Abstract
Bacteriocins are antimicrobial peptides generally active against bacteria closely related to the producer. Escherichia coli produces two types of bacteriocins, colicins and microcins. The in vitro efficacy of isolated colicins E1, E6, E7, K and M, was assessed against Escherichia coli strains from patients with bacteraemia of urinary tract origin. Colicin E7 was most effective, as only 13% of the tested strains were resistant. On the other hand, 32%, 33%, 43% and 53% of the tested strains exhibited resistance to colicins E6, K, M and E1. Moreover, the inhibitory activity of individual colicins E1, E6, E7, K and M and combinations of colicins K, M, E7 and E1, E6, E7, K, M were followed in liquid broth for 24 hours. Resistance against individual colicins developed after 9 hours of treatment. On the contrary, resistance development against the combined action of 5 colicins was not observed. One hundred and five E. coli strains from patients with bacteraemia were screened by PCR for the presence of 5 colicins and 7 microcins. Sixty-six percent of the strains encoded at least one bacteriocin, 43% one or more colicins, and 54% one or more microcins. Microcins were found to co-occur with toxins, siderophores, adhesins and with the Toll/Interleukin-1 receptor domain-containing protein involved in suppression of innate immunity, and were significantly more prevalent among strains from non-immunocompromised patients. In addition, microcins were highly prevalent among non-multidrug-resistant strains compared to multidrug-resistant strains. Our results indicate that microcins contribute to virulence of E. coli instigating bacteraemia of urinary tract origin.
Highlights
Antibiotic resistance of bacterial pathogens is one of the greatest global threats to public health care
To gain further insight into the role bacteriocins play among natural E. coli populations, we studied their prevalence among the investigated strains as well as associations of microcins with virulence factor genes, phylogenetic group, multidrug resistance (MDR) and epidemiology
Our results showed that only combinations of colicins exhibited effective antimicrobial activity, precluding evolution of resistance and that, microcins may contribute to development of E. coli bacteraemia of urinary tract origin
Summary
Antibiotic resistance of bacterial pathogens is one of the greatest global threats to public health care. Colicins act by either: (i) membrane permeabilization, (ii) nuclease activity or (iii) inhibition of peptidoglycan and lipopolysaccharide O-antigen synthesis [6]. Their activity requires binding to a specific receptor in the outer membrane and translocation through the outer membrane to the target by the Tol or TonB machinery [7]. Class II microcins are higher molecular mass peptides (5-10 kDa), and are subdivided into two subclasses: class IIa microcins which may contain disulfide bonds but no further post-translational modifications (L, ColV and 24), and class IIb linear microcins that have a Cterminal posttranslational modification by the attachment of catechol of the salmochelin type (E492, H47, I47 and M) [8]
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