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T Abee

Publications and source records attributed to T Abee.

At least 55 records · Page 3Linked to original sources
PubMed1997

Interactions of nisin and pediocin PA-1 with closely related lactic acid bacteria that manifest over 100-fold differences in bacteriocin sensitivity.

The natural variation in the susceptibilities of gram-positive bacteria towards the bacteriocins nisin and pediocin PA-1 is considerable. This study addresses the factors associated with this variability for closely related lactic acid bacteria. We compared two sets of nonbacteriocinogenic strains for which the MICs of nisin and pediocin PA-1 differed 100- to 1,000-fold: Lactobacillus sake DSM20017 and L. sake DSM20497 and Pediococcus dextrinicus and Pediococcus pentosaccus. Strikingly, the bacteriocin-sensitive and -insensitive strains showed a similar concentration-dependent dissipation of their membrane potential (delta psi) after exposure to these bacteriocins. The bacteriocin-induced dissipation of delta psi below the MICs for the insensitive strains did not coincide with a reduction of intracellular ATP pools and glycolytic rates. This was not observed with the sensitive strains. Analysis of membrane lipid properties revealed minor differences in the phospho- and glycolipid compositions of both sets of strains. The interactions of the bacteriocins with strain-specific lipids were not significantly different in a lipid monolayer assay. Further lipid analysis revealed higher in situ membrane fluidity of the bacteriocin-sensitive Pediococcus strain compared with that for the insensitive strain, but the opposite was found for the L. sake strains. Our results provide evidence that the association of bacteriocins with the cell membrane and their subsequent insertion take place in a similar way for cells that have a high or a low natural tolerance towards bacteriocins. For insensitive strains, overall membrane constitution rather than mere membrane fluidity may preclude the formation of pores with sufficient diameters and lifetimes to ultimately cause cell death.

Adenosine Triphosphate↗
PubMed1997

Betaine and L-carnitine transport by Listeria monocytogenes Scott A in response to osmotic signals.

The naturally occurring compatible solutes betaine and L-carnitine allow the food-borne pathogen Listeria monocytogenes to adjust to environments of high osmotic strength. Previously, it was demonstrated that L. monocytogenes possesses an ATP-dependent L-carnitine transporter (A. Verheul, F. M. Rombouts, R. R. Beumer, and T. Abee, J. Bacteriol. 177:3205-3212, 1995). The present study reveals that betaine and L-carnitine are taken up by separate highly specific transport systems and support a secondary transport mechanism for betaine uptake in L. monocytogenes. The initial uptake rates of betaine and L-carnitine are not influenced by an osmotic upshock, but the duration of transport of both osmolytes is directly related to the osmotic strength of the medium. Regulation of uptake of both betaine and L-carnitine is subject to inhibition by preaccumulated solute. Internal betaine inhibits not only transport of external betaine but also that of L-carnitine and, similarly, internal L-carnitine inhibits transport of both betaine and L-carnitine. The inhibition is alleviated upon osmotic upshock, which suggests that alterations in membrane structure are transmitted to the allosteric binding sites for betaine and L-carnitine of both transporters at the inner surface of the membrane. Upon osmotic downshock, betaine and L-carnitine are rapidly released by L. monocytogenes as a consequence of activation of a channel-like activity. The osmolyte-sensing mechanism described is new and is consistent with various unexplained observations of osmoregulation in other bacteria.

Betaine↗
PubMed1996

Experimental studies on the infectivity of non-culturable forms of Campylobacter spp. in chicks and mice.

