Snow angels - the microbiology of freshly fallen snow: implications for immunocompromised patients

The frequency of seasonal snowfall results in the transient covering of gardens/amenity sites/open public spaces, which encourages recreational interaction mainly with children. No data is available demonstrating the microbiological composition of such fallen snow and therefore a study was undertaken to examine the microbiology of snow from 37 sites, estimating (i) total viable count (TVC), (ii) identification of bacteria, and (iii) the presence of Pseudomonas aeruginosa. Mean TVC count of 8.3 colony-forming units (cfu)/ml snow melt water, 51.7 cfu/ml, 865 cfu/ml and 2,197 cfu/ml, was obtained for public amenity sites, domestic gardens, public open spaces and melting snow from public footpaths, respectively. No bacterial organisms (<10 cfu/ml) were detected in 5/14 (35.7%) open public spaces, 2/5 (40%) amenity sites and in 1/10 (10%) domestic gardens. Pseudomonas aeruginosa was not detected from any snow sample examined. Bacterial diversity consisted of 15 bacterial species (11 Gram-positive/four Gram-negative). The six Gram-positive genera identified from snow were Actinomyces, Bacillus, Brevibacillus, Micrococcus, Staphylococcus and Streptococcus. The four Gram-negative genera identified were Enterobacter, Pantoea, Pseudomonas and Xanthomonas. Bacillus licheniformis was the most commonly isolated organism from snow; it was isolated from every snow type. Snow may contain a diverse range of bacteria, many of which are capable of causing human infections.