Although ROS is known to cause DNA damage, it also attacks cell

membranes through formation of lipoperoxide (16,17). To explore the possibility that damage to DNA is responsible for the high sensitivity of V. vulnificus to ROS, we examined cytotoxic agents known to be highly specific for DNA, namely, UV, mitomycin C, and methyl methane sulfonate, for their killing effect on V. vulnificus and E. coli. We found that all of these agents kill V. vulnificus much more efficiently than they do E. coli (Fig. 4). Thus, we showed that cells of V. vulnificus are more susceptible to DNA-damaging agents, including Silmitasertib solubility dmso ROS, than are those of E. coli. The primary aim of the present study was to substantiate the remarkable but solitary report of successful HBO treatment of an advanced case of severe V. vulnificus infection (7). Our findings described herein seem to have achieved this purpose. First, we clearly demonstrated the efficacy of HBO treatment alone in a mouse footpad infection model, a beneficial effect being present without chemotherapeutic or surgical

MLN8237 cell line interventions (Fig. 1). In addition, HBO brought about marked viability loss in cells of V. vulnificus in vitro, whereas we did not observe such an effect with E. coli (Fig. 2a). These results support the notion that HBO is an effective therapy for human infections caused by V. vulnificus. However, we wish to emphasize that our observations do not necessarily encourage the use of HBO alone in the treatment of human cases. Rather, HBO therapy should be regarded as a powerful adjunct modality, not only for clostridial gas gangrene (1,2) but also for severe V. vulnificus infection. However, we should be alert for oxygen toxicity, a well-known side effect of HBO, when using HBO against this infection. Two different mechanisms have so far been proposed for the effectiveness of HBO in the treatment of infectious diseases. One is the direct action of oxygen on the offending microbes and the

other is the indirect effect of increased amounts of dissolved oxygen in plasma and infected tissue (1, 2). As to the direct effect of HBO on bacteria, its in vitro bactericidal activity against the obligate anaerobe Clostridium perfringens has been well established (9, 18). Against facultative bacteria, HBO appears to be mostly bacteriostatic as so far studied (19–21), with the exceptions of its bactericidal effect on Vibrio cholerae (comma) (19) and Pseudomonas Calpain aeruginosa (20). On the other hand, the indirect mechanism may include increased microbicidal activity of leucocytes (22) as well as the anti-inflammatory and anti-edemic effects of oxygen, which would help accelerate wound healing (23). One of the interesting aspects of the present study is the mechanism by which the facultative bacterium V. vulnificus behaves as an oxygen-sensitive organism under HBO conditions. Possibly, there is a difference between V. vulnificus and E. coli in oxygen tolerance, which is not manifest in the air, but becomes evident under HBO.