Comparison of the efficacy of Rose Bengal and erythrosin in photodynamic therapy against Enterobacteriaceae.

The aim of this study was to evaluate the effects of the photosensitizers Rose Bengal and erythrosin combined with a light-emitting diode (LED) on Enterobacteriaceae. Twelve Enterobacteriaceae strains isolated from the oral cavities of patients undergoing prolonged antibiotic therapy, including three Escherichia coli, three Enterobacter cloacae, three Klebsiella oxytoca and three Klebsiella pneumoniae, were studied. An Enterobacteriaceae suspension (10(6) cells/ml) was prepared from each clinical strain isolated from the human oral cavity and subjected to the following treatments: LED and Rose Bengal, LED and erythrosin, LED and physiological solution, and physiological solution only as control. A blue LED unit (460 nm), and Rose Bengal and erythrosin at a concentration of 50 micromol/l were used. After incubation at 37 degrees C for 48 h, the number of colony-forming units (CFU) was calculated and subjected to analysis of variance (ANOVA). The Enterobacterial strains were sensitive to photodynamic therapy with Rose Bengal. There was a reduction of approximately 7.14 log10 for Enterobacter cloacae, 7.73 log10 for Escherichia coli, 6.76 log10 for Klebsiella pneumoniae and 7.21 log10 for Klebsiella oxytoca. However, photodynamic therapy using erythrosin did not reduce the numbers of CFUs per milliliter compared to the control group. The use of the LED alone had no toxic effect on the strain tested. The Enterobacteriaceae strains studied were sensitive to photodynamic therapy with Rose Bengal.

The effect of electron beam irradiation on the survival of Salmonella enterica serovar typhimurium and psychrotrophic bacteria on raw chicken breasts stored at four degrees celsius for fourteen days.

The effect of high-energy electron beam irradiation on the survival of Salmonella enterica serovar Typhimurium and psychrotrophic bacteria on commercial chicken breast meat was evaluated. Fresh chicken breast meat was purchased from a local poultry processor, inoculated with 8 log10 cfu/mL Salmonella, packaged in Styrofoam trays and over wrapped with a polyvinyl chloride film, and subjected to 0, 1, 2, or 3 kGy of irradiation. The packaged samples were stored at 4 degrees C and analyzed for Salmonella Typhimurium and psychrotrophic organisms at 0, 2, 4, 6, 8, 10, 12, and 14 d of storage. Direct plating and enrichment methods were used for S. Typhimurium analyses. The direct plating method revealed a 4 log reduction in Salmonella for chicken breasts inoculated and treated with 1, 2, or 3 kGy of irradiation. Psychrotrophic counts were conducted at 7 degrees C for 10 d and 25 degrees C for 5 d to determine the effect of incubation methods on the recovery of psychrotrophic organisms. The enrichment method resulted in the repair of injured Salmonella cells and an elevated Salmonella Typhimurium count for all irradiation dosages when compared with data reported for the direct plating method. In general, psychrotrophic counts increased as storage time increased. However, psychrotrophic counts decreased (P < 0.05) as the irradiation dosage increased.

Active components of intestinal bacteria for abdominal irradiation-induced inhibition of lung metastases.

We have previously reported that abdominal irradiation of mice inhibited lung metastases of a weakly immunogenic fibrosarcoma, and that transmigration after the irradiation of Enterobacter cloacae into mesenteric lymph nodes coincided with this phenomenon. In this paper, we show that Escherichia coli as well as E. cloacae reduce the number of metastatic lung colonies when these bacteria were intravenously injected into mice prior to the tumour cell challenge. The inhibition was caused not only by the administration of living bacteria but also by that of killed bacteria. Bacterial lipopolysaccharide (LPS), a component of membrane, replaced at least in part the effect of whole bacteria. Transfer of spleen cells from LPS-treated mice into intact recipients prominently inhibited metastatic development in the recipient mice. 'Cross transfer' between LPS high responders and LPS low responders suggested an indirect activity of transferred spleen cells. The antimetastatic activity of LPS depended on the tumour cell type; metastasis of fibrosarcomas was extensively inhibited by LPS irrespective of tumour immunogenicity while that of adenocarcinomas was only slightly inhibited. These results suggest that non-immunological mechanisms are involved in the antimetastatic activity of LPS.

The in vitro bactericidal effect of microwave energy on bacteria that cause prostatitis.

OBJECTIVES: We investigated the in vitro nonthermal effects of microwaves delivered from Prostatron 2.0 on Escherichia coli and Enterobacter cloacae. METHODS: The fingers of powder-free, sterile gloves were ligated, and bacterial solutions were transferred into the remaining area of the glove. The gloves were then sealed using silk ligatures. One set of gloves was subjected to the microwave treatment while another set was placed in a temperature-matched waterbath to act as control samples. The gloves containing the treatment group were taped around the probe, at the site where microwave energy exits the probe. During the treatment period, the temperatures from the urethral probe and the rectal probe were carefully monitored. RESULTS: The mean (+/-SD) energy delivered was 46.6 +/- 9.5 kJ (range 30.0 to 59.5) for the 10 trials on E. coli and colony counts in the experimental microwaved gloves decreased significantly compared with control samples (5.26 +/- 4.5 x 10(5) versus 10.16 +/- 9.3 x 10(5) CFU/mL, P = 0.02). For the experiments on E. cloacae the mean (+/-SD) energy applied was 38.5 +/- 12.5 kJ, and a significant decrease in colony counts of microwaved samples was also observed compared with controls (11.04 +/- 4.8 x 10(5) versus 20.08 +/- 10.1 x 10(5) CFU/mL, P = 0.004). CONCLUSIONS: Microwave energy, delivered from Prostatron 2.0, independent of heat production has an in vitro bactericidal effect on laboratory-cultured E. coli and E. cloacae.

