Research: Characterization and Plasmid Profiling of Salmonella Enteritidis Isolated from Broiler Chickens
Salmonella Enteritidis is considered one of the main causes of economic losses among poultry industry and production. The present study was aimed to characterize Salmonella Enteritidis isolated from broiler chickens and provide an insight toward plasmid profile of these isolates. A total of 125 samples were collected from broiler chickens; and bacteriological isolation was carried out using tetrathionate broth and MacConkey agar medium. Five isolates of S. Enteritidis were obtained by serotyping using O and H antisera and confirmed by Polymerase Chain Reaction (PCR). Plasmid profile which was carried out on these isolates indicated that this five isolates having three different plasmid profiles concluding that phenotypically similar strains of SE may be genotypically different and plasmid profile is a simple method that could detect this genotypic variation.
Salmonella detection by bacteriological methods usually requires 5-11 days (Humbert et al., 1997) and samples with low numbers of Salmonella cells may give false-negative results.
In our study here, the total number of S. Enteritidis isolated from cecal samples of poultry farms was 4% which agreed with result obtained by Ebel et al., (1992) who recorded S. Enteritidis in 3 % of chicken pooled cloacal samples. contradictory, our finding were not agreed with results obtained by Dreesen et al., (1992) who isolated S. Enteritidis from cloacal samples of laying hens at an incidence of 18.4%. Also, Corkish et al., (1994) reported that 17 % of the flocks were carrier for S. Enteritidis and Neif and Hoop (1998) isolated S. Enteritidis from caecal content of layers with an incidence of 50%.
PCR is a sensitive technique for detection of pathogens and our study confirmed that detection of 312 bp DNA fragment using specific primers is good for detection of S. Enteritidis and this result agreed with results obtained by Oliveira et al., (2002) and Eyigor and Carli (2003) who found that 312 bp notifies the presence of S. Enteritidis DNA.
There are different methods for typing of S. Enteritidis as. Serotyping, phage typing, randomly Amplified Polymorphic DNA, Plasmid Profiling, Restriction Fragment Length Polymorphism and IS200, Ribotyping.
Serotyping depending on O and H antigens which is the one of the oldest methods, it is the commonly used method to differentiate members of the genus Salmonella following the biochemical identification.
Bacterial strains can be typed according to the plasmid content or plasmid profile of each isolate. Plasmids are not considered as a stable strain characteristic as they can be lost or undergo re-arrangement by conjunctive transfer (Liebana, 2002 and Domig et al., 2003) and therefore plasmid profiling is usually used as additional methods for typing.
Disadvantages of plasmid profiling are not always associated with epidemiological identical strains and lost by repeated subculture of bacteria over long period of times. Chadfield et al., (2001). Plasmid profiling was sensitive when it was applied for the typing of S. Typhimurium, S. Virchow and S. Gallinarum strains (Mohan et al., 1994; Liebana, 2002). Controversially; (Adams and Moss 2000) mentioned that Plasmid profiling sometimes met with some success as an epidemiological tool, distinctive and stable method for typing. Plasmid profile of S. Enteritidis isolated in our study indicated the presence of a common heavy plasmid of approximate size of 19.5 Kbp and this agreed with the result of Hegazy (2002). Also, three different plasmid profiles have been identified from the five confirmed S. Enteritidis isolates; profile No 1 having plasmids of molecular size 19.5 Kbp and 13.25 Kbp (lane 1 and 3), profile No 2 having plasmids of molecular size 19.5 and 3.25 Kbp (lane 2) and profile No 3 having plasmids of molecular size 19.5 Kbp , 13.25 Kbp 3,25 Kbp ( lane 4 and 5). The difference noted here in plasmid profiling of the five confirmed S. Enteritidis isolates; indicated that phenotypically similar strains, of S. Enteritidis may be genotypically different. So, plasmid profiling is considered a simple technique that could be used a genotyping method especially in case of epidemiological studies.
1- Cecal, liver and spleen samples are a good source for isolation of S. Enteritidis to detect the presence of infection with it inside poultry farms.
2- PCR technique is a sensitive confirmatory method detection of S. Enteritidis.
3- Plasmid profiling is a simple rapid applicable method that could be used as an epidemiological typing method for S. Enteritidis.