ABSTRACT
BACKGROUND: Shiga toxin-producing Escherichia coli (STEC) is one of the most common and widely distributed foodborne pathogens that has been frequently implicated in gastrointestinal and urinary tract infections. Moreover, high rates of multiple antibiotic-resistant E. coli strains have been reported worldwide. Due to the emergence of antibiotic-resistant strains, bacteriophages are considered an attractive alternative to biocontrol pathogenic bacteria. Characterization is a preliminary step towards designing a phage for biocontrol. METHODS: In this study, we describe the characterization of a bacteriophage designated phiC119, which can infect and lyse several multidrug-resistant STEC strains and some Salmonella strains. The phage genome was screened to detect the stx-genes using PCR, morphological analysis, host range was determined, and genome sequencing were carried out, as well as an analysis of the cohesive ends and identification of the type of genetic material through enzymatic digestion of the genome. RESULTS: Analysis of the bacteriophage particles by transmission electron microscopy showed that it had an icosahedral head and a long tail, characteristic of the family Siphoviridae. The phage exhibits broad host range against multidrug-resistant and highly virulent E. coli isolates. One-step growth experiments revealed that the phiC119 phage presented a large burst size (210 PFU/cell) and a latent period of 20 min. Based on genomic analysis, the phage contains a linear double-stranded DNA genome with a size of 47,319 bp. The phage encodes 75 putative proteins, but lysogeny and virulence genes were not found in the phiC119 genome. CONCLUSION: These results suggest that phage phiC119 may be a good biological control agent. However, further studies are required to ensure its control of STEC and to confirm the safety of phage use.
ABSTRACT
The increase of Salmonella enterica strains showing resistance against antibiotics has resulted in limiting the effective treatment of human infections. The present study characterized the resistance to tetracycline in S. enterica serovar Typhimurium strains, recovered from irrigation water in distinct regions in the Culiacan Valley, an important agricultural region in Mexico for horticultural crops that are exported to the United States. Analysis of the genomic diversity by pulse-field gel electrophoresis (PFGE) typing showed that the Salmonella Typhimurium strains were grouped into four distinct genotypic clusters, indicating genomic diversity among 12 strains examined. The polymerase chain reaction and DNA sequencing analysis demonstrated that the tet(A) gene was found on the genomic DNA and was located within a truncated version of transposon Tn1721. The comparative analysis of the tet(A) gene sequence in Salmonella Typhimurium strains identified high sequence similarity to the tet determinant of plasmid RP1, which is homologous to the tet gene in Tn1721. The findings show the presence of tet(A) among the tetracycline-resistant Salmonella Typhimurium strains isolated from irrigation water used for growing fresh fruits and vegetables.
