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Most outbreaks of Shiga toxin-producing Escherichia coli (STEC) are attributed to consumption of contaminated foodstuffs including beef and dairy products. In this study, we evaluated the prevalence of non-O157 STEC cultured from beef and dairy cattle and collected in Xinjiang Uygur Autonomous Region in China. Results identified 67 non-O157 STEC recovered from the 793 samples including beef cattle (10.28%, 43/418) and dairy cattle (6.40%, 24/375). A total of 67 non-O157 STEC was sequenced allowing for in silico analyses of their serotypes, virulence genes, and identification of the corresponding multilocus sequence types (STs). Twenty-one O serogroups and nine H serotypes were identified and the dominant serotype identified was O22:H8. One stx1 subtype (stx1a) and four stx2 subtypes (2a, 2b, 2c, and 2d) were found in the 67 non-O157 STEC isolates. The results revealed that stx1a+stx2a-positive STEC isolates were predominant (32.83%, 22/67), followed by stx1a+stx2d (29.85%, 20/67) and stx2a alone (17.91%, 12/67). Non-O157 STEC isolates carried virulence genes ehxA (98.51%), subA (53.73%), and cdtB (17.91%). Of the four adherence-associated genes tested, eaeA was absent, whereas lpfA and iha were present in 67 and 55 non-O157 STEC isolates, respectively. The STEC isolates were divided into 48 pulsed-field gel electrophoresis patterns and 10 STs, and ST446 (O22:H8) was the dominant clone (22.38%). Our results revealed that there was a high genetic diversity among non-O157 STEC isolated from beef and dairy cattle, some of which have potential to cause human diseases.

Foodborne disease caused by nontyphoidal Salmonella (NTS) is one of the most important food safety issues worldwide. The objectives of this study were to carry out microbial monitoring on the prevalence of NTS in commercial ground pork, investigate consumption patterns, and conduct a quantitative microbiological risk assessment (QMRA) that considers cross-contamination to determine the risk caused by consuming ground pork and ready-to-eat food contaminated during food handling in the kitchen in Chengdu, China. The food pathway of ground pork was simplified and assumed to be several units according to the actual situation and our survey data, which were collected from our research or references and substituted into the QMRA model for simulation. The results showed that the prevalence of NTS in ground pork purchased in Chengdu was 69.64% (95% confidence interval [CI], 60.2-78.0), with a mean contamination level of -0.164 log CFU/g. After general cooking, NTS in ground pork could be eliminated (contamination level of zero). The estimated probability of causing salmonellosis per day was 9.43E-06 (95% CI: 8.82E-06-1.00E-05), while the estimated salmonellosis cases per million people per year were 3442 (95% CI: 3218-3666). According to the sensitivity analysis, the occurrence of cross-contamination was the most important factor affecting the probability of salmonellosis. To reduce the risk of salmonellosis caused by NTS through ground pork consumption, reasonable hygiene prevention and control measures should be adopted during food preparation to reduce cross-contamination. This study provides valuable information for household cooking and food safety management in China.

Salmonella enterica remains an important foodborne pathogen in all regions of the world, with Typhimurium as one of the most frequent serotypes causing foodborne disease. However, the past two decades have seen a rapid worldwide emergence of a new Salmonella serotype, namely monophasic variant of S. Typhimurium, whose antigenic formula is 1,4,[5],12:i:-. It has become one of the 2-5 most common Salmonella serotypes responsible for animal and human infections in different regions. The global epidemic of monophasic S. 1,4,[5],12:i:- has mainly been characterized by an increase in multidrug-resistant S. 1,4,[5],12:i:- isolated in Europe since 1997. The unexpected link to swine has escalated monophasic S. Typhimurium infections to the status of a global public health emergency. The large-scale application of whole genome sequencing (WGS) in the last 10 years has revealed the phylogenetic associations of the bacterium and its antimicrobial resistance (AMR) genes. Local and global transmission reconstructed by WGS have shown that different clones have emerged following multiple independent events worldwide, and have elucidated the role of this zoonotic pathogen in the spread of AMR. This article discusses our current knowledge of the global ecology, epidemiology, transmission, bacterial adaptation, and evolution of this emerging Salmonella serotype.

