Ras-guanine nucleotide exchange factor sos2 is dispensable for mouse growth and development

The mammalian sos1 and sos2 genes encode highly homologous members of the Son-of-sevenless family of guanine nucleotide exchange factors. They are ubiquitously expressed and play key roles in transmission of signals initiated by surface protein tyrosine kinases that are transduced into the cell through the action of membrane-associated Ras proteins. Recent reports showed that targeted disruption of the sos1 locus results in embryonic lethality. To gain insight into the in vivo function of sos2, we disrupted its catalytic CDC25-H domain by means of gene targeting techniques. Mating among heterozygous sos2(+/-) mice produced viable sos2(-/-) offspring with a normal Mendelian pattern of inheritance, indicating that the loss of sos2 does not interfere with embryo viability in the uterus. Adult homozygous mutant sos2(-/-) mice reached sexual maturity at the same age as their wild-type littermates, and both male and female null mutants were fertile. Histopathological analysis showed no observable differences between mutant and wild-type mice. Our results show that unlike the case for sos1, sos2 gene function is dispensable for normal mouse development, growth, and fertility.

A tomato peroxidase involved in the synthesis of lignin and suberin

The last step in the synthesis of lignin and suberin has been proposed to be catalyzed by peroxidases, although other proteins may also be involved. To determine which peroxidases are involved in the synthesis of lignin and suberin, five peroxidases from tomato (Lycopersicon esculentum) roots, representing the majority of the peroxidase activity in this organ, have been partially purified and characterized kinetically. The purified peroxidases with isoelectric point (pI) values of 3.6 and 9.6 showed the highest catalytic efficiency when the substrate used was syringaldazine, an analog of lignin monomer. Using a combination of transgenic expression and antibody recognition, we now show that the peroxidase pI 9.6 is probably encoded by TPX1, a tomato peroxidase gene we have previously isolated. In situ RNA hybridization revealed that TPX1 expression is restricted to cells undergoing synthesis of lignin and suberin. Salt stress has been reported to induce the synthesis of lignin and/or suberin. This stress applied to tomato caused changes in the expression pattern of TPX1 and induced the TPX1 protein. We propose that the TPX1 product is involved in the synthesis of lignin and suberin.

Stimulation of the dopamine 1 receptor increases lung edema clearance

We previously reported that lung edema clearance was stimulated by dopamine (DA). The purpose of this study was to determine whether the DA-mediated stimulation of edema clearance occurs via an adrenergic or dopaminergic regulation of alveolar epithelial Na, K-ATPase. When isolated perfused rat lungs were coinstilled with DA and SCH 23390 (a specific D(1) receptor antagonist), there was a dose-dependent attenuation of the stimulatory effects of DA. Coinstillation with S-sulpiride (a specific D(2) receptor antagonist) or propranolol (a beta-adrenergic antagonist) did not alter DA-stimulated clearance. Similarly, the specific dopaminergic D(1) agonist fenoldopam increased lung edema clearance, but quinpirole (a specific dopaminergic D(2) agonist) did not. (125)I-SCH 23982 binding studies suggested that D(1) receptors are expressed on alveolar type II (ATII) cells with an apparent dissociation constant (K(d)) of 4.4 nM and binding maximum (Bmax) 9.8 pmol/mg. Consistent with these results, the D(1) receptor messenger RNA (mRNA) and protein were detected in ATII cells by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. These data demonstrate a novel mechanism involving the activation of dopaminergic D(1) receptors which mediates DA-stimulated edema removal from rat lungs.

Invasive disease caused by ciprofloxacin-resistant uropathogenic Escherichia coli

To evaluate the invasiveness of ciprofloxacin-resistant Escherichia coli isolated from the urinary tract, the susceptibility to ciprofloxacin of Escherichia coli strains from patients with invasive urinary tract infection was compared with that of isolates from patients with noninvasive disease. In a 14-month period, 2054 different isolates of Escherichia coli were analyzed, of which 554 (27%) were resistant to ciprofloxacin. One hundred twelve (5.4%) strains were isolated from patients with invasive disease. Resistance was significantly less frequent in isolates from patients with invasive disease (4.5%) than in isolates from patients with noninvasive disease (28.3%) (OR, 0.12; CI 95%, 0.05-0.29; P<0.001). Most ciprofloxacin-resistant strains associated with invasive disease were isolated from bacteremic patients who had recently undergone an invasive procedure involving the urinary tract. Invasive disease is caused more frequently by ciprofloxacin-susceptible strains of Escherichia coli, suggesting that resistance to ciprofloxacin may decrease the invasiveness of uropathogenic Escherichia coli.

