title: Activity spectrum of colicins produced by Shigella sonnei and genetic mechanism of colicin resistance in conspecific S. sonnei strains and Escherichia coli.
abstract: Colicin-mediated killing is an example of allelopathy, which has been found among several bacteria. Screening of 42 strains of Shigella sonnei isolated from diarrheal patients revealed that 39 (93%) S. sonnei strains were positive for colicin production against Escherichia coli DH5α. In the PCR-based detection of the colicin types, 36 (92.3%) were identified as E3, 2 (5.1%) as E3 and E8, and 1 (2.6%) as E3 and E2. Representative S. sonnei strains producing heterologous colicins exhibited antagonism against diarrheagenic Escherichia coli (DEC) groups. Although it is known that mutation in the colicin receptor renders the host resistant to colicin, there is a dearth of information on the genetic characterization of such mutants. In the fluctuation test, colicin-resistant E. coli mutants were found to occur spontaneously at the rates of 2.51 × 10(-8) and 5.52 × 10(-8) per generation when exposed to colicins E3 and E8 and colicins E3 and E2, respectively. Genotypic characterization of colicin-resistant E. coli (EC(Cr)) and S. sonnei (SS(Cr)) strains displayed mutations in the btuB gene, which encodes the receptor for vitamin B12 uptake. This gene was interrupted by various insertion sequences, such as IS1, IS2, and IS911. Complementation of EC(Cr) and SS(Cr) with plasmid-borne btuB (pbtuB) accomplished restoration of the colicin-susceptible phenotype. The vitamin B12 uptake assay gave an insight into the physiological relevance of the btuB mutation. Our studies provide insights into the latent influence of S. sonnei colicins in governing the existence of some of the shigellae and all of the DEC and the genetic mechanism underlying the emergence of resistance.
authors.affiliation: Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Fatema
authors.initials: F
authors.lastname: Calcuttawala
authors.affiliation: Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Chellaram
authors.initials: C
authors.lastname: Hariharan
authors.affiliation: Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Gururaja P
authors.initials: GP
authors.lastname: Pazhani
authors.affiliation: Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Santanu
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Division of Bacteriology, National Institute of Cholera and Enteric Diseases, Kolkata, India tramu@vsnl.net.
authors.forename: Thandavarayan
authors.initials: T
authors.lastname: Ramamurthy
mesh_terms: D064089:Allelopathy; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001483:Base Sequence; D001692:Biological Transport / Q000235:genetics; D003087:Colicins / Q000494:pharmacology*; D004251:DNA Transposable Elements / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics*; D005243:Feces / Q000382:microbiology; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D012764:Shigella sonnei / Q000302:isolation & purification / Q000378:metabolism*; D014805:Vitamin B 12 / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; C044592:BtuB protein, E coli; D003087:Colicins; D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D014805:Vitamin B 12