Mitochondrial creatine sensitivity is lost in the D2.mdx model of Duchenne muscular dystrophy and rescued by the mitochondrial-enhancing compound Olesoxime

Duchenne muscular dystrophy (DMD) is associated with distinct mitochondrial stress responses. Here, we aimed to determine whether the prospective mitochondrial-enhancing compound Olesoxime prevents early-stage mitochondrial stress in limb and respiratory muscle from D2.mdx mice using a proof-of-concept short-term regimen spanning 10-28 days of age. As mitochondrial-cytoplasmic energy transfer occurs via ATP- or phosphocreatine-dependent phosphate shuttling, we assessed bioenergetics with or without creatine in vitro. We observed that disruptions in Complex I-supported respiration and H₂O₂ emission in D2.mdx quadriceps and diaphragm were amplified by creatine demonstrating mitochondrial creatine insensitivity manifests ubiquitously and early in this model. Olesoxime selectively rescued or maintained creatine sensitivity in both muscles, independent of the abundance of respiration-related mitochondrial proteins or mitochondrial creatine kinase cysteine oxidation in quadriceps. Mitochondrial calcium retention capacity and glutathione were altered in a muscle-specific manner in D2.mdx but were generally unchanged by Olesoxime. Treatment reduced serum creatine kinase (muscle damage) and preserved cage hang-time, microCT-based volumes of lean compartments including whole body, hindlimb and bone, recovery of diaphragm force after fatigue, and cross-sectional area of diaphragm type IIX fibre, but reduced type I fibres in quadriceps. Grip strength, voluntary wheel-running and fibrosis were unaltered by Olesoxime. In summary, locomotor and respiratory muscle mitochondrial creatine sensitivities are lost during early stages in D2.mdx mice but are preserved by short-term treatment with Olesoxime in association with specific indices of muscle quality suggesting early myopathy in this model is at least partially attributed to mitochondrial stress.

Synergistic activation of mitochondrial metabolism and the glutathione redox couple protects HepG2 hepatocarcinoma cells from palmitoylcarnitine-induced stress

Fatty acid stress can have divergent effects in various cancers. We explored how metabolic and redox flexibility in HepG2 hepatocarcinoma cells mediates protection from palmitoylcarnitine. HepG2 cells, along with HCT 116 and HT29 colorectal cancer cells were incubated with 100 μM palmitoylcarnitine for up to 48 h. Mitochondrial H₂O₂ emission, glutathione, and cell survival were assessed in HT29 and HepG2 cells. 100 μM palmitoylcarnitine promoted early growth in HepG2 cells by ~8% after 48 h versus decreased cell survival observed in HT29 and HCT 116 cells. Palmitoylcarnitine increased mitochondrial respiration at physiological and maximal concentrations of ADP, while lowering cellular lactate content in HepG2 cells, suggesting a switch to mitochondrial metabolism. HepG2 cell growth was associated with an early increase in H₂O₂ emission by 10 min, followed by a decrease in H₂O₂ at 24 h that corresponded with increased glutathione content, suggesting a redox-based compensatory mechanism. In contrast, abrogation of HT29 cell proliferation was related to decreased mitochondrial respiration (likely due to cell death) and decreased glutathione. Concurrent glutathione depletion with BSO prevented palmitoylcarnitine-induced growth in HepG2 cells, indicating that glutathione was critical for promoting growth following palmitoylcarnitine. Inhibiting UCP2 with genipin sensitized HepG2 cells to palmitoylcarnitine, suggesting that activation of UCP2 may be a 2nd redox-based mechanism conferring protection. These findings suggest that HepG2 cells possess inherent metabolic and redox flexibility relative to HT29 cells that confers protection from palmitoylcarnitine-induced stress via adaptive increases in mitochondrial respiratory control, glutathione buffering, and induction of UCP2.

The fatty acid derivative palmitoylcarnitine abrogates colorectal cancer cell survival by depleting glutathione

Previous evidence suggests that palmitoylcarnitine incubations trigger mitochondrial-mediated apoptosis in HT29 colorectal adenocarcinoma cells, yet nontransformed cells appear insensitive. The mechanism by which palmitoylcarnitine induces cancer cell death is unclear. The purpose of this investigation was to examine the relationship between mitochondrial kinetics and glutathione buffering in determining the effect of palmitoylcarnitine on cell survival. HT29 and HCT 116 colorectal adenocarcinoma cells, CCD 841 nontransformed colon cells, and MCF7 breast adenocarcinoma cells were exposed to 0 μM, 50 μM, and 100 μM palmitoylcarnitine for 24-48 h. HCT 116 and HT29 cells showed decreased cell survival following palmitoylcarnitine compared with CCD 841 cells. Palmitoylcarnitine stimulated H₂O₂ emission in HT29 and CCD 841 cells but increased it to a greater level in HT29 cells due largely to a higher basal H₂O₂ emission. This greater H₂O₂ emission was associated with lower glutathione buffering capacity and caspase-3 activation in HT29 cells. The glutathione-depleting agent buthionine sulfoximine sensitized CCD 841 cells and further sensitized HT29 cells to palmitoylcarnitine-induced decreases in cell survival. MCF7 cells did not produce H₂O₂ when exposed to palmitoylcarnitine and were able to maintain glutathione levels. Furthermore, HT29 cells demonstrated the lowest mitochondrial oxidative kinetics vs. CCD 841 and MCF7 cells. The results demonstrate that colorectal cancer is sensitive to palmitoylcarnitine due in part to an inability to prevent oxidative stress through glutathione-redox coupling, thereby rendering the cells sensitive to elevations in H₂O₂. These findings suggest that the relationship between inherent metabolic capacities and redox regulation is altered early in response to palmitoylcarnitine.

Early myopathy in Duchenne muscular dystrophy is associated with elevated mitochondrial H2 O2 emission during impaired oxidative phosphorylation

BACKGROUND

Muscle wasting and weakness in Duchenne muscular dystrophy (DMD) causes severe locomotor limitations and early death due in part to respiratory muscle failure. Given that current clinical practice focuses on treating secondary complications in this genetic disease, there is a clear need to identify additional contributions in the aetiology of this myopathy for knowledge-guided therapy development. Here, we address the unresolved question of whether the complex impairments observed in DMD are linked to elevated mitochondrial H2 O2 emission in conjunction with impaired oxidative phosphorylation. This study performed a systematic evaluation of the nature and degree of mitochondrial-derived H2 O2 emission and mitochondrial oxidative dysfunction in a mouse model of DMD by designing in vitro bioenergetic assessments that attempt to mimic in vivo conditions known to be critical for the regulation of mitochondrial bioenergetics.

