Polymorphisms and intronic structures in the 18S subunit ribosomal RNA gene of the fungi Scytalidium dimidiatum and Scytalidium hyalinum. Evidence of an IC1 intron with an His-Cys endonuclease gene

The fungi Scytalidium dimidiatum (Nattrassia mangiferae synanamorph) and Scytalidium hyalinum are mainly encountered in (sub)tropical areas as plant pathogens and agents of human dermatomycosis. Because the classification and differentiation of these two species is unclear, we studied 22 S. dimidiatum and 15 S. hyalinum isolates in order to identify potential species-specific insertions and polymorphisms in the 18S subunit ribosomal gene. The presence of an IE intron in S. dimidiatum, together with a single polymorphism (A in S. dimidiatum, G in S. hyalinum) in the coding region, allowed us to differentiate these two species in most cases. Moreover, in one S. dimidiatum isolate we found a group IC1 intron containing a putative truncated His-Cys endonuclease gene. This enzyme shows strong similarity to the intronic homing endonuclease of Physarum polycephalum. Based on these results and our previous findings, we propose an evolutionary pathway for 18S rDNA S. dimidiatum insertions, implying independent events.

Growth and exopolysaccharide production during free and immobilized cell chemostat culture of Lactobacillus rhamnosus RW-9595M

AIMS

Biomass and exopolysaccharide (EPS) production were studied during chemostat cultures in whey permeate medium with Lactobacillus rhamnosus RW-9595M-free cells and cells immobilized on solid porous supports (ImmobaSil).

METHODS AND RESULTS

A continuous culture with free cells was conducted for 9 days at dilution rates (D) between 0.3 and 0.8 h(-1) in yeast extract (YE)/mineral supplemented whey permeate. Maximum EPS production (1808 mg l(-1)) and volumetric productivity (542.6 mg l(-1) h(-1)) were obtained for a low D of 0.3 h(-1). A continuous fermentation in a two-stage bioreactor system, composed of a first stage with immobilized cells and a second stage inoculated with free cells produced in the first reactor, was carried out for 32 days. The influence of YE concentration, temperature and dilution rate, and their interactions on biomass, EPS and lactic acid production was investigated. A statistically significant model was found only for lactic acid production. Marked cell morphological and physiological changes led to the formation of very large cell-containing aggregates and a low mean soluble EPS production (138 mg l(-1)). Aggregate volumetric productivity of the two-stage system varied between 5.7 and 49.5 g l(-1) h(-1) for different fermentation conditions and times. Aggregates contained a very high biomass concentration, estimated at 74% of aggregate dry weight by nitrogen analysis and 4.3 x 10(12) CFU g(-1) by a DNA extraction method and a high nonsoluble polysaccharide content (14.2%). At age 24 days, insoluble EPS concentration and volumetric productivity were 1250 mg l(-1) and 2240 mg l(-1) h(-1) respectively. The physiological changes were shown to be reversible when cells were incubated during three successive batch cultures.

CONCLUSIONS

EPS production and volumetric productivity during continuous free-cell chemostat cultures with L. rhamnosus RW-9595M are among the highest values reported for lactobacilli in literature. Immobilization and continuous culture resulted in low soluble EPS production and large morphological and physiological changes of L. rhamnosus RW-9595M, with formation of macroscopical aggregates mainly composed of biomass and nonsoluble EPS.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study on continuous EPS production by immobilized LAB. Immobilization and culture time-induced cell aggregation and could be used to produce new synbiotic products with very high viable cell and EPS concentrations.

Purification, characterization and amino acid sequencing of divergicin M35: a novel class IIa bacteriocin produced by Carnobacterium divergens M35

