Objective:To understand the serotype distribution, drug resistance and molecular characterization of invasive non-typhoid Salmonella (iNTS) in Guangdong Province from 2018 to 2022 and provide scientific evidence for the prevention and treatment of blood flow infection caused by Salmonella. Methods:Serological identification, antimicrobial susceptibility testing, multilocus sequence typing (MLST), and whole genome sequencing were performed on Salmonella isolated from blood and stool samples in Guangdong from 2018 to 2022. Simultaneously, annotated the sequencing results for drug resistance genes and virulence factors by a microbial gene annotation system. Results:The 136 iNTS strains were divided into 25 serotypes, and Salmonella enteritidis accounted for 38.24% (52/136). The OR of other iNTS serotypes were calculated with Salmonella typhimurium as the control. The OR values of Oreninburg, Rysson, and Pomona serotypes were the highest, which were 423.50, 352.92, and 211.75, respectively. The drug resistance rate of iNTS was 0.74%-66.91%, which was lower than that of non-iNTS (3.90%-77.21%). The main iNTS of drug resistance were ampicillin and tetracycline, with resistance rates of 66.91% (91/136) and 50.00% (68/136), respectively, while the resistance rates to ciprofloxacin (5.88%,8/136), ceftazidime (5.88%,8/136), gentamicin (5.13%,7/136) and cefoxitin (0.74%, 1/136) were relatively low. iNTS carried a variety of drug-resistance genes and virulence factors, but no standard virulence factor distribution has been found. MLST cluster analysis showed that iNTS was divided into 26 sequence types, and ST11 accounted for 38.24% (52/136). Conclusions:The iNTS strains in Guangdong were dominated by Salmonella enteritidis, of which three serotypes, Oreninburg, Rison, and Pomona, may be associated with a higher risk of invasive infection during 2018 to 2022 . iNTS was sensitive to clinical first-line therapeutic drugs (cephalosporins and fluoroquinolones), with highly diverse sequences and clear phylogenetic branches. ST11 was the local dominant clone group.

Objective:To study the epidemiological and genetic characteristics of coxsackievirus B3 (CVB3) circulating in Guangdong Province from 2008 to 2021.Methods:This study collected the specimens of hand, foot, and mouth disease (HFMD) cases from 2008 to 2021 that were positive for other enteroviruses except for enterovirus 71 (EV71), coxsackievirus A16 (CVA16), and CVA6, as well as the specimens of herpangina and neonatal infection cases from 2020 to 2021. Enteroviruses in these specimens were detected and their types were identified. CVB3 strains were isolated and the entire VP1 sequences of CVB3 strains were amplified and sequenced. The genetic features of CVB3 strains were analyzed using DNAStar 7.1 and MEGA 6.06 software packages.Results:Among 3 484 HFMD cases positive for other enteroviruses from 2008 to 2021, CVB3-positive cases accounted for 1.6% (57/3 484); among 560 cases of herpangina from 2020 to 2021, CVB3-positive cases accounted for 2.1% (12/560); one neonatal infection case in 2021 was positive for CVB3. CVB3-positive cases accounted for 67.1% (47/70) in 2021 and 18.6% (13/70) in 2020, while there were less than five cases in other years. Forty-eight CVB3 strains were isolated and the entire VP1 sequences of 26 CVB3 strains were obtained. Phylogenetic analysis indicated that the CVB3 strains could be divided into eight genotypes (A-H) and the strains of genotypes A, D and E were prevalent in the Chinese mainland. The 26 CVB3 strains isolated in Guangdong Province shared 80.2%-100.0% nucleotide homology, and belonged to two genotypes of D and E, with genotype D prevalent from 2008 to 2017 and genotype E prevalent from 2020 to 2021.Conclusions:CVB3 is prevalent sporadically in Guangdong Province from 2008 to 2017, but the epidemic intensity increased during 2020 and 2021. CVB3 strains of genotypes D and E are prevalent in Guangdong Province during 2008 to 2021, with genotype E being the prevalent genotype during 2020 and 2021.

