RESUMEN

Stenotrophomonas maltophilia is an emerging nosocomial bacterial pathogen which is currently isolated with increasing frequency from the airways of cystic fibrosis (CF) patients. In this study 13 S. maltophilia strains (11 isolated from the airways of independent CF patients, and two non-CF respiratory reference strains) have been characterized for the expression of several virulence-associated factors. In particular, the ability to form biofilm on abiotic surfaces has been determined and correlated with different features, such as motility, adherence and the ability to invade A549 respiratory epithelial cells. Moreover, the presence of a flagellum-associated gene as well as that of the StmPr1 gene, which encodes an extracellular protease, have been determined by Southern blot hybridization. Our data indicate that the different degree of biofilm formation exhibited by the 11 CF isolates does not correlate with motility, ability to adhere to and invade A549 cells, or with the presence of flagella. On the other hand, among the CF isolates the StmPr1 gene was found only in two strains, both able to establish chronic lung infections in CF patients. Moreover, only four of the strains analyzed show a temperature-independent antibiotic-resistance profile, suggesting either a different origin of these strains or an intervening adaptation to host tissues.

Asunto(s)

Fibrosis Quística/microbiología , Células Epiteliales/microbiología , Sistema Respiratorio/microbiología , Stenotrophomonas maltophilia/patogenicidad , Factores de Virulencia , Antibacterianos/farmacología , Adhesión Bacteriana , Biopelículas/crecimiento & desarrollo , Línea Celular , Farmacorresistencia Bacteriana , Células Epiteliales/metabolismo , Flagelos/genética , Flagelos/metabolismo , Genes Bacterianos , Humanos , Sistema Respiratorio/citología , Stenotrophomonas maltophilia/aislamiento & purificación , Stenotrophomonas maltophilia/fisiología , Virulencia , Factores de Virulencia/genética , Factores de Virulencia/metabolismo

RESUMEN

The role in virulence of the Shigella flexneri ospB-phoN2 operon has been evaluated. Here we confirm that OspB is an effector and show that apyrase, the product of phoN2, may be a virulence factor, since it is required for efficient intercellular spreading. Apyrase may be important in a deoxynucleoside triphosphate-hydrolyzing activity-independent manner, suggesting that it may act as an interaction partner in the process of IcsA localization.

Asunto(s)

Apirasa/fisiología , Proteínas Bacterianas/metabolismo , Proteínas de Unión al ADN/metabolismo , Shigella flexneri/metabolismo , Factores de Transcripción/metabolismo , Apirasa/genética , Proteínas de la Membrana Bacteriana Externa/fisiología , Transporte Biológico , Operón , Shigella flexneri/patogenicidad , Factores de Virulencia

RESUMEN

We have investigated the major Escherichia coli histone-like proteins (H-NS, HU, FIS, and IHF) as putative factors involved in the maintenance of the overall DNA looped arrangement of the bacterial nucleoid. The long-range architecture of the chromosome has been studied by means of an assay based on in vivo genomic fragmentation mediated by endogenous DNA gyrase in the presence of oxolinic acid. The fragmentation products were analysed by CHEF electrophoresis. The results indicate that in vivo a large fraction of the bacterial chromatin constitutes an adequate substrate for the enzyme. DNA fragments released upon oxo-treatment span a size range from about 1000 kb to a limit-size of about 50 kb. The latter value is in excellent agreement with the average size reported for bacterial chromosomal domains. The DNA gyrase-mediated fragmentation does not appear to be significantly altered in strains depleted in histone-like proteins as compared to an E. coli wild type strain. This suggests that these proteins may not represent critical determinants for the maintenance of the supercoiled loop organisation of the E. coli chromosome.

Asunto(s)

Proteínas Bacterianas/química , ADN Bacteriano/química , Proteínas de Unión al ADN/química , Proteínas de Escherichia coli , Escherichia coli/química , Secuencias de Aminoácidos/genética , Proteínas Portadoras/química , Daño del ADN/efectos de los fármacos , Daño del ADN/fisiología , Girasa de ADN/metabolismo , Escherichia coli/genética , Factor Proteico para Inverción de Estimulación , Factores de Integración del Huésped , Cinética , Mutación , Ácido Oxolínico/metabolismo , Estructura Terciaria de Proteína

