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Tanise Vendruscolo Dalmolin et al
Table 1. Minimal Inhibitory Concentration (MIC)a of Several Antibiotics for Escherichia coli and Klebsiella pneumoniae Coharboring blaKPC/mcr-1 Genes Antibiotic
E. coli 3431F, MIC (mg/L)
Ertapenem Meropenem Imipenem
Ciprofloxacin Amikacin
Gentamicin Tigecycline Colistin
32 32
≥32 4 2 1
0.25 4
aPerformed by broth microdilution.
E. coli 5798F, MIC (mg/L)
16 8
16
≥64 8 2 1 4
E. coli 6699F, MIC (mg/L)
256 256 256 32 8 4
0.5 4
K. pneumoniae 3111F, MIC (mg/L)
256 256 256
≥64 16 32 1 4
128 128 16 64 8
0.5
0.25 0.25
K. pneumoniae 6701F, MIC (mg/L)
colistin, as already described in Shigella sonnei.8 Interestingly, the truncated mcr-1 gene could be reactivated after conjugation experiments, resulting in a colistin resistant phenotype.9 However, a truncated gene is not the only reason to justify the susceptibility; one study reported an E. coli colistin-susceptible mcr-1 positive isolate that presented an intact gene.10 Therefore, further studies are needed to elucidate the reason why the mcr-1gene of
the
K. pneumoniae 6701F in this study does not promote resistance to colistin. In fact, colistin-susceptible mcr-1 isolates may be con- tributing to a silent spread of the mcr-1 gene, which may be transferred to multidrug-resistant isolates such as the CPE described in this study. In conclusion, the current prevalence of mcr-1 is very low, but
the detection of 2 isolates in 2018 coharboring blaKPC/mcr-1 genes is a warning for a possible increase in the prevalence of these isolates in the coming years. Considering the association of mcr-1 with the broad-spectrum resistance mechanisms (eg, carbapenemases), this emergence is of great concern.
Acknowledgments. The authors would like to thank Luiza Castro for technical support.
Financial support. This work was supported by Fundo de Incentivo a Pesquisa e Eventos do Hospital de Clínicas de Porto Alegre (FIPE/HCPA project no. 16-0559) and by a grant from the Conselho Nacional de Desen- volvimento Científico e Tecnológico—Brazil (CNPq).
Conflicts of interest. All authors report no conflicts of interest relevant to this article.
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