Isoform-specific insertion near the Grb2-binding domain modulates the intrinsic guanine nucleotide exchange activity of hSos1

Two human hSos1 isoforms (Isf I and Isf II; Rojas et al., Oncogene 12, 2291-2300, 1996) defined by the presence of a distinct 15 amino acid stretch in one of them, were compared biologically and biochemically using representative NIH3T3 transfectants overexpressing either one. We showed that hSos1-Isf II is significantly more effective than hSos1-Isf I to induce proliferation or malignant transformation of rodent fibroblasts when transfected alone or in conjunction with normal H-Ras (Gly12). The hSos1-Isf II-Ras cotransfectants consistently exhibited higher saturation density, lower cell-doubling times, increased focus-forming activity and higher ability to grow on semisolid medium and at low serum concentration than their hSos1-Isf I-Ras counterparts. Furthermore, the ratio of GTP/GDP bound to cellular p21ras was consistently higher in the hSos1-Isf II-transfected clones, both under basal and stimulated conditions. However, no significant differences were detected in vivo between Isf I- and Isf II-transfected clones regarding the amount, stability and subcellular localization of Sos1-Grb2 complex, or the level of hSos1 phosphorylation upon cellular stimulation. Interestingly, direct Ras guanine nucleotide exchange activity assays in cellular lysates showed that Isf II transfectants consistently exhibited about threefold higher activity than Isf I transfectants under basal, unstimulated conditions. Microinjection into Xenopus oocytes of purified peptides corresponding to the C-terminal region of both isoforms (encompassing the 15 amino acid insertion area and the first Grb2-binding motif) showed that only the Isf II peptide, but not its corresponding Isf I peptide, was able to induce measurable rates of meiotic maturation, and synergyzed with insulin, but not progesterone, in induction of GVBD. Our results suggest that the increased biological potency displayed by hSos1-Isf II is due to higher intrinsic guanine nucleotide exchange activity conferred upon this isoform by the 15 a.a. insertion located in proximity to its Grb2 binding region.

Ventilator-associated lung injury decreases lung ability to clear edema in rats

Ventilator-associated lung injury (VALI) is caused by high tidal volume (VT) excursions producing microvascular leakage and pulmonary edema. However, the effects of VALI on lung edema clearance and alveolar epithelial cells' Na,K-ATPase function have not been elucidated. We studied lung edema clearance in the isolated-perfused rat lung model after ventilation for 25, 40, and 60 min with high VT (peak airway opening pressure [Pao] of approximately 35 cm H2O) and compared them with low VT ventilation (Pao approximately 8 cm H2O), moderate VT ventilation (Pao approximately 20 cm H2O), and nonventilated rats. Lung edema clearance in control rats was 0.50 +/- 0.02 ml/h and decreased after 40 and 60 min of high VT to 0.26 +/- 0.03 and 0.11 +/- 0.08 ml/h, respectively (p < 0.01), but did not change after low VT and moderate VT ventilation at any time point. Lung permeability to small (22Na+, [3H]mannitol) and large solutes (fluorescein isothiocyanate-tagged albumin [FITC-albumin]) increased significantly in rats ventilated for 60 min with high VT, compared with low VT, moderate VT, and control rats (p < 0.01). Paralleling the impairment in lung edema clearance we found a decrease in Na,K-ATPase activity in alveolar type II (ATII) cells isolated from rats ventilated with moderate VT and high VT for 40 min without changes in alpha1 Na,K-ATPase mRNA. We reason that VALI decreases lung ability to clear edema by inhibiting active sodium transport and Na,K-ATPase function in the alveolar epithelium.