RESUMEN

The mechanism of pathogenicity in Shigella and enteroinvasive Escherichia coli (EIEC) requires the co-ordinated expression of several genes located on both the virulence plasmid and the chromosome. We found that cells lacking a functional FIS protein (factor for inversion stimulation) are partially impaired in expressing the virulence genes and that full expression is totally restored when Shigella wild-type fis gene is offered in trans. We also identified virF, among the virulence genes, as a target of FIS-mediated activation and showed that FIS binds to four specific sites in the promoter region of virF. Previous studies have demonstrated that the expression of VirF, the first positive activator of a multistep regulatory cascade, is subject to temperature-dependent regulation by H-NS, one of the main nucleoid-associated proteins. We now demonstrate that two of the four FIS sites overlap one of the two H-NS sites responsible for thermoregulation (H-NS site I). FIS was found to exercise a direct positive transcriptional control at permissive temperature (37 degrees C), when H-NS fails to repress virF, as well as an indirect effect by partially counteracting H-NS inhibition at the transition temperature (32 degrees C). Our data indicate that FIS may be relevant for the rapid increase in virF expression after penetration of bacteria into the host.

Asunto(s)

Proteínas Bacterianas/genética , Proteínas Portadoras/metabolismo , Proteínas de Unión al ADN/metabolismo , Proteínas de Escherichia coli , Escherichia coli/genética , Escherichia coli/patogenicidad , Regulación Bacteriana de la Expresión Génica , Shigella/genética , Factores de Transcripción/metabolismo , Factores de Virulencia , Secuencia de Bases , Sitios de Unión , Proteínas Portadoras/genética , Huella de ADN , Proteínas de Unión al ADN/genética , Factor Proteico para Inverción de Estimulación , Factores de Integración del Huésped , Datos de Secuencia Molecular , Plásmidos/genética , Regiones Promotoras Genéticas , Unión Proteica , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Elementos de Respuesta/genética , Shigella/fisiología , Temperatura , Factores de Transcripción/genética , Transcripción Genética , Virulencia/genética

RESUMEN

The expression of plasmid-borne virF of Shigella encoding a transcriptional regulator of the AraC family, is required to initiate a cascade of events resulting in activation of several operons encoding invasion functions. H-NS, one of the main nucleoid-associated proteins, controls the temperature-dependent expression of the virulence genes by repressing the in vivo transcription of virF only below a critical temperature (approximately 32 degrees C). This temperature-dependent transcriptional regulation has been reproduced in vitro and the targets of H-NS on the virF promoter were identified as two sites centred around -250 and -1 separated by an intrinsic DNA curvature. H-NS bound cooperatively to these two sites below 32 degrees C, but not at 37 degrees C. DNA supercoiling within the virF promoter region did not influence H-NS binding but was necessary for the H-NS-mediated transcriptional repression. Electrophoretic analysis between 4 and 60 degrees C showed that the virF promoter fragment, comprising the two H-NS sites, undergoes a specific and temperature-dependent conformational transition at approximately 32 degrees C. Our results suggest that this modification of the DNA target may modulate a cooperative interaction between H-NS molecules bound at two distant sites in the virF promoter region and thus represents the physical basis for the H-NS-dependent thermoregulation of virulence gene expression.

Asunto(s)

Proteínas Bacterianas/genética , Proteínas de Unión al ADN/metabolismo , Regulación Bacteriana de la Expresión Génica , Regiones Promotoras Genéticas , Proteínas Represoras/metabolismo , Shigella flexneri/genética , Factores de Virulencia , Secuencia de Bases , ADN Bacteriano , Escherichia coli/genética , Escherichia coli/patogenicidad , Datos de Secuencia Molecular , Shigella flexneri/patogenicidad , Temperatura , Transcripción Genética

RESUMEN

We have investigated the role of H-NS, one of the major components of the bacterial nucleoid, in the expression of the virF gene present on the large virulence plasmid of Shigella and enteroinvasive Escherichia coli in response to different environmental conditions. VirF is an AraC-like protein which activates at least two promoters, virB and virG, both repressed by H-NS. Band shift experiments reveal that the affinity of H-NS for the virF and virB promoters is comparable, while the affinity for the virG promoter is higher. Polyacrylamide gel electrophoresis of three DNA fragments containing the virF, the virB and the VirG promoters demonstrates, in agreement with computer predictions, that they have an intrinsically curved structure, confirming the preference of H-NS for bent DNA. In vivo transcriptional analysis of virF mRNA shows that H-NS negatively controls the expression of virF at 30 degrees C. The expression of a virF-lacZ translational fusion in E.coli wild type and in an hns-defective derivative grown at 30 degrees or 37 degrees C and at pH 6.0 or 7.0 indicates that, in the absence of H-NS, virF expression becomes insensitive to temperature and to limited pH changes. Our results strongly suggest that H-NS controls virF expression by binding to the virF promoter and by repressing its expression at low temperature and at low pH.

