Prevalence of the paa gene (porcine attaching and effacing associated) in porcine enteropathogenic Escherichia coli (PEPEC) associated with postweaning diarrhea in south Brazil

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Prevalence of the paa gene (porcine attaching and effacing associated) in porcine enteropathogenic Escherichia coli (PEPEC) associated with postweaning diarrhea in south Brazil

Marilda C. Vidotto^I; Elaine C.T. Florian^III; Mario A. Ono^II

^IDepartamento de Medicina Veterinária Preventiva, Universidade Estadual de Londrina, Londrina, PR, Brazil

^IIDepartamento de Ciencias Patológicas, Universidade Estadual de Londrina, Londrina, PR, Brazil

^IIIDepartamento de Bioquímica e Biotecnologia, Universidade Estadual de Londrina, Londrina, PR, Brazil

^{Send correspondence to}

ABSTRACT

Paa (porcine attaching and effacing associated) may be an important virulence factor E. coli of piglets with diarrhea. This study showed for the first time in Brazil the prevalence of the paa gene (22%) in E. coli strains isolated from piglets and these isolates also harboured genes for other adhesins and toxins LT II, STa and STb.

Key words: Escherichia coli, pig, PEPEC, paa gene, postweaning diarrhea.

Neonatal diarrhea and postweaning diarrhea (PWD) in pigs are diseases of considerable economic importance and are characterized by watery diarrhea, dehydration, loss of body weight and sometimes death of infected pigs (Nagy and Fekete, 1999). Enterotoxigenic E. coli (ETEC) is an important cause of PWD, and its pathogenicity involves the adherence of the pathogen to the small intestine by means of specific adhesion factors (fimbriae) and production of one or several exotoxins responsible for disease development. ETEC produce heat-stable (Sta or Stb) and/ or heatlabile (LT) enterotoxin that cause fluid and electrolyte secretion (Nagy and Fekete, 1999)

However, non-enterotoxigenic porcine E. coli strains have been associated with PWD and neonatal diarrhea in swine by adhesion to intestinal epithelial cells in a characteristic attaching and effacing (A/E) pattern. This porcine enteropathogenic E. coli (PEPEC) produces an outer membrane protein (intimin), which is involved in the intimate attachment of the bacteria to enterocytes and induced typical A/E lesion in a pig ileal explant model (Zhu et al., 1994, 1995). The A/E lesion contributes to the initial phases of PEPEC pathogenicity (Batisson et al., 2003).

The gene that induces this lesion was designated paa (porcine A/E-associated gene) (Nagy and Fekete, 1999; An et al., 1999), and its sequence revealed an open reading frame of 753 bp encoding a 27.6-kDa protein, that shows similarity with Paa of enterohemorrhagic E. coli O157:H7 strains (Batisson et al., 2003). The A/E activity of PEPEC is highly correlated with the presence of the LEE (locus of enterocyte effacement) detected by DNA probes derived from the LEE of human enteropathogenic E. coli (EPEC) strain E2348/69 (An et al., 2000).

In Brazil there is a lack of information about the prevalence of the paa gene of porcine E. coli. The objective of the present study was to evaluate the presence of paa gene, and its correlation with the presence of enterotoxin STa, STb and LT encoding genes of E. coli strains isolated from piglets with diarrhea in Northern region of Paraná State, Brazil, described in a previous study (Vidotto et al., 2009).

Three hundred Escherichia coli strains isolated from 100 piglets with diarrhoea from different farms in Paraná State (Vidotto et al., 2009) were tested for the presence of the paa gene by polymerase chain reaction assay (PCR). The E. coli HB101strain (Boyer and Roulland-Dssoix, 1969) was included as negative control.

The base sequences for specific oligonucleotide primers used in this study were constructed based on the regions of conserved sequences between the paa gene of ETEC and PEPEC 045 (GeneBanK U82533.4), PAA PEPEC O45-F: 5'-TCTTCTGCTGCTTATGCTGATA TC-3' and PAA PEPEC O45-R: 5'-TTACCAGCCATA TTTTTTGAATGC-3', annealing at nucleotides 37 to 60 and 718 to 738 of the paa gene, respectively. Bacterial DNA to be amplified was released from whole organisms by boiling, and PCR was carried out in a total volume of 25 µL containing 5 µL template DNA, each of the primers at 20 pmol, 200µM dNTPs, PCR buffer and 1.5 U Taq DNA polymerase (Invitrogen). PCR amplifications consisted of 30 cycles of 94 ºC for 1 min, annealing temperature specific for each primer for 1 min and 72 ºC for 2 min. The amplified DNA was visualized in 1.5% agarose gels stained with ethidium bromide. The 100-pb ladder (Promega, Madison, WI) was used as standard.

