Production of heat-stable, methanol-soluble enterotoxin by Yersinia enterocolitica

Genetic Diversity among Yersinia enterocolitica Isolated from Chicken and Fish in and around Coimbatore City, India

BACKGROUND

Yersinia enterocolitica is rapidly emerging worldwide as an enteric pathogen and has become a major cause of diarrhea even in developed countries. The aim of this study was to characterize and genetic diversity analysis among Y. enterocolitica strains isolated from fish and chicken sources.

METHODS

From 44 strains, 55% (24 strains) found to be positive for Y. enterocolitica by colony morphology, biochemical tests and 16S rRNA. We investigate the diversity of Y. enterocolitica by hemolytic activity, antimicrobial resistance, RAPD, ERIC and REP-PCRs PCR, profiling of outermembrane proteins and lipopolysaccarides.

RESULTS

Forty one percent of the strains were found to be the producers of haemolysin at 37 °C but not at 28 °C. All the isolates were exhibiting multi-drug resistance and found sensitive to chloramphenicol, and resistant to ciprofloxacin and amoxicillin. Eight, eleven and twelve different genotypic patterns were observed in RAPD, ERIC and REP-PCRs respectively. Five isolates have produced high molecular weight protein (HMWP) with a molecular weight of 150 - 220 kDa. Mostly LPS produce identical profiles, 22 strains have produced smooth LPS, while 2 strains have produced the rough LPS pattern.

CONCLUSION

Genotyping tools strongly confirm the co-existence wide genetic diversity among the strains tested. By using any or the combination of these molecular tools, epidemiological investigation on Y. enterocolitica could be elucidated effectively. These results showed that the REP-PCR is more informative and discriminative than other for analysis of Y. enterocolitica diversity.

Transcriptional analysis of long-term adaptation of Yersinia enterocolitica to low-temperature growth

To analyze the transcriptional response of Yersinia enterocolitica cells to prolonged growth at low temperature, a collection of luxCDABE transposon mutants was cultivated in parallel at optimal (30 degrees C) and suboptimal (10 degrees C) temperatures and screened for enhanced promoter activities during growth until entering stationary phase. Among 5,700 Y. enterocolitica mutants, 42 transcriptional units were identified with strongly enhanced or reduced promoter activity at 10 degrees C compared to 30 degrees C, and changes in their transcriptional levels over time were measured. Green fluorescent protein fusions to 10 promoter regions confirmed the data. The temporal order of induction of the temperature-responsive genes of Y. enterocolitica was deduced, starting with the expression of cold shock genes cspA and cspB and the elevated transcription of a glutamate-aspartate symporter. Subsequently, cold-adapted cells drastically up-regulated genes encoding environmental sensors and regulators, such as UhpABC, ArcA, and methyl-accepting chemotaxis protein I (MCPI). Among the most prominent cold-responsive elements that were transcriptionally induced during growth in early and middle exponential phase are the insecticidal toxin genes tcaA and tcaB, as well as genes involved in flagellar synthesis and chemotaxis. The expression pattern of the late-exponential- to early-stationary-growth phase is dominated by factors involved in biodegradative metabolism, namely, a histidine ammonia lyase, three enzymes responsible for uptake and utilization of glycogen, the urease complex, and a subtilisin-like protease. Double-knockout mutants and complementation studies demonstrate inhibitory effects of MCPI and UhpC on the expression of a putative hemolysin transporter. The data partially delineate the spectrum of gene expression of Y. enterocolitica at environmental temperatures, providing evidence that an as-yet-unknown insect phase is part of the life cycle of this human pathogen.

YplA is exported by the Ysc, Ysa, and flagellar type III secretion systems of Yersinia enterocolitica

Yersinia enterocolitica maintains three different pathways for type III protein secretion. Each pathway requires the activity of a specific multicomponent apparatus or type III secretion system (TTSS). Two of the TTSSs are categorized as contact-dependent systems which have been shown in a number of different symbiotic and pathogenic bacteria to influence interactions with host organisms by targeting effector proteins into the cytosol of eukaryotic cells. The third TTSS is required for the assembly of flagella and the secretion of the phospholipase YplA, which has been implicated in Y. enterocolitica virulence. In this study, YplA was expressed from a constitutive promoter in strains that contained only a single TTSS. It was determined that each of the three TTSSs is individually sufficient for YplA secretion. Environmental factors such as temperature, calcium availability, and sodium chloride concentration affected the contribution of each system to extracellular protein secretion and, under some conditions, more than one TTSS appeared to operate simultaneously. This suggests that some proteins might normally be exported by more than one TTSS in Y. enterocolitca.

Production of enterotoxin by Yersinia bercovieri, a recently identified Yersinia enterocolitica-like species

Yersinia bercovieri, a recently identified Y. enterocolitica-like species, produces a heat-stable enterotoxin (designated YbST) which has biologic activity in infant mice and increases short circuit current in Ussing chambers. Although YbST has some properties in common with the heat-stable enterotoxins of Y. enterocolitica (YST I and YST II), it appears to be a novel toxin because (i) it was not neutralized by anti-YST I antiserum, (ii) YbST-neutralizing antiserum did not neutralize YST I, and (iii) Y. bercovieri strains did not hybridize with genetic probes for yst I, yst II, and other known enterotoxins.