Asunto(s)

Proteínas Bacterianas/biosíntesis , Proteínas de Unión al ADN/metabolismo , Escherichia coli/genética , Proteínas Represoras/metabolismo , Shigella/genética , Factores de Virulencia , Frío , ADN Bacteriano/química , Escherichia coli/patogenicidad , Regulación Bacteriana de la Expresión Génica , Concentración de Iones de Hidrógeno , Conformación de Ácido Nucleico , Regiones Promotoras Genéticas , Unión Proteica , Shigella/patogenicidad , Transcripción Genética

RESUMEN

We have previously shown that integration of the virulence plasmid pINV into the chromosome of enteroinvasive Escherichia coli and of Shigella flexneri makes these strains noninvasive (C. Zagaglia, M. Casalino, B. Colonna, C. Conti, A. Calconi, and M. Nicoletti, Infect. Immun. 59:792-799, 1991). In this work, we have studied the transcription of the virulence regulatory genes virB, virF, and hns (virR) in wild-type enteroinvasive E. coli HN280 and in its pINV-integrated derivative HN280/32. While transcription of virF and of hns is not affected by pINV integration, transcription of virB is severely reduced even if integration does not occur within the virB locus. This indicates that VirF cannot activate virB transcription when pINV is integrated, and this lack of expression accounts for the noninvasive phenotype of HN280/32. Virulence gene expression in strains HN280 and HN280/32, as well as in derivatives harboring a mxiC::lacZ operon fusion either on the autonomously replicating pINV or on the integrated pINV, was studied. The effect of the introduction of plasmids carrying virB (pBNI) or virF (pHW745 and pMYSH6504), and of a delta hns deletion, in the different strains was evaluated by measuring beta-galactosidase activity, virB transcription, and virB-regulated virulence phenotypes like synthesis of Ipa proteins, contact-mediated hemolysis, and capacity to invade HeLa cells. The introduction of pBN1 or of the delta hns deletion in pINV-integrated strains induces temperature-regulated expression or temperature-independent expression, respectively, of beta-galactosidase activity and of all virulence phenotypes, while an increase in virF gene dosage does not, in spite of a high-level induction of virB transcription. Moreover, a wild-type hns gene placed in trans fully reversed the induction of beta-galactosidase activity due to the delta hns deletion. These results indicate that virB transcription is negatively regulated by H-NS both at 30 and at 37 degrees C in pINV-integrated strains and that there is also a dose-dependent effect of VirF on virB transcription. The negative effect of H-NS on virB transcription at the permissive temperature of 37 degrees C could be due to changes in the DNA topology occurring upon pINV integration that favor more stable binding of H-NS to the virB promoter DNA region. At 30 degrees C, the introduction of the high-copy-number plasmid pMYSH6504 (but not of the low-copy-number pHW745) or of the deltahns deletion induces, in strains harboring an autonomously replicating pINV, beta-galactosidase activity, virB transcription, and expression of the virulence phenotypes, indicating that, as for HN280/32, the increase in virF gene dosage overcomes the negative regulatory effect of H-NS on virB transcription. Moreover, we have found that virF transcription is finely modulated by temperature and, with E. coli K-12 strains containing a virF-lacZ gene fusion, by H-NS. This leads us to speculate that, in enteroinvasive bacteria, the level of Virf inside the cell controls the temperature-regulated expression of invasion genes.

Asunto(s)

Proteínas de la Membrana Bacteriana Externa/metabolismo , Cromosomas Bacterianos/genética , Proteínas de Unión al ADN/metabolismo , Escherichia coli/genética , Escherichia coli/patogenicidad , Regulación Bacteriana de la Expresión Génica , Plásmidos/genética , Factores de Virulencia , Animales , Proteínas Bacterianas/genética , Secuencia de Bases , Replicación del ADN , Infecciones por Escherichia coli/genética , Genes Bacterianos/genética , Cobayas , Células HeLa , Hemólisis , Humanos , Enfermedades Intestinales/microbiología , Datos de Secuencia Molecular , Eliminación de Secuencia , Transcripción Genética , Virulencia/genética