The significance of non-culturable forms of Campylobacter spp., especially with regard to the epidemiology of this organism in poultry flocks, was explored. Two different experiments were conducted to produce non-culturable Campylobacter spp. and test their ability to colonize the animal gut. In the first experiment a mixture of 28 different strains of Campylobacter spp. from various sources was inoculated in both sterilized surface water and potassium phosphate buffer and stored at 4 degrees C. After Campylobacter spp. were no longer detectable by culture in the microcosms, the mixtures of non-culturable cells were used to challenge both chicks and mice. Recovery of non-culturable Campylobacter spp. from the animals was not successful at 4 weeks after administration. In the second experiment the survival of six individual strains of Campylobacter spp. in sterilized surface water at 4 degrees C was studied and the resulting non-culturable cells were used to challenge chicks. None of the campylobacter strains could be recovered from the chicks at 2 weeks after administration. We conclude that occurrence of non-culturable forms of Campylobacter spp. capable of colonizing chicks is not a common phenomenon and that non-culturable forms of Campylobacter spp. are likely to be insignificant for importantly to the epidemiology of the organism in Dutch broiler flocks.

Animals↗
PubMed1996

A Novel Method for Continuous Determination of the Intracellular pH in Bacteria with the Internally Conjugated Fluorescent Probe 5 (and 6-)-Carboxyfluorescein Succinimidyl Ester.

A novel method based on the intracellular conjugation of the fluorescent probe 5 (and 6-)-carboxyfluorescein succinimidyl ester (cFSE) was developed to determine the intracellular pH of bacteria. cFSE can be taken up by bacteria in the form of its diacetate ester, 5 (and 6-)-carboxyfluorescein diacetate succinimidyl ester, which is subsequently hydrolyzed by esterases to cFSE in the cytoplasm. When Lactococcus lactis cells were permeabilized with ethanol, a significant proportion of cFSE was retained in the cells, which indicated that cFSE was bound intracellularly. Unbound probe could be conveniently extruded by a short incubation of the cells in the presence of a fermentable sugar, most likely by exploiting an active transport system. Such a transport system for cFSE was identified in L. lactis, Listeria innocua, and Bacillus subtilis. The intracellular pH in bacteria can be determined from the ratio of the fluorescence signal at the pH-sensitive wavelength (490 nm) and the fluorescence signal at the pH-insensitive wavelength (440 nm). This cFSE ratio method significantly reduced problems due to the efflux of fluorescent probe from the cells during the measurement. Moreover, the method described was successfully used to determine the intracellular pH in bacteria under stress conditions, such as elevated temperatures and the presence of detergents.

Journal Article↗
PubMed1996

Influence of environmental parameters on phosphatidylcholine phospholipase C production in Listeria monocytogenes: a convenient method to differentiate L. monocytogenes from other Listeria species.

The ability to produce phosphatidylcholine phospholipase C (lecithinase) is associated with virulence in pathogenic species of Listeria. Levels of production vary greatly among members of the genus, and this virulence factor is not readily detectable in many members of the pathogenic species on conventional agar media containing egg yolk, a common substrate for the enzyme. In this study, the influence of a variety of environmental parameters, including temperature, pH, and salt concentration, on the production of lecithinase by a number of strains was evaluated. Lecithinase production by Listeria monocytogenes LO28 in brain heart infusion medium was optimal at 1.75 to 2.0% NaCl; pH 7.0 to 7.3, and 37 to 40 degrees C, and the presence of oxygen had no effect. In a chemically defined medium, the optimal NaCl concentration and temperature were lower at 0.75 to 1.0% NaCl and 33.5 degrees C. As detection of virulence factors is useful to assist in the identification and differentiation of Listeria species, this report shows that lecithinase activity can conveniently be detected within 36 h on a relatively inexpensive medium. Under the conditions described, L. monocytogenes could be distinguished from other members of the genus as a result of distinct lecithin degradation which was not evident in L. innocua, L. seeligeri, L. ivanovii, L. welshimeri, or L. murrayi/grayi.

Culture Media, Serum-Free↗
PubMed1995

Pore-forming bacteriocins of gram-positive bacteria and self-protection mechanisms of producer organisms.

