Radioactive Oligonucleotide Probes Research Articles

Expression of multi-drug resistance 1 mRNA in human and rodent tissues: reduced levels in Parkinson patients

The membrane transporter multi-drug resistance 1 (MDR1, P-gp) regulates the bioavailability of endogenous and exogenous compounds and has been implicated in disorders such as Parkinson's disease, cancer, epilepsy, human immunodeficiency virus disease, and inflammatory bowel disease. To promote further understanding of the role of MDR1 in disease, we have characterized cellular MDR1 mRNA expression in post-mortem human and fresh-frozen Sprague-Dawley rat tissues by using radioactive oligonucleotide probe in situ hybridization. We report MDR1 mRNA in human and rat endothelial cells of small vessels in the brain and pia mater. Mdr1 mRNA is also expressed in the blood vessel walls of rat sensory dorsal root and sympathetic ganglia. In peripheral tissues, we have observed MDR1 mRNA in human and rat liver and renal tubules and in human adrenal cortex and the epithelial lining of rat intestine. In female and male reproductive tissues of rat, strong gene activity has been found in steroid-hormone-synthesizing cells. Quantification of MDR1 mRNA in human striatum has revealed reduced levels in Parkinson patients compared with control individuals. The high expression of MDR1 mRNA in blood vessels of the nervous system, in tissues involved in absorption and excretion, and in tissues forming barriers to the environment support the physiological role of MDR1 as a regulator of intracellular levels of endogenous and exogenous compounds.

Relapse to cocaine seeking increases activity-regulated gene expression differentially in the prefrontal cortex of abstinent rats

Alterations in the activity of the prefrontal and orbitofrontal cortices of cocaine addicts have been linked with re-exposure to cocaine-associated stimuli. Using an animal model of relapse to cocaine seeking, the present study investigated the expression patterns of four different activity-regulated genes within prefrontal cortical brain regions after 22 h or 15 days of abstinence during context-induced relapse. Rats self-administered cocaine or received yoked-saline for 2 h/day for 10 days followed by 22 h or 2 weeks of abstinence when they were re-exposed to the self-administration chamber with or without levers available to press for 1 h. Brains were harvested and sections through the prefrontal cortex were processed for in situ hybridization using radioactive oligonucleotide probes encoding c-fos, zif/268, arc, and bdnf. Re-exposure to the chamber in which rats previously self-administered cocaine but not saline, regardless of lever availability, increased the expression of all genes in the medial prefrontal and orbitofrontal cortices at both time points with one exception: bdnf mRNA was significantly increased in the medial prefrontal cortex at 22 h only if levers previously associated with cocaine delivery were available to press. Furthermore, re-exposure of rats to the chambers in which they received yoked saline enhanced both zif/268 and arc expression selectively in the orbitofrontal cortex after 15 days of abstinence. These results support convergent evidence that cocaine-induced changes in the prefrontal cortex are important in regulating drug seeking following abstinence and may provide additional insight into the molecular mechanisms involved in these processes.

Amino acid transporter (VIAAT, VGLUT2) and chloride cotransporter (KCC1, KCC2 and NKCC1) expression in the vestibular nuclei of intact and labyrinthectomized rat

We report the first investigation of whether unilateral labyrinthectomy in adult rats affects the expression of two amino acid transporters, vesicular glutamate transporter 2 (VGLUT2) and vesicular inhibitory amino acid transporter (VIAAT) and of chloride cotransporters (KCC1, KCC2 and NKCC1) in the intact and deafferented medial vestibular nuclei (MVN). In situ hybridization with specific radioactive oligonucleotide probes and immunofluorescent methods were used in normal and unilaterally labyrinthectomized rats at various times following the lesion: 5 h, and 1, 3 and 8 days. In normal animals, several brainstem regions including the lateral, medial, superior and inferior vestibular nuclei contained VGLUT2, VIAAT and KCC2 mRNA. In contrast, no or a very faint labeling was observed with KCC1 and NKCC1 probes. In unilaterally lesioned rats, there was no asymmetry between the two MVN with any of the oligonucleotide probes at any time after the lesion. Similarly, there were no differences in the intensity of MVN labeling between controls and lesioned animals. Finally, no over-expression of the cotransporter KCC1 and NKCC1 was found in ipsilateral or controlateral MVN in lesioned rats at any time. Immunohistochemical experiments gave similar conclusions. Our findings suggest that the recovery of the resting discharge of the deafferented MVN neurons, and consequently the functional compensation of the deficits, are not dependent on changes in the expression of amino acid transporters (VIAAT, VGLUT2), and chloride cotransporters (KCC1, KCC2 and NKCC1) or on their mRNAs.