Objective:To analyze the evolutionary characteristics and variation of etiological agent in an acute hemorrhagic conjunctivitis (AHC) outbreak in a city of Guangdong province in May, so as to provide scientific basis for formulating a new round of measures for prevention and control of AHC epidemic.Methods:In this study, 20 conjunctival swabs were collected from AHC patients, and enterovirus, human enterovirus 70 (HEV70) and coxsackievirus A 24 variant (CVA24v) nucleic acids were detected by real-time fluorescence quantitative PCR. In addition, the VP1 and 3Cpro regions of the CVA24v positive samples were sequenced to analyze their evolutionary relationship with the CVA24v strains circulating in China and abroad.Results:All the 20 eye swab samples were EV-positive, and CVA24v-positive, with a positive rate of 100.00%, and all were HEV70-negative.The genomes of CVA24v in VP1 and 3Cpro regions of CVA24v in 5 and 7 samples were successfully sequenced. Based on molecular characterization analysis of VP1 and 3Cpro regions, it was found that the CVA24v isolated in this outbreak had the greatest nucleotide similarity with the CVA24v strains isolated in Thailand in 2014 and French Reunion Islands in 2015. The phylogenetic analysis of 3Cpro and VP1 regions showed that the CVA24v isolated in this outbreak is clustered together with the CVA24v that was prevalent in Thailand in 2014 and the French Reunion Islands in 2015, and have high affinity. Compared with CVA24v isolated in Guangdong in 2010, Thailand in 2014, and French Reunion Islands in 2015, CVA24v isolated in this outbreak was replaced at 4 amino acid sites in 3Cpro region and 1 amino acid site in VP1 region.Conclusions:The cause of this outbreak is enterovirus CVA24v, which has the highest similarity to CVA24v isolated in Thailand in 2014 and in the French Reunion Islands in 2015. There were new amino acid mutations in both 3Cpro and VP1 regions.

Objective To investigate the infection status, serotype distribution, drug sensitivity and molecular characteristics of diarrheagenic Escherichia coli (DEC) in patients with diarrhea in Guangdong Province. Methods Fecal samples were collected, cultured and isolated by traditional methods. Suspected Escherichia coli isolates were confirmed by multiplex PCR used for detecting specific virulence genes and bio-chemical methods. Positive strains were serotyped, characterized for drug sensitivity and analyzed by pulsed-field gel electrophoresis ( PFGE). Results The total positive rate of DEC in patients with diarrhea was 6.26%. The positive rates of enteropathogenic Escherichia coli (EPEC), enterotoxigenic Escherichia coli (ETEC), enterohemorrhagic Escherichia coli (EHEC), enteroadherent Escherichia coli (EAEC) and en-teroinvasive Escherichia coli (EIEC) were 2. 47% , 1. 54% , 1. 32% , 0. 62% and 0. 09% , respectively, with infections primarily in children aged 0-<7 years. The total seropositive rate was 52. 54% , with EHEC accounting for 15. 00% . DEC showed high sensitivity to imipenem, ciprofloxacin, ceftazidime and cefo-taxime. The multidrug resistance rate of DEC was 58. 45% , with EPEC being the most serious for multidrug resistance. PFGE results showed that ETEC, EHEC, EPEC and EAEC had a high degree of polymorphism. Conclusion EPEC is the predominant type of DEC circulating in Guangdong Province. Third-generation cephalosporins are the first drugs of choice for treating infections in children. Ciprofloxacin can be used to treat adults. The problem of multiple drug resistance of DEC is severe and efforts to monitor DEC infections and drug resistance should be strengthened.

Objective To investigated the etiologic characteristics of Shigella (S.) sonnei strains causing outbreaks and sporadic cases in some areas of Guangdong province and Guangxi Zhuang Autonomous Region during 2014-2016. Methods Fourteen S. sonnei strains isolated from outbreaks and 6 S. sonnei strains from sporadic cases from Guangdong and Liuzhou of Guangxi Zhuang Autonomous Region were tested for antimicrobial resistance and analyzed by pulsed-field gel electrophoresis (PFGE). Six typical strains were selected for whole genome sequencing typing and compared with 51 strains isolated both at home and abroad from NCBI genome database. Results The antibiotic resistance test indicated the isolates had high resistance rate to ampicillin, tetracycline, gentamicin, trimethoprim/sulfamethoxazole and nalidixic acid, while sensitive to azithromycin, chloromycetin and imipenem. PFGE showed high similarity (93.2%) among the strains isolated from different areas. The whole genome sequencing analysis also revealed that all the typical strains wereclustered into a same evolution branch, close to some strains from Korea. Conclusions The S. sonnei strains isolated from some areas of Guangdong and Guangxi Zhuang Autonomous Region showed high resistance to commonly used antibiotics, but they were sensitive to azithromycin, chloramphenicol and imipenem. The isolates in this study also showed similar PFGE patterns and close phylogenic evolution.

