DPA, dipicolinic acid.

  • f ERT, ertapenem.

  • g Temocillin resistance percentage calculated on the zone diameter around temocillin table (Rosco).

  • h Sensitivity of detection of temocillin resistance by MALDI-TOF MS. The resistance detected by temocillin disks (Rosco) was used as a reference.