[New therapeutic options in Alzheimer's disease]

INTRODUCTION

At present, cholinesterase inhibitors constitute the basis for therapy of Alzheimer's disease (AD); these drugs were rationally introduced given the loss of central cholinergic neurotransmission, even though there are many other systems affected in AD, including glutamatergic pathway.

DEVELOPMENT

In addition to the loss of central cholinergic neurotransmission, biochemical evidence suggests glutamatergic dysfunction in AD and thus, therapeutic strategies directed at the glutamatergic system may be useful. These drugs include milacemide, cicloserine and ampakines (positive modulation) and memantine (negative modulation). Lithium seems to be a promising agent in AD, although the mechanism of action is poorly understood. Finally anti-inflammatory agents may be another therapeutic approach to AD.

CONCLUSION

In addition to drugs acting on the cholinergic system, a large number of drugs with different mechanism could be used for the treatment and prevention of AD.

[Long-term evolution of the doses of Botulinum toxin used in laryngeal and cervical dystonias]

INTRODUCTION

Dystonia is a neurological condition characterised by involuntary movements that give rise to abnormal postures. Different strategies have been used in the treatment of focal dystonias, but the most widely accepted at the present time involves the use of botulinum toxin type A (BTA) injections. Yet, despite its widespread use, the ideal dosages for long-term treatment are still not known with precision.

AIMS

The purpose of this study is to report on our experience with long-term BTA therapy in laryngeal (LD) and in cervical dystonia (CD).

PATIENTS AND METHODS

We reviewed the data concerning the dosages of BTA injected in 10 patients with LD who received treatment in our centre over a period of eight years. We also analysed the data regarding the doses of BTA injected over an eight-year period in 17 patients with CD. The data were analysed using an ANOVA for paired data.

RESULTS

No significant differences were found in the highest dosages of BTA needed for the treatment of LD throughout the progression of the disease (p=0.84). These data contrast with those obtained from the analysis of the treatment of CD, which do show a gradual increase in the dose of toxin that is required (p<0.0001).

CONCLUSIONS

These findings suggest that the long-term response to treatment is different in the two conditions.

Influence of Storage and Preservation on Fossomatic Cell Count and Composition of Goat Milk

This study was designed to evaluate the effects of different test conditions on the somatic cell count (SCC) and composition of goat milk. To this end, 3600 tests were performed on 1800 aliquots taken from 40 goat milk samples using a combined instrument set-up based on flow cytometry for SCC and Fourier transform infrared analysis for fat, total protein, lactose, total solids, and freezing point determinations. The conditions tested were storage temperature (refrigeration and freezing), use of a preservative [no preservative (NP), azidiol (AZ), and bronopol (BR)], and age of the milk samples at each storage temperature (24 h to 42 d at refrigeration temperature and 21 to 105 d at freezing temperature). Significant effects on logSCC variation were shown by the storage temperature, the preservation treatment, the interaction of storage temperature x preservation treatment, and milk age within the interaction of storage temperature x preservative. Highest counts were recorded in the BR-preserved milk samples (logSCC = 5.877), and lowest counts were recorded in milk samples preserved using AZ (logSCC = 5.803). The use of frozen/thawed samples led to a significantly decreased logSCC for the treatments AZ and NP; the logSCC was not modified when BR-preserved frozen/thawed samples were analyzed. During storage, variations in the SCC observed for BR-preserved samples stored at refrigeration temperature for up to 25 d and at freezing temperature for all times tested were always < 10%. The preservation treatment was the main factor affecting the milk composition variables examined. Highest values of most variables were obtained in the BR-preserved samples, and the lowest values were obtained in the AZ-preserved samples. The freezing point was lower in the preserved samples than in the NP samples. The levels of milk constituents recorded in the BR-preserved samples were independent of both the storage temperature and age of milk sample. Our findings indicate that the freezing point of goat milk must be interpreted according to the preservative used.

