Probing limits on spatial resolution using nonlinear optical effects and nonclassical light

Using a simple optical setup to detect and characterize transmission gratings in the far field, we demonstrate that going beyond the diffraction limit is not possible using linear interaction of nonclassical illumination with the target grating. We also confirm that nonlinear optical interactions with the target grating, or with the optical medium around it, do allow improvement in resolution.

Optical pattern recognition by use of a segmented semiconductor optical amplifier

A technique for high-speed, all-optical pattern recognition based on cross correlation in a segmented semiconductor optical amplifier (SSOA) is presented. A counterpropagating pump-probe setup is used to perform cross correlation of the spatial gain-loss pattern in the SSOA with the optical data pattern (pump), and the result is read out with a counterpropagating probe. Cross correlation of 4-bit patterns at 85 Gbits/s is experimentally demonstrated. Simulations show reasonable agreement with experimental measurements and are used to address scalability to higher bit rates and longer data patterns.

Inability of encapsulated Klebsiella pneumoniae to assemble functional type 1 fimbriae on their surface

We screened phase variants of Klebsiella pneumoniae isolates for the expression of capsule and type 1 fimbriae and found that all of the 22 blood isolates were encapsulated and did not express type 1 fimbriae while 10 of 11 urinary tract isolates expressed type 1 fimbriae but were unencapsulated. Phase variants from selected isolates were found to be either unencapsulated and fimbriated or lacked both structures. Variants expressing both structures were not detected. Fimbrial subunits FimH and FimA were localized in the periplasmic space of the parent strain and on the surface of the unencapsulated variants. The results suggest that capsule formation impedes assembly of pre-formed fimbrial subunits on the bacterial surface.

Programmable high-bit-rate pattern generator with a segmented semiconductor optical amplifier

We have demonstrated that spatial gain modulation in a segmented semiconductor optical amplifier can be converted to a temporal signal. A four-segment amplifier was used to generate digital return-to-zero patterns at 40 Gbits/s , and this technique should be readily scalable to more than 100 Gbits/s .

Inhibiting interspecies coaggregation of plaque bacteria with a cranberry juice constituent [published erratam appear in J Am Dent Assoc 1999 Jan;130(1):36 and 1999 Mar;130(3):332]

Dental plaque stability depends on bacterial adhesion to acquired pellicle, and on interspecies adhesion (or coaggregation). A high-molecular-weight cranberry constituent at 0.6 to 2.5 milligrams per milliliter reversed the coaggregation of 49 (58 percent) of 84 coaggregating bacterial pairs tested. It acted preferentially on pairs in which one or both members are gram-negative anaerobes frequently involved in periodontal diseases. Thus, the anticoaggregating cranberry constituent has the potential for altering the subgingival microbiota, resulting in conservative control of gingival and periodontal diseases. However, the high dextrose and fructose content of the commercially available cranberry juice makes it unsuitable for oral hygiene use, and the beneficial effect of the high-molecular-weight constituent requires animal and clinical studies.

Subnanosecond switching, plasma electrode pockels cell for high-contrast imaging with partially coherent light

A high-contrast optical switch for imaging partially coherent light (~150 times the diffraction limit) requires that it have a large angular acceptance. We describe the development of a high-speed Pockels cell that uses a thin crystal to simultaneously achieve high-contrast (greater than 1800:1) and large-angular acceptance (greater than 7 mrad for a 5-mm aperture). A KD*P crystal was used in a longitudinal-mode configuration with plasma discharges forming low-resistance, high optical transmission electrodes to couple the switching voltage. Rise times of the switched optical pulse of the order of 500 ps were observed. Characterization of the device in the near and far fields was also performed.

Optical bit-pattern recognition by use of dynamic gratings in erbium-doped fiber

We present a novel optical bit-pattern-recognition technique that uses erbium-doped fiber at room temperature. Counterpropagating beams write a patterned gain-depletion grating in pumped erbium-doped fiber. This grating, recorded in the erbium gain medium, can be used for correlation with other optical bit patterns. We have demonstrated correlation of arbitrary return-to-zero bit patterns of as many as 8 bits at 1 Gbit/s . Theory suggests that scaling to higher bit rates is feasible.

