| Salmonella is an important food-borne pathogen which can cause some human and animal diseases, such as gastroenteritis,enteric fever, bacteraemia,extra-intestinal localised infection like osteomyelitis, endovascular infection or focal abscess and Reiter's syndrome. Salmonellosis is often caused by ingesting contaminated food or water, or occasionally by contact with infected persons or animals. At present, many developed countries have gained substantial insight about the ecology, epidemiology and pathogenicity of Salmonella and set up complete monitoring and control system against it. The objectives of this study were: (1) develop a PCR assay for the detection of Salmonella; (2) evaluate the PCR assay by testing abundance different types of samples; (3) detect the antimicrobial susceptibility of the isolates in this study with disk diffusion method recommended by Clinical and Laboratory Standard Institute in 2007.1. Development of a PCR assay for the detection of Salmonella sppA PCR assay targeting Salmonella enterotoxin stn gene was developed in this study. Specificity of the assay was evaluated by testing 17 standrad strians of Salmonella. The PCR results showed that, the 260 bp genus-specific band appeared from all the 17 strains, which indicated there were no false negative results . And 17 reference strains such as Escherichia coli (ATCC 25922), enterohemorrhagic Escherichia coli, enteropathogenic Escherichia coli, enteroinvasive Escherichia coli, Klebsiella pneumonia , Shigella dysenteriae, Shigella flexneri 2a, Proteus vulgaris, Proteus mirabilis, Citrobacter freundii, Enterobacter cloacae, Providencia bacteria, Pseudomonas aeruginosa, fecal Streptococcus, Staphylococcus, Bacillus cereus, lactic acid bacteri were further detected. There was no specific band amplified from these 17 non-Salmonella strains, which suggested that this method was specific with no false positive results. It was shown that the PCR assay could detect artificial Salmonella contaminated samples, and the detection limit was 43.85pg DNA or 1CFU after cultivation. These results suggested that a specific and sensitive PCR method was successfully established, and this new method provided a useful way for the detection and monitoring of Salmonella.2. Preliminary application of the PCR assay for the different types of samplesFrom July 2008 to January 2009, 1082 samples of anus swab, liver and eggs from avian, 466 samples of anus mop, meat and lymph node from swine, 58 water samples from pool and environment in Yangzhou region were detected by the PCR assay, and Salmonella was isolated from the positive samples. Results showed that: there were 41 positives out of avian samples , 15 positives of swine samples, 2 positives out of water samples. We totally gained 58 isolates of Salmonella. The PCR method was verified by abundance samples, which indicated that it was suitable for detection of samples from avian, swine, water, etc, and applicable for different types of sample tests such as the anus mop, liver, water samples, meat.3. Antibiotic resistance of Salmonella isolates100 salmonella isolates were tested for their sensitivity to 18 antimicrobial agents by the disk diffusion method recommended by Clinical and Laboratory Standard Institute in 2007. The results showed that the level of antibiotic resistance of Salmonella is high, and the situation of multiple antibiotic resistance of Salmonella is not optimistic. Although 100 salomnella isolates were highly sensitive to cephalosporins, they were strongly resistant to nalidixic acid, tetracycline and streptomycin. Studies on drug-resistant spectrum showed that the multi-drug resistance of 100 isolates ranging from 2 resistance to 13 resistance, mainly concentrated in the 2 resistance to 5 resistance and 13 resistance, which accounted for 78.13%. These data showed that in our country, the phenomenon of multi-drug resistance of Salmonella is very serious. The isolates were highly resistant to a broad spectrum of drugs in our study, especially four Salmonella isolates resistance to 13 kinds of antibiotics.In this study, isolates from different sources showed different sensitivity level to different types of antimicrobial. Therefore, it is important to choose rational drugs or medication based on the results of sensitivity test in the clinical application of antibiotic to prevent and control of Salmonellosis. More attention should be paid to the emergence of multi-drug resistance salmonella, which would cause serious health threats to the entire population. So, in clinical medicine and veterinary science, antibiotics must be carefully and scientifically used. |
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