Serotypes, virulence genes and intimin types of verotoxin-producing Escherichia coli and enteropathogenic E. coli isolated from healthy dairy goats in Spain

Faecal samples from 222 healthy dairy goats on 12 farms in Spain, as well as bulk tank milk samples of these farms, were screened for the presence of verotoxin-producing Escherichia coli (VTEC) and enteropathogenic E. coli (EPEC). VTEC and EPEC were isolated in 47.7 and 7.7% of the animals, respectively. VTEC were isolated more frequently from adults and replacement animals than from goat kids. In contrast, EPEC were detected more frequently from goat kids than from replacement animals and adults. VTEC or EPEC strains were not detected in the bulk tank milk samples. Although a selective enrichment protocol was used, the serotype O157:H7 was not detected. The most frequent serotypes among the 106 VTEC strains isolated from goats were O5:H-, O76:H19, O126:H8, O146:H21, ONT:H- and ONT:H21. None VTEC strain was eae-positive. The absence of the eae gene in the VTEC strains could indicate that these strains are less virulent for humans that the classical eae-positive enterohaemorrhagic E. coli types. However, 16% of VTEC strains isolated from healthy goats belonged to serotypes associated with haemolytic uraemic syndrome in humans. The ehxA gene was detected in 84.9 and 52.9% of the VTEC and EPEC from goats, respectively. The beta1, theta/gamma2 and zeta were the most frequent intimin types among the 17 EPEC strains studied and the most prevalent serotypes of these strains were O156:H25 and O177:H11. Our data show that in Spain healthy goats are an important reservoir of VTEC and EPEC, and a potential source of infection for humans.

Effect of Clinical Contagious Agalactia on the Bulk Tank Milk Somatic Cell Count in Murciano-Granadina Goat Herds

From 19 herds of Murciano-Granadina goats, weekly bulk tank somatic cell count (BTSCC) were performed from October to April, and suspicious milk (n = 182), synovial fluid, and ocular swabs (n = 15) from diseased goats were processed for mycoplasma isolation and identification. Also BTSCC from 65 herds were determined (n = 2693). A mixed model procedure was used to establish the effect of the herd and the lactation month on the BTSCC. Monthly rolling values were calculated for each herd using data collected over the preceding 3 complete months, and 4 different BTSCC thresholds were considered: 1,750,000, 1,500,000, 1,000,000, and 750,000 cells/mL. The mean log BTSCC for the 7-mo study period was 5.89 +/- 0.28 for herds without mycoplasma detection from clinical cases, 5.91 +/- 0.31 for mycoplasma-infected herds without clinical contagious agalactia (CA), and 6.47 +/- 0.32 for the herd with clinical CA. The posthoc tests revealed that only the herd that suffered a clinical CA outbreak showed counts that were significantly higher. No significant differences were found for BTSCC between herds not showing clinical episodes of CA, regardless of whether the mycoplasma had been isolated or not. The 1,750,000-cells/mL threshold would only be surpassed by a few herds with serious mastitis problems (clinical outbreak of CA for example). Seventy percent of the goat herds studied were in compliance with the proposed European Union legal limit of 1,500,000 cells/mL for goat milk.

Influence of intramammary infection and non-infection factors on somatic cell counts in dairy goats

A total of 1304 goat udder halves were sampled monthly during an entire lactation (6262 samples) with the aim of identifying factors affecting milk somatic cell count (SCC). Bacteriological analyses for identification of mastitis pathogens were carried out on all samples and SCC was also determined. All animals were examined for infection by caprine arthritis-encephalitis virus (CAEV) using a commercial ELISA test kit. Results obtained were arranged in two databases (whole-lactation average half-udder database and monthly half-udder database) and two mixed models were applied. Random effects of half udder nested into flock and fixed effects of flock, intramammary infection (IMI) status, number of kids born, length of lactation and interaction of parity with IMI status were significant for the first database. CAEV infection and its interaction with IMI status was not significant. Milk SCC was significantly increased for infected udder halves and milk from udder halves infected with minor pathogens had lower SCC than udder halves infected with major pathogens. For healthy udder halves, SCC was higher in older animals but this effect was not evident in halves with IMI. Multiple birth and short-duration lactation were factors associated with elevated milk SCC. The second mixed model considered repeated measures in time for consecutive samplings throughout lactation (stage of lactation) which was also a significant factor with increasing stage of lactation. The influence of all these factors should be taken into account in the establishment of more reliable diagnostic SCC thresholds for IMI.

Influence of sampling time on bacteriological diagnosis of goat intramammary infection

Intramammary infection in seven commercial goat herds was studied using premilking and postmilking samples for purposes as bacteriological diagnosis. Using a positive result on both premilking and postmilking samples as the definitive diagnosis, we compared the efficacy of single samples collected either premilking or postmilking. With this aim, 2268 bacteriological culture results were compared. The kappa values (0.60) showed moderate agreement between the two samples. Specificity and positive predictive value were higher for postmilking samples than for premilking samples. Specificity of postmilking samples was 99.4% for coagulase-negative staphylococci, 99.9% for Gram-negative bacilli, 100% for streptococci, 99.9% for corynebacteria and 100% for mixed cultures. Premilking samples specificity was 96.6, 99.5, 99.7, 99.8 and 99.8%, respectively. False positive diagnoses were more frequent for premilking samples. The results suggest that postmilking samples should be used to diagnosis of goat intramammary infection.

