Effects of nisin on growth of bacteria attached to meat

Nisin had an inhibitory effect on gram-positive bacteria (Listeria monocytogenes, Staphylococcus aureus, and Streptococcus lactis) but did not have an inhibitory effect on gram-negative bacteria (Serratia marcescens, Salmonella typhimurium, and Pseudomonas aeruginosa) attached to meat. Nisin delayed bacterial growth on meats which were artificially inoculated with L. monocytogenes or Staphylococcus aureus for at least 1 day at room temperature. If the incubation temperature was 5 degrees C, growth of L. monocytogenes was delayed for more than 2 weeks, and growth of Staphylococcus aureus did not occur. We also found that the extractable activity of nisin decreased rapidly when the meats were incubated at ambient temperatures and that this decrease was inversely related to the observed inhibitory effect. These findings disclosed that nisin delays the growth of some gram-positive bacteria attached to meat. However, nisin alone may not be sufficient to prevent meat spoilage because of the presence of gram-negative and other nisin-resistant gram-positive bacteria.     

Effects of nisin on growth of bacteria attached to meat.

Nisin had an inhibitory effect on gram-positive bacteria (Listeria monocytogenes, Staphylococcus aureus, and Streptococcus lactis) but did not have an inhibitory effect on gram-negative bacteria (Serratia marcescens, Salmonella typhimurium, and Pseudomonas aeruginosa) attached to meat. Nisin delayed bacterial growth on meats which were artificially inoculated with L. monocytogenes or Staphylococcus aureus for at least 1 day at room temperature. If the incubation temperature was 5 degrees C, growth of L. monocytogenes was delayed for more than 2 weeks, and growth of Staphylococcus aureus did not occur. We also found that the extractable activity of nisin decreased rapidly when the meats were incubated at ambient temperatures and that this decrease was inversely related to the observed inhibitory effect. These findings disclosed that nisin delays the growth of some gram-positive bacteria attached to meat. However, nisin alone may not be sufficient to prevent meat spoilage because of the presence of gram-negative and other nisin-resistant gram-positive bacteria.     

Heterotrophic bacteria attached to seaweeds

Viable counts of heterotrophic bacteria attached to the green algae, Monostroma nitidum Wittrock and Enteromorpha linza (Linné) J. Agardh, ranged from 10⁴ to 10⁶/cm², and those attached to the red alga Porphyra suborbiculata Kjellman from 10³ to 10⁴/cm². These bacterial populations were larger than those attached to the brown alga Eisenia bicyclis (Kjellman) setchell ranging from 10¹ to 10⁴/cm². The bacterial populations in the environmental sea water. Nabem Inlet and Otsuchi Bay (Japan), were 10³/ml. Orange and yellow pigmented bacteria were predominant on the green and red algae, but not in the bacterial populations of the brown alga and the sea water. Most of the pigmented bacteria were identified as belonging to the Flavobacterium-Cytophaga group. A beneficial relationship was suggested between the green algae and the pigmented bacteria. Proportions of Vibrionaceae were small on the green algae.     

Survival of bacteria in carcasses.

Bacteria injected into the bloodstream of guinea pigs shortly before death decreased in number in carcass tissues for about 1 h after death. If initial bacterial numbers were sufficiently low, all bacteria were eliminated, and carcass tissues were sterile 24 h after death. Carcass tissue sterility was maintained with an initial density of Clostridium perfringens or Salmonella typhimurium of 20 cells per g or with an initial density of the other species examined of several hundred cells per gram. With larger numbers of strict and facultative anaerobes, growth commenced after 3 h in carcasses incubated at 30 degrees C. Spores of C. perfringens were killed over the same period as vegetative cells, but growth did not commence until 8 h after death. Bactericidal activity in carcass tissues must therefore be taken into account in evaluating the significance of reports of deep-tissue contamination of carcasses from meat animals.     

Disinfection of bacteria attached to granular activated carbon.

Heterotrophic plate count bacteria, coliform organisms, and pathogenic microorganisms attached to granular activated carbon particles were examined for their susceptibility to chlorine disinfection. When these bacteria were grown on carbon particles and then disinfected with 2.0 mg of chlorine per liter (1.4 to 1.6 mg of free chlorine residual per liter after 1 h) for 1 h, no significant decrease in viable counts was observed. Washed cells attached to the surface of granular activated carbon particles showed similar resistance to chlorine, but a progressive increase in sublethal injury was found. Observations made by scanning electron microscope indicated that granular activated carbon was colonized by bacteria which grow in cracks and crevices and are coated by an extracellular slime layer. These data suggest a possible mechanism by which treatment and disinfection barriers can be penetrated and pathogenic bacteria may enter drinking water supplies.     