Technique for measurement of the Raman gain coefficient in optical fibers

We demonstrate a simple, novel technique for measurement of the Raman gain spectrum in optical fibers. We measure the stimulated Raman scattered power generated by a square pulse as a function of its pulse width. Because of fiber dispersion, increasing the pulse width increases the interaction length of the pump and Stokes pulses and leads to a higher Stokes power. The dependence of growth rate of Stokes power on pulse width gives the Raman gain coefficient. Our technique does not require calibration against a standard or absolute measurement of the Stokes signal. We show that gain values obtained with this technique agree well with direct pump-probe measurements.

Invasive ability of C. jejuni/coli isolates from children with diarrhea and the effect of iron-regulated proteins

The invasive ability of C. jejuni/coli strains isolated from children with diarrhea was studied using an in vitro HEp-2 cell invasion assay. The ratio between the number of intracellular bacteria and the number of bacteria in the inoculum was determined (invasion index). It was found that under anaerobic conditions, there was a significant decrease in the invasion index as compared to standard conditions (5% CO2). Of 11 strains tested, seven were determined as invasive on the basis of invasion indexes within the range of 0.0002-0.01. In a previous study [D. Schwartz et al., Zbl. Bakt. 280, 338-347 (1994)], it was found, that most of the C. jejuni/coli isolates tested produced an outer membrane protein when grown under conditions of iron depletion (IRP). The IRP were detected in eight of the nine strains tested in the present study (five invasive and three non-invasive strains). In one non-invasive strain, IRP was not detected. When kept under conditions of iron depletion, one of the invasive strains exhibited a significant increase in invasive capacity. The results suggest that iron depletion seems to stimulate the invasion capacity of C. jejuni/coli in vitro.

Nonopsonic phagocytosis of microorganisms

Nonopsonic phagocytosis mediated by phagocyte receptors that recognize corresponding adhesins on microbial surfaces has attracted increasing interest as a potential host defense mechanism against extracellular pathogens and as a means of survival in the host for intracellular pathogens. Three types of nonopsonic phagocytosis involving carbohydrate-protein interactions (also termed lectinophagocytosis), protein-protein interactions, and hydrophobic interactions are discussed. A prominent receptor on phagocytic cells involved in recognizing pathogens belongs to the CD11/CD18 integrins. It mediates both opsonophagocytosis and nonopsonic phagocytosis and exhibits multiple specificity for different microbial adhesins. In other cases, similar specificity toward a microbial ligand (e.g. the Klebsiella pneumoniae capsule) is shared by dual molecules, one of which (e.g. the mannose-binding protein in serum) mediates opsonophagocytosis and the other (e.g. the macrophage mannose receptor) mediates nonopsonic phagocytosis of the microorganisms. In addition, we discuss how nonopsonic phagocytosis can trigger the phagocytes to release inflammatory agents and cause tissue injury. Further studies of the molecular mechanisms of nonopsonic phagocytosis, in particular those underlying the up-regulation of the phagocytic receptors by various agents, should lead to the development of new approaches for the prevention of infectious diseases.

Optical clock recovery from a data stream of an arbitrary bit rate by use of stimulated Brillouin scattering

Using a fiber-optic stimulated-Brillouin-scattering amplifier as an active filter, we have demonstrated optical clock recovery from 5-Gbit/s return-to-zero-format optical data. Definite patterns and pseudorandom bit sequences were tested. This scheme requires no prior knowledge of the clock frequency and is well suited for operation at higher data rates.