Proteinaceous antimicrobial compounds are produced by a diversity of species ranging from bacteria to humans. This review focuses on the mode of action of pore-forming bacteriocins produced by Gram-positive bacteria. The mechanism of action of specific immunity proteins, which protect the producer strains from the lethal action of their own products (producer self-protection), are also discussed.

Amino Acid Sequence↗
PubMed1995

Physiology of food poisoning microorganisms and the major problems in food poisoning control.

There remains considerable public concern regarding the current high level of food poisoning disease in Europe and the fact that, year by year, it continues to rise rather than fall. At the same time, there are strong and increasing demands from consumers for foods that are more convenient, fresher, more natural, less heavily processed (e.g. 'REPFEDS' and 'Sous Vide' foods, mildly heated and distributed at chill temperatures; Lund and Notermans, 1992), less heavily preserved (e.g. less acid, less salt, less sugar; Gould, 1995) and less reliant on additive preservatives than hitherto (e.g. sulphite, nitrite, organic acids and esters; Russell and Gould, 1991). Most of these trends result in a general reduction in the intrinsic preservation of foods. Furthermore, many food poisoning microorganisms escape the attention of preservation techniques altogether, reaching the consumer more or less directly from contaminated foods, most often foods of animal origin. It has therefore been argued that a substantial reduction in food poisoning in the near future will be difficult to achieve unless we obtain a greatly improved understanding of the physiology of the most important target organisms (Knochel and Gould, 1995). This knowledge must then be exploited in ways which effectively improve our means for the control of these hazards and reduce the risk to the consumer. A three year AAIR Concerted Action Programme (PL920630: 'Physiology of Food Poisoning Microorganisms') was therefore initiated in 1992 in order to bring together research groups working on the physiology and related aspects of food poisoning microorganisms. The principal objectives of the programme were: 1. To determine the physiological, biochemical and genetical bases of the organisms' survival of and responses to food-relevant stresses; 2. to determine the physiological and genetical factors influencing infectivity and toxinogenesis; 3. to understand the physiological bases of those synergistic systems that are already empirically applied or that have future potential; 4. to make a wide range of modern techniques in which particular members have expertise more widely available. As can be read in the subsequent contributions to this special issue, the area is a fruitful one for microbiological research and the Programme has been successful in bringing together disparate strands of the topic. It has also highlighted areas where this scientific knowledge may be better exploited in improving the microbiological safety of foods for the consumer.

Bacterial Physiological Phenomena↗
PubMed1995

Bacteriocins: modes of action and potentials in food preservation and control of food poisoning.

Lactic acid bacteria (LAB) play an essential role in the majority of food fermentations, and a wide variety of strains are routinely employed as starter cultures in the manufacture of dairy, meat, vegetable and bakery products. One of the most important contributions of these microorganisms is the extended shelf life of the fermented product by comparison to that of the raw substrate. Growth of spoilage and pathogenic bacteria in these foods is inhibited due to competition for nutrients and the presence of starter-derived inhibitors such as lactic acid, hydrogen peroxide and bacteriocins (Ray and Daeschel, 1992). Bacteriocins, are a heterogenous group of anti-bacterial proteins that vary in spectrum of activity, mode of action, molecular weight, genetic origin and biochemical properties. Currently, artificial chemical preservatives are employed to limit the number of microorganisms capable of growing within foods, but increasing consumer awareness of potential health risks associated with some of these substances has led researchers to examine the possibility of using bacteriocins produced by LAB as biopreservatives. The major classes of bacteriocins produced by LAB include: (I) lantibiotics, (II) small heat stable peptides, (III) large heat labile proteins, and (IV) complex proteins whose activity requires the association of carbohydrate or lipid moieties (Klaenhammer, 1993). Significantly however, the inhibitory activity of these substances is confined to Gram-positive bacteria and inhibition of Gram-negatives by these bacteriocins has not been demonstrated, an observation which can be explained by a detailed analysis and comparison of the composition of Gram-positive and Gram-negative bacterial cell walls (Fig. 1). In both types the cytoplasmic membrane which forms the border between the cytoplasm and the external environment, is surrounded by a layer of peptidoglycan which is significantly thinner in Gram-negative bacteria than in Gram-positive bacteria. Gram-negative bacteria possess an additional layer, the so-called outer membrane which is composed of phospholipids, proteins and lipopolysaccharides (LPS), and this membrane is impermeable to most molecules. Nevertheless, the presence of porins in this layer will allow the free diffusion of molecules with a molecular mass below 600 Da. The smallest bacteriocins produced by lactic acid bacteria are approximately 3 kDa and are thus too large to reach their target, the cytoplasmic membrane (Klaenhammer, 1993; Stiles and Hastings, 1991). However, Stevens et al. (1991) and Ray (1993) have demonstrated that Salmonella species and other Gram-negative bacteria become sensitive to nisin after exposure to treatments that change the permeability barrier properties of the outer membrane (see below). This review will focus on the mode of action of lantibiotics (class I) and class II LAB bacteriocins and their potentials in food preservation and control of food poisoning.

