Prevalence of Streptococcus suis Isolated from Clinically Healthy Sows in China

Streptococcus suis is an important pathogen in pigs. Transmission of this pathogen is generally believed to occur between healthy carrier sows and their offspring, so the carrier status of S. suis in healthy sows is important for the control of S. suis infections in pigs, especially in suckling and growing pigs. In this study, the prevalence of S. suis isolated from clinically healthy sows in China was studied for the first time. A total of 1 043 tonsil samples were collected from clinically healthy sows from 10 regions in China from 2005 to 2007. Among the 421 S. suis isolates, 31 strains were identified as capsular type 2. The results showed that S. suis was widespread in swine herds in China with the carrier rates in different herds ranging from 19.5 to 93.9%. Overall, 40.4 and 3.0% of clinically healthy sows harbored S. suis and capsular type 2 in their palatine tonsils, respectively. Statistically significant differences of carrier rates of S. suis and capsular type 2 between the different farms were observed, which was independent of herd sizes and geographic distributions of different herds.

Comparative Research on Serogroups Distribution and Antimicrobial Resistance of Escherichia coil Isolates from Poultry in Different Areas of China

A total of 241 Escherichia coli （E. coli） isolates from 349 avian samples （292 from cloacae, 29 from feed and water, 28 from dust and padding） were collected from Northeast, South, North, and Central China in recent years. The percentage of isolation was 69.1%. There are 67 serogroups each with 1-2 isolates distributed in different regions, and some of these regions had the preponderant serogroups. Antimicrobial-resistance （AR） of E. coli was so severe that the majority were multi-AR. Fifty percent strains were resistant to 10-19 antimicrobial drugs. Overall, the isolates represented resistance to nalidixic acid （88.1%）, tetracycline （85.7%）, sulfamethoxazole （81.0%）, trimethoprim-sulfamethpxazole （77.1%）, ampicillin （76.2%）, amoxilline （74.3%）, streplomycin （66.2%）, fluoroquinolones （57.1-66.7%）, chloramphenicol （52.9%）, gentamicin （39.0%）, and kanamycin （36.2%）. The isolates were sensitive to cefalexin, amoxilline-clavulanic acid, amikacin, and florfenicol with an AR rate of 0-19,5% only, The results showed that the AR was more severe in chicken farms in which the antibiotics were used broadly and repeatedly. This study indicated the AR characterization of E, coli in different areas of China. It will be a foundation for studying AR mechanism and regulating the usage of antimicrobial in the poultry industry.

Heterogeneity and Secondary Structure Analysis of 3' Untranslated Region in Classical Swine Fever Viruses

The attenuated vaccine strains of CSFV have a 12-nucleotides （nt） insertion in the 3＇-UTR of genome as compared to that of CSFV virulent strains. In this study, we found a distinct heterogeneity in the 3＇-UTR of attenuated Thiverval and HCLV strains. The longest 3＇-UTR of Thiverval strain was 259 base pairs （bp） with a 32-nt insertion, the shortest 3＇-UTR had only 233 bp with a 6-nt insertion. The longest 3＇-UTR of HCLV strain was 244 bp with a 17-nt insertion and the shortest 3＇ UTR was 235 bp with a 8-nt insertion. Compared with the published sequences of 3＇-UTR of vaccine and virulent strains, the 3＇-UTR of CSFV vaccine strains have two variable regions where insertion among the different vaccine strains were frequently found. The first is located between the second conservative TALk codon and the start of T-rich region where we found the variable length insertion in the same vaccine strain Thiveral or HCLV and the second is located between the end of T-rich region and the front of GAA eodon, however, a 4-nt deletion was found in this region in the virulent Shimen strain. These two regions may represent the ＂hot spot＂ for mutation. Modeling the secondary structures of the 3＇-UTR suggests that the T-rich insertion could result in the change of structure and free energy, thus affecting the stability of the 3＇-UTR structure. These findings will help to understand the mechanism of attenuated vaccines and improve vaccine safety, stability, and efficacy.

Studies on Antimicrobial Resistance Transfer In vitro and Existent Selectivity of Avian Antimicrobial-Resistant Enterobacteriaccae In vivo

Increasing antimicrobial resistance （AR） has become a severe problem of public health in the world, whereas control of the AR of bacteria will be based on investigation of the AR mechanism. Furthermore, understanding the existent selectivity of AR organisms from animals can prevent the emergence and diffusion of AR effectively. PCR amplifications of gyrA and parC genes have been performed for detecting fluoroquinolones-resistance （FR） genes. A conjugational transfer test has been carried out using a donor which is resistant to tetracycline （TE）, ampicillin （AMP）, sulfamethoxazole-trimethoprim （SXT）, and a recipient which is sensitive to TE, AMP, and SXT. The AR strains have been passed 20 passages. Two groups of chicken inoculated multi-AR Escherichia coli （E. coli） and multi-AR Salmonella, respectively, are mix-fed. The result shows that amino acid codons of Ser-83 and Asp-87 are mutations from gyrA and there are no mutations from parC genes in all the FR strains. Resistance to TE, AM, and SXT can transfer among E. coli and the conjugal transfer frequency of TE is 3×10^-7. AR can inherit in 20 passages at least. The multi-AR E. coli and Salmonella can be isolated from all chickens three days after inoculation but CIP-resistant strains decrease during the time run out and disappear at 23 days after inoculation. The results indicate that the mutations of gene gyrA are correlative with the FR phenotype. AR genes that are not connected to the chromosome can transfer horizontally and vertically. AR bacteria can diffuse quickly and eliminate naturally from the host if the chicken is not under the pressure of this antibiotic.