Iron-regulated proteins in outer membranes of Campylobacter jejuni diarrhoea isolates and immune response to the proteins in patients

The outer membrane protein (OMP) profiles from 8 Campylobacter jejuni and 5 Campylobacter coli fecal isolates grown under various conditions were compared by SDS-PAGE. The bacteria were grown under usual conditions, in iron-deficient medium (Dip) and on iron-supplemented medium (Fe). The OMP profiles of most bacterial strains grown under usual conditions, or in the Fe-supplemented medium, contained four major bands of approximately 31, 45, 63-66 and 97 kDa, and in addition, a number of minor bands. It was found that OMP from 10 of 13 strains tested and grown on iron deficient medium contained an intensive band of a protein in the molecular weight region of 76 kDa which was lacking in the OMP of bacteria grown in the presence of iron (iron-regulated protein). Sera from 11 children with C. jejuni infection analyzed by Western blot recognized the 76 kDa bands, in contrast to only one out of 10 control sera from healthy children. The Western-blot experiments demonstrated also various bands of other OMP components, both in OMP-Dip and OMP-Fe. The 45 kDa (porin protein) was recognized by all 11 serum samples from C. jejuni-infected patients and in 8 out of 10 control sera. The data suggested that the 76 kDa iron-regulated protein was expressed by bacteria during infection and it stimulated the immune response in children infected with C. jejuni.

Frequency tuning of a distributed feedback dye laser with two transmission gratings

Distributed feedback dye lasers, which use a holographic grating, present a very simple and reliable way to generate ultrashort pulses. We have developed a new technique for wavelength tuning of this type of laser by projecting the image of a second grating into the dye cell. Single-line operating and tuning was demonstrated with transform-limited output pulses on a picosecond time scale.

Plasmid profiles and antimicrobial susceptibility of Campylobacter jejuni isolated from Israeli children with diarrhea

Thirty Campylobacter jejuni (C. jejuni) strains isolated from stools of Israeli children with enteritis were tested for sensitivity to eight antimicrobial agents (MIC) and the presence of plasmids. It was found that all the isolates were sensitive to ciprofloxacin, ofloxacin, furazolidone and erythromycin. Of the 30 strains tested, 21 (70%) were found to be tetracycline-resistant, a relatively high resistance rate as compared with data from other countries and previous reports from Israel. Plasmids were detected in 17 out of 30 C. jejuni isolates (55.6%). A total of nine different plasmid profiles could be distinguished; six profiles were represented by one strain each. Of the 21 tetracycline-resistant strains, plasmids were found in 17 isolates (80%) carrying from 1-2 to 5 plasmids of various sizes. No plasmids were found in tetracycline-sensitive strains, with the exception of one isolate which contained a 24.4 MDa plasmid and was co-trimoxazole-resistant. Our studies indicate a relatively high percentage of tetracycline-resistant C. jejuni isolates in the Tel Aviv area. In 80% of these strains, various plasmid profiles were detected.

Generation of intense 10-ps, 193-nm pulses using simple distributed feedback dye lasers and an ArF(*) amplifier

A pair of holographic distributed feedback dye lasers is used to generate 10-ps pulses at two selected wavelengths that are mixed in a BBO crystal to produce a pulse ~ 10 ps in duration at 193 nm. This seed pulse is subsequently amplified in an ArF(*) excimer laser to an energy of 10-15 mJ with <40 microJ in amplified spontaneous emission. The pulses are nearly transform limited and diffraction limited.

Phagocytosis of Escherichia coli mediated by mannose resistant non-fimbrial haemagglutinin (NFA-1)

We examined the interaction between a urinary isolate of E. coli carrying non-fimbrial MR adhesin (NFA-1) and human polymorphonuclear leukocytes (PMN). We found that the organisms attach to PMN and the attachment was dose dependent and saturable. It was inhibited by isolated NFA-1, but not by mannoside. Recombinant plasmid encoding NFA-1 adhesin conferred binding capacity on a non-adhesive strain. The attachment of the bacteria carrying NFA-1 to PMN was associated with oxidative burst and inhibited by isolated NFA-1. The data taken together suggest that NFA-1 mediates the attachment of the bacteria to PMN. The attachment is followed by ingestion and killing of the organisms, but at a slower rate than with bacteria bound via type 1 fimbriae.