Time course of active and passive liquid and solute movement in the isolated perfused rat lung model

The isolated perfused rat lung model (IL) is used to study alveolar epithelial transport properties. Most of the previous studies have been done over a short period of time and have not used the same preparation as a control and intervention group. We evaluated whether the IL preparation could be used for a prolonged period of time (5 h) and studied the rates of active Na+ transport, lung liquid clearance, and passive movement of solutes. Active Na+ transport and lung liquid clearance were stable from 1 to 5 h. The passive movement of small solutes (Na+, mannitol) did not change significantly, and albumin movement increased slightly at the fifth hour. Total RNA isolated from IL after 5 h was intact, and the Na+-K+-ATPase activity in alveolar type II cells isolated at the end of 5-h experiments was equal to Na+-K+-ATPase function from freshly isolated alveolar type II cells. Finally, we measured the stimulatory effect of the beta-adrenergic-agonist terbutaline and the inhibitory effect of the Na+-K+-ATPase-antagonist ouabain by using the same animal as a control. Accordingly, the isolated perfused lung model is functionally stable for at least 5 h, and it could be utilized to evaluate the effect of different interventions by using the same preparation.

Analysis of the expression of two thiolprotease genes from daylily (Hemerocallis spp.) during flower senescence

A cDNA clone encoding a daylily (Hemerocallis spp.) thiolprotease (SEN11), whose expression is strongly upregulated in flower tepal senescence, has been isolated. The amino acid sequence, deduced from the nucleotide sequence, showed highest similarity to plant thiolproteases of Vigna mungo, Phaseolus vulgaris and Hemerocallis (SEN102), and contains a putative ER retention signal that has been described in Vigna mungo. SEN102 and SEN11 transcripts were not detectable in flower buds at the opening stage, but two peaks of transcripts were seen after 9 h and 19 h, in both petals and sepals, when wilting symptoms were apparent. The pattern of protease activity migrating on a 26.3 kDa protein was similar to the SEN102 and SEN11 transcript profiles. These two genes were also expressed in stamens and leaves, but their transcripts were undetectable in carpels and rhizomes. The expression of SEN102 was lower in the senescent leaf than in the green leaf. The pattern of expression of these genes suggests their involvement in the protein hydrolysis occurring in tepals at the late senescence stage, whereas in leaves they could be involved in the constitutive protein turnover machinery. Exogenous gibberellic acid application to cut flowers increased transcripts of both genes.

Transformation suppressor activity of C3G is independent of its CDC25-homology domain

The guanine nucleotide releasing protein C3G was initially identified as a Crk SH3-binding protein and recently shown to exhibit exchange activity on Rap1 proteins. Overexpression in NIH3T3 cells of a full-length C3G cDNA isolated from human placenta markedly reduced the focus forming activity of cotransfected, malignantly activated, ras oncogenes (5-7-fold). C3G also had a reverting effect on sis-mediated transformation, decreasing the number of c-sis-induced foci by a factor of 5-10-fold. The observed inhibitory effect of C3G on focus-forming activity of Ras and Sis was always higher than that observed with Rap1A, a known target of C3G. The inhibition of focus formation observed in the presence of C3G was not due to toxic effects on cell viability, since transfected C3G cells exhibited the same survival and growth rates as untransfected NIH3T3 cells or cells transfected with plasmid vector alone. Surprisingly, as opposed to Rap1A, which has no effect on Raf-1 oncogene-mediated transformation, C3G also reduced dramatically (6-8-fold) the number of v-raf-induced foci in transfected NIH3T3 cells. The inhibitory effect on Raf-induced transformation suggests that C3G has other functional targets in addition to Rap1. A C3G mutant (C3G deltaCat) lacking the catalytic domain (CDC25-H) but retaining the rest of the N-terminal sequences, including the Crk-binding domain, exhibited similar ability than full length C3G to inhibit focus formation. In contrast, a C3G mutant (C3G Cat), containing the catalytic domain only but lacking the rest of the N-terminal sequences, did not have any inhibitory effect on transformation mediated by the oncogenes tested. The C3G-derived gene products overexpressed in our transfected cell lines localized to the cytoplasm and did not change the basal MAPK or JNK activity of those cell lines nor their ability to activate the kinases in response to agonists. Our results suggest that the N-terminal region of C3G, and not its catalytic domain, may be responsible for the inhibitory effects observed.

