Solvent-Assisted Hot Melt Extrusion of a Thermally Labile, High Melting Point Compound

Molecular dispersions are a highly effective method of increasing bioavailability for a poorly soluble active pharmaceutical ingredient (API) and can be prepared on a large scale by hot melt extrusion (HME). Processing thermally labile active pharmaceutical ingredients (APIs) via HME is generally more difficult, with operating temperatures limited to below that of the API melting point. API melting is considered essential to facilitate the formation of a fully homogeneous amorphous system. Processing below the melting point renders the system much more susceptible to residual crystalline content; hence, HME is not suitable for APIs which degrade upon melting. In the following work, meloxicam (MEL) was used as a model API, possessing properties of high melting temperature and thermal lability. In this proof of concept work, a modified HME method, termed solvent-assisted HME, was used to overcome this issue and prepare an amorphous solid dispersion using HME, wherein a solvent was incorporated in the formulation blend during extrusion and removed post-processing. Formulations containing 10%wt meloxicam (MEL) and 90%wt polyvinylpyrrolidone vinyl acetate (PVPVA) copolymer were extruded using a twin-screw extruder at temperatures below the melting point of MEL. Dimethylformamide (DMF) solvent was added directly into the extruder barrel through a liquid addition port, resulting in extrudate products having a higher conversion of API to the amorphous form. The incorporation of solvent allowed a significant reduction in processing temperatures due to its increased mobility, while also driving the conversion of the API to its amorphous form. The solvent was successfully reduced through a secondary drying step using a vacuum oven. This advancement has demonstrated the potential for thermally labile APIs to be processed via HME expanding the applications of this technology.

A comparative study between hot-melt extrusion and spray-drying for the manufacture of anti-hypertension compatible monolithic fixed-dose combination products

The purpose of this work was to investigate the application of different advanced continuous processing techniques (hot melt extrusion and spray drying) to the production of fixed-dose combination (FDC) monolithic systems comprising of hydrochlorothiazide and ramipril for the treatment of hypertension. Identical FDC formulations were manufactured by the two different methods and were characterised using powder X-ray diffraction (PXRD) and modulated differential scanning calorimetry (mDSC). Drug dissolution rates were investigated using a Wood's apparatus, while physical stability was assessed on storage under controlled temperature and humidity conditions. Interestingly both drugs were transformed into their amorphous forms when spray dried, however, hydrochlorothiazide was determined, by PXRD, to be partially crystalline when hot melt extruded with either polymer carrier (Kollidon® VA 64 or Soluplus®). Hot melt extrusion was found to result in significant degradation of ramipril, however, this could be mitigated by the inclusion of the plasticizer, polyethylene glycol 3350, in the formulation and appropriate adjustment of processing temperature. The results of intrinsic dissolution rate studies showed that hot-melt extruded samples were found to release both drugs faster than identical formulations produced via spray drying. However, the differences were attributable to the surface roughness of the compressed discs in the Wood's apparatus, rather than solid state differences between samples. After a 60-day stability study spray dried samples exhibited a greater physical stability than the equivalent hot melt extruded samples.

Gastroretentive extended-release floating granules prepared using a novel fluidized hot melt granulation (FHMG) technique

The objective of this work was to investigate the feasibility of using a novel granulation technique, namely, fluidized hot melt granulation (FHMG), to prepare gastroretentive extended-release floating granules. In this study we have utilized FHMG, a solvent free process in which granulation is achieved with the aid of low melting point materials, using Compritol 888 ATO and Gelucire 50/13 as meltable binders, in place of conventional liquid binders. The physicochemical properties, morphology, floating properties, and drug release of the manufactured granules were investigated. Granules prepared by this method were spherical in shape and showed good flowability. The floating granules exhibited sustained release exceeding 10 h. Granule buoyancy (floating time and strength) and drug release properties were significantly influenced by formulation variables such as excipient type and concentration, and the physical characteristics (particle size, hydrophilicity) of the excipients. Drug release rate was increased by increasing the concentration of hydroxypropyl cellulose (HPC) and Gelucire 50/13, or by decreasing the particle size of HPC. Floating strength was improved through the incorporation of sodium bicarbonate and citric acid. Furthermore, floating strength was influenced by the concentration of HPC within the formulation. Granules prepared in this way show good physical characteristics, floating ability, and drug release properties when placed in simulated gastric fluid. Moreover, the drug release and floating properties can be controlled by modification of the ratio or physical characteristics of the excipients used in the formulation.

