Biomedical subjects

M F Patterson

Publications and source records attributed to M F Patterson.

27 records · Page 2Linked to original sources

PubMed1995

Combined effect of gamma radiation and heating on the destruction of Listeria monocytogenes and Salmonella typhimurium in cook-chill roast beef and gravy.

The effect of heating alone (60, 65 or 70 degrees C), heating after irradiation (0.8 kGy) and heating after irradiation and storage for 14 days at 2-3 degrees C on the destruction of Listeria monocytogenes and Salmonella typhimurium in artifically inoculated minced cook-chill roast beef and gravy was investigated. Inoculated minced roast beef samples (5 g) were heated in Stomacher bags completely immersed in a water bath at each of the test temperatures. Survivors were enumerated and D and z values were determined for each of the pathogens. Observed thermal D values for two strains of L. monocytogenes at 60, 65 and 70 degrees C in the absence of pre-irradiation were 90.0-97.5 s, 34.0-53.0 s and 22.4-28.0 s, respectively, whereas thermal D values after pre-irradiation were 44.0-46.4 s, 15.3-16.8 s and 5.5-7.8 s at 60, 65 and 70 degrees C, respectively. This reduction in D values provides evidence for radiation-induced heat-sensitisation in L. monocytogenes. There was some evidence of heat-sensitisation of S. typhimurium at 60 degrees C, but not at either 65 or 70 degrees C. The z value also decreased as a consequence of pre-irradiation to a dose of 0.8 kGy (11.0-12.7 degrees C). The radiation-induced heat-sensitivity in L. monocytogenes was found to persist for up to 2 weeks storage at 2-3 degrees C prior to heating. As cook-chill products are intended to be reheated prior to consumption the results of the present study suggest that any L. monocytogenes present in a cook-chill product would be more easily killed during reheating if it were to be treated with a low dose of gamma radiation during manufacture.

Cold Temperature↗

PubMed1995

Sensitivity of Campylobacter spp. to irradiation in poultry meat.

The sensitivity of Campylobacter jejuni (three strains), Camp. coli (three strains), Camp. fetus (one strain) and Camp. lari (one strain) to irradiation in poultry meat was investigated. There was no significant difference in the counts obtained on Blood or Skirrows agar. Preston agar gave a significantly lower recovery of the pathogens after irradiation so these results were not included in calculations of D10 values. The D10 values ranged from 0.12 to 0.25 kGy and there was a significant difference in the radiation sensitivity between different Campylobacter spp. and within strains of the same species. These values indicate that Campylobacter spp. are more radiation-sensitive than Salmonella and Listeria monocytogenes irradiated under similar conditions. Therefore irradiation treatments suggested to eliminate the latter from poultry carcasses would also be sufficient to remove Campylobacter.

Animals↗

PubMed1994

Effects of membrane potential on just detectable movement in rat skeletal muscle: effects of denervation.

The potential, Vt, at which a brief test depolarization first elicited movement was determined using two-microelectrode point voltage clamp. We expected that inactivation of excitation-contraction coupling at conditioning potentials between -60 and 0 mV would shift Vt to more positive potentials, and that fibers would become inactivatable with less conditioning depolarization in EDL than soleus. The curve relating Vt to conditioning potential had a negative slope (which was insensitive to addition of 1 mM cobalt or replacement of calcium with 20 mM CaEGTA) between -60 and -35 mV and a steep positive slope with further depolarization Unexpectedly, fibers became inactivatable with less conditioning depolarization in soleus than in EDL when Vt was measured with 50 msec test pulses. However, the positive shift in Vt became less steep as test pulse duration lengthened in soleus fibers. When Vt obtained with test pulses approaching rheobase (10 msec in EDL and 500 msec in soleus) was compared, EDL fibers became inactive with less conditioning depolarization than soleus fibers. The increase in Vt became steeper with 1 mM cobalt or 20 mM CaEGTA and was shifted to more positive potentials by denervation in soleus fibers. We conclude that inactivation (i) does not strongly influence threshold contractions at conditioning potentials between -60 and -40 mV and (ii) influences Vt between -40 and 0 mV in a manner that depends on test pulse duration.

Animals↗

PubMed1993

Effect of low-dose irradiation on growth of and toxin production by Staphylococcus aureus and Bacillus cereus in roast beef and gravy.

The effect of irradiation (2 kGy) on growth of and toxin production by Staphylococcus aureus and Bacillus cereus in roast beef and gravy during storage at abuse temperatures (15 and 22 degrees C) was assessed by inoculation studies. Irradiation resulted in a 3-4 log10 reduction in numbers of both pathogens. Whenever B. cereus and S. aureus numbers reached 10(6) and 10(7) cfu/g, respectively, during storage their toxins were detectable. As the time taken to attain these levels was longer in irradiated than in unirradiated samples, toxin production by both pathogens was delayed by irradiation. When samples initially containing low levels (10(2)/g) of S. aureus were irradiated no toxin was produced during subsequent storage at 15 or 22 degrees C. Diarrhoeal toxin produced by B. cereus was detected after 2 days at 22 degrees C, but not at 15 degrees C, in samples containing 10(2) cells/g prior to irradiation. When higher numbers (10(6)/g) of either pathogen were present prior to irradiation, toxins were produced by both pathogens at 22 degrees C, but not at 15 degrees C. Microbial competition had an effect on the growth of B. cereus and S. aureus after irradiation when a low initial inoculum was applied. However, when a higher inoculum was used the pathogens outnumbered their competitors and competition effects were less important. It was concluded that low-dose irradiation would improve the microbiological safety of roast beef and gravy.

