| Based on the army network monitoring platformfor infectious disease, this study was aimed to develop the standardized monitoring technique and to subtype the important bacterial pathogens including Shigella, Streptococcus suisand Acinetobacterbaumanniin order to analyse the genetic variation and changing trends of these pathogens. The results obtained in this study will play an important role inmaking and adjusting the prevention and control strategies.Shigella spp.,an important infectious agents with a number of serotypes which can cause acute diarrhea, easily experiences genetic variation in the process of transmission. So it will pose a major challenge for the prevention and control of shigellosis. In this study 165 Shigella strains were selected to analyse the regional variation. The Shigellaflexneriserotype 1b isolates from Kunming and Xinjiang formed different clusters respectively, revealing obvious regional variation. The S. sonnei isolates showed no clear regional difference as they had high genetic relatedness and the strains from different regions had the same genotypes. Frequent serotype switching was observed among the S. flexneriserotype2strains.The serotypes of strains were confirmed by using the commercially available antisera kit (Denka Seiken, Tokyo, Japan) and a panel of monoclonal antibodies against Shigellaflexneri (MASF) (Reagensia AB, Stockholm, Sweden). During the routine surveillance of shigellosis in our laboratory,S.flexneriserotype1cwas detectedin our country for the first time, and we also identifiedseveral newS.flexneriserotypes, provisionally named as S.flexneriserotype2c and serotype 4y. Api20E test kits were used to observe the biochemical reactions of the serologically atypical strains of S.flexneri. Surprisingly, serotype 4yhaddifferent biochemical characteristics from otherserotypes, and it was identified as a suspected biochemical profile with 52.9% probability of Escherichia coil and 44.5% probability of Shigellaby using Apilabplus software analysis.To explore the genetic diversity, regional variation and understand the epidemiology of Shigella, Pulsed field gel electrophoresis (PFGE) was used in this study to characterize the clinical isolates of Shigella. There are significant genotypicdifferences between the isolates of Shigella and strains of the same pulsetypespreadindifferent regions by using PFGEanalysis. The S.flexneri serotype 1c isolates in different genetic clusters showed high genetic similarity with the S.flexneri serotype 1a and 1b strains respectively. MLST analysis of S.flexneri serotype 1c showed that they belonged to ST100, ST104 and ST105 respectively. PFGE and MLST analysis had similar results that the serotype 1c strains isolated in Shanghai revealed different levels of genetic similarity for each other, and had higher genetic differences with the strains isolated in Xinjiang. So, S.flexneri serotype 1c strains in China may have several epidemic clones which may be derived from different ancestors.PFGE analysis of S.flexneri serotype 2c strains indicated that most strains had a high genetic similarity with S.flexneri serotype 2a and 2b strains, but two additional strains had low genetic relatedness with other S.flexneri serotype 2 strains. MLST analysis showed that all of the S.flexneri serotype 2c strains belonged to ST100.PFGE cluster analysis describing the genetic similarity among the serotype 4y and other serotypes of S.flexneri showed that different serotypes formed diverse clusters. Five S.flexneri serotype 4y strains isolated in 2007 from a same hospital in Shanghai showed high genetic similarity, and a strain isolated in 2005 inShanghai was closely related to a strain isolated in Beijing in the same year. This result suggested that S.flexneri serotype 4y strains may have spread between Beijing and Shanghai in 2005, and they experienced genetic variation during the dissemination process and then caused a small epidemic in Shanghai. S.flexneri serotype 4y strains had 44.0% similarity with other serotypes of S.flexneri, which was identical with the result of biochemical identification. MLST analysis of S.flexneri serotype 4y strains showed that they all belonged to another new ST (ST99) with 7 new alleles, which had great difference with other STs of S.flexneri.The antimicrobial susceptibilities of serologically atypical S.flexneri strains were determined by the Kirby-Bauer method with commercial antimicrobial discs (Oxoid, United Kingdom). The antibiotic discs used in this study were cefotaxime, ceftazidime, amoxicillin/clavulanic acid, ampicillin/sulbactam, ciprofloxacin, norfloxacin, levofloxacin, ampicillin, tetracycline, sulfamethoxazole/trimethoprim, chloramphenicol,imipenem, gentamicin and nalidixic acid. All of the serologically atypical strains showed serious multidrug resistance, among which . were resistant to imipenem. But S.flexneri serotype 1c strains were completely resistant to ampicillin,nalidixic acid,tetracycline,ampicillin/sulbactam,amoxicillin/clavulanic acid and chloramphenicol, and of them 85.7% were resistant to sulfamethoxazole/trimethoprim. Among the serotype 2c strains, 100%, 94.1%, 88.2%, 82.4%, 76.4%, 76.4%, 70.6% and 64.7% were resistant to nalidixic acid, ampicillin, chloramphenicol, tetracycline, ampicillin/sulbactam, amoxicillin/clavulanic, levofloxacin and sulfamethoxazole/trimethoprim respectively. All serotype 4y strains were resistant to nalidixic acid and ampicillin, and also 85.7% were resistant toamoxicillin/clavulanic and gentamicin. The emergence of multiple resistance among S.flexneri isolates will pose a major public health problem. In this study, 54.8% of the atypical strains were resistant to three commonly used antibiotics, including ampicillin, tetracycline, and sulfamethoxazole/trimethoprim.Furthermore, whole genome sequencing was conducted to explore the genetic difference and evolution of the serotype 4y, and the whole genome analysis is going on.In our country, most strains isolated from human were chosen in MLST analysis of Streptococcus suis. In order to understand the population structure and genetic relationship of S. suis, 32 strains isolated from pigs and 12 strains isolated from human were analysed by MLST. Five STs were identified, among which ST1andST7 were the two most common STs and mainly responsible for humanhighly pathogenicS.suis infection, and other three STs, ST19, ST20andST91, were detected for the first time in our country. Comparative analysis from the data of S.suis MLST database showed that three majorclonal groups (ST1, ST27 andST87) had existedin China. Strains belonging to ST1clonalgrouphadcaused2 large outbreaksin Jiangsu and SichuanProvince. It is reproted that some of the ST27 clone group strains can also result in humanhighly pathogenicS.suis infection in Thailand, and the strains belonging to the ST87clonalgroup can seldom infect human. However, in recent years, more and more STs of S. suis which can infect human have been found. So, the monitoring of S. suis is very important to prevent the large scale dissemination of S. suis .Carbapenem-resistant Acinetobacterbaumanni strains with New Delhimetallo-beta-lactamase–1 (NDM-1) were screened from the samples collected from a hospital, and a blaNDM-1-positive strain was detected. To the best of our knowledge, this is the first report of A. baumannii with NDM-1 inChina. PFGEanalysis showed thatthe blaNDM-1-positive strain was genetically distinct and had different PFGE banding pattern with other A. baumannii strains from this hospital. It was suggested that the blaNDM-1-positive strain did not spread in the hospital. |
