Global Distribution of O-Serotypes and Antibiotic Resistance in Extraintestinal Pathogenic Escherichia coli (ExPEC) Collected From the Blood of Bacteremia Patients Across Multiple Surveillance Studies

Abstract Background Extraintestinal pathogenic Escherichia coli (ExPEC) is the leading cause of bacteremia worldwide, with older populations having increased risk of invasive bacterial disease. Increasing resistance to first-line antibiotics and emergence of multidrug-resistant (MDR) strains represent major treatment challenges. ExPEC O-serotypes are key targets for potential multivalent conjugate vaccine development. Therefore, we evaluated the O-serotype distribution and antibiotic resistance profiles of ExPEC strains causing bloodstream infections across four regions. Methods Blood culture isolates from patients aged ≥60 years collected during five retrospective E. coli surveillance studies in Europe, North America, Asia-Pacific and South America (2011–2017) were analyzed. Isolates were O-serotyped by agglutination; O-genotyping was performed for non-typeable isolates. Antimicrobial susceptibility testing was also conducted. Results Among 3217 ExPEC blood culture isolates, the most ubiquitous O-serotype was O25 (22.9% [n = 737]), followed by O2, O6, O1, O75, O15, O8, O16, O4, O18, O77-group, O153, O9, O101/O162, O86, and O13 (prevalence of ≥1%). The prevalence of these O-serotypes was generally consistent across regions, apart from South America; together, these 16 O-serotypes represented 77.6% of all ExPEC bacteremia isolates analyzed. Overall MDR frequency was 10.7%, with limited variation between regions. Within the MDR subset (n = 345), O25 showed a dominant prevalence of 63.2% (n = 218). Conclusions Predominant O-serotypes among ExPEC bacteremia isolates are widespread across different regions. O25 was the most prevalent O-serotype overall and particularly dominant among MDR isolates. These findings may inform the design of multivalent conjugate vaccines that can target the predominant O-serotypes associated with invasive ExPEC disease in older adults.