ABSTRACT
In this study, we evaluated gas plasma surface sterilization methods in a specific sterilizer. We have introduced a new monitoring method using 0.4 microm pore size membranes, which in this study gave the information corresponding to 3000 exposed biological indicators per treatment cycle. This enabled us to compare the fraction of inoculates that showed no growth after exposure for 30 different locations in the chamber, and hereby identify weak and strong spots in the chamber with regard to sporicidal effect. Membranes were also used to expose a broad spectrum of soil bacteria for plasma treatment at four different conditions. The organisms were identified using PCR and sequencing. The test showed that Bacillus stearothermophilus spores were inactivated at the slowest rate among the tested microorganisms. Further alpha-proteobacteria (Gram negative) seemed more sensitive than the rest of the tested organisms. The microspot evaluation approach has been a most useful tool in the assessment of sterilization performance in sterilizers that do not have clear measurable parameters related to the sterilization.
Subject(s)
Sterilization , Biocompatible Materials , Geobacillus stearothermophilus , Hydrogen Peroxide , Peracetic Acid , Radio Waves , Spores, BacterialABSTRACT
Three strains of Gram-negative, aerobic, yellow-pigmented, chemo-organotrophic bacteria, motile by a polar flagellum, were isolated from the rhizosphere of spring barley (Hordeum vulgare L.) at a research field near Copenhagen, Denmark. The three strains, LJ79, LJ96T and LJ99, formed visible colonies on one-tenth-strength tryptic soy broth supplemented with agar (1/10 TSBA) after incubation for 6 days at 15 degrees C. The strains hydrolysed starch, casein (skimmed milk), gelatin and various pentoses and hexoses and grew on MacConkey agar and full-strength TSBA. Growth on 1/10 TSBA occurred at 4-30 degrees C, pH 6-9 and 0-3 % (w/v) NaCl. The strains had identical 16S rRNA gene sequences and ERIC (enterobacterial repetitive intergenic consensus sequence) fingerprint profiles, but could be differentiated by their RAPD (random amplified polymorphic DNA) fingerprint patterns. Strain LJ96(T) had a DNA G+C content of 64.3 mol% and the major fatty acids were 15 : 0 iso (23.4 %), 17 : 1 iso omega9c (25.5 %) and 17 : 0 iso (18.1 %). Phylogenetic analysis of the 16S rRNA gene sequences of the three strains showed 96 % sequence similarity to Rhodanobacter lindaniclasticus LMG 18385T, 95 % to Frateuria aurantia DSM 6220T and 96 % to Fulvimonas soli LMG 19981T. Using LJ96T DNA as probe, DNA-DNA hybridizations documented the relationship of the three strains to a single species (87.4-98.7 % relatedness) and showed less than 30 % relatedness to Frateuria aurantia DSM 6220T and Fulvimonas soli DSM 14263T. Rhodanobacter lindaniclasticus LMG 18385T is not extant and the strain not available from any public strain collections, thus DNA-DNA hybridization could not include this strain. On the basis of genotypic and phenotypic characteristics, the three yellow-pigmented strains could also be differentiated from Frateuria aurantia, Fulvimonas soli and Rhodanobacter lindaniclasticus. The name Luteibacter rhizovicinus gen. nov., sp. nov. is proposed, with the type strain LJ96T (=DSM 16549T=ATCC BAA-1015T).
