Effects of Ultraviolet Radiation on the Gram-positive marine bacterium Microbacterium maritypicum.

Although extensive information is available on the effect ultraviolet (UV) radiation has on Gram-negative marine bacteria, there is a scarcity of data concerning UV radiation and Gram-positive marine bacteria. The focus of this paper is on Microbacterium maritypicum, with the Gram-negative Vibrio natriegens being used as a standard of comparison. M. maritypicum exhibited growth over a NaCl range of 0-1000 mM: , with optimum growth occurring between 0 and 400 mM: NaCl. In contrast, V. natriegens grew over a NaCl span of 250-1000 mM: , with best growth being observed between 250 and 600 mM: NaCl. UV radiation experiments were done using the medium with 250 mM: NaCl. For solar (UV-A and B) radiation and log-phase cells, M. maritypicum was determined to be three times more resistant than V. natriegens. For germicidal (UV-C) radiation, the pattern of resistance of the log-phase cells to the lethal effects of the radiation was even more pronounced, with the Gram-positive bacterium being more than 12 to 13 times more resistant. Similar data to the solar and germicidal log-phase UV kill curves were obtained for stationary-phase cells of both organisms. Photoreactivation was observed for both types of cells exposed to UV-C but none for cells treated with UV-A and B. When log phase cells of M.maritypicum were grown at 0.0 and 0.6 M: NaCl and exposed to UV-C radiation, no difference in survivorship patterns was noted from that of 0.25 M: NaCl grown cells. Although this study has only focused on two marine bacteria, our results indicate that the Gram-positive M. maritypicum could have a built-in advantage for survival in some marine ecosystems.

The effects of salt concentration and growth phase on MRSA solar and germicidal ultraviolet radiation resistance.

The extensive use of antimicrobial drugs has led to the widespread emergence of resistant bacterial strains. One such organism, methicillin-resistant Staphylococcus aureus, is now found extensively in both healthcare facilities and diverse community settings such as households, correctional facilities, and athletic teams. The importance of ultraviolet radiation as an adjunctive therapy to reduce bioburden and improve wound status in patients has been documented. An in vitro study to assess the effects of different types of ultraviolet radiation on antibiotic-resistant strains was conducted to provide information that will aid in the development of rational UV irradiation medical protocols. Methicillin-resistant Staphylococcus aureus was found to be sensitive to both germicidal (ultraviolet C) and solar (ultraviolet A and B) ultraviolet radiation (ultraviolet C substantially more lethal). For both types of ultraviolet radiation, as the medium concentration of sodium chloride increased, the methicillin-resistant Staphylococcus aureus cells exhibited increased sensitivity. It also was shown for both types of ultraviolet radiation that kill curves were comparable for log and stationary phase methicillin-resistant Staphylococcus aureus cells. Photoreactivation was observed for Pseudomonas aeruginosa PAO-1 but not for methicillin-resistant Staphylococcus aureus when ultraviolet C was applied to log phase cells. The Gram-negative Pseudomonas aeruginosa PAO-1 was considerably more sensitive than the Gram-positive methicillin-resistant Staphylococcus aureus to ultraviolet C radiation. The experiments reveal that medium composition exerts a substantial effect on methicillin-resistant Staphylococcus aureus ultraviolet resistance and that this species lacks photoreactivation capacity. This suggests that in a clinical setting, eradication of the bacterium may be achieved at far lower doses of ultraviolet radiation than would be indicated by treatment protocols that do not account for ionic conditions.