At the beginning of the COVID-19 pandemic in 2020, meat-packaging plants were among the largest epicenters of COVID-10 outbreaks. The study by U.S. researchers examined the viability of the SARS-CoV-2 Delta variant, incubated with environmental biofilms from three different meat packaging plants, on materials such as stainless steel, PVC, and ceramic tile chips. They also evaluated how viral presence affected biofilm biomass. The results showed that the SARS-CoV-2 Delta variant remained viable and infectious for up to five days following incubation with and without each of the environmental biofilms on all surfaces tested. But, the viability of virus was significantly reduced after exposure to Plant B and Plant C biofilms. At the same time, the incubation with viruses increased the biovolume of all three biofilms.
The escalating number of COVID-19 cases in meat packaging plants at the onset of COVID-19 pandemic in 2020 could be attributed to a variety of factors including the virus’s spread via HVAC systems, the shared use of equipment and workspaces among workers, and the viral ability to cohabitate with other biological organisms.
Biofilms are a thin layer of microbial communities that adhere to each other on organic or inorganic surfaces. These complex colonies of microorganisms serve as protective coatings that provide a hostile environments for the growth and survival of bacterial cells. They also protect microbes from unfavorable environments, like heat, ultraviolet light, cold, disinfectant chemicals, and increase the level of bacterial resistance to antimicrobial agents. In meat packaging plants, environmental biofilms are commonly found on solid, slick surfaces like tile flooring, PVC, or on stainless steel.
About the study
SARS-CoV-2 delta was incubated with- and without environmental biofilms from three different meat packaging plants (Plant A, B and C) on materials that are usually present in meat packaging plants, like stainless steel, PVC, and ceramic tile chips. The viability of SARS-CoV-2 was evaluated through a double overlay plaque assay and real-time quantitative PCR. The authors employed plaque assay to determine the number of infectious virus particles on different surfaces with- and without environmental biofilms, and to assess the viral impact on biofilm biomass. The real-time quantitative PCR technique was used to detect viral RNA on each material tested. The mean number of biofilm cells was represented as colony forming units per mL (CFU/mL).
The results demonstrated that the SARS-CoV-2 Delta variant remained not only detectable, but also viable on all materials tested. However, the viability of the virus was highly correlated with the microorganisms that were present in the biofilms. SARS-CoV-2 Delta variant viability was significantly reduced after exposure to Plant B biofilm, as well as to Plant C biofilm. After 5 days of incubation of viruses in the presence of microorganisms that form biofilm from Plants B, the viral viability was reduced on each material tested. When viruses were incubated in the presence of microorganisms that form biofilm from Plant C on stainless steel or PVC, there was a 46.88 – 207.04-fold reduction in viral viability, and a 146.41 – 374.53-fold reduction in viral infectivity compared to viral initial titer. However, after exposure to the biofilm from Plant A, there was no significant reduction in viral infectivity on any of the materials tested.
Importantly, the biofilm biovolume increased in response to the presence of SARS-CoV-2 Delta variant. The five-day incubation of viruses in the presence of each of the environmental biofilms resulted in an increase in the biovolume of all three biofilms by 1.47 – 24.69-fold on all materials tested, compared to the biovolume of all three biofilms that were not incubated with viruses. The authors suggested that the increase in biovolume observed in all three biofilms following exposure to viruses may be attributable to the defense mechanisms employed by bacteria in response to unfavorable environments.
The results of the study have been published on a preprint server and are currently under peer review.
Chitlapilly Dass S et al. SARS-CoV-2 Delta Variant Remains Viable in Environmental Biofilms found in Meat Packaging Plants BioRxiv 2023.06.15.545172. (Open Access) https://doi.org/10.1101/2023.06.15.545172