METHODS

Mitochondrial bioenergetics were compared with functional and histopathological indices of myopathy early in DMD (4 weeks) in D2.B10-DMDmdx /2J mice (D2.mdx)-a model that demonstrates severe muscle weakness. Adenosine diphosphate's (ADP's) central effect of attenuating H2 O2 emission while stimulating respiration was compared under two models of mitochondrial-cytoplasmic phosphate exchange (creatine independent and dependent) in muscles that stained positive for membrane damage (diaphragm, quadriceps, and white gastrocnemius).

RESULTS

Pathway-specific analyses revealed that Complex I-supported maximal H2 O2 emission was elevated concurrent with a reduced ability of ADP to attenuate emission during respiration in all three muscles (mH2 O2 : +17 to +197% in D2.mdx vs. wild type). This was associated with an impaired ability of ADP to stimulate respiration at sub-maximal and maximal kinetics (-17 to -72% in D2.mdx vs. wild type), as well as a loss of creatine-dependent mitochondrial phosphate shuttling in diaphragm and quadriceps. These changes largely occurred independent of mitochondrial density or abundance of respiratory chain complexes, except for quadriceps. This muscle was also the only one exhibiting decreased calcium retention capacity, which indicates increased sensitivity to calcium-induced permeability transition pore opening. Increased H2 O2 emission was accompanied by a compensatory increase in total glutathione, while oxidative stress markers were unchanged. Mitochondrial bioenergetic dysfunctions were associated with induction of mitochondrial-linked caspase 9, necrosis, and markers of atrophy in some muscles as well as reduced hindlimb torque and reduced respiratory muscle function.

CONCLUSIONS

These results provide evidence that Complex I dysfunction and loss of central respiratory control by ADP and creatine cause elevated oxidant generation during impaired oxidative phosphorylation. These dysfunctions may contribute to early stage disease pathophysiology and support the growing notion that mitochondria are a potential therapeutic target in this disease.

Impairments in left ventricular mitochondrial bioenergetics precede overt cardiac dysfunction and remodelling in Duchenne muscular dystrophy

KEY POINTS

Ninety-eight per cent of patients with Duchenne muscular dystrophy (DMD) develop cardiomyopathy, with 40% developing heart failure. While increased propensity for mitochondrial induction of cell death has been observed in left ventricle, it remains unknown whether this is linked to impaired mitochondrial respiratory control and elevated H₂ O₂ emission prior to the onset of cardiomyopathy. Classic mouse models of DMD demonstrate hyper-regeneration in skeletal muscle which may mask mitochondrial abnormalities. Using a model with less regenerative capacity that is more akin to DMD patients, we observed elevated left ventricular mitochondrial H₂ O₂ and impaired oxidative phosphorylation in the absence of cardiac remodelling or overt cardiac dysfunction at 4 weeks. These impairments were associated with dysfunctions at complex I, governance by ADP and creatine-dependent phosphate shuttling, which results in a less efficient response to energy demands. Mitochondria may be a therapeutic target for the treatment of cardiomyopathy in DMD.

ABSTRACT

In Duchenne muscular dystrophy (DMD), mitochondrial dysfunction is predicted as a response to numerous cellular stressors, yet the contribution of mitochondria to the onset of cardiomyopathy remains unknown. To resolve this uncertainty, we designed in vitro assessments of mitochondrial bioenergetics to model mitochondrial control parameters that influence cardiac function. Both left ventricular mitochondrial responsiveness to the central bioenergetic controller ADP and the ability of creatine to facilitate mitochondrial-cytoplasmic phosphate shuttling were assessed. These measurements were performed in D2.B10-DMD^mdx /2J mice - a model that demonstrates skeletal muscle atrophy and weakness due to limited regenerative capacities and cardiomyopathy more akin to people with DMD than classic models. At 4 weeks of age, there was no evidence of cardiac remodelling or cardiac dysfunction despite impairments in ADP-stimulated respiration and ADP attenuation of H₂ O₂ emission. These impairments were seen at both submaximal and maximal ADP concentrations despite no reductions in mitochondrial content markers. The ability of creatine to enhance ADP's control of mitochondrial bioenergetics was also impaired, suggesting an impairment in mitochondrial creatine kinase-dependent phosphate shuttling. Susceptibly to permeability transition pore opening and the subsequent activation of cell death pathways remained unchanged. Mitochondrial H₂ O₂ emission was elevated despite no change in markers of irreversible oxidative damage, suggesting alternative redox signalling mechanisms should be explored. These findings demonstrate that selective mitochondrial dysfunction precedes the onset of overt cardiomyopathy in D2.mdx mice, suggesting that improving mitochondrial bioenergetics by restoring ADP, creatine-dependent phosphate shuttling and complex I should be considered for treating DMD patients.

The superoxide dismutase mimetic tempol does not alleviate glucocorticoid-mediated rarefaction of rat skeletal muscle capillaries

Sustained elevations in circulating glucocorticoids elicit reductions in skeletal muscle microvascular content, but little is known of the underlying mechanisms. We hypothesized that glucocorticoid‐induced oxidative stress contributes to this phenomenon. In rats that were implanted with corticosterone (CORT) or control pellets, CORT caused a significant decrease in muscle glutathione levels and a corresponding increase in protein carbonylation, an irreversible oxidative modification of proteins. Decreased endothelial nitric oxide synthase and increased endothelin‐1 mRNA levels were detected after 9 days of CORT, and blood flow to glycolytic muscles was diminished. Control and CORT rats were treated concurrently with drinking water containing the superoxide dismutase mimetic tempol (172 mg/L) or the α‐1 adrenergic receptor antagonist prazosin (50 mg/L) for 6 or 16 days. Both tempol and prazosin alleviated skeletal muscle protein carbonylation. Tempol failed to prevent CORT‐mediated capillary rarefaction and was ineffective in restoring skeletal muscle blood flow. In contrast, prazosin blocked capillary rarefaction and restored skeletal muscle blood flow to control levels. The failure of tempol to prevent CORT‐induced skeletal muscle microvascular rarefaction does not support a dominant role of superoxide‐induced oxidative stress in this process. Although a decrease in protein carbonylation was observed with prazosin treatment, our data suggest that the maintenance of skeletal muscle microvascular content is related more closely with counteracting the CORT‐mediated influence on skeletal muscle vascular tone.