Inability of toxin inhibitors to neutralize enhanced toxicity caused by bacteria adherent to tissue culture cells

Toxicity to Y-1 adrenal mouse cells caused by heat-labile toxin secreted by an enterotoxigenic strain of Escherichia coli (H-10407-p) was 40-fold enhanced in mixtures containing organisms capable of adhering to the Y-1 cells compared with monolayers exposed to organisms whose adherence was inhibited by mannoside. Severalfold the concentrations of anti-heat-labile toxin antibodies required to neutralize the toxicity of nonadherent bacteria were unable to neutralize the toxicity caused by adherent bacteria. The cytolytic activity toward tissue culture cells and mouse peritoneal macrophages caused by streptolysin S carried by Streptococcus pyogenes was severalfold increased in mixtures containing organisms capable of adhering to the target cells compared with mixtures containing nonadherent bacteria. The ability of trypan blue and RNA core to inhibit the cell-bound streptolysin S was determined in tissue culture cells containing adherent streptococci and mixtures of streptococci randomly colliding with erythrocytes. Both inhibitors were markedly less effective in neutralizing cytolysis than in their ability to neutralize hemolysis. We conclude that compared with toxins produced by nonadherent bacteria, those produced by bacteria adherent to cells are targeted more efficiently and become relatively inaccessible to neutralization by toxin inhibitors.

ELISA for Campylobacter jejuni antibodies in Israeli children with diarrhea and in healthy soldiers

An ELISA test was employed to detect Campylobacter jejuni antibodies, using as antigen the glycine-HCl buffer extract of a local isolate. The antibody response (IgG, IgA and IgM) was examined in a group of 32 children (age 0-12 years) with C. jejuni enteritis diagnosed by the isolation of the agent. Controls were represented by two groups of children matched according to their age and sex: a) children with enteritis of unknown etiology, and b) healthy children. In addition, 66 healthy soldiers (aged 18-19), from whom serum specimens were collected during the first year of military service, were tested. The results indicated that the serodiagnosis of C. jejuni infection by ELISA is specific and sensitive regarding each Ig tested. The test for IgG was the most sensitive (72%) and that for IgM the most specific (100%). The healthy young adult soldiers showed significantly higher mean levels of IgG and IgA antibodies than the healthy children, suggesting that in Israel exposure to C. jejuni commonly occurs during early childhood. The ELISA for C. jejuni can improve the diagnosis of campylobacteriosis for clinical and epidemiological purposes.

An autochthonous phaeohyphomycotic nail infection in Canada caused by Hendersonula toruloidea

A case of an autochthonous toenail infection caused by Hendersonula toruloidea is presented. H. toruloidea was characterized by thick, branching septate brown-walled hyphae of a non-dermatophyte in microscopic tissue mounts in 25% Na0H with 5% glycerol. Cultures grew out on Littman's agar and Sabouraud peptone glucose agar plus chloramphenicol, but only if cycloheximide was not present. In vitro, the H. toruloidea isolate was characterized by copious 1-to 2-celled hyaline to dark-brown arthroconidia deriving from the fragmentation of aerial hyphae. It is likely that more infections due to H. toruloidea will be diagnosed if cycloheximide-free media are routinely used in the isolation of organisms from suspected dermatophyte infections.

Generation of KrF laser pulses on a picosecond time scale using electro-optic modulation

A new technique has been developed for the generation and shaping of KrF laser pulses on a picosecond time scale using a fast electro-optic modulator. Subnanosecond electrical pulses with an amplitude much greater than the half-wave voltage are applied to the Pockels cell, which generates a train of short ultraviolet pulses. The first pulse in this train is then isolated and shortened to 30 psec by the combined effect of propagation through a saturated amplifier and optical breakdown in xenon.