Preparation and evaluation of sustained-release matrix tablets based on metoprolol and an acrylic carrier using injection moulding

Sustained-release matrix tablets based on Eudragit RL and RS were manufactured by injection moulding. The influence of process temperature; matrix composition; drug load, plasticizer level; and salt form of metoprolol: tartrate (MPT), fumarate (MPF) and succinate (MPS) on ease of processing and drug release were evaluated. Formulations composed of 70/30% Eudragit RL/MPT showed the fastest drug release, substituting part of Eudragit RL by RS resulted in slower drug release, all following first-order release kinetics. Drug load only affected drug release of matrices composed of Eudragit RS: a higher MPT concentration yielded faster release rates. Adding triethyl citrate enhanced the processability, but was detrimental to long-term stability. The process temperature and plasticizer level had no effect on drug release, whereas metoprolol salt form significantly influenced release properties. The moulded tablets had a low porosity and a smooth surface morphology. A plasticizing effect of MPT, MPS and MPF on Eudragit RS and Eudragit RL was observed via DSC and DMA. Solubility parameter assessment, thermal analysis and X-ray diffraction demonstrated the formation of a solid solution immediately after production, in which H-bonds were formed between metoprolol and Eudragit as evidenced by near-infrared spectroscopy. However, high drug loadings of MPS and MPF showed a tendency to recrystallise during storage. The in vivo performance of injection-moulded tablets was strongly dependent upon drug loading.

Comparative vaccine efficacy of different isoforms of recombinant protective antigen against Bacillus anthracis spore challenge in rabbits

The next-generation human anthrax vaccine developed by the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) is based upon purified Bacillus anthracis recombinant protective antigen (rPA) adsorbed to aluminum hydroxide adjuvant (Alhydrogel). In addition to being safe, and effective, it is important that such a vaccine be fully characterized. Four major protein isoforms detected in purified rPA by native PAGE during research and development were reduced to two primary isoforms in bulk material produced by an improved process performed under Good Manufacturing Practices (GMP). Analysis of both rPA preparations by a protein-isoaspartyl-methyl-transferase assay (PIMT) revealed the presence of increasing amounts of iso-aspartic acid correlating with isoform content and suggesting deamidation as the source of rPA charge heterogeneity. Additional purification of GMP rPA by anion exchange chromatography separated and enriched the two principal isoforms. The in vitro and in vivo biological activities of each isoform were measured in comparison to the whole GMP preparation. There was no significant difference in the biological activity of each isoform compared to GMP rPA when analyzed in the presence of lethal factor using a macrophage lysis assay. Vaccination with the two individual isoforms revealed no differences in cytotoxicity neutralization antibody titers when compared to the GMP preparation although one isoform induced more anti-PA IgG antibody than the GMP material. Most importantly, each of the two isoforms as well as the whole GMP preparation protected 90-100% of rabbits challenged parenterally with 129 LD50 of B. anthracis Ames spores. The equivalent biological activity and vaccine efficacy of the two isoforms suggests that further processing to separate isoforms is unnecessary for continued testing of this next-generation anthrax vaccine.

Duration of protection of rabbits after vaccination with Bacillus anthracis recombinant protective antigen vaccine

Long-term protection of rabbits that had been vaccinated with two doses of a recombinant protective antigen (rPA) vaccine was examined against an aerosol spore challenge with the Ames isolate of Bacillus anthracis at 6 and 12 months. At 6 months after the primary injection, survival was 74.1% (20/27) with quantitative ELISA titer of 22.3 microg of anti-rPA IgG per millilitre and toxin neutralizing antibody (TNA) assay titer of 332. At 12 months after the primary injection, only 37.5% (9/24) of the rabbits were protected with quantitative ELISA titer of 19.8 microg of anti-rPA IgG per millilitre and TNA assay titer of 286. There was a significant loss of protection (p = 0.0117) and a significant difference in survival curves (p = 0.0157) between the 6- and 12-month groups. When ELISA or TNA assay titer, gender, and challenge dose were entered into a forward logistic regression model, week 26 ELISA titer (p = 0.0236) and week 13 TNA assay titer (p = 0.0147) for the 6-month group, and week 26 ELISA titer (p = 0.0326) and week 8 TNA assay titer (p = 0.0190) for the 12-month group, were significant predictors of survival. Neither gender nor challenge dose were identified as having a statistically significant effect on survival. Booster vaccinations with rPA may be required for the long-term protection of rabbits against anthrax.

