735. Vancomycin-Resistant vanB- and vanA/vanB-type Enterococcus faecium Causing Invasive Infections in Adult Patients in Chile
Authors: Diaz Lorena , Rivas Lina M , Martinez Jose R W , Peters Anne S , Riquelme Maria Paz , de Paula Baptista Rodrigo , Panesso Diana , Tran Truc T , Singh Kavindra , Miller William R , Antolinez Yohanna , Sanfurgo Valentina , Bugueno Francisca , Quiroz Valeria E , Soto Katherine D , Quesille-Villalobos Ana M , Rojas Pamela , Rioseco Maria , Moreno Juan , Rafael Araos , Arias Cesar A , Munita José M , Garcia Patricia 
Published: November 2023

Abstract

Background
Vancomycin-resistant enterococci has increased globally in recent decades, with Enterococcus faecium (VREfm) being the most prevalent species. Although the prevalence of VREfm in Chile is high (∼70%), its molecular epidemiology is not well-described. Here, we used whole genome sequencing (WGS) to characterize the circulating lineages of VREfm in Chile.

VRE= Vancomycin resistant Enterococcus faecium, SD=Standard deviation, IQR=in˝ter-quartile range; ¥ comorbidities included diagnoses apart from the primary cause for admission such as hypertension, chronic kidney disease and coronary artery disease; *Chi-square or Fisher´s exact were used for categorial variables; T-test for continues variables; P value&lt;0.05 was considered significant.•

Methods
A total of 96 invasive clinical VREfm isolates causing invasive infections were collected from 96 patients admitted to 3 hospitals in Chile as part of an ongoing surveillance program (2018 – 2022). Clinical data including demographics, source of infection, and hospital outcomes were collected. All isolates were subjected to WGS on an Illumina platform. After assembly, in silico MLST and resistome were determined. Further, 5 representative strains were sequenced with Oxford Nanopore Technology (ONT) to further characterize the location of the van gene cluster.

Results
The mean age of the cohort was 62 years, with 61% of males and a mean Charlson Comorbidity Score of 3. All isolates were resistant to vancomycin, ampicillin and ciprofloxacin and remained susceptible to linezolid. Resistance to teicoplanin (16%), high-level resistance to gentamicin (48%) and streptomycin (20%) was also observed. A total of 75 VREfm harbored vanB, with the most common STs being ST17 (23%) and ST656 (25%). Only 7 VREfm isolates carried vanA, 43% of which corresponded to ST17. Surprisingly, 14 VREfm simultaneously carried vanA and vanB (vanA/vanB), most of them belonging to ST233 (50%) or ST2137 (36%). For the VREfm vanA/vanB isolates, the vanB cluster was located on the chromosome, while the vanA gene cluster was harbored on a plasmid (ca. 45Mb) which also contained ermB. A summary of the clinical characteristics of the cohort is shown in Table 1.

Conclusion
vanB was the most frequently observed genotype in Chile, with ST17 and ST656 accounting for most isolates. Importantly, a substantial proportion of VREfm carried both vanA and vanB clusters in Chile, which was mainly observed in two different genomic lineages (ST233 and ST2137). Active surveillance of VREfm is essential to monitor the epidemiology of this critical pathogen in South America.

Disclosures
William R. Miller, M.D., Merck: Grant/Research Support|UpToDate: Honoraria