Rev Esp Quimioter 2013:26(1):34-38
Invasion of solid culture media: a widespread phenotypic feature of clinical bacterial isolates
F. GÓMEZ-AGUADO, M. T. CORCUERA, C. GARCÍA-REY, M. L. GÓMEZ-LUS, C. RAMOS, M. J. ALONSO, J. PRIETO
Objectives. The in-depth growth in solid culture media is a common feature in filamentous fungi and yeasts. However, there are very few bacterial species in which this phenomenon has been documented. The aim of this work was to assess the agar invasiveness of a wide range of Gram-positive and Gram-negative bacterial species of clinical interest.
Material and methods. Three different clinical isolates for each of eleven bacterial species were plated onto Columbia blood agar and let grow up to 15 days. Isolated colonies were processed by histological methods, embedded in epoxy resin, and then, semithin sections were stained with toluidine blue and visualized by light microscopy.
Results. Growth within the agar was observed in at least one strain in 9 of the 11 studied species. Invasions of Gramnegative rods were small, not plentiful, and round or triangleshaped. In Gram-positive cocci, invasions were of big size, abundant and of variable shape (lentiform, globular, irregular, arrowhead) depending on the species.
Conclusions: We propose that the growth within the agar can indicate a survival strategy common to many bacterial species, and so far, not previously reported. This strategy could be either a nutrient gradient tropism or the spread and colonization of new ecological niches, with potential implications in pathogeny.
Rev Esp Quimioter 2013:26(1):34-38 [pdf]