Skeletal site-specific effects of endurance running on structure and strength of tibia, lumbar vertebrae, and mandible in male Sprague–Dawley rats

Bone microarchitecture, bone mineral density (BMD), and bone strength are affected positively by impact activities such as running; however, there are discrepancies in the magnitude of these effects. These inconsistencies are mainly a result of varying training protocols, analysis techniques, and whether or not the skeletal sites measured are weight bearing. This study’s purpose was to determine the effects of endurance running on sites that experience different weight bearing and load. Eight-week-old male Sprague–Dawley rats (n = 20) were randomly assigned to either a group with a progressive treadmill running protocol (25 m/min for 1 h, incline of 10%) or a nontrained control group for 8 weeks. The trabecular structure of the tibia, lumbar vertebra (L3), and mandible and the cortical structure at the tibia midpoint were measured using microcomputed tomography to quantify bone volume fraction (i.e., bone volume divided by total volume (BV/TV)), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and cortical thickness. BMD at the proximal tibia, lumbar vertebrae (L1–L3), and mandible was measured using dual energy X-ray absorptiometry. The tibia midpoint strength was measured by 3-point bending using a materials testing system. Endurance running resulted in superior bone structure at the proximal tibia (12% greater BV/TV (p = 0.03), 14% greater Tb.N (p = 0.01), and 19% lower Tb.Sp (p = 0.05)) but not at other sites. Contrary to our hypothesis, mandible bone structure was altered after endurance training (8% lower BV/TV (p < 0.01) and 15% lower Tb.Th (p < 0.01)), which may be explained by a lower food intake, resulting in less mechanical loading from chewing. These results highlight the site-specific effects of loading on the skeleton.

Adipose tissue depot specific differences of PLIN protein content in endurance trained rats

Adipose tissue is classified as either white (WAT) or brown (BAT) and differs not only by anatomical location but also in function. WAT is the main source of stored energy and releases fatty acids in times of energy demand, whereas BAT plays a role in regulating non-shivering thermogenesis and oxidizes fatty acids released from the lipid droplet. The PLIN family of proteins has recently emerged as being integral in the regulation of fatty acid storage and release in adipose tissue. Previous work has demonstrated that PLIN protein content varies among adipose tissue depots, however an examination of endurance training-induced depot specific changes in PLIN protein expression has yet to be done. Male Sprague-dawley rats (n = 10) underwent 8-weeks of progressive treadmill training (18-25 m/min for 30-60 min at 10% incline) or remained sedentary as control. Following training, under isoflurane induced anesthesia epidydmal (eWAT), inguinal subcutaneous (iWAT) and intrascapular brown adipose tissue (BAT) was excised, and plasma was collected. Endurance training resulted in an increase in BAT PLIN5 and iWAT PLIN3 content, while there was no difference in PLIN protein content in endurance trained eWAT. Interestingly, endurance training resulted in a robust increase in ATGL and CGI-58 in eWAT alone. Together these results suggest the potential of a depot specific function of PLIN3 and PLIN5 in adipose tissue in response to endurance training.

Mitochondrial Bioenergetics and Fiber Type Assessments in Microbiopsy vs. Bergstrom Percutaneous Sampling of Human Skeletal Muscle

Microbiopsies of human skeletal muscle are increasingly adopted by physiologists for a variety of experimental assays given the reduced invasiveness of this procedure compared to the classic Bergstrom percutaneous biopsy technique. However, a recent report demonstrated lower mitochondrial respiration in saponin-permeabilized muscle fiber bundles (PmFB) prepared from microbiopsies vs. Bergstrom biopsies. We hypothesized that ADP-induced contraction (rigor) of smaller length microbiopsy PmFB causes a greater reduction in maximal respiration vs. Bergstrom, such that respiration could be increased by a myosin II ATPase-inhibitor (Blebbistatin; BLEB). Eleven males and females each received a 2 mm diameter percutaneous microbiopsy and a 5 mm diameter Bergstrom percutaneous biopsy in opposite legs. Glutamate/malate (5/0.5 mM)—supported respiration in microbiopsy PmFB was lower than Bergstrom at submaximal concentrations of ADP. 5 μM BLEB reduced this impairment such that there were no differences relative to Bergstrom ± BLEB. Surprisingly, pyruvate (5 mM)-supported respiration was not different between either biopsy technique ±BLEB, whereas BLEB increased succinate-supported respiration in Bergstrom only. H₂O₂ emission was lower in microbiopsy PmFB compared to Bergstrom PmFB in the presence of BLEB. Microbiopsies contained fewer type I fibers (37 vs. 47%) and more type IIX fibers (20 vs. 8%) compared to Bergstrom possibly due to sampling site depth and/or longitudinal location. These findings suggest that smaller diameter percutaneous biopsies yield lower glutamate-supported mitochondrial respiratory kinetics which is increased by preventing ADP-induced rigor with myosin inhibition. Microbiopsies of human skeletal muscle can be utilized for assessing mitochondrial respiratory kinetics in PmFB when assay conditions are supplemented with BLEB, but fiber type differences with this method should be considered.

Increases in skeletal muscle ATGL and its inhibitor G0S2 following 8 weeks of endurance training in metabolically different rat skeletal muscles

Adipose triglyceride lipase (ATGL) catalyzes the rate-limiting removal of the first fatty acid from a triglyceride. ATGL is activated by comparative gene identification-58 and inhibited by G(0)/G(1) switch gene-2 protein (G0S2). Research in other tissues and cell culture indicates that inhibition is dependent on relative G0S2-to-ATGL protein content. G0S2 may also have several roles within mitochondria; however, this has yet to be observed in skeletal muscle. The purpose of this study was to determine if muscle G0S2 relative to ATGL content would decrease to facilitate intramuscular lipolysis following endurance training. Male Sprague-Dawley rats (n = 10; age 51-53 days old) were progressively treadmill trained at a 10% incline for 8 wk ending with 25 m/min for 1 h compared with control. Sciatic nerve stimulation for hind-limb muscle contraction (and lipolysis) was administered for 30 min to one leg, leaving the opposing leg as a resting control. Soleus (SOL), red gastrocnemius (RG), and white gastrocnemius were excised from both legs following stimulation or control. ATGL protein increased in all trained muscles. Unexpectedly, G0S2 protein was greater in the trained SOL and RG. In RG-isolated mitochondria, G0S2 also increased with training, yet mitochondrial G0S2 content was unaltered with acute contraction; therefore, any role of G0S2 in the mitochondria does not appear to be acutely mediated by content alone. In summary, G0S2 increased with training in oxidative muscles and mitochondria but not following acute contraction, suggesting that inhibition is not through relative G0S2-to-ATGL content but through more complicated intracellular mechanisms.