RESUMEN

One hundred twelve Shigella flexneri strain isolated from children with diarrheal disease in Somalia in 1983, 1984, 1988, and 1989 were analyzed for serotype, plasmid profile, and genetic location of antimicrobial resistance determinants. The prevalent serotypes were 4 (46% of the isolates), 1b (16%), 2a (16%), 3a (12%), and 6 (8%). Each serotype was associated with a characteristic predominant plasmid profile, whereas no specific correlation between antimicrobial resistance patterns and single serotypes was found. All but three of the strains were resistant at least to ampicillin, chloramphenicol, spectinomycin, and tetracycline. Of these resistant strains, 41 were resistant to sulfonamide and streptomycin and 14 were resistant to trimethoprim or trimethoprim and kanamycin. The genes for resistance to ampicillin, chloramphenicol, spectinomycin, and tetracycline formed a linkage group located on the chromosome of the strains of all serotypes. The genes for resistance to sulfonamide and streptomycin were located on a 6.3-kb plasmid in strains of serotypes 1b, 2a, and 4. Conjugative trimethoprim or trimethoprim and kanamycin resistance plasmids with lengths of 80 to 110 kb were present in strains of serotypes 1b, 2a, 3a, and 4. The systematic presence of a chromosomal component in this uncommon genetic plasmid-chromosome configuration may play a role in the emergence of increased genetic stability of resistance patterns in S. flexneri.

Asunto(s)

Disentería Bacilar/microbiología , Shigella flexneri/efectos de los fármacos , Shigella flexneri/genética , Niño , Mapeo Cromosómico , Farmacorresistencia Microbiana/genética , Disentería Bacilar/epidemiología , Genes Bacterianos , Humanos , Resistencia a la Kanamicina/genética , Factores R/genética , Factores R/aislamiento & purificación , Estudios Seroepidemiológicos , Serotipificación , Shigella flexneri/clasificación , Somalia/epidemiología , Trimetoprim/farmacología

RESUMEN

Epidemiologically related, non-lactose-fermenting (NLF) Escherichia coli strains of serotype O4 have been isolated at a high frequency from children with diarrhea in Somalia (M. Nicoletti, F. Superti, C. Conti, A. Calconi, and C. Zagaglia, J. Clin. Microbiol. 26:524-529, 1988). In order to define the virulence potential of these strains, we characterized the replication properties of their high-molecular-weight plasmids and studied the genetic locations and organization of the aerobactin (aer) and hemolysin (hly) determinants encoded by 23 NLF O4 E. coli strains. Southern blot hybridizations, mobilization assays of nonconjugative plasmids, and incompatibility-exclusion experiments conducted with a conjugative incompatibility group FI (IncFI) plasmid showed that (i) 20 out of the 23 strains examined harbor a 160- to 180-kb IncFI plasmid that shares homology with the basic replicons RepFIA, RepFIB, and (except for the plasmid of one strain) RepFIC, and 22 strains also contain a 40- to 140-kb IncFII plasmid sharing homology with the RepFIIA replicon; (ii) the IncFI plasmid is nonconjugative and carries antibiotic resistance genes; (iii) the aer system is located on the IncFI plasmids and/or the chromosomes in the three strains not harboring IncFI, and it is found in an inverted orientation; (iv) the hly determinants are located on the chromosome, and their genetic organization is well conserved and closely resembles that of the reference hemolytic plasmid pHly152; and (v) Hly- mutants obtained by transposon insertion mutagenesis are not cytotoxic to HeLa cell monolayers, indicating that hemolysin is responsible for the high cytotoxic activity we have previously reported for these strains. The structural organization of the plasmid-encoded aer operon, together with the finding that those plasmids also carry antibiotic resistance genes, indicates that the IncFI plasmid of the NLF O4 E. coli strains studied more closely resembles aer-encoding virulence IncFI Salmonella R plasmids than E. coli ColV plasmids. The data presented here cannot rule out whether the strains examined are potentially intestinal or extraintestinal pathogens. Nevertheless, the genetic organization of the virulence genes, together with the epidemiological behavior and the wide spectrum of antibiotic resistance of the NLF O4 E. coli strains, indicates that these strains are structured as typical E. coli pathogenic isolates of human origin.