Isolated Sos1 PH domain exhibits germinal vesicle breakdown-inducing activity in Xenopus oocytes

Purified, bacterially expressed PH domains of Sos1, IRS-1, betaARK, and PLCdelta1 were analyzed functionally by means of microinjection into full grown, stage VI Xenopus laevis oocytes. Whereas the PH domains from IRS-1, betaARK, or PLCdelta1 did not show any effect in the oocytes, injection of the purified Sos1 PH domain resulted in induction of significant rates of germinal vesicle breakdown and meiotic maturation. Furthermore, the Sos1 PH domain exhibited also significant synergy with insulin or coinjected normal Ras protein in induction of germinal vesicle breakdown, although it did not affect the rate of progesterone-induced maturation. These results suggest that purified, isolated PH domains retain, at least in part, their functional specificity and that Xenopus oocytes may constitute a useful biological system to analyze the functional role of the Sos1 PH domain in Ras signaling pathways.

A 15 amino acid stretch close to the Grb2-binding domain defines two differentially expressed hSos1 isoforms with markedly different Grb2 binding affinity and biological activity

We compared structure, expression and functional properties of two hSos1 cDNA isoforms (IsfI and Isf II) isolated, respectively, from human fetal brain and adult skeletal muscle libraries. IsfI and IsfII nucleotide sequences differ only by the presence in IsfII of an inframe 45 hp insertion located near the first proline-rich motif required for Grb2 binding. Some human tissues express only one isoform whereas others express different proportions of both in fetal and adult stages. In vitro binding assays and in vivo functional studies showed that MI exhibits significantly higher Grb2 binding affinity and biological activity than IsfI. These results suggest that functionally different hSos1 isoforms, with differential tissue expression and distribution, play important regulatory roles in the mechanisms controlling Ras activation in different tissues and/or developmental stages.

Expression of alternative forms of Ras exchange factors GRF and SOS1 in different human tissues and cell lines

DNA probes and antibodies specific for different coding regions of human SOS1 and GRF genes were used to screen expression of these genes in a variety of adult and fetal human tissues and cell lines. Despite previous reports of the exclusive expression of hGRF RNA in brain, we also observed expression of this gene in various other tissues including lung and pancreas, as well as several tumor cell lines. At least three different hGRF mRNA transcripts were observed depending on the probe used, with the larger transcripts being detected by probes corresponding to the 5' end of the gene while smaller transcripts were detected by probes corresponding to the 3' end. Expression of hSOS1-related transcripts was more ubiquitous and homogeneous than with hGRF, with similar levels of specific transcripts being detected in most tissues and cell fines tested. Three to five different transcripts were detected in human tissues when using probes for the 5' end and middle regions of this gene, whereas only two were detected with probes corresponding to the 3' end. Screening of multiple human tumor cell lines showed ubiquitous expression of three specific transcripts, although the level and ratio of each of these transcripts varied widely among individual cell lines. Consistent with the variety of transcripts detected, several protein forms were also identified in Western immunoblots with antisera raised against specific domains of hSOS1 and human Ras-GRF gene products. Fluorescence in situ chromosomal hybridization suggested that, in both cases, the multiple forms arise from single chromosomal loci. The heterogeneity of hGRF and hSOS1 gene products detected (which appear to retain in most cases a functional catalytic domain), suggests that differentially expressed, alternatively spliced hSOS1 and hGRF forms may contribute to fine regulation of Ras activation in different tissues or at different stages of development.

Molecular cloning of the hom-thrC-thrB cluster from Bacillus sp. ULM1: expression of the thrC gene in Escherichia coli and corynebacteria, and evolutionary relationships of the threonine genes

A 6.5 kb DNA fragment containing the gene (thrC) encoding threonine synthase, the last enzyme of the threonine biosynthetic pathway, has been cloned from the DNA of Bacillus sp. ULM1 by complementation of Escherichia coli and Brevibacterium lactofermentum thrC auxotrophs. Complementation studies showed that the thrB gene (encoding homoserine kinase) is found downstream from the thrC gene, and analysis of nucleotide sequences indicated that the hom gene (encoding homoserine dehydrogenase) is located upstream of the thrC gene. The organization of this cluster of genes is similar to the Bacillus subtilis threonine operon (hom-thrC-thrB). An 1.9 kb BclI fragment from the Bacillus sp. ULM1 DNA insert 351 amino acids was found corresponding to a protein of 37462 Da. The thrC gene showed a low G + C content (39.4%) and the encoded threonine synthase is very similar to the B. subtilis enzyme. Expression of the 1.9 kb BcI DNA fragment in E. coli minicells resulted in the formation of a 37 kDa protein. The upstream region of this gene shows promoter activity in E. coli but not in corynebacteria. A peptide sequence, including a lysine that is known to bind the pyridoxal phosphate cofactor, is conserved in all threonine synthase sequences and also in the threonine and serine dehydratase genes. Amino acid comparison of nine threonine synthases revealed evolutionary relationships between different groups of bacteria.

