Karen Mattick

Effect of Challenge Temperature and Solute Type on Heat Tolerance of Salmonella Serovars at Low Water Activity

ABSTRACT Salmonella spp. are reported to have an increased heat tolerance at low water activity (aw; measured by relative vapor pressure [rvp]), achieved either by drying or by incorporating solutes. Much of the published data, however, cover only a narrow treatment range and have been analyzed by assuming first-order death kinetics. In this study, the death ofSalmonella enterica serovar Typhimurium DT104 when exposed to 54 combinations of temperature (55 to 80°C) and aw (rvp 0.65 to 0.90, reduced using glucose-fructose) was investigated. The Weibull model (LogS = −btn) was used to describe microbial inactivation, and surface response models were developed to predict death rates for serovar Typhimurium at all points within the design surface. The models were evaluated with data generated by using six different Salmonella strains in place of serovar Typhimurium DT104 strain 30, two different solutes in place of glucose-fructose to reduce aw, or six low-awfoods artificially contaminated with Salmonella in place of the sugar broths. The data demonstrate that, at temperatures of ≥70°C, Salmonella cells at low aw were more heat tolerant than those at a higher aw but below 65°C the reverse was true. The same patterns were generated when sucrose (rvp 0.80 compared with 0.90) or NaCl (0.75 compared with 0.90) was used to reduce aw, but the extent of the protection afforded varied with solute type. The predictions of thermal death rates in the low-aw foods were usually fail-safe, but the few exceptions highlight the importance of validating models with specific foods that may have additional factors affecting survival.

Survival and Filamentation of Salmonella enterica Serovar Enteritidis PT4 and Salmonella enterica Serovar Typhimurium DT104 at Low Water Activity

ABSTRACT In this study we investigated the long-term survival of and morphological changes in Salmonella strains at low water activity (aw). Salmonella enterica serovar Enteritidis PT4 and Salmonella enterica serovar Typhimurium DT104 survived at low aw for long periods, but minimum humectant concentrations of 8% NaCl (aw, 0.95), 96% sucrose (aw, 0.94), and 32% glycerol (aw, 0.92) were bactericidal under most conditions. Salmonella rpoS mutants were usually more sensitive to bactericidal levels of NaCl, sucrose, and glycerol. At a lethal aw, incubation at 37°C resulted in more rapid loss of viability than incubation at 21°C. At aw values of 0.93 to 0.98, strains of S. enterica serovar Enteritidis and S. enterica serovar Typhimurium formed filaments, some of which were at least 200 μm long. Filamentation was independent of rpoS expression. When the preparations were returned to high-aw conditions, the filaments formed septa, and division was complete within approximately 2 to 3 h. The variable survival ofSalmonella strains at low aw highlights the importance of strain choice when researchers produce modelling data to simulate worst-case scenarios or conduct risk assessments based on laboratory data. The continued increase in Salmonellabiomass at low aw (without a concomitant increase in microbial count) would not have been detected by traditional microbiological enumeration tests if the tests had been performed immediately after low-aw storage. If Salmonellastrains form filaments in food products that have low awvalues (0.92 to 0.98), there are significant implications for public health and for designing methods for microbiological monitoring.

The survival of foodborne pathogens during domestic washing-up and subsequent transfer onto washing-up sponges, kitchen surfaces and food.

In this study, the survival of Salmonella, Campylobacter and Escherichia coli O157: H7, when exposed to a range of constant temperatures (47-60 degrees C), in hard or soft water, in the presence/absence of detergent (0-0.3%) and organic matter, and during drying, was investigated. Further experiments used a washing-up process simulation, where soiled dishes contaminated with bacteria were washed in a bowl of warm water containing detergent. In addition, this study considered the risk of bacterial transfer onto (1) sterile dishes and sponges via contaminated water, (2) kitchen surfaces wiped with a contaminated sponge, (3) items placed in direct contact with a contaminated kitchen surface, (4) food placed on a contaminated dish or (5) dishes from contaminated food. A proportion of dishes remained contaminated with all pathogen types after a typical washing-up. Water hardness did not appear to affect survival. E. coli, and to a lesser extent Salmonella, survived towel- or air-drying on dishes and after towel-drying the cloth became contaminated on every occasion, regardless of the test organism. A proportion of sterile dishes washed after contaminated dishes became contaminated with pathogens but transfer from dishes onto food was rare. Washing-up sponges frequently became contaminated with pathogens. The results of this study highlight the potential for survival and cross contamination of food borne pathogens in the kitchen environment.

Teaching and assessing medical ethics: where are we now?

Objectives: To characterise UK undergraduate medical ethics curricula and to identify opportunities and threats to teaching and learning. Design: Postal questionnaire survey of UK medical schools enquiring about teaching and assessment, including future perspectives. Participants: The lead for teaching and learning at each medical school was invited to complete a questionnaire. Results: Completed responses were received from 22/28 schools (79%). Seventeen respondents deemed their aims for ethics teaching to be successful. Twenty felt ethics should be learnt throughout the course and 13 said ethics teaching and learning should be fully integrated horizontally. Twenty felt variety in assessment was important and three tools was the preferred number. A shortfall in ethics core competencies did not preclude graduation in 15 schools. The most successful aspects of courses were perceived to be their integrated nature and the small group teaching; weaknesses were described as a need for still greater integration and the heavily theoretical aspects of ethics. The major concerns about how ethics would be taught in the future related to staffing and staff development. Conclusions: This study describes how ethics was taught and assessed in 2004. The findings show that, although ethics now has an accepted place in the curriculum, more can be done to ensure that the recommended content is taught and assessed optimally.