Molecular cloning and characterisation of the genes for a non-fimbrial adhesin from Escherichia coli

A non-fimbrial adhesin (NFA-1) from the uropathogenic Escherichia coli strain 827 responsible for agglutination of human erythrocytes was cloned using the cos 4 cosmid vector. A clone was isolated which promoted haemagglutination and showed the same biological properties as the adhesin produced by the wild type strain. Both express adhesin at 37 degrees C, but not 18 degrees C nor in the presence of 1% glucose. Adhesin purified from the clone formed high molecular weight aggregates which were resolved to the 21 K dalton subunit protein seen in the wild type strain on denaturation. Binding to human kidney cells by the clone and the wild type E. coli, from which the genes were cloned, were compared in an ELISA assay and shown to be the same. The genes for the adhesin were isolated on a 15.5 kilobase BamHI-EcoRI fragment which was subjected to gamma delta mutagenesis. The NFA-1 operon was localised to a 6.5kb region of this fragment.

Antibodies against enterotoxigenic Escherichia coli in the colostrum isolated from infants with diarrhea

The role of certain types of Escherichia coli in infectious diarrhea in infants and young children is well known. Infants who are breast-fed are less prone to gastroenteritis during their first year of life. Antibodies against three types of fimbrial antigens (adhesions) of enterotoxigenic E. coli (ETEC) in the colostrum were studied. The hemagglutination inhibition test method was used to detect antibodies against ETEC adhesions, i.e. colonization factors, I and II and fimbria type I. The colostrum of mothers on the 1st and 3rd day post partum was standard for the presence of antibodies. The results show that most of the colostrum samples contained antibodies against adhesions of the types of ETEC that we worked with. This study will enhance the knowledge as to why mothers should breast-feed their babies.

Nonfimbrial, mannose-resistant adhesins from uropathogenic Escherichia coli O83:K1:H4 and O14:K?:H11

Nonfimbrial, mannose-resistant hemagglutinins (nonfimbrial adhesions [NFA] NFA-1 and NFA-2) were extracted from two agar-grown urinary isolates of Escherichia coli strains 827 (O83:K1:H4) and 54 (O14:K?:H11). The proteins were purified to homogeneity by ammonium sulfate precipitation and column chromatography. Nonfimbrial adhesins are soluble proteins, which tend to form aggregates of molecular weight above 10(6). NFA-1 and NFA-2 consist of subunits of 21,000 and 19,000 molecular weight, respectively. Both hemagglutinins caused hemagglutination of human erythrocytes and bound to human kidney cell monolayers. The binding of bacteria and hemagglutinins was assessed by using suitable antisera as detectors in an enzyme-linked immunosorbent assay. NFA-1 and NFA-2 inhibited the adherence of their respective strains to human kidney cells in a linear dose response. NFA-2 also inhibited heterologous strain adherence, but NFA-1 did not. Hemabsorption of bacterial suspension with erythrocytes at 4 degrees C, followed by differential centrifugation, enabled us to obtain a bacterial suspension lacking nonfimbrial adhesins in the supernatant and an adhesin-enriched bacterial suspension that was eluted from erythrocytes at 40 degrees C. Bacteria eluted from erythrocytes exhibited a higher adherence capacity than unfractionated cells. Bacteria of the fraction lacking adhesins did not adhere to human kidney cells. Electron microscope examinations showed the presence of an extracellular capsule-like layer in adhering E. coli 827, but not in nonadhering bacteria. E. coli 54 did not express the adhesin as a capsule. We conclude that E. coli 827 and 54 produce extracellular adhesins consisting of soluble proteins which are differently expressed and antigenically distinct. The adhesins seem to share a common receptor and mediate the adherence of two uropathogenic E. coli strains to epithelial cells.

Infant mouse model of adherence and colonization of intestinal tissues by enterotoxigenic strains of Escherichia coli isolated from humans

The ability of enterotoxigenic Escherichia coli H10407, which possesses colonization factor antigen I, to colonize the intestinal mucosa of infant mice was considerably better than that of its colonization factor antigen I-negative derivative H10407-P. The latter strain previously was shown to lack cell adhering ability in vitro and to have a diminished capacity to infect human volunteers as compared with the parent strain. D-Mannose blocked both colonization by an enterotoxigenic E. coli isolate (801) possessing both mannose-resistant and mannose-sensitive adhesins and the in vitro adherence of the strain to intestinal segments of infant mice. A derivative of another enterotoxigenic E. coli strain (lacking both mannose-sensitive and mannose-resistant adhesins obtained by in vivo passage showed a significant increase in colonizing ability in comparison with the parent strain. We conclude that the infant mouse model of infection of intestinal mucosa complemented by in vitro adherence assays with excised intestinal tissue is suitable for the study of the bacterial properties responsible for the various stages of intestinal colonization by human enterotoxigenic E. coli.