Expression of invasin and motility are coordinately regulated in Yersinia enterocolitica

The Yersinia enterocolitica inv gene encodes the primary invasion factor invasin, which has been previously shown to be critical in the initial stages of infection. The expression of inv is influenced by growth phase and temperature and is maximal during late exponential-early stationary phase at 23 degrees C. In addition, motility of Y. enterocolitica is regulated by temperature. Y. enterocolitica cells are motile when grown at lower temperatures (30 degrees C or below), while bacteria grown at 37 degrees C are nonmotile. This study was initiated to determine the molecular basis for the temperature regulation of inv expression. Two mutants were isolated that both showed a significant decrease in invasin expression but are hypermotile when grown at 23 degrees C. The first mutant (JB1A8v) was a result of a random mTn5Km insertion into the uvrC gene. The uvrC mutant JB1A8v demonstrated a significant decrease in inv and an increase in fleB (encodes flagellin) expression. These results suggest that expression of inv and flagellin genes is coordinated at the level of transcription. The second regulatory mutant, JB16v, was a result of a targeted insertion into a locus similar to sspA which in E. coli encodes a stationary-phase regulator. The E. coli sspA gene was cloned and assayed for complementation in both of the regulatory mutants. It was determined that E. coli sspA restored invasin expression in both the uvrC mutant and the sspA mutant. In addition, the complementing clone decreased flagellin levels in these mutants.

The novel heat-stable enterotoxin subtype gene (ystB) of Yersinia enterocolitica: nucleotide sequence and distribution of the yst genes

The gene (ystB) encoding the novel subtype of the heat-stable enterotoxin (Y-STb) was cloned from the chromosome of a clinical isolate of Yersinia enterocolitica 84-50 (serotype O:5, biotype 1A) and the nucleotide sequence was determined. The ystB contained 216 base pairs that encoded a protein of 71 amino acid residues. The C-terminal 30 residues of the precursor protein exactly corresponded to the amino acid sequence of the Y-STb toxin, purified from the culture supernatant of the wild strain. Homology search revealed that there are 76.9% nucleotide sequence similarity between ystB and the Yersinia kristensenii ST gene, and 73.5% with the Y. enterocolitica prototype sequence of yst (ystA). When tested with the PCR generated ystB specific probe, 36 of 304 Y. enterocolitica strains from 18 countries hybridized with the probe. All the ystB probe positive strains belonged to biotype 1A and mostly to the so-called non-pathogenic serotype O:5, O:6, O:7,8 O:7,13 and O:10, while ystA was predominantly found among the pathogenic serotypes (78.5%). Out of 36 ystB gene positive strains, 18 were clinical origin from six countries, which were also positive in the suckling mice assay suggesting that ystB may play an important role in the pathogenesis, and the so-called non-pathogenic serotypes could be virulent for human.

Yersinia enterocolitica: the charisma continues

Yersinia enterocolitica, a gram-negative coccobacillus, comprises a heterogeneous group of bacterial strains recovered from animal and environmental reservoirs. The majority of human pathogenic strains are found among distinct serogroups (e.g. O:3, O:5,27, O:8, O:9) and contain both chromosome- and plasmid (60 to 75 kb)-mediated virulence factors that are absent in "avirulent" strains. While Y. enterocolitica is primarily a gastrointestinal tract pathogen, it may produce extraintestinal infections in hosts with underlying predisposing factors. Postinfection sequelae include arthritis and erythema nodosum, which are seen mainly in Europe among patients with serogroups O:3 and O:9 infection and HLA-B27 antigen. Y. enterocolitica is acquired through the oral route and is epidemiologically linked to porcine sources. Bacteremia is prominent in the setting of immunosuppression or in patients with iron overload or those being treated with desferrioxamine. metastatic foci following bacteremia are common and often involve the liver and spleen. Of particular concern is blood transfusion-related bacteremia. Evidence has accumulated substantiating the role of Y. enterocolitica as a food-borne pathogen that has caused six major outbreaks in the United States. The diagnosis of Y. enterocolitica gastroenteritis is best achieved through isolation of the bacterium on routine or selective bacteriologic media. When necessary, serogrouping, biogrouping, and assessment for plasmid-encoded virulence traits may aid in distinguishing virulent from "avirulent" strains. Epidemiologically, outside of identified food-borne outbreaks, the source (reservoir) of Y. enterocolitica in sporadic cases is speculative. Therefore, prevention and control measures are difficult to institute.