Regional Micrometastasis of Low Rectal Cancer in Mesorectum: A Study Utilizing HE Stain on Whole-Mount Section and ISH Analyses on Tissue Microarray

Aim: To investigate the regional spread of microscopic tumor nodules in the mesorectum of patients with low rectal cancer, and to provide further pathological evidence for optimal procedure selection of radical resection for rectal cancer. Methods: Sixty-two patients with low rectal cancer underwent low anterior resection and total mesorectal excision (TME). Surgical specimens were sliced transversely on serial embedded blocks at 2.5-mm intervals, and stained with hematoxylin and eosin (HE). On whole-mount sections the mesorectum was divided into 3 regions: the outer region of the mesorectum (ORM), the middle region of the mesorectum (MRM), and the inner region of the mesorectum (IRM). Microscopic metastatic foci were investigated for metastatic mesorectal region, frequency, types, involvement of the lymphatic system, and correlation with the primary tumor. Tumor-suspect nodules previously considered disease free by HE stain on whole-mount section were examined by in situ hybridization (ISH) on tissue microarray (TMA) through detecting mRNAs of CEA and CK20 with non radioactive biotin-tagged oligonucleotide probes. Results: Microscopic spread of the tumor was observed in 50.0 percent of patients (31 out of 62, 24 by HE stain on whole-mount section and 7 by ISH on TMA) and that in the ORM was observed in 38.7 percent of the patients (24 out of 62, 16 observed by HE stain on whole-mount section and 8 by ISH on TMA). Microscopic tumor foci spread in the circumferential resection margin (CRM) occurred in 8.1 percent of the patients (5 out of 62, 4 observed by HE stain on whole-mount section and one by ISH on TMA), and distal mesorectum (DMR) involvement was detected in 6.5 percent (4 out of 62, all observed by HE stain on whole-mount section), with the spread extending to within 3 cm from the lower margin of the tumor. Most (26 of 31) of the patients with microscopic spread in mesorectum had TNM Stage III diseases. Conclusions: The results of the present study support the theory that complete excision of the mesorectum without destruction of the ORM is essential for surgical management of low rectal cancer, and an optimal DMR clearance resection margin of no less than 4 cm was referenced. Five patients with microscopic tumor nodule spread in the CRM observed in the study suggested that microscopic metastases exist in pelvic lateral areas and in the mesorectum simultaneously, indicating the significance of preoperative and/or postoperative radiochemotherapy.

Identification of the sites of expression of triple a syndrome mRNA in the rat using in situ hybridisation

Triple A syndrome is characterised by achalasia, alacrima, adrenocorticotropin-resistant adrenal insufficiency and a variable and progressive neurological phenotype. It is caused by mutations in a gene that is normally referred to as the triple A syndrome gene ( AAAS) and which has recently been shown to encode a nuclear pore protein named ALADIN ( alacrima, achalasia, a drenal insufficiency neurologic disorder). In this study we performed in situ hybridisation with radioactive oligonucleotide probes in the adult and developing rat and present the first detailed map of AAAS mRNA expression. Consistent with a role for AAAS in adrenal function, we detected high levels of its mRNA in the adrenal cortex. On the other hand hepatocytes, enteric smooth muscle and fibroblasts had relatively little or no detectable AAAS mRNA. In both the peripheral and central nervous systems, AAAS mRNA was abundantly expressed. Neurons in sensory and sympathetic ganglia expressed high levels. CNS expression was highest in neurons of the cerebral cortex, cerebellum, hippocampus, motor-associated nuclei of the brainstem including cranial nerve nuclei, and ventral horn of the spinal cord. Although neuronal expression of AAAS mRNA was striking, non-neuronal cells including those of the circumventricular organs and fibrous astrocytes also expressed AAAS mRNA. Within the developing embryo, the highest levels of expression were found in neural tissues. These findings indicate a widespread but not ubiquitous or uniform expression of AAAS mRNA in the rat. Robust expression in neural systems associated with cognitive, motor and sensory functions is consistent with the myriad of symptoms experienced by patients with triple A syndrome.