Bacteriocins↗
PubMed1995

The role of peptide metabolism in the growth of Listeria monocytogenes ATCC 23074 at high osmolarity.

The growth of Listeria monocytogenes ATCC 23074 in defined medium is sensitive to high osmolarity when compared with its growth in complex media, such as brain heart infusion (BHI). The two major contributors to this difference in growth rate are the availability in BHI of the osmoprotectant glycine betaine and peptides. Peptone plays two major roles: firstly as a nutritional supplement for protein synthesis, and secondly as a source of amino acids and peptides that serve as a mechanism of maintaining turgor. In the presence of peptone the total amino acid pool at high osmolarity is substantial and even in the presence of glycine betaine the amino acid pool makes a major contribution to turgor maintenance. At high osmolarity there is a general increase in amino acid pools, with particularly substantial pools of glutamate, aspartate, proline, hydroxyproline and glycine. Peptides are also accumulated by cells from the peptone supplied in the medium. Glycine-containing peptides are accumulated in the cytoplasm under all conditions. Specific glycine- and proline-containing peptides stimulate growth at high osmolarity. The peptide prolyl-hydroxyproline accumulates in cells to high levels in response to growth at high osmolarity, and the pools of the derived amino acids also show a dependence on the external osmotic pressure. However, proline only confers significant osmoprotection when supplied as peptides. The significance of these data in the context of the occurrence of L. monocytogenes in foods with high peptide content is discussed.

Amino Acids↗
PubMed1995

A di- and tripeptide transport system can supply Listeria monocytogenes Scott A with amino acids essential for growth.

Listeria monocytogenes takes up di- and tripeptides via a proton motive force-dependent carrier protein. This peptide transport system resembles the recently cloned and sequenced secondary di- and tripeptide transport system of Lactococcus lactis (A. Hagting, E. R. S. Kunji, K. J. Leenhouts, B. Poolman, and W. N. Konings, J. Biol. Chem. 269:11391-11399, 1994). The peptide permease of L. monocytogenes has a broad substrate specificity and allows transport of the nonpeptide substrate 5-aminolevulinic acid, the toxic di- and tripeptide analogs, alanyl-beta-chloroalanine and alanyl-alanyl-beta-chloroalanine, and various di- and tripeptides. No extracellular peptide hydrolysis was detected, indicating that peptides are hydrolyzed after being transported into the cell. Indeed, peptidase activities in response to various synthetic substrates were detected in cell extracts obtained from L. monocytogenes cells grown in brain heart infusion broth or defined medium. The di- and tripeptide permease can supply L. monocytogenes with essential amino acids for growth and might contribute to growth of this pathogen in various foods where peptides are supplied by proteolytic activity of other microorganisms present in these foods. Possible roles of this di- and tripeptide transport system in the osmoregulation and virulence of L. monocytogenes are discussed.