Structural studies on the PH domains of Db1, Sos1, IRS-1, and beta ARK1 and their differential binding to G beta gamma subunits

Pleckstrin homology (PH) domains are approximately 110 amino acid residues in length and are structurally conserved in a number of intracellular signaling proteins. A role for these domains has been postulated for beta ARK, which binds to G beta gamma subunits. We have quantified the binding of individual (His)6-tag PH domains of human Db1, human Sos1, rat IRS-1, human beta ARK, and human beta ARK with an extra 33-residue C-terminal extension (beta ARK + C) to G beta gamma subunits. Our in vitro binding studies show that all of the PH domains (apart from Sos1), bind G beta gamma subunits in a dose-dependent manner, but beta ARK + C binds 4 times as much G beta gamma at saturation as the others. The IRS-1 PH domain has a similar half-maximal concentration of G beta gamma binding (18 nM) to beta ARK + C (30 nM), suggesting that the IRS-1 PH domain has sufficient determinants for G beta gamma binding. The beta ARK PH domain alone has a half-maximal value of 45 nM but a drastically reduced extent of G beta gamma binding, suggesting that both the PH domain and the C-terminal 33 residues are necessary for maximal binding. Db1 has a half-maximum concentration of G beta gamma binding of 45 nM and a maximal extent of binding similar to that of beta ARK, but it is difficult to demonstrate saturable binding of G beta gamma to Sos1. Since it was previously predicted that the C-terminal PH domain of Pleckstrin [Tyers, M., et al. (1988) Nature 333, 470-473] contains a potential calcium binding site, we have tested the different PH domains for calcium binding. Only the PH domain of Db1 bound 45Ca2+ with a Kd of 10 microM. CD spectroscopy of the purified recombinant PH domains indicated that they are predominantly beta-sheet structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Up-regulation of a cysteine protease accompanies the ethylene-insensitive senescence of daylily (Hemerocallis) flowers

The flowers of daylily (Hemerocallis x hybrida cv. Cradle Song) open at midnight, start to senesce 12 h later, and are completely senescent by the following midnight. Differential screening of a cDNA library constructed from tepals of flowers showing incipient senescence revealed 25 clones that were strongly up-regulated in senescent tepals. Re-screening and interactive Southern analysis of these clones revealed 3 families of up-regulated clones. Transcripts of one clone, SEN10, were not detectable at midnight, but increased dramatically as senescence proceeded. The derived amino acid sequence of the full-length cDNA (SEN102) has strong homology with cysteine proteases that have been reported from other plant tissues. The sequence contains a secretory signal peptide and a probable prosequence upstream of the mature protein. Amino acids critical to the active site and structure of cysteine proteases are conserved, and the C-terminus of the polypeptide has a unique putative endoplasmic reticulum retention signal -RDEL.

Use of restriction fragment length polymorphism as a genetic marker for typing Mycobacterium avium strains

Restriction fragment length polymorphism (RFLP) was used to study 75 clinical isolates identified as Mycobacterium avium. Two repetitive insertion sequences, IS1311 and IS900, were used as DNA probes. Although less than 25% of isolates showed RFLP patterns with IS900, all strains gave banding patterns with IS1311. M. avium strains isolated from patients with AIDS exhibited marked polymorphism with both probes.