Transient reduction in the tRNA 4-thiouridine content induced by ultraviolet A during post-irradiation growth in Enterobacter cloacae.

The influence of previous exposure to ultraviolet-A radiation (UVA) was studied on the susceptibility of Enterobacter cloacae to undergo the growth delay effect. Comparison of growth curves corresponding to irradiated and control cells showed that a previous treatment with UVA almost abolished the growth delay effect. UV absorption spectra of tRNA, and reverse phase HPLC analysis of hydrolysed tRNA, demonstrated a low content of 4-thiouridine in E. cloacae cells grown after UVA exposure at low doses. Since 4-thiouridine is the UVA target responsible for initiation of growth delay, this observation explained the influence of previous exposure to UVA on the susceptibility of this organism to undergo growth delay. A similar but weaker alteration was found when Escherichia coli was assayed. The results suggest that, in addition to cross-linking with cytidine residues, the content of 4-thiouridine in tRNA may be modified by UVA by an unknown mechanism.

Sublethal effects of ultraviolet A radiation on Enterobacter cloacae.

We report the sublethal effects of ultraviolet A (UVA) on Enterobacter cloacae in comparison with those produced in Escherichia coli. UVA-induced sublethal effects were investigated in either bacterial membrane and at tRNA level. Limited dependence on oxygen concentration for photoinduced inhibition of biochemical membrane functions and low levels of oxidative damage during the irradiation period were found in En. cloacae. On the other hand, ultraviolet spectroscopy and reversed-phase HPLC analysis of hydrolysed tRNA showed that radio induced damage to tRNA is similar in En. cloacae and E. coli. Nevertheless, growth delay induced by UVA in En. cloacae was shorter than that found in E. coli submitted to the same experimental conditions. A limited post-irradiation ppGpp accumulation and the absence of any influence of the membrane damage on the growth delay extent seem to be responsible for the shortness of this effect in En. cloacae. Most of the differences between En. cloacae and E. coli could be attributed to an increased ability of En. cloacae to overcome oxidative stress during UVA exposure.

Ultraviolet-B lethal damage on Pseudomonas aeruginosa.

Pseudomonas aeruginosa has shown an increased sensitivity compared with that of Escherichia coli and Enterobacter cloacae, when they were exposed to 0.4 kJ/m2 of ultraviolet-B radiation. The rapid decay in cell viability observed in Pseudomonas aeruginosa after the irradiation was influenced by factors such as culture media and the presence of pyocyanine during the irradiation. The radioinduced lethal damage could be prevented by photoreactivating treatment, indicating that pyrimidine dimer formation was the mechanism causing bacterial death. The results indicate that several environmental conditions may act as protective agents against ultraviolet-B-induced damage.

Enhancement of microbiological safety levels of aseptically admixed total parenteral nutrition solutions through low-dose gamma irradiation.

This study was undertaken to determine the effect of low-dose gamma irradiation on aseptically admixed total parenteral nutrition (TPN) solutions to which large inocula of three test bacterial species were added. Microbiological safety levels were quantified in terms of sterility assurance levels (SALs), indicating the probability of contamination occurring expressed as 10-n. The radiation sensitivity (D10 values) of test bacteria in TPN solutions inoculated with a series of bacteria recognized as common contaminants of these products, was determined. Attainable SALs of TPN solutions containing test bacteria were subsequently calculated from the D10 values. Results showed that a minimum absorbed radiation dose as low as 1.5 kGy improved the SAL of aseptically prepared TPN solutions from a probability value of 10(-3) to a value of less than 10(-8) for the microorganisms investigated. At an absorbed dose as high as 8.3 kGy, no measurable changes in amino acid, electrolyte, glucose and lipid components of the solutions were detected. These findings have important implications for the enhancement of microbiological safety levels of aseptically prepared intravenous fluids in general.

Further studies on RpoS in enterobacteria: identification of rpoS in Enterobacter cloacae and Kluyvera cryocrescens.

RpoS, the alternative sigma factor sigma(s), is important for bacterial survival under extreme conditions. Many enterobacteria are opportunistic human pathogens and their ability to survive in a changing environment could be an essential step for their virulence. To determine the presence of this gene in enteric bacteria, an Escherichia coli rpoS probe was constructed and used to detect the presence of this gene in different species. A gene homologous to rpoS was found in Citrobacter amalonaticus, Enterobacter cloacae, Klebsiella planticola, Kluyvera cryocrescens, Serratia rubidaea, Shigella sonnei, and Yersinia ruckeri. Providencia stuartii and Proteus vulgaris were the only tested enterobacteria that did not show any signal with the E. coli rpoS probe or that did not lead to amplification of an rpoS fragment using specific primers. The rpoS gene from E. cloacae and from K. cryocrescens was cloned and sequenced and a mutant allele was constructed in E. cloacae. Survival rates under different harsh conditions were followed in order to determine the effect of rpoS inactivation in exponential- and stationary-phase cells of both strains. E. cloacae rpoS mutants were more sensitive to extreme pH, high osmolarity, and high temperature than the wild-type.