Standardized quantitative in situ hybridization using radioactive oligonucleotide probes for detecting relative levels of mRNA transcripts verified by real-time PCR

In situ hybridization (ISH) is an essential technique for mapping gene expression in the brain. Although many ISH protocols provide for quantitative analysis of individual mRNAs in different brain regions or across experimental conditions, this technique has lacked the necessary standardization for quantitative comparisons between different mRNA transcripts. We have developed a standardized quantitative ISH (SQuISH™) protocol that utilizes multiple radioactive oligonucleotide probes, providing for increased sensitivity, decreased background and accurate comparison of relative mRNA levels. We evaluated the SQuISH™ protocol against a riboprobe-based ISH procedure by comparing the mRNA expression levels in the brain for two transcripts, insulin receptor substrate p53 (IRSp53) and Calsenilin. The results of these two methods were then validated by real-time quantitative PCR. Both protocols exhibited identical mRNA expression patterns for IRSp53 and Calsenilin. In three brain regions analyzed, the levels of IRSp53 mRNA expression were ∼1.5-fold higher with the riboprobe-based ISH than with the SQuISH™ procedure, although the relative abundance in regional expression levels was similar between the two methods. In contrast, the levels of Calsenilin mRNA expression were 10–17-fold higher with the riboprobe-based ISH than with the SQuISH™ procedure and the relative abundance in regional expression levels was different. When compared to the real-time PCR results, the SQuISH™ method showed almost identical relative levels of IRSp53 to Calsenilin mRNA in all three brain regions analyzed, while the riboprobe-based procedure showed a completely opposite trend. These results support the accuracy of the SQuISH™ protocol for determining relative mRNA levels in the brain.

Standardized quantitative in situ hybridization using radioactive oligonucleotide probes for detecting relative levels of mRNA transcripts verified by real-time PCR

Standardized quantitative in situ hybridization using radioactive oligonucleotide probes for detecting relative levels of mRNA transcripts verified by real-time PCR

An in situ hybridization and immunofluorescence study of glycinergic receptors and gephyrin in the vestibular nuclei of the intact and unilaterally labyrinthectomized rat.

We investigated whether the expression of glycinergic receptor (GLYR) subunits of gephyrin and of their mRNAs in the medial vestibular nuclei are affected following unilateral labyrinthectomy. Specific radioactive oligonucleotide probes recognizing the sequences encoding alpha1-3 and ss subunits of GLYR and the anchoring protein gephyrin were used to probe sections of vestibular nuclei. Signals in these in situ hybridization experiments were detected with film or by emulsion photography. Animals were killed at various times following the lesion: 5 h, 1, 3, 8, 30 and 60 days. Specific monoclonal GLYR and gephyrin antibodies were also used to determine GLYR and gephyrin immunoreactivity in control and operated rats (5 h, 1, 3 and 8 days post-lesion). In normal animals, several brainstem regions including the lateral, medial, superior and inferior vestibular nuclei contained mRNAs for gephyrin and the alpha1 and beta subunits of GLYR, and expressed the GLYR and gephyrin polypeptides. In unilaterally labyrinthectomized rats, no asymmetry was detected on autoradiographs between the two medial vestibular nuclei with any of the oligonucleotide probes used, or at any time following the lesion. No difference in the immunofluorescence staining was observed between the intact and deafferented medial vestibular nuclei of lesioned animals or between the vestibular nuclei of lesioned and controls rats. Thus, deafferentation of the vestibular nuclei did not affect the expression of gephyrin, of the various GLYR subunits, or of their mRNAs in the deafferented and intact medial vestibular nuclei. It is therefore unlikely that GLYR and gephyrin modulation contribute significantly to the recovery of the resting discharge of the deafferented medial vestibular neurons and consequently to the restoration of a normal posture and eye position.

Expression of adenosine A2a receptors gene in the olfactory bulb and spinal cord of rat and mouse

The expression of adenosine A2a receptors (A2aR) in the mammalian striatum is well known. In contrast the exact distribution of A2aR in other regions of the central nervous system remains unclear. The aim of this study was to investigate the A2aR gene expression in the rat olfactory bulb and spinal cord, two regions which are seldom included in mapping studies. Secondly, we compared the A2aR expression in the rat and in the mouse brain. Hybridization histochemistry was performed with an S 35-labelled radioactive oligonucleotide probe. The results show strong expression of A2aR in the mouse and rat striatum in accordance with previous reports. In the olfactory bulb a weak but specific expression of A2aR was found in the granular cell layer in both species. In contrast, no significant expression of the A2aR gene was observed in other parts of the brain or the rat spinal cord. The presence of the A2aR in the mammalian olfactory bulb suggests a functional role for this receptor in olfaction.

