title: Light scattering sensor for direct identification of colonies of Escherichia coli serogroups O26, O45, O103, O111, O121, O145 and O157.
abstract: BACKGROUND
  Shiga-toxin producing Escherichia coli (STEC) have emerged as important foodborne pathogens, among which seven serogroups (O26, O45, O103, O111, O121, O145, O157) are most frequently implicated in human infection. The aim was to determine if a light scattering sensor can be used to rapidly identify the colonies of STEC serogroups on selective agar plates.
  
  
  RESULTS
  Initially, a total of 37 STEC strains representing seven serovars were grown on four different selective agar media, including sorbitol MacConkey (SMAC), Rainbow Agar O157, BBL CHROMagarO157, and R&F E. coli O157:H7, as well as nonselective Brain Heart Infusion agar. The colonies were scanned by an automated light scattering sensor, known as BARDOT (BActerial Rapid Detection using Optical scattering Technology), to acquire scatter patterns of STEC serogroups, and the scatter patterns were analyzed using an image classifier. Among all of the selective media tested, both SMAC and Rainbow provided the best differentiation results allowing multi-class classification of all serovars with an average accuracy of more than 90% after 10-12 h of growth, even though the colony appearance was indistinguishable at that early stage of growth. SMAC was chosen for exhaustive scatter image library development, and 36 additional strains of O157:H7 and 11 non-O157 serovars were examined, with each serogroup producing unique differential scatter patterns. Colony scatter images were also tested with samples derived from pure and mixed cultures, as well as experimentally inoculated food samples. BARDOT accurately detected O157 and O26 serovars from a mixed culture and also from inoculated lettuce and ground beef (10-h broth enrichment +12-h on-plate incubation) in the presence of natural background microbiota in less than 24 h.
  
  
  CONCLUSIONS
  BARDOT could potentially be used as a screening tool during isolation of the most important STEC serovars on selective agar plates from food samples in less than 24 h.
authors.affiliation: Molecular Food Microbiology Laboratory, Department of Food Science, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Yanjie
authors.initials: Y
authors.lastname: Tang
authors.affiliation: School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Huisung
authors.initials: H
authors.lastname: Kim
authors.affiliation: Molecular Food Microbiology Laboratory, Department of Food Science, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Atul K
authors.initials: AK
authors.lastname: Singh
authors.affiliation: Molecular Food Microbiology Laboratory, Department of Food Science, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Amornrat
authors.initials: A
authors.lastname: Aroonnual
authors.affiliation: School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Euiwon
authors.initials: E
authors.lastname: Bae
authors.affiliation: Bindley Bioscience Center, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Bartek
authors.initials: B
authors.lastname: Rajwa
authors.affiliation: USDA-ARS, Eastern Regional Research Center, Wyndmoor, Pennsylvania, United States of America.
authors.forename: Pina M
authors.initials: PM
authors.lastname: Fratamico
authors.affiliation: Molecular Food Microbiology Laboratory, Department of Food Science, Purdue University, West Lafayette, Indiana, United States of America; Department of Comparative Pathobiology, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Arun K
authors.initials: AK
authors.lastname: Bhunia
mesh_terms: D015373:Bacterial Typing Techniques / Q000295:instrumentation*; D019453:Escherichia coli O157 / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D005798:Genes, Bacterial; D008027:Light; D012542:Scattering, Radiation; D065288:Serogroup