Leisure walking has been an important topic in space-time behavior and public health research. However, prior studies pay little attention to the integration and the characterization of diverse and multilevel demands of leisure walking. This study constructs a theoretical framework of leisure walking behavior demands from three different dimensions and levels of activity participation, space-time opportunity, and health benefit. On this basis, through a face-to-face survey in Nanjing, China (N = 1168, 2017–2018 data), this study quantitatively analyzes the characteristics of leisure walking demands, as well as the impact of the built environment and individual factors on it. The results show that residents have a high demand for participation and health benefits of leisure walking. The residential neighborhood provides more space opportunities for leisure walking, but there is a certain constraint on the choice of walking time. Residential neighborhood with medium or large parks is more likely to satisfy residents’ demands for engaging in leisure walking and obtaining high health benefits, while neighborhood with a high density of walking paths tends to limit the satisfaction of demands for space opportunity and health benefit. For residents aged 36 and above, married, or retired, their diverse demands for leisure walking are more likely to be fulfilled, while those with high education, medium-high individual income, general and above health status, or children (

Analyzing patterns of urban development should consider the network structure among cities as well as the formation of the function and role of each city in the network. The flow analysis of various factors between cities is based on urban network and space of flow theories. This study used Hebei Province of China as the case. The comprehensive status of each city in the regional urban network was measured by simulating the economic, information, traffic, and financial flow among cities. Results indicate that the development pattern can be divided into three levels with a multi-core and multi-node network structure. In addition, the flow analysis method can predict 67% of urban developmental level. Furthermore, some policy recommendations are put forward to facilitate regional integrated development in Hebei province.

Most outbreaks of Shiga toxin-producing

Background The interaction between different drug-resistant mutations is important to the development of drug resistance and its evolution. In this study, we aimed to reveal the potential relationships between mutations conferring resistance to two important antituberculosis drugs streptomycin (STR) and fluoroquinolones (FLQ). Materials and methods We used an in vitro competitive fitness assay to reveal the interactions between different mutations of rpsL and gyrA in drug-resistant Mycobacterium smegmatis, followed by the analysis of the frequency of rpsL and gyrA mutation combinations in 213 STR-FLQ dual-resistant clinical Mycobacterium tuberculosis isolates from Sichuan region, which was also investigated by the whole genome data from 3,056 global clinical M. tuberculosis isolates. Results The strains with K43R and K88R mutation in rpsL showed no difference in relative fitness compared with their susceptible ancestor, while K43N, K43M, K43T, and K88E exhibited a significantly lower relative fitness (P

A total of 122 Lactobacillus strains were isolated from household-prepared or commercial yogurts and pickles in Sichuan, among which 15 representative strains, along with another 37 strains isolated from human guts, were analyzed for their antimicrobial resistance (AMR) to 17 clinically significant antimicrobials applied in China by agar dilution method. The correlation of AMRs in Lactobacillus plantarum from fermented foods and human gut was examined. The AMRs varied with Lactobacillus species. For L . plantarum , the distributions of minimum inhibitory concentration to 12 antimicrobials were correlated between food and gut source ( P P > 0.05) except to norfloxacin, where the AMR was more severe in gut than in foods ( P plantarum , the severity of resistance to most antimicrobials in lactobacilli from fermented foods and human gut gradually converged, with gut ones taking the leading role. Accordingly, AMR in human gut lactobacilli was more likely the consequence of clinical medication instead of acquired from fermented foods. Lactobacillus strains widely utilized in fermented foods would unlikely aggravate their AMR in human guts.