Evaluation of an anti-rPA IgG ELISA for measuring the antibody response in mice

A recombinant protective antigen (rPA)-based enzyme-linked immunosorbent assay (ELISA) was developed to measure the serological response of female A/J mice after inoculation with the new rPA-based anthrax vaccine. Several fundamental parameters of the ELISA were evaluated: specificity, precision, accuracy, linearity, and stability. Experimental results suggested that the quantitative anti-rPA IgG ELISA could be used to measure antibody levels in female A/J mice and may be useful as a potency assay to monitor consistency of manufacture of a rPA-based vaccine for planned clinical trials.

Development of an in vitro-based potency assay for anthrax vaccine

The potency assay currently used to evaluate consistency of manufacture for the anthrax vaccine is contingent upon meeting specified parameters after statistical analysis of the percent survival and time to death of vaccinated guinea pigs after challenge with spores of a virulent strain of Bacillus anthracis. During the development of a new anthrax vaccine based upon recombinant protective antigen (rPA) adsorbed to aluminum hydroxide gel (Alhydrogel), we found that the serological response of female A/J mice, as measured by a quantitative anti-rPA IgG ELISA, may be an effective method to monitor a manufacturer's consistency for rPA-based vaccines. An advantage of the proposed in vitro-based potency assay is that it will not need stringent biosafety containment measures as required by the current guinea pig potency assay.

Defining a serological correlate of protection in rabbits for a recombinant anthrax vaccine

In these studies, a serological correlate of protection against anthrax was identified in New Zealand white (NZW) rabbits that had been given one or two injections of various amounts of recombinant protective antigen (rPA) combined with aluminum hydroxide adjuvant (Alhydrogel). Rabbits were subsequently challenged by the aerosol route with spores of the Ames isolate of Bacillus anthracis. Results suggested that the antibody response, as determined by the quantitative anti-rPA IgG ELISA and toxin neutralizing antibody (TNA) assay, were significant predictors (P<0.0015) of protection against a B. anthracis aerosol spore challenge in rabbits.

Mu dI1(Ap lac) mutagenesis of Yersinia pestis plasmid pFra and identification of temperature-regulated loci associated with virulence

The F1 capsule of Yersinia pestis, encoded by the 100 kb plasmid pFra, is often assumed to be essential for full virulence of Y. pestis. However, virulent strains of Y. pestis that are F1- and either pFra+ or pFra- have been reported. To assess the role of pFra-encoded factors in virulence, mutants in pFra with insertions of the defective transposing bacteriophage Mu dl(Ap lac) were obtained, by using the wild type (wt) and the pLcr-cured derivative of strain C092. Mutants that exhibited temperature regulation of lactose fermentation and retarded electrophoretic mobility of pFra were selected. A total of 15 insertion mutants were isolated in the wt strain (12 of which had a single insertion in the genome, in pFra); and 24 mutants in the isogenic pLcr- derivative. Four of the pLcr+ mutants, and none of the pLcr- mutants, were F1-. All F1- mutants were decreased in virulence for mice compared to the wt parent; and five of the F1+ mutants also were significantly attenuated in mice. Fusion end-joints of insert DNA were cloned into Escherichia coli by using pMLB524, a vector for rescuing operon fusions of lacZ. Recombinants were obtained which contained pFra inserts ranging from < 2kb to approximately 36 kb, and the insertions occurred at several sites on pFra. All of the four F1- mutants tested mapped within the F1 capsule operon (caf1). The remaining five attenuated mutants sequenced were F1+ and mapped outside of but near the operon. Sequencing and complete analysis of the pFra insertions mutants could facilitate identification of new potential virulence factors.

