title: Optical forward-scattering for identification of bacteria within microcolonies.
abstract: The development of methods for the rapid identification of pathogenic bacteria is a major step towards accelerated clinical diagnosis of infectious diseases and efficient food and water safety control. Methods for identification of bacterial colonies on gelified nutrient broth have the potential to bring an attractive solution, combining simple optical instrumentation, no need for sample preparation or labelling, in a non-destructive process. Here, we studied the possibility of discriminating different bacterial species at a very early stage of growth (6 h of incubation at 37 °C), on thin layers of agar media (1 mm of Tryptic Soy Agar), using light forward-scattering and learning algorithms (Bayes Network, Continuous Naive Bayes, Sequential Minimal Optimisation). A first database of more than 1,000 scatterograms acquired on 7 gram-negative strains yielded a recognition rate of nearly 80%, after only 6 h of incubation. We investigated also the prospect of identifying different strains from a same species through forward scattering. We discriminated, thus, four strains of Escherichia coli with a recognition rate reaching 82%. Finally, we show the discrimination of two species of coagulase-negative Staphylococci (S. haemolyticus and S. cohnii), on a commercial selective pre-poured medium used in clinical diagnosis (ChromID MRSA, bioMérieux), without opening lids during the scatterogram acquisition. This shows the potential of this method--non-invasive, preventing cross-contaminations and requiring minimal dish handling--to provide early clinically-relevant information in the context of fully automated microbiology labs.
authors.affiliation: Department of Technology for Biology and Healthcare, CEA-LETI MINATEC, 17 avenue des Martyrs, 38054, Grenoble, France, pierre.marcoux@cea.fr.
authors.forename: Pierre R
authors.initials: PR
authors.lastname: Marcoux
authors.forename: Mathieu
authors.initials: M
authors.lastname: Dupoy
authors.forename: Antoine
authors.initials: A
authors.lastname: Cuer
authors.forename: Joe-Loïc
authors.initials: JL
authors.lastname: Kodja
authors.forename: Arthur
authors.initials: A
authors.lastname: Lefebvre
authors.forename: Florian
authors.initials: F
authors.lastname: Licari
authors.forename: Robin
authors.initials: R
authors.lastname: Louvet
authors.forename: Anil
authors.initials: A
authors.lastname: Narassiguin
authors.forename: Frédéric
authors.initials: F
authors.lastname: Mallard
mesh_terms: D000362:Agar; D001185:Artificial Intelligence; D001419:Bacteria / Q000145:classification* / Q000254:growth & development* / Q000302:isolation & purification; D001431:Bacteriological Techniques / Q000379:methods*; D003470:Culture Media / Q000737:chemistry; D055096:Optical Devices; D055620:Optical Phenomena
chemical_list: D003470:Culture Media; D000362:Agar