In addition to safety and risk issues, urban resilience research should focus more comprehensive and universal contradictions. Considering the main contradictions of Chinese urban development, and the connotation of urban resilience, a theoretical framework is constructed based on the contradiction between supply and demand of the daily activity-environment system. Furthermore, an assessment index system of urban resilience is also developed that considers both volume and quality of demand and supply and has a grade standard. Finally, utilizing multi-source geographic big data, Nanjing is taken as a case study, the spatial characteristics and optimization path of urban resilience are identified. The main conclusions are as follows: (1) The activity-environment system resilience presents a "center-periphery" sprawling spatial structure, and it is mainly at the level of "reluctant resilience" and "almost lack of resilience". (2) The evolution of the activity-environment system resilience is still absolutely volume driven, and the positive drive of relative quality is limited or even reversed. In addition, all the bilateral local spatial autocorrelations are generally represented as "center-periphery" separated spatial structures, but it is not always consistent with the overall trend. (3) For the governance of urban resilience, it is necessary to focus on common improvement and matching of absolute volume and relative quality in contents, orderly flow, accumulation and dispersion of supply and demand in ideas, and the strong support of new ideas and technologies in methods.

With their distinctive sensory characterizations and unique processing technologies, Chinese ethnic meat products possess great potential for development and continuity in modern China's meat industry. Due to the greater demand for meat products and higher quality and safety concerns in economically fast growing China, the development and continuity of ethnic meat products face its own unique challenges. In this review, the classification of typical ethnic products and their characteristics, and the research progress on their quality and processing technologies are discussed. The application of innovative and green technologies to improve the safety and quality of ethnic meat products for greater industrialization and sustainable development is highlighted. Furthermore, the strategy for promoting the production of Chinese ethnic meat products during the next five years is presented.

The prevalence of Staphylococcus aureus in 2160 bulk ready-to-eat foods from the Sichuan province of China during 2013&ndash, 2016 was investigated. The antibiotic resistance and the associated genes, as well as biofilm formation capacity of the S. aureus isolates were measured. Furthermore, the relationship between the antibiotic resistance and the resistant genes was discussed. It was found that 54 S. aureus isolates were recovered, and their prevalence in meat products, dairy, fruit and vegetables, and desserts were 31 (2.6%), six (3.0%), nine (2.2%) and eight (2.3%), respectively. Most strains (52/54) were resistant to at least one of the antibiotics, and 21 isolates were identified as multidrug-resistant (MDR) S. aureus. Three isolates were found to be methicillin-resistant S. aureus. Penicillin, erythromycin, clindamycin, tetracycline and inducible clindamycin resistance were determined as the predominant antibiotics, and the isolates with the phenotypic resistance on these five antibiotics were all determined positive for the resistant gene associated. In total, 33 of 54 S. aureus isolates showed biofilm formation capacity, including two strong biofilm producers, one moderate and 30 weak ones. Two S. aureus isolates with strong biofilm formation abilities showed multi-drug resistance, and one moderate biofilm producer was resistant to two categories of antibiotics.

The plasmid-mediated high-level tigecycline resistance gene, tet(X4), was detected in seven Escherichia coli isolates from pork in two Chinese provinces. Two isolates belonged to the epidemic spreading sequence type ST101. Tet(X4) was adjacent to ISVsa3 and concurrent with floR in all seven isolates. In addition to IncFIB, the replicon IncFII was found to be linked to tet(X4). This report follows a recent detection of tet(X3)/(X4) in E. coli from animals and humans in China.

The plasmid-mediated high-level tigecycline resistance gene, tet(X4), was detected in seven Escherichia coli isolates from pork in two Chinese provinces. Two isolates belonged to the epidemic spreading sequence type ST101. Tet(X4) was adjacent to ISVsa3 and concurrent with floR in all seven isolates. In addition to IncFIB, the replicon IncFII was found to be linked to tet(X4). This report follows a recent detection of tet(X3)/(X4) in E. coli from animals and humans in China.