Biodefense-driven murine model of pneumonic melioidosis

A whole-body mouse model of pneumonic melioidosis was established for future evaluation of biodefense vaccine candidates. The aerosol 50% lethal doses of Burkholderia pseudomallei strain 1026b for BALB/c and C57BL/6 mice and the times to death, dissemination in organs, and tissue loads after exposure of the mice to low- and high-dose aerosols are reported. In addition, rpsL mutant backgrounds were attenuated in this acute model of disease.

Immune response to Yersinia outer proteins and other Yersinia pestis antigens after experimental plague infection in mice

There is limited information concerning the nature and extent of the immune response to the virulence determinants of Yersinia pestis during the course of plague infection. In this study, we evaluated the humoral immune response of mice that survived lethal Y. pestis aerosol challenge after antibiotic treatment. Such a model may replicate the clinical situation in humans and indicate which virulence determinants are expressed in vivo. Immunoglobulin G enzyme-linked immunosorbent assay and immunoblotting were performed by using purified, recombinant antigens including F1, V antigen, YpkA, YopH, YopM, YopB, YopD, YopN, YopE, YopK, plasminogen activator protease (Pla), and pH 6 antigen as well as purified lipopolysaccharide. The major antigens recognized by murine convalescent sera were F1, V antigen, YopH, YopM, YopD, and Pla. Early treatment with antibiotics tended to reduce the immune response and differences between antibiotic treatment regimens were noted. These results may indicate that only some virulence factors are expressed and/or immunogenic during infection. This information may prove useful for selecting potential vaccine candidates and for developing improved serologic diagnostic assays.

Protective efficacy of recombinant Yersinia outer proteins against bubonic plague caused by encapsulated and nonencapsulated Yersinia pestis

To evaluate the role of Yersinia outer proteins (Yops) in conferring protective immunity against plague, six yop loci from Yersinia pestis were individually amplified by PCR, cloned, and expressed in Escherichia coli. The recombinant proteins were purified and injected into mice. Most Yop-vaccinated animals succumbed to infection with either wild-type encapsulated Y. pestis or a virulent, nonencapsulated isogenic variant. Vaccination with YpkA significantly prolonged mean survival time but did not increase overall survival of mice infected with the nonencapsulated strain. The only significant protection against death was observed in YopD-vaccinated mice challenged with the nonencapsulated strain.

The enteric Campylobacter: they are everywhere

Although Campylobacter spp. are perhaps the most ubiquitous bacterial pathogens known to man, laboratory diagnosis of Campylobacter enteritis is not particularly problematic. The organism's ability to thrive at elevated temperatures facilitates its isolation directly from stool. Enteric infection with Campylobacter spp., despite its invasive nature, is usually self-limiting in the otherwise healthy individual. Management of enteric Campylobacter infection, therefore, is not complex and for most cases simply involves an appropriate rehydration strategy. In addition to the 'tried and true' approaches of good sanitation and thorough cooking of meats to prevent Campylobacter infection, recent advances in vaccine development appear promising.

Protection against experimental bubonic and pneumonic plague by a recombinant capsular F1-V antigen fusion protein vaccine

The current human whole-cell vaccine is ineffective against pneumonic plague caused by typical F1 capsule positive (F1+) strains of Yersinia pestis. The authors found this vaccine to also be ineffective against F1-negative (F1-) Y. pestis strains, which have been isolated from a human case and from rodents. For these reasons, the authors developed a recombinant vaccine composed of a fusion protein of F1 with a second protective immunogen, V antigen. This vaccine protected experimental mice against pneumonic as well as bubonic plague produced by either an F1+ or F1- strain of Y. pestis, gave better protection than F1 or V alone against the F1+ strain, and may provide the basis for an improved human plague vaccine.

Protection of mice from fatal bubonic and pneumonic plague by passive immunization with monoclonal antibodies against the F1 protein of Yersinia pestis

Monoclonal antibodies (MAbs) to the fraction 1 (F1) protein of Yersinia pestis protected mice against fatal pneumonic as well as bubonic plague from wild-type F1+ organisms. The rare isolation of a virulent F1- isolate from surviving animals supports earlier studies suggesting that improved vaccines should consist of immunogens to protect against F1- variants. The high degree of protection with IgG MAb suggests that secretory IgA is not required for protection from pneumonic plague.

