RESUMEN
A radiation-resistant bacterial isolate from gamma-radiation-processed (5 kGy) semidried prawns was identified as a new strain of Macrococcus caseolyticus and was designated as M. caseolyticus (A) on the basis of morphological and biochemical characterization and 16S rRNA sequencing. DNA-DNA hybridization studies with M. caseolyticus DSM 20597(T) further confirmed the isolate as M. caseolyticus. Major fatty acids present in M. caseolyticus (A) were C14:0, C16:1ω11c, and C18:1ω9c, whereas C15:0anteiso, C16:0iso, and C18:0iso were absent. The closest match for the isolate, as per fatty acid methyl ester analysis, was M. caseolyticus DSM 20597(T). However, the similarity index was significantly low (0.112), which indicates that the isolate could be a new strain of M. caseolyticus. The decimal reduction dose (D10) for M. caseolyticus (A), M. caseolyticus JCSC5402, and Staphylococcus aureus MTCC96 was 1.18, 0.607, and 0.19 kGy, respectively. This is the first report on radiation resistance of M. caseolyticus. Macrococcus caseolyticus (A) is more resistant to gamma and UV radiation stress than are M. caseolyticus JCSC5402 and S. aureus MTCC96; however, it is sensitive to heat as well as desiccation stress.
Asunto(s)
Crustáceos/microbiología , Mariscos/microbiología , Staphylococcaceae/aislamiento & purificación , Staphylococcaceae/efectos de la radiación , Animales , Crustáceos/efectos de la radiación , Ácidos Grasos/análisis , Ácidos Grasos/metabolismo , Irradiación de Alimentos , Rayos gamma , Filogenia , Mariscos/efectos de la radiación , Staphylococcaceae/genética , Staphylococcaceae/metabolismoRESUMEN
Light activation of photosensitizing dyes in presence of molecular oxygen generates highly cytotoxic reactive oxygen species leading to cell inactivation. Nucleic acids are molecular targets of this photodynamic action but not considered the main cause of cell death. The in vivo effect of the photodynamic process on the intracellular nucleic acid content of Escherichia coli and Staphylococcus warneri was evaluated herein. Two cationic porphyrins (Tetra-Py(+)-Me and Tri-Py(+)-Me-PF) were used to photoinactivate E. coli (5.0µM; 10(8)cellsmL(-1)) and S. warneri (0.5µM; 10(8)cellsmL(-1)) upon white light irradiation at 4.0mWcm(-2) for 270min and 40min, respectively. Total nucleic acids were extracted from photosensitized bacteria after different times of irradiation and analyzed by agarose gel electrophoresis. The double-stranded DNA was quantified by fluorimetry and the porphyrin binding to bacteria was determined by spectrofluorimetry. E. coli was completely photoinactivated with both porphyrins (5.0µM), whereas S. warneri was only completely inactivated by Tri-Py(+)-Me-PF (0.5µM). The hierarchy of nucleic acid changes in E. coli was in the order: 23S rRNA>16S rRNA>genomic DNA. The nucleic acids of S. warneri were extensively reduced after 5min with Tri-Py(+)-Me-PF but almost unchanged with Tetra-Py(+)-Me after 40min of irradiation. The amount of Tri-Py(+)-Me-PF bound to E. coli after washing the cells is higher than Tetra-Py(+)-Me and the opposite was observed for S. warneri. The binding capacity of the photosensitizers is not directly related to the PDI efficiency or nucleic acid reduction and this reduction occurs in parallel with the decrease of surviving cells.