Objective To analyze the serotype distribution and antibiotic resistance characteristics of Salmonella strains isolated in Guangdong province for better understanding the condition of Salmonella infection in patients with diarrhea.Methods Fecal samples collected from patients with diarrhea in Guangdong province were used to isolate Salmonella strains.Biochemical analysis was performed to identify these isolated strains.Serotyping and antimicrobial susceptibility testing were carried out for further analysis of the isolated Salmonella strains.Results The rate of Salmonella infection was 7.64％in 2015, and the male to female patient ratio was 1.52∶1.A total of 2 377 patients of all age groups were positive for Salmonella infection and the patients aged 0-6 years accounted for 81.74％.The isolation rate of Salmonella strains in the summer and autumn was higher than that in the winter and spring (10.73％ vs 4.24％;X2=463.77, P<0.01).The Salmonella isolation rates in different areas were as follows: 16.82％ in Zhuhai, 15.85％ in Heyuan, 11.81％ in Yangjiang, 10.68％ in Jiangmen, 8.49％ in Zhongshan, 8.07％ in Maoming, 8.05％ in Jieyang, 7.35％ in Shaoguan, 6.97％ in Foshan, 6.03％ in Dongguan, 5.48％ in Guangzhou and 0.00％ in Zhanjiang.And the differences between different regions were statistically significant (X2=367.67, P<0.01).The 2 377 isolated Salmonella strains were classified into 108 serotypes except for oneSalmonella strain that could not be classified.The top four predominant serotypes were 4,5,12:i:-, Salmonella enteritidis,Salmonella stanley and Salmonella typhimurium.Most Salmonella strains were sensitive to imipenem, azithromycin, ceftazidime, cefotaxime and trimethoprim/sulfamethoxazole, but multidrug resistance was common among those strains.Conclusion Salmonella serotypes of 4,5,12:i:-and Salmonella enteritidis are the predominant pathogens causing human Salmonella infections in Guangdong province.Ceftazidime and cefotaximeare are preferred in the treatment of Salmonella infections.Surveillance for drug resistance in Salmonella should be strengthened as multidrug resistant strains have become a serious problem in Guangdong province.

Objective To prepare simulated stool specimens for proficiency testing ( PT) by mix-ing lentils with Salmonella, Shigella and Escherichia coli strains and to establish an assessment scheme for the detection of Salmonella and Shigella in clinical samples. Methods Salmonella, Shigella and Escherich-ia coli strains were respectively spiked to lentils in Cary-Blair transport medium to create simulated stool specimens. Various ratios of Escherichia coli to Salmonella strains were spiked to lentils to prepare mixed simulated stool specimens. The accuracy and stability of prepared stool samples for PT were tested in-house. Results of sample detection were collected from participating laboratories for further external quality assess-ment. Results The Escherichia coli and Salmonella strains mixed at ratios of 100 ∶ 1 to 106 ∶ 1 could be ef-ficiently isolated from the media. Enrichment was needed in order to effectively isolate Salmonella strains from the media when the ratios of Escherichia coli to Salmonella strains were 104 ∶ 1 to 106 ∶ 1. Of the16 participating laboratories, 14 laboratories (87. 5%) received a grade of“satisfactory” and the other 2 labo-ratories (12. 5%) received a grade of “mainly satisfactory”. Conclusion The simulated stool specimens and the PT procedures designed in this study were suitable for proficiency testing program on the detection of Salmonella, Shigella and other similar microbes.

