Göran Molin

Numerical Taxonomy of Psychrotrophic Pseudomonads

The taxonomy of 218 psychrotrophic pseudomonad strains (200 field strains from meat and 18 type and reference strains) was numerically studied by 174 biochemical and physiological tests. All strains were Gram-negative rods, oxidative positive and motile by means of one or more polar flagella. The strains clustered into 15 groups, of which 9 were regarded as major clusters. The major clusters were designated as Pseudomonas fragi (112 strains), P. fluorescens biotype III (7 strains), P. fluorescens biotype I (16 strains). P. aureofaciens/chlororaphis (3 strains), P. fluorescens biotype II (3 strains), P. putida biotype I (4 strains), Alteromonas putrefaciens (10 strains) and Aeromonas hydrophila biotype I (5 strains). One major cluster, containing 21 strains (cluster 2), was left unassigned. The phenotypic data indicate that this cluster might represent a new species. The P. fluorescens/P. putida complex matched closely the descriptions of Stanier et al. (1966), but the two largest clusters (1 and 2) were not in agreement with any species described in the eighth edition of Bergeys Manual of Determinative Bacteriology. Cluster 1 included the type strain (ATCC 4973) of the hitherto incompletely described P. fragi. A simplified scheme for the separation between P. fragi, P. fluorescens, P. putida and cluster 2 is presented.

The resistance to carbon dioxide of some food related bacteria

SummaryThe growth inhibitory effect of 100% carbon dioxide (CO2) at 25° C was evaluated on Aeromonas hydrophila, Bacillus cereus ATCC 14579, Brochothrix thermosphact ATCC 11509, Citrobacter freundii, Clostridium sporogenes ATCC 19404, Escherichia coli ATCC 11775, Lactobacillus sp. (homofermentative), Lactobacillus viridescens, Staphylococcus aureus, Streptococcus faecalis, Yersinia enterocolitica, and Yersinia frederiksenii. The organisms were studied in batch cultures and the maximum specific growth rate (μmax) was determined in air, 5% CO2 + nitrogen and 100% CO2; from which the relative inhibitory effect of CO2 was estimated for each organism. Using 100% CO2 reduced the growth rate for all test organisms. Compared to growth in air, the relative inhibitory effect of 100% CO2 was highest for Bac. cereus, Br. thermosphacta and A. hydrophila (> 75%), and lowest for E. coli, Str. faecalis and the Lactobacillus spp. (53%–29%). Compared to anaerobic growth, the relative inhibitory effect of 100% CO2 was generally somewhat lower and the succession of CO2-resistance was slightly altered for some organisms but drastically increased for Br. thermosphacta. The relative inhibitory effect was highest on Bac. cereus, A. hydrophila and Y. frederiksenii (67%–52%) and lowest on Y. enterocolitica, Br. thermosphacta and the Lactobacillus spp. (26%–8%). The anaerobic growth in nitrogen was generally slower than the aerobic growth. The exceptions were Streptococcus faecalis (only 2% reduction) and Clostridium sporogenes (no aerobic growth). In 100% CO2Str. faecalis, Citrobacter freundii and Escherichia coli had highest μmax and Brochothrix thermosphacta, Bacillius cereus and Staphylococcus aureus the lowest.

Carbon dioxide evolution of refrigerated meat

The carbon dioxide (CO(2)) evolution from pork loins stored in air or nitrogen at 5°C was measured. The loins were cut immediately after slaughter (pre-rigor meat.), or approximately 20 h after slaughter (post-rigor meat). CO(2) evolution rate was highest during the first day (2·3 × 10(-3)mlcm(-2)h(-1)) and then declined to approximately 0·5 × 10(-3)mlcm(-2)h(-1). The rate was fairly constant during this later phase, and there were no large differences between aerobically and anaerobically stored meat, or between pre-rigor meat and post-rigor meat. Four hypotheses for the origin of the CO(2) evolution are discussed: (1) diffusion from a pre-formed pool in the meat; (2) aerobic energy metabolism of the meat cells; (3) other biochemical reactions of the meat cells; and (4) microbial activity. None of the hypotheses completely supports the experimental results of the investigation. The impact of these findings on the vacuum packaging of meat is discussed.

