Molecular characterization of Staphylococcus aureus ST6 and ST7 isolates from food-borne illness outbreaks / 中华预防医学杂志

Objective: To analyze the Staphylococcal enterotoxins, Staphylococcal enterotoxin genes, drug resistance and molecular typing of 41 Staphylococcus aureus isolates from 2 food-borne illness outbreaks on 21 August and 27 September 2020 in Guangzhou. Methods: A total of 41 Staphylococcus aureus isolates from 2 outbreaks were analyzed by multilocus sequence typing (MLST) and spa typing. The Staphylococcal enterotoxins typing and the Staphylococcal enterotoxin genes of the isolates were analyzed by ELISA and PCR, respectively. The antimicrobial susceptibility of the isolates was performed by disc diffusion. 21 Staphylococcus aureus isolates were characterized using whole genome sequencing (WGS). Based on the whole genome single nucleotide polymorphism (SNP), the phylogenetic tree was constructed by Snippy. Results: 41 Staphylococcus aureus isolates were divided into 2 types by MLST and spa typing: ST6-t701 and ST7-t091. 2 ST7-t091 isolates were identified as methicillin-resistant Staphylococcus aureus (MRSA). 25 ST7-t091 isolates and 14 ST6-t701 isolates were methicillin-sensitive Staphylococcus aureus (MSSA), and were resistant to 7 and 6 antibiotics, respectively. All isolates were positive for sea by PCR. WGS revealed all 21 isolates carried scn, sak, sea, hla, hld, hlgA, hlgB, hlgC, lukD virulence genes. The results showed the isolates contained an immune evasion cluster type D which located in bacteriophage ϕSa3. The SNP phylogenetic tree showed 2 MRSA ST7-t091 were constituted a separate clade from the 12 MSSA ST7-t091 isolates and 7 ST6-t701 isolates showed high similarity to each other. Conclusion: Base on the results of phylogenetic analysis, the 2 food-borne illness outbreaks occurred on 21 August and 27 September 2020 are caused by the combination of the MRSA ST7-t091 strain and the MSSA ST7-t091 strain, and the MSSA ST6-t701 strain, respectively. All isolates have high level of antibiotic resistance and carry high virulent genes.

Molecular subtyping of Staphylococcus aureus isolated from a severe food-poisoning / 中华预防医学杂志

<p><b>OBJECTIVE</b>To study the molecular types of Staphylococcus aureus isolated from a severe food-poisoning and to trace the possible strains.</p><p><b>METHODS</b>Real-time PCR was applied to detect nuc gene as a specific marker for S. aureus, mecA gene encoding methicillin resistance and 5 other genes encoding staphylococcal enterotoxins (sea, seb, see, sed, see). Isolates were also performed with 16S rRNA oligonucleotide sequence analyzing by DNAStar MegAlign 5.0 software and pulse-field gel electrophoresis (PFGE) by BioNumerics Version 4.0 software.</p><p><b>RESULTS</b>The nuc gene was detected from the 10 isolated strains, sea and seb genes were detected from 7 strains. There were 4 16 S rRNA types and 5 PFGE types found from all the strains.</p><p><b>CONCLUSIONS</b>Three relative S. aureus strains were involved in the severe food-poisoning at least. Molecular subtyping might give a molecular epidemiological evidence and support the source tracing of an outbreak.</p>

Application of pulse-field gel electrophoresis analysis in source-tracking of food-borne disease caused by Vibrio parahaemolyticus / 中华预防医学杂志

<p><b>OBJECTIVE</b>To apply pulse-field gel electrophoresis analysis(PFGE) in analysing a case of food poisoning caused by Vibrio parahaemolyticus.</p><p><b>METHODS</b>PFGE using restriction enzyme Not I was employed in molecular subtyping of thirty strains of V. parahaemolyticus isolated from a case of food poisoning in Guangzhou city and PFGE patterns were analyzed by using BioNumerics Version 4.0 software to perform cluster analysis. Pattern profiles were compared by using the Dice coefficient and unweighted pair group method with arithmetic averages (UPGMA).</p><p><b>RESULTS</b>Thirty strains were of the same type of pulsotype.</p><p><b>CONCLUSIONS</b>Molecular subtyping by PFGE might disclose the epidemiological relationships of the strains from humans, food and the environment, giving a strong molecular epidemiological evidence and a support for the source-tracking of outbreak events.</p>