Identification and analysis of Escherichia coli proteins that interact with the histidine kinase NtrB in a yeast two-hybrid system

In this work we used the yeast two-hybrid (Y2H) system to deepen our understanding of protein-protein interactions that are involved in the nitrogen regulatory network in Escherichia coli. Three different genes, encoding GlnB, GlnK and AspA, respectively, were found among 64 positive clones identified from E. coli Sau3AI Y2H libraries using the nitrogen regulator NtrB as bait. Structural and functional analysis of the prey clones provided information on library features and the degree of saturation achieved in the screens. Further analysis revealed that the C-terminal kinase domain of NtrB is required for the interaction with GlnK, while AspA(91-312) interacts specifically with the conserved histidine phosphotransfer domain of NtrB, thus providing additional evidence for the involvement of the conserved transmitter module of the histidine kinase NtrB in input sensory functions.

Effect of freezing goat milk samples on recovery of intramammary bacterial pathogens

With the aim of evaluating the effect of freezing goat milk samples on recovery of intramammary pathogens, 1200 milk samples from udder halves with subclinical intramammary infection were studied. Samples (20 ml) were frozen at -20 and at -80 degrees C. Thawing was carried out at room temperature at 7, 14, 21, 28, 58, 118, 178, 236 and 730 days after collection and bacteriological analyses were carried out to determine the number of colony forming units/ml (CFU/ml). Mixed model statistical analysis showed that bacterial group, temperature of storage, interaction of bacterial group and temperature of storage and the interaction of bacterial group, time and temperature of storage were statistically significant effects. For coagulase negative staphylococci (CNS), least squares means of log CFU/ml recovered at -20 and -80 degrees C were not different. Nevertheless, for Gram negative bacilli (GNB) a significant decrease was detected in samples frozen at -20 vs. -80 degrees C. At both temperatures and at different times of storage, significant increases were detected between log CFU/ml of CNS and values on day zero. At -20 degrees C, a significant decrease in GNB recovery was detected between freezing days zero and 730. This difference was not detected when goat milk samples infected by GNB were frozen at -80 degrees C. The results show that frozen milk samples can be useful in goat subclinical mastitis control programs.

Factors constraining adherence to referral advice for severely ill children managed by the Integrated Management of Childhood Illness approach in Imbabura Province, Ecuador

AIM

Low referral completion rates in developing countries undermine the Integrated Management of Childhood Illness (IMCI) strategy for lowering child mortality. This study sought to identify factors constraining adherence to referral advice in a health system using the IMCI approach.

METHODS

Caregivers of 160 children urgently referred to hospital were prospectively interviewed. Caregivers who accessed and did not access hospital were compared for potential referral constraining factors, including demographics, family dynamics, the severity of their child's illness, their interaction with the health system, self-perceived problems, and physical and financial access.

RESULTS

67/160 (42%) referred children did not access hospital. Six factors were associated with non-access, including two health worker actions: not being given a referral slip [adjusted odds ratio (OR)= 15.3, 95% confidence interval (95% CI) 4.4-64.6] and not being told to go to the hospital immediately (adjusted OR = 5.3, 95% CI 1.9-16.3). Receiving both of these interventions reduced the risk of not accessing hospital to 19%, from 96% for those who received neither intervention. Several indicators of illness severity, including caregivers' ranking of their children's illness severity, the presence of severe illness signs and mortality, were investigated and found not to be important explanatory factors.

CONCLUSION

Providing a referral slip and counseling the caregivers of severely ill children to go to the hospital immediately appear to be powerful tools for increasing successful referral outcomes.

Polyclonal antibodies to xenogeneic endothelial cells induce apoptosis and block support of tumor growth in mice

In this study, we demonstrate that vaccination of rabbits with murine endothelial cells yields polyclonal immunoglobulin (IgG) with potent antiangiogenic activity. The mechanism of this response appears to be through apoptosis of endothelial cells in vitro. Induction of polyclonal IgG in a xenogeneic host may be useful in passive immunotherapy of a variety of cancers. In fact, the antibody showed antitumor activity in three mouse tumor models (murine B16F10 melanoma, murine SVR angiosarcoma, and human DLD-1 colorectal adenocarcinoma). The polyclonal antibody generated here demonstrated utility in radioimaging of tumors in vivo, using positron emission tomography (PET) imaging, and suggested an antitumor effect in vivo. The results suggest that the antitumor effect in vivo may be related to antiangiogenic effects. Furthermore, anti-endothelial cell antibodies such as these could be useful reagents in isolating specific targets that comprise and induce the antiangiogenic effect.

