| Salmonellosis is a general term of diseases in human beings and animals infected by different serotypes of Salmonella. Food poisoning caused by Salmonella often ranks forefront among bacterial food poisoning around the world, leading to reduction in production capacity, which has a significant impact on animal husbandry economy. It not only seriously impedes the development of stockbreeding, but also serves as a threat to the health of human, having become the focus of public health issues. In this study, we mainly investigated Salmonella contamination in several poultry farms located in Hai’an County of Jiangsu Province and clinical samples derived from poultry disease clinic in Yangzhou Universit. The blood samples were collected for antibody detection, meanwhile, Salmonella isolated from clinical liver samples, the farms cloacal swabs, eggs and environmental samples were used for serotype identification, drug sensitivity test, molecular classification and identification of virulence gene. These results will contribute to the establishment of disease prevention and control measures.During the period between 2014 and 2015, a total of 1600 blood samples were collected from four chicken farms in Hai’an, adopting different feeding patterns from each other, with samples collected four times respectively for each farm. Serotyping was performed using slide agglutination method, and 165 positive samples were detected, with positive rate being 10.3%. The positive rate of farms with open rearing was 22%, significantly higher than that of farms taking other feeding methods (with 7.4% of semi-closed feeding, and 4.5% of closed feeding); in summer the positive rate was 20.3%, dramatically higher than that in other quarters (with 8.3% in winter,7.5% in spring, and 5.3% in autumn). Twelve strains of Salmonella isolated from 1600 samples of cloacal swabs, and the positive rate was 0.75%. Among these four farms, the isolation rate of open-rearing was 1.5%(6/400), higher than that of semi-closed feeding 0.63%(5/800), and closed feeding 0.25%(1/400). Meanwhile, no Salmonella isolates were identified in eggs, forage or environmental samples.Eighteen strains of Salmonella were isolated from 161 clinical samples derived from poultry disease clinic in Yangzhou University, and the positive rate was 11.2%. Among these clinical samples, the isolation rate of Salmonella in samples from Yangzhou was the highest 13.6%(11/81); then the isolation rate of samples from both Zhenjiang and Lai’an were 12.5%; followed by Huai’an (8.7%), Nantong (7.4%), and Nanjing (7.1%).Test serology experiment and drug sensitivity in the 30 isolates of Salmonella, The results of serology experiment showed that among the 30 isolates of Salmonella, there were 20 strains is 1,9,12:-:-(Salmonella gallinarum or Salmonella pullorum),5 strains is 1,4,[5],12:i:1,2 (Salmonella typhimurium),3 strains is 1,4,[5],12:b:1,2(Salmonella paratyphi B) and 2 strains is 1,9,12:g,m:[1,7](Salmonella enteritidis). The resistance of these 30 strains of Salmonella isolates were studied using 12 kinds of antibiotic, and the results showed that the Salmonella isolates were highly sensitive to amikacin, enrofloxacin, ciprofloxacin, ammonia aztreonam, kanamycin with sensitive ratio reaching 100%; while remarkably resistant to tetracycline (resistance rate was 40%); resistant to other antibiotics in different degrees. There were 18 strains of Salmonella being resistant to at least 2 antimicrobial drugs. Salmonella isolates from different regions showed diverse resistance rates, among which the isolates from Nantong area had multi drug resistance, resistant to four kinds of antibiotic with resistance ratio reaching 16.7%. Meanwhile, there appeared to have different degree of resistance among different serotypes of Salmonella isolates, with Gallinarum or Pullorum showing the highest resistance rate, followed by Typhimurium, whereas Enteritidis had the lowest resistance ratio.In order to further understand the genetic variation of isolates, seven housekeeping genes of Salmonella, including aroC, dnaN, hemD, hisD, purE, sucA and thrA, were chosen for multilocus sequence typing (MLST) analysis, which was conducted upon the 30 isolates of Salmonella and 26 strains of isolated templates. A total of 8 different sequencing types (STs) were identified, consisting of ST11, ST19, ST86, ST92, ST99, ST1690, ST2039 and ST2151, among which ST2151 was a newly discovered ST type. Cluster analysis was performed using software including eBURST and MEGA to study the correlation of the evolution. The dominant pathogenicity island genes of Salmonella, including sitC (SPI-1), invA(SPI-1), spiC (SPI-2), sifA (SPI-2), misL (SPI-3), orfL (SPI-4), pipD (SPI-5), and other important structural virulence genes (pefA, iroN, msgA and lpfC), were picked for identification. Among them, the positive identification rates of sitC, spiC, orfL and pipD were all 100%, and the identification rates of iroN, msgA, lpfC and sifA serving as conserved pathogenicity island genes were 92.5%,95%, 97.5%, and 97.5%, respectively, whereas the detection rate of misL gene was the lowest, with only 45%. |
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