Survival of nosocomial pathogenic bacteria at ambient temperature

Staphylococcus aureus and many gram-negative rods are prevalent nosocomial pathogens. The mechanisms by which these organisms persist and spread within the hospital environment have not been clearly defined. We found that these bacteria have an extraordinary capability for survival in the environment. The viabilities of staphylococcal and gram-negative (Escherichia coli and Pseudomonas aeruginosa) isolates were assessed on three environmental surfaces: a non-nutrient surface, a woven cotton fiber, and a blood protein coagulum. The bacteria were dried on these surfaces and quantitatively subcultured over six months. The viability was consistently higher on dried blood surfaces. Viability was next highest on cotton strings. For both of these environments, staphylococci appeared to lose viability between three and six months, while E. coli and P. aeruginosa survived longer. Survival on a clean non-nutrient surface (tubes alone) for all organisms was much briefer and did not extend beyond four weeks. Such extended survival on blood and fiber surfaces, as observed in part, explains the difficulty in controlling colonization of patients by and spread of these nosocomial pathogens.