Expression of adenosine A2a receptor gene in rat dorsal root and autonomic ganglia

The adenosine A2a receptors (A2aR) play an important role in the purinergic mediated neuromodulation. The presence of A2aR in the brain is well established. In contrast, little is known about their expression in the periphery. The purpose of this study was to investigate the expression of A2aR gene in the autonomic (otic, sphenopalatine, ciliary, cervical superior ganglia and carotid body) and in the dorsal root ganglia of normal rat. Hybridization histochemistry with S 35-labelled radioactive oligonucleotide probes was used. An expression of A2aR gene was found in the large neuronal cells of the rat dorsal root ganglia. The satellite cells showed no expression of A2aR gene. In the superior cervical ganglion, isolated ganglion cells expressed A2aR. In the carotid body clusters of cells with a strong A2aR gene expression were found. In contrast, the ciliary and otic ganglia did not expressed A2aR gene, and only few small sized A2aR expressing cells were demonstrated in the sphenopalatine ganglion. The discrete distribution of A2aR gene expression in the peripheral nervous system speaks for a role of this receptor in the purinergic modulation of sensory information as well as in the sympathetic nervous system.

Enterotoxin production by coagulase-negative staphylococci isolated from goats' milk and cheese

An antigen related to the Enterotoxin E from Staphylococcus aureus was produced by ten of 187 coagulase-negative staphylococci (CNS) isolated from goats' milk, whey and cheese in quantities ranging from 10 to 90 ng ml supernatant. The enterotoxin-producing strains were identified at the species level as S. simulans, S. xylosus, S. equorum, S. lentus and S. capitis. Detection of the enterotoxins was done by the VIDAS SET test (bioMérieux) and by an indirect double-sandwich ELISA technique using anti-enterotoxin monoclonal antibodies. The results obtained were further confirmed by Southern blotting, using two radioactive oligonucleotide probes that hybridized specifically with the gene of S. aureus coding for the enterotoxin E.

Effects of unilateral cochlea ablation on the distribution of calretinin mRNA and immunoreactivity in the guinea pig ventral cochlear nucleus

The predominantly neuronal, calcium-binding protein calretinin is highly expressed in the guinea pig auditory system. Within the ventral cochlear nucleus (VCN), calretinin-positive auditory nerve fibers terminate on many calretinin-containing bushy, octopus, and multipolar cells. The abundance of calretinin in the cochlear nucleus provides an ideal system for examining the effects of altered neuronal input on the expression of this calcium-binding protein. The present experiments examined the effects of unilateral cochlea ablation on calretinin immunoreactivity and mRNA levels in the VCN. Calretinin mRNA was labeled by in situ hybridization histochemistry using a radioactive oligonucleotide probe and was quantified by optical density measures on autoradiograms. Survival times of 1, 7, and 56 days postlesion were examined. The results revealed a consistent increase in calretinin mRNA in the rostral portion of the ipsilateral anterior VCN 1 day postlesion but no effect on calretinin mRNA in this region at 7 and 56 days postlesion. The intensity of immunohistochemical label was also increased at 1 and 7 days after surgery. In contrast, calretinin mRNA was not affected 1 day postlesion in the ipsilateral posterior VCN but was decreased at both 7 and 56 days postlesion. The decrease in calretinin mRNA in the posterior VCN at longer survival times was accompanied by decreased immunolabeling of fibers projecting from VCN cells to the superior olivary complex. These results suggest that calretinin gene expression is regulated in part by auditory nerve activity in some cochlear neurons but that additional factors related to the unique cellular milieu also control calretinin expression.