Asunto(s)

Mapeo Cromosómico , Diarrea/microbiología , Escherichia coli/genética , Genes Bacterianos , Proteínas Hemolisinas/genética , Ácidos Hidroxámicos/metabolismo , Factores R/genética , Niño , Escherichia coli/patogenicidad , Humanos , Plásmidos , Virulencia/genética

RESUMEN

The ability of enteroinvasive Escherichia coli and Shigella flexneri to cause disease depends on the presence of a large virulence plasmid (pINV). In this report we show that pHN280, the pINV of the O135:K-:H- enteroivasive strain E. coli HN280, and pWR100, the pINV of S. flexneri serotype 5 strain M90T, are able to integrate into a specific site on the host chromosome. pINV-integrated HN280 and M90T strains required methionine (Met-) to grow in minimal medium, were noninvasive, did not produce contact-mediated hemolysin, and had lost the ability to bind Congo red (Crb-) at 37 degrees C. Immunoblots of whole bacterial extracts from pHN280-integrated HN280 derivatives revealed that integration severely reduced the expression of ipa and virG (icsA) plasmid genes. Met- HN280 and M90T derivative strains spontaneously generated Met+ revertants that either contained excised forms of pINV or had lost pINV. Restriction analysis of excised pINVs showed that they either were virtually identical to parental pINVs (precise excision) or had suffered some deletion (imprecise excision). Precisely excised pINVs expressed the full pattern of virulence, whereas imprecisely excised pINVs were always Crb- and noninvasive. The revertion to Met+ was shown to be recA dependent, indicating that homologous plasmid and chromosomal DNA sequences are involved in the integration-excision process. The maintainance of pINV through integration and downregulation of its virulence genes may represent an advantageous mechanism for enteroinvasive bacteria, particularly when they are outside host cells and/or have to face adverse environmental conditions.

Asunto(s)

Cromosomas/microbiología , Escherichia coli/patogenicidad , Regulación Bacteriana de la Expresión Génica/genética , Plásmidos/genética , Shigella flexneri/patogenicidad , Animales , Western Blotting , Escherichia coli/genética , Escherichia coli/crecimiento & desarrollo , Cobayas , Células HeLa , Queratoconjuntivitis/microbiología , Metionina/genética , Mutagénesis Sitio-Dirigida/genética , Fenotipo , Shigella flexneri/genética , Shigella flexneri/crecimiento & desarrollo , Transfección , Virulencia/genética

Asunto(s)

Elementos Transponibles de ADN/genética , Farmacorresistencia Bacteriana/genética , Salmonella/genética , Antibacterianos/farmacología , Elementos Transponibles de ADN/efectos de los fármacos , Pruebas de Sensibilidad Microbiana , Salmonella/efectos de los fármacos , Salmonella/patogenicidad , Virulencia

RESUMEN

Tn1935, a 23.5-kb transposon mediating resistance to ampicillin, kanamycin, mercury, spectinomycin, and sulfonamide was isolated from pZM3, an IncFIme virulence plasmid from Salmonella wien. Tn1935 possesses the entire sequence of Tn21 and contains two additional DNA segments of 0.95 and 2.7 kb carrying the ampicillin and kanamycin resistance genes, respectively. The latter is part of a composite element since it is flanked by two IS15-like insertion sequences (IS1936) in direct orientation. IS1936 is about 800 bp long and is closely related to IS15 delta, IS26, IS46, IS140, and IS176. Functional analysis of IS1936-mediated cointegrates shows that both insertion sequences are active and able to form cointegrates at the same frequency. Resolution of the cointegrates requires the presence of the host Rec system. The presence of the composite IS1936-element within Tn1935 supports the hypothesis that multidrug resistance transposons evolved by insertion of antibiotic determinants which are themselves transposable.

Asunto(s)

Elementos Transponibles de ADN , Escherichia coli/genética , Resistencia a la Kanamicina/genética , Factores R , Salmonella/genética , Antibacterianos/farmacología , ADN Bacteriano/genética , ADN Bacteriano/ultraestructura , Farmacorresistencia Microbiana/genética , Microscopía Electrónica , Fenotipo , Plásmidos , Mapeo Restrictivo

RESUMEN

A hospital-based systematic sample of 1667 children with severe diarrhoeal disease was studied in Mogadishu, Somalia, throughout 1983 and 1984. One or more enteric pathogens were found in 61% of the patients. Rotavirus (25%), enterotoxigenic Escherichia coli (11%), Shigella spp. (9%), Aeromonas hydrophila (9%), Giardia lamblia trophozoites (8%), Campylobacter jejuni (8%), and Vibrio cholerae non-O1 (6%) were the most frequently identified pathogens. Age-specific detection rates of enteric pathogens and helminths, seasonal patterns, and relationship of some specific infections with feeding status and main clinical features have been defined for all the sample examined.

