Biomedical subjects

R K Selander

Publications and source records attributed to R K Selander.

At least 55 records · Page 3Linked to original sources

PubMed1991

Molecular genetic basis for complex flagellar antigen expression in a triphasic serovar of Salmonella.

Strains of most Salmonella serovars produce either one (monophasic) or two (diphasic) antigenic forms of flagellin protein, but strains capable of expressing three or more serologically distinct flagellins ("complex" serovars) have occasionally been reported. A molecular genetic analysis of a triphasic strain of the normally diphasic serovar Salmonella rubislaw revealed that it has three flagellin genes, including the normal fliC (phase 1) and fljB (phase 2) chromosomal genes encoding type r and type e,n,x flagellins, respectively, and a third locus (herein designated as flpA) that is located on a large plasmid (pRKS01) and codes for a type d flagellin. The coding sequence of the plasmid-borne gene is similar to that of a phase 1 chromosomal gene, but the sequence of its promoter region is homologous to that of a phase 2 chromosomal gene. The irreversible loss of the ability to express a type d flagellin that occurs when the triphasic strain is grown in the presence of d antiserum is caused by deletion of part or all of the flpA gene. Thus, the molecular basis for the unusual serological reactions of the triphasic strain of S. rubislaw and, by inference, other complex serovars of Salmonella is explained. Plasmids of the type carried by the triphasic strain of S. rubislaw provide a mechanism for the generation of new serovars through the lateral transfer and recombination of flagellin genes.

Base Sequence↗

PubMed1991

Characterization of Neisseria meningitidis serogroup A strains from an outbreak in France by serotype, serosubtype, multilocus enzyme genotype and outer membrane protein pattern.

In an attempt to determine the epidemiological relationship between cases of infection caused by Neisseria meningitidis serogroup A in France between August 1987 and December 1988, and an outbreak which occurred in Mecca in August 1987, markers such as serotype, serosubtype, multilocus enzyme genotype and outer membrane protein (OMP) pattern were used to characterize the bacterial isolates. From a total of 28 cases, 20 strains were isolated. Sixteen isolates, including one which undoubtedly originated from the Mecca epidemic, were homogenous (serotype 4, serosubtype P1.9, multilocus enzyme genotype of clone III-1, identical OMP pattern). Four isolates had a different OMP pattern with little or no P1 protein, no P4 and no P6. Two of these isolates belonged to other clones (I.1 and group I) and they were considered to be unrelated to the Mecca epidemic strains. The origin of the remaining two isolates was not clear. It is concluded that the majority of the Neisseria meningitidis serogroup A strains recently isolated in France originate from the Mecca epidemic.

Adolescent↗

PubMed1991

Genetic relationships among strains of Neisseria meningitidis causing disease in Italy, 1984-7.

Since 1984 a change in the epidemiological pattern of meningococcal disease in Italy has occurred with a predominance of Neisseria meningitidis of serogroup C (76%), serotype 2a and a high proportion of strains resistant to sulphonamides (71%). In order to understand better the epidemiology of the group C N. meningitidis strains responsible for the disease over the last years in Italy, we studied the genetic features of phenotypically closely related strains, by enzyme electrophoresis. The results showed that the genetic and the phenotypic characteristics of the 57 strains studied were similar, suggesting that spread of a single clone during recent years in our country. This result is in agreement with the circulation of strains typical of epidemic situations, despite the decreasing incidence of meningococcal disease in Italy.

Electrophoresis, Starch Gel↗

PubMed1991

Reference collection of strains of the Salmonella typhimurium complex from natural populations.

A collection of 72 reference strains of the Salmonella typhimurium complex of clones recovered from a variety of hosts and environmental sources in diverse geographic locations has been established for use in studies of variation in natural populations. Included are strains of the serovars S. typhimurium, S. saintpaul, S. heidelberg, S. paratyphi B (including variety java) and S. muenchen. The strains, which have been characterized by enzyme electrophoresis for allelic variation in 24 chromosomal structural genes and represent 48 distinctive multilocus genotypes (electrophoretic types or ETs), exemplify the full range of genotypic variation in the S. typhimurium complex. Evolutionary genetic relationships among the ETs are indicated in a phylogenetic tree generated by the neighbour-joining method from a matrix of Nei's standard genetic distance.

Alleles↗

PubMed1991

Open-field parameters and maze learning in aggressive and nonaggressive male mice.