To investigate the characteristics of tet(X4)-carrying E. coli from retail raw meat, three hundred and eleven retail raw meat samples including chicken, pork, duck, and beef were collected for screening for tigecycline resistant isolates in Sichuan Province, China. We detected 25 (8.0%, 95%CI: 5.3%–11.6%) tet(X4) positive E. coli isolates from 311 retail meat with the highest prevalence (13.4%, 95%CI: 7.3%–21.8%) observed in pork. All the tet(X)-carrying isolates were analyzed by antimicrobial susceptibility testing, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE), conjugation experiments, and whole genome sequencing (WGS) to study the phylogenetic relationship and genomic characteristics. Conjugation and S1-PFGE profiling showed 6 isolates (24.0%) successfully transferred the resistant phenotype with frequencies from 3.63 × 10−5 to 7.68 × 10−2. Simultaneously, tet(X4), floR, and the characteristic structure of adjacent abh gene and cassette flanked by ISCR2 were identified in all 25 isolates, and a structure of abh-tet(X4)-ISCR2-virD2-floR was aligned as an important genetic pattern around tet(X4). Two dominant sequence types (STs) ST1638 (n = 4) and ST48 (n = 4) were identified by in silico MLST. Single nucleotide polymorphisms analysis revealed two potential clone-like transmission clusters which showed high concordance with the local spatio-temporal epidemiology, suggesting that clonal transmission events were very likely. The presence of tet(X4) in multiple different clone complexes (CCs) and the identification of two clone-like transmission indicates its potentially extensive and successful spread among different food-producing animals.

Improving natural disaster resilience is one of the important methods for coping with climate change and natural disasters, and quantitative evaluation of natural disaster resilience is the primary problem to be solved urgently. In this paper, an index system for evaluating regional flood disaster resilience is constructed based on a review of the literature regarding natural disaster resilience and with full consideration of the five dimensions (i.e., nature, society, economy, technology and management) which have a great influence on flood disaster resilience. Subsequently, the overall level and five dimensions of flood disaster resilience in the Chaohu Lake Basin can be evaluated quantitatively by adopting analytic network process to dynamically analyze the influencing relationships of factors. The results obtained in this research indicate that: (1) overall, the majority of the Chaohu Lake Basin exhibits intermediate to high flood disaster resilience, but there are distinct variations within the basin. The resilience is clearly influenced by the natural dimension indexes, the highest resilience levels are mainly located in the hilly, mountainous regions, and the lowest resilience levels mainly occur in the south–southeast plain of the Chaohu Lake Basin and the river estuary of the Chaohu Lake. Considering the administrative regions, the regions with the greatest areas of intermediate and high resilience are Hefei Municipal District, Chaohu City, Feidong County, Feixi County, Lujiang County, Hanshan County, Shucheng County, most parts of He County, Wuwei County and Jiujiang District of Wuhu City. (2) Preliminary validation indicates that evaluation results regarding flood disaster resilience in the Chaohu Lake Basin are consistent with the actual conditions. Therefore, the evaluation results and method can provide a valuable approach to the rapid diagnosis of weak links in the construction of flood disaster resilience infrastructure and will ultimately improve the level of flood disaster resilience in the Chaohu Lake Basin.

Mutations in rpsL, rrs, and gidB are well linked to streptomycin (STR) resistance, some of which are suggested to be potentially associated with Mycobacterium tuberculosis genotypic lineages in certain geographic regions. In this study, we aimed to investigate the mutation characteristics of streptomycin resistance and the relationship between the polymorphism of drug-resistant genes and the lineage of M. tuberculosis isolates in Sichuan, China. A total of 227 M. tuberculosis clinical isolates, including 180 STR-resistant and 47 pan-susceptible isolates, were analyzed for presence of mutations in the rpsL, rrs and gidB loci. Mutation K43R in rpsL was strongly associated with high-level streptomycin resistance (P < 0.01), while mutations in rrs and gidB potentially contributed to low-level resistance (P < 0.05). No general association was exhibited between STR resistance and Beijing genotype, however, in STR-resistant strains, Beijing genotype was significantly correlated with high-level STR resistance, as well as the rpsL mutation K43R (P < 0.01), indicating that Beijing genotype has an evolutionary advantage under streptomycin pressure. Notably, in all isolates of Beijing genotype, a dual mutation E92D (a276c) and A205A (a615g) in gidB was detected, suggesting a highly significant association between this dual mutation and Beijing genotype.

