[abstract] Does hyperbaric oxygen act as a natural antibiotic? Semi-quantitative analysis of the effect of different oxygen tensions on selected bacteria

Abstract

Introduction/Background: The aim of this experiment was to investigate the hyperbaric oxygen capability to act as a natural antibiotic, testing cidal and cytostatic effects on some selected ATCC (American-Type-Culture- Collection) bacteria. Materials and methods: We prepared a 2ml tryptose broth suspension of S Aureus (STAU)/ATCC-29213, E Coli (ESCO)/ATCC-25922, P Aeruginosa (PSAE)/ ATCC-27853, E Faecalis (ENFA)/ATCC-29212 and kept these preparations at 37°C for 24 hours. From these suspensions we prepared four sets (12 BD-FalconTubes each; GroupA1, A2 ,B, C) of a three-step 1:100 serial dilution (4950μl of 0.45%NaCl and 5μl of bacterial suspension) for any ATC -group to be tested in our Experimental Hyperbaric Chamber. Group A1 has been exposed to 100% O2 at 2.8ATA x 75 minutes, Group A2 to 100%O2 at 2.5ATA x 75 minutes, Group B to 21% O2 at 2.8ATAx75 minutes and Group C to 21% O2 at 1.0ATA x 75 minutes Refrigeration was applied during the 10-minute journey from the laboratory to the chamber and back. A total of 48 chocolate-agar plates of manually streaked bacteria were then incubated, at the end of the test at 37°C x 24 hours. Results: [STAU, ESCO, PSAE, ENFA]: No difference between A1 and B groups. 1st dilution (the higher content in bacteria): - [STAU,PSAE,ENFA]: no difference between the four groups (A1, A2, B, C), [10^6cfu/ml], - [ESCO]: no difference between the four groups (A1, A2, B, C), [10^5cfu/ml] 2nd dilution: - [PSAE,ENFA]: no difference between the four groups (A1, A2, B, C), [10^5cfu/ml] - [STAU,ESCO]: A1, A2, B groups showed 10^3cfu/ml, C group 10^4cfu/ml 3rd dilution: - [ESCO]: no difference between the four groups (A1, A2, B, C), [10^3cfu/ml] - [PSAE]: A1, B groups showed 10^3cfu/ml, A2 group 10^4 cfu/ml, C group 10^5cfu/ml - [STAU,ENFA]: no growth in A1,B groups, while A2 and C groups 10^3cfu/ml Summary/Conclusions: Apart specific differences due to the characteristics of each bacteria group, the cidal and cytostatic effects are more evident as the pressure increases and are not dependent on the O2 tension applied.