Carnobacterium divergens M35, isolated from a commercial sample of frozen smoked mussels, produces a new bacteriocin, divergicin M35, a class IIa bacteriocin. Divergicin M35 is sensitive to pronase-E, alpha-chymotrypsin and proteinase K, but not to trypsin and withstands thermal treatments up to 121 degrees C for 30 min. Divergicin M35 was extracted from the culture supernatant of C. divergens M35 using an SP-Sepharose cation-exchange column, desalted and purified on a C18 Sep-Pack column and further purified by reverse phase-high pressure liquid chromatography. This procedure allowed the recovery of 10% of the bacteriocin present in the culture supernatant with purity higher than 99%. Divergicin M35 had a molecular mass of 4518.75 Da as determined by mass spectrometry, a pI value of 8.3 and positive net charge (+3). The amino acid sequence of divergicin M35 was found to consist of 43 amino acid with four cysteine residues (Cys10, 15, 25, 43) and showed 80.5% homology with divercin V41 (80.5%) and 80.0% with bavaricin MN. Divergicin M35 showed powerful antilisterial activity, especially against Listeria monocytogenes and was also active against carnobacteria but not against strains of Lactococcus, Lactobacillus, Enterococcus, Bifidobacteria and Escherichia. Divergicin M35 production began in late exponential phase and reached a maximum activity of 65,000 AU/ml in early stationary phase. Initial broth pH, Tween 80 and acetate did not affect C. divergens M35 growth or divergicin production. This bacteriocin may be a potential tool for inhibiting L. monocytogenes in seafood products that do not usually undergo an adequate heat treatment.

Increased stress tolerance of Bifidobacterium longum and Lactococcus lactis produced during continuous mixed-strain immobilized-cell fermentation

AIMS

The effect of immobilization and long-term continuous culture was studied on probiotic and technological characteristics of lactic acid and probiotic bacteria.

METHODS AND RESULTS

A continuous culture in a two-stage system was carried out for 17 days at different temperatures ranging from 32 to 37 degrees C, with a first reactor containing Bifidobacterium longum ATCC 15707 and Lactococcus lactis subsp. lactis biovar. diacetylactis MD immobilized separately in gel beads, and a second reactor operated with free cells released from the first reactor. The tolerance of free cells from both strains produced in the effluent medium of both reactors to hydrogen peroxide, simulated gastric and intestinal juices, antibiotics and nisin, and freeze-drying markedly increased with culture time and was generally higher after 6 days than that of stationary-phase cells produced during free-cell batch fermentations. The reversibility of the acquired tolerance of B. longum, but not L. diacetylactis, to antibiotics was shown during successive free-cell batch cultures.

CONCLUSIONS

Free cells produced from continuous immobilized-cell culture exhibited altered physiology and increased tolerance to various chemical and physico-chemical stresses.

SIGNIFICANCE AND IMPACT OF THE STUDY

Continuous culture with immobilized cells could be used to produce probiotic and lactic acid bacteria with enhanced technological and probiotic characteristics.

Intérêt de la torche à plasma en biologie clinique. Quelles applications en toxicologie ?

The multi-elementary quantitation method using inductively coupled plasma mass spectrometry has been widely developed for use with biological fluids. Many elements can be quantified simultaneously in biological fluids, including: Li, Be, B, Al, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Mo, Pd, Cd, Sn, Sb, Te, Ba, W, Pt, Hg, Tl, Pb, Bi, U. The validation procedure is described by the French Society of Clinical Biology. Results for urine are corrected after creatinine determination. We report applications in clinical toxicology and forensic toxicology. Advances in inductively coupled plasma mass spectrometry in the field of clinical biology are particularly important for toxicological analysis. This powerful tool is helpful for better patient care and for the search for cause of death.

Valence-bond crystal in a pyrochlore antiferromagnet with orbital degeneracy

We discuss the ground state of a pyrochlore lattice of threefold orbitally degenerate S=1/2 magnetic ions. We derive an effective spin-orbital Hamiltonian and show that the orbital degrees of freedom can modulate the spin exchange, removing the infinite spin-degeneracy characteristic of pyrochlore structures. The resulting state is a collection of spin-singlet dimers, with a residual degeneracy due to their relative orientation. This latter is lifted by a magnetoelastic interaction, induced in the spin-singlet phase space, that forces a tetragonal distortion. Such a theory provides an explanation for the helical spin-singlet pattern observed in the B spinel MgTi2O4.

Quantification by real-time PCR of Lactococcus lactis subsp. cremoris in milk fermented by a mixed culture

During cheese making, interactions between different strains of lactic acid bacteria play an important role. However, few methods are available to specifically determine each bacterial population in mixed cultures, in particular for strains of the same species. The aim of this study was to develop a real-time PCR quantification method to monitor the population of Lactococcus cremoris ATCC 19257 in mixed culture with Lactobacillus rhamnosus RW-9595M and the bacteriocin-producing microorganism Lc. diacetylactis UL719. The specificity of the two primers 68FCa33 and 16SR308 used to amplify a 240-bp fragment of DNA from Lc. cremoris was demonstrated by conventional PCR. Using these primers for real-time PCR, the detection limit was 2 cfu/reaction or 200 cfu of Lc. cremoris ATCC 19257 per millilitre of mixed culture in milk. In pure culture batch fermentation, good correlation was obtained between real-time PCR and the conventional plating method for monitoring Lc. cremoris growth. In mixed culture batch fermentation, Lb. rhamnosus and Lc. cremoris decreased due to nisin Z production by Lc. diacetylactis. The decrease of the Lc. cremoris cell population detected by real-time PCR was not possible to observe by the plate count method in the presence of a Lc. diacetylactis population that was 1 log higher.