Objective To understand the effect ofserotyping on Salmonella isolates,by use of Microsphere-based Liquid Array method,among diarrhea patients,in Guangdong.Methods Salmonella isolated from humans in Guangdong province were serotyped on the Microsphere-based Liquid Array platform with SSA kit.Results A total of 4 942 Salmonella strains with 189 serotypes,were identified in Guangdong province in 2010-2014.The top 100 serotypes accounted for 98.08％ (4 847/4 942) of all the strains.98％ of the top 100 species serotypes could completely be serotyped with SSA kit.In order to detect O antigen among 198 isolates with SSA kit,181 strains were carrying the O antigen,with the coincidence rate as 100％.However,under the SSA,98.32％ (528/537) of the H antigen could be detected and were consistent with the traditional serum agglutination test.The coincidence rate of fljB gene was 93.09％ (175/188),with false negative rate and false positive rate of fljB gene as 7.35％ (9/134) and 7.41％ (4/54) respectively.The coincidence rate of sdf gene and Vi gene were 100％.11 out of the 12 Salmonella strains could not be serotyped under the traditional methods but were successfully serotyped by the molecular serotyping method.Conclusions Using the SSA kit,more than 96％ of the anthropogenic Salmonella strains could be serotyped in Guangdong province.Comparing with the traditional methods,the coincidence rate of serotyping appeared over 98％.Under the Microsphere-based Liquid Array techniques,the molecular serotyping method appeared faster and more accurate on Salmonella serotyping than those traditional methods.

Objective To investigate the serotypes, antimicrobial resistance, virulence genes and molecular characteristics of food-borne Vibrio parahaemolytieus isolated in Guangdong province in 2014.Methods Sixty V.parahaemolyticus strains were tested in this study.The serotyping and antibiotic resistance test were conducted, while the tdh and trh gens of the strains were detected with conventional PCR, and pulsed field gel electrophoresis (PFGE) and multiple locus sequence typing (MLST) were conducted too.Results The 60 strains belonged to 13 serotypes, the major serotypes included O3 : K6, O4: K8, O 1 : K36 and O4: KUT.The antibiotic resistance test indicated the isolates were highly resistant to ampicillin (100.0％), sulfonamides (43.3％) and cefalotin (28.3％).Up to 56.7％(34/60) of the strains were resistant to two or more antibiotics, and 2 strains showed resistance to three antibiotics.The virulence gene detection indicated that 63.3％ (38/60) of the strains carded tdh+trh-, while only 1 strain carried tdh+trh+.The 60 strains digested by Not I belonged to 48 different PFGE patterns and 3 clusters.The cluster B included the strains isolated from sporadic food borne cases with serotype of O3:K6 and similarity of 62.6％-100.0％.The cluster C included O4:K8 strains with the PFGE pattem similarity of 56.7％-62.5％.The MLST indicated that the 60 strains had 26 sequence types (STs).The ST-3 was predominant, including 33 strains (serotypes O3:K6 and O1 : K36).The four O4:K8 strains formed another predominant colony, which was different from ST-3.Conclusion The etiologic characteristics of V.parahaemolyticus varied, which might be one of the reasons for high incidence of food-bome V.parahaemolyticus infection in Guangdong.The molecular characteristics of O4: K8 strain were differem from the other predominant serotypes.Close attention should be paid to the possible outbreak caused by O4: K8 strain in this area.

To compare and evaluate the discriminatory ability and potential value of pulsed field gel electrophoresis (PF-GE) and multiple locus VNTRs analysis (MLVA) on the genotyping of Brucella ,a total of 60 strains of Brucella and three standards (16M ,544A ,1330S) were genotyped simultaneously by PFGE and MLVA .The result indicated that the similarity coefficient among the 63 isolates was from 72 .1-100 .0% by PFGE ,and could distinguish three species of B .melitensis ,B .su-is and B .abortus at the similarity level of 94 .4% .There were 14 clusters and 29 PFGE types identified by PFGE with discrim-inatory index (DI) of 0 .957 5 at the similarity level of 100% ;the similarity coefficient among the 63 isolates was from 16 .9-100 .0% by MLVA ,and could distinguish three species of Brucella at the similarity level of 52 .3% .There were 8 clusters and 47 MLVA types identified by MLVA with discriminatory index (DI) of 0 .985 2 at the similarity level of 100% .It's suggested that PFGE and MLVA could be used to distinguish three species of Brucella in the similarity coefficient of certain ,but could not effectively distinguish the type in the same species .Both of these two methods could be used for Brucella molecular typing , but MLVA is better than PFGE for its relatively higher discriminating ability .