Standard antimicrobial susceptibility tests are performed in vitro under normal room oxygen conditions to predict the in vivo effectiveness of antimicrobial therapy. The aim of this study was to conduct a comprehensive analysis of the effect of different oxygen levels on the antibiotic susceptibility of two strains of Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae. It was found that anoxic conditions caused reduced sensitivity of bacteria to aminoglycoside antibiotics in four of six bacteria used in the study. In addition, oxygen limitation decreased the susceptibility of P. aeruginosa strains and K. pneumoniae strains to piperacillin/tazobactam and azithromycin, respectively. In contrast, five of six bacteria became more susceptible to tetracycline antibiotics under oxygen-limiting conditions. Our data highlight the importance of considering the potential in vivo oxygen levels within the infection site when setting susceptibility breakpoints for evaluating the therapeutic potential of a drug and its effect on antibiotic sensitivity of the pathogen.

Endospores have the ability to withstand extreme temperature, desiccation, ultraviolet radiation and chemicals which make them a threat to the food and healthcare industry. Green tea polyphenols (GTP), contain anti-microbial and anti-spore properties but not stable. In this study, two modified lipophilic green tea polyphenols, epigallocatechin-3-gallate-sterate (EGCG-S) and crude lipophilic green tea polyphenols (LTP), were used to compare their anti-spore effect with EGCG and crude GTP. Purified endospores from Bacillus cereus (B. cereus), B. megaterium and B. subtilis were treated with 1% or 5% of four tea polyphenols. Log reduction showed colony forming units (CFU) reduced significantly in all treated samples, ranging from 1.27 to 4.31 with no survivals (CFU = 0) in four samples (P < 0.05). Average percentage of inhibition for these polyphenols treatment ranged from 91.68% to 100%. The EGCG-S and LTP have equal or better anti-spore activities compared with EGCG and GTP.EGCG-S and LTP were further used to carry out time course study on B. cereus.The results indicated that 15 min of treatment of 1% and 5% LTP and EGCG-S are able to inhibit 98.7% to 100% of germination. Transmission and scanning electron microscopy studies showed that EGCG-S caused surface disruption and damaged spores structural integrity. EGCG-S and LTP are stable anti-spore agents may aid in preventing food and beverage spoilage caused by sporeforming bacteria as well as preventing contamination in the medical industry.