Immobilization of infant fecal microbiota and utilization in an in vitro colonic fermentation model

Bacteria isolated from infant feces were immobilized in polysaccharide gel beads (2.5% gellan gum, 0.25% xanthan gum) using a two-phase dispersion process. A 52-day continuous culture was carried out in a single-stage chemostat containing precolonized beads and fed with a medium formulated to approximate the composition of infant chyme. Different dilution rates and pH conditions were tested to simulate the proximal (PCS), transverse (TCS), and distal (DCS) colons. Immobilization preserved all nine bacterial groups tested with survival rates between 3 and 56%. After 1 week fermentation, beads were highly colonized with all populations tested (excepted Staphylococcus spp. present in low numbers), which remained stable throughout the 7.5 weeks of fermentation, with variations below 1 log unit. However, free-cell populations in the circulating liquid medium, produced by immobilized cell growth, cell-release activity from gel beads, and free-cell growth, were altered considerably by culture conditions. Compared to the stabilization period, PCS was characterized by a considerable and rapid increase in Bifidobacterium spp. concentrations (7.4 to 9.6 log CFU/mL), whereas Bifidobacterium spp., Lactobacillus spp., and Clostridium spp. concentrations decreased and Staphylococcus spp. and coliforms increased during TCS and DCS. Under pseudo-steady-state conditions, the community structure developed in the chemostat reflected the relative proportions of viable bacterial numbers and metabolites generally encountered in infant feces. This work showed that a complex microbiota such as infant fecal bacteria can be immobilized and used in a continuous in vitro intestinal fermentation model to reproduce the high bacterial concentration and bacterial diversity of the feces inoculum, at least at the genera level, with a high stability during long-term experiment.

3-hydroxypropionaldehyde: applications and perspectives of biotechnological production

3-hydroxypropionaldehyde (3-HPA) forms, together with HPA-hydrate and HPA-dimer, a dynamic, multi-component system (HPA system) used in food preservation, as a precursor for many modern chemicals such as acrolein, acrylic acid, and 1,3-propanediol (1,3-PDO), and for polymer production. 3-HPA can be obtained both through traditional chemistry and bacterial fermentation. To date, 3-HPA has been produced from petrochemical resources as an intermediate in 1,3-PDO production. In vivo, glycerol is converted in one enzymatic step into 3-HPA. The 3-HPA-producing Lactobacillus reuteri is used as a probiotic in the health care of humans and animals. The biotechnological production of 3-HPA from renewable resources is desirable both for use of 3-HPA in foods and for the production of bulk chemicals. The main challenge will be the efficient production and recovery of pure 3-HPA.

[Differential diagnosis of onychomycosis]

In order to give an effective treatment to a patient with nail disorders, a correct aetiological diagnosis is necessary. Distal and lateral thickening of nail bed and nail plate with onycholysis, deep or superficial leuconychia, melanonychia, paronychia, distal and lateral onycholysis, and total dystrophic onychomycosis are the common physical signs of onychomycosis which represent 50 per cent out of nails disorders. Nail disorders due to cutaneous or general diseases with similar alteration of nail configuration may be confused with onychomycosis. In many cases, an aetiological trend is given by a total body examination of the skin and the mucosa. To diagnose correctly a non fungal nail disorder from an onychomycosis sometimes is a real challenge. According non fungal nail disorder and fungal nail infection may be associated, so a mycological examination and sometimes histopathological examination are very helpful to establish a good diagnosis.

Production of antibacterial substances by bifidobacterial isolates from infant stool active against Listeria monocytogenes

AIMS

This study aimed to characterize new isolates of human bifidobacteria, evaluate some of their probiotic potential and to screen these isolates for their effectiveness at inhibiting Listeria monocytogenes in vitro.

