At the beginning of the COVID-19 pandemic in 2020, meat-packaging plants were among the largest epicenters of COVID-10 outbreaks. This study by researchers from the United States investigated the viability of the Delta variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), incubated with environmental biofilms from three meat packaging plants, on materials such as stainless steel, PVC, and ceramic tiles. They also examined how viral presence affected biofilm biomass.
The authors noted that the escalating number of COVID-19 cases in meat packaging plants at the onset of the COVID-19 pandemic in 2020 could be attributed to a variety of factors such as virus 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 thin layers 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 environment for the growth and survival of bacterial cells. They also protect microbes from unfavorable environments, like heat, ultraviolet light, cold, and disinfectant chemicals, and increase bacterial resistance to antimicrobial agents. In meat packaging plants, environmental biofilms are commonly found on solid, surfaces like tile flooring, PVC, or stainless steel.
About the study
Delta variant of the SARS-CoV-2 was incubated with- and without environmental biofilms from three meat packaging plants (marked as Plant A, B, and C) on materials usually present in meat packaging plants, like stainless steel, PVC, and ceramic tiles. The viability of SARS-CoV-2 was evaluated through a double overlay plaque assay and real-time quantitative polymerase chain reaction (PCR). The plaque assay was utilized to determine the number of infectious virus particles on different surfaces with- and without environmental biofilms and to evaluate the impact of SARS-CoV-2 on biofilm biomass. The real-time quantitative PCR detected SARS-CoV-2 RNA on each material tested. The mean number of biofilm cells was represented as colony-forming units per mL (CFU/mL).
Results
Delta variant of the SARS-CoV-2 was detectable and viable on all materials tested. The viability of the SARS-CoV-2 incubated with environmental biofilms from three meat packaging plants highly correlated with the microorganisms in the biofilms. The viability of viruses was significantly reduced after exposure to Plant B and Plant C biofilms.
The incubation of viruses with microorganisms forming Plant B biofilm for five days reduced the viral viability on every material tested. The incubation of viruses with microorganisms forming Plant C biofilm reduced the viral viability on stainless steel or PVC by 47 – 207-fold, and viral infectivity by 146 – 375-fold, compared to the viral initial titer. In contrast, exposure of viruses to the biofilm from Plant A did not reduce viral infectivity on any of the materials tested.
Importantly, biofilm biovolume increased in response to the presence of the Delta variant of the SARS-CoV-2. The incubation of viruses with each environmental biofilm for five days increased the biovolume of all three biofilms by 1.5 – 25-fold on all materials tested, compared to the biovolume of all three biofilms that were not incubated with viruses. According to the authors, an increase in biovolume observed in all three biofilms in response to the presence of the viruses may be attributable to the bacterial defense mechanisms against unfavorable environments.
Conclusion
This study showed that the Delta variant of the SARS-CoV-2 remained viable and infectious for up to five days after incubation with and without each environmental biofilm, on all surfaces tested. However, exposure to Plant B or Plant C biofilms significantly reduced viral viability. The incubation with viruses increased the biovolume of all three biofilms.
This study has been published on a preprint server and is currently under peer review.
Journal Reference
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