Grazing of attached bacteria by heterotrophic microflagellates

Four species of heterotrophic microflagellates were examined for their ability to graze attached and unattached bacteria. The species tested displayed pronounced differences in their ability to graze the bacteriumPseudomonas halodurans attached to chitin particles. Two species of microflagellates (Monas andCryptobia sp.) efficiently grazed unattached bacteria but showed little or no ability to graze attached or aggregated cells. In contrast,Rhynchomonas nasuta andBodo sp. showed marked preferences for attached and aggregated bacteria and a limited ability to graze unattached cells. The density of attached bacteria was reduced by an order of magnitude due to grazing byBodo andR. nasuta, even though the density of unattached bacteria was 5–90× the density of attached cells. The maximum densities attained by microflagellates in the cultures were related to the density of unattached bacteria forMonas andCryptobia but not forBodo andR. nasuta. Growth of the latter two species appeared to be related to the density of attached or aggregated bacteria. Based on the results of these experiments, it is concluded that the pelagic existence of microflagellates that graze attached bacteria may be strongly linked to the distribution of suspended particles and their associated bacteria. In addition, the removal of attached bacteria by microflagellates can significantly affect the density of bacteria attached to particles in the plankton. This activity may have important implications for the controversy concerning the relative importance of attached and free-living bacteria in the plankton.     

Effects of chilling on tomato fruit texture

The effects of chilling on tomato ( Lycopersicon esculentum Mill cv. Caruso) texture were investigated using fruit stored at 22°C (nonchilled) or 5°C (chilled) for 28 days. or at 5°C for 15 days before transfer to 22°C to facilitate ripening during and additional 13 days (prechilled). Prechilled fruit exhibited symptoms of slight chilling injury, i.e. development of mealiness, accelerated softening relative to that of nonchilled fruit and nonuniform surface colour development. The firmness of all fruit decreased during ripening and chilled storage when measured by flat plate compression and puncture, especially during the early stages of ripening of nonchilled and prechilled fruit. The compression firmness of pericarp tissue similarly decreased during ripening of nonchilled and prechilled fruit, but was maintained during chilling. Total moisture content (ca 94%) of tissue, uronide content (32-35% w/w) and extracted β-galactosidase activity did not differ significantly ( P > 0.05) among fruit during ripening and chilled storage. The degree of uronide methyl esterification in ethanol-insoluble solids prepared from pericarp tissue (EIS) was relatively low for all fruit. i.e. <40%. EIS from which greater levels of pectinesterase were extracted (i.e. nonchilled>chilled>prechilled) exhibited decreased levels of uronide methyl esterification. Markedly elevated levels of β-glucosidase activity were extracted from prechilled EIS. Total polygalacturonase activity (mainly as PGI) and autolysis of enzyme-extracted EIS were inversely correlated ( P ≤ 0.05) only with the loss of nonchilled fruit and tissue firmness and prechilled fruit firmness. Results suggest a possible role for β-glucosidase in textural changes of prechilled fruit and tissue (e.g. loss of firmness, development of mealiness) and also implicate loss of skin strength in the softening of whole fruit during chilling.     

Antimicrobial activity of surface attached marine bacteria in biofilms

Relatively little is known about the microbial ecology of biofilm communities or the diversity of antimicrobial molecules that they produce to regulate these communities. This study tested whether the production of antimicrobial activity in biofilm cultures is enhanced towards competing bacteria found in those biofilms. First, the production of antimicrobial activity of marine bacteria grown in biofilms was tested. Fourteen of the 105 marine isolates tested were found to produce antimicrobial factors when grown in biofilms. The antimicrobial activity produced by these isolates in biofilms was more potent and inhibited a broader range of target bacteria grown in biofilms compared to shaken liquid cultures. In a separate experiment, we found that cultivation in biofilms containing produced metabolites from an ‘inducer’ bacterium stimulated the production of antimicrobial molecules by ‘producer’ bacteria that were active against the ‘inducer’ bacterium. Overall, the study suggests that surface attached marine bacteria can target their antimicrobial activity towards competing bacteria in biofilms.     

Air sampling methods for VOCs related to field-scale biosecure swine mortality composting

Monitoring specific volatile organic compounds (VOCs) as markers of biosecure carcass degradation is a promising method to test progress and completion of the composting process. The objective of this study was to test the feasibility of using existing aeration ducts in composting units as practical sampling locations. The secondary objective was to test the feasibility of using marker VOC concentrations in aeration ducts to elucidate information about airflow patterns inside composting units. Marker VOC concentrations were significantly higher in the upper aeration duct and this duct can typically be used to collect air samples instead of placing special air sampling probes inside the composting units. Occasionally, the airflow direction inside composting units can change. Marker VOC concentrations can be used to decide the airflow direction inside the composting units. In this study, higher VOC concentrations were measured from the upper aeration duct, and this duct was shown to be an outlet.     

Antimicrobial susceptibility of enterococci recovered from commercial swine carcasses: effect of feed additives

Enterococcus faecium is an important nosocomial pathogen often displaying multiple antibiotic resistance. The increase in clinical isolates can be attributed in part to hospital practices in antibiotic usage, but there is concern that antibiotic-resistant strains might also originate in animals fed rations containing antibiotic growth promoters. Ingestion of meat from carcasses contaminated with faecal enterococci might then result in human colonization or resistance gene transfer to human enterococci. Because there are few comparisons of bacteria isolated from matched animals that have, or have not, been fed a diet containing antibiotic, two such groups of pig carcasses were sampled at a commercial abattoir. Forty isolates from each group of pigs were tested for their resistance to avilamycin and tylosin. Although a modest number of pigs was examined, and the number of strains of E. faecium tested was small, there was no evidence that the feeding of a growth promoter caused selection of enterococci resistant to tylosin or avilamycin.     