Approaches to learning and studying in medical students: validation of a revised inventory and its relation to student characteristics and performance

Introduction  Inventories to quantify approaches to studying try to determine how students approach academic tasks. Medical curricula usually aim to promote a deep approach to studying, which is associated with academic success and which may predict desirable traits postqualification.

Calculating Salmonella Inactivation in Nonisothermal Heat Treatments from Isothermal Nonlinear Survival Curves

Salmonella cells in two sugar-rich media were heat treated at various constant temperatures in the range of 55 to 80 degrees C and their survival ratios determined at various time intervals. The resulting nonlinear semilogarithmic survival curves are described by the model log10S(t) = -b(T)tn(T), where S(t) is the momentary survival ratio N(t)/N0, and b(T) and n(T) are coefficients whose temperature dependence is described by two empirical mathematical models. When the temperature profile, T(t), of a nonisothermal heat treatment can also be expressed algebraically, b(T) and n(T) can be transformed into a function of time, i.e., b[T(t)] and n[T(t)]. If the momentary inactivation rate primarily depends on the momentary temperature and survival ratio, then the survival curve under nonisothermal conditions can be constructed by solving a differential equation, previously suggested by Peleg and Penchina, whose coefficients are expressions that contain the corresponding b[T(t)] and n[T(t)] terms. The applicability of the model and its underlying assumptions was tested with a series of eight experiments in which the Salmonella cells, in the same media, were heated at various rates to selected temperatures in the range of 65 to 80 degres C and then cooled. In all the experiments, there was an agreement between the predicted and observed survival curves. This suggests that, at least in the case of Salmonella in the tested media, survival during nonisothermal inactivation can be estimated without assuming any mortality kinetics.

Distinct epidemiological patterns of Norwalk-like virus infection.

Norwalk‐like viruses (NLV) are important economically as a cause of both sporadic gastroenteritis in the community and large outbreaks in hospitals and other institutional settings. Despite the description of several antigenic types relatively little is known about the epidemiology of these individual types. NLVs were detected by electron microscopy in faecal specimens from 706 outbreaks of gastroenteritis that represented 68% of all outbreaks of non‐bacterial gastroenteritis. These outbreaks took place in the counties of West and North Yorkshire and Humberside during six winter seasons between July 1992 and June 1998. NLV strains from 671 outbreaks were typed by antigen capture enzyme linked immunosorbent assays (ELISA) based on antisera made to recombinant virus‐like particles of three antigenically distinct NLVs; Norwalk (NV), Mexico (MXV) and Grimsby (GRV) viruses. GRV was the predominant strain for five of the six winter seasons and overall was associated with 61% of NLV outbreaks. MXV was responsible for a single epidemic peak in the winter of 1993/94 but was also observed at other times throughout the study period. NV was only associated with two outbreaks in 1994 that were epidemiologically linked. Strains from the remaining 32% of outbreaks were non‐reactive in all three ELISA. Thus, a single NLV antigenic type seems to have predominated during the period 1992 to 1998 in the UK. J. Med. Virol. 62:99–103, 2000.

High-quality learning: harder to achieve than we think?

Context  High‐quality learning in the context of medical education can be defined by current conceptions of a deep approach to learning and studying, in combination with metacognitive skills such as personal organisation and reflection on learning. Modern undergraduate education aims to provide an environment that will promote high‐quality learning, but this is not as easy to achieve as it might at first seem. Part of the difficulty arises because it is student perceptions of the learning and assessment environment that determine the adopted approach to studying and these are notoriously hard to predict.

Teaching and learning pathology: a critical review of the English literature

Aim  There are few publications summarising the main issues concerning pathology teaching and learning within undergraduate medical degrees. This article examines the themes that have emerged from the literature over the last 2 decades.

The use of ‘hot wash’ treatments to reduce the number of pathogenic and spoilage bacteria on raw retail poultry

Abstract The development of a hot water treatment to reduce bacterial numbers on poultry carcasses is described. Initial trials identified suitable time/temperature for hot water immersion treatments and in subsequent work an experimental in-line processing unit was constructed and evaluated. Microbiological testing for organisms that are indicators for potential food spoilage (aerobic plate count) and human disease (Enterobacteriaceae, Campylobacter ) was performed to assess the benefit of the treatment. A treatment of 75 °C for 30 s significantly reduced the numbers of bacteria but the chicken skin tended to tear as the legs and wings were moved into position for a neat pack appearance (trussing). A treatment of 70 °C for 40 s, however, did not detrimentally affect the chicken skin. In addition, aerobic plate, Enterobacteriaceae and Campylobacter counts for treated samples were significantly lower than the controls ( P =0.005) for 8 days under typical chilled storage conditions.