Serotypes of E. coli isolated from avian species in Lombardia and Emilia Romagna (North Italy)

Abstract In this paper we report the results of n.105 E. coli strains serotyping, isolated during the period 2000-2004 in Lombardia and Emilia Romagna (North Italy) from avian species (poultry and turkeys), starting from cloacal swabs. The most frequently identified serogroup was O78 both in poultry and turkeys, with a large prevalence over the other detected serogroups. Remarkable was the non typeable percentage among the examined strains, datum which is in accordance with our and other authors’ previous studies.


Introduction
Avian pathogenic Escherichia coli (APEC) cause aerosacculitis, polyserositis, septicaemia and other mainly extraintestinal diseases in poultry, turkeys and other avian species. APEC are found in the intestinal microflora of healthy birds and most of the diseases associated with them are secondary to environmental and host predisposing factors (Dho-Moulin and Fairbrother, 1999).
The study consisted in the serotyping of n.105 E. coli strains, isolated during the period 2000-2004 in Lombardia and Emilia Romagna (North Italy) from poultry and turkeys, reared both in rural and intensive units. These animals represented an heterogeneous picture of the avian population bredeed in Lombardia and Emilia-Romagna.
E. coli strains were isolated from cloacal swabs at one of the n.17 Provincial Diagnostic Sections of the Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna, Brescia (IZSLER), using standard bacteriological methods. Further examination for the characterization of the isolated strains i.e. determination of serogroup, was performed at IZSLER "Specialized Bacteriology Department".
A part of each broth culture (50 µl) was put in contact with the same volume of each antiserum in U bottom polystyrene microtitre plates and incubated for 24 hours at 37 °C in a moist box to cause a slow sero-agglutination (SAL). The broth culture (50 µl) was also put in contact with the same volume of PPS to estimate the auto-aggluti-  nating power of each strain. Negative reactions were indicated by a sharp point, whereas positive reactions by a carpet. The E. coli strain was considered non typeable when agglutination was observed in four or more microwells. In addition, titration was carried out if agglutination was observed towards 2 or 3 antisera. The titre was determined by SAL using 50 µl of the broth culture and 6 base dilutions of the positive antisera and corresponded to the highest positive dilution.

Results and discussion
Figures 1 and 2 schematically report the results of O antigens' detection carried out in poultry and turkeys during last five years (2000)(2001)(2002)(2003)(2004).
A large number of isolates was untypeable, 49.2% and 65% in poultry and turkeys respectively. The comprehensive results of serotyping for the considered avian species are reported in table 1.

Conclusions
In previous reports other Authors indicated a predominance of O78, O88, O8 and O2 serogroups (Gross, 1994;Blanco et al., 1998); in our study O78 was the most frequently recovered serogroup; this datum is in accordance with previous demonstra-tions (Cloud et al., 1985;Blanco et al., 1998). Concerning the other E. coli serogroups identified in this study, they have already been reported from cases of avian colibacillosis (Barnes and Gross, 1997).
We have to consider that many pathogenic isolates do not belong to these identified serogroups, and they are commonly designated as "untypeable"; this results in difficulties in identifying APEC strains in veterinary laboratories.
However, at the moment the characterization of isolated strains, constitutes an indicative suggestion of E. coli serogroups mostly diffused in Lombardia and Emilia Romagna (North Italy) regions.