A novel insertion element from Mycobacterium avium, IS1245, is a specific target for analysis of strain relatedness

The insertion sequence IS1245 is a novel mycobacterial repetitive element identified in Mycobacterium avium. It encodes a transposase which exhibits a 64% amino acid similarity with IS1081, an insertion element present in the M. tuberculosis complex. The host range of IS1245 appears limited to M. avium as this element was not identified in M. intracellulare or in any other of 18 mycobacteria species tested. When IS1245 was used for restriction fragment length polymorphism (RFLP) analysis, human isolates characteristically presented a high number of copies (median, 16; range, 3 to 27) and a diversity of RFLP patterns comparable to that found by pulsed-field gel electrophoresis. Isolates from nonhuman sources differed both in number of copies and in RFLP pattern diversity: while swine isolates shared the characteristics of human strains, those from several avian sources exhibited a very low copy number of IS1245 and appeared clonal on the basis of RFLP.

Transcriptional analysis and regulatory signals of the hom-thrB cluster of Brevibacterium lactofermentum

Two genes, hom (encoding homoserine dehydrogenase) and thrB (encoding homoserine kinase), of the threonine biosynthetic pathway are clustered in the chromosome of Brevibacterium lactofermentum in the order 5' hom-thrB 3', separated by only 10 bp. The Brevibacterium thrB gene is expressed in Escherichia coli, in Brevibacterium lactofermentum, and in Corynebacterium glutamicum and complements auxotrophs of all three organisms deficient in homoserine kinase, whereas the Brevibacterium hom gene did not complement two different E. coli auxotrophs lacking homoserine dehydrogenase. However, complementation was obtained when the homoserine dehydrogenase was expressed as a fusion protein in E. coli. Northern (RNA) analysis showed that the hom-thrB cluster is transcribed, giving two different transcripts of 2.5 and 1.1 kb. The 2.5-kb transcript corresponds to the entire cluster hom-thrB (i.e., they form a bicistronic operon), and the short transcript (1.1 kb) originates from the thrB gene. The promoter in front of hom and the hom-internal promoter in front of thrB were subcloned in promoter-probe vectors of E. coli and corynebacteria. The thrB promoter is efficiently recognized both in E. coli and corynebacteria, whereas the hom promoter is functional in corynebacteria but not in E. coli. The transcription start points of both promoters have been identified by primer extension and S1 mapping analysis. The thrB promoter was located in an 87-bp fragment that overlaps with the end of the hom gene. A functional transcriptional terminator located downstream from the cluster was subcloned in terminator-probe vectors.

Analysis and expression of the thrC gene of Brevibacterium lactofermentum and characterization of the encoded threonine synthase

The thrC gene of Brevibacterium lactofermentum was cloned by complementation of Escherichia coli thrC auxotrophs. The gene was located by deletion mapping and complementation analysis in a 2.9-kb Sau3AI-HindIII fragment of the genome. This fragment also complemented a B. lactofermentum UL1035 threonine auxotroph that was deficient in threonine synthase. A 1,892-bp DNA fragment of this region was sequenced; this fragment contained a 1,446-bp open reading frame that encoded a 481-amino-acid protein having a deduced M(r) of 52,807. The gene was expressed in E. coli, by using the phage T7 system, as a 53-kDa protein. The promoter region subcloned in promoter-probe plasmids was functional in E. coli. A Northern analysis revealed that the gene was expressed as a monocistronic 1,400-nucleotide transcript. The transcription start point of the thrC gene was located by S1 mapping 6 bp upstream from the translation initiation codon, which indicated that this promoter was one of the leaderless transcription-initiating sequences. The threonine synthase overexpressed in B. lactofermentum UL1035 was purified almost to homogeneity. The active form corresponded to a monomeric 52.8-kDa protein, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme required pyridoxal phosphate as its only cofactor to convert homoserine phosphate into threonine.

Cloning and nucleotide sequence of Mycobacterium tuberculosis gyrA and gyrB genes and detection of quinolone resistance mutations

