The research team worked with strains of Enterococcus and Lactobacillus originally isolated from traditional fermented dairy products, including Enterococcus faecium KE5, Enterococcus durans KE6, Lactobacillus rhamnosus 2012, and Lactobacillus helveticus KG5. These strains were cultivated in a specialized curd whey medium under anaerobic conditions, and their cell-free supernatants were concentrated five-fold before the active compounds were separated. Bacteriocins—ribosomally synthesized antimicrobial peptides classified as Generally Regarded As Safe—were purified by gel filtration on Sephadex columns, while exopolysaccharides, high-molecular-weight carbohydrate polymers, were precipitated with ethanol and likewise purified chromatographically. High-performance liquid chromatography confirmed that the exopolysaccharide fractions were heteropolysaccharides composed primarily of glucose and galactose.

To benchmark the postbiotics against clinical reality, the team assembled a demanding test panel drawn from internationally recognized culture collections, including the American Type Culture Collection and the UK’s National Collection of Type Cultures. The panel deliberately included both susceptible control strains and notorious resistant phenotypes: an ESBL- and AmpC-producing Klebsiella pneumoniae, a multidrug-resistant Pseudomonas aeruginosa, an OXA-48 carbapenemase-producing Acinetobacter baumannii, methicillin-resistant Staphylococcus aureus, and resistant strains of Streptococcus pneumoniae and Enterococcus faecalis. Resistance mechanisms were confirmed phenotypically through double-disk synergy and modified Hodge tests, and carbapenemase genes including KPC, NDM, and OXA were verified by polymerase chain reaction.

The initial screening established a standardized effective dose of 5 milligrams per milliliter against the model organism Salmonella typhimurium G-38, determined by the serial dilution method. This concentration was then applied across the broader pathogen panel using agar diffusion assays, allowing direct comparison with standard antibiotic discs interpreted according to EUCAST clinical breakpoints. The stepwise design meant that every postbiotic preparation and every antibiotic faced the same targets under the same conditions, a comparison the authors argue is rarely attempted at this scale for both Gram-positive and Gram-negative resistant strains.

Concentration-dependence emerged as a defining theme. All exopolysaccharide preparations achieved nearly complete growth inhibition at 100 milligrams per milliliter, but their activity fell away steeply at lower doses, with the exception of the preparation from E. faecium KE5, which retained measurable effects down to 1 milligram per milliliter. Bacteriocins told a similar but sharper story: all preparations inhibited 95 to 100 percent of growth at 10 to 50 milligrams per milliliter, yet only the bacteriocin from E. faecium KE5 sustained substantial activity at 5 milligrams per milliliter, a property the researchers describe as dose sustainability. L. rhamnosus 2012 stood apart for producing two distinct bacteriocins of different molecular weights, 1.42 and 0.60 kilodaltons, which broadened its inhibitory spectrum.

The comparative results against antibiotics revealed what the authors call an erosion of susceptibility among resistant isolates. The ESBL- and AmpC-producing K. pneumoniae strain showed complete resistance to beta-lactams and only 5 percent susceptibility to carbapenems, while remaining fully susceptible to fluoroquinolones and aminoglycosides. Among the non-fermenting Gram-negatives, the resistant P. aeruginosa strain and the OXA-48-positive A. baumannii resisted most antibiotic classes, with the Pseudomonas control strain itself showing only 10 percent susceptibility to beta-lactams and none to fluoroquinolones. Resistant Gram-positive cocci fared little better, with the resistant S. pneumoniae strain showing just 28.5 percent susceptibility to beta-lactams and complete resistance to fluoroquinolones and aminoglycosides.

Against this backdrop of patchy antibiotic performance, the purified bacteriocins from L. rhamnosus 2012 and E. faecium KE5 delivered the study’s most striking result: 100 percent inhibitory activity against every tested reference strain, regardless of resistance phenotype. Whether a pathogen carried ESBL enzymes, carbapenemase genes, or methicillin resistance made no difference to the bacteriocins’ performance under the experimental conditions. The exopolysaccharides, by contrast, showed far weaker and more variable effects, with most Enterobacteriaceae isolates classified as resistant to them. The authors attribute the disparity to fundamental biochemical differences: bacteriocins are thought to kill directly by permeabilizing bacterial membranes and forming pores, whereas exopolysaccharides act more indirectly, potentially by interfering with adhesion or biofilm formation.

That mechanistic interpretation comes with important caveats. The researchers acknowledge that the proposed membrane-disruption pathways remain hypotheses, since no direct membrane permeability assays or electron microscopy imaging were performed. Diffusion-based assays also carry inherent limitations for large molecules, and the exopolysaccharides, at molecular weights of 10 to 44 kilodaltons, may simply diffuse poorly through agar, understating their true activity. The authors also stress that the narrower spectrum of the postbiotics, while potentially advantageous for preserving the host microbiome, means they cannot simply replace broad-spectrum antibiotics across the board.