Characterization of lipolytic inhibitor G(0)/G(1) switch gene-2 protein (G0S2) expression in male Sprague-Dawley rat skeletal muscle compared to relative content of adipose triglyceride lipase (ATGL) and comparitive gene identification-58 (CGI-58)

The rate-limiting enzyme in lipolysis, adipose triglyceride lipase (ATGL), is activated by comparative gene identification-58 (CGI-58) and inhibited by the G(0)/G(1) switch gene-2 (G0S2) protein. It is speculated that inhibition of ATGL is through a dose dependent manner of relative G0S2 protein content. There is little work examining G0S2 expression in lipolytic tissues, and the relative expression across oxidative tissues such as skeletal muscle has not yet been described. Three muscles, soleus (SOL), red gastrocnemius (RG), and white gastrocnemius (WG) were excised from 57-day old male Sprague-Dawley rats (n = 9). QRT-PCR was used for mRNA analysis, and western blotting was conducted to determine protein content. ATGL and G0S2 protein content were both greatest in the lipolytic SOL, with the least amount of both ATGL and G0S2 protein content found in the WG. CGI-58 protein content however did not mirror ATGL and G0S2 protein content, since the RG had the greatest CGI-58 protein content when compared to the SOL and WG. When comparing our tissues based on CGI-58-to-ATGL ratio and G0S2-to-ATGL ratio, it was discovered that contrary to oxidative demand, the glycolytic WG had the greatest activator CGI-58-to-ATGL ratio with the oxidative SOL having the least, and no differences in G0S2-to-ATGL across the three muscle types. These data suggest that the content of G0S2 relative to the lipase in skeletal muscle would not predict lipolytic potential.

Changes in mitochondrial perilipin 3 and perilipin 5 protein content in rat skeletal muscle following endurance training and acute stimulated contraction

NEW FINDINGS

What is the central question of this study? The aim was to determine whether mitochondrial protein content of perilipin 3 (PLIN3) and perilipin 5 (PLIN5) is increased following endurance training and whether mitochondrial PLIN5 protein is increased to a greater extent in endurance-trained rats when compared with sedentary rats following acute contraction. What is the main finding and its importance? Mitochondrial PLIN3 but not PLIN5 protein was increased in endurance-trained compared with sedentary rats, suggesting a mitochondrial role for PLIN3 due to chronic exercise. Contrary to our hypothesis, acute mitochondrial PLIN5 protein was similar in both sedentary and endurance-trained rats. Endurance training results in an increased association between skeletal muscle lipid droplets and mitochondria. This association is likely to be important for the expected increase in intramuscular fatty acid oxidation that occurs with endurance training. The perilipin family of lipid droplet proteins, PLIN(2-5), are thought to play a role in skeletal muscle lipolysis. Recently, results from our laboratory demonstrated that skeletal muscle mitochondria contain PLIN3 and PLIN5 protein. Furthermore, 30 min of stimulated contraction induces an increased mitochondrial PLIN5 content. To determine whether mitochondrial content of PLIN3 and PLIN5 is altered with endurance training, Sprague-Dawley rats were randomized into sedentary or endurance-trained groups for 8 weeks of treadmill running followed by an acute (30 min) sciatic nerve stimulation to induce lipolysis. Mitochondrial PLIN3 protein was ∼1.5-fold higher in red gastrocnemius of endurance-trained rats compared with sedentary animals, with no change in mitochondrial PLIN5 protein. In addition, there was an increase in plantaris intramuscular lipid storage. Acute electrically stimulated contraction in red gastrocnemius from sedentary and endurance-trained rats resulted in a similar increase of mitochondrial PLIN5 between these two groups, with no net change in PLIN3 in either group. Plantaris intramuscular lipid content decreased to a similar extent in sedentary and endurance-trained rats. These results suggest that while total mitochondrial PLIN5 content is not altered by endurance training, PLIN5 does have an acute role in the mitochondrial fraction during muscle contraction. Conversely, mitochondrial PLIN3 does not change acutely with muscle contraction, but PLIN3 content was increased following endurance training, indicating a role in chronic adaptations of skeletal muscle.

Higher PLIN5 but not PLIN3 content in isolated skeletal muscle mitochondria following acute in vivo contraction in rat hindlimb

Contraction-mediated lipolysis increases the association of lipid droplets and mitochondria, indicating an important role in the passage of fatty acids from lipid droplets to mitochondria in skeletal muscle. PLIN3 and PLIN5 are of particular interest to the lipid droplet-mitochondria interaction because PLIN3 is able to move about within cells and PLIN5 associates with skeletal muscle mitochondria. This study primarily investigated: 1) if PLIN3 is detected in skeletal muscle mitochondrial fraction; and 2) if mitochondrial protein content of PLIN3 and/or PLIN5 changes following stimulated contraction. A secondary aim was to determine if PLIN3 and PLIN5 associate and whether this changes following contraction. Male Long Evans rats (n = 21; age, 52 days; weight = 317 ± 6 g) underwent 30 min of hindlimb stimulation (10 msec impulses, 100 Hz/3 sec at 10-20 V; train duration 100 msec). Contraction induced a ~50% reduction in intramuscular lipid content measured by oil red-O staining of red gastrocnemius muscle. Mitochondria were isolated from red gastrocnemius muscle by differential centrifugation and proteins were detected by western blotting. Mitochondrial PLIN5 content was ~1.6-fold higher following 30 min of contraction and PLIN3 content was detected in the mitochondrial fraction, and unchanged following contraction. An association between PLIN3 and PLIN5 was observed and remained unaltered following contraction. PLIN5 may play a role in mitochondria during lipolysis, which is consistent with a role in facilitating/regulating mitochondrial fatty acid oxidation. PLIN3 and PLIN5 may be working together on the lipid droplet and mitochondria during contraction-induced lipolysis.

