Abstract
The impact of the Gram-negative bacterium Escherichia coli (E. coli) on the microbiomic and pathogenic phenomena occurring in humans and other warm-blooded animals is relatively well-recognized. At the same time, there are scant data concerning the role of E. coli strains in the health and disease of cold-blooded animals. It is presently known that reptiles are common asymptomatic carriers of another human pathogen, Salmonella, which, when transferred to humans, may cause a disease referred to as reptile-associated salmonellosis (RAS). We therefore hypothesized that reptiles may also be carriers of specific E. coli strains (reptilian Escherichia coli, RepEC) which may differ in their genetic composition from the human uropathogenic strain (UPEC) and avian pathogenic E. coli (APEC). Therefore, we isolated RepECs (n = 24) from reptile feces and compared isolated strains’ pathogenic potentials and phylogenic relations with the aforementioned UPEC (n = 24) and APEC (n = 24) strains. To this end, we conducted an array of molecular analyses, including determination of the phylogenetic groups of E. coli, virulence genotyping, Pulsed-Field Gel Electrophoresis-Restriction Analysis (RA-PFGE) and genetic population structure analysis using Multi-Locus Sequence Typing (MLST). The majority of the tested RepEC strains belonged to nonpathogenic phylogroups, with an important exception of one strain, which belonged to the pathogenic group B2, typical of extraintestinal pathogenic E. coli. This strain was part of the globally disseminated ST131 lineage. Unlike RepEC strains and in line with previous studies, a high percentage of UPEC strains belonged to the phylogroup B2, and the percentage distribution of phylogroups among the tested APEC strains was relatively homogenous, with most coming from the following nonpathogenic groups: C, A and B1. The RA-PFGE displayed a high genetic diversity among all the tested E. coli groups. In the case of RepEC strains, the frequency of occurrence of virulence genes (VGs) was lower than in the UPEC and APEC strains. The presented study is one of the first attempting to compare the phylogenetic structures of E. coli populations isolated from three groups of vertebrates: reptiles, birds and mammals (humans).
Highlights
The complex phylogenetic structure of Escherichia coli species [1,2,3] is strong evidence for the clonal evolution of this bacterium; recent publications suggest that recombination processes are playing a greater significant role [4,5,6,7,8]
The assignment of the RepEC, uropathogenic strain (UPEC) and avian pathogenic E. coli (APEC) strains to the respective phylogroups is presented in Figure 1 and Figures A1–A3 (Appendix A.)
1 and Figure S1 indicate that 92% and 5% of RepEC strains belonged to the nonpathogenic
Summary
The complex phylogenetic structure of Escherichia coli species [1,2,3] is strong evidence for the clonal evolution of this bacterium; recent publications suggest that recombination processes are playing a greater significant role [4,5,6,7,8]. Groups A and B1 mainly include nonpathogenic commensal E. coli strains, while extraintestinal pathogenic E. coli are clustered to groups. The use of Multi-Locus Sequence Typing (MLST) has enabled a more accurate determination of the phylogenetic structure of E. coli species by targeting their housekeeping genes and assigning strains to an appropriate Sequence Type (ST) [9,11,12]. New phyllo groups have been formed and referred to as group C, which contains nonpathogenic strains of E. coli, closely related to representatives of the B1 group [16], group E, whose representatives (including, among others, E. coli O157:H7 strains) are associated with strains of group D [13,14,15] and, group F, clustering extraintestinal pathogenic E. coli closely related with the B2 group representatives [13]. The latest Clermont report revealed a new group intermediate between the F and B2 phylogroups, which has been designated as phylogroup G [18]
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