Transcription of the mutL repair, miaA tRNA modification, hfq pleiotropic regulator, and hflA region protease genes of Escherichia coli K-12 from clustered Esigma32-specific promoters during heat shock

The amiB-mutL-miaA-hfq-hflX-hflK-hflC superoperon of Escherichia coli contains genes that are important for diverse cellular functions, including DNA mismatch repair (mutL), tRNA modification (miaA), pleiotropic regulation (hfq), and proteolysis (hflX-hflK-hflC). We show that this superoperon contains three E simga(32)-dependent heat shock promoters, P(mutL)HS,P(miaA)HS, and P1(hfq)HS, in addition to four E sigma(70)-dependent promoters, P(mutL), P(miaA), P2(hfq), and P3(hfq). Transcripts from P(mutL)HS and P(miaA)HS were most prominent in vivo during extreme heat shock (50 degrees C), whereas P1(hfq)HS transcripts were detectable under nonshock conditions and increased significantly after heat shock at 50 degrees C. The P(mutL)HS, P(miaA)HS, and P1(hfq)HS transcripts were not detected in an rpoH null mutant. All three promoters were transcribed by E sigma (32) in vitro at 37 degrees C and contain -35 and -10 regions that resemble the E sigma(32) consensus. In experiments to assess the possible physiological relevance of the P(mutL)HS and P(miaA)HS promoters, we found that E. coli prototrophic strain MG 1655 increased in cell mass and remained nearly 100% viable for several hours at 50 degrees C in enriched media. In these cells, a significant fraction of mutL and hfq-hflA region transcripts were from P(mutL)HS and P1(hfq)HS, respectively, and the amounts of the miaA, hfq, hflX, hflK, and hflC transcripts increased in comparison with those in nonstressed cells. The cellular amounts of MutL and the hfq gene product (HF-I protein) were maintained during heat shock at 44 or 50 degrees C. Consistent with their expression patterns, miaA and hfq were essential for growth and viability, respectively, at temperatures of 45 degrees C and above. Together, these results suggest that there is a class of E sigma(32) promoters that functions mainly at high temperatures to ensure E. coli function and survival.

MyfF, an element of the network regulating the synthesis of fibrillae in Yersinia enterocolitica

The Yersinia enterocolitica surface antigen Myf is a fibrillar structure that resembles CS3 fimbriae. Gene myfA encodes the 21-kDa major subunit of the antigen, while genes myfB and myfC are required for the transport and assembly of pilin subunits at the bacterial cell surface. Here we show that the expression of Myf is regulated at the transcriptional level by temperature and pH. Gene myfA is transcribed at 37 degrees C and in acidic medium. The transcription start is preceded by a putative -10 box for the vegetative RNA polymerase as well as by sequences resembling the consensus sequence recognized by sigma 28. Thus, myfA could be transcribed either from a classical sigma 70 promoter or from a sigma 28 promoter. Transcription of myfA requires at least two genes, myfF and myfE, situated immediately upstream from myfA. The myfF product does not show similarity to any known regulatory protein. It is an 18.5-kDa protein with no typical helix-turn-helix motif and a unique hydrophobic domain in the NH2-terminal part. T7 expression, osmotic shock, fractionation experiments, and TnphoA fusion analyses carried out in Escherichia coli suggest that MyfF is associated with the inner membrane by means of its hydrophobic domain whereas the hydrophilic part protrudes in the periplasm. These features strikingly evoke ToxS, a protein involved in regulation of Tcp pilus production in Vibrio cholerae. MyfE resembles PsaE, a protein involved in regulation of pH6 antigen in Yersinia pestis. Genes myfF and myfE are presumably part of a whole regulatory network. MyfF could be an element of the signal transducing system.

Regulation of the Yersinia enterocolitica enterotoxin Yst gene. Influence of growth phase, temperature, osmolarity, pH and bacterial host factors

The chromosome of Yersinia enterocolitica encodes an enterotoxin called Yst. We analysed transcription of chromosomal yst'--luxAB and plasmid-borne yst'--lacZ operon fusions and we observed that regulation of yst expression occurs at transcriptional level. In a wild-type strain, yst was transcribed from at least two major promoters. yst transcription reached a maximum at the entry to the stationary phase and significantly varied in different Y. enterocolitica strains. In some strains, it gradually decreased during the course of our work, suggesting the existence of a mechanism switching the expression of yst to a silent state. Changes in the status of bacterial host factors rather than modifications in the yst gene are responsible for this silencing. Negative regulator YmoA participates in yst silencing and temperature regulation of yst. YmoA was also required for proper growth-phase regulation of yst, although it is not the only factor involved in this regulation. Physico-chemical parameters of the environment play an important role in yst transcription. In usual culture media (e.g. tryptic soy broth), the enterotoxin gene was transcribed only at temperatures below 30 degrees C, which argued against the role of Yst in a prolonged diarrhoea at body temperatures. However, yst transcription could be induced at 37 degrees C by increasing osmolarity and pH to the values normally present in the ileum lumen. This finding reconciles the observations concerning yst expression in a host environment and in bacterial cultures, thus supporting the idea that enterotoxin Yst is a virulence factor of Y. enterocolitica.

