Evaluation of the Pathogenic Potential of Escherichia coli Strains Isolated from Eye Infections

While primarily Gram-positive bacteria cause bacterial eye infections, several Gram-negative species also pose eye health risks. Currently, few studies have tried to understand the pathogenic mechanisms involved in E. coli eye infections. Therefore, this study aimed to establish the pathogenic potential of E. coli strains isolated from eye infections. Twenty-two strains isolated between 2005 and 2019 from patients with keratitis or conjunctivitis were included and submitted to traditional polymerase chain reactions (PCR) to define their virulence profile, phylogeny, clonal relationship, and sequence type (ST). Phenotypic assays were employed to determine hemolytic activity, antimicrobial susceptibility, and adhesion to human primary corneal epithelial cells (PCS-700-010). The phylogenetic results indicated that groups B2 and ST131 were the most frequent. Twenty-five virulence genes were found among our strains, with ecp, sitA, fimA, and fyuA being the most prevalent. Two strains presented a hemolytic phenotype, and resistance to ciprofloxacin and ertapenem was found in six strains and one strain, respectively. Regarding adherence, all but one strains adhered in vitro to corneal cells. Our results indicate significant genetic and virulence variation among ocular strains and point to an ocular pathogenic potential related to multiple virulence mechanisms.

Decreased susceptibility to imipenem and ceftazidime in early virulent Raoultella spp. strains retrieved from human intestinal infections

The genus Raoultella spp. is comprised of four species, namely, R. electrica, R. ornithinolytica, R. planticola, and R. terrigena, which are rarely reported to cause infections in humans. This study aimed to characterize six strains of Raoultella spp. isolated from stool samples from patients with diarrhea. The strains included in the study were previously identified by biochemical methods as K. pneumoniae, during a surveillance study conducted in 1987. In the present study, the strains were re-identified by MALDI TOF and 16S rRNA sequencing and subsequently subjected to virulence gene screening by PCR, hemolytic activity, biofilm formation, hypermucoviscosity phenotype, capacity to interact with Caco-2 cells, and antimicrobial susceptibility test. Our results revealed that, among the six strains, three were identified as R. ornithinolytica and three as R. planticola. The genes related to iron uptake systems (aero1, aero2, iutA, entB, and ybtS) and adhesin (mrkD) were found in all strains. Furthermore, all strains demonstrated the ability to interact in vitro with Caco-2 cells and form biofilms. In general, the strains studied were sensitive to the antimicrobials tested; however, it was possible to observe high MICs for imipenem compared to ertapenem and meropenem and high minimal inhibitory concentrations (MICs) for ceftazidime, except for one strain. Our results show the occurrence of virulent strains of Raoultella spp. with high MICs for imipenem and ceftazidime causing diarrhea. We hope that our findings can contribute to the understanding of the evolution of this species since, as far as we know, these are the oldest isolates reported so far.