The study of bacterial growth is a challenging field since it aims to describe the behavior of microorganisms under different physical or chemical conditions. Bacterial growth as a biofilm is of particular interest as these gel-like structures are detrimental for all applications where "clean" surfaces are most important, and are related to failure of infection treatment, food spoilage and oil pipeline contamination, amongst others. In this work we applied a different technique to monitor the growth rate of a methicillin resistance Staphylococcus aureus strain in complex medium in the absence and in the presence of a sub-inhibitory concentration of oxacillin, a clinical relevant b-lactam antibiotic. The two bacterial cultures were incubated at 37ºC (body temperature) with aeration and their optical densities were monitored at 620 nm along time for almost 8 hours of growth. Furthermore, the population´s cell viable counts were determined along time by plating several dilutions of the bacterial cultures. Simple shear flow experiments were applied to aliquots of the bacterial cultures in the beginning of the growth procedure and at the same time points at which the optical density and cell viable counts were determined. All the rheological measurements were performed at reduced temperature to "freeze" the bacterial growth at each time tested. The sterile broth was also incubated in the same conditions and tested, as control for the rheological behavior. In all samples a shear thickening behaviour was observed. The rheological measurements allowed to characterize the viscosity in function of the shear rate and to compare the viscosity for different growth time, at fixed shear rates. At the beginning of the growth curve, the viscosity of the culture appeared to be smaller than the broth viscosity. Only for intermediate and longer growth times the viscosity showed higher values than the broth viscosity. For higher shear rate values, all the flow curves tend into the same curve - the broth flow curve. After 300 min the bacterial growth revealed a significant increase, corresponding to the exponential phase of growth. Such alteration was screened in the viscosity vs growth time curve, in agreement with the data obtained by optical density measurement. Also from these measurements and as expected, the growth rate of the population challenged with antibiotic was slower than for the population grown in optimal conditions. We aim to implement and develop a new methodology to study bacterial growth in different environments and to characterize the mechanical properties of biofilms.
|Title of host publication||Book of Proceedinsg “Rheology trends: from nano to macro systems”|
|Publication status||Published - 1 Jan 2011|
|Event||Ibereo - |
Duration: 1 Jan 2011 → …
|Period||1/01/11 → …|