title: Phenotypic and genetic changes in the life cycle of small colony variants of Salmonella enterica serotype Typhimurium induced by streptomycin.
abstract: BACKGROUND
  Small colony variants (SCVs), constituting a slow-growing subpopulation of bacteria that facilitates persistence in lethal environmental conditions, are able to revert to the phenotype of rapid growth for further proliferation and transmission. Salmonella enterica serotype Typhimurium is one of the most important foodborne pathogens. This study investigated the genetic mechanisms how SCVs induced by streptomycin reverted to the fast-growing phenotype and the phenotypic changes of SCVs among their complete life cycle in S. Typhimurium.
  
  
  METHODS
  Salmonella Typhimurium SCVs were obtained by streptomycin treatment and their revertants were collected in the absence of antibiotics. The fitness, antimicrobial susceptibility, biofilm formation, and the biofilm-related genes expression were analyzed in comparison to their wild type strain, and the whole genome sequencing was performed to identify the genetic changes in the life cycle of S. Typhimurium SCVs.
  
  
  RESULTS
  Small colony variants were characterized by an increased antimicrobial resistance to streptomycin (64-fold), imipenem (twofold), and gentamicin (fourfold). A significant increase in biofilm production with higher expression of csgB was observed in SCVs (P < 0.01). The genetic alterations of all SCVs occurred in ubiE gene (coenzyme Q8 and menaquinone synthesis) with frameshift mutations. However, all fast-growing revertants again lost the trait of increased biofilm production (P > 0.05), in which two modes of the genetic changes for reversing to the rapidly growing form were observed: four revertants harbored a secondary mutation in ubiE, which reinstated most of the amino acid sequence of the ubiE, and other four revertants harbored a mutation in prfB.
  
  
  CONCLUSIONS
  Salmonella Typhimurium could switch to the phenotype of SCVs under the treatment of streptomycin by a mutation in ubiE, partially combined with increased production of biofilm, and these SCVs could escape from growth restriction by a compensatory mutation in prfB or a new mutation in ubiE. These findings may contribute to establishing phenotype-directed treatments against SCVs of S. Typhimurium.
authors.affiliation: Key Laboratory of Bio-resources and Eco-environment of the Ministry of Education, College of Life Sciences, Sichuan University, 29# Wangjiang Rd., Chengdu, Sichuan, 610064, P. R. China.
authors.forename: Wanli
authors.initials: W
authors.lastname: Li
authors.affiliation: Shenzhen Major Infectious Disease Control Key Laboratory, Shenzhen Centre for Disease Control and Prevention, Shenzhen, Guangdong, 518055, P. R. China.
authors.forename: Yinghui
authors.initials: Y
authors.lastname: Li
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, 100071, P. R. China.
authors.forename: Yarong
authors.initials: Y
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, 100071, P. R. China.
authors.forename: Yujun
authors.initials: Y
authors.lastname: Cui
authors.affiliation: Key Laboratory of Bio-resources and Eco-environment of the Ministry of Education, College of Life Sciences, Sichuan University, 29# Wangjiang Rd., Chengdu, Sichuan, 610064, P. R. China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Shenzhen Major Infectious Disease Control Key Laboratory, Shenzhen Centre for Disease Control and Prevention, Shenzhen, Guangdong, 518055, P. R. China.
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Shi
authors.affiliation: Shenzhen Major Infectious Disease Control Key Laboratory, Shenzhen Centre for Disease Control and Prevention, Shenzhen, Guangdong, 518055, P. R. China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Shenzhen Major Infectious Disease Control Key Laboratory, Shenzhen Centre for Disease Control and Prevention, Shenzhen, Guangdong, 518055, P. R. China.
authors.forename: Qiongcheng
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Key Laboratory of Bio-resources and Eco-environment of the Ministry of Education, College of Life Sciences, Sichuan University, 29# Wangjiang Rd., Chengdu, Sichuan, 610064, P. R. China. qunsun@scu.edu.cn.
authors.forename: Qun
authors.initials: Q
authors.lastname: Sun
authors.affiliation: Shenzhen Major Infectious Disease Control Key Laboratory, Shenzhen Centre for Disease Control and Prevention, Shenzhen, Guangdong, 518055, P. R. China. huqinghua03@163.com.
authors.forename: Qinghua
authors.initials: Q
authors.lastname: Hu
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D016368:Frameshift Mutation; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D016680:Genome, Bacterial; D005839:Gentamicins / Q000494:pharmacology; D059014:High-Throughput Nucleotide Sequencing; D015378:Imipenem / Q000494:pharmacology; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D010454:Peptide Termination Factors / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D013307:Streptomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D005839:Gentamicins; D010454:Peptide Termination Factors; D015378:Imipenem; D008780:Methyltransferases; D013307:Streptomycin
keywords: Biofilm; Salmonella; Small colony variants; prfB; ubiE