Animals↗

PubMed1992

Actions of perchlorate ions on rat soleus muscle fibres.

1. The effects of perchlorate (ClO4-) on contraction have been studied in rat soleus muscle fibres using (i) potassium (K+) contracture and (ii) two-microelectrode-point voltage clamp techniques. 2. Membrane potentials (Vm) at all external [K+] were 3-5 mV more negative in ClO4-. The hyperpolarization could not be attributed to a change in Na+, K+, or Cl- permeability, or to an effect on the Na(+)-K+ pump. 3. ClO4- shifts the voltage dependence of tension activation, and contraction threshold, to more negative membrane potentials without altering maximum tension. Consequently, twitches and submaximal K+ contractures were potentiated, whereas tetanic contractions and 200 mM-K+ contractures were unaltered. 4. The decay of K+ contractures during steady depolarization with ClO4- developed a slow exponential phase with an average time constant of 6.05 +/- 0.76 min at -38 mV, and 1.68 +/- 0.15 min at -19 mV. This slow component was (a) under the rapid control of the surface Vm and (b) did not depend on external Ca2+. 5. Inactivation of E-C coupling was measured with a test 200 mM-K+ depolarization following 3-10 min depolarizations in conditioning solutions containing 20-120 mM-K+. ClO4- induced a negative shift in the curve-relating test K+ contracture amplitude to conditioning Vm but did not alter the rate of repriming of tension upon repolarization. 6. The results suggest that ClO4- increases the amount of activator produced during depolarization and thus allows the slow inactivation step in excitation-contraction (E-C) coupling to be reflected in the decay of K+ contracture tension. 7. A 'perchlorate contracture', which did not depend on the activation of E-C coupling, was observed. The contracture depended on external Ca2+, but not on voltage-dependent Ca2+ channels or Na(+)-Ca2+ exchange.

Animals↗

PubMed1991

A numerical taxonomic study of lactic acid bacteria isolated from irradiated pork and chicken packaged under various gas atmospheres.

Ninety-four Gram-positive, catalase-negative bacteria, isolated from pork and chicken that had been packed in modified atmospheres and irradiated to 1.75 and 2.5 kGy respectively, were studied. The majority of the strains were Lactobacillus saké. Numerical taxonomy, with the group average clustering strategy, revealed the existence of six clusters at the 85% similarity level. The largest, Cluster 1, contained 78 (83%) of the test strains along with three Lact. sak'e strains. Cluster 2 contained three test strains and the type strains of Carnobacterium piscicola and Carn. divergens. Cluster 3 contained two chicken strains and Lact. curvatus. Cluster 4 contained a pork strain and Leuconostoc dextranicum. Clusters 5 and 6 contained four pork and two chicken strains respectively and no type strains. Four test strains remained unclustered as did the other reference strains included in the study.

Animals↗

PubMed1987

An outbreak of infection with a methicillin-resistant Staphylococcus aureus in a special care baby unit: value of topical mupirocin and of traditional methods of infection control.

This report deals with the problems associated with a high incidence rate of methicillin-resistant Staphylococcus aureus in low birth weight infants in a regional special care baby unit. Strict isolation facilities were not used and the outbreak was promptly brought under control by the use of intensive traditional methods of infection control and the use of topical mupirocin in a paraffin base.

Administration, Topical↗

PubMed1987

Correlation between antibiotic sensitivity testing by conventional and conductivity measurements.

A high correlation in the susceptibilities of 44 strains isolated from clinical material to a variety of antimicrobial agents was found between the minimum inhibitory concentration and conductivity measurements. Some discrepancy was found for vancomycin and teicoplanin when tested against 21 strains of staphylococci. Similarly, discrepancies were seen with azlocillin, chloramphenicol and gentamicin when tested against strains of aerobic and facultatively anaerobic Gram-negative bacilli. In the majority of cases in which discrepancies were noted, this reflected differences in relative, and not absolute, susceptibility. With five strains of Pseudomonas, however, there was a poor correlation with three of four antibiotics studied. The advantage of this technique is that sensitivities are available within 4-6 h.

Anti-Bacterial Agents↗

PubMedDate not supplied

The stability of deoxynivalenol and 3-acetyl deoxynivalenol to gamma irradiation.

The stability of deoxynivalenol and 3-acetyl deoxynivalenol to irradiation by 60Co-gamma radiation under various conditions was investigated. Deoxynivalenol and 3-acetyl deoxynivalenol were irradiated on maize, in aqueous solution and in the dry state. Breakdown of the toxins was monitored by high performance liquid chromatography. Both deoxynivalenol and 3-acetyl deoxynivalenol were more sensitive to irradiation when irradiated in aqueous solution than when irradiated on maize. Breakdown of deoxynivalenol and 3-acetyl deoxynivalenol in aqueous solution began at 1 kGy and 5 kGy respectively and both toxins were completely destroyed by 50 kGy. When irradiated on maize, breakdown of the toxins only began after irradiation to 20 kGy and 80-90% of the toxins remained after irradiation to 50 kGy. Irradiation of the toxins did not cause the formation of new compounds of increased toxicity to baby hamster kidney cells. Both DON and 3-A DON were stable to irradiation to 50 kGy when irradiated in the dry condition. The use of low dose gamma irradiation to destroy preformed toxins present on grain does not appear to be a suitable method for the detoxification of grain contaminated with deoxynivalenol and 3-acetyl deoxynivalenol because of the high irradiation dose that would be required for their destruction (> 50 kGy).

Animals↗