D.E.S. Stewart-Tull

Heat transfer analysis of Staphylococcus aureus on stainless steel with microwave radiation

Staphylococcus aureus (NCTC 6571; Oxford strain) on stainless steel discs was exposed to microwave radiation at 2450 MHz and up to 800 W. Cell viability was reduced as the exposure time increased, with complete bacterial inactivation at 110 s, attaining a temperature of 61·4 °C. The low rate of temperature rise, RT, of the bacterial suspension as compared with sterile distilled water or nutrient broth suggests a significant influence of the microwave sterilization efficacy on the thermal properties of the micro‐organisms. The heat transfer kinetics of thermal microwave irradiation suggest that the micro‐organism has a power density at least 51‐fold more than its surrounding liquid suspension. When the inoculum on the stainless steel disc was subjected to microwave radiation, heat conduction from the stainless steel to the inoculum was the cause of bacteriostasis with power absorbed at 23·8 W for stainless steel and 0·16 W for the bacteria‐liquid medium. This report shows that the microwave killing pattern of Staph. aureus on stainless steel was mainly due to heat transfer from the stainless steel substrate and very little direct energy was absorbed from the microwaves.

Bactericidal action of high-power Nd:YAG laser light on Escherichia coli in saline suspension

Infra‐red light (1064 nm) from a high‐power Nd:YAG laser caused more than 90% loss of viability of Escherichia coli during exposures that raised the temperature of PBS suspensions of the bacteria to 50 °C in a thermocouple‐equipped cuvette. In contrast, there was minimal loss of viability after heating the same suspensions to 50 °C in a water‐bath, or in a PCR thermal cycler. The mechanism of laser killing at 50 °C was explored by differential scanning calorimetry, by laser treatment of transparent and turbid bacterial suspensions, and by optical absorbancy studies of E. coli suspensions at 1064 nm. Taken together, the data suggested that the bactericidal action of Nd:YAG laser light at 50 °C was due partly to thermal heating and partly to an additional, as yet undefined, mechanism. Scanning electron microscopy revealed localized areas of surface damage on laser‐exposed E. coli cells.

Inactivation of bacteria and yeasts on agar surfaces with high power Nd : YAG laser light

G.D. WARD, I.A. WATSON, D.E.S. STEWART‐TULL, A.C. WARDLAW AND C.R. CHATWIN. 1996. Near infrared light from a high‐powered, 1064 nm, Neodymium : Yttrium Aluminium Garnet (Nd : YAG) laser killed a variety of Gram‐positive and Gramnegative bacteria and two yeasts, lawned on nutrient agar plates. A beam (crosssectional area, 1.65 cm2) of laser light was delivered in 10 J, 8 ms pulses at 10 Hz, in a series of exposure times. For each microbial species, a dose/response curve was obtained of area of inactivation vs energy density (J cm−2). The energy density that gave an inactivation area (IA) equal to 50% of the beam area was designated the IA50‐value and was plotted together with its 95% confidence limits. Average IA50‐values were all within a threefold range and varied from 1768 J cm−2 for Serratia marcescens to 4489 J cm−2 for vegetative cells of Bacillus stearothermophilus. There were no systematic differences in sensitivity attributable to cell shape, size, pigmentation or Gram reaction. At the lowest energy densities where inactivation was achieved for the majority of organisms (around 2000 J cm−2), no effect was observed on the nutrient agar surface, but as the energy density was increased, a depression in the agar surface was formed, followed by localized melting of the agar.

The Use of Adjuvants in Experimental Vaccines

As mentioned in Chapter 9 , Freunds complete adjuvant (FCA), produced by the Statens Seruminstitut (Copenhagen, Denmark), was chosen as the standard adjuvant preparation because of its extensive use in experimental vaccines in animals, its strong adjuvant effect, and the considerable literature describing its activity. The combination of mineral oil (Bayol 55) and dead mycobacterial organisms produces a specific cellular reaction in experimental animals. The mycobacteria in FCA stimulate the formation of epithelioid macrophage cells and also the maturation of plasmablasts to plasma cells. The effect was greater when the oil and mycobacterial fraction were combined. Numerous studies have shown that the oil emulsion was responsible for the retention of the antigen at the site of inoculation. This depot provides a slow and prolonged antigenic stimulus to antibody-forming cells. FCA stimulates active humoral and cell-mediated immune responses but there may be concomitant adverse side-effects because of the reactogenicity of some types of mineral oil, particularly the formation of the epithelioid macrophage granuloma at the site of injection and local ulceration when the injection is given subcutaneously. In addition, other contraindications have been recorded, e.g., pyrogenicity, stimulation of experimental autoimmune diseases, and adjuvani. arthritis (reviewed in detail by Stewart-Tull[1, 2]).

