Serotyping of Escherichia Coli Isolated from Piglet Diarrhea

Aim: The aim was to investigate the different strains of Escherichia coli isolated from diarrheic piglets by serological typing. Materials and Methods: A total of 150 isolates consists of 66 from diarrheic feces and 84 from intestinal contents were subjected to serological typing. The isolates were referred to National Salmonella and E. Result: Of 150 isolates, 90 isolates were serotyped into 20 different serogroups, 4 isolates were rough and remaining 56 isolates were refractory to serotype. The most frequently encountered serogroups were O76 Conclusion: The results in the present study showed that variable strains of E. coli are responsible for diarrhea in piglets.


Introduction
Gastrointestinal disorders in pigs are a great economic challenge to intensive pig farming.They cause substantial economic losses due to mortality, stunted growth, and prolonged time for reaching slaughter weight [1].Pathogenic Escherichia coli is a common agent responsible for a variety of intestinal disorders.Porcine neonatal diarrhea and post weaning diarrhea caused by enterotoxigenic E. coli (ETEC) result in significant mortality and morbidity, and are economically important diseases of pigs [2].
Secretory diarrhea is associated with ETEC infection and is mediated by any one of the several enterotoxin including heat-labile enterotoxin, heat stable enterotoxin-a, and heat stable enterotoxin-b [3].The ETEC colonization in the small intestine is mediated by fimbriae that attach to the receptors on the villous enterocytes [4].Fimbriae including K88 (F4), K99 (F5), 987P (F6), F18, and F41 are commonly found and porcine E. coli strains expressing these fimbriae are clinically important for porcine diarrhea [5,6].Certain serotypes of E. coli are far more likely to be associated with some of the virulence factor of diarrheagenic E. coli than other serotypes.
The purpose of the present study was to find out the frequency of different serotypes among diarrheal cases in piglets below 2 months of age.

Ethical approval
Collection of samples was done as per standard procedure.

Collection of samples
The samples were collected from piglets below 2 months of age with the history of diarrhea viz.yellowish watery feces with the offensive smell, dehydration, and weakness.Rectal swabs were collected aseptically and diluted in phosphate buffered saline and preserved in the refrigerator until used.Then the intestinal contents from dead piglets were also collected aseptically and preserved in the refrigerator until used.Piglets died of diarrhea revealed typical lesions of gastroenteritis viz.stomachs contained undigested material, watery to blood mixed fluid in the intestine and mild catarrhal enteritis to severe hemorrhagic gastroenteritis.

Isolation and identification of E. coli
The rectal swabs and intestinal contents were inoculated into MacConkey's lactose agar for primary isolation by streak plate following a standard protocol [7].Pink-colored colonies representing coliforms were picked and subcultured in eosin methylene blue agar plates for purification of the isolates.Characterization and identification of the organisms were made by a standard protocol described earlier [8] on the basis of the criteria viz.colony morphology, morphological characteristics in Gram's staining, and biochemical characteristics.

Serotyping of E. coli
The purified colonies were subcultured into nutrient agar slants and preserved at 4°C.The duplicate cultures were referred to National Salmonella and Escherichia coli Research center, Kasauli, Himachal Pradesh for serological typing.
The common serogroups of E. coli observed in the present study and recorded earlier by different workers from different parts of the world were O5, O24, O25, O76, O120, O80, O84, O100, O116 [10][11][12].The other serogroups O60, O100, O116, O117, and O120 were reported from diarrheic piglets in Korea [13].Serogroup O80 has been reported from 23.56 % of E. coli strains isolated from diarrheic piglets in Western China [14].No reports have been found regarding prevalence of serotype viz.O3, O36, O42, O64, O84, O87, O132, O140, and O158.Thus, further characterization of their virulence factors is the most important.Moreover, there are certain serotypes which were refractory to serotyping, and they are also important for detection of their virulence factors.
The frequencies of serogroups could vary from area to area and over time to time [15,16].Moreover, the virulence genes in E. coli vary with the geographical area [17].

Conclusion
The results indicate that the regional difference or other selective advantages may result in E. coli strains with certain O-serogroups adapting to survival in the swine intestine and their environment.Hence, variable serogroups of E. coli are associated with diarrhea in piglets causing mortality in young pigs causing heavy economic losses to pig industry.The results provide preliminary information about the various serotypes of E. coli responsible for diarrhea in piglets in around organized farms of Guwahati, Assam and constitute an important database for the implementation of prevention, diagnosis, and treatment measures.

Authors' Contributions
MR collected samples for the present study.Rest of the authors equally contributed in the preparation of

Strain of E. coli from diarrheic feces Strain of E. coli from intestinal contents Total number of strains
E. coli = Escherichia coli