Passive transfer of protection against Bacillus anthracis infection in a murine model

Passive transfer of lymphocytes and sera from mice immunised using two different formulations containing recombinant protective antigen (rPA) have been used to further elucidate the mechanism of protection against Bacillus anthracis infection. The results demonstrated that an antibody response maybe important in protection against B. anthracis infection, under the conditions tested. The results provide further data for the development of an improved anthrax vaccine.

Human immune responses to the UK human anthrax vaccine

The IgG anti-protective antigen subclass antibody response of individuals who had been infected with anthrax was compared with that of healthy individuals immunized with the UK licensed anthrax vaccine. The predominant subclass in both groups was IgG1. In addition, IgG3 was seen in convalescent serum while vaccinees produced IgG2, IgG3 and IgG4 subclass. The significance of these results is discussed. Further work is required to determine the role of antibodies in mediating protective immunity in man.

Immune correlates of protection against anthrax

Bacillus anthracis protective antigen (PA) has been produced from a recombinant B. subtilis and its efficacy, when combined with the Ribi adjuvant (MPL-TDW-CWS) or alhydrogel, has been compared with that of the licensed UK human vaccine, in guinea pigs challenged with aerosolized Ames strain spores. Recombinant PA combined with the Ribi adjuvant performed as well as PA from B. anthracis cultures in previous reports (Ivins & Welkos 1986; Ivins et al. 1990; Turnbull et al. 1991; Jones et al. 1996; McBride et al. 1998) giving protection in 100% of animals exposed to the highest challenge dose of the Ames strain of B. anthracis that can be administered practically (retained lung doses of approximately 106 spores). In attempts at identifying markers of protection in immunized individuals, rPA in combination with the Ribi adjuvant induced a marker IgG2 response in guinea pigs with no significant differences in IgG1 levels when compared with other vaccine formulations (McBride et al. 1998). In BALBc mice, rPA with the Ribi adjuvant induced a higher IgG2a response compared with rPA with anhydrogel and the human vaccine. To examine the role of anti-PA-specific antibodies in protection, guinea pig sera is being passively transferred into guinea pigs and SCID mice, followed by protection. Similarly, B- and T-lymphocytes from immunized BALB/c mice are being separately and passively transferred into SCID mice with subsequent challenge. The neutralizing ability of the PA-specific antibodies is being studied using an in vitro macrophage lysis assay.

Definitive identification of Bacillus anthracis--a review

The word 'problem' is seen with some frequency in relation to clear differentiation between Bacillus anthracis and B. cereus. In fact, although the close relationship of these two species is undisputed, it is only in the case of a few borderline isolates, rarely encountered in practice, that any sort of identification problem exists. Until recently this was only important to the taxonomist who found it unsatisfactory not to be able to identify definitively such isolates. To most others, if the isolate was unable to produce anthrax in a laboratory animal, it was discarded as irrelevant without being named, or it was called B. cereus or given a name such as B. anthracis similis, or even a totally unrelated name. More recently, in view of the new light in which B. anthracis is increasingly seen, resulting from its putative association with bioaggression, clear identification has become a more critical issue. This paper reviews the current state of the art and suggests the way forward for the future.

World Health Organization activities on anthrax surveillance and control

The achievements of a World Health Organization Anthrax Working Group, established in 1990, have been the production of two editions of guidelines on anthrax surveillance and control and the formulation of templates to assist countries in the construction of their surveillance and control programmes. The latter was made possible by the active participation of the Department of Animal Production and Health, Ministry of Agriculture, Food and Fisheries, Zambia and the Livestock Development Programme, Mongu, Western Province, Zambia in a model country programme designed by the Working Group for the purpose. This paper elaborates on these achievements, particularly the lessons learned from the experience of Western Province, Zambia.

Protective efficacy of a recombinant protective antigen against Bacillus anthracis challenge and assessment of immunological markers

The efficacy of recombinant Bacillus anthracis Protective Antigen (rPA) produced in Bacillus subtilis and formulated in Alhydrogel or MPL-TDM-CWS (Ribi adjuvant) has been tested and compared to the licensed UK human vaccine in guinea pigs challenged by the aerosol route with the Ames strain of B. anthracis. rPA combined with the Ribi adjuvant was found to be the only formulation to provide 100% protection from challenge. Analysis of immunological parameters in the individual animals revealed significant differences between the rPA/Ribi vaccine group and rPA/Alhydrogel and human vaccine groups for antigen specific lymphocyte proliferation, PA neutralisation and antigen specific IgG2 levels, but indicated no significant differences in PA-specific IgG1 levels. rPA formulated in Alhydrogel induced a mainly IgG1 response whilst the rPA/Ribi vaccine produced a predominantly IgG2 response.

Airborne movement of anthrax spores from carcass sites in the Etosha National Park, Namibia

Tests for airborne movement of anthrax spores downwind from three heavily contaminated carcass sites were carried out under a range of wind conditions. Anthrax spores were detected in just three of 43 cyclone or gelatin filter air samples taken at distances of 6, 12 and 18 m from the sites. In addition, nine positives resulted during sampling sessions in which the site was mechanically disturbed, with a further five positives being found in sessions subsequent to those in which the site had been disturbed. The three positive samples not related to man-made disturbance were associated with the highest winds experienced during the study. Despite colony counts exceeding 100 on the culture plates in three instances, calculations showed that these represented very low worst case probable spore inhalation rates for animals or humans exposed to such levels. The low number of positives, the clear pattern of rapidly declining numbers of anthrax spores with distance downwind from the centres of the sites apparent on settle plates, and the persisting levels of contamination despite wind and rain, collectively suggest that the anthrax spores were associated with fairly heavy particles, although this was not seen by electron microscopy on soil samples from the sites. Overall, the findings are interpreted as indicating that it is very unlikely that Etosha animals contract anthrax by the inhalation route while simply in transit near or across a carcass site. The significance of the observations in relation to weather conditions in the Etosha, other studies on particulate aerosols in the region, and reports of long-distance airborne movement of microbes, is discussed.

Experimentally assessed public health risks associated with pigs from farms experiencing anthrax

Following an outbreak of anthrax in an intensive pig rearing unit in north Wales in 1989 a study was initiated by the Ministry of Agriculture, Fisheries and Food to assess public health risks during such an outbreak. Of 50 pigs infected by the addition of Bacillus anthracis spores to their feed, two died of anthrax six and eight days later. The remainder were observed for 21 days and exhibited only mild and transient clinical signs of disease. As judged by the results of bacteriological culture of appropriate tissues from the survivors, it was concluded that meat from healthy pigs killed 21 days after the latest case during an outbreak would not pose a public health risk.