Nutritional requirements for synthesis of heat-stable enterotoxin by Yersinia enterocolitica

A defined medium that supported the growth of and synthesis of heat-stable enterotoxin (YST) by clinical isolates of Yersinia enterocolitica at levels equivalent to those observed in a complex Trypticase soy broth-0.6% yeast extract medium was developed. The defined medium contained four amino acids (L-methionine, L-glutamic acid, glycine, and L-histidine), inorganic salts, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffer, and potassium gluconate as the carbon source. Methionine was required for growth by most strains of Y. enterocolitica used in this study; thus, it was not possible to determine whether it was also required for the synthesis of YST. The other 17 amino acids commonly found in proteins did not stimulate the synthesis of YST when added to the defined medium. The yield of YST observed with other carbon sources fermented by Y. enterocolitica ranged from 4- to 26-fold lower than that obtained with potassium gluconate. The divalent cations Ca2+ and Mn2+ had no effect on the synthesis of YST; however, concentrations of Fe2+ above 10 microM inhibited the synthesis of the enterotoxin. The addition of a mixture of pyrimidines containing thymine, cytosine, and uracil, each at a concentration of 2.0 mM, stimulated the synthesis of YST by 10 to 15%, whereas a mixture of adenine and guanine, each at a similar concentration, inhibited the synthesis of YST. Vitamins had no effect on the amounts of YST produced by Y. enterocolitica strains grown in the defined medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of enterotoxin production by Yersinia enterocolitica and identification of a novel heat-stable enterotoxin produced by a noninvasive Y. enterocolitica strain isolated from clinical material

Twenty-eight clinical isolates of Yersinia enterocolitica were investigated for their abilities to produce heat-stable enterotoxin (YST). All 21 invasive strains (serogroup O3 biotype 4) carried the previously described gene for YST (yst), with toxin detectable in culture supernatants from 20 strains. One of seven noninvasive, biotype 1A strains also had enterotoxic activity, despite failure to hybridize with a probe for yst. The toxin produced by this noninvasive (serogroup O6) strain resembled YST in terms of molecular size, heat stability, and solubility in methanol. It differed from YST, however, with respect to regulation of its production by temperature and its mechanism of action, which did not appear to involve cyclic GMP.

Role of Yersinia enterocolitica Yst toxin in experimental infection of young rabbits

We constructed a Yst-negative mutant of Yersinia enterocolitica W1024 by reverse genetics, and we compared the virulence of the yst+ and yst isogenic strains in an experimental oral infection of the young rabbit. The rabbits infected with the yst+ strain suffered from the diarrhea and lost weight, and most of them died. By contrast, the occurrence of diarrhea, weight loss, and death in the group of rabbits infected with the yst mutant was as low as that in the group of uninfected rabbits. Bacteria from both strains were excreted in the feces and induced a serum antibody response against Yop proteins. The yst mutant disappeared more rapidly from the feces. We conclude that the enterotoxin Yst is a major factor involved in the Y. enterocolitica-associated diarrhea in the young rabbit. Given the similarity with the symptoms observed for children, this result suggests that Yst could also be an important factor in diarrhea in young children infected with Y. enterocolitica.

Nucleotide sequence of yst, the Yersinia enterocolitica gene encoding the heat-stable enterotoxin, and prevalence of the gene among pathogenic and nonpathogenic yersiniae

The gene encoding the heat-stable enterotoxin (yst) was cloned from the chromosome of Yersinia enterocolitica W1024 (serotype O:9), and the nucleotide sequence was determined. The yst gene encodes a 71-amino-acid polypeptide. The C-terminal 30 amino acids of the predicted protein exactly correspond to the amino acid sequence of the toxin extracted from culture supernatants (T. Takao, N. Tominaga, and Y. Shimonishi, Biochem. Biophys. Res. Commun. 125:845-851, 1984). The N-terminal 18 amino acids have the properties of a signal sequence. The central 22 residues are removed during or after the secretion process. This organization in three domains (Pre, Pro, and mature Yst) resembles that of the enterotoxin STa of Escherichia coli. The degree of conservation between the E. coli and Y. enterocolitica toxins is much lower in the Pre and the Pro domains than in the mature proteins. The mature toxin of Y. enterocolitica is much larger than that of E. coli, but the active domain appears to be highly conserved. The yst gene of Y. enterocolitica introduced in E. coli K-12 directed the secretion of an active toxin. The cloned yst gene was used as an epidemiological probe among a collection of 174 strains representative of all Yersinia species except Yersinia pestis and numerous Y. enterocolitica subgroups. In Y. enterocolitica, there was a clear-cut difference between pathogenic and nonpathogenic strains: 89 of 89 pathogenic and none of 51 nonpathogenic strains contained yst-homologous DNA, suggesting that Yst is involved in pathogenesis. Among the other Yersinia species, only four strains of Yersinia kristensenii had DNA homologous to yst.

