Abstract
Galleria mellonella larvae are an alternative in vivo model for investigating bacterial pathogenicity. Here, we examined the pathogenicity of 71 isolates from five leading uropathogenic E. coli (UPEC) lineages using G. mellonella larvae. Larvae were challenged with a range of inoculum doses to determine the 50% lethal dose (LD50) and for analysis of survival outcome using Kaplan-Meier plots. Virulence was correlated with carriage of a panel of 29 virulence factors (VF). Larvae inoculated with ST69 and ST127 isolates (104 colony-forming units/larvae) showed significantly higher mortality rates than those infected with ST73, ST95 and ST131 isolates, killing 50% of the larvae within 24 hours. Interestingly, ST131 isolates were the least virulent. We observed that ST127 isolates are significantly associated with a higher VF-score than isolates of all other STs tested (P≤0.0001), including ST69 (P<0.02), but one ST127 isolate (strain EC18) was avirulent. Comparative genomic analyses with virulent ST127 strains revealed an IS1 mediated deletion in the O-antigen cluster in strain EC18, which is likely to explain the lack of virulence in the larvae infection model. Virulence in the larvae was not correlated with serotype or phylogenetic group. This study illustrates that G. mellonella are an excellent tool for investigation of the virulence of UPEC strains. The findings also support our suggestion that the incidence of ST127 strains should be monitored, as these isolates have not yet been widely reported, but they clearly have a pathogenic potential greater than that of more widely recognised clones, including ST73, ST95 or ST131.
Highlights
Escherichia coli is the major cause of extraintestinal infections including urinary tract infection (UTI), Gram-negative bacteraemia and neonatal meningitis
All ST69 strains belonged to phylogenetic group D, ST73 to both group D (13 strains) and B2 (7 strains), ST95 to both group D (4 strains) and B2 (6 strains), ST127 belonged to groups D (4 strains) and B2 (6 strains), and ST131 belonged to groups D (2 strains), B2 (17 strains) and B1 (1 strain) (Table S1)
Uropathogenic E. coli (UPEC) are a major cause of UTI and the severity of the infection is due to the contribution of many virulence factors including adhesins, toxins, siderophores and capsule
Summary
Escherichia coli is the major cause of extraintestinal infections including urinary tract infection (UTI), Gram-negative bacteraemia and neonatal meningitis. Uropathogenic E. coli (UPEC) are the most frequent cause of UTI, being responsible for up to 85% of community acquired UTI and 40% of nosocomial UTI [1,2,3]. Multilocus sequence typing (MLST) is the current method used to investigate the genetic differences between isolates of UPEC. This method has been used to good effect to identify UPEC as well as other important pathogenic E. coli [1,4,5,6]. Numerous other recent studies have highlighted the virulence and antimicrobial resistance of members of these clones [6,7,8,9,10]
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