A staining technique for attached bacteria and its correlation to extracellular carbohydrate production

Bacterial extracellular polysaccharides have been shown to be involved in the attachment process of cell to solid substratum. The method described here permits study of polysaccharides and their association with the substrate surface, using a novel staining technique for light microscopy. The method can be applied both in the laboratory and in situ and appears to be independent of polysaccharide composition and structure.     

The effect of temperature and relative humidity on the survival of bacteria attached to dry solid surfaces

The effect of relative humidity (r.h.) (0%, 34% and 75%) and temperature (4, 15 and 25°C) on the desiccation survival of Pseudomonas sp., Acinetobacter calcoaceticus , a coryneform, Staphylococcus sp., and Staphylococcus aureus attached to and grown on glass surfaces was studied. The survival of Gram-negative and Gram-positive species was similar. Bacterial survival was shortest at 25°C for all species studied, and in most cases longest at 4°C. The effect of r.h. on survival varied with species. The number of microcolonies and the number of cells within microcolonies for Pseudomonas sp. increased on the dry surfaces after 7 d incubation under all desiccation conditions.     

Coagulase-negative staphylococci and coliform bacteria associated with mechanical defeathering of poultry carcasses

Coagulase-negative staphylococci and coliform bacteria were isolated from defeathering machines and carcasses at a commercial poultry processing plant Initially, the predominant staphylococci on carcasses were Staphylococcus xylosus and Staph simulans but during defeathering, these organisms were replaced by Staph. sciuri. Since Staph sciuri predominated in the defeathering machines, the machinery appeared to be responsible for contaminating carcasses.
Among the coliform bacteria, Escherichia coli was the principal organism isolated from both carcasses and defeathering machines However use of a biotyping scheme revealed no clear change in the pattern of carcass contamination during defeathering and it was concluded that E. coli is unlikely to colonize the machines.     

Effects of chilling on structural aspects of early preantral mouse follicles

Chilling injury is one of the major limiting factors for achieving optimal cryopreservation of gametes. This study aimed to determine potential chilling-induced damage on several structural aspects of early preantral mouse follicles. Mechanically isolated intact early preantral follicles (type 3b-4) were exposed to 0 degrees C for 1, 5, 10, or 30 min. Control and chilled follicles were analyzed by confocal microscopy after staining for tubulin, F-actin, and chromatin, and by electron microscopy. Chilling for only 1 min was sufficient to cause depolymerization of microtubules in the oocyte and the surrounding granulosa cell layer as evidenced by a substantial decrease in fluorescence intensity after antitubulin labeling. Cooling for longer periods caused alterations in microtubule organization in the follicle-enclosed oocyte. These alterations included the loss of interphase microtubules, concomitant with the formation of perinuclear or cortical microtubule asters and sometimes a complete disappearance of microtubules. The extent of microtubule modification was related to the time of chilling, but was fully reversible after rewarming follicles at 37 degrees C for 1 h. Chilling had only minor effects on the actin-containing elements located predominantly in the oocyte cortex and the transzonal projections. Ultrastructural analysis confirmed that oocyte-somatic cell interactions were present. There was no influence on the chromatin configuration within the follicle-enclosed oocyte. These results indicate that mouse follicles are relatively tolerant to direct chilling injury and, as a consequence, are able to withstand the cooling-warming steps during conventional cryopreservation procedures.     

Measurement of the activity of attached bacteria using a sorption microcalorimeter

A method is described in which a flow sorption microcalorimeter was used to measure the heat production of Vibrio alginolyticus attached to polyacrylamide beads. Starved cells were attached to the beads and placed in the column of the calorimeter. Heat production from the metabolism of glucose by the attached cells was then determined. The specific rate of heat production of cells on the surface is compared with that of cells growing in solution. The results show a lowered rate of heat production per cell by the attached bacteria.     

A microautoradiographic study of the activity of attached and free-living bacteria

Microautoradiography, combined with epifluorescent microscopy, was used to evaluate the uptake of tritiated amino acids by a marine Pseudomonas sp. A comparison was made between the activity of bacteria free-living in the medium and bacteria which were attached to glass, polyethylene or polystyrene substrata. The proportion of active bacteria was lower for free-living cells (53–82%) and those attached to polystyrene (53–76%) than for those attached to glass (77–99%) or polyethylene (73–96%). For bacteria attached to glass, assimilated labelled substrate was retained within the cell over 3 h, whereas with polyethylene, labelled material was released from the cells and adsorbed on the surrounding substratum. Hence the physiological activity of attached bacteria depended on the chemical composition of the substratum.