Significant differences were observed in thigmotaxis, ambulation, and latency to move (time to start ambulating) between highly aggressive (TA) and low aggressive (TNA) male mice. The former displayed more thigmotaxis, ambulated more, and had a shorter latency to move than the TNA animals. Also they voided a greater number of urinary spots and defecated less than TNA. Further they were superior to the TNA mice in maze-learning capacity. The tendency to enter inner partitions of the field as well as total ambulation increased after learning by TA mice. The training toward nonaggressiveness of TA mice suppressed aggressive responses, thigmotaxis, and the number of urinary spots but enhanced defecation. All measures returned to their initial levels after one month of rest. The attacking behaviour of TA animals increased both thigmotaxis and ambulation.

Aggression↗

PubMed1990

A single clone of Staphylococcus aureus causes the majority of cases of toxic shock syndrome.

Genetic relationships among 315 isolates of the bacterium Staphylococcus aureus expressing toxic shock syndrome toxin-1 (TSST-1) recovered primarily from humans with toxic shock syndrome (TSS) in five countries on two continents were determined by analyzing electrophoretically demonstrable allelic variation at 20 chromosomal enzyme loci. Forty-nine distinctive electrophoretic types (ETs), representing multilocus enzyme genotypes, were identified. Cluster analysis of the ETs revealed two major phylogenetic divisions separated at a genetic distance of 0.35 and seven branches diverging from one another at distances greater than or equal to 0.20. A single clone (ET 41) accounted for 88% of cases of TSS with a female urogenital focus and 53% of TSS cases involving nonurogenital (predominantly wound) infections. With few exceptions, strains representing different phylogenetic lines had characteristic TSST-1 gene (tst) restriction fragment length polymorphism patterns obtained by digestion of genomic DNA with Cla I. Strains recovered from ovine and bovine hosts with mastitis were genotypically distinct from the major human TSS clone. The expression of TSST-1 in cell lineages representing the total breadth of multilocus genotypic diversity in the species S. aureus as a whole is interpreted as evidence that the TSST-1 gene is evolutionarily old. The recovery of a single clone from the majority of individuals afflicted with TSS having a urogenital focus and from the genital tract of a large proportion of asymptomatic female carriers strongly suggests that this clone is especially well adapted for colonization of these anatomic sites.

Animals↗

PubMed1990

Brazilian purpuric fever: evolutionary genetic relationships of the case clone of Haemophilus influenzae biogroup aegyptius to encapsulated strains of Haemophilus influenzae.

As a first step toward identifying the evolutionary origin of a pathogenic clone of Haemophilus influenzae biogroup aegyptius causing Brazilian purpuric fever, chromosomal variation and genetic relationships were indexed among 17 isolates of biogroup aegyptius and 2209 previously characterized encapsulated H. influenzae strains recovered from 30 countries on six continents. Biogroup aegyptius isolates form three distinct evolutionary lineages of the species H. influenzae and isolates of the case clone are genetically not closely related to other isolates classified as biogroup aegyptius. The Brazilian purpuric fever case clone was found to be genetically allied with H. influenzae isolates producing serotype c polysaccharide capsule. The population genetic evidence suggests that biogroup aegyptius isolates may represent cell lineages occasionally transmitted from nonhuman hosts or spawned from a much larger base population consisting of genetically diverse nonpathogenic precursor clones.

Biological Evolution↗

PubMed1990

Resolution of recent evolutionary divergence among Escherichia coli from related lineages: the application of pulsed field electrophoresis to molecular epidemiology.

Escherichia coli infecting the urinary tract and other extraintestinal sites are often identical in many phenotypic and genotypic characteristics. To discriminate among pathogenic E. coli isolates, chromosomal DNA was digested with restriction endonucleases that recognize eight base pair sequences and the resulting 20-25 fragments were resolved by pulsed field gel electrophoresis (PFGE). Different restriction fragment profiles were detected for isolates obtained from different patients, including isolates of the same evolutionary lineage that were identical in electrophoretic type, serotype, and antibiotic sensitivities. In contrast, isolates obtained from separate sites of infection within the same patient had identical restriction profiles. These results indicate that PFGE can resolve recent evolutionary divergence within E.coli lineages and, consequently, offers a powerful new means for precisely performing molecular epidemiology. In addition, these studies provide genetic evidence that E. coli urinary tract infection within a given patient is typically due to the expansion of a single bacterial clone.

Biliary Tract Diseases↗

PubMed1990

Differentiation between Actinobacillus (Haemophilus) actinomycetemcomitans, Haemophilus aphrophilus and Haemophilus paraphrophilus by multilocus enzyme electrophoresis.

