Airborne Pseudomonas species in Healthcare Facilities in a Tropical Setting

Pseudomonas species are nosocomial pathogens that are capable of colonising moist surfaces. Little is known whether they get airborne. The study was undertaken to 1) characterise Gram-negative bacteria in indoor air of different hospitals; 2) characterise Pseudomonas sp. by phenotypic and genotypic methods; 3) determine homology of study environmental Pseudomonas isolates and correlate with established pathogenic strains' sequences.

Samples were collected (duplicates) at the time of peak activity, by exposing media-containing plates (blood agar and MacConkey agar) for 30 minutes. Plates were incubated aerobically at 37°C for 24-48 h. Microorganisms were identified by standard microbiological procedures. Polymerase chain reaction targeting Pseudomonas specific 16S-rDNA was performed to obtain 618 bp amplicons. Representative strains were sequenced and compared with established sequences of pathogenic Pseudomonas strains from existing database for evolutionary details.

A total of six hospitals comprising 13 wards, 7 intensive care units (ICUs) and 8 operating rooms (ORs) were sampled over one-year period. A variety of Gram-negative bacilli were isolated, of which Pseudomonas sp. was predominant. Indoor air of 10 wards (77%), 5 ICUs (71%), 4 ORs (50%) harboured Pseudomonas. Similar strains of Pseudomonas stutzeri were isolated from indoor air of different hospitals. Phylogenetic analysis showed these environmental strains to be closely related to the pathogenic Pseudomonas stutzeri strain from the GenBank database.

Isolation of airborne Pseudomonas stutzeri from different hospitals suggests a possible new reservoir in the hospital environment, indicating the need for appropriate engineering control measures to contain the spread of these nosocomial agents.