Combined Carbon Dioxide Inhibition and Oxygen Limitation of the Growth of Pseudomonas fragi 72 in Batch and Continuous Culture

Summary: The effect of CO2 inhibition and O2 limitation on the growth of Pseudomonas fragi strain 72 was studied in carbon and/or energy limited continuous culture using citric acid as the growth substrate. The influence of different CO2 concentrations on the maximal growth capacity, estimated as the dilution rate at which the culture density begins to fall (Dnb) or the dilution rate at which biomass output rate is maximal (Dnm), was demonstrated together with the differences in influence of CO2 inhibition and O2 limitation, on the steady-state characteristics of the culture. The combined effect of CO2 inhibition and O2 limitation was measured. Comparative studies made in batch cultures suggested that continuous culture was more sensitive to change than the batch culture.nThe maximum specific growth rate of the organism decreased when the CO2 concentration was increased. However, the results from the continuous cultures revealed a plateau in the curve of Dnb versus CO2 concentration (between 3-5% and 12% CO2). This plateau could not be seen from the μmax determinations (batch).nUnlike O2 limitation the CO2 inhibition did not disturb the regularity of the curves of the steady-state characteristics. Two levels of O2 limitation were indicated from the curve of biomass versus dilution rate, a minor one, slightly reducing the biomass concentration of the culture and a major one, significantly reducing the biomass. An O2 concentration of 5% of the incoming gas (dissolved oxygen tension in the culture: 3-5%) had no effect on the steady-state characteristics of the culture, while 0-4% O2 significantly affected the curve of biomass versus dilution rate (dissolved oxygen tension 0-0.4%).nThe combined effect of oxygen limitation and 12% CO2, further altered the steady-state characteristics and the biomass curve started to decrease at very low dilution rates. Thus, the two inhibitory agents co-operated and their joint growth restricting effect was considerably stronger than the strongest agent alone. The question whether the restricting effect of the two together should be regarded as “synergistic” or “additive”, is still open to discussion even though some evidence was obtained which suggested the former.

Inactivation of bacillus spores in dry systems at low and high temperatures.

A plot of the thermal resistance of Bacillus subtilis var. niger spores (log D value) against temperature was linear between 37 and 190 degrees C (z = 23 degrees C), provided that the relative humidity of the spore environment was kept below a certain critical level. The corresponding plot for Bacillus stearothermophilus spores was linear in the range 150 to 180 degrees C (z = 29 degrees C) but departed from linearity at lower temperatures (decreasing z value). However, the z value of 29 degrees C was decreased to 23 degrees C if spores were dried before heat treatment. The straight line corresponding to this new z value was consistent with the inactivation rate at a lower temperature (60 degrees C). The data indicate that bacterial spores which are treated in dry heat at an environmental relative humidity near zero are inactivated mainly by a drying process. By extrapolation of the thermal resistance plot obtained under these conditions for B. subtilis var. niger spores, the D value at 0 degrees C would be about 4 years.

Bacterial translocation: Impact of probiotics

There is a considerable amount of data in humans showing that patients who cannot take in nutrients enterally have more organ failure in the intensive care unit, a less favourable prognosis, and a higher frequency of septicaemia, in particular involving bacterial species from the intestinal tract. However, there is little evidence that this is connected with translocation of bacterial species in humans. Animal data more uniformly imply the existence of such a connection. The main focus of this review is to describe different ways to alter the luminal milieu to decrease bacterial translocation. It is possible to reduce absorption of endotoxin by administration of bile salts in obstructive jaundice. Increasing the oral intake of glutamine will reduce bacterial translocation in rats with radiation-induced gut injury. The bacterial microflora plays a very important role in maintaining the normal intestinal ecological environment and supplying preferred fuels to the inn testinal wall, consequently supporting the intestinal barrier. Disruption of the balance of intestinal bacterial microflora may increase the incidence of bacterial translocation by modifying intestinal barrier function. Bacterial species such as enteric Gram-negatives and Gram-positive cocci are more prone to translocation, whereas lactobacilli seem to have a protective effect. Administration of live lactobacilli either orally or by enema will reduce translocation. The mechanisms underlying the decreased translocation are not obvious. One effect may be mediated via an action on the intestinal wall and its permeability. Recently, the results of three randomized studies on the use of L. plantarum in patients with pancreatitis, undergoing liver transplantation or upper gastrointestinal surgery have been published, which all indicate a potential role for lactobacilli in translocation. In conclusion, by altering the luminal content of bacteria it seems possible to reduce the incin dn ence of secondary infections. The influence of the luminal milieu on bacterial translocation is not fully understood. There is convincing evidence from experimental studies, but only circumstantial evidence from clinical studies. Keywords: Bacterial translocation; barrier function; lactobacilli; probiotics.

Gut–liver axis

Background Liver function, the intestine and the immune system are intricately linked. These organs influence one another and are all affected by nutrients and their route of delivery. Gut-liver axis appears to have a central role in response to sepsis, systemic inflammation and multiple organ dysfunction. Discussion We reviewed the interaction between the liver and the gastrointestinal tract, in health and disease. The role of the gut as a central organ for infection has been reviewed, and selective decontamination of the digestive tract. Liver diseases can be affected by different gut factors. Liver regeneration, growth factors and hepatotropic substances are important for recovery after liver diseases and surgery. The controversy about intestinal transplantation and simultaneous intestinal/liver transplantation has been reviewed. We also reviewed nutritional support in liver diseases and the alteration of the luminal content of the gut in acute liver injury.