papA Gene of Avian Pathogenic Escherichia coli

Abstract

<p>P fimbrial adhesins may be associated with the virulence of avian pathogenic <em>Escherichia coli</em> (APEC). However, most APECs are unable to express P fimbriae even when they are grown under conditions that favor P fimbrial expression. This failure can be explained by the complete absence of the <em>pap</em> operon or the presence of an incomplete <em>pap</em> operon in Pap-negative APEC strains. In the present study, we analyzed the <em>pap</em> operon, specifically the<em>papA</em> gene that encodes the major fimbrial shaft, to better understand the <em>pap</em> gene cluster at the genetic level. First, by PCR, we examined a collection of 500 APEC strains for the presence of 11 genes comprising the <em>pap</em> operon. Except for <em>papA</em>, all the other genes of the operon were present in 38% to 41.2% of APEC, whereas the <em>papA</em> was present only in 10.4% of the APEC tested. Using multiplex PCR to probe for allelic variants of <em>papA</em>, we sought to determine if the low prevalence of <em>papA</em> among APEC was related to genetic heterogeneity of the gene itself. It was determined that the <em>papA</em> of APEC always belongs to the F11 allelic variant. Finally, we sequenced the ‘<em>papA</em> region’ from two <em>papA</em>-negative strains, both of which contain all the other genes of the <em>pap</em> operon. Interestingly, both strains had an 11,104-bp contig interrupting <em>papA</em> at the 281-bp position. This contig harbored a streptomycin resistance gene and a classic Tn<em>10</em> transposon containing the genes that confer tetracycline resistance. However, we noted that the <em>papA</em> gene of every <em>papA</em>-negative APEC strain was not interrupted by an 11,104-bp contig. It is likely that transposons bearing antibiotic resistance genes have inserted within <em>pap</em> gene cluster of some APEC strains, and such genetic events may have been selected for by antibiotic use.</p>