Statin-AE: a novel angiostatin-endostatin fusion protein with enhanced antiangiogenic and antitumor activity

The combination of angiostatin and endostatin has been shown to have synergistic antiangiogenic and antitumor effects when the genes for these proteins are delivered to tumor cells by retroviral gene transfer. Here we report the construction of a murine angiostatin-endostatin fusion gene (Statin-AE) which shows enhanced antiangiogenic activity on human umbilical vein endothelial cell (HUVEC) tube formation in vitro compared with angiostatin or endostatin alone. Similarly, the fusion gene demonstrates antiangiogenic effects in vivo and antitumor activity in a B16F10 melanoma model when co-delivered by retroviral packaging cell inoculation in mice. The fusion gene demonstrates significantly greater inhibition of tumor growth compared with angiostatin, endostatin or the combination of genes.

Effect of intramammary infection by Staphylococcus caprae on somatic cell counts and milk composition in goats

Since its identification by Devirese et al. (1983), Staphylococcus caprae has been frequently isolated from udder halves of goats with subclinical intramammary infection (IMI) (Contreras et al. 1995; Poutrel et al. 1996). Several different studies have demonstrated the capacity of Staph. caprae to persist throughout lactation (Poutrel et al. 1996; Contreras et al. 1997; Bedidi-Madani et al. 1998a) and during the dry period (Poutrel, 1984). Bedidi-Madani et al. (1998a) found that isolates of Staph. caprae from udders of uninfected goats express potential virulence factors (different exoproteins and slime); other researchers have occasionally isolated it from clinical cases of goat mastitis (Deinhofer & Pernthaner, 1995), or from human clinical specimens associated with bone and joint infection (Vandenesh et al. 1995; Shuttleworth et al. 1997). In spite of these forms of pathogenicity, some studies have not shown significant increases in somatic cell count (SCC) of milk from goat udder halves infected by Staph. caprae (Deinhofer & Pernthaner, 1995; Poutrel et al. 1996). Moreover, there is a lack of information on the effect of infection by this mammary pathogen on milk yield and composition. Knowledge of repercussions for hygiene and production would be useful in mastitis control programmes in view of the high frequency of isolation (higher than 22% of the staphylococci isolated) of Staph. caprae in dairy goat herds (Contreras et al. 1995; Poutrel et al. 1996). The aim of the present investigation was to ascertain the significance of persistent subclinical IMI by Staph. caprae on SCC, milk yield and physical-chemical parameters of Murciano-Granadina goat milk at mid-lactation.

Treatment of Papillon-Lefèvre syndrome periodontitis

BACKGROUND, AIMS

Conventional mechanical treatment of Papillon-Lefèvre syndrome periodontitis has a poor prognosis. This report describes an effective antimicrobial treatment of rapidly progressing periodontitis in an 11-year old girl having Papillon-Lefèvre syndrome.

METHOD

Clinical examination included conventional periodontal measurements and radiographic analysis. Occurrence of major suspected periodontopathic bacteria was determined by selective and non-selective culture and by polymerase chain reaction (PCR) identification. Presence of cytomegalovirus and Epstein-Barr type 1 virus was determined by a nested-PCR detection method. Therapy included scaling and root planing, oral hygiene instruction, and systemic amoxicillin-metronidazole therapy (250 mg of each/3 times daily/10 days) which, based on follow-up microbiological testing, was repeated after 4 months. Supportive periodontal therapy took place at 2 visits during a 16-month period.

RESULTS

At baseline, 10 of 22 available teeth demonstrated severe periodontal breakdown. At 16 months, probing and radiographic measurements revealed no teeth with additional attachment loss, and several teeth exhibited significant reduction in gingivitis and pocket depth, increase in radiographic alveolar bone height and clinical attachment level, and radiographic evidence of crestal lamina dura. Baseline subgingival microbiota included Actinobacillus actinomycetemcomitans (3.4% of total isolates), Prevotella nigrescens (16.4%), Fusobacteriumnucleatum (14.3%) and Peptostreptococcus micros (10.6%), as well as cytomegalovirus and Epstein-Barr type 1 virus. At termination of the study, culture and PCR examinations showed absence of A. actinomycetemcomitans, P. micros and herpesviruses, and P. nigrescens and F.nucleatum each comprised less than 0.1 % of subgingival isolates.

