Microbiological Contamination Risk in SCUBA Diving Cylinders: An Experimental Study.

Introduction: The microbiological safety of compressed air in SCUBA diving cylinders is a crucial yet often overlooked aspect of diving safety. Despite regular maintenance, microbial contamination can cause respiratory illnesses, especially during the air-filling procedure. Given the impact of temperature increases on bacterial viability, this study evaluates the survival of Streptococcus pneumoniae (S. pneumoniae) and Pseudomonas aeruginosa (P. aeruginosa) within diving SCUBA cylinders during and after the air-filling process. Methods: A mixture of Streptococcus pneumoniae (ATCC 49619) and P. aeruginosa (ATCC 27853) was prepared using 25 ml of each bacterial strain at a 0.5 McFarland standard to contaminate the clean scuba cylinder. The mixture was poured into the cylinder to ensure full surface contact. The scuba cylinder was filled according to standard procedures, with temperature monitored at regular intervals using a precise thermometer. Measurements were repeated at increments of 10 bar until the cylinder reached 200 bar. After all air was released, 50 ml of sterile saline was poured into the cylinder to collect any remaining contamination. Swab samples were taken from the cylinder's gas outlet. Microbiological analysis was performed using filter, saline, and swab samples. Results: Growth of S. pneumoniae was observed on filters. Bacterial growth was detected on filters as follows: 1 CFU on the first filter, 3 CFU on the second, 2 CFU on the third, 2 CFU on the fourth, and 3 CFU on the fifth filter. Saline collected from the cylinder exhibited a bacterial count of 200 CFU/ml, with growth of S. pneumoniae detected. The swab sample taken from the gas inlet of the cylinder also revealed the presence of S. pneumoniae. However, no growth of P. aeruginosa was observed in any of the collected samples. Discussion: According to the results, S. pneumoniae can withstand the compressed air-filling process in diving cylinders, but P. aeruginosa cannot, possibly because of its increased sensitivity to pressure. Though no clinical cases of infection from cylinder air have been reported, these findings highlight how crucial it is to use additional sterilizing procedures in addition to temperature and pressure control to guarantee the microbiological safety of scuba diving equipment.