METHODS AND RESULTS

Thirty-four Bifidobacterium isolates from infant faeces were identified by fructose-6-phosphate phosphoketolase and PCR. Six isolates, coded RBL67, RBL68, RBL69, RBL70, RBL85 and RBL86, showed higher antagonistic activity against L. monocytogenes. Neutralized culture supernatants of these strains did not inhibit L. monocytogenes when tested by agar diffusion method. However, the concentration of supernatant by speed-vac resulted in the formation of an inhibitory effect with supernatants from strains RBL67, RBL68 and RBL70. This effect was shown to be related to heat-stable proteinaceous compound(s) which were resistant to heating at 100 degrees C for 5 min but not to pronase-E, proteinase-K or trypsin. The extraction of the inhibitory compounds by methanol-acetone extraction procedure indicated that four strains (RBL67, RBL68, RBL69 and RBL70) were mostly soluble in acetone. However, strain RBL85 produced inhibitory substances that were soluble in methanol.

CONCLUSION

Infant bifidobacterial isolates produce heat-stable proteinaceous compounds active against L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Production of antibacterial substances by bifidobacteria would improve intestinal bacterial ecology and inhibit intestinal pathogens.

Exopolysaccharide production during batch cultures with free and immobilized Lactobacillus rhamnosus RW-9595M

AIMS

Exopolysaccharides (EPS) were produced by Lactobacillus rhamnosus RW-9595M during pH-controlled batch cultures with free cells and repeated-batch cultures with cells immobilized on solid porous supports (ImmobaSil).

METHODS AND RESULTS

Cultures were conducted in supplemented whey permeate (SWP) medium containing 5 or 8% (w/w) whey permeate. For free-cell batch cultures in 8% SWP medium, very high maximum cell counts (1.3 x 10(10) CFU ml(-1)) and EPS production (2350 mg l(-1)) were measured. A high EPS production (1750 mg l(-1)) was measured after four cycles for a short incubation period of only 7 h. Several methods for immobilized biomass determination based on analysis of biomass components (proteins, ATP and DNA) were tested. The DNA analysis method proved to be the most appropriate under these circumstances. This method revealed a high maximum immobilized biomass of 8.5 x 10(11) CFU ml(-1) support during repeated immobilized cell cultures in 5% SWP. The high immobilized biomass increased maximum EPS volumetric productivity (250 mg l(-1) h(-1) after 7 h culture) compared with free-cell batch cultures (110 mg l(-1) h(-1) after 18 h culture).

CONCLUSIONS

High EPS productions were achieved during batch cultures of Lact. rhamnosus RW-9595M in SWP medium, exceeding 1.7 g EPS per litre. Repeated-batch cultures with immobilized cells resulted in increased EPS productivity compared with traditional free-cell cultures.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study clearly shows the high potential of the strain Lact. rhamnosus RW-9595M and immobilized cell technology for production of EPS as a functional food ingredient.

Pneumocystis carinii pneumonia in patients with hematologic malignancies: a descriptive study

Objectives. A retrospective multicentric study was conducted over a five-year period to evaluate the clinical and laboratory characteristics and outcome of patients with proven Pneumocystis carinii pneumonia (PCP) complicating hematologic malignancies.Results. The study included 60 HIV-negative patients with 18 non-Hodgkin's malignant lymphoma (30%), 13 chronic lymphocytic leukaemia (21.7%), 10 acute leukemia (16.6%), 5 multiple myeloma (8.3%), 4 Waldenström's diseases (6.6%), 4 chronic myeloid leukemia (6.6%), 3 myelodysplasia (5%), 2 Hodgkin's diseases (3.3%) and 1 thrombopenia. Bronchoalveolar lavage was diagnostic in all patients. Forty-nine patients received cytotoxic drugs (81.7%), 25 (41.7%) a long-term corticotherapy and 15 (25%) underwent bone marrow transplantation. Twenty-seven patients (45%) required admission in the intensive care unit, 35 (58.3%) received an adjunctive corticotherapy and 18 mechanical ventilation (30%). Twenty patients (33.3%) died of PCP. A previous long-term corticotherapy (p=0.04), high respiratory (p=0.05) and pulse rates (p=0.02), elevated C reactive protein (p=0.01) and mechanical ventilation (OR=13.37; IC: 1.9-50) were associated with a poor prognosis. Adjunctive corticotherapy did not modify the prognosis.Conclusions. These results suggest that PCP can occur during the course of various hematologic malignancies, not only lymphoproliferative disorders. Prognosis remains poor. The diagnosis should be advocated more frequently and earlier to improve the prognosis.

