Heat transfer analysis of <i>Staphylococcus aureus</i> on stainless steel with microwave radiation

&lt;i&gt;Staphylococcus aureus&lt;/i&gt; (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, &lt;i&gt;R&lt;sub&gt;T&lt;/sub&gt;&lt;/i&gt;, 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 &lt;i&gt;Staph. Aureus&lt;/i&gt; on stainless steel was mainly due to heat transfer from the stainless steel substrate and very little direct energy was absorbed from the microwaves

Virulence spectra of typed strains of Campylobacter jejuni from different sources: a blinded in vivo study

&lt;i&gt;Campylobacter jejuni&lt;/i&gt; is a major cause of human diarrhoeal disease, but specific virulence mechanisms have not been well defined. The aims of the present blinded study were to measure and compare the &lt;i&gt;in vivo&lt;/i&gt; properties of 40 serotyped, biotyped and genotyped &lt;i&gt;C. jejuni&lt;/i&gt; isolates from different sources and genetic makeup. An 11-day-old chick embryo lethality assay, which measured embryo deaths and total viable bacteria over 72 h following inoculation of bacteria into the chorioallantoic membrane, revealed a spectrum of activity within the &lt;i&gt;C. jejuni&lt;/i&gt; strains. Human and chicken isolates showed similar high virulence values for embryo deaths while the virulence of the bovine isolates was less pronounced. A one-way ANOVA comparison between the capacity of the strains to kill the chick embryos after 24 h with cytotoxicity towards cultured CaCo-2 cells was significant (&lt;i&gt;P&lt;/i&gt;=0.025). After inoculation with a &lt;i&gt;Campylobacter&lt;/i&gt; strain, mouse ligated ileal loops were examined histologically and revealed degrees of villous atrophy, abnormal mucosa, dilation of the lumen, congestion and blood in lumen, depending on the isolate examined. A total pathology score', derived for each &lt;i&gt;C. jejuni&lt;/i&gt; strain after grading the pathology features for degree of severity, showed no apparent relationship with the source of isolation. Some relationship was found between amplified fragment length polymorphism groups and total ileal loop pathology scores, and a one-way ANOVA comparison of the mouse pathology scores against total chick embryo deaths after 72 h was significant (&lt;i&gt;P&lt;/i&gt;=0.049)

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

Infra-red light (1064 nm) from a high-power Nd:YAG laser caused more than 90% loss of viability of &lt;i&gt;Escherichia coli&lt;/i&gt; 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 &lt;i&gt;E. Coli&lt;/i&gt; cells

Laser inactivation of surfaces and detection of bacteria

No abstract available