Escherichia coli Bacteriocins: Antimicrobial Efficacy and Prevalence among Isolates from Patients with Bacteraemia

Zgur-Bertok D (2011) Escherichia coli Bacteriocins: Antimicrobial Efficacy and Prevalence among Isolates from Patients with Bacteraemia. PLoS ONE 6(12): e28769. doi:10.1371/journal.pone.0028769 Escherichia coli Bacteriocins: Antimicrobial Efficacy and Prevalence among Isolates from Patients with Bacteraemia Marus ka Budic 0 Matija Rijavec 0 Z iva Petkovs ek 0 Darja Z gur-Bertok 0 Mark Alexander Webber, University of Birmingham, United Kingdom 0 Department of Biology, Biotechnical Faculty, University of Ljubljana , Ljubljana , Slovenia 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. - Funding: This study was financed by grant P1-0198 from the Slovenian Research Agency. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Antibiotic resistance of bacterial pathogens is one of the greatest global threats to public health care. To prevent selection and dissemination of resistance, the use of traditional antibiotics must be limited and alternative effective therapies must be sought [1]. Of high potential are bacteriocins, ribosomally synthesized proteinaceous compounds that are generally active against bacteria closely related to the producer [2,3,4,5]. Escherichia coli is known to produce two types of bacteriocins, classified by their molecular weight into colicins (25-80 kDa) and microcins (,10 kDa). Colicins and microcins are similar in many ways, but in contrast to colicins, microcin synthesis is not lethal to the producing strain and is not regulated by the DNA damage inducible SOS system. Further, almost all colicins are plasmid encoded, whereas microcin encoding genes are also found on the chromosome. 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]. On the other hand, microcins have been classified according to the presence, nature and localization of post-translational modifications, gene cluster organization, and leader peptide sequences. Class I microcins are peptides with a molecular mass below 5 kDa, and are subjected to extensive posttranslational modifications (B17, C7 and J25). 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]. E. coli strains belong to the commensal intestinal flora however, particular strains are the causative agents of serious intestinal and extraintestinal infections [9]. In addition, E. coli strains cause postweaning diarrhea (PWD) and edema disease in swine [10]. Extraintestinal pathogenic E. coli strains (ExPEC) are a common cause of urinary tract infections, neonatal meningitis, osteomyelitis, pneumonia, surgical site infections, skin and soft tissue infections (SSTI) and bacteraemia. Virulence factors produced by ExPEC namely, adhesins, siderophores, toxins, such as ahemolysin and cytotoxic necrotizing factor, as well as proteins impairing the innate immune response, such as TcpC, facilitate bacterial growth and persistence in the host [11,12,13,14]. Bacterial bacteraemia and septicaemia represent a significant emerging clinical problem. More than 40% of bacteraemia cases, community and hospital acquired, are instigated by pathogenic E. coli strains and represent the main cause of mortality as well as a large economic burden. Most cases of E. coli septicaemia are secondary to urinary tract infection. The aim of the present study was to investigate the in vitro inhibitory activity of several isolated colicins requiring distinct receptor/translocation systems and exhibiting different mechanisms of action namely, colicin M inhibiting peptidoglycan synthesis, E6 instigating hydrolysis of rRNA, E7 cleaving DNA and the pore formers E1 and K, against a collection of E. coli strains isolated from patients with bacteraemia of urinary tract origin. We also tested the efficacy of combined application of three (E7, K, M) and five colicins (E1, E6, E7, K, M), respectively. In addition, 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. Results and Discussion Sensitivity of uroseptic E. coli strains to colicins Testing the isolated colicins against 105 E. coli strains from patients with bacteraemia of urinary tract origin, revealed that colicin E7 was most effective, as 87% of the tested strains were susceptible. On the (...truncated)