The emergence of multidrug-resistant strains of Mycobacterium tuberculosis has resulted in increased interest in the fluoroquinolones (FQs) as antituberculosis agents. To investigate the frequency and mechanisms of FQ resistance in M. tuberculosis, we cloned and sequenced the wild-type gyrA and gyrB genes, which encode the A and B subunits of the DNA gyrase, respectively; DNA gyrase is the main target of the FQs. On the basis of the sequence information, we performed DNA amplification for sequencing and single-strand conformation polymorphism analysis to examine the presumed quinolone resistance regions of gyrA and gyrB from reference strains (n = 4) and clinical isolates (n = 55). Mutations in codons of gyrA analogous to those described in other FQ-resistant bacteria were identified in all isolates (n = 14) for which the ciprofloxacin MIC was > 2 micrograms/ml. In addition, we selected ciprofloxacin-resistant mutants of Mycobacterium bovis BCG and M. tuberculosis Erdman and H37ra. Spontaneously resistant mutants developed at a frequency of 1 in 10(7) to 10(8) at ciprofloxacin concentrations of 2 micrograms/ml, but no primary resistant colonies were selected at higher ciprofloxacin concentrations. Replating of those first-step mutants selected for mutants with high levels of resistance which harbored gyrA mutations similar to those found among clinical FQ-resistant isolates. The gyrA and gyrB sequence information will facilitate analysis of the mechanisms of resistance to drugs which target the gyrase and the implementation of rapid strategies for the estimation of FQ susceptibility in clinical M. tuberculosis isolates.

Directed mutagenesis of a regulatory palindromic sequence upstream from the Brevibacterium lactofermentum tryptophan operon

A cloned 9.6-kb fragment of Brevibacterium lactofermentum DNA, carrying the entire trp operon and upstream regulatory sequences, produces a polycistronic 7.0-kb transcript as detected by hybridization with an internal probe. The transcription start point (tsp) was identified by S1 mapping. The operator-promoter (OP) region subcloned in Escherichia coli and B. lactofermentum promoter-probe vectors exhibited about tenfold higher activity in B. lactofermentum. A 14-bp wild-type (wt) palindrome located at bp -15 to -28 was mutated to change the conserved adenine adjacent to the axis of symmetry. The wt and mutated OP regions were coupled to the amy reporter gene (encoding alpha-amylase [Amy]) or to the 5' region (trpE and trpG genes) of the trp operon, for expression studies. Constructions with the regulatory signals coupled to the wt trpE-trpG genes were introduced in a B. lactofermentum trpE mutant (obtained by gene disruption). The mutation in the palindrome did not affect the promoter activity in B. lactofermentum or E. coli when grown in minimal medium. Tryptophan repressed the OP as assayed by the anthranilate synthase (AS) activity in B. lactofermentum in constructions with the wt OP region, but surprisingly, caused a large stimulation of either AS or the Amy reporter activity, in constructions with the mutated OP. The palindromic sequence is, therefore, involved in a dual repression-stimulation control of expression of the trp operon.

Meningitis due to Aeromonas species: case report and review

In recent years, Aeromonas species has been reported to cause extraintestinal infections with a growing frequency. Meningitis due to Aeromonas species is, however, a rare entity. We report a case of aeromonas meningitis in a 54-year-old man with a history of chronic alcoholic liver disease who, after an episode of gastroenteritis, developed an acute clinical picture characteristic of meningitis with septic shock and ecthyma gangrenosum. Aeromonas veronii (biogroup sobria) was isolated from cultures of blood as well as from cultures of stool, peritoneal fluid, skin lesion, and CSF specimens (obtained by lumbar puncture). Our review of seven additional cases of aeromonas meningitis in the world literature revealed that this condition is generally secondary to metastatic dissemination from primary bacteremia. Aeromonas meningitis, which may or may not be preceded by gastroenteritis, presents clinically as bacterial meningitis, although the presence of skin lesions may increase suspicion of the diagnosis. Third-generation cephalosporins are probably the therapy of choice for patients with aeromonas meningitis.

The bleomycin resistance gene of transposon Tn5 is an excellent marker for transformation of corynebacteria

Corynebacteria are highly sensitive to the glycopeptide antibiotic bleomycin. The bleomycin resistance gene of transposon Tn5 is expressed very efficiently in Brevibacterium lactofermentum. This gene constitutes an excellent marker for selection of transformants of corynebacteria. The bleomycin resistance gene is expressed from the same promoter as the neomycin resistance gene, which is already used as marker in many vectors of corynebacteria. The promoter of the neo-ble cluster is expressed in a variety of Gram-negative and Gram-positive microorganisms and eucaryotic organisms.

