Molecular mechanism of virulence, microbiological susceptibility, host factor and clinical outcome of blood stream infection caused by Escherichia coli

Background: Frequency of bloodstream infections (BSI) caused by Escherichia coli have increased steadily in recent years. The extra intestinal pathogenic Escherichia coli (ExPEC) are implicated in causing UTI, pneumonia, intra-abdominal infection and meningitis often leading to secondary bacteraemia. Outcome of E.coli bacteraemia is dependent on the virulence of pathogen and host specific factors. Role of ExPEC virulence genes (VGs) in the pathogenesis and outcome is not much explored. E.coli possesses moreVGs (adhesins, protectins, capsules, toxins, iron acquisition) compared to other Enterobacterales. There are very few studies from India reporting the role of VGs of ExPEC in the development of sepsis. Present study was proposed to look for the overall frequency and microbiological susceptibility of E.coli in BSIs, associated risk factors, possession of VGs and clinical outcome. Methods: Clinically suspected BSI growing E.coli from blood cultures (1st Feb 2022- 31st Jan 2023) were subjected for susceptibility test by Vitek2 and conventional PCR using primers for - adhesins (fimH, papA eaeA), siderophores (feoB, iutA), capsule (kpsMTII), and invasion (ibeA).Demographics, risk factors for survival and outcome were summarized and analysed by Chi-square test, Kaplan–Meier curve &amp; Cox regression. Possession of VGs were correlated with clinical outcome and a P value <0.05 were considered statistically significant. Results: Frequency of E.coli BSIs was 0.92% (100/ 10,800).The median population age was 47 years with a male predominance (56%). Major source of bacteraemia was UTI (43%) followed by intra-abdominal infections (12%) and others. High rate of resistance (>75 %) was shown to ciprofloxacin, amoxiclav and all cephalosporins. Susceptibility to colistin was 100% followed by amikacin (>80%) and carbapenems (70-80 %). The thirty-day mortality was 23% (23/100) and 30-days survival analysis was statistically significant. Based on Cox-Regression Analysis, CVC (HR = 6.9, p = 0.001), solid tumor (HR = 8.8, p = 0.003) and, urinary catheterization (HR=6.8, p=0.013) were significantly contributing to the mortality. Among the VGs, feoB was possessed by 83% of the isolates followed by kpsMTIII (73%), fimH (70%), iutA (59%), and others. The most frequent combination observed was feoB +fimH (68%). However, correlation between 30-day mortality &amp; possession of feoB +fimH combination. was statistically insignificant (p= 0.12). Discussion: The finding of 23% thirty-day mortality in our study was comparable to a similar study from Europe (2021) where the probability of death was 19.5% and. there was a strong positive correlation with the virulence genes. In our study, although majority had single or combination genes but the correlation was not significant which could be due to small sample size. Conclusion: All isolates possessed differentVGs encoding multiple virulence factors and > 50% mortality were associated with feoB +fimH combination. This knowledge may be useful for detecting virulent strains and predicting clinical outcome in E.coli BSI.