Biomedical subjects
E Hitchings
Publications and source records attributed to E Hitchings.
Comparative evaluation of the MGIT and BACTEC culture systems for the recovery of Mycobacterium avium subsp. paratuberculosis from milk.
AIMS: To compare the detection capabilities of the non-radiometric MGIT (Mycobacteria Growth Indicator Tubes) and radiometric BACTEC 460TB culture systems (Becton Dickinson, Cowley, Oxford, UK) for recovering Mycobacterium avium subsp. paratuberculosis from milk. METHODS AND RESULTS: Ultra heat treated (UHT) milk samples spiked with different levels of M. paratuberculosis (10-107 cells ml-1) were inoculated into MGIT and BACTEC media (containing recommended supplements) with and without prior chemical decontamination of the milk samples with 0.75% (w/v) cetylpyridinium chloride for 5 h. Time for the detection of growth in days was recorded for each culture system, and a M. paratuberculosis count for each milk sample was calculated from BACTEC readings using a published formula. Correlation between MGIT and BACTEC detection times was 0.6983. Both culture systems were capable of detecting 10-100 M. paratuberculosis cells ml-1 in milk within 30-40 days when no decontamination treatment was applied, but only 102-103 cells ml-1 or greater when chemical decontamination was applied before culture. CONCLUSIONS, SIGNIFICANCE AND IMPACT OF STUDY: The non-radiometric MGIT system could be substituted for the radiometric BACTEC system for the culture of M. paratuberculosis from milk without loss of detection sensitivity. Chemical decontamination before culture caused a significant reduction in numbers of viable M. paratuberculosis in all spiked milk samples resulting in decreased detection capability for both culture systems.
Heat resistance of Bacillus cereus, Salmonella typhimurium and Lactobacillus delbrueckii in relation to pH and ethanol.
The aim of the present work was to investigate the effect of ethanol alone and in combination with low pH on the heat resistance of specific bacteria. The bacteria chosen are representative of heat resistant and heat sensitive pathogens (Bacillus cereus and Salmonella typhimurium) and of relatively heat resistant spoilage microorganisms (Lactobacillus delbrueckii). The chosen bacteria were treated at different temperatures ranging between 70 and 97 degrees C for B. cereus, 48 and 54 degrees C for S. typhimurium and 44 and 60 degrees C for L. delbrueckii, in media of different pH (3, 5 and 7) and ethanol content (0, 2.5, 5, 7.5 and 10%). Both factors proved to be very effective in reducing the heat resistance of the bacteria examined in this work. At pH 7, an increase in ethanol content up to 10% caused D values to decrease by up to 100-fold (S. typhimurium). A drop from pH 7 to pH 3 also caused up to a 100-fold reduction in the D values (S. typhimurium). For B. cereus the regression analysis of the log10 of the D value in relation to temperature, pH and ethanol content was used to produce a second order polynomial equation. The z values increased at decreasing pH and cells were more sensitive to ethanol at lower pH. For S. typhimurium the polynomial equation produced to describe the relationship between log10 of the D values and temperature and ethanol content was also a second order equation indicating that the relationship between z values and ethanol was non-linear. For L. delbrueckii, z values were independent of the ethanol content of the heating medium. Acid tolerance at 25 and 37 degrees C (L. delbrueckii and S. typhimurium) and acid adaptation (S. typhimurium) were also tested. L. delbrueckii was more ethanol and pH tolerant than S. typhimurium at heat treatment temperatures whilst S. typhimurium was more acid tolerant than L. delbrueckii at incubation temperatures (25 and 37 degrees C). Acid adaptation increased the tolerance of S. typhimurium to low pH at 25 degrees C but failed to improve its thermal resistance at 48 degrees C. In all bacteria used, the effects of pH and ethanol were more evident at lower treatment temperatures and therefore their significance becomes greater in view of reduced thermal processing and/or changes in product formulation.