On the mechanism of resistance to channel-forming colicins (PacB) and tellurite, encoded by plasmid Mip233 (IncHI3)

Abstract

Plasmids of the H incompatibility complex confer protection against all known channel-forming colicins (PacB character) and resistance to potassium tellurite (Te r ) to Escherichia coli strains. A DNA clone (2.2 kbp) from plasmid Mip233 (IncHI3) expressing PacB-Te r phenotypes was studied. DNA sequence analysis revealed a high degree of homology with the enzyme O-acetylserine sulfhydrylase. Size of the PacB-Te r transcript was estimated as 1200 bases. A single polypeptide was found on SDS^polyacrylamide gel with a molecular mass estimated of 34 kDa. The effect of channel-forming colicins and tellurite was analyzed at physiological and transcriptional levels. Results suggest that the pacB gene product could be a reductase-like enzyme. It is also suggested that presence of the PacB character among H plasmid confers selective advantage on cells sharing an ecological niche. ß

Colicin E1 addition to the swine diet prevents post weaning diarrhea

“…Other bacterial cells that possess the plasmid to make the colicin, also have the immunity protein so they survive in the event of colicin secretion by another cell (Alonso, et al, 2000). The immunity protein provides the best defense against secreted colicins and is part of the colicin plasmid which is constituitively produced by the cell in the bacterial lipid bilayer (Espesset, et al, 1994).…”

“…They work by altering the receptor binding motif slightly to stop the colicin encoded on the plasmid from attacking "self" cells (Alonso, et al, 2000). Other bacteria may be resistant or tolerant to colicin invasion as well (Alonso, et. al, 2000).…”

“…al, 2000). Bacteria showing resistance to colicin may have mutated their receptors just enough to evade colicin binding (Alonso, et. al, 2000).…”

“…al, 2000). Colicins show remarkable specificity for their targets, as even a one amino acid mutation in their structure can prevent colicin binding (Alonso, et al, 2000;Cao and Klebba, 2002). Changes in the translocation structure can result in colicin tolerance.…”

“…Colicin tolerance exists when mutations Tol and Ton transport systems are altered in such a way that the bacteria use a slightly different transportation system to actively bring in nutrients. This tolerance is said to be overcome by simply adding more colicin to the mix, however (Alonso, et. al, 2000).…”