Differentiation of Bacillus anthracis and other 'Bacillus cereus group' bacteria using IS231-derived sequences

Sequences based on the conserved 20 bp inverted repeat of IS231 variants were used as polymerase chain reaction-based fingerprinting primers of the member species of the Bacillus cereus group (B. anthracis, B. cereus, B. thuringiensis and B. mycoides), because of their close association with transposons, principally Tn4430 in B. thuringiensis. Fingerprints of B. anthracis were simple, and specifically allowed its identification and sub-differentiation from other members of the group. Fingerprints for B. cereus were strain-specific; those for B. thuringensis gave a 1650 bp product, characteristic of IS231 variants A-F. The same reaction conditions gave one or two bands for both B. anthracis and B. cereus that differed by restriction endonuclease mapping from the B. thuringiensis PCR product and established IS231 restriction maps; this does not preclude some kind of relationship between these products and IS231.

Evaluation of the Biolog system for the identification of Bacillus anthracis

The potential of the Biolog system for the identification of Bacillus anthracis was evaluated. In-house generated databases allowed the correct identification of 19 of 20 isolates of B. anthracis within 24 h. Five strains of the closely related B. cereus/thuringiensis group were misidentified as B. anthracis. For this reason the test could only serve as a primary screen with further testing being required to confirm identity. In addition 20% of all the strains of bacilli examined during the study gave unreadable reaction profiles due to false-positive reactions.

Ecology and epidemiology of anthrax in the Etosha National Park, Namibia

Analysis of mortality records has revealed distinct patterns in the incidence of anthrax in elephant and plains ungulates. The seasonal peak among the former is in November at the end of the dry season, while among the latter it occurs in March towards the end of the rainy season. Among elephants, there has been a notable spread of the disease to the west of the Park. Age and sex analyses indicate that, except for zebra, proportionally greater numbers of adult males die of anthrax among the species predominantly affected; however, zebra carcases are difficult to sex. In a study to identify possible environmental sources of infection, B. anthracis was detected in 3.3% of 92 water and 3.0% of 230 soil samples collected at different times of the year from 23 sites not associated with known cases of anthrax. Slight seasonal differences were noted with 5.7% positives occurring in the cold-dry period (May to August), 3.5% in the hot-dry season (September to December) and 1.4% in the hot-wet season (January to April). Higher rates (26.0% of 73 samples) were found in water from waterholes in the western part of the Park at the time of an outbreak in elephants. The possible importance of scavenger faeces was confirmed with > 50% of vulture, jackal and hyaena faeces collected from the vicinity of confirmed anthrax carcases yielding B. anthracis, sometimes in substantial numbers, while no spores were found in faeces not associated with known anthrax carcases. Despite terminal B. anthracis levels of usually > 10(7) cfu/milliliters in the blood of animals dying of anthrax, spore levels in soil contaminated by such blood at sites of anthrax carcases ranged from undetectable to a few tens of thousands. The rapid loss of viability in soil and water of anthrax bacilli was monitored experimentally and the importance of soil type demonstrated. Survival and extent of sporulation of the bacilli in water were shown to be dependent on the rate at which the blood was diluted out. Other relevant parameters examined were background flora, pH and sunlight.

Differentiation of Bacillus anthracis from other Bacillus cereus group bacteria with the PCR

Variation among isolates of Bacillus anthracis was examined by using restriction fragmentation patterns and the PCR performed with arbitrary and sequence-specific oligonucleotide primers. The patterns were compared with the patterns generated from strains of closely related species belonging to the "Bacillus cereus group" of bacteria, including B. cereus, Bacillus thuringiensis, and Bacillus mycoides. All B. anthracis profiles were identical for each of 18 restriction enzymes, each of 10 arbitrary PCR primers, and a repetitive extragenic palindrome-specific PCR primer. The PCR profiles generated with a coliphage M13-based primer exhibited slight pattern variation in a 400- to 500-bp band region. The B. anthracis profiles were unique compared with the profiles of the other species examined. In these other species, strain-to-strain variations were observed. Our results showed that isolates of B. anthracis are almost completely homogeneous, indicating a clonal lineage, and are distinct from other members of the B. cereus group and that B. anthracis, as a species in its own right, may have evolved only relatively recently.

The development and assessment of DNA and oligonucleotide probes for the specific detection of Bacillus anthracis

Two DNA probes and a number of oligonucleotide probes were designed from the virulence factor genes of Bacillus anthracis. These probes were tested for specificity against 52 B. anthracis strains and 233 Bacillus strains encompassing 23 other species. A rapid slot blotting technique was used for screening the large numbers of isolates involved. All probes tested appeared to be specific for B. anthracis under high stringency conditions. These probes could differentiate between virulent and avirulent strains. The probes were also applied to the detection of B. anthracis in routine environmental and clinical samples. A non-radioactive hybridization and detection system based on digoxigenin-11-dUTP was developed.

Isolation and purification of Aeromonas sobria cytotonic enterotoxin and beta-haemolysin

Aeromonas sp., grown in tryptone soya broth supplemented with yeast extract, 0.6%, pH 7.5, and incubated with agitation at 100 oscillations/min for 15 h at 37 degrees C produced optimal amounts of beta-haemolysin and cytotonic enterotoxin. More prolonged incubation resulted in the loss of enterotoxic activity and anion exchange chromatographic analysis indicated the presence of a moiety capable of breaking down the toxin. Anion exchange fast protein liquid chromatography resulted in a single peak of haemolytic activity and two peaks with enterotoxic activity. The cytotonic enterotoxin was purified from the fraction most active in the infant mouse assay; the second peak, which did not cross-react immunologically, may represent a second cytotonic enterotoxin. Neither peak was observed in the chromatographic fractions of filtrates from strains devoid of activity in the infant mouse assay. Purified enterotoxin, estimated to have a mol. wt of 15 kDa by SDS-PAGE, caused fluid accumulation in the infant mouse assay, was non-haemolytic to rabbit erythrocytes, caused an increase in cAMP activity in tissue culture cells and did not cross-react immunologically with components of cholera toxin or the whole toxin. Purified beta-haemolysin had an estimated mol. wt of 55 kDa, lysed rabbit erythrocytes and did not cause fluid accumulation in the infant mouse test.