Freund’s Complete and Incomplete Adjuvants, Preparation, and Quality Control Standards for Experimental Laboratory Animals Use

Quality control and quality assurance procedures are discussed for the agreed benchmark standard Freunds complete adjuvant (FCA). In addition, the use of the incomplete adjuvant (FIA) in the preparation of antisera is discussed. A major problem is the use of a safe and suitable mineral oil in FCA and FIA; manufacturers should provide infra-red spectra and gas liquid chromatography analyses. A range of safety tests, toxicity, pyrogenicity and endotoxin assays and advice on practical procedures for the use of these adjuvants are described.

Bactericidal effects of high-power Nd:YAG laser radiation on Staphylococcus aureus

The effect of laser radiation on Staphylococcus aureus 6571 (Oxford strain) was studied with high-power Nd:YAG laser radiation between 50 and 300 W. A range of laser pulse repetition frequencies (PRF) from 5 to 30 Hz, with a combination of pulse energies from 2 to 30 J were applied; this covered a range of energy densities from 800 to . The area of inactivation of S. aureus, lawned on nutrient agar plates, was quantified as a function of energy density and exposure time. The shortest exposure time which produced an area of inactivation equal to 50% of the beam area was achieved at a PRF of 30 Hz, pulse energy of 10 J, and with an exposure time of 10.75 s; this was equivalent to an applied energy density of . No bacterial inactivation was observed at relatively low-power settings for PRF, pulse energies and exposure time of: 20 Hz, 3 J and 34 s; 25 Hz, 2 J and 45 s and 30 Hz, 2 J and 35 s, respectively. These results shows that pulse energy, PRF and exposure time are important criteria when considering inactivation of micro-organisms by laser radiation.

Comparative bactericidal activities of lasers operating at seven different wavelengths

Seven laser instruments, delivering radiation at a selection of wavelengths in the range of 0.355 to 118 mm, were investigated for their ability to kill Escherichia coli as a lawn of the bacteria on nutrient agar culture plates. Easily the most effective was a 600-W CO2 laser operating at 10.6 mm, which produced 1.2- cm2 circular zones of sterilization at energy densities of around 8 J cm22 in a 30-msec exposure. Circular zones with an area of 0.7 cm2 were achieved with 200 W from a Nd:YAG laser delivering 8-ms, 10-J pulses of 1.06 mm radiation at 20 Hz. The exposure time, however, was 16 s and the energy density (1940 J cm22) was more than 240 times higher than with the CO2 laser. This difference is believed to be partly due to the much higher absorption of radiation at 10.6 mm than at 1.06 mm, by water in the bacterial cells and the surrounding medium (nutrient agar). Sterilization was observed after exposure to frequency-tripled Nd:YAG laser radiation at 355 nm (3.5 J cm22). Lasers that were totally ineffective in killing Escherichia coli (with their wavelength and maximum energy densities tested) were the far infrared laser (118 mm; 7.96 J cm22), the laser diode array (0.81 mm; 13,750 J cm22), and the argon ion laser (0.488 mm; 2210 J cm22). The speed at which laser sterilization can be achieved is particularly attractive to the medical and food industries.

Acellular pertussis vaccine prepared by a simple extraction and toxoiding procedure

An extract containing predominantly pertussis toxin (PT) and filamentous haemagglutinin (FHa) was obtained from culture supernates of Bordetella pertussis by a single-step procedure using dye-ligand chromatography. The pathophysiological activities associated with the pertussis toxin component were removed by treatment with a water-soluble carbodiimide. The product was stable at 4 degrees C, was non-toxic for mice, induced high levels of IgG antibodies to both PT and FHa in vaccinated animals as judged by ELISA, and protected mice from intracerebral and intranasal challenge with B. pertussis.

Immunostimulation with peptidoglycan or its synthetic derivatives

For a time during the 1960s the emphasis shifted from prevention to treatment of infectious diseases. The resurgence of interest in vaccine development arose because of the realization that continued antibiotic therapy brought its own problems. For example, a leprosy patient treated with rifampicin for long periods gradually developed a secondary resistance to the drug. This problem was exacerbated when a close relative contracted a leprosy infection which did not respond to rifampicin treatment; an example of primary drug resistance [1].

Effect of laser and environmental parameters on reducing microbial contamination of stainless steel surfaces with Nd:YAG laser irradiation

Aims:  The effect of laser (pulse repetition frequency, pulse energy and exposure time) and environmental parameters (pH, NaCl concentration and wet or dry samples) of Nd:YAG laser decontamination of stainless steel inoculated with Escherichia coli, Staphylococcus aureus and Listeria monocytogenes was investigated.