In the transitional period of China's urbanization, commuting problems and demands are diversified and multi-level, so commuting research topics, viewpoints, and analysis paths should be organically combined to dynamically adapt to the complex commuting contradictions. Based on this, this paper introduces the resilience theory to improve the research paradigm of commuting behavior. Taking Nanjing, China as a case study, with the help of the survey data of commuting behavior of typical communities, this paper provides an empirical analysis of the characteristics and influencing factors of urban residents&rsquo, commuting behavior from the perspective of resilience theory. The results show that: (1) in the face of commuting pressure, to a large extent, most commuters can still obtain commuting adaptability and a medium level or higher of commuting resilience, and (2) personal attributes, living and employment environment, and commuting environment all have significant heterogeneity effects on commuting pressure, commuting adaptability, and commuting resilience. From the perspective of resilience theory, the means of regulating commuting conflicts are flexible, which can not only directly reduce commuting pressure or optimize commuting adaptability, but also improve commuting resilience according to the specific commuting scenarios constructed by commuting pressure and adaptability. On the whole, the principles of comprehensive improvement, on-demand supply, and dynamic adjustment should be followed.

Background The interaction between different drug-resistant mutations is important to the development of drug resistance and its evolution. In this study, we aimed to reveal the potential relationships between mutations conferring resistance to two important antituberculosis drugs streptomycin (STR) and fluoroquinolones (FLQ). Materials and methods We used an in vitro competitive fitness assay to reveal the interactions between different mutations of rpsL and gyrA in drug-resistant Mycobacterium smegmatis, followed by the analysis of the frequency of rpsL and gyrA mutation combinations in 213 STR–FLQ dual-resistant clinical Mycobacterium tuberculosis isolates from Sichuan region, which was also investigated by the whole genome data from 3,056 global clinical M. tuberculosis isolates. Results The strains with K43R and K88R mutation in rpsL showed no difference in relative fitness compared with their susceptible ancestor, while K43N, K43M, K43T, and K88E exhibited a significantly lower relative fitness (P

Tuber pseudoexcavatum, Tuber sinoaestivum, and Tuber indicum are the 3 most important truffles growing in southeast China; however, their cultivation is still inefficient owing to the lack of understanding regarding the composition and function of the bacterial and fungal communities from the soils around the fruit bodies and the ectomycorrhiza of these truffles. The aim of this study was to disclose the microbial communities in truffle-producing soils in Huidong County, Sichuan, China, by using barcoded pyrosequencing. Approximately 350 000 quality-controlled sequences were obtained and grouped into 14 025 bacterial operational taxonomic units (OTUs) and 4385 fungal OTUs, which included 29 bacterial and 7 fungal phyla, respectively. The bacterial genus Acidobacterium and fungal genera Modicella, Pseudogymnoascus, and Mortierella were significantly more abundant in the control soils than in the truffle-producing soils (P < 0.05), while the bacterial genus Sphingomonas (Alphaproteobacteria) and arbuscular mycorrhizal fungal genus Glomus were significantly enriched in truffle-producing soil than in the control (P < 0.05), indicating their different roles within truffle grounds. Notably, some nonfungal organisms detected by 18S rDNA pyrosequencing were of high abundance, among which Cercozoa and Ochrophyta were significantly (P < 0.05) more abundant in truffle soils than in control soils, indicating their interactions with truffles.