Fraction 1 capsular antigen (F1) purification from Yersinia pestis CO92 and from an Escherichia coli recombinant strain and efficacy against lethal plague challenge

As a first step in formulating an improved plague vaccine, we developed a simple purification strategy that produced high yields of pure cell-associated and culture supernatant-derived fraction 1 capsular antigen (F1) from both avirulent Yersinia pestis C092 (Pgm- Lcr-) and an Escherichia coli F1-producing recombinant strain. Cell-associated F1 was partially purified by sequential ammonium sulfate precipitations of a sodium chloride extract of acetone-dried bacteria harvested from broth cultures. Cell-free F1 was precipitated directly from culture supernatants with a single application of 30% ammonium sulfate. By exploiting the aggregative property of F1, large quantities of purified high-molecular-weight F1 species from both cell extracts and supernatants were isolated in the void volume of a preparative gel filtration column. Highly purified, endotoxin-free F1, combined with two different adjuvants, induced very high F1 titers in mice and protected them against either subcutaneous (70 to 100% survival) or aerosol (65 to 84% survival) challenge with virulent organisms. This protection was independent of the source of the antigen and the adjuvant used. F1-induced protection against both subcutaneous and aerosol challenge was also significantly better than that conferred by immunization with the licensed killed whole-cell vaccine. Our results indicate that F1 antigen represents a major protective component of previously studied crude capsule preparations, and immunity to F1 antigen provides a primary means for the host to overcome plague infection by either the subcutaneous or respiratory route.

Relationship between virulence and immunity as revealed in recent studies of the F1 capsule of Yersinia pestis

Yersinia pestis, the causative agent of plague, possesses multiple virulence determinants encoded on its three plasmids and on its chromosome. We evaluated the role of the protein capsule F1 in virulence an immunity against plague. Strains lacking F1, either those that are naturally occurring or those with genetically defined nonpolar mutations in the structural gene, retained their virulence for mice and nonhuman primates. However, both active immunization with F1, from either a recombinant vector or Y. pestis, and passive immunization with F1 monoclonal antibody protected mice from experimental infection with wild-type F1-positive organisms. These results suggest that protective immunogens like F1 need not be essential for virulence. The rare isolation of virulent F1-negative organisms from F1-immunized animals infected with F1-positive strains supports this conclusion and also suggests that, in addition to F1, an optimal vaccine against plague should include essential virulence factors as immunogens.

mxiA of Shigella flexneri 2a, which facilitates export of invasion plasmid antigens, encodes a homolog of the low-calcium-response protein, LcrD, of Yersinia pestis

The plasmid-encoded invasion plasmid antigen (Ipa) export accessory locus of Shigella flexneri 2a, mxiA, was cloned, and the complete DNA sequence of the gene was determined. The mixA open reading frame was found to encode a polypeptide of 74.03 kDa with a pI of 5.02. A hydropathy analysis of the predicted protein revealed a hydrophilic C terminus and an extremely hydrophobic N terminus without a cleavable signal sequence but with several potential membrane-spanning regions. While a homology search did not reveal any significant relatedness of the mxiA DNA sequence to any known bacterial gene sequences, the derived amino acid sequence of MxiA was found to be highly homologous (68%) to the sequence of the protein encoded by the low-calcium-response locus, lcrD, of Yersinia pestis. The lcrD encodes an inner membrane regulatory protein that has an N-terminal membrane anchor and that is implicated in facilitating the export of Y. pestis outer membrane proteins (G. V. Plano, S. S. Barve, and S. C. Straley, J. Bacteriol. 173:7293-7303, 1991). Congo red binding, HeLa cell invasion, and Ipa excretion were restored in two avirulent mxiA fusion mutants when they were transformed with a cloned copy of the mxiA gene. Furthermore, the expression of the cloned mxiA gene was independent of any vector-specified promoter, suggesting that the transcription of mxiA is driven by its own promoter in this clone. In contrast, the overexpression of mxiA that resulted when it was placed under the control of the lac promoter was found to be deleterious in Escherichia coli. We conclude that mxiA is a homolog of the Y. pestis lcrD locus and may function similarly in S. flexneri, either by directly affecting the excretion of virulence factors or by regulating the expression of export accessory genes.