Genetic relationships among isolates assigned to Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus and H. paraphrophilus were determined by analysis of electrophoretically demonstrable allelic variation in 14 structural genes encoding metabolic enzymes. Among the 51 isolates analysed there were 25 electrophoretic types (ETs), among which mean genetic diversity per locus was 0.753. Cluster analysis of ETs demonstrated one well-defined group of 11 ETs representing solely the genotypes of all 17 isolates assigned to A. actinomycetemcomitans. The remaining 14 ETs represented the genotypes of the 34 isolates of H. aphrophilus and H. paraphrophilus. With the exception of ATCC 13252, all strains of H. aphrophilus were closely related, whereas strains assigned to H. paraphrophilus included distantly related lineages, some of which were similar to those of H. aphrophilus and should be assigned to this species. Thus, the study showed that there is no significant overall genetic similarity between A. actinomycetemcomitans and the two Haemophilus spp.

Actinobacillus↗

PubMed1990

Urogenital, maternal and neonatal isolates of Haemophilus influenzae: identification of unusually virulent serologically non-typable clone families and evidence for a new Haemophilus species.

A collection of 117 strains of Haemophilus influenzae, including 112 non-typable isolates recovered predominantly in the USA and France from genital, obstetric and neonatal sources, was characterized by the electrophoretic mobilities of 10 metabolic enzymes. Eighty-six distinctive multilocus chromosomal genotypes (electrophoretic types, ETs) were distinguished on the basis of allele profiles at the enzyme loci. Isolates of five allied biotype IV ETs were highly divergent from all other strains and hybridization of chromosomal DNA revealed that they undoubtedly represent a previously unrecognized species of Haemophilus. Isolates representing these ETs were recovered predominantly from obstetric infections and serious neonatal diseases and apparently possess specific tropism for the genital tract. Strains of these five ETs were present in samples from both the USA and France, but only in the USA did they cause bacteraemia and meningitis, an occurrence which probably reflects differences in patient management between the two countries. Although strains assigned to H. influenzae (sensu stricto) were strongly polymorphic in multilocus enzyme genotype, 69% of isolates recovered from patients with meningitis and/or septicaemia were assigned to only two clone families, a result suggesting that some serologically nontypable strains of H. influenzae originating from the genital tract are unusually virulent.

Alleles↗

PubMed1990

Mice selectively bred for an open field activity increase after maze learning.

A unidirectional selective breeding experiment performed over six generations resulted in a line of mice (S6), which differed from the maintained unselected Swiss albino strain, called normal (N) strain, in the following respects: S6 mice increased their open field activity after maze learning significantly more than N mice. S6 mice ambulated more and exhibited more thigmotactic behaviour in a circular open field than N mice. S6 mice were superior than N mice in regard to maze learning capacity. Finally, S6 mice were interpreted as significantly less emotional according to their defecation, more responsive to novelty according to their urine pattern and more aggressive than N mice.

Animals↗

PubMed1990

Genetic structure of natural populations of the nitrogen-fixing bacterium Rhizobium meliloti.

The genetic structure of populations of the symbiotic nitrogen-fixing soil bacterium Rhizobium meliloti was examined by analysis of electrophoretically demonstrable allelic variation in 14 metabolic, presumably chromosomal, enzyme genes. A total of 232 strains were examined, most of which were isolated from southwest Asia, where there is an unsurpassed number of indigenous host species for R. meliloti. The collection consisted of 115 isolates recovered from annual species of Medicago in Syria, Turkey, and Jordan; 85 isolates cultured from two perennial species of Medicago (M. sativa [alfalfa] and M. falcata) in northern Pakistan and Nepal; and 32 isolates collected at various localities in North and South America, Europe, South Africa, New Zealand, and Australia, largely from M. sativa. Fifty distinctive multilocus genotypes (electrophoretic types [ETs]) were identified, and cluster analysis revealed two primary phylogenetic divisions separated at a genetic distance of 0.83. By the criterion of genetic differentiation conventionally applied in defining species limits among members of the family Enterobacteriaceae and certain other bacteria, the two primary divisions of R. meliloti represent distinct evolutionary species. Division A included 35 ETs represented by 209 strains from the eastern Mediterranean basin, northern Pakistan, Nepal, and various other localities worldwide. This division contained the nine commercial alfalfa inoculant strains examined. Division B included 15 ETs represented by 23 isolates, 21 of which were isolated from annual medic species growing in previously uninoculated soils in the eastern Mediterranean basin. The two remaining strains in division B, both representing the same ET, were isolated in the United States and Australia.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗

PubMed1990

Restriction fragment length polymorphisms among uropathogenic Escherichia coli isolates: pap-related sequences compared with rrn operons.