The study of urban life resilience from the perspective of supply and demand and supported by spatial big data is an innovative attempt to investigate traditional related research topics, ideas and methods. On the basis of interpreting the connotation of resilience behind the main contradictions and urban transformation in China at present and introducing the perspective of supply and demand to shape the analysis framework of urban life resilience, this study takes Nanjing as a typical case to study the spatial characteristics of urban life resilience and proposes pertinent adjustment strategies with support from spatial big data. Results show the following. (1) Spatial differentiation among urban livelihood, activity and comprehensive life resilience is significant and presents a ‘centre-periphery’ spatial structure with different gradients that show increasing and decreasing trends. (2) Urban livelihood and activity resilience mainly show low-high spatial negative autocorrelation characteristics. Residents in central urban areas are more likely than others to pursue activity resilience, due to agglomeration, whereas residents in towns outside central urban areas are not greatly affected by urban life resilience due to the low level of population agglomeration. (3) The agglomeration characteristics of coupling coordination level are not significant as the distribution of low-level coupling coordination areas is mixed, with only the coupling coordination level of peripheral towns being slightly high. The strategy of improving urban life resilience should focus on priority, pertinence, cross-regional dynamic guidance, coordinated governance of related urban problems and the impact of new science and technology and urban development concepts.

International audience; China ranks second next to India among 22 high-burden countries despite decades' effort on tuberculosis (TB) control. The Sichuan province today contains the second-largest number of TB cases among Chinese provinces, where the prevalence of drug-resistant TB, especially MDR-TB, is much higher than the average level in eastern China. In this study, the population structure and the transmission characteristics of drug-resistant TB in Sichuan province were studied by spoligotyping and 24-locus Mycobacterial interspersed repetitive units-variable number tandem DNA repeats (MIRU-VNTR), applied to a total of 306 clinical isolates. Spoligotyping-based analysis showed that Beijing family represented 69.28% of all isolates and constituted the largest group (66.24%) of MDR-TB in Sichuan. The remaining isolates, accounting for 33.76% of MDR isolates, belonged to the ill-defined T family, Manu2, H3, LAM9, and other minor unassigned clades. The discriminatory power evaluated for spoligotyping was poor (HGI=0.595), but high for 24-locus MIRU-VNTRs (HGI=0.999). The number of the most discriminatory loci (h>0.6) was 12, including locus 424, 802, 960, 1644, 1955, 2163b, 2996, 3007, 3192, 3690, 4348 and 4052. It was concluded that 24-locus MIRU-VNTRs could be a more discriminatory tool for differentiating clinical isolates from Sichuan region. The small clustering size obtained from the current population structure analysis suggested that the high prevalence of drug-resistant TB in this region might be attributed partially to the acquired resistance due to inappropriate drug use rather than active transmission of drug-resistant TB (primary resistance).

Mixed infections and heteroresistance of Mycobacterium tuberculosis contribute to the difficulty of diagnosis, treatment, and control of tuberculosis. However, there is still no proper solution for these issues. This study aimed to investigate the potential relationship between mixed infections and heteroresistance and to determine the high-risk groups related to these factors. A total of 499 resistant and susceptible isolates were subjected to spoligotyping and 24-locus variable-number tandem repeat methods to analyze their genotypic lineages and the occurrence of mixed infections. Two hundred ninety-two randomly selected isolates were sequenced on their rpoB gene to examine mutations and heteroresistance. The results showed that 12 patients had mixed infections, and the corresponding isolates belonged to Manu2 ( n = 8), Beijing ( n = 2), T ( n = 1), and unknown ( n = 1) lineages. Manu2 was found to be significantly associated with mixed infections (odds ratio, 47.72; confidence interval, 9.68 to 235.23; P < 0.01). Four isolates (1.37%) were confirmed to be heteroresistant, which was caused by mixed infections in three (75%) isolates; these belonged to Manu2. Additionally, 3.8% of the rifampin-resistant isolates showing no mutation in the rpoB gene were significantly associated with mixed infections (χ 2 , 56.78; P < 0.01). This study revealed for the first time that Manu2 was the predominant group in the cases of mixed infections, and this might be the main reason for heteroresistance and a possible mechanism for isolates without any mutation in the rpoB gene to become rifampin resistant. Further studies should focus on this lineage to clarify its relevance to mixed infections.

