Tigecycline in combination with other antibiotics against clinical isolates of carbapenem-resistant Klebsiella pneumoniae in vitro.

BACKGROUND

To investigate the activity of 5 antibiotic monotherapies, including colistin (COL), meropenem (MEM), amikacin (AMK), levofloxacin (LEV), and tigecycline (TGC), when combined with 4 other antibiotics against clinical isolates of carbapenem-resistant Klebsiella pneumoniae (CRKP) in vitro.

METHODS

The minimum inhibitory concentrations (MICs) of 5 antibiotics against 40 CRKP isolates were determined by micro-broth dilution method. There were synergistic effects between TGC combinations in the 10 CRKP isolates detected with checkerboard microdilution method. Time-kill assay was used to assess the monotherapies and the TGC combinations against 4 distinct sequence typing (STs) CRKP isolates. Polymerase chain reaction (PCR) tests were used to detect the carbapenemase genes, extended-spectrum beta lactamase (ESBL) genes, colistin resistance gene, and quinolone resistance genes, while multilocus sequence typing (MLST) was performed for 10 CRKP isolates.

RESULTS

The MICs of TGC, COL, MEM, AMK, and LEV were 0.5-2, 2-32, 4-256, 1-16,384, and 0.5-64 µg/mL, respectively. The combinations exerted a significant synergism or additive effect via the checkerboard technique for most tested CRKP isolates, but a portion of the CRKP isolates had an indifferent effect except for the TGC-AMK combination. In addition, time-kill assays revealed that TGC enhanced the bactericidal activity of the 4 other antibiotics. Among 10 CRKP isolates, blaKPC-2 (90%), blaSHV (100%), and blaacc(6')-Ib (100%) were the most common carbapenemase genes, ESBL genes, and quinolone resistance genes, respectively. ST76 (70%) was the most predominant clone, followed by ST11 (10%), ST375 (10%), and ST530 (10%).

CONCLUSIONS

In contrast to the currently recommended TGC therapy, our in vitro data suggest that TGC combinations may be a valid therapeutic option against CRKP, even in the presence of 1 antibiotic resistant isolate in TGC combination therapy. TGC-AMK combination is a cost-effective option for treating CRKP in the eastern region of Heilongjiang Province. In addition, TGC combinations might circumvent the overuse of carbapenems during the era of multi-drug resistance in Klebsiella pneumoniae (KP).