title: Proposal for a method to estimate nutrient shock effects in bacteria.
abstract: BACKGROUND
  Plating methods are still the golden standard in microbiology; however, some studies have shown that these techniques can underestimate the microbial concentrations and diversity. A nutrient shock is one of the mechanisms proposed to explain this phenomenon. In this study, a tentative method to assess nutrient shock effects was tested.
  
  
  RESULTS
  To estimate the extent of nutrient shock effects, two strains isolated from tap water (Sphingomonas capsulata and Methylobacterium sp.) and two culture collection strains (E. coli CECT 434 and Pseudomonas fluorescens ATCC 13525) were exposed both to low and high nutrient conditions for different times and then placed in low nutrient medium (R2A) and rich nutrient medium (TSA).The average improvement (A.I.) of recovery between R2A and TSA for the different times was calculated to more simply assess the difference obtained in culturability between each medium. As expected, A.I. was higher when cells were plated after the exposition to water than when they were recovered from high-nutrient medium showing the existence of a nutrient shock for the diverse bacteria used. S. capsulata was the species most affected by this phenomenon.
  
  
  CONCLUSIONS
  This work provides a method to consistently determine the extent of nutrient shock effects on different microorganisms and hence quantify the ability of each species to deal with sudden increases in substrate concentration.
authors.affiliation: LEPAE, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal. nazevedo@fe.up.pt
authors.forename: Nuno F
authors.initials: NF
authors.lastname: Azevedo
authors.forename: Sofia M
authors.initials: SM
authors.lastname: Bragança
authors.forename: Lúcia C
authors.initials: LC
authors.lastname: Simões
authors.forename: Laura
authors.initials: L
authors.lastname: Cerqueira
authors.forename: Carina
authors.initials: C
authors.lastname: Almeida
authors.forename: Charles W
authors.initials: CW
authors.lastname: Keevil
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Vieira
mesh_terms: D001419:Bacteria / Q000254:growth & development*; D001431:Bacteriological Techniques / Q000379:methods*; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry*; D004926:Escherichia coli / Q000254:growth & development; D020580:Methylobacterium / Q000254:growth & development; D050296:Microbial Viability; D009997:Osmotic Pressure; D011551:Pseudomonas fluorescens / Q000254:growth & development; D020578:Sphingomonas / Q000254:growth & development; D013312:Stress, Physiological
chemical_list: D003470:Culture Media