Observation with microcalorimetry: Behaviour of P. aeruginosa in mixed cultures with S. aureus and E. coli

Abstract

Bacteria exist as mixed cultures of different species in their natural environments. However, most laboratory characterization experiments, for instance, susceptibility testings are routinely conducted on pure species of bacteria. Interactions that may naturally occur and their consequent effects on the metabolisms of the individual species are missed by this approach. In this work, we explored the potential of isothermal microcalorimetry (IMC), a technique which has been established to characterize microorganisms to study the behaviour of mixed cultures of Pseudomonas aeruginosa with Staphylococcus aureus and Escherichia coli. The species were firstly studied as pure culture at 10 6 CFU/mL densities in nutrient broth (NB). The species were then introduced into NB to give an equivalent inoculum of 10 6 CFU/mL of each. Additionally, the inoculum density of one species was maintained at 10 6 CFU/mL and the other varied between 10 3-10 5 CFU/mL. The IMC power-time curves were characteristic for the species in the medium. The total heat output (Qt), amplitude of first peak (P1), time of registration of first peak (t1), final metabolic/maximum peak (Pfmax) and time of registration of the final metabolic/maximum peak (tfmax) were calculated from the power-time data. A mixed culture of P. aeruginosa and S. aureus at equal densities exhibited metabolism synonymous to P. aeruginosa alone. When the density of P. aeruginosa was decreased, S. aureus gradually recovered showing power-time profiles that demonstrated this. The plate count data collected at the end of IMC experiments corroborated with the observation in the IMC. Mixed cultures of P. aeruginosa and E. coli at equal densities showed power-time profiles representative of both species demonstrating the co-dominance of the organisms. However the plate counts data showed P. aeruginosa was inhibited in growth.

Expanding the Scope of an Amphoteric Condensed Tannin, Tanfloc, for Antibacterial Coatings

“…Subsequently, the samples were washed with a buffer (0.1 mol/L sodium cacodylate and 0.1 mol/L sucrose) for 10 min. The samples were then subjected to drying with increasing concentrations of ethanol solutions (35,50,75, and 100%) for 10 min each. Before SEM imaging, the surfaces were coated with a thin layer of gold at a thickness of 10 nm (n = 2) and the SEM parameters were optimized and chosen as follows: accelerating voltage of 15 kV, working distance of 10 mm, and vacuum pressure below 3 × 10 −4 Pa.…”

“…S. aureus, commonly found on human skin, is often associated with infections related to medical devices, while P. aeruginosa is frequently implicated in hospital-acquired infections and triggers oxidative stress and inflammation. Understanding how biomaterial surfaces interact with both types of bacteria is necessary, as they require different strategies for controlling their infections [49][50][51]. Glass and tissue culture polystyrene were chosen as negative controls because they do not have antimicrobial and antiadhesive activities [49].…”