Even so, the case for bacteriocins as complementary agents is compelling on several fronts. Unlike antibiotics that suppress bacterial metabolism and synthesis, bacteriocins tend to damage target cell structures directly, which the authors argue reduces the likelihood of resistance emerging. They are active at very low concentrations, are completely metabolized in the human body, and generally show low toxicity. Previous work by the same group indicated that bacteriocins and exopolysaccharides from these strains can inhibit pneumonia-causing pathogens, and the current data open the possibility of combination preparations—bacteriocins paired with exopolysaccharides or with conventional drugs—that could enhance efficacy while lowering antibiotic doses and resistance pressure.

The study’s authors frame their endemic Armenian strains as a valuable reservoir for next-generation antimicrobials, with potential applications spanning nutrition, prevention, and eventually therapy. They are careful, however, to position the findings as preliminary in vitro observations. Before any clinical translation, in vivo efficacy and toxicological studies will be required to establish whether the dose sustainability and uniform activity seen on agar plates survive the far harsher conditions of a living host. For now, the message is that the microscopic inhabitants of traditional fermented foods may hold molecules that drug-resistant bacteria have not yet learned to defeat.

Subject of Research: Antimicrobial activity of bacteriocins and exopolysaccharides from lactic acid bacteria against multidrug-resistant human pathogens

Article Title: Antimicrobial properties of postbiotics of different LAB against multidrug resistance bacteria

Article References: Tkhruni, F., Danova, S., Melik-Andreasyan, G., Aleksanyan, N., & Israyelyan, A. (2026). Antimicrobial properties of postbiotics of different LAB against multidrug resistance bacteria. Pharmacia, 73, Article e189800. https://doi.org/10.3897/pharmacia.73.e189800

Image Credits: AI Generated

DOI: 10.3897/pharmacia.73.e189800

Keywords: antimicrobial resistance, postbiotics, bacteriocins, exopolysaccharides, lactic acid bacteria, multidrug-resistant bacteria, probiotics, Enterococcus faecium, Lactobacillus rhamnosus, ESBL, carbapenemase, fermented milk

The motivation behind the work stems from a growing environmental reckoning with conventional surfactants. These workhorse molecules, which make up 10 to 20 percent of most cosmetic emulsions, are designed to reduce tension at the boundary between water and oil, allowing otherwise incompatible phases to blend into smooth, shelf-stable products. Yet many synthetic surfactants persist in the environment for years. Perfluorinated compounds in particular are prized by formulators for their robustness but are notoriously resistant to degradation, while linear alkylbenzene sulfonates have been linked to biochemical and pathological harm in aquatic ecosystems. Regulators and consumers alike have been pushing the cosmetics industry to find biodegradable alternatives that do not sacrifice performance.

Biosurfactants, amphiphilic molecules produced by microorganisms that combine a water-loving polar head with an oil-loving hydrophobic tail, have long been touted as such an alternative. Lactic acid bacteria are especially attractive producers because they carry the Generally Recognized as Safe designation, meaning their metabolites face fewer regulatory hurdles in food and personal-care applications. The obstacle has been practical: production yields are often low and fermentation substrates expensive, pushing up costs and limiting commercial adoption. Researchers have therefore been hunting for high-performing producer strains in unconventional places, from cassava-processing effluents to traditional fermented foods.

Pendidam, the spontaneously fermented skimmed cow’s milk consumed around Ngaoundere in Cameroon’s Adamaoua region, had already caught the attention of the research group. Earlier work by Mbawala and colleagues had shown that the drink teems with Lactobacillus strains capable of producing surface-active compounds. In the new study, the team collected six Pendidam samples from vendors at four sites across the city, including the Petit marché, Dang, Wakwa and the Grand marché, and transported them to the laboratory under refrigeration within two hours of purchase.

From those samples the researchers isolated twelve presumptive Lactobacillus strains, all of which proved to be Gram-positive, non-motile, catalase- and oxidase-negative rods with heterofermentative metabolism, growing across a temperature range of 15 to 45 degrees Celsius and tolerating salt concentrations up to 6.5 percent. The authors are careful to note that these phenotypic traits, while consistent with members of the former Lactobacillus group and suggestive of the reclassified genus Lactiplantibacillus, are not sufficiently discriminating for definitive taxonomic assignment following the genus’s recent fragmentation into more than twenty genera; molecular identification by 16S rRNA gene sequencing remains a stated priority for future work.

