Occupational exposure to bacterial single cell protein induces inflammation in lung and blood

Abstract

Bacterial single cell protein (BSCP) is used as a protein enrichment in livestock and fish feed, and is extracted from dried bacterial mass. In the production of BSCP, workers are exposed to organic dust containing high levels of endotoxins that may induce acute airway inflammation. However, the long term effect on the airways of such exposure is not known, and we have examined inflammatory markers in induced sputum and blood among BSCP exposed workers. We included 21 non-smoking production workers (age 31–42 (range; mean 35)) without respiratory symptoms and 21 healthy non-exposed references (age 21–52 (range; mean 34)). Airborne endotoxin concentrations were measured, and induced sputum samples and blood samples were collected from the workers and non-exposed references. The airborne endotoxin concentration measured in inhaled air during the work shift was 430 EU/m³ (50–2000) (median (range)). The percentage of neutrophils in induced sputum was 79% (66–93) (median (25th–75th percentiles)) and 31% (25–45) (p < 0.001) for operators and references, respectively. Protein analysis in induced sputum supernatant showed significantly elevated levels of interleukins IL-1β and IL-12 (p < 0.05), while blood analysis showed significantly elevated levels of PDGF-BB (platelet-derived growth factor-BB) and RANTES (regulated upon activation normally T cell expressed and secreted) (p < 0.05). Workers exposed to BSCP had an airway inflammation characterized by a high level of neutrophils. However, only a few cytokines were elevated in lung and blood, which could imply low inflammatory activity suggestive of possible adaptation mechanisms due to daily exposure to BSCP, or that the inflammation reaction was a dose-related response occurring at higher levels.

Acknowledgments

Anne Pharo is acknowledged for excellent laboratory technical assistance. We thank Norferm for their cooperation and all the workers taking part in this study. Financial support was kindly provided by Norferm, the Research Council of Norway, and the Working Environmental Fund granted by the Confederation of Norwegian Enterprise.

Declaration of interest: LIBS has been reimbursed by Norferm DA, the manufacturer of BSCP, for travel expenses. WE has received financial support from Norferm DA for the exposure study.