Two novel virulence loci, mxiA and mxiB, in Shigella flexneri 2a facilitate excretion of invasion plasmid antigens

A bank of over 4,200 lacZ protein fusions in Shigella flexneri 2a was screened for fusions to temperature-regulated promoters. One mutant, BS260, was completely noninvasive on HeLa cells and mapped to a region on the 220-kb virulence plasmid in which we had previously localized several avirulent temperature-regulated operon fusions (A.E. Hromockyj and A.T. Maurelli, Infect. Immun. 57:2963-2970, 1989). The phenotype of BS260 was similar to that of the previously identified mxi (membrane expression of invasion plasmid antigens) mutants, since it made wild-type intracellular levels of the invasion plasmid antigens (Ipa) but was deficient in the surface expression of IpaB and IpaC. Six kilobases of DNA upstream of the BS260 fusion end joint were cloned, but no temperature-regulated promoter was found, whereas the fusion end joint clone of the noninvasive mxi operon fusion mutant BS226 contained a temperature-regulated promoter. The locus defined by BS260 was designated mxiA, and that defined by BS226 was designated mxiB. Closer analysis of the mxiA and mxiB phenotypes by a cell-free enzyme-linked immunosorbent assay revealed that the mutants failed to excrete IpaB and IpaC into the culture medium, whereas wild-type cells actively released these antigens. Excretion of the ipa polypeptides from wild-type bacteria was confirmed by Western blot analysis of culture supernatants. Protease protection experiments revealed that wild-type S. flexneri 2a actually had much lower levels of surface-exposed IpaB and IpaC relative to those in the total antigen pool. In addition, examination of cellular fractions showed that, although there was no IpaB or IpaC in the outer membrane of BS260 and BS226, the antigens did accumulate in the cytoplasmic membrane. A 76-kDa temperature-regulated polypeptide in wild-type S. flexneri was identified as the putative mxiA gene product. These results strongly suggest that IpaB and IpaC represent truly excreted proteins of S. flexneri and that the mxiA and mxiB loci on the plasmid code for accessory proteins required to facilitate their export through the bacterial outer membrane. These data also suggest that mxiA is part of an operon that specifies additional mxi genes. The products of this operon may constitute a unique multicomponent protein secretion apparatus involved in the transport of Shigella virulence determinants.

Characterization of CS4 and CS6 antigenic components of PCF8775, a putative colonization factor complex from enterotoxigenic Escherichia coli E8775

PCF8775 is a putative colonization factor complex present on the surface of 10 to 20% of enterotoxigenic Escherichia coli strains and has been reported to be composed of antigen CS6 (morphology undefined) expressed alone or together with either of the rigid fimbrial antigens CS4 and CS5. To better define the individual components of this complex and the determinants of their expression, we prepared antiserum to the PCF8775 complex as it was expressed on prototype strain E8775 and then used the antiserum to identify the subunit structure of the antigens, to study their morphology, and to detect expression of individual components of the complex after transfer of plasmids into laboratory strain HB101. CS4 was purified from strain E8775, confirmed to be fimbrial by electron microscopy, and found to be composed of a 22-kilodalton protein subunit whose N-terminal amino acid sequence (1 to 20) was similar to that of colonization factor antigen I. Transconjugants that express CS6 but not CS4 were obtained by mating prototype strain E8775 with HB101. CS6 expression was mediated by a 61-megadalton plasmid. Expression of CS6 in the transconjugants correlates with expression of a 16-kilodalton cell surface protein. The CS6 antigen was confirmed to be present on the cell surface by immunogold labeling, but its morphology was beyond the limits of resolution by electron microscopy.

Characterization of the plasmid from Escherichia coli RDEC-1 that mediates expression of adhesin AF/R1 and evidence that AF/R1 pili promote but are not essential for enteropathogenic disease