CONCLUSION

This study suggests that controlling the periodontopathic microbiota by appropriate antibiotic and conventional periodontal therapy can arrest Papillon-Lefèvre syndrome periodontitis.

Aggressive periodontitis associated with Fanconi's anemia. A case report

BACKGROUND

Fanconi's anemia is an autosomal recessive disease associated with chromosomal breakage as well as pancytopenia, skin pigmentation, renal hypoplasia, cardiac defects, microcephaly, congenital malformations of the skeleton, hypogonadism, and increased risk of leukemia. The present report describes the periodontal clinical and microbiological status of an 11-year old male having Fanconi's anemia.

METHODS

Polymerase chain reaction analysis to detect human cytomegalovirus (HCMV), Epstein-Barr type 1 virus, and herpes simplex virus (HSV) was performed on paper-point samples pooled from either 3 periodontal sites with advanced attachment loss or 3 gingivitis sites with no clinical attachment loss. Anaerobic bacterial culture examination was performed on the pooled periodontitis sample.

RESULTS

The patient suffered from pancytopenia, allergy, asthma, hearing impairment, and mental retardation. Dentition consisted of 7 primary teeth, 11 erupted permanent teeth, and 14 unerupted permanent teeth. Most erupted teeth showed severe gingival inflammation with some gingival overgrowth and various degrees of periodontal attachment loss. Genomes of HCMV and HSV were detected in the pooled periodontitis sample and HCMV in the pooled gingivitis sample. The periodontitis sample but not the gingivitis sample revealed HCMV mRNA of major capsid protein, suggestive of active viral infection. The periodontitis sample also yielded Actinobacillus actinomycetemcomitans (1.1% of total isolates), FusobActerium species (7.9%), Campylobacter species (2.2%), Peptostreptococcus micros (3.4%), and Candida albicans (0.3%).

CONCLUSIONS

Oral features of Fanconi's anemia may include increased susceptibility to periodontitis. It is likely that underlying host defense impairment coupled with periodontal infection by HCMV and A. actinomycetemcomitans contribute to the severe type of periodontitis associated with Fanconi's anemia.

Herpes viruses and periodontopathic bacteria in early-onset periodontitis

OBJECTIVES

This study examined the occurrence of human herpes viruses and suspected periodontopathic bacteria in early-onset periodontitis patients who experienced progressive disease in at least 2 periodontal sites during the maintenance phase of therapy.

MATERIAL AND METHODS

In each of 16 individuals (9 male and 7 female; mean age 33.1+/-2.6 years), subgingival plaque samples were collected from 2 deteriorating and 2 stable periodontitis sites. A nested polymerase chain reaction method determined the presence of human cytomegalovirus (HCMV), Epstein-Barr virus type 1 (EBV-1) and herpes simplex virus (HSV). A 16s rRNA polymerase chain reaction method identified Porphyromonas gingivalis, Dialister pneumosintes, Bacteroides forsythus and Actinobacillus actinomycetemcomitans.

RESULTS

HCMV was detected in 59.4% of active and in 12.5% of stable sites (p<0.001), EBV-1 in 43.8% of active and in 12.5 % of stable sites (p=0.01), HSV in 34.5% of active and in 9.4% of stable sites (p=0.03), and co-infection with any of the 3 test herpesviruses in 43.8% of active and in 3.1% of stable sites (p<0.001). P. gingivalis was detected in 71.9% of active and in 37.5% of stable sites (p=0.01), D. pneumosintes in 62.5% of active and in 18.8% of stable sites (p=0.04), co-infection with P. gingivalis and D. pneumosintes in 50% of active and in 0% of stable sites (p<0.001), and co-infection with any 3 or 4 of the test bacteria in 40.6% of active and in 0% of stable sites (p=0.001). All periodontitis sites showing herpesvirus co-infection and all but one site showing P. gingivalis and D. pneumosintes co-infection revealed bleeding upon probing.

CONCLUSIONS

HCMV, EBV-1, HSV and herpesvirus co-infection, as well as P. gingivalis, D. pneumosintes and P. gingivalis-D. pneumosintes co-infection were statistically associated with active periodontitis. Herpesviruses are immunosuppressive and may set the stage for overgrowth of subgingival P. gingivalis, D. pneumosintes and other periodontopathic bacteria. Understanding the significance of herpesviruses in human periodontitis may allow for improved diagnosis, more specific therapy and, ultimately, disease prevention.