Asunto(s)

Diarrea/microbiología , Adolescente , Factores de Edad , Animales , Infecciones por Campylobacter/microbiología , Niño , Preescolar , Diarrea/parasitología , Diarrea Infantil/microbiología , Diarrea Infantil/parasitología , Disentería Bacilar/microbiología , Infecciones por Escherichia coli/microbiología , Giardiasis/parasitología , Humanos , Lactante , Recién Nacido , Infecciones por Rotavirus/microbiología , Estaciones del Año , Somalia , Vibriosis/microbiología

RESUMEN

Eleven FIme plasmids representative of those identified in epidemic strains of Salmonella wien and Salmonella typhimurium isolated in North Africa, Europe, and the Middle East have been examined for the presence of determinants of toxigenicity, adherence, and iron-sequestering mechanisms. Chemical and genetic data indicated that all plasmids code for a hydroxamate-mediated iron assimilation system. Detailed analysis of derivative plasmids and cloned fragments of FIme plasmid pZM61 demonstrated that the general genetic and structural organization of the DNA region containing the genes for hydroxamate biosynthesis and cloacin DF13 receptor was virtually identical to that described for the aerobactin-mediated iron uptake system of pColV-K30. This DNA region is part of a composite element that is 16.7 kilobases long and carries its IS1 modules as inverted repeats. A very similar element is present in either orientation in all nine FIme plasmids analyzed.

Asunto(s)

Elementos Transponibles de ADN , Genes Bacterianos , Ácidos Hidroxámicos/farmacología , Hierro/metabolismo , Plásmidos , Salmonella/genética , Secuencia de Bases , Virulencia

Asunto(s)

Liasas de Carbono-Oxígeno , Escherichia coli/genética , Operón , Factor Rho/genética , Factores de Transcripción/genética , Proteínas de la Membrana Bacteriana Externa , Bacteriófago lambda , Escherichia coli/metabolismo , Genes Bacterianos , Liasas/metabolismo , Maltosa/metabolismo , Mutación , Porinas , Receptores Virales/genética , Transcripción Genética

RESUMEN

lamB, the structural gene for lambda receptor, is the second gene of the malK-lamB operon in the malB region of the Escherichia coli K12 chromosome. lamB is essentially not expressed in the absence of an active malT gene product, the activator of the maltose regulon. A malT strain is resistant to phage lambda. We show that: (i) Introduction of rho mutations in malT mutants restores lamB expression to a level sufficient to render the strain sensitive to phage lambda; (ii) This restoration is not dependent on the main promoter of the malK lamB operon. It depends on the distal part of the malK gene. We propose that rho inactivation unmasks the activity of a promoter located near the distal end of malK. Experiments with Mu insertions in gene malK suggest that in the (-) orientation a Mu promoter is also able to allow lamB expression in a rho background.

Asunto(s)

Escherichia coli/genética , Genes , Factor Rho/metabolismo , Factores de Transcripción/metabolismo , Transcripción Genética , Proteínas de la Membrana Bacteriana Externa , Bacteriófago lambda/metabolismo , Enzimas de Restricción del ADN , Escherichia coli/metabolismo , Genotipo , Porinas , Receptores Virales/metabolismo

RESUMEN

The plasmids from six clinical strains of Salmonella wien have been characterized. All the S. wien strains were found to carry three types of plasmids: an IncFI R-Tc Cm Km Ap (resistance to tetracycline, chloramphenicol, kanamycin, and ampicillin) plasmid, either conjugative or nonconjugative, of large size (90 to 100 megadaltons); an R-Ap Su Sm (resistance to ampicillin, sulfonamide, and streptomycin) plasmid of 9 megadaltons; and a very small (1.4 megadaltons) cryptic plasmid. The characteristics of conjugative R plasmids, recombinant between F'lac pro and the FI nonconjugative plasmid, indicated that regions coding for the donor phenotype were present on this plasmid. The molecular and genetic features of the R plasmids were very close to those described for the R plasmids isolated from S. wien strains of different origin. This fact supported the hypothesis of a clonal distribution of this serotype in Algeria and Europe. The analysis used to identify transposable elements showed the presence of only TnA elements, which were located on both the R-Tc Cm Km Ap and R-Ap Su Sm plasmids. They contained the structural gene for a TEM-type beta-lactamase and had translocation properties analogous to those reported for other TnA's.

Asunto(s)

Factores R , Recombinación Genética , Salmonella/genética , Ampicilina/farmacología , Conjugación Genética , Salmonella/efectos de los fármacos , Estreptomicina/farmacología , Sulfonamidas/farmacología