Margaret F. Patterson

Microbiology of pressure‐treated foods

High hydrostatic pressure has the potential to produce high quality foods that are microbiologically safe and with an extended shelf-life. Micro-organisms vary in their response to high pressure. Bacterial spores are the most resistant group and they cannot be significantly inactivated by pressure alone. Combination treatments using high pressure and heat have been proposed as a method of producing shelf-stable low acid foods. Viruses are less resistant than bacterial spores and their infectivity can be abolished without destroying their ability to elicit antibodies, leading to the possibility of vaccine production. Yeasts, moulds and vegetative bacteria vary in their response to pressure, depending on factors such as species, strain, processing temperature and substrate, and these are reviewed in the paper. A knowledge of how these factors interact is necessary in order to select the optimum processing conditions for foods. A number of pressure-treated foods are already commercially available and these are discussed in the paper.

Solutes determine the temperature windows for microbial survival and growth

Microbial cells, and ultimately the Earths biosphere, function within a narrow range of physicochemical conditions. For the majority of ecosystems, productivity is cold-limited, and it is microbes that represent the failure point. This study was carried out to determine if naturally occurring solutes can extend the temperature windows for activity of microorganisms. We found that substances known to disorder cellular macromolecules (chaotropes) did expand microbial growth windows, fungi preferentially accumulated chaotropic metabolites at low temperature, and chemical activities of solutes determined microbial survival at extremes of temperature as well as pressure. This information can enhance the precision of models used to predict if extraterrestrial and other hostile environments are able to support life; furthermore, chaotropes may be used to extend the growth windows for key microbes, such as saprotrophs, in cold ecosystems and manmade biomes.

High-Pressure Treatment of Foods

The use of high hydrostatic pressure as a method to preserve food is discussed, including examples of commercial applications from around the world. The effects of high pressure on microorganisms (pathogenic and spoilage bacteria, viruses, yeasts, and molds) are explained and details are given on intrinsic and extrinsic factors affecting their response to high pressure.

Sensitivity of foodborne pathogens to irradiation in the components of a chilled ready meal

The sensitivity of five foodborne pathogens to irradiation in the components of a roast beef meal (beef, gravy, cauliflower, roast potato and mashed potato) was investigated. Bacillus cereus (vegetative cells) was the most radiation-sensitive (D 10 = 0·126–0·288 kGy) of the pathogens studied. Clostridium perfringens (vegetative cells), Salmonella typhimurium and Listeria monocytogenes had similar D 10 ranges (0·342–0·586, 0·371–0·697 and 0·301–0·648 kGy, respectively). Staphylococcus aureus had D 10 values ranging from 0·252–0·427 kGy. When irradiated in gravy the pathogens generally had lower D 10 values than in any of the other four components.

Sensitivity of bacteria to irradiation on poultry meat under various atmospheres

The sensitivity of seven bacterial species inoculated on to sterile poultry meat and irradiated under various atmospheres (air, CO2, vacuum and nitrogen) was investigated. The irradiation sensitivities of Streptococcus faecalis and Staphylococcus aureus were unaffected by atmosphere. The other micro‐organisms (Pseudomonas putida, Salmonella typhimurium, Escherichia coli, Moraxella phenylpyruvica and a Lactobacillus sp.) were more sensitive (their D10 values decreased) when irradiated in atmospheres other than air. In general, a vacuum or CO2 atmosphere during irradiation was found to have the most lethal effect. Plating media were found to have a significant effect on the recovery of irradiated E. coli and Salm. typhirium.

Hb H hydrops foetalis syndrome: a case report and review of literature

Haemoglobin H (Hb H) disease is caused by deletion or inactivation of three α‐globin genes, leaving only one intact and active α‐globin gene. People with Hb H disease usually have moderate anaemia, but are generally thought to be asymptomatic. Some Hb H disease patients require transfusions, and there are reports of fetuses with Hb H disease who have severe anaemia in utero resulting in fatal hydrops foetalis syndrome. We now report a case of Hb H hydrops foetalis syndrome, caused by the inheritance of a hitherto novel α‐globin gene point mutation (codon 35 TCC→CCC or Serine→Proline) and an α‐thalassaemia deletion of the Filipino type removing all ζ‐α‐globin genes on the other chromosome 16. The infant was delivered prematurely because of pericardial effusion and fetal distress, and was found to have severe anaemia and congenital anomalies. A review of the relevant literature on this syndrome is presented, and serves to underscore the phenotypic variations of Hb H disease and the need for surveillance for this condition among newborns and genetic counselling in communities with a high proportion of at‐risk populations.

Sensitivity of Listeria monocytogenes to irradiation on poultry meat and in phosphate-buffered saline

The sensitivity of four strains of Listeria monocytogenes to irradiation on poultry meat and in phosphate‐buffered saline was investigated. The D10 values on poultry meat were 0.417–0.553 kGy depending on strain and plating medium used. Lower values were obtained in phosphate‐buffered saline. Generally tryptone soya yeast extract and McBride agars gave a better recovery (higher D10 value) than listeria selective agar. The D10 values for L. monocytogenes were similar to those reported for Salmonella spp. irradiated under similar conditions. Therefore irradiation doses suggested to eliminate salmonellas from poultry carcasses would also be sufficient to remove L. monocytogenes.

Phylogenetic characterization of a novel radiation-resistant bacterium from irradiated pork: description of Hymenobacter actinosclerus sp. nov.

A phylogenetic analysis was performed on a red-pigmented, radiation-resistant, Gram-negative, rod-shaped organism originating from irradiated pork. Comparative 16S rRNA gene sequencing showed the bacterium was a member of the Cytophaga-Flavobacterium-Bacteroides line of descent and represents a new subline within the genus Hymenobacter. A new species, Hymenobacter actinosclerus, is described for this novel radiation-resistant bacterium. The type strain of Hymenobacter actinosclerus is CCUG 39621T.

Role for compatible solutes glycine betaine and L-carnitine in listerial barotolerance

ABSTRACT Increased listerial barotolerance at elevated osmolarity is attributed, in part, to the presence of accumulated betaine and l-carnitine. The percentage of listerial survival following exposure to 400 MPa for 5 min increased from 0.008 to 0.02% with added l-carnitine (5 mM) and to 0.05% with added betaine (5 mM). Furthermore, listerial cells incapable of transporting compatible solutes fail to adapt to high pressure at elevated osmolarity.

Comparison of 40 Salmonella enterica serovars injured by thermal, high-pressure and irradiation stress

Aim:  To investigate and compare the inherent resistance of 40 Salmonella serovars to heat, irradiation and high‐pressure stress.