Among the adhesin-encoding virulence operons associated with uropathogenic Escherichia coli, only pap (pyelonephritis-associated pilus)-related gene clusters typically exhibit variation in their structure and chromosomal copy number. To access further such variability, we compared pap restriction fragment length polymorphisms (RFLPs) with those detected among rRNA (rrn) operons, which encode an essential host function unrelated to virulence. To place such findings in a phylogenetic perspective, the E. coli isolates were also characterized by using multilocus enzyme electrophoresis. Variation in the rrn RFLP profiles correlated with evolutionary divergence resolved by multilocus enzyme electrophoresis; isolates with identical rrn profiles represented the same or closely related electrophoretic types. In contrast, such isolates frequently had different pap-related RFLPs, indicating that these genetic variations have developed recently relative to the changes associated with essential rrn operons or metabolic enzymes. Despite such fluctuations, two lines of evidence indicate conditions under which the pap-related RFLPs can be stably maintained. First, for each of 20 patients with urosepsis, both the primary urinary tract isolate and the concurrent blood isolate were identical. Second, although obtained from different patients, some isolates representing the same electrophoretic type also had identical pap-related RFLPs. Thus, the genotypic diversity of this virulence adhesin operon was not generated during the course of acute infection or during laboratory manipulations. Since fecal E. coli isolates frequently carry chromosomally encoded pap-related gene clusters, these findings suggest that the intra- and interchromosomal recombination events generating the polymorphisms associated with the pap-related sequences likely occur among the E. coli of the commensal reservoir.

Base Sequence↗

PubMed1990

Genetic population structure, clonal phylogeny, and pathogenicity of Salmonella paratyphi B.

Genetic diversity and relationships among 123 strains of Salmonella paratyphi B (serotype 1,4,[5],12:b:[1,2]) were estimated from an assessment of electrophoretically demonstrable allelic variation at 24 chromosomal enzyme gene loci. Fourteen electrophoretic types, marking clones, were distinguished, the phylogeny of the clonal lineages was reconstructed, and biotype and other phenotypic characters were mapped onto this structure. Most d-tartrate-negative strains are members of an abundant, globally distributed clone (Pb 1) that is polymorphic for many biotype characters (including d-tartrate utilization), bacteriophage type, rRNA pattern, and colicin M and phage ES18 sensitivity. This clone is largely responsible for S. paratyphi B enteric fever in humans. In contrast, d-tartrate-positive strains (formerly known as S. java) occurred in all seven of the clonal lineages identified by population genetic analysis, although most d-tartrate-positive isolates belong to only two clones (Pb 3 and Pb 4), which vary in frequency geographically. Monophasic strains represent four closely related clones forming a distinctive phylogenetic lineage. The Kauffmann hypothesis of convergence in serotype among distantly related cell lineages through recombination (via phage transduction or other means) may account for the considerable genotypic diversity among clones of S. paratyphi B. Pb 4, Pb 6, and Pb 7 are more closely allied with clones of S. typhimurium and S. saintpaul than with other clones of S. paratyphi B. Sensitivity or resistance to colicin M and phage ES18 and the electrophoretic pattern of the rRNA, which were incorporated into a recently proposed scheme for the identification of types of S. paratyphi B, individually or in combination fail to mark clones or other meaningful phylogenetic subdivisions.

Colicins↗

PubMed1990

Evolutionary genetic relationships of clones of Salmonella serovars that cause human typhoid and other enteric fevers.

Multilocus enzyme electrophoresis was employed to measure chromosomal genotypic diversity and evolutionary relationships among 761 isolates of the serovars Salmonella typhi, S. paratyphi A, S. paratyphi B, S. paratyphi C, and S. sendai, which are human-adapted agents of enteric fever, and S. miami and S. java, which are serotypically similar to S. sendai and S. paratyphi B, respectively, but cause gastroenteritis in both humans and animals. To determine the phylogenetic positions of the clones of these forms within the context of the salmonellae of subspecies I, comparative data for 22 other common serovars were utilized. Except for S. paratyphi A and S. sendai, the analysis revealed no close phylogenetic relationships among clones of different human-adapted serovars, which implies convergence in host adaptation and virulence factors. Clones of S. miami are not allied with those of S. sendai or S. paratyphi A, being, instead, closely related to strains of S. panama. Clones of S. paratyphi B and S. java belong to a large phylogenetic complex that includes clones of S. typhimurium, S. heidelberg, S. saintpaul, and S. muenchen. Most strains of S. paratyphi B belong to a globally distributed clone that is highly polymorphic in biotype, bacteriophage type, and several other characters, whereas strains of S. java represent seven diverse lineages. The flagellar monophasic forms of S. java are genotypically more similar to clones of S. typhimurium than to other clones of S. java or S. paratyphi B. Clones of S. paratyphi C are related to those of S. choleraesuis. DNA probing with a segment of the viaB region specific for the Vi capsular antigen genes indicated that the frequent failure of isolates of S. paratyphi C to express Vi antigen is almost entirely attributable to regulatory processes rather than to an absence of the structural determinant genes themselves. Two clones of S. typhisuis are related to those of S. choleraesuis and S. paratyphi C, but a third clone is not. Although the clones of S. decatur and S. choleraesuis are serologically and biochemically similar, they are genotypically very distinct. Two clones of S. typhi were distinguished, one globally distributed and another apparently confined to Africa; both clones are distantly related to those of all other serovars studied.

