A heat-resistant, spore-forming bacterium that survives ultra-high-temperature (UHT) processing has long frustrated dairy producers, because even after milk is flash-heated at intense temperatures, its spores can germinate and multiply, spoiling the product on the shelf.
The research team isolated the bacterium, designated strain Ab.359 TZ, from local UHT milk collected in Fars Province, Iran, and registered its genetic sequence in the NCBI database under accession number PX916884. The organism is known as a persistent spoilage agent in dairy because its spores tolerate the very heat treatments designed to sterilize milk, meaning that contamination control must focus on preventing germination and outgrowth after processing rather than on killing the spores outright.
To characterize the essential oil, the researchers used gas chromatography–mass spectrometry, a technique that separates and identifies the individual volatile compounds in a mixture. The analysis showed that the oil was dominated by two phenolic monoterpenes: thymol, accounting for 32.51 percent of the composition, and carvacrol, at 32.17 percent.
The team then tested the oil against the bacterium in broth culture and in a UHT milk model over a five-day observation period, expressing oil concentrations as volume per volume. The minimum inhibitory concentration, the lowest dose that prevented visible growth of the organism, was determined to be 0.09 percent (v/v), a relatively small amount that suggests the oil is potent against this strain.
When the oil was applied, it produced an initial reduction in vegetative-cell counts, the actively growing and dividing form of the bacterium. Rather than eliminating the population entirely, the treatment delayed the subsequent recovery of the population and pushed back the timing of sporulation, the process by which the bacterium forms its protective, heat-resistant spores.
In the UHT milk model specifically, the effects included suppression of spore outgrowth and a dampening of the overall bacterial population recovery during the experimental period.
Importantly, the researchers report that complete inhibition of spore germination was not observed. The oil restrained, but did not fully prevent, the transition from dormant spore to growing cell. This partial effect is a realistic and honest characterization of what a natural antimicrobial can achieve against an organism as resilient as H. sporothermodurans, and it frames the oil as a population-dynamics modifier rather than a sterilizing agent.
The authors conclude that Zataria multiflora essential oil can suppress vegetative proliferation and spore-associated population dynamics of this strain under the experimental conditions used, and they suggest the findings highlight its potential as a natural preservative strategy for controlling spoilage-associated microbial dynamics in UHT milk. However, they are explicit that further studies are required before any practical application, including evaluations of sensory acceptability, long-term efficacy under relevant storage conditions, and overall suitability for use in dairy products.
Those caveats are substantial. Whether the concentrations effective in broth and in a five-day laboratory model would remain effective over the weeks of ambient shelf life expected of UHT products, and whether they would interact with milk proteins or fats in ways that change their activity, are questions the current study does not answer. The work was conducted on a single strain isolated from a single region, so efficacy against the broader diversity of H. sporothermodurans isolates found in dairy processing environments remains to be established.
Subject of Research: Antimicrobial activity of Zataria multiflora essential oil against the spore-forming bacterium Heyndrickxia sporothermodurans isolated from UHT milk
Article Title: Antimicrobial activity of Zataria multiflora essential oil against Heyndrickxia sporothermodurans isolated from UHT milk
Article References: Gholami, A., Mohkam, M., Asoudeh-Fard, A., Omidifar, N., Mousavi, S. M., Hashempour, M. H., & Chashmpoosh, M. (2026). Antimicrobial activity of Zataria multiflora essential oil against Heyndrickxia sporothermodurans isolated from UHT milk. Annals of Microbiology. https://doi.org/10.1186/s13213-026-01875-5
Image Credits: AI Generated
DOI: 10.1186/s13213-026-01875-5
Keywords: Zataria multiflora, essential oil, Heyndrickxia sporothermodurans, UHT milk, spore germination, thymol, carvacrol, food spoilage, dairy preservation, minimum inhibitory concentration, GC-MS, natural preservatives
News Source: Drew Townsend. (October 29, 2026). Research report: Antimicrobial activity of Zataria multiflora essential oil against Heyndrickxia sporothermodurans isolated from UHT milk. Scienmag.