Impact of nisin producing culture and liposome-encapsulated nisin on ripening of Lactobacillus added-Cheddar cheese

This study aimed to evaluate the effects of incorporating liposome-encapsulated nisin Z, nisin Z producing Lactococcus lactis ssp. lactis biovar. diacetylactis UL719, or Lactobacillus casei-casei L2A adjunct culture into cheese milk on textural, physicochemical and sensory attributes during ripening of Cheddar cheese. For this purpose, cheeses were made using a selected nisin tolerant cheese starter culture. Proteolysis, free fatty acid production, rheological parameters and hydrophilic/hydrophobic peptides evolution were monitored over 6 mo ripening. Sensory quality of cheeses was evaluated after 6 mo. Incorporating the nisin-producing strain into cheese starter culture increased proteolysis and lipolysis but did not significantly affect cheese rheology. Liposome-encapsulated nisin did not appear to affect cheese proteolysis, rheology and sensory characteristics. The nisinogenic strain increased the formation of both hydrophilic and hydrophobic peptides present in the cheese water extract. Sensory assessment indicated that acidic and bitter tastes were enhanced in the nisinogenic strain-containing cheese compared to control cheese. Incorporating Lb. casei and the nisinogenic culture into cheese produced a debittering effect and improved cheese flavor quality. Cheeses with added Lb. casei and liposome-encapsulated nisin Z exhibited the highest flavor intensity and were ranked first for sensory characteristics.

Kinetics of plasma and erythrocyte metformin after acute administration in healthy subjects

OBJECTIVES

Although the existence of a deep compartment for metformin has long been hypothesized, there is still little direct information concerning metformin distribution in individual tissues in man. The only available study involves chronic metformin therapy. In that study, the measurement of metformin in erythrocytes provided a reliable indicator of metformin distribution and of potential accumulation. To determine the kinetics of metformin in plasma and in erythrocytes after acute oral administration, we performed the present study in healthy subjects after a single oral dose of metformin and compared the pharmacokinetics parameters in erythrocytes to those in plasma.

METHODS

Six nondiabetic participants took the study dose of 850 mg metformin at 8: 00 AM after a non-standardized breakfast (i.e., as recommended in clinical practice). Blood samples were collected for metformin measurement in plasma and in erythrocytes at 0, 1, 2, 3, 4, 6, 9, 24, 33, 48, 57, and 72 h.

RESULTS

Maximum metformin concentration was attained at 3.0 +/- 0.3 h in plasma and 4.7 +/- 0.5 h in erythrocytes. This difference was not significant. Metformin concentrations peaked at a maximum almost 6 times higher in plasma than in erythrocytes (1.7 +/- 0.1 and 0.3 +/- 0.0 mg/l, respectively). However, because the elimination half-life of metformin was much longer in erythrocytes (23.4 +/- 1.9 h vs. 2.7 +/- 1.2 h), there was no difference in area under the curve between plasma and erythrocytes. The distribution volume (plasma) was calculated to be 146 +/- 11 l. Plasma and erythrocytes concentration-time curves showed that metformin was not detectable in plasma 24 hours after the oral administration, while it remained detectable in erythrocytes up to 48 hours. Metformin concentrations crossed approximately 13 hours after having reached their maximum values in plasma, approximately 16 h after metformin intake.

CONCLUSION

Having demonstrated the rapid elimination of metformin from plasma and its slow disappearance from erythrocytes, the presents results should contribute to adjustment of metformin dosage to renal function, assessment of drug compliance, and retrospective analysis (when blood samples are drawn with delay) of the link between metformin and development of lactic acidosis. Most importantly, the present findings should help to ascertain the optimal dosage of metformin, particularly in elderly patients.

Measurement of metformin concentration in erythrocytes: clinical implications

AIMS

Although pharmacokinetics studies have long suggested a deep compartment for the antidiabetic drug metformin, there is still little information concerning metformin accumulation by individual tissues in man. In the present study, the erythrocyte was chosen to represent this putative deep compartment and metformin concentration in erythrocytes (EM) was compared with that in plasma (PM) to delineate clinical implications.