Alleles↗

PubMed1990

Sequence invariance of the antigen-coding central region of the phase 1 flagellar filament gene (fliC) among strains of Salmonella typhimurium.

Previous studies of the phase 1 flagellar filament protein (flagellin) in strains of five serovars of Salmonella indicated that the central region of the fliC gene encoding the antigenic part of the protein is hypervariable both between and within serovars. To explore the possible use of this variation as a source of information on the phylogenetic relationships of closely related strains, we used the polymerase chain reaction technique to sequence part of the central region of the phase 1 flagellar genes of seven strains of Salmonella typhimurium that were known to differ in chromosomal genotype, as indexed by multilocus enzyme electrophoresis. We found that the nucleotide sequences of the central region were identical in all seven strains and determined that both the previously published sequence of the fliC gene in S. typhimurium LT2 and a report of a marked difference in the amino acid sequence of the phase 1 flagellins of two isolates of this serovar are erroneous. Our finding that the fliC gene is not evolving by sequence drift at an unusually rapid rate is compatible with a model that invokes lateral transfer and recombination of the flagellin genes as a major evolutionary process generating new serovars (antigen combinations) of salmonellae.

Amino Acid Sequence↗

PubMed1990

Recombination of Salmonella phase 1 flagellin genes generates new serovars.

To determine the evolutionary mechanisms generating serotypic diversity in Salmonella strains, we sequenced the central, antigen-determining part of the phase 1 flagellin gene (fliC) in strains of several serovars for which estimates of chromosomal genomic relatedness had been obtained by multilocus enzyme electrophoresis. The nucleotide sequence of this region was identical in several chromosomally divergent strains of Salmonella heidelberg (phase 1 antigen r) but differed by 19% from the corresponding and similarly invariant sequence in strains of the closely related serovar Salmonella typhimurium (phase 1 antigen i). Mutational drift of the sequence present in the common ancestor is unlikely to have generated the difference between the phase 1 flagellins of these two serovars, which we attribute instead to a recombination event. This interpretation is supported by evidence that Salmonella strains of very diverse chromosomal backgrounds but similar phase 1 antigens may have closely similar nucleotide sequences for this highly polymorphic region. We suggest that lateral transfer and recombination of phase 1 flagellin genes is a major evolutionary mechanism generating new Salmonella serovars.

Alleles↗

PubMed1990

Conversion of Pseudomonas aeruginosa to the phenotype characteristic of strains from patients with cystic fibrosis.

Isolates of Pseudomonas aeruginosa from cystic fibrosis patients are unusual; they are often susceptible to the bactericidal effect of human serum, have a rough lipopolysaccharide, and produce an exopolysaccharide that is responsible for the characteristic mucoid phenotype. In contrast, strains from the environment and from patients with other diseases usually have smooth lipopolysaccharide, do not produce very much mucoid exopolysaccharide, and are phenotypically nonmucoid. The predominance of mucoid strains of P. aeruginosa in infections of patients with cystic fibrosis has not been explained. In the lower airways, where P. aeruginosa persists in cystic fibrosis, nutrients for bacterial growth may be limited. We investigated whether growth of P. aeruginosa under conditions of suboptimal nutrition causes conversion to the characteristic cystic fibrosis phenotype. Ninety-two strains of P. aeruginosa were maintained for up to 90 days in a minimal medium with acetamide as the sole carbon source. In 56 (52%) of 107 cultures, isolates with rough lipopolysaccharide emerged, and in 20 (19%) of 104 nonmucoid cultures, mucoid isolates were recovered. Strains with rough lipopolysaccharide also were sensitive to the bactericidal effect of normal human serum. Under conditions of suboptimal nutrition in vitro, isolates of P. aeruginosa emerged that produced rough lipopolysaccharide and were mucoid, typical of many isolates from cystic fibrosis patients. This peculiar phenotype may arise as a consequence of nutritional limitation within the cystic fibrosis respiratory tract rather than from features unique to these strains of bacteria.

Blood Bactericidal Activity↗