Streptomycin Induced Stress Response in Salmonella enterica Serovar Typhimurium Shows Distinct Colony Scatter Signature

PLoS One. 2015 Aug 7;10(8):e0135035. doi: 10.1371/journal.pone.0135035. eCollection 2015.

Abstract

We investigated the streptomycin-induced stress response in Salmonella enterica serovars with a laser optical sensor, BARDOT (bacterial rapid detection using optical scattering technology). Initially, the top 20 S. enterica serovars were screened for their response to streptomycin at 100 μg/mL. All, but four S. enterica serovars were resistant to streptomycin. The MIC of streptomycin-sensitive serovars (Enteritidis, Muenchen, Mississippi, and Schwarzengrund) varied from 12.5 to 50 μg/mL, while streptomycin-resistant serovar (Typhimurium) from 125-250 μg/mL. Two streptomycin-sensitive serovars (Enteritidis and Mississippi) were grown on brain heart infusion (BHI) agar plates containing sub-inhibitory concentration of streptomycin (1.25-5 μg/mL) and a streptomycin-resistant serovar (Typhimurium) was grown on BHI containing 25-50 μg/mL of streptomycin and the colonies (1.2 ± 0.1 mm diameter) were scanned using BARDOT. Data show substantial qualitative and quantitative differences in the colony scatter patterns of Salmonella grown in the presence of streptomycin than the colonies grown in absence of antibiotic. Mass-spectrometry identified overexpression of chaperonin GroEL, which possibly contributed to the observed differences in the colony scatter patterns. Quantitative RT-PCR and immunoassay confirmed streptomycin-induced GroEL expression while, aminoglycoside adenylyltransferase (aadA), aminoglycoside efflux pump (aep), multidrug resistance subunit acrA, and ribosomal protein S12 (rpsL), involved in streptomycin resistance, were unaltered. The study highlights suitability of the BARDOT as a non-invasive, label-free tool for investigating stress response in Salmonella in conjunction with the molecular and immunoassay methods.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Agar
  • Anti-Bacterial Agents / chemistry
  • Bacterial Proteins / genetics
  • Drug Resistance, Bacterial*
  • Humans
  • Immunoassay
  • Mass Spectrometry
  • Microbial Sensitivity Tests
  • Reverse Transcriptase Polymerase Chain Reaction
  • Salmonella typhimurium / drug effects*
  • Scattering, Radiation
  • Serogroup
  • Streptomycin / chemistry*

Substances

  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Agar
  • Streptomycin

Grant support

This research was supported through a cooperative agreement with the Agricultural Research Service of the US Department of Agriculture project number 1935-42000-072-02G and the Center for Food Safety Engineering at Purdue University.