W.M. Waites

Effect of Flagella on Initial Attachment of Listeria monocytogenes to Stainless Steel

ABSTRACT At 22°C a flagellin mutant of Listeria monocytogeneswas found to attach to stainless steel at levels 10-fold lower than wild-type cells, even under conditions preventing active motility. At 37°C, when flagella are not produced, attachment of both strains was identical. Therefore, flagella per se facilitate the early stage of attachment.

Ecology of Microbial Saprophytes and Pathogens in Tissue Culture and Field-Grown Plants: Reasons for Contamination Problems In Vitro

Abstract This review compares published surveys of microbial populations in plant tissue and cell cultures with the microbial saprophytes and pathogens found on field grown plants and microbial populations in the laboratory environment. From this comparison and the measured reduction in contamination after improvements in working practices in the laboratory, conclusions can be drawn about the importance of the explant and the laboratory as sources of contamination. Mechanisms of pathogenicity in vitro are described to explain why bacteria, fungi, and yeasts that are not pathogenic to plants in the field become pathogens in plant tissue cultures. Conversely, plant metabolism and its effect on the tissue culture environment are described to explain why prokaryotes, viruses, and viroids that cause disease in the field can stay latent in vitro. Detection methods for latent contaminants in plant tissue cultures are summarized, and the strategies and methods for prevention or treatment of contamination are disc...

Enzymes from isolates of Pseudomonas fluorescens involved in food spoilage

Aims: Psychrotrophic Gram‐negative bacteria, such as Pseudomonas species, pose a significant spoilage problem in refrigerated meat and dairy products due to secretion of hydrolytic enzymes, especially lipases and proteases. This study characterized the enzymes produced by strains of Pseudomonas fluorescens isolated from pasteurized milk.

Effect of combinations of antibiotics on micropropagated Clematis, Delphinium, Hosta, Iris and Photinia

The phytotoxic effects of antibiotic treatment on micropropagated Clematis, Delphinium, Hosta, Iris and Photinia were determined by assessing multiplication and rooting rates of plants in vitro and weaning success and flowering in vivo.

Effect of medium acidity on growth and rooting of different plant species growing in vitro

Micropropagated Choisya, Daphne, Delphinium, Hemerocallis, Hosta, Iris and Photinia were found to adjust the pH of Murashige and Skoogs plant tissue culture medium (initial pH 5.6 or 3.5) to different values depending on the species. When plant growth and rooting rates were determined after plants had been grown on media initially adjusted or buffered to values between 2.6 and 5.7 the different plant species were also found to have distinct pH requirements for optimal growth and/or rooting rates.

Chlorine resistance of strains of Staphylococcus aureus isolated from poultry processing plants

Strains of Staphylococcus aureus which colonize defeathering machinery and become endemic within poultry processing plants appear to be resistant to the normal cleaning and disinfection processes. The resistance of endemic strains to chlorine was compared with that of isolates from the natural skin flora of poultry. Endemic strains were almost eight times more resistant and this was due primarily to their ability to grow in macroclumps but also to the production of an extracellular slime layer.

Detection of rope spoilage in bread caused by Bacillus species

Rope spoilage of bread by eight Bacillus isolates obtained from a bakery environment was examined via direct inoculation of slices of bread with bacterial culture. The three types of loaf examined were two soft grain varieties, one containing vinegar and the other containing calcium propionate as the preservative agent, and a white variety containing calcium propionate. Differences in rope production caused by batch variation were studied by comparing seven loaves of each type of bread. Not all isolates were capable of causing extensive rope, but isolates of Bacillus subtilis, B. licheniformis, B. megaterium and B. pumilus were able to produce such spoilage. Limited rope was also caused by pre‐existing Bacillus species within the loaves. The amount of rope production by an isolate was not constant on all loaf types or even between different batches of the same variety, indicating that approaches that rely on direct inoculation of loaves with culture are not applicable for assessing the rope‐inducing potential of Bacillus isolates. However, it was clear from this study that vinegar in soft grain loaves was more effective than calcium propionate at inhibiting rope.

Inactivation of Bacillus subtilis spores on packaging surfaces by u.v. excimer laser irradiation

Ultraviolet (u.v.) laser irradiation has been used to inactivate Bacillus subtilis spores deposited on to planar aluminium‐ and polyethylene‐coated packaging surfaces. Kill kinetics were found to be diphasic, with an initial rapid inactivation phase followed by tailing. Although no definitive evidence was obtained, it is thought that spores located within packaging crevices/pores were primarily responsible for the observed tailing. Surviving spores were also found on the unexposed underside of cards and, to a lesser extent, within clumps. The log count reduction in B. subtilis was dependent on spore loading and total u.v. dose. In comparison, packaging surface composition, fluence (2–18 Jm−2) and frequency (40–150 Hz) had only a negligible effect. By irradiating boards carrying 106 spores, with a dose of 11·5 J cm−2, a log count reduction >5 was obtained. The mode of spore inactivation was primarily through DNA disruption. This was confirmed by the high sensitivity of spores lacking protective, small, acid‐soluble proteins, in addition to the high frequency of auxotrophic and asporogenous mutations found amongst survivors.

The growth of Listeria monocytogenes in cheese packed under a modified atmosphere.

E. WHITLEY, D. MUIR and W.M. WAITES.2000. The effect of Modified Atmosphere Packaging (MAP) on the growth of Listeria monocytogenes in mould ripened cheeses was studied at refrigeration temperatures (2–8·3 °C) over a storage period of 6 weeks. Control experiments in cling film with no atmospheric modification produced a lag time before growth of up to 1 week and rapid subsequent growth. MAP with a CO2 concentration of less than 20% allowed growth to occur but when O2 was incorporated; the lag time was reduced from 3 to 2 weeks and subsequent growth was also faster, producing an increase in cell numbers of 1·4 log cycles over the incubation period. N2–MAP in the absence of O2 increased the lag time to 3 weeks and slowed growth, while the inclusion of CO2 extended the lag to 3 weeks and slowed subsequent growth even more. In MAP with 80:10:10 (v/v/v) N2:CO2:O2, there was a lag period of 2–3 weeks before growth of L. monocytogenes occurred, while the total viable aerobic count (TVAC) decreased by 2–3 log cycles and the total Lactobacillus count showed little change. It was concluded that MAP was not suitable for preventing the growth of L. monocytogenes in such cheeses.

Spoilage of bread by bacillus

Abstract Bacteria belonging to the genus Bacillus are capable of causing the food spoilage condition in bread known as rope. This involves mainly Bacillus subtilis , but also B. licheniformis, B. megaterium and B. cereus . Rope is characterized by a sweet fruity odour, often described as resembling overripe pineapples, together with patchy discolouration and softening of the loaf crumb. Differentiation of microorganisms can be carried out in a variety of ways. These include classical methods, for example for Gram stain, commercially available kits, such as the Analytical Profile Index (API) strip, and modern molecular methods, such as ribotyping. The various methods used to differentiate the strains are an important aid in highlighting the areas within the bakery processing line that are involved in contributing to the food spoilage condition known as ropey bread.