Factors affecting production and activity of phospholipase C by Yersinia enterocolitica

The production of phospholipase C by Yersinia enterocolitica strain SG was optimum at 37 degrees C at pH 6.5. No enzyme activity could be detected when the organism was grown at extreme pH values (pH greater than 8.5 or less than 5.0). The enzyme production was maximum when the organism was grown under static conditions in TSB medium. All solvents and salts inhibited the enzyme activity, whereas loss of activity was 95% in presence of methanol (20%) and 99% in presence of sodium azide (0.2 mol/l). The enzyme activity was increased twofold in the presence of cysteine and decreased by 98% in the presence of sodium perchlorate (0.2 mol/l).

Rapid photometric assay of growth of Mycoplasma mycoides subsp. capri

A new spectrophotometric technique for evaluation of early growth in liquid culture of Mycoplasma mycoides subsp. capri has been developed. As turbidity does not appear until after incubation to 18 h the method utilizes the change in absorbance of the medium at 550 nm to monitor growth. The change in absorbance of the medium (which contains phenol red) occurs when the pH changes due to microbial growth. For measurement of growth at later stages when turbidity is proportional to number of colony forming units, two other wavelengths (450 nm and 700 nm) have been suggested.

Occurrence of virulence markers in species of Yersinia isolated from animals in Nigeria

Fourteen strains of Yersinia species isolated from apparently healthy pigs and cattle in Nigeria were screened for four virulence markers using six test systems. These were two in vitro assays, namely, calcium dependency and autoagglutination, both at 37 degrees C, the Serény test in guinea-pigs and the detection of heat-stable enterotoxin (ST) by the rabbit ileal loop test, the ligated intestine test in pigs and the infant mouse system. Seven of the 14 strains of Yersinia were positive for one or more of these tests. Six of nine strains of Y. enterocolitica and one of four Y. intermedia were positive in one or more tests. The only strain of Y. frederiksenii isolated was negative in all six test systems. All three strains of Y. enterocolitica, serotype 0:8 and the only serotype 0:3 isolated were positive in one or more tests. However, only two of five strains of Y. enterocolitica serotype 0:12, 26, the most frequently encountered, were positive. A good correlation was observed between test results of calcium dependency, autoagglutination and Serény assays. The results indicate that cattle and pigs have the potential to transmit virulent strains of Y. enterocolitica to human beings in Nigeria.

Suppression of heat-stable enterotoxin production by Yersinia spp. in milk

One of 16 raw milk isolates of Yersinia enterocolitica and Y. intermedia produced heat-stable enterotoxin (ST) in milk at 25 degrees C but not at 4 degrees C after 21 days of incubation. A catabolite repression of ST synthesis by the lactose-fermenting strain of Y. enterocolitica was observed when 4.6% lactose was added to trypticase soy broth. However, the lactose-fermenting strain was killed by acid produced by lactose fermentation in milk and did not produce ST in milk with the pH adjusted to neutrality. This study suggested that lactose and fat in milk are not the fundamental inhibitors of ST synthesis by Y. enterocolitica and that repression of ST synthesis may be related to other components.

Acute yersinia infections in man increase intestinal permeability for low-molecular weight polyethylene glycols (PEG 400)

The passive intestinal permeability of patients with acute diarrhoea was investigated with a liquid meal of oral rehydration fluid containing differently sized, low-molecular weight polyethylene glycols (PEG 400). The recovery of test molecules was measured in 6 h specimens of urine. The subjects suffered from acute infections caused by yersinia bacteria accompanied by joint pains. They were investigated during the infection and at least 3-4 weeks later when they had recovered clinically. It was found that yersinia infections were associated with increased urinary recovery of PEG molecules, and with reduced restriction towards the larger PEG molecules. After the infection, the resorption of PEGs returned towards normal. Thus, the altered restriction of the gut wall towards the passage of probe molecules might help to explain the extraintestinal manifestations often seen in connection with these agents.

Enterotoxin production at 4, 22, and 37 degrees C by Yersinia enterocolitica and Yersinia enterocolitica-like bacteria isolated from porcine tonsils and pork products

Altogether, 71 strains of Yersinia enterocolitica and Yersinia enterocolitica-like bacteria from porcine tonsils and pork products were examined for their ability to produce enterotoxin using the infant mouse assay. Of these, 37 strains (52.1 %) produced enterotoxin at 22 °C, 3 were positive at 4 and 22 °C, and 1 was enterotoxigenic at 22 and 37°C. No strain was positive at all 3 temperatures. The highest prevalence of enterotoxin production at 22°C was detected in serotype 0:11 (80.0%), followed by 0:3/ biotype 4 (74.2 %), and 0:12 (66.7 %). Enterotoxin production at 4°C was recorded in 2 (15.4 %) of the Yersinia kristensenii strains (0:11, 0:12) and 1 of the Yersinia enterocolitica strains, (0:3) examined. One Yersinia kristensenii strain (0:11) was enterotoxigenic at 37 °C. The results indicate that enterotoxin production is a common feature of yersiniae isolated from porcine tonsils and pork products in Norway and may represent a possible source of food borne intoxication.

