Multiple Antimicrobial Resistance Region of a Putative Virulence Plasmid from an Escherichia coli Isolate Incriminated in Avian Colibacillosis

Abstract

Infections due to Escherichia coli have been costly to the poultry industry, but the exact virulence mechanisms used by these organisms to cause disease in birds remain undefined. Several factors have been shown to contribute to the virulence of avian E. coli, and many of the genes encoding these factors have been found on large conjugative plasmids. Because of the occurrence of antimicrobial resistance genes on these same plasmids, it is possible that the use of antimicrobial agents may select for persistence of E. coli containing such plasmids. In the present study, a subclone of one of these plasmids was identified as likely containing some virulence and antimicrobial resistance genes. In an effort to better understand the relationship between virulence and resistance in these plasmids, this subclone was sequenced and the sequence analyzed. Analysis of this 30-kilobase (kb) region of plasmid pTJ100 revealed a mosaic of virulence genes, insertion sequences, antimicrobial resistance cassettes, and their remnants. Many of the resistance genes found in this region were expressed under laboratory conditions, indicating that certain antimicrobial agents, including disinfectants, antibiotics, and heavy metals, could promote selection of E. coli containing such plasmids in the production environment. Also, analysis of the G + C content of this clone indicated that it is the likely consequence of a complex evolution with components derived from various sources. The occurrence of many mobile elements in conjunction with antimicrobial resistance and virulence genes in this 30-kb region may indicate that the genetic constitution of the clone is quite plastic. Although further study will be required to better define this plasmid's role in avian E. coli virulence, the sequence described here is, to our knowledge, the longest known contiguous sequence of a ColV plasmid yet presented. Analysis of this sequence indicates that this clone and its parent plasmid may be important to the pathogenesis of avian colibacillosis and the evolution of avian E. coli virulence. KeywordsEscherichia coli, avian colibacillosis, antimicrobial resistance, disinfectant resistance, heavy metal resistance, virulence, R plasmid, poultry, Tn21, pTJ100 SUMMARY. Infections due to Escherichia coli have been costly to the poultry industry, but the exact virulence mechanisms used by these organisms to cause disease in birds remain undefined. Several factors have been shown to contribute to the virulence of avian E. coli, and many of the genes encoding these factors have been found on large conjugative plasmids. Because of the occurrence of antimicrobial resistance genes on these same plasmids, it is possible that the use of antimicrobial agents may select for persistence of E. coli containing such plasmids. In the present study, a subclone of one of these plasmids was identified as likely containing some virulence and antimicrobial resistance genes. In an effort to better understand the relationship between virulence and resistance in these plasm...

Comparison of Escherichia coli isolates implicated in human urinary tract infection and avian colibacillosis

“…Some of the genes that were found to be widely distributed among both UPEC and APEC are known for their contribution to APEC virulence and have been localized to large, transmissible R plasmids, such as pTJ100 (Johnson et al, , 2004. Similar plasmids have been identified in UPEC (Sorsa et al, 2003), and several of these pTJ100-associated genes have been found on the UPEC chromosome in PAIs (Dobrindt et al, 2001(Dobrindt et al, , 2002Oelschlaeger et al, 2002a,b).…”

“…Test and control organisms were examined for the presence of several genes (Table 1) known for their association with ExPEC or APEC virulence, using multiple PCR assays. The APEC genes of interest have been associated with APEC plasmids, such as pTJ100 (Johnson et al, , 2004. pTJ100 is a large plasmid known to contain many of the genes associated with APEC virulence, including the iron-acquisition operons, aerobactin *These genes are listed as pTJ100-related, but they could also be listed with the protectins.…”

“…AY545598) and sit (GenBank accession no. AY553855); the ColV operon ; certain genes associated with serum resistance, iss and traT (Johnson et al, 2004); and tsh . Interestingly, pTJ100 also shows similarities in genetic content to a UPEC plasmid (Sorsa et al, 2003) and PAI (Dobrindt et al, 2001(Dobrindt et al, , 2002Oelschlaeger et al, 2002a,b).…”

Characterizing the APEC pathotype

“…Targeted genes and their descriptions are summarized in Table I, and the primer sequences used in the amplification studies are summarized in Table II. Genes from APEC that were used in genotyping have been localized to a large, conjugative R plasmid, known as pTJ100 that encodes aerobactin and ColV production [25,26]. All primers used in the amplification studies were obtained from Sigma-Genosys (The Woodlands, TX, USA) and Integrated DNA Technologies (Coralville, IA, USA).…”

“…ExPEC genes were included since ExPEC cause extraintestinal diseases in human beings, much as APEC do in birds. All the APEC-related genes used in this study have been found on a large, conjugative R plasmid, known as pTJ100, from a virulent avian E. coli strain [25,26].…”