Serology and anthrax in humans, livestock and Etosha National Park wildlife

Results are presented from a number of epidemiological studies using enzyme immunoassays (EIA) based on the purified anthrax toxin antigens, protective antigen, lethal factor and oedema factor. Studies on sera from a group of 62 human anthrax patients in Turkey and from cattle in Britain following two unrelated outbreaks of anthrax show that EIA using protective antigen can be a useful diagnostic aid and will detect subclinical infections in appropriate circumstances. A serological survey on wildlife in the Etosha National Park, Namibia, where anthrax is endemic, showed that naturally acquired anthrax-specific antibodies are rare in herbivores but common in carnivores; in carnivores, titres appear to reflect the prevalence of anthrax in their ranges. Problems, as yet unresolved, were encountered in studies on sera from pigs following an outbreak of anthrax on a farm in Wales. Clinical details, including treatment, of the human and one of the bovine outbreaks are summarized and discussed in relation to the serological findings.

Bacillus anthracis but not always anthrax

Gram-positive bacilli isolated during epidemiological investigations which, on the basis of conventional tests, resemble Bacillus anthracis but which fail to produce the capsule or to induce anthrax in test animals have long been dismissed in clinical and veterinary laboratories as B. cereus or simply as unidentified Bacillus spp. and thereupon discarded as inconsequential. In this study, the application of newly available DNA probe, polymerase chain reaction and specific toxin antigen detection technology has revealed that a proportion of such strains are B. anthracis which lack the plasmid carrying the capsule gene (pXO2). While these techniques cannot, of course, be used to confirm the identities of strains resembling B. anthracis but which also lack the plasmid carrying the toxin genes (pXO1), the likelihood that these also are bona fide B. anthracis becomes more acceptable. (As yet no naturally occurring pXO1-/2+ strains have been found.) At this point, the significance of the presence of such avirulent forms of B. anthracis in specimens can only be a subject for speculation, but the possibility that they may be indicators of virulent parents somewhere in the system being examined must be considered.

Anthrax vaccines: past, present and future

Most livestock vaccines in use throughout the world today for immunization against anthrax are derivatives of the live spore vaccine formulated by Sterne in 1937 and still use descendants of his strain 34F2. Credit belongs to this formulation for effective control in many countries with considerable reduction, sometimes complete elimination, of the disease in animals and, since man generally acquires it from livestock, in man also. However, there are some contraindications of its use and situations in which it cannot be easily administered, and room for development of a successor is discussed. The human vaccines, formulated for at-risk occupations and situations, date from the 1950s (UK vaccine) and 1960s (US vaccine). The rather greater need for improvement of these as compared with the veterinary vaccine stimulated valuable research during the 1980s which has led to a number of promising candidate alternatives for the future.

Anthrax in wildlife in the Luangwa Valley, Zambia

An abnormally high mortality among hippos (Hippopotamus amphibius) in the Luangwa River valley between June and November 1987 and estimated to number more than 4000 deaths was attributed to anthrax. Several other species, particularly Cape buffalo (Syncerus caffer) and elephant (Loxodonta africana), appear to have been affected. A smaller outbreak of anthrax in hippos occurred between August and September 1988, approximately 100 km up-river. A field study was arranged in August 1989 to assess the extent of environmental contamination by Bacillus anthracis and the risks to people in the area, to study possible methods of control and to equip local laboratory staff for continued monitoring of the disease. The study confirmed the enzootic status of the region. The characteristics of the outbreaks of anthrax in 1987 and 1988, and the results of the field study are described.

Antibodies to anthrax toxin in humans and guinea pigs and their relevance to protective immunity

A forerunning study on the relationship between antibodies to the protective antigen (PA) and lethal factor (LF) components of anthrax toxin and protective immunity has been expanded and extended to include the third toxin component, the edema factor (EF). It was found that protection against the "vaccine resistant" Ames strain was possible in the absence of detectable anti-LF and anti-EF antibodies. Evidence is given that PA may be the essential anthrax-derived antigen for protection, but that equally essential is that it be presented to the host's immune system in such a manner as to provide stimulation of more than just production of antibody to PA. Titers to the three components in sera of individuals with histories of clinically diagnosed anthrax as well as from human vaccinees are included in the report.

Purification of anthrax-toxin components by high-performance anion-exchange, gel-filtration and hydrophobic-interaction chromatography

A procedure has been developed for purification of the tripartite anthrax-toxin components. This involves sequential high-performance anion-exchange, gel-filtration and hydrophobic-interaction chromatography. From an initial culture volume of 15 litres, typical yields of 8 mg of protective antigen, 13 mg of lethal factor and 7 mg of oedema factor are produced to higher degrees of purity than have previously been achieved by conventional chromatographic techniques.

Development of antibodies to protective antigen and lethal factor components of anthrax toxin in humans and guinea pigs and their relevance to protective immunity

A competitive inhibition enzyme-linked immunosorbent assay (ELISA) was developed to detect antibodies in serum to the protective antigen (PA) and lethal factor (LF) components of anthrax toxin. Current human vaccination schedules with an acellular vaccine induce predictable and lasting antibody titers to PA and, when present in the vaccine, to LF. Live spore vaccine administered to guinea pigs in a single dose conferred significantly better protection than the human vaccines (P less than 0.001), although they elicited significantly lower (P less than 0.0005) anti-PA and anti-LF titers at time of challenge with virulent Bacillus anthracis. Substantial anti-PA and anti-LF titers may not, therefore, indicate solid protective immunity against anthrax infection. The ELISA system was also shown to be capable of detecting anti-PA and anti-LF antibodies in the sera of individuals with histories of clinical anthrax. The advantage of ELISA over the Ouchterlony gel diffusion test and indirect microhemagglutination assay are demonstrated. There was a highly significant degree of correlation between ELISA and the indirect microhemagglutination assay (P less than 0.0005); but ELISA was markedly superior in terms of reproducibility, reliability, specificity, and simplicity in performance and stability of the bound antigen.