Convergence of two global transcriptional regulators on nitrogen induction of the stress-acclimation gene nblA in the cyanobacterium Synechococcus sp. PCC 7942

Cyanobacteria respond to environmental stress conditions by degrading their phycobilisomes, the light harvesting complexes for photosynthesis. The expression of nblA, a key gene in this process, is controlled by the response regulator NblR in Synechococcus sp. PCC 7942. Here we show that, under nitrogen stress, nblA is also regulated by NtcA, the global regulator for nitrogen control. NtcA activation of nblA was found to be nitrogen-specific and did not take place under sulphur stress. Transcripts from the two major transcription start points (tsp) for the nblA gene were induced in response to nitrogen and sulphur starvation. The most active one (tspII) required both NblR and NtcA to induce full nblA expression under nitrogen starvation. NblR and NtcA bound in vitro to a DNA fragment from the nblA promoter region, suggesting that, under nitrogen stress, both NblR and NtcA activate the main regulated promoter (PnblA-2) by direct DNA-binding. The structure of PnblA-2 differs from that of the canonical NtcA-activated promoter and it is therefore proposed to represent a novel type of NtcA-dependent promoter. We analysed expression patterns from ntcA and selected NtcA targets in NtcA(-), NblR(-) and wild-type strains, and discuss data suggesting further interrelations between phycobilisome degradation and nitrogen assimilation regulatory pathways.

Dental disease indices and caries related oral microflora in children with phenylketonuria

The purpose of this study was to investigate the dental caries, plaque and gingivitis indices and caries related oral flora in children with classic phenylketonuria. Forty-one children at The Great Ormond Street Hospital for Children and controls were included in the study. The main findings were: No significant difference in the decayed, missing and filled surfaces of the primary and permanent teeth between the phenylketonuria children and the controls. A significantly greater mean plaque score for the control children compared with the phenylketonuria children (p < 0.01) for the permanent teeth only. A significantly greater number of white opacities in the permanent teeth of the phenylketonuria group compared with the control group (p < 0.02). No significant differences in the caries related microflora.

Relationships between infection with caprine arthritis encephalitis virus, intramammary bacterial infection and somatic cell counts in dairy goats

Somatic cell counts, the bacteriological condition of the milk and antibodies against caprine arthritis encephalitis virus (CAEV) were measured monthly throughout lactation in 121 lactating goats of the Murcia-Granada breed in four commercial dairy goat herds. The prevalence of bacterial intramammary infection was 5.6 per cent and the prevalence of CAEV infection was 20.6 per cent. An analysis of variance revealed a significant effect of herd, intramammary infection and the interaction between intramammary infection and CAEV on the somatic cell count. In udder halves free of intramammary infection, the somatic cell counts were significantly lower in seronegative goats than in seropositive goats (P<0.05), but the difference was not significant in udder halves persistently infected by bacteria. There was a significant increase in somatic cell counts due to bacterial intramammary infection (P<0.01) in the seronegative goats, but this effect was not present in the seropositive animals.

Two-hybrid analysis of domain interactions involving NtrB and NtrC two-component regulators

Signal transduction by two-component regulatory systems involves phosphorylation of the receiver domain of a response regulator by the transmitter domain of the cognate histidine kinase. In the NtrBC system, phosphorylation of NtrC by NtrB results in transcriptional activation of nitrogen-regulated genes. We have used the yeast two-hybrid system to probe interactions between domains of the NtrB and NtrC proteins from Klebsiella pneumoniae. We constructed fusions from each of a series of proteins or protein domains to the activation and the DNA-binding domains of GAL4 and analysed expression of GAL1:lacZ and GAL1:HIS3 reporters in yeast. The DNA-binding domain of NtrC and the so-called sensor domain of NtrB appeared to provide the major determinants for dimerization of the fusion proteins. A strong and specific interaction was also shown between NtrB and NtrC, localized to the HN region of the NtrB transmitter module and to the NtrC receiver domain, whereas other domains of these proteins do not appear to contribute to the recognition specificity. The results presented here indicate that communication between two-component partners also involves protein-protein interactions that can be detected in vivo, suggesting that the yeast two-hybrid system is a powerful genetic tool for identifying functional partners of prokaryotic signal transduction pathways.