Using analytic hierarchy process and entropy method to determine the weight of index, fuzzy comprehensive evaluation model of risk assessment was constructed in this paper. Flood risk index and risk rating of area along the Yangtze River in Anhui province were drawn by using GIS spatial analysis technology. From disaster causing factors, inducing environment and bearing body, average maximum 3 day rainfall, rainstorm number, vegetation coverage, river network density, standard deviation of the elevation, population density, proportion of rural population, density of GDP, per capita net income of farmers, and cultivated land area ratio were selected as evaluation indicators. The results show that flood risk rating and risk index of area along the Yangtze River in Anhui province has a spatial distribution characteristics from south to north gradually reduced.

Genotypes ofMycobacterium tuberculosiscomplex (MTBC) vary with the geographic origin of the patients and can affect tuberculosis (TB) transmission. This study was aimed to further differentiate spoligotype-defined clusters of drug-resistant MTBC clinical isolates split in Beijing (n=190) versus non-Beijing isolates (n=84) from Sichuan region, the second high-burden province in China, by IS6110-restriction fragment length polymorphism (RFLP) and 24-locus MIRU-VNTRs. Among 274 spoligotyped isolates, the clustering ratio of Beijing family was 5.3% by 24-locus MIRU-VNTRs versus 2.1% by IS6110-RFLP, while none of the non-Beijing isolates were clustered by 24-locus MIRU-VNTRs versus 9.5% by IS6110-RFLP. Hence, neither the 24-locus MIRU-VNTR was sufficient enough to fully discriminate the Beijing family, nor the IS6110-RFLP for the non-Beijing isolates. A region adjusted scheme combining 12 highly discriminatory VNTR loci with IS6110-RFLP was a better alternative for typing Beijing strains in Sichuan than 24-locus MIRU-VNTRs alone. IS6110-RFLP was for the first time introduced to systematically genotype MTBC in Sichuan and we conclude that the region-adjusted scheme of 12 highly discriminative VNTRs might be a suitable alternative to 24-locus MIRU-VNTR scheme for non-Beijing strains, while the clusters of the Beijing isolates should be further subtyped using IS6110-RFLP for optimal discrimination.

Summary Rifampin is a key component of standard short-course first-line therapy against Mycobacterium tuberculosis , and rifampin resistance of this pathogen has been reported to be related to rpoB gene mutations. The objective of this study was to characterize the rpoB gene mutations in rifampin-resistant M. tuberculosis isolates circulated in Sichuan. Sequencing of rpoB gene and spoligotyping were performed on 268 randomly selected isolates from January 2008 to May 2010. The results indicated that 207 (97.2%) rifampin-resistant isolates had mutations at 26 codons in the amplified region with 50 different genotypes, while 1 (1.8%) of 55 susceptible isolates had a nonsense mutation. The most common mutations were in codon 531 (55.9%), 526 (16.4%), 516 (10.3%) and 511 (8.9%). Among the 213 resistant isolates, 150 (70.4%) belonged to the Beijing family and mutation at codon 531 (TCG→TTG) was associated with Beijing genotype ( χ 2 , 9.8305; p , 0.0017). It is demonstrated that the frequency of 511 (CTG→CCG) mutations in Sichuan was higher than in other provinces of China, as well as other geographic regions worldwide. It is suggested that only a small portion (2.7%) of rifampin-resistant Beijing genotype isolates in Sichuan be spread by clonal expansion during the study period.