Characterization of enterotoxin produced by four Yersinia enterocolitica strains of pig origin

All four isolates of Yersinia enterocolitica and one isolate of Y. frederiksenii from pigs were found to be enterotoxigenic. Whole-cell preparations of Y. enterocolitica isolates did not induce any change in the rabbit ligated gut test after 6 and 18 h of inoculation, but Y. frederiksenii on the other hand showed a positive gut response at 18 h. Cell-free supernatant (CFS) of all five isolates induced dilatation in the rabbit gut up to 6 h, after which Y. enterocolitica became negative, while Y. frederiksenii continued to show a reaction up to 18 h. CFS of all five isolates were also found positive with the infant mouse test. Of the five isolates of Yersinia, three gave a positive reaction for the permeability factor on rabbit skin. Yersinia enterotoxin could be concentrated by methanol extraction. It was stable at 100 degrees C for 20 min and at 120 degrees C for 15 min. However, its activity was lost at low (2.0) and high pH (10.0). Enterotoxic preparations of Y. enterocolitica lost part of their enterotoxic activity upon dialysis.

Factors affecting detection of Yersinia enterocolitica heat-stable enterotoxin by the infant mouse test

With regard to the assay of heat-stable enterotoxin (ST) from Yersinia enterocolitica, we made a comparative study of the conventional infant mouse test read at 4 h and a modified infant mouse test read at 2 h. The influence of several factors, such as the medium used to prepare ST, lysing of bacterial cells from the broth cultures used to prepare ST, and the temperature at which the inoculated mice were kept during the test, was also investigated. Thus, with a few exceptions, Pai-Mors medium was more suitable than Casamino Acids-yeast extract medium, for the preparation of yersinial ST. Gut/carcass weight ratios obtained with lysed supernatants or with supernatants from whole cultures of Y. enterocolitica were similar, suggesting that most of the ST produced by this microorganism in broth cultures is extracellular. The amount of ST produced by Y. enterocolitica, as well as the ambient temperature at which inoculated mice were kept during the assay, was found to influence gut/carcass weight ratios obtained with both tests. Enterotoxigenicity and the temperature at which mice were kept were interrelated, such that for weakly enterotoxigenic strains there were no significant differences among gut/carcass weight ratios for the conventional and modified infant mouse tests carried out at 18 or 25 degrees C, but at 30 degrees C the values in the modified test were higher for most ST preparations with Pai-Mors medium. The influence of ambient temperature was more pronounced at 37 degrees C, since most strains produced negative results in the conventional test at this temperature. We conclude that the conventional infant mouse test is adequate for assaying yersinial ST, provided that the temperature at which mice are kept during the assay is fixed at around 25 degrees C.

Evaluation of virulence factor testing and characteristics of pathogenicity in Yersinia enterocolitica

The virulence of 10 strains of Yersinia enterocolitica containing 42- to 44-megadalton plasmids (serogroups O:3; O:4,32; O:8; O:9; O:13,7; and O:21) was compared in mice and guinea pigs. Adult mice were more responsive than guinea pigs to the Sereny-like conjunctivitis test. In tests on suckling mice, all Yersinia strains harboring plasmids were lethal, whereas all strains without plasmids were nonlethal. All strains of serogroups O:4,32; O:8; O:13,7; or O:21 which harbored a plasmid gave positive results in the mouse Sereny, peroral, and intraperitoneal tests. A positive reaction in these tests was correlated with the ability of the strains to elaborate lipase. Because the Sereny, peroral, and intraperitoneal tests measured the same virulence factor(s), the findings in any of these three tests would accurately predict the results of the other two tests. Mice which survived the Sereny and peroral tests were subsequently challenged intraperitoneally with 1,000 mouse lethal doses of the virulent WA (O:8) strain. Those inoculated with plasmid-harboring strains were protected, whereas those inoculated with plasmid-free strains were not.

Effect of Yersinia enterocolitica ST on cyclic guanosine 3',5'-monophosphate levels in mouse intestines and cultured cells

We determined the effect of heat-stable enterotoxin produced by Yersinia enterocolitica (Y. enterocolitica ST) on cyclic nucleotide levels in the intestines of 6-day-old mice and in cultured cell line cells. The concentration of cyclic guanosine 3',5'-monophosphate (cyclic GMP) in homogenates of the intestines increased four- to fivefold by 3 min after intragastric administration of 10 units of purified Y. enterocolitica ST. This increase continued for 60 min, and then the concentration of cyclic GMP fell toward the levels of the controls. On the other hand, fluid accumulation in the intestines was not evident until 60 min after administration of the toxin. Thus, the increase in intestinal cyclic GMP concentration preceded measurable fluid accumulation. The effect on both cyclic GMP levels and fluid accumulation was abolished by treatment of the ST with either alkali solution (pH 10.7) or 2-mercaptoethanol. Likewise, cyclic GMP levels in cultured cells (CCL-6, HeLa, L, and Mm-1 cells) increased dose-dependently by 10 min after incubation of the cells with the ST. Cyclic adenosine 3',5'-monophosphate levels in both intestines and cultured cells were not affected by the toxin.

