Genetic description of VanD phenotype vanA genotype in vancomycin-resistant Enterococcus faecium isolates from a Bone Marrow Transplantation Unit.

BACKGROUND: Vancomycin-resistant Enterococcus faecium (VREfm) is an important agent of hospital-acquired infection. VanA phenotype is characterized by resistance to high levels of vancomycin and teicoplanin and is encoded by the vanA gene, whereas VanD phenotype is characterized by resistance to vancomycin and susceptibility or intermediate resistance to teicoplanin; however, some isolates carry a VanD phenotype with a vanA genotype, but there are many gaps in the knowledge about the genetic mechanisms behind this pattern. OBJECTIVE: To characterize the genetic structure, clonality, and mobile genetic elements of VRE isolates that display a VanD-vanA phenotype. RESULTS: All vanA VRE-fm isolates displayed minimum inhibitory concentration (MIC) for vancomycin > 32µg/mL and intermediate or susceptible MIC range for teicoplanin (8-16µg/mL). The isolates were not clonal, and whole-genome sequencing analysis showed that they belonged to five different STs (ST478, ST412, ST792, ST896, and ST1393). The absence of some van complex genes were observed in three isolates: Ef5 lacked vanY and vanZ, Ef2 lacked vanY, and Ef9 lacked orf1 and orf2; moreover, another three isolates had inverted positions of orf1, orf2, vanR, and vanS genes. IS1542 was observed in all isolates, whereas IS1216 in only five. Moreover, presence of other hypothetical protein-encoding genes located downstream the vanZ gene were observed in six isolates. CONCLUSION: VRE isolates can display some phenotypes associated to vanA genotype, including VanA and VanB, as well as VanD; however, further studies are needed to understand the exact role of genetic variability, rearrangement of the transposon Tn1546, and presence of insertion elements in isolates with this profile.

Colistin-resistant Enterobacteriaceae infections: clinical and molecular characterization and analysis of in vitro synergy.

We described 27 polyclonal colistin-resistant Enterobacteriaceae (MIC 4-16 µg/mL) infections (12 pneumonia, 12 urinary tract infection (UTI), two Bacteremia, and one skin/soft tissue infection) in which 74% harbored KPC. The isolates were polyclonal, 6 STs were identified and the colistin resistance was due to chromosome mutations. Eight patients with UTI received monotherapy, and combination therapy was given to 19 patients. Overall mortality was 37%. In vitro synergy using time-kill assay was observed in 14 of 19 (74%) isolates tested; the synergistic effect was observed for almost all isolates for the combination of three drugs: colistin, amikacin, and tigecycline. The Kaplan-Meier survival curve showed no significant difference comparing combination therapy with 2, 3, or more drugs and risk factors associated with death were dialysis and shock. These findings reinforce the fact that colistin in combination with other classes of drugs can be useful in treating infections caused by colistin-resistant CRE.