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SARS-CoV-2 Delta variant remained viable in environmental biofilms, increasing their volumes

Jun 22, 2023 | About the Virus

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 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant, incubated with environmental biofilms from three different 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 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 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

The SARS-CoV-2 Delta variant was incubated with- and without environmental biofilms from three different meat packaging plants (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 authors used plaque assay 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. SARS-CoV-2 RNA on each material tested was detected by the real-time quantitative PCR. The mean number of biofilm cells was represented as colony-forming units per mL (CFU/mL).

Results

The SARS-CoV-2 Delta variant was not only detectable but also viable on all materials tested. The viability of the SARS-CoV-2 incubated with environmental biofilms from three different meat packaging plants highly correlated with the microorganisms in the biofilms.

The viability of the virus was significantly reduced after exposure to Plant B and Plant C biofilms. After five days of incubation with microorganisms forming Plant B biofilm, the viral viability was reduced on every material tested. When viruses were incubated in the presence of microorganisms forming Plant C biofilm, the viral viability was reduced on stainless steel or PVC by 46.88 – 207.04-fold, and viral infectivity was reduced by 146.41 – 374.53-fold, compared to viral initial titer. In contrast, after exposure to the biofilm from Plant A, there was no significant reduction in viral infectivity on any of the materials tested.

The results also showed that biofilm biovolume increased in response to the presence of the SARS-CoV-2 Delta variant. After incubation of viruses in the presence of each of the environmental biofilms for five days, the biovolume of all three biofilms increased 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 increased biovolume observed in all three biofilms after exposure to viruses may be attributable to the bacterial defense mechanisms in response to unfavorable environments.

Conclusion

The results showed that the SARS-CoV-2 Delta variant remained viable and infectious for up to five days after incubation with and without each environmental biofilm, on all surfaces tested. However, viral viability was significantly reduced after exposure to Plant B or Plant C biofilms. 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

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