The destruction of spores of Bacillus subtilis by the combined effects of hydrogen peroxide and ultraviolet light

Ultraviolet light irradiation of bacterial spores in the presence of hydrogen peroxide has been shown to produce synergistic kills when compared with ultraviolet light (u.v.) and hydrogen peroxide used sequentially. This use in combination has been patented for the commercial sterilization of packaging before filling with UHT-processed products. Previous results have shown that lamps producing u.v. light with a maximum output at about 254 nm were extremely effective. Results obtained using a Synchrotron radiation source to produce a narrow band of irradiation now shows that the greatest kill of spores of Bacillus subtilis in the presence of hydrogen peroxide is obtained with radiation at ˜270 nm. Such results suggest that the action of the u.v. light is not directly on the spore DNA but may be related to the production of free hydroxyl radicals from hydrogen peroxide.     

Isolation ofAcholeplasma oculi from human amniotic fluid in early pregnancy

Acholeplasmas have been isolated from a variety of animals, insects, and plants, but onlyAcholeplasma laidlawii has previously been found in humans. We have isolatedAcholeplasma oculi in pure culture from the amniotic fluid of a woman at 19 weeks of gestation. The organism was positively identified by growth inhibition, epi-immunofluorescence, and arbutin hydrolysis. Demonstration of organisms directly in amniotic fluid by DNA fluorochrome and immunofluorescence staining provided additional evidence that the isolate was genuine and not a medium contaminant. The remainder of the pregnancy was unremarkable, and a full-term male infant was delivered without complications. Even though there is some evidence possibly associatingA. oculi with various diseases in livestock, the prevalence and significance ofA. oculi in humans has not been determined.     

Dynamic light-scattering studies on the effect of heat and disinfectants on spores of Bacillus cereus.

The relative stability of spores of Bacillus cereus grown at three different temperatures was examined by using quasi-elastic light scattering (q.l.s.) in conjunction with turbidity and scanning electron microscopy (s.e.m.). Cultures grown at 20, 30 and 40 degrees C (BC20, BC30 and BC40 respectively) were compared in terms of (i) their effective hydrodynamic radius, rH, as determined from q.l.s. and (ii) their gross morphology, as determined from s.e.m. The effects of autoclaving at 121.1 degrees C on both these properties was also examined. We observed (1) that cultures BC20 and BC30 appeared to have similar values for rH, whereas that of BC40 appeared some 50% higher, and (2) BC40 had a correspondingly much lower heat resistance (its structural integrity was lost after about 20 min autoclaving, whereas that of BC20 and BC30 was retained even after 80 min autoclaving). These data were in good agreement with independent measurements of heat-resistance coefficients. Changes in the hydrodynamic radius, polydispersity (both using q.l.s.) and turbidity were monitored with time on addition of the disinfectants sodium hypochlorite and peracetic acid; again BC40 appeared to have a lower resistance.     

Detection of the site of contamination by Staphylococcus aureus within the defeathering machinery of a poultry processing plant

Counts of Staphylococcus aureus from samples of neck skin taken from poultry carcasses at different stages of processing showed that the numbers decreased approximately 10-fold during scalding but increased by almost 1000-fold during plucking, reaching up to 10⁴/g. Swab samples taken from the defeathering machinery yielded counts of ca. 10³/swab at the entry to the first plucker but these increased to ca. 10⁷at the exit, with a subsequent decrease through the second and third machines. Counts of other organisms growing on the Baird-Parker isolation medium showed much lower levels at the exit to the first plucker, suggesting that this was the major site of contamination at which S. aureus grew preferentially. Data obtained from four visits to the processing plant over a period of 10 months suggested that the incidence of S. aureus on the birds is affected by the season (summer or winter) whereas levels in the plucking machines depended on the day of sampling.     

The use of toluidine blue for in situ detection of micro-organisms in foods

The use of toluidine blue to stain cryosections of food samples to detect sites of microbial growth was examined. The method successfully detected colonies and single cells of both yeasts and bacteria at magnifications of x 400 or below in the majority of foods studied. The method demonstrates great potential for studying the micro-environments in which micro-organisms grow.     

Plasmid profiles as indicators of the source of contamination of Staphylococcus aureus endemic within poultry processing plants.

A total of 530 strains of Staphylococcus aureus were isolated from the defeathering machinery of a chicken processing plant and from neck skin samples of carcasses at different stages of processing in two visits 4 weeks apart. Eleven different plasmid profiles were detected in the isolates, eight being common to both visits. The plasmid profiles of the strains forming the majority of the population on the freshly slaughtered birds were rarely present in the strains isolated from the pluckers (except at the entry to the first plucker) and were present in only a small proportion of the strains isolated from carcasses after plucking. However, the profiles from the strains isolated from the pluckers on both visits were different from those forming the majority of the population on the incoming birds but formed the major part of the carcass flora after plucking, suggesting that such strains were endemic. These strains were found as a small proportion of the isolates made from the incoming birds, suggesting that this was the route by which the endemic strains were introduced into the plant. Such endemic strains exhibited a clumping growth, even in liquid shake culture, which may have made it easier for them to become established on the pluckers and to resist cleaning and disinfection. This clumping phenotype was correlated with the presence of a 7.5-megadalton plasmid.     

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

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 discussed.     

Biochemical properties of Clostridium bifermentans spores.

As previously found for spores of Bacillus species, dormant spores of Clostridium bifermentans contained essentially no adenosine triphosphate, a high level of adenosine monophosphate, a high level of 3-phosphoglyceric acid, and much transfer ribonucleic acid lacking a 3'-terminal adenosine monophosphate residue. As in spores of Bacillus species, germination of C. bifermentans spores was accompanied by utilization of the 3-phosphoglyceric acid, a large increase in the adenosine triphosphate level, and the disappearance of defective transfer ribonucleic acid. In contrast to spores of Bacillus species, dormant spores of C. bifermentans contained little free amino acid.