Intestinal carriage of Bacillus cereus: faecal isolation studies in three population groups

The results of examinations of stools for Bacillus cereus among three unrelated groups of individuals are presented. The groups consisted of (1) healthy school-children aged 6-11 years in a rural region of South Africa examined during each of the four seasons of the year; (2) 15 healthy volunteers comprising staff of a London microbiology laboratory and their families examined on each of 3 consecutive weeks; (3) 75 unrelated young children, 2 months to 5 years of age, in a second rural region of South Africa examined during a pilot study of 1 week's duration on the aetiology of rural gastroenteritis. The stools of the last group were submitted as being related to present or recent diarrhoea in the respective children. In group 1, B. cereus isolation rates ranged from 24.3% at the autumn visit to 43% at the summer visit with a significantly higher rate of isolation in the summer than at other seasons of the year (P less than 0.05). B. cereus was isolated from 40% of group 2 volunteers on week 1, none on week 2 and 20% on week 3. The organism was detected in the 12 positive specimens at levels of approximately 10(2)/g and constituted 2.5-30% of the total aerobic spore-forming bacillus population in the stools. In group 3, B. cereus was recovered from 18.7% of the stool samples and was isolated consecutively with other pathogens (enteropathogenic Escherichia coli and rotavirus) on only five occasions. In groups 1 and 3, less than 5% of the stools had '3+' levels of B. cereus (greater than 10 colonies per direct plate culture). B. cereus was readily isolated from all of 10 food samples, representative of the typical diet of the group 1 individuals, and was present in substantial numbers (10(4) to 5.5 X 10(6)/g) in half of them. The isolation results, supported by serotyping, indicated that carriage of B. cereus in stools is transient and its presence at any one time reflects solely its intake with foods.

In vitro and in vivo cholera toxin production by classical and El Tor isolates of Vibrio cholerae

A comparative study was carried out on the in vitro production of cholera toxin by 19 Vibrio cholerae El Tor isolates from patients with cholera in South Africa, one El Tor isolate from a patient in Malawi (a country approximately 1000 km north-northeast of South Africa), 6 El Tor and 12 classical type isolates from patients in Bangladesh, and 5 culture collection classical strains. Identical phage types and indistinguishable toxigenicities among the South African and Malawi V. cholerae, representing isolations obtained over a 10-year period, indicated that essentially a single strain was involved in the cholera of these regions. Similarly, phage typing and toxin profiles indicated that the 12 classical and 6 El Tor V. cholerae cultures in Bangladesh, all isolated in November 1983, represented just two strains. As assessed by titrations in Y-1 mouse adrenal and Chinese hamster ovary cell lines, the general order of toxigenicities was Bangladesh and culture collection classical greater than Bangladesh El Tor greater than southern African El Tor. The African isolates consistently gave rise to very low titers. Their relative reluctance to produce the toxin in vitro compared with the culture collection classical strains, particularly strain 569B, was confirmed by rocket electrophoresis. In somewhat of a contrast, maximum in vivo titers in rice water stools from cholera patients in South Africa and from both classical and El Tor type cholera patients in Bangladesh were essentially equal. It is postulated that under the continuous culture conditions that occur in vivo, cholera toxin concentrations can accumulate to a maximum level, depending on the rate of purging by the diarrheal fluid rather than the toxigenicity of the infecting stain. The relevance of these findings to the relative severities of classical and El Tor types of cholera is discussed.

Passage of Salmonella enteritidis and Salmonella thompson through chick ileocecal mucosa

The passage of Salmonella enteritidis and S. thompson across the cecal mucosa has been visualized in an electron microscope study with the freshly hatched chick as a model. The uptake of salmonellae by macrophages took place in the cecal lumen; the macrophages became abnormal and often ruptured to release organisms back into the lumen. The entry of bacteria into the epithelial cells was associated with a series of pathological changes, beginning with the appearance of active Golgi apparatus and the production of a variety of lysosomal vesicles. Salmonellae became sequestered within lysosomes but were unaffected by the presence of hydrolytic enzyme. Epithelial cell death was related to particularly large numbers of bacteria. Fragments of invaded epithelial cells, especially those undergoing cell death, contributed to the cytoplasmic debris and released further salmonellae into the lumen. Bacteria were never observed in large numbers below the basement membrane, and there was no significant pathology in the lamina propria tissue. Wandering cells, identified as macrophages and containing the bacteria, were observed spanning the epithelial and lamina propria regions through breaks in the basement membrane. It is suggested that the passage of bacteria from the epithelium to the lamina propria is primarily the result of capture and transport within host macrophages.

Enterotoxin production in relation to taxonomic grouping and source of isolation of Aeromonas species

A total of 19 of 20 (95%) strains of Aeromonas hydrophila biovar hydrophila and 16 of 17 (94%) strains of Aeromonas sobria isolated from a variety of clinical and environmental sources were found to be enterotoxin positive. Only 2 of 18 (11%) A. hydrophila biovar anaerogenes and 2 of 13 (15%) unidentified Aeromonas strains from a similar variety of sources produced enterotoxin. No association was apparent between the source of isolation, in particular diarrheal stools, and enterotoxigenicity; 41% of the isolates from diarrheal stools were enterotoxin negative. A strong correlation was noted between ability to produce enterotoxin and positive results in six characters: lysine decarboxylase and Voges-Proskauer reactions, production of gas from glucose, gluconate oxidation, xanthine hydrolysis, and hemolysis of human erythrocytes. In the majority of cases (35 of 39 strains), enterotoxigenicity was detected using cell-free filtrates of brain heart infusion broth cultures grown at 36 degrees C for 15; however, the other four positive isolates were detected after growth in the same broth at 30 degrees C or in Casamino Acids-yeast extract broth at 30 or 37 degrees C. It is recommended that for enterotoxin tests, strains should be grown in both media at both temperatures. The infant mouse test was found to be a simple and reliable method for detection of the enterotoxin. The toxin proved to be heat labile and not neutralized by cholera antitoxin.

Non-gastrointestinal Bacillus cereus infections: an analysis of exotoxin production by strains isolated over a two-year period

Isolates of Bacillus cereus from 118 cases, and two maternity unit outbreaks, of non-gastrointestinal infection were grouped on the basis of their estimated probable involvement in the infections from which they were isolated: (i) high probability--48 strains; (ii) intermediate--16 strains; (iii) low--7 strains; (iv) very low ("irrelevant")--49 strains. Rabbit skin test, haemolysin and phospholipase assays were used to determine exotoxin activities of strains within each group. The results suggest a significant relation between the virulence of an isolate as reflected in the degree to which it appeared responsible for the signs and symptoms of an infection, and its toxigenicity in the skin test. This is attributed to the ability of B cereus strains to synthesise, in varying degrees, a necrotic enterotoxin, possibly in conjunction with the primary haemolysin (cereolysin). The cases analysed in this study support the contention that B cereus, when isolated from an infection, may not be an inconsequential contaminant and should not be too readily dismissed as such.