Demonstration of electro-optical switching at the 26 cm x 26 cm aperture using plasma electrodes

We have constructed and tested a longitudinal Pockels cell with a clear aperture of 26 cm x 26 cm. Transparent plasma electrodes formed in a low-pressure glow discharge were used to apply a uniform electric field to a 1-cm thick KDP crystal. Optical switching times of 50 nsec were achieved with a bare KDP crystal. Significant improvement in switching time resulted from using a glass-plate-KDP-crystal sandwich.

Electro-optic harmonic conversion switch for large-aperture multipass laser systems

We have demonstrated electro-optically tuned second-harmonic generation using Type I KDP inside a plasma-electrode discharge cell. An axial voltage of +/-52 kV is required to switch a 1.064-microm beam by conversion to 0.53/microm, in agreement with theory. Electro-optically tuned harmonic generation may be combined with a recently developed transparent plasma electrode to produce a large-aperture switch for multipass laser systems.

Electro-optical switches with plasma electrodes

A transparent electrode concept using low-pressure ionized gas in the glow discharge regime is proposed for largeaperture electro-optic switch applications. A longitudinal Pockels cell and an electro-optically tuned second-harmonic-generation cell using KDP have successfully demonstrated the concept.

Adherence properties of enterotoxigenic Escherichia coli (ETEC) isolated in the Tel-Aviv area

We tested the expression of adherence properties of Enterotoxigenic Escherichia coli (ETEC) strains isolated in the Tel-Aviv area by examining their hemagglutination (HA) patterns, and their adherence in vitro to Human Kidney (Huk) cells in tissue culture. Hemagglutination patterns of 75 ETEC and 63 non-ETEC strains isolated from stool samples were examined. The strains were tested for mannose-sensitive hemagglutination (MSHA) capacity of guinea pig erythrocytes, and for mannose-resistant hemagglutination (MRHA) capacity of human and bovine erythrocytes. The distribution of HA patterns among groups of non-ETEC and ETEC predominating strains was compared. (The latter contained strains which were isolated from 21 stool samples as at least two identical isolates.) The ratio of strains containing at least one of MS and MR hemagglutinins was found to be significantly higher in the group of ETEC-predominating strains than in non-ETEC. Eleven of 21 ETEC- predominating strains showed MRHA, and in ten of them Colonization Factor Antigens, CFA/I or CFA/II were identified by HA inhibition and agglutination using specific antisera. The influence of the bacterial culture conditions on expression of MSHA and MRHA and on adherence capacity of the bacteria to HuK cell culture was tested. Results show that ETEC strains exhibited a wide range of phenotypic manifestations of type and strength of adhesions. The variations depend not only on strain but also on culture condition and the type of target cells used in the experiments. In some strains a correlation was observed in the expression of adhesions using various experimental models; in others this correlation was not found. These findings suggest that, although CFAs were relatively common among ETEC-predominating strains isolated in the Tel-Aviv area, other adhesions could be involved in the pathogenic process.

An outbreak (?) caused by Escherichia coli O126:K71:H5 in premature infants

The strain E. coli O126:K71:H5 was recovered during a 6 week period, from stool samples of 13 premature infants hospitalized in the Premature Infants Nursery Unit. Of a total of 147 tested stool samples, 69 were positive. This strain was also recovered for a long period from the respiratory tract of one of the infants. The strain had a low virulence for the infants. No clear relationship could be demonstrated between clinical status and recovery of the strain. The strain did not possess any of the well defined pathogenic mechanisms, namely enterotoxins LT and ST, and invasiveness. The production of a thermolabile substance toxic for Vero cells was demonstrated. The strain possessed both guinea pig mannose-sensitive and human mannose resistant hemagglutinins. In spite of the production of thermolabile toxic substance for Vero cells and in spite of its contagiousness and intestinal tract colonization capacity, the strain displayed the characteristics of an opportunistic pathogen rather than classic EPEC.