METHODS

A reference group of 58 patients with well-tolerated metformin treatment was studied to provide standard mean metformin concentrations in the fasting state. Secondly, to provide transverse data reflecting clinical practice, the authors reviewed an investigation group of 93 metformin-treated patients with available PM and EM, which had been requested either to adjust metformin dosage to renal function, or to screen for potential metformin accumulation following renal failure, metformin overdose or lactic acidosis. Thirdly, the case of an individual with major metformin accumulation was studied to provide information about metformin elimination.

RESULTS

From the bulk of data, we performed three types of analyses: (1) PM and EM were compared. In the investigation group, this comparison was extended to subgroups separated according to low-to-normal, moderately increased or highly increased metformin concentration. (2) Correlative analyses of PM, EM and serum creatinine were performed. (3) A kinetic study of the spontaneous decline of PM and EM was conducted. PM and EM were, respectively, 0.5 +/- 0.4 mg/l and 0.8 +/- 0.4 mg/l in the reference group, and 11.7 +/- 17.8 mg/l (mean +/- SD, range 0.0-71.9 mg/l) and 7.5 +/- 9.4 mg/l (0.0-34 mg/l) in the investigation group, mean serum creatinine of which was 290 +/- 258 micro mol/l. In the low-to-normal PM subgroup (n = 28), PM and EM were, respectively, 0.39 +/- 0.38 mg/l and 0.84 +/- 0.68 mg/l (p < 0.001). In the moderately increased PM subgroup (from therapeutic concentrations +2 SD to 5 mg/l, n = 24), PM and EM were 2.82 +/- 1.13 mg/l and 2.72 +/- 2.03 mg/l (NS). In the sharply increased PM subgroup (> 5 mg/l, n = 41), PM and EM were 27.6 +/- 23.2 mg/l and 17.0 +/- 11.4 mg/l (p = < 0.001). PM and EM were tightly correlated (r = 0.72 in the reference group and r = 0.90 in the investigation group, p < 0.001 for both). Metformin concentrations were also correlated with those of serum creatinine, but more so in the investigation group; in subgroups, a positive correlation was found only at high metformin concentrations and in erythrocytes. The kinetic study performed in the patient with major metformin accumulation showed that PM and EM dropped within less than 3 days from a maximum concentration of 80.0 mg/l and 20.4 mg/l, respectively, to 0.67 mg/l and 6.52 mg/l.

CONCLUSIONS

In conclusion, metformin appears to accumulate in erythrocytes and, consequently, may be part of a deep compartment for the drug. This evidence of slow decline in erythrocyte metformin concentration may contribute to retrospective diagnosis of metformin accumulation and to refinements in adjusting metformin dosage to renal function.

Antibacterial activities of nisin Z encapsulated in liposomes or produced in situ by mixed culture during cheddar cheese ripening

This study investigated both the activity of nisin Z, either encapsulated in liposomes or produced in situ by a mixed starter, against Listeria innocua, Lactococcus spp., and Lactobacillus casei subsp. casei and the distribution of nisin Z in a Cheddar cheese matrix. Nisin Z molecules were visualized using gold-labeled anti-nisin Z monoclonal antibodies and transmission electron microscopy (immune-TEM). Experimental Cheddar cheeses were made using a nisinogenic mixed starter culture, containing Lactococcus lactis subsp. lactis biovar diacetylactis UL 719 as the nisin producer and two nisin-tolerant lactococcal strains and L. casei subsp. casei as secondary flora, and ripened at 7 degrees C for 6 months. In some trials, L. innocua was added to cheese milk at 10(5) to 10(6) CFU/ml. In 6-month-old cheeses, 90% of the initial activity of encapsulated nisin (280 +/- 14 IU/g) was recovered, in contrast to only 12% for initial nisin activity produced in situ by the nisinogenic starter (300 +/- 15 IU/g). During ripening, immune-TEM observations showed that encapsulated nisin was located mainly at the fat/casein interface and/or embedded in whey pockets while nisin produced by biovar diacetylactis UL 719 was uniformly distributed in the fresh cheese matrix but concentrated in the fat area as the cheeses aged. Cell membrane in lactococci appeared to be the main nisin target, while in L. casei subsp. casei and L. innocua, nisin was more commonly observed in the cytoplasm. Cell wall disruption and digestion and lysis vesicle formation were common observations among strains exposed to nisin. Immune-TEM observations suggest several modes of action for nisin Z, which may be genus and/or species specific and may include intracellular target-specific activity. It was concluded that nisin-containing liposomes can provide a powerful tool to improve nisin stability and availability in the cheese matrix.