Polymerase chain reaction detection of human immunodeficiency virus DNA in human periradicular lesions

Human immunodeficiency virus (HIV) has been previously reported to be present in the dental pulp of a patient with AIDS. The present report investigated the feasibility of polymerase chain reaction (PCR) amplification to detect the HIV proviral DNA in cells from periradicular lesions from an HIV-positive patient. The standard PCR amplification with 30 cycles and the nested PCR consisting of two 25-cycle amplifications were used. Samples from each reaction were separated by nondenaturing polyacrylamide gel electrophoresis and stained with ethidium bromide for visualization. Gels were electroblotted to nylon membranes, which were then fixed, denatured, and dried. Membranes were hybridized to specific radioactive oligonucleotide probes and placed next to Kodak XAR film for visualization of the HIV-specific bands. No evidence of HIV-specific reaction was observed in cells (negative control) or in two periradicular lesions from two HIV-negative patients. The ethidium bromide strains revealed that PCR amplification of DNA extracts from two lesions from the HIV-positive patient yielded PCR bands (with both primer pairs) which corresponded to HIV-specific bands of the expected size.

NK1 receptor expression by cholinergic interneurones in human striatum.

Neurokinin-1 (NK1) receptor expression in human striatum was analysed using the polymerase chain reaction. To determine whether cholinergic interneurones express this receptor, in situ hybridization histochemistry was then applied to caudate nucleus and putamen. Radioactive oligonucleotide probes specific for choline acetyltransferase (ChAT) and NK1 receptor mRNA were used on adjacent cryostat sections. All of the 160 identified neurones positive for ChAT were also labelled for NK1 receptor. Moreover, in the caudate nucleus, NK1 receptor mRNA was detected in a population of large neurones that were not cholinergic. These results are consistent with the hypothesis that NK1 receptor-mediated mechanisms are involved in the function of cholinergic interneurones. This might be relevant to pharmacological or pathophysiological situations where substance P inputs are modified.

Capillary electrophoresis: detection of hybridization between synthetic oligonucleotides and HIV-1 genomic DNA amplified by polymerase-chain reaction

The polymerase chain reaction (PCR) is one of the most efficient techniques for measuring the viral load of HIV-infected samples. Determination of the specificity of PCR products is usually based on Southern blotting and hybridization of the amplified DNA to radioactive oligonucleotide probes specific for sequences comprised between the PCR primers. The recent introduction of capillary electrophoresis (CE) for identification of HIV-1 and HTLV-I PCR products appears interesting in light of its reproducibility, sensitivity and because it is fast and suitable for detection of DNA/DNA and DNA/RNA hybrids. We demonstrate that specific hybridization of a HIV-1 oligonucleotide probe to single-stranded DNA obtained by unbalanced PCR is detectable by capillary electrophoresis. This enabled us the application of a one-step, non-radioactive protocol to demonstrate the specificity of amplification of HIV-1 genomic sequences by PCR. This procedure is simple, reproducible and is suggested as an integral part of automated diagnostic systems based on the use of laboratory work stations for DNA isolation, preparation of PCR reactions and analysis of PCR products.

DETECTION OF HEPATITIS-C VIRUS BY UNBALANCED POLYMERASE-CHAIN REACTION, HYBRIDIZATION TO SYNTHETIC OLIGONUCLEOTIDES AND CAPILLARY ELECTROPHORESIS

Polymerase chain reaction (PCR) has been reported as one of the most efficient techniques to detect hepatitis C virus (HCV) RNA. The determination of the specificity of PCR products is usually based on 'nested' PCR, Southern blotting and hybridization of the amplified DNA to radioactive oligonucleotide probes recognizing sequences comprised between the PCR primers. The recent introduction of capillary electrophoresis (CE) to analyse DNA fragments and PCR products appears to be very interesting because this technology is rapid, reproducible, sensitive and could be suitable to detect DNA/DNA and DNA/RNA hybrids. We demonstrate that specific hybridization of an HCV oligonucleotide probe to single stranded HCV-DNA obtained by unbalanced PCR is detectable by capillary electrophoresis, therefore enabling a one-step, non-radioactive protocol to demonstrate the specificity of amplification of HCV sequences by PCR.

