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.

Phylogenetic analysis and PCR-restriction fragment length polymophism identification of Salmonella based on grOEL gene sequence / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the value of grOEL gene sequence in phylogenetic analysis and typing of Salmonella.</p><p><b>METHODS</b>The grOEL gene was amplified by PCR, sequenced and analyzed using Bioedit and DNAstar software. The Salmonella strains were identified using PCR-restriction fragment length polymophism (PCR-RFLP).</p><p><b>RESULTS</b>The conservative and variable regions of grOEL gene of Salmonella serogroup were separately distributed and most of the small mutant regions distributed intermittently among the conservative regions. The phylogenetic tree of Salmonella based on the nucleotides differed from that generated based on the amino acid sequence. O8, O9 and O10 had the closest consanguinity, and 5 patterns were identified by PCR-RFLP.</p><p><b>CONCLUSION</b>The grOEL gene can be used as a genetic marker for phylogenetic analysis of Salmonella and also as a target sequence for Salmonella typing identification.</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>