title: Evolution and role of corded cell aggregation in Mycobacterium tuberculosis cultures.
abstract: The aim of this study was to evaluate the evolution and role of corded cell aggregation in Mycobacterium tuberculosis cultures according to growth time and conditions. Thus, in standard culture using aerated 7H9 Middlebrook broth supplemented with 0.05% Tween 80, a dramatic CFU decrease was observed at the end of the exponential phase. This phase was followed by a stable stationary phase that led to dissociation between the optical density (O.D.) and CFU values, together with the formation of opaque colonies in solid culture. Further analysis revealed that this was due to cording. Scanning electron microscopy showed that cording led to the formation of very stable coiled structures and corded cell aggregations which proved impossible to disrupt by any of the physical means tested. Modulation of cording with a high but non-toxic concentration of Tween 80 led to a slower growth rate, avoidance of a sudden drop-off to the stationary phase, the formation of weaker cording structures and the absence of opaque colonies, together with a lower survival at later time-points. An innovative automated image analysis technique has been devised to characterize the cording process. This analysis has led to important practical consequences for the elaboration of M. tuberculosis inocula and suggests the importance of biofilm formation in survival of the bacilli in the extracellular milieu.
authors.affiliation: Unitat de Tuberculosi Experimental (UTE), Fundació Institut d'Investigació en Ciències de la Salut Germans Trias i Pujol, Universitat Autònoma de Barcelona, CIBERES, Crtra. de Can Ruti, Camí de les Escoles s/n, Edifici Escoles, 08916 Badalona, Spain.
authors.forename: Neus
authors.initials: N
authors.lastname: Caceres
authors.forename: Cristina
authors.initials: C
authors.lastname: Vilaplana
authors.forename: Clara
authors.initials: C
authors.lastname: Prats
authors.forename: Elena
authors.initials: E
authors.lastname: Marzo
authors.forename: Isaac
authors.initials: I
authors.lastname: Llopis
authors.forename: Joaquim
authors.initials: J
authors.lastname: Valls
authors.forename: Daniel
authors.initials: D
authors.lastname: Lopez
authors.forename: Pere-Joan
authors.initials: PJ
authors.lastname: Cardona
mesh_terms: D018441:Biofilms; D002449:Cell Aggregation / Q000502:physiology*; D015169:Colony Count, Microbial; D003311:Cord Factors / Q000502:physiology*; D005615:Freezing; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008855:Microscopy, Electron, Scanning; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure; D011136:Polysorbates / Q000494:pharmacology; D013312:Stress, Physiological / Q000502:physiology
chemical_list: D003311:Cord Factors; D011136:Polysorbates
keywords: Corded cell aggregation; Cording; Culture growth characteristics; Mycobacterium tuberculosis