Assessing inhibitory activity of probiotic culture supernatants against Pseudomonas aeruginosa: a comparative methodology between agar diffusion, broth culture and microcalorimetry

Abstract

Cell free supernatants (CFS) obtained from probiotic species are routinely used to preliminary investigate the antimicrobial activity of potential probiotic isolates by the agar well diffusion and broth culture. Both methods have documented limitations. In this work, the potential of isothermal microcalorimetry (IMC), a technique based on the measurement of heat produced by growing bacteria was used to investigate the antimicrobial effects of two commercial probiotic species (Lactobacillus acidophilus LA-5 ® and Bifidobacterium lactis BB-12 ® ) and one reference strain (Bifidobacterium bifidum ATCC 11863) against Pseudomonas aeruginosa NCIMB 8628 using unmodified, neutralised and heat-treated CFS. P. aeruginosa was inhibited in growth by the unmodified CFS of all the species. No inhibitory activity was recorded for neutralised CFS of all the species using the agar well diffusion assay. Plate count during co-incubation of P. aeruginosa with the neutralised CFS of all the species showed no inhibition. However, IMC data showed significant inhibition with neutralised CFS obtained from the two Bifidobacterium species suggesting presence of other non-acidic inhibitory compounds in the CFS. The results in this work demonstrated that IMC has potential in probiotic bioassay as it has the capability to record in real-time and capture even subtle effects, which could be unnoticed with traditional assays.

Assessing Viability and Stress Tolerance of Probiotics—A Review

“…Isothermal microcalorimetry is a technology that is based on that heat is produced by a replicating, metabolizing bacterial population (Mihhalevski et al, 2011;Garcia et al, 2017;Fredua-Agyeman and Gaisford, 2019;Nykyri et al, 2019). The heat production is approximately 2 pW per cell, enabling measurements in bacterial samples with cell concentrations from approximately 106 CFU/ml (Fredua-Agyeman and Gaisford, 2019).…”

“…The heat production is then recorded for as long as it occurs (Braissant et al, 2010). By following the heat production of the bacterial population, it is possible to obtain real-time, continuous viability data, in contrast to for example plate count enumeration that only gives the endpoint of the viability measurement (Braissant et al, 2010;Fredua-Agyeman and Gaisford, 2019). From the heat measurement, several different growth specific data can be estimated, such as biomass yield and specific growth rate (Mihhalevski et al, 2011).…”

Probiotics Potential of Yeast and Lactic Acid Bacteria Fermented Foods and the Impact of Processing: A Review of Indigenous and Continental Food Products

“…The probiotic microorganisms generally belong to the species Bifidobacterium, Streptococcus (thermophilus), Enterococcus, and Lactobacillus. [8]…”

Lessons Learned from Faecal Microbiota Transplantation in Cirrhosis

“…Equally, they may have a secondary role in inhibiting bacterial growth, including that of Pseudomonas spp. [28], methicillin-resistant Staphylococcus aureus, Shigella spp. and Escherichia coli [29], thus potentially protecting against spontaneous bacterial peritonitis in decompensated patients.…”