RDEC-1, an Escherichia coli strain that adheres to rabbit mucosa and causes an attaching, effacing lesion, expresses the pilus adhesin AF/R1 which determines in vitro attachment to rabbit intestinal brush borders. In order to determine the role of AF/R1 pili in the pathogenesis of enteropathogenic diarrhea in rabbits, we localized the genes for AF/R1 expression, constructed an AF/R1- strain, and compared the virulence of the AF/R1+ and AF/R1- strains with particular attention to the development of attaching, effacing lesions. We introduced Tn5 into the 86-megadalton (MDa) conjugative plasmid known to mediate expression of AF/R1 pili and transferred the derivative plasmids into laboratory strain HB101. Transconjugant M5 was found to contain the 86-MDa plasmid from RDEC-1 and to express AF/R1 pili. Pilus expression on M5 was confirmed by reaction with antiserum raised against purified AF/R1 pili and allowed the bacteria to adhere to the rabbit ileum in an in vitro assay. Three Tn5 insertions in the 86-MDa plasmid were obtained which resulted in loss of AF/R1 expression. Part of the plasmid was mapped, including a region necessary for AF/R1 pilus expression. AF/R1- mutant strain M34 was constructed, and its pathogenesis was investigated. M34 produced disease in rabbits but was less virulent than the parent. The characteristic effacing lesions of RDEC-1 and enteropathogenic E. coli developed in the intestine of rabbits infected with either M34 or RDEC-1, although with M34 they were much less frequent and did not involve the small bowel. We conclude that AF/R1 pilus expression is not essential for the attaching, effacing lesion but serves as an accessory virulence factor which promotes an initial interaction of RDEC-1 with normal epithelial cells.

Effect of Hydrogen Peroxide and Sodium Chloride on Enumeration of Thermally Stressed Cells of Staphylococcus aureus

Evidence is presented suggesting that the decreased enumeration of heat-stressed Staphylococcus aureus cells on selective media is the result of accumulation of metabolic H₂O₂. It accumulates due to the decreased activity of catalase caused by the synergistic effects of heat and NaCl. Heated cells enumerated anaerobically on tryptic soy agar (TSA) containing 6.5% NaCl (TSAS 6.5) exhibited a 200-fold increase compared to cells enumerated aerobically on the same medium. The anaerobic counts on TSAS 6.5 were similar to the aerobic counts on TSA. Increases in both death and injury occurred when S. aureus was propagated in tryptic soy broth (TSB) plus 10% NaCl (TSBS) instead of TSB before thermal injury. Addition of catalase to TSA and TSA containing 7.5% NaCl (TSAS) increased the count to approximately the same levels on TSA and TSAS as that found following thermal injury after propagation in TSB. Catalase activity was 12-fold higher in stationary phase cells propagated in TSB than in TSBS. Indirect evidence indicates that toxic levels of H₂O₂ accumulated rapidly, causing one to two log decreases in enumeration after 30 to 60 min incubation on TSAS.

Catalase activity during the recovery of heat-stressed Staphylococcus aureus MF-31

Sublethal heating of Staphylococcus aureus produced little loss of catalase activity, but incubation of the injured cells in tryptic soy broth, with or without 10% NaCl added, produced an 85% decrease in catalase activity. Cells recovered in tryptic soy broth demonstrated increases in catalase levels after approximately 5 h, whereas in tryptic soy broth with 10% NaCl the levels remained low for at least 12 h. Thus, the loss of catalase activity during the recovery period was greater than during the heat treatment.

Heat inactivation of catalase from Staphylococcus aureus MF-31

The effects of heat on catalase from Staphylococcus aureus lysates were examined. Catalase activity increased with increasing concentrations of potassium phosphate buffer, when heated at temperatures between 50 and 65 degrees C for 10 min. Inactivation of catalase by NaCl during heating was demonstrated. Extended heating of S. aureus cells at 52 degrees C resulted in a slight decrease in catalase activity of the resultant lysates. This decrease was more pronounced in the presence of salt. Heating at 62 degrees C caused a decrease in catalase activity, but not complete inactivation. These results implicate the combined effects of heat, and NaCl in the inactivation of catalase from S. aureus. The findings are consistent with the hypothesis that H2O2 may accumulate as a result of decreased catalase activity and be responsible for the decreased colony-forming ability of stressed S. aureus.

Comparison of microdilution and broth dilution techniques for the susceptibility testing of yeasts to 5-fluorocytosine and amphotericin B

Microdilution and broth dilution techniques were compared for the susceptibility testing of 50 clinical yeast isolates to 5-fluorocytosine and amphotericin B. Good correlation between methods was obtained with all isolates except Cryptococcus neoformans.