Amino Acids↗
PubMed1995

Characterization of uptake and hydrolysis of fluorescein diacetate and carboxyfluorescein diacetate by intracellular esterases in Saccharomyces cerevisiae, which result in accumulation of fluorescent product.

Flow cytometry is a rapid and sensitive method which may be used for the detection of microorganisms in foods and drinks. A key requirement for this method is a sufficient fluorescence staining of the target cells. The mechanism of staining of the yeast Saccharomyces cerevisiae by fluorescein diacetate (FDA) and 5- (and 6-)carboxyfluorescein diacetate (cFDA) was studied in detail. The uptake rate of the prefluorochromes increased in direct proportion to the concentration and was not saturable, which suggests that transport occurs via a passive diffusion process. The permeability coefficient for cFDA was 1.3 x 10(-8) m s-1. Once inside the cell, the esters were hydrolyzed by intracellular esterases and their fluorescent products accumulated. FDA hydrolysis (at 40 degrees C) in cell extracts could be described by first-order reaction kinetics, and a rate constant (K) of 0.33 s-1 was calculated. Hydrolysis of cFDA (at 40 degrees C) in cell extracts was described by Michaelis-Menten kinetics with an apparent Vmax and Km of 12.3 nmol.min-1.mg of protein-1 and 0.29 mM, respectively. Accumulation of fluorescein was most likely limited by the esterase activity, since transport of FDA was faster than the hydrolysis rate. In contrast, accumulation of carboxyfluorescein was limited by the much slower transport of cFDA through the cell envelope. A simple mathematical model was developed to describe the fluorescence staining. The implications for optimal staining of yeast cells with FDA and cFDA are discussed.

Biological Transport, Active↗
PubMed1995

Temperature-dependent membrane fatty acid and cell physiology changes in coccoid forms of Campylobacter jejuni.

The effect of temperature and the availability of nutrients on the transition of spiral Campylobacter jejuni cells to coccoid forms was investigated. Ageing of spiral C. jejuni cells in either nutrient-poor or nutrient-rich environments resulted in the formation of nonculturable coccoid cells at 4, 12, and 25 degrees C after different periods, with the cells incubated at 4 degrees C in nutrient-deficient media remaining culturable the longest. To study the phenomenon, ATP levels, protein profiles, and fatty acid compositions were monitored under conditions where the transition from spiral to coccoid cells occurred. During storage, the levels of intracellular ATP were highest in cells incubated at low temperatures (4 and 12 degrees C) and remained constant after a small initial decrease. During the transformation from spiral to coccoid forms, no alteration in protein profiles could be detected; indeed, inhibition of protein synthesis by chloramphenicol did not influence the transition. Furthermore, DNA damage by gamma irradiation had no effect on the process. Membrane fatty acid composition of cocci formed at low temperatures was found to be almost identical to that of spiral cells, whereas that of cocci formed at 25 degrees C was clearly different. Combining these results, it is concluded that the formation of cocci is not an active process. However, distinctions between cocci formed at different temperatures were observed. Cocci formed at 4 degrees C show characteristics comparable to those of spirals, and these cocci may well play a role in the contamination cycle of C. jejuni.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1995

An ATP-dependent L-carnitine transporter in Listeria monocytogenes Scott A is involved in osmoprotection.