Chemical and structural similarities in wall polysaccharides of some Penicillium, Eupenicillium and Aspergillus species

Various fractions were extracted from cell-wall material of Eupenicillium crustaceum, Penicillium brevi-compactum, P. decumbens, Aspergillus flavipes and A. ochraceus. The most characteristic fractions, which may have chemotaxonomic relevance, were F1I, an alpha-(1-3) glucan (alkalisoluble, water-insoluble), which amounted to 16.2-32.5% of the cell-wall material, and F1S (alkali and water-soluble) which represented 2.5-6.2% of the cell-wall material and was identified as a beta-(1-5) galactan. 13C-NMR spectra of the F1S fractions showed the same pattern for all the fungal species, characteristic of beta-(1-5) linked galactofuranose.

[The recurrence of duodenal ulcer in patients undergoing treatment with ranitidine and placebo. A multicenter study]

This randomised, double-blind multicenter study was conducted in order to evaluate the long-term effect (one year) of 150 mg ranitidine vs placebo in 51 patients with healed duodenal ulcer. Seventeen patients had ulcer recurrence at the end of follow-up, one among the 24 patients that received ranitidine and 16 among the 27 patients that received placebo (p = 0.00009). No side effects was detected. Our results support the usefulness of a one-year maintenance therapy with 150 mg ranitidine.

[Epidemic outbreak of methicillin-resistant Staphylococcus aureus in a general hospital. Preliminary report]

The incidence of MRSA infections in Spain had remained in a low level through the years, being MRSA usually less than 1.5% of all S. aureus isolates. Since October 1988, we have detected in our hospital a MRSA outbreak. The epidemic started in the surgical wards, and spread through the rest of the institution. The incidence of cases was higher in the ICU's, areas that act as "multipliers" of the outbreak. In spite of standard control measures, the total number of patients with MRSA was 245 in April 1990. We studied prospectively a sample of 100 MRSA patients: thirty-six percent were colonized and 46% infected. The more common source of infection was the lower respiratory tract and primary bacteremia. The infection-related mortality was 30%. Our MRSA strain belong to phage type III, and shows a characteristic multiple antibiotic resistant pattern, the MRSA strain is sensitive to vancomycin, fusidic acid, phosphomycin and cotrimoxazole. Over the entire outbreak period, the MRSA strain developed resistance to rifampin, imipenem-cilastatin and ciprofloxacin. In spite of all control measures implemented, the outbreak can not have been totally controlled, and MRSA is now an endemic pathogen in our institution. Therefore, major changes in therapeutic approach to nosocomial infections have been since then introduced.

[The biological behavior of colorectal carcinoma in young patients]

Patients of the Instituto Nacional de la Nutrición Salvador Zubirán under 40 years of age with colorectal carcinoma were compared with similar patients above 40 in a retrospective and longitudinal study. Patterns of presentation, stage at diagnosis, degree of tumor differentiation and survival were analyzed. Abdominal pain, rectal bleeding and weight loss were the most frequent clinical manifestations in both groups. Constipation was more common in the young adults (60.5% vs 34.2%; p less than 0.05). In both groups, rectosigmoid was the most frequent location of the neoplasm. Cecal carcinoma was found in 2.6% of patients under 40 years and in 11.8% (p less than 0.05) in older patients. There was a higher frequency of mucinous tumors in the young patients (26% vs 13%; p = NS). Colon cancer in both groups were in advanced stage at presentation. The survival rate for young adults was 30%, and 21% for the other group (p = NS). The degree of tumor differentiation did not affect survival in both groups. Dukes stage was the only prognostic factor identified. The need for early recognition of colorectal cancer in young adults is emphasized by the greater incidence of advanced disease and poor prognosis.

Extracellular galactosaminogalactan from Penicillium frequentans

Penicillium frequentans secreted an exopolysaccharide composed mainly of N-acetyl-galactosamine (48.4%) and galactose, mannose and glucose in the ratio 4:1:1, that were alpha - (1----4) and alpha - (1----3) linked predominantly. Greater polysaccharide production was achieved in old cultures grown statically with glucose as carbon source.

Cerebrospinal fluid fistula from fractured acrylic cranioplasty plate. Case report

The authors report a patient who developed a cerebrospinal fluid fistula secondary to a fractured methyl methacrylate cranioplasty plate. There was no external evidence of trauma. X-ray films showed no evidence of the fracture. It is suggested that the impregnation of methyl methacrylate with a radiopaque material would result in visualization of such fractures.