Is MIC increase of meropenem against Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae correlated with the increase of resistance rates against some other antibiotics with Gram-negative activity?

OBJECTIVE: To assess MIC distribution for meropenem and the other antibiotics with Gram-negative activity against KPC-Kp clinical isolates collected at our hospital in 2013-2016. METHODS: Susceptibility of KPC-Kp strains was tested by broth microdilution method, using customized 96-well plates, and was interpreted according to the EUCAST recommendations. RESULTS: Among 169 consecutive KPC-Kp clinical isolates 26.6% were susceptible to meropenem. Among meropenem-resistant isolates (124/169), 58.9% had an MIC for meropenem between 16 and 64mg/L. The overall resistance rate for the other antibiotics resulted very high for both ciprofloxacin and levofloxacin (99.0%), moderate for amikacin (37.4%) and low for gentamicin (11.2%), colistin (8.2%) and tigecycline (7.7%). Aminoglycosides had a dichotomous behavior in relation to meropenem MIC increase. Resistance rate for gentamicin persisted <20% across all meropenem MIC values. Conversely, that for amikacin raised from <20% in presence of meropenem MIC ≤8mg/L up to around 80% in presence of meropenem MIC≥64mg/L. Resistance rates for tigecycline and colistin persisted <20% in presence of meropenem MICs up to 64mg/L. CONCLUSION: The overall susceptibility rates of antibiotics with Gram-negative activity may greatly vary among KPC-Kp clinical isolates. A tight relationship between meropenem MIC increase and the resistance rate for amikacin was documented.