Detection of in vivo expression of interleukin-10 using a semi-quantitative polymerase chain reaction method in Schistosoma mansoni infected mice

A modified polymerase chain reaction (PCR) assay for analysis of cytokine gene expression from reverse-transcribed (R/T) RNA obtained from small numbers of cells is described in detail. This method employs a previously described dot-blot format and utilizes a target specific radioactive oligonucleotide probe which hybridizes to the PCR amplified product, thus increasing both specificity and sensitivity. This obviates the need for repeated electrophoresis gels and easily accomodates large experiments (e.g., numerous samples or kinetic studies), using small amounts of RNA from low cell numbers. Manipulation of many samples is further enhanced with the use of a PCR thermocycler, which like the dot-blot apparatus is designed in a 96-well format. We describe the use of the house-keeping enzyme hypoxanthine phosphoribosyltransferase (HPRT) as an internal standard, which is especially suitable since its range of detectability of expression is similar to that of the cytokines under test. This enables one to obtain an accurate measure of losses or degradation of RNA, as well as controlling for efficiency of the R/T and PCR reactions. These reactions are further controlled by inclusion of a standard curve consisting of a titration of a known amount of RNA from a cell line expressing the cytokine under test. As well as controlling for the R/T-PCR, this standard curve also enables one to obtain a semi-quantitative measure of cytokine expression by different cell populations during an immune response. We show that this method can be used successfuly for studying differential expression of IL-10 in different microenvironments during infection of mice with Schistosoma mansoni.

The use of the polymerase chain reaction for the detection of Simian immunodeficiency virus in experimentally infected macaques

A rapid, non-radioactive assay for the detection of proviral Simian immunode-ficiency virus (SIV) in tissue-culture cells is described. The assay is based on the co-amplification of the SIV env and gag genes by the polymerase chain reaction (PCR). When the gag PCR product is blotted onto a nylon membrane and hybridised to a radioactive oligonucleotide probe, the assay can also be used to detect the SIV gag gene in DNA isolated directly from experimentally infected cynomolgus macaque lymphocytes. This provides a valuable assay for the presence of proviral SIV during animal trials of AIDS vaccines and chemotherapeutics.

Topography and ontogeny of the neurons expressing vasopressin, oxytocin, and somatostatin genes in the rat brain: an analysis using radioactive and biotinylated oligonucleotides.

1. The use of radioactive and biotinylated oligonucleotide probes has been optimized to detect and analyze by in situ hybridization, neurons expressing neuropeptide genes (vasopressin, oxytocin, somatostatin). 2. In situ hybridization was performed on cryostat-cut sections obtained from tissues perfused with 1% formaldehyde. Radioactive probes were labeled by tailing with 35S-dATP and revealed with autoradiography. Biotinylated probes were obtained either by the incorporation of 11-biotin dUTP or by the addition of biotinylated nucleotides to the oligonucleotide during its synthesis. Biotin was revealed with streptavidin alkaline phosphatase and the appropriate substrate. 3. In the adult rat brain, radioactive and biotinylated probes revealed peptidergic neurons. The biotinylated probes provided an optimal cellular and subcellular resolution with a sensitivity similar to that observed with radioactive probes. Staining was selectively restricted to the cytoplasm and to the proximal part of processes. 4. Biotinylated vasopressin probes with 10 biotins added demonstrated magnocellular neurons and parvocellular neurons in the suprachiasmatic nucleus and the bed nucleus stria terminalis. 5. Vasopressin gene expression was studied during ontogeny in the rat fetus and neonate. Vasopressin mRNA was first detectable at gestational day 16 in the supraoptic nucleus in neurons of neuroblastic appearance. An aspect similar to the one present in adult was found at gestational day 19 in magnocellular neurons and at day 3 postnatal in parvocellular neurons. 6. The results confirm that radioactive oligonucleotide probes are efficient tools to investigate neuropeptide gene expression by in situ hybridization and demonstrate that biotinylated oligonucleotides are very efficient and provide a much higher resolution than radioactive probes with a reasonable sensitivity.

Non-radioactive oligonucleotide probe for detection of clinical enterotoxigenic Escherichia Coli isolates of bovine origin

Oligonucleotides (32 or 34 mer) corresponding to enterotoxigenic Escherichia coli ST Ia (ST-P) toxin were tailed with Bio-11-dUTP using terminal deoxynucleotidyl transferase. Plasmids from clinica E.Coli isolates were prepared by modified rapid alkaline lysis procedure and dot-spotted. Biotinylated oligonucleotide probes were hybridized to detect the St Ia toxin gene. The results were in agreement with that obtained by radioactive oligonucleotide probes. Of 135 clinical isolates (sampled from 6 different regions of France), only 7 (5.2 %) were found to be ST Ia +. These 7 isolates were the only ones to be found positive for the K99 adhesive pili antigen. Both the proves were specific to the ST Ia toxin gene and failed to detect the closely related ST Ib (ST-H) toxin gene. Possibilities of their wide usage in clinical labs are discussed.