Listeria monocytogenes is a gram-positive, psychotrophic, food-borne pathogen which is able to grow in osmotically stressful environments. Carnitine (beta-hydroxy-L-tau-N-trimethyl aminobutyrate) can contribute significantly to growth of L. monocytogenes at high osmolarity (R. R. Beumer, M. C. te Giffel, L. J. Cox, F. M. Rombouts, and T. Abee, Appl. Environ. Microbiol. 60:1359-1363, 1994). Transport of L-[N-methyl-14C]carnitine in L. monocytogenes was shown to be energy dependent. Analysis of cell extracts revealed that L-carnitine was not further metabolized, which supplies evidence for its role as an osmoprotectant in L. monocytogenes. Uptake of L-carnitine proceeds in the absence of a proton motive force and is strongly inhibited in the presence of the phosphate analogs vanadate and arsenate. The L-carnitine permease is therefore most likely driven by ATP. Kinetic analysis of L-carnitine transport in glucose-energized cells revealed the presence of a high-affinity uptake system with a Km of 10 microM and a maximum rate of transport (Vmax) of 48 nmol min-1 mg of protein-1. L-[14C]carnitine transport in L. monocytogenes is significantly inhibited by a 10-fold excess of unlabelled L-carnitine, acetylcarnitine, and tau-butyrobetaine, whereas L-proline and betaine display, even at a 100-fold excess, only a weak inhibitory effect. In conclusion, an ATP-dependent L-carnitine transport system in L. monocytogenes is described, and its possible roles in cold adaptation and intracellular growth in mammalian cells are discussed.

Adenosine Triphosphate↗
PubMed1994

Generation of a proton motive force by the excretion of metal-phosphate in the polyphosphate-accumulating Acinetobacter johnsonii strain 210A.

The strictly aerobic, polyphosphate-accumulating Acinetobacter johnsonii strain 210A degrades its polyphosphate when oxidative phosphorylation is impaired. The endproducts of this degradation, divalent metal ions and inorganic phosphate, are excreted as a neutral metal-phosphate (MeHPO4) chelate via the electrogenic MeHPO4/H+ symport system of the organism. The coupled excretion of MeHPO4 and H+ in A. johnsonii 210A can generate a proton motive force. In membrane vesicles and deenergized cells, a membrane potential of about -70 mV and transmembrane pH gradient of about -8 mV were formed in response to an imposed outwardly directed MeHPO4 concentration gradient of 120 mV (initial value). The MeHPO4 efflux-induced proton motive force could drive energy-requiring processes, such as the accumulation of L-proline and L-lysine and the synthesis of ATP via the membrane-bound F0F1 H(+)-ATPase. In vivo 31P NMR studies of polyphosphate degradation in anaerobic cell suspensions revealed the presence of a considerable outwardly directed phosphate gradient across the cytoplasmic membrane corresponding to a MgHPO4 concentration gradient of at least 100 mV. This MgHPO4 concentration gradient was maintained for several hours. Thus, energy recycling by MeHPO4/H+ efflux will contribute significantly to the overall production of metabolic energy from the degradation of polyphosphate in A. johnsonii 210A.

Acinetobacter↗
PubMed1994

Substrate specificity of the two phosphate transport systems of Acinetobacter johnsonii 210A in relation to phosphate speciation in its aquatic environment.

In natural waters and domestic waste waters in which divalent metal ions are present in excess of Pi, H2PO4-, HPO4(2-), and MeHPO4 prevail at pH values physiological for Acinetobacter johnsonii 210A (pH 5.5-8.0). In view of the ability of this organism to extensively accumulate Pi and divalent cations in cytoplasmic polyphosphate granules, the substrate specificity of its two Pi transport systems was studied. The constitutive, proton motive force-driven Pi carrier, previously shown to be dependent on divalent cations, plays a major role in the divalent cation and Pi flux by translocating MeHPO4 rather than Pi. This notion is confirmed by the observation that divalent cations are cotransported with Pi in a 1:1 stoichiometry in proteoliposomes containing reconstituted Pi carrier protein. In contrast, the Pi repressible, periplasmic binding protein-dependent Pi transport system mediates the uptake of H2PO4- and HPO4(2-). Pi uptake, but not MeHPO4 uptake, was stimulated in cells under Pi limitation, and the periplasmic Pi-binding protein has affinity for H2PO4- and HPO4(2-), but not for MeHPO4. When operating in concert, both systems enable A. johnsonii 210A to efficiently acquire Pi from its habitat through uptake of the predominant Pi species.

Acinetobacter↗