Application of pulse-field gel electrophoresis analysis in the source-tracking of cholera epidemics / 中华流行病学杂志

<p><b>OBJECTIVE</b>To apply pulse-field gel electrophoresis analysis(PFGE) in the analysis of cholera outbreak events and to determine the molecular epidemiological characteristics of Vibrio cholerae ( V. cholerae) isolates.</p><p><b>METHODS</b>PFGE using restriction enzyme Not I was employed in the molecular subtyping of forty-one strains of V. cholerae isolated in cholera outbreak events from 2003 to 2005 in Guangzhou area and PFGE patterns were analyzed by BioNumerics Version 4.0 software to perform cluster analysis. Pattern profiles were compared by utilizing of Dice coefficient and UPGMA(unweighted pair group method with arithmetic averages). Comparison of PFGE typing results was performed with phage-biological typing and pathogenicity-associated genes typing.</p><p><b>RESULTS</b>In cholera outbreak events, PFGE could discriminate epidemiologically related and unrelated strains, having more discriminatory power than phage-biological typing and pathogenicity-associated genes-typing.</p><p><b>CONCLUSIONS</b>Molecular sub-typing by PFGE could disclose the epidemiological relationships of strains from humans and the environment, providing molecular epidemiological evidence and support for the source-tracking of cholera outbreak events.</p>

Analysis of characteristics of major pathogenicity-related genes of Vibrio cholerae isolated in Guangzhou area from 2001 to 2005 / 中华预防医学杂志

<p><b>OBJECTIVE</b>To apply multiplex polymerase chain reaction (MPCR) assay and sequencing in study of the carrying status of four pathogenicity-related genes of Vibrio cholerae (V.cholerae) and the variation of ctxA.</p><p><b>METHODS</b>Primers targeting cholera toxin sub-unit A gene (ctxA), toxin-coregulated pilus gene (tcpA), accessory cholera enterotoxin gene (ace), zonula occludens toxin gene (zot) were designed and the MPCR method was applied to detect the pathogenicity-related genes of 276 strains of V.cholerae isolates. The amplified fragments of ctxA gene were sequenced and the genetic homology of the amplified fragments of ctxA was analyzed.</p><p><b>RESULTS</b>Of the 276 strains of V.cholerae, 93.9% strains from human sources belong to the pathogenicity-related genes type A (ctxA(+)tcpA(+)ace(+)zot(+) type) and 6.1% belong to pathogenicity-related genes type C (ctxA(-)tcpA(-)ace(-)zot(-) type). Type A strains from clinical sources were isolated from patients with mild to severe symptom and carriers, among which 68.5% were isolated from patients with mild symptom and 21.9% from carriers. All 63.6% of type C strains from clinical sources were isolated from patients with mild symptom and 36.4% from carriers. The proportion of type C strains that caused mild symptom was higher than that of type A strains. Of the 78 strains isolated from the environment, 9.0% strains belong to pathogenicity-related type A and 35.9% belong to the pathogenicity-related genes type B (ctxA(-)tcpA(-)ace(+)zot(+) type), while 55.1% belong to pathogenicity-related genes type C. The sequencing results showed little genetic variation among the amplified fragments for ctxA.</p><p><b>CONCLUSION</b>MPCR disclosed the polymorphic status of pathogenicity-related gene patterns in V.cholerae isolates of Guangzhou, providing effective means for further study on evolution of pathogenicity-related genes among V.cholerae isolates from human and environmental sources. This study also offers significant guidance for effective prevention, control and warning against cholera epidemic in local area.</p>