Enterotoxigenic Escherichia coli (ETEC) isolated in the Tel-Aviv (Israel) area

The prevalence of enterotoxigenic E coli (ETEC) as a pathogenic agent of diarrhoea in the Tel-Aviv (Israel) area was determined, and the isolated E. coli strains characterized. During three periods (summer 1977, summer 1978, and summer 1979), a total of 335 specimens were tested for the presence of E. coli producing LT and ST toxin. Most of the specimens were from sporadic ambulatory diarrhoea cases (children and adults) attending a number of health care clinics in Tel-Aviv. Two to five colonies were tested from each sample. ETEC was detected in 69 cases (20%): LT/ST strains were isolated from 9 cases (2.7%); LT from 7 cases (2.1%); and ST from 53 cases (15.2%). ETEC was isolated in all age groups. In 19 specimens, 2 or more of 4 colonies tested were enterotoxigenic and were identical according to biotype, antibiotic sensitivity, and serogroup. These findings suggest that enterotoxigenic strains predominated in the bacterial population of the stool specimen. Part of the isolated ETEC strains belonged to serotypes already known as enterotoxigenic in different geographic areas of the world. The most frequently encountered were serogroups O8 (9 cases) represented by at least three serotypes, among them O8:K40:H9, and serotype O6:K15:H16 (5 cases); a number of serotypes were represented only by two cases or by single cases. Among 16 LT-producing stains (LT/ST and LT-only), 13 belonged to 3 serogroups, while ST-only strains represented a large spectrum of serotypes, some of which are now known as enterotoxigenic. Several serotypes common in other geographical locations were not detected.

The effect of attapulgite and charcoal on enterotoxicity of Vibrio cholerae and Escherichia coli enterotoxins in rabbits

Vibrio cholerae and certain strains of Escherichia coli produce heat-labile enterotoxins which play a significant role in the pathogenesis of the intestinal disease. Activated attapulgite, a heated magnesium aluminum silicate, was previously shown to prevent the toxic effects of endotoxin. The present study has revealed that this drug inhibits the toxic effects of cholera and E. coli enterotoxins in the intestinal loop of rabbits, when toxin and attapulgite are pre-incubated prior to injection. Up to 50 to 100 minimal effective doses are inhibited. Attapulgite is effective also when injected separately, albeit simultaneously, into the intestinal loops, but not when administered after the toxin. Since supernates of toxinattapulgite mixtures are non-toxic, it is postulated that attapulgite acts by adsorption and that the attached enterotoxin is no longer toxic to the rabbit intestine. The previously reported effect of charcoal on V. cholerae enterotoxin paralleling that of attapulgite, was confirmed. In contrast to the effects of these absorbents on isolated toxin, both failed to prevent enterotoxicity in the rabbit model of an enterotoxin-producing strain of E. coli.

Sh. dysenteriae serotypes2,4,8-immunochemistry and phage receptor activity

Among three analyzed serotypes of Shigella dysenteriae, namely, the serotypes 2,4 and 8, the serotype 2 proved to be a strong immunogen in rabbits, inducing anti-polysaccharide antibodies as well as antiprotein antibodies in all the animals. In contrast, the serotypes 4 and 8 were weak immunogens and among the rabbits some have synthesized only anti-proteins while others had antibodies against the somatic conjugate. Aside from the somatic antigens, large amounts of proteins were isolated from all the strains; however, the numerous determinants of these proteins were proven with the help of a serum to proteins from Sh. sonnei. The polysaccharides were specific for the serotype. The sensitivity of Sh. dysenteriae strains to phage P1 and the phage receptor actigity of different bacterial extracts were examined. By using the phage receptor neutralization test, it was possible to demonstrate that the receptor substance is a common component present in the lipopolysaccharide. The nature of neutralization has been discussed.