Virulence and phenotypic characterization of Yersinia enterocolitica isolated from humans in the United States

Yersinia enterocolitica was recently reclassified into Yersinia enterocolitica sensu stricto and three additional species. With this new classification, it was of interest to reexamine pathogenicity previously ascribed to Y. enterocolitica. All available clinical isolates of Y. enterocolitica sent to the Centers for Disease Control from 1970 through 1980 were selected for characterization and comparison. One-hundred such strains had been submitted, from 21 states. Most (85%) were biotype 1, and O:8 was the most common of the 24 serotypes encountered. All strains were examined by several virulence assays. Two strains caused conjunctivitis in guinea pigs, 7 were lethal for mice, 54 invaded HEp2 cells, 18 produced a heat-stable enterotoxin, 9 were calcium dependent, 20 autoagglutinated, and 34 had a distinctive colonial morphology at 37 degrees C. Ten isolates of each of the new species that had previously been grouped with Y. enterocolitica (Y. kristensenii, Y. intermedia, and Y. frederiksenii) were characterized and were generally negative in all assays. This study points out pathogenicity differences among Yersinia species, confirms the complex nature of virulence in Y. enterocolitica, and confirms that no single current assay correlates with virulence in Y. enterocolitica.

Enterotoxin production in milk at 22 and 4 degrees C by Escherichia coli and Yersinia enterocolitica

Enterotoxigenic Escherichia coli (five strains) and Yersinia enterocolitica (five strains) were cultivated in sterile milk at 22 and 4 degrees C. The bacteria grew well at both temperatures. Three strains of E. coli produced heat-labile enterotoxin in the milk at 22 degrees C as demonstrated by enzyme-linked immunosorbent assay. Heat-stable enterotoxins were not detected in milk by the infant mouse test.

Further purification and characterization of heat-stable enterotoxin produced by Yersinia enterocolitica

Heat-stable enterotoxin (ST) of Yersinia enterocolitica was produced under defined conditions. It was first detected in the culture supernatant of the late-logarithmic phase of growth and increased lineally during the the stationary phase of growth. The ST level became maximum at the decline phase of growth, and the ST was not detected in the lysate of bacteria obtained from the decline phase of growth. The ST was extensively purified from the culture supernatant, and about a 1,905-fold purification was achieved with a yield of 8.9%. The minimal effective dose of the purified ST was approximately 25 ng in the suckling mouse assay. The purified ST gave a single 280-nm absorbing peak on polyacrylamide disc gel electrophoresis and had a maximum absorption at 272 nm, and its molecular weight was 9,700 by Sephadex G-75 superfine gel filtration. The biological activity of the purified ST was lost by treatment with 2-mercaptoethanol, suggesting that the ST contained disulfide bridges in the molecule which were required for the development of toxic activity. The purified ST was heat stable at 100 degrees C for 10 min between pH 2.2 and 8.0, but not at pH values greater than 9.0 or in 2 N HCl. The treatment of the ST with trypsin resulted in a retarded elution of the ST activity by Sephadex F-75 superfine gel filtration and a passage through a UM-20 membrane filter.

The pathogenicity of Yersinia enterocolitica strains isolated from various sources in four test systems

Six tests were applied to 39 strains of Yersinia enterocolitica of various serotypes and from several sources in an attempt to relate the test to pathogenicity of the strains. The tests that were used were the pig gut loop test and the infant mouse test for heat stable enterotoxin, the Sereny and HeLa cell tests for invasiveness, inhibition of growth on magnesium oxalate agar, and the ability to cause diarrhea in infant mice. The pig gut loop test was found to be unsuitable for detection of heat stable enterotoxin but 20 strains produced heat stable enterotoxin that was detected in infant mice. None of the strains was positive in the Sereny test but 21 invaded HeLa cells. The growth of 20 strains was inhibited at 37 degrees C on magnesium oxalate agar and, in the orally-infected mice, 23 strains caused diarrhea or death. These findings indicate a discrepancy between the infant mouse test and the ligated intestine test in pigs for heat stable enterotoxin and a significant difference in Y. enterocolitica heat stable enterotoxin compared with Escherichia coli heat stable enterotoxin because the former failed to elicit a significant response in pig intestine.

An enterotoxin-negative strain of Yersinia enterocolitica serotype O:3 is capable of producing diarrhea in mice

A strain of Yersinia enterocolitica serotype O:3 that consistently produced heat-stable enterotoxin at 22 but not at 37 degrees C and another strain of the same serotype which did not produce enterotoxin at 22 degrees C were both positive for autoagglutination at 35 degrees C, a test that has been related to virulence in yersiniae. Both strains were infective for HeLa cells and produced guinea pig conjunctivitis. Mice infected with either strain through their drinking water developed diarrhea and excreted the organism in high numbers in the feces. A control strain of serotype O:3 positive for enterotoxin and HeLa cell infectivity but negative for autoagglutination was avirulent. Extracts of feces and intestines from mice with diarrhea were negative for enterotoxin. The results indicate that the heat-stable enterotoxin produced in vitro by some strains of Y. enterocolitica and measured by the infant mouse assay plays no role in pathogenesis as described by the mouse diarrhea model.

