Phylogenetic Analysis and Plasma Resistance of Blood-Derived Escherichia coli Isolates that Cause Bacteremia at a Tertiary Care Hospital in Japan.

INTRODUCTION

Escherichia coli is a leading cause of human bacteremia, and multidrug-resistant clones such as ST131 and ST1193 have spread worldwide. However, few studies have investigated the genetic background including the evolutionary lineages of blood-derived E. coli isolates in patients with bacteremia in Japan. Furthermore, the factors contributing to its survival in the bloodstream are poorly understood.

METHODS

From November 2019 to October 2021, we examined 132 consecutive blood-derived E. coli isolates from patients with bacteremia at Kagoshima University Hospital for multilocus sequence analysis and analysis of virulence factors, such as plasma resistance and biofilm formation. We then compared the microbiological and clinical characteristics between the main sequence type (ST) groups.

RESULTS

The most prevalent ST group was ST131 (22.7%), which included ST131-C1 (12.9%) and ST131-C2 (6.8%), followed by ST73 (19.7%), ST95 (12.1%), and ST1193 (5.3%). The median plasma resistance index (PRI) was highest for ST131-C1 (0.590), followed by ST1193 (0.574), ST95 (0.466), ST131-C2 (0.432), and ST73 (0.335). The median biofilm index (BI) was highest for ST73 (0.229), followed by ST131-C2 (0.213), ST95 (0.185), ST131-C1 (0.131), and ST1193 (0.099). There was a weak inverse correlation between the PRI and BI (p=0.0159). The ST131-C1 and ST1193 strains accounted for a relatively high proportion of cases originating from non-urinary tract infections with poor prognosis.

CONCLUSIONS

ST131-C1 and ST1193 clones showed phenotypic characteristics associated with greater plasma resistance and/or may be associated with bloodstream survival. This study may offer a new perspective on the mechanisms underlying E. coli survival in the bloodstream.