Of 100 piglets with diarrhea, 22% presented E. coli that carried paa genes. The presence of the paa gene (Table 1) was correlated with the presence of genes that encode fimbrial adhesins F4, F5, F6, F18, F41 and the toxins LT II, STa and STb found in these studied strains (Vidotto et al., 2009). Some strains that carried the paa gene also harboured genes for others adhesins and toxins (Table 1). There was no significant association of paa gene with the other virulence genes when analyzed by chi-square test (p > 0.05).

The presence of ETEC virulence factors, fimbriae and enterotoxins production, are common features of isolates associated with diarrhea during the pre-weaning and weaning periods (Nagy and Fekete, 1999, 2005), but some E. coli strains isolated from piglets with diarrhea were non-enterotoxigenic, and presented intimin (paa gene) responsible for A/E lesions (Zhu et al., 1995). The serogroup O45 is particularly important among PEPEC strains, and based on their virulence gene content, O45 PEPEC strains displayed significant differences from typical EPEC and could be regarded as atypical EPEC, that are defined as LEE-positive E. coli lacking stx1 and stx2 genes (Bruant et al., 2009).

In the present study, the paa gene was detected in 22% of E. coli isolated from diarrhoeic piglets, from the Northern Region of Paraná State, and this gene was associated with other virulence factors from ETEC. We found the paa gene in isolates that carried additional virulence encoding genes such as faeG (F4), fanC (F5), fasA (F6), fedA (F18), f41, estA (STa), estB (STb) and elt (LT). The pathotype F4⁺ F18⁺ F41⁺ Paa⁺ STa⁺ STb⁺ and LT⁺ were found among the strains. These data suggest that the various virulence genes together can be link to resistance genes on plasmids. The paa gene was found on high molecular weight plasmids that codify tetracycline resistance (Leclerc et al., 2007).

Similarly Leclerc et al. (2007) found the paa gene with virulence genes associated with pig ETEC, estA that encodes STa, estB that encodes STb, elt that encodes LT, astA that encodes EAST1 and faeG that is a part of the F4 operon. The occurrence of enterotoxins was also associated with specific fimbriae in E. coli from pigs and several strains produced more than one fimbrial antigen (Nagy and Fekete, 2005; Toledo et al., 2012; Vidotto et al., 2009).

The prevalence of the paa gene (22%) found in this study was different than that found by others, Zhang et al. (2007) found a prevalence of 60% in E. coli strains isolated from young pigs with diarrhea in the US, and Boerlin et al. (2005) detected paa in 92% of porcine ETEC isolated in Canada.

The paa gene sequence is similar to that of the EPEC eae gene that codifies intimin (Zhu et al., 1994), and the eae gene also have been found in 25.7% of isolates in Brazil (Martins et al., 2000), 28.33% in China (Cheng et al., 2006); and 27% of isolates in Mexico (Toledo et al., 2012).

In conclusion, this study showed for the first time in Brazil the prevalence of the paa gene in E. coli strains isolated from piglets with diarrhea, and confirms the combination of various virulence genes in ETEC and porcine EPEC, suggesting that the paa gene could play a role in virulence.

Acknowledgments

We thank Dra. Ana Vergínia Libos Messetti and Dra. Vanderli Marino Melem for statistical analysis. This work was supported by "Conselho Nacional de Desenvolvimento Científico e Tecnológico" (CNPq).

Submitted: October 17, 2011

Approved: July 23, 2012

All the content of the journal, except where otherwise noted, is licensed under a Creative Commons License CC BY-NC.

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Publication Dates

• Publication in this collection
  09 Oct 2013
• Date of issue
  2013

History

• Received
  17 Oct 2011
• Accepted
  23 July 2012