Gram-Negative, Oxidase-Positive Bacteria in Rainwater and Wind Samples

Gram-negative, rod-shaped, oxidase-positive bacteria, such as Aeromonas and Pseduomonas, are widespread in the environment. Aeromonas are emerging human pathogens associated with extraintestinal and opportunistic infections. Though there are various biological particles known in the atmosphere, these microbial communities are poorly characterized. Bacteria have the ability to remain suspended in the air for prolonged periods of time and can be transmitted through both airborne and droplet means. This study aimed to isolate Aeromonas and other similar bacteria from samples from the troposphere in order to learn more about the distribution of these organisms. Eleven precipitation and wind samples were aseptically collected in Abilene, Texas, and plated onto Aeromonas Blue Medium plates with and without ampicillin. The 16S rDNA sequences were amplified from 28 Gram-negative, oxidase-positive isolates. The analyzed sequences showed that none of the isolates belonged to the genus Aeromonas, but did include Pseudomonas, Sphingomonas, Massilia, Naxibacter, Paracoccus, Novosphingobium, and Mesorhizobium, giving clues to the distribution of these organisms. Furthermore, six isolates appeared to be novel species of bacteria, and several more were uncultured before this study.