Detection of Yersinia enterocolitica heat-stable enterotoxin by suckling mouse bioassay

A comparison of heat-stable enterotoxins from Escherichia coli and Yersinia enterocolitica by the suckling mouse bioassay showed that whereas E. coli heat-stable enterotoxin evoked a maximum ratio of gut weight to remaining body weight after a 4-h incubation period, the maximum ratio for Y. enterocolitica was achieved at 2 h, decreasing thereafter to values regarded as negative (less than 0.083). This action of Y. enterocolitica heat-stable enterotoxin may give false-negative results for the standard suckling mouse bioassay.

Enterotoxins from gram-negative bacteria relevant for veterinary medicine

The chemistry, mechanism of action, assay methods, pharmacology, and prevention and treatment of diarrhoea due to toxins of gram-negative microbes are discussed. Other virulence factors are mentioned briefly. Special emphasis is placed on non-specific treatment by oral rehydration.

Enterotoxin production and thermal resistance of Yersinia enterocolitica in milk

Three of 36 raw milk isolates of Yersinia enterocolitica produced enterotoxin in milk at 25 degrees C, but not at 4 degrees C. No strain tested could survive pasteurization.

Heat-stable enterotoxin produced by Yersinia enterocolitica isolated from patients

Twenty-three strains of Yersinia enterocolitica were isolated from children with gastrointestinal illness and examined for the production of enterotoxins by using both suckling mouse and Chinese hamster ovary (CHO) cell assay systems. Six strains were found to be enterotoxigenic in the suckling mouse assay, but all strains were negative in the CHO cell assay. Enterotoxin was detected in the culture supernatant when organisms were grown at 25 C but not at 37 C. Enterotoxin in a 15-fold concentrated culture supernatant was precipitated by adding absolute ethanol to a concentration of 90%. However, after being dialyzed against distilled water in Spectra/por 6 membrane tubing, it was soluble in 80% acetone. One unit dose of partially purified enterotoxin was 5.0 micrograms of protein/mouse in the suckling mouse assay. The molecular weight of enterotoxin was between 10,000 and 50,000 daltons as determined by ultrafiltration. It was stable to heat (121 C X 20 min or 100 C X 60 min). These observations indicated that Y. enterocolitica isolated in Japan also produce an enterotoxin similar to the heat-stable enterotoxin of Escherichia coli. However its physiochemical properties seem to be different from those of E. coli.

Experimental Yersinia enterocolitica enteritis in rabbits

Young rabbits weighing 500 to 800 g were inoculated orogastrically with clinical isolates of Yersinia enterocolitica (serotype O:3; enterotoxigenic; HeLa cell invasive) at a dose of 1.4 X 10(10) bacteria suspended in 10% sodium bicarbonate solution. Diarrhea developed in 41 (87%) of 47 rabbits, with a mean +/- standard deviation onset at 5.4 +/- 2.4 days. The attack rate and onset of diarrhea were correlated with inoculum size. The 50% infectious dose was 2.9 X 10(8) bacteria. Bacterial colonization occurred in almost all rabbits, regardless of inoculum size. Seroconversion was demonstrated in 30 (71%) of 42 rabbits with or without diarrhea. Histopathological alterations were present in the jejuna, ilea, and colons of rabbits with diarrhea; the most pronounced changes were generally noted in the ilea. Crypt abscesses localized at the depth of the intestinal glands were observed consistently and were composed of a bacterial nidus admixed with and enveloped by inflammatory cells comprised of eosinophils, neutrophils, and mononuclear cells. Rabbits inoculated with a raw fish isolate of Y. enterocolitica (serotype O:6,30; non-enterotoxigenic; HeLa cell noninvasive) did not exhibit infection clinically, bacteriologically, or pathologically.

Pathogenic properties of Yersinia enterocolitica

A total of 88 isolates of Yersinia enterocolitica was examined for heat-stable enterotoxin production and ability to penetrate HeLa cells and evoke keratoconjunctivitis in guinea pigs (Séreny test) as potential pathogenic properties. All 49 isolates belonging to serotypes O:3, O:8, O:9, and O:5,27 and only 5 of 39 strains of other serotypes were HeLa positive. Séreny-positive strains were found only in serotype O:8. Heat-stable enterotoxin production was almost ubiquitous in all serotypes. Y. enterocolitica strains were classified into five groups with regard to their potential pathogenic properties.

Effects of heat-stable enterotoxin of Yersinia enterocolitica on ion transport and cyclic guanosine 3',5'-monophosphate metabolism in rabbit ileum

Strains of Yersinia enterocolitica produce a heat-stable enterotoxin which is positive in the suckling mouse bioassay. Partial purification by a procedure previously worked out for heat-stable Escherichia coli enterotoxin yielded a substance which increases particulate guanylate cyclase activity and short-circuit current and inhibits active Cl-absorption in rabbit ileal mucosa. These effects of Y. enterocolitica enterotoxin are similar to those of heat-stable E. coli enterotoxin, suggesting a common mechanism of action.