Screening for biosurfactant production relied on two complementary assays. In the hydrocarbon overlay test, bacterial colonies grown on agar were covered with palm oil; the appearance of clear halos containing microemulsions signaled secretion of surface-active compounds. The oil spreading test provided quantitative confirmation: drops of cell-free culture supernatant were deposited onto a thin oil layer floating on water, and the diameter of the resulting clear zone, which correlates with biosurfactant concentration, was measured. Five isolates, subsequently designated S1 through S5, produced clear zones ranging from 6 to 28 millimeters, comfortably exceeding the 3-millimeter threshold above the negative control that the field considers evidence of genuine biosurfactant production.

The crude biosurfactants were then extracted by ethanol precipitation from scaled-up cultures and put through their paces. Emulsification indices, a measure of the emulsified layer formed when biosurfactant solution is mixed with palm oil, ranged from 67.33 to 72 percent, values slightly below those reported for some purified lactobacilli biosurfactants in the literature but respectable for unpurified crude extracts. More striking were the surface tension measurements. At a concentration of 4 grams per 100 milliliters, solutions of the biosurfactants from isolates S1 and S5 lowered the surface tension of water from 70.90 millinewtons per meter to levels comparable with sodium dodecyl sulfate, the benchmark anionic surfactant used as the positive control.

The decisive test came when the biosurfactants were formulated into water-in-oil beauty milks alongside xanthan gum, sesame oil, glycerol and shea butter, with the commercial sorbitan monostearate SPAN 60 and a marketed body milk serving as positive controls. Laser diffraction analysis using a Malvern Mastersizer 2000 revealed that emulsions stabilized with the bacterial surfactants formed droplets between 4.94 and 7.61 micrometers in diameter, dramatically finer than the 16.34-micrometer droplets of the negative control. The standout was isolate S5, whose biosurfactant yielded the smallest droplets of all, significantly finer even than those produced by the synthetic SPAN 60. According to the authors, this reflects rapid adsorption of the amphiphilic molecules at newly created oil-water interfaces during high-shear homogenization, where they form protective films that generate steric and, depending on molecular composition, electrostatic repulsion between droplets, suppressing coalescence and Ostwald ripening.

Viscosity told a complementary story. Formulations containing the bacterial biosurfactants ranged from 967 to 1715 millipascal-seconds, compared with roughly 1998 millipascal-seconds for both controls, and the differences tracked closely with droplet size. Emulsions with the finest droplets, such as those made with the S5 biosurfactant, maintained relatively high viscosity, consistent with emulsion theory: smaller droplets present a larger total interfacial area, increasing interactions between dispersed and continuous phases and raising resistance to flow. Higher viscosity in turn slows droplet mobility, reducing collision frequency and the risk of creaming or phase separation during storage. The combination of fine droplet size and appropriate rheology, the authors argue, positions the S5 biosurfactant as the most promising candidate of the five tested for cosmetic formulation.

The study’s novelty lies less in the individual measurements than in its integrated approach and its source material. Biosurfactants from lactic acid bacteria have mostly been studied for antimicrobial, antiadhesive and probiotic properties; direct deployment as emulsifiers in cosmetic products has rarely been evaluated, and never before with strains from Pendidam. By connecting microbiological screening with rigorous physicochemical characterization of finished emulsions, the work makes the case that traditional fermented foods are an underexplored reservoir of industrially useful microbes, and one that comes with built-in cultural and economic advantages for the communities that produce them. The path to commercialization still requires purification and structural characterization of the biosurfactants, definitive molecular identification of the producing strains, long-term stability testing and safety evaluation, but the baseline data now exist. For an industry under pressure to replace persistent synthetic surfactants with biodegradable molecules, the answer may have been fermenting quietly in a Cameroonian milk calabash all along.

Subject of Research: Biosurfactants from Lactobacilli isolated from Pendidam fermented milk for stabilizing water-in-oil cosmetic emulsions

Article Title: Improvement of water in oil emulsion physicochemical stability using biosurfactants from indigenous Lactobacilli isolated from Pendidam

Article References: Wandji, V. N., Tsatsop, R. K. T., Mouafo, H. T., & Mbawala, A. (2026). Improvement of water in oil emulsion physicochemical stability using biosurfactants from indigenous Lactobacilli isolated from Pendidam. Discover Industrial Chemistry and Materials, 1(1), Article 20. https://doi.org/10.1007/s44508-026-00021-y

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00021-y

Keywords: biosurfactants, Lactobacilli, Pendidam, emulsifiers, cosmetics, lactic acid bacteria, water-in-oil emulsion, droplet size, viscosity, surface tension, fermented milk, sustainable ingredients