Airborne gram-negative bacterial flora in animal houses.

The concentration and the species composition of airborne gram-negative bacteria were studied in four cattle houses, one pig house and one poultry barn. On average only between 0.02 and 5.2% of the total number of culturable aerobic bacteria were identified as gram-negative bacteria. Obligate anaerobic gram-negative bacteria were not isolated at all. In the airborne gram-negative bacterial flora the following bacterial families dominated: the Enterobacteriaceae, the Pseudomonadaceae and the Neisseriaceae. Within the family of the Enterobacteriaceae the species Escherichia coli and Enterobacter agglomerans were predominant. In animal houses using straw as bedding material Ent. agglomerans was most frequent, whereas in animal houses without litter E. coli was mainly found. Airborne Neisseriaceae were isolated very frequently in cow barns with Acinetobacter lowffii as the primary species. Airborne Pseudomonadaceae were found in high concentrations during periods of high air humidity. The results presented may also give some indications on the origin and sources of airborne endotoxins in animal housing.