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B G Spratt

Publications and source records attributed to B G Spratt.

At least 55 records · Page 3Linked to original sources
PubMed1996

Multiply antibiotic-resistant Streptococcus pneumoniae recovered from Spanish hospitals (1988-1994): novel major clones of serotypes 14, 19F and 15F.

We analysed a collection of 95 multiply antibiotic-resistant pneumococci, recovered since 1988 from 14 Spanish hospitals, that have MICs > or = 0.25 microgram benzylpenicillin ml-1. The majority of the isolates were of serogroups 14, 23, 6, 19 and 15, which are currently the serogroups mainly associated with multiresistance in Spain. All of the serogroup 23 isolates were members of the major Spanish serotype 23F multiresistant clone. Similarly, most of the serogroup 6 isolates were members of the major multiresistant serotype 6B clone, or variants of this clone. Eighteen of the 24 isolates of serogroup 19 were members of a highly penicillin-resistant clone that appears to be a serotype 19F variant of the major Spanish serotype 23F multiresistant clone. Eighteen of the 25 isolates of serotype 14 were members of a previously uncharacterized highly penicillin-resistant clone. Thirteen of the 16 isolates of serogroup 15 were members of a single previously unreported clone of serotype 15F that had moderate levels of resistance to penicillin. Approximately 65% of the multiresistant pneumococci that are currently circulating in Spain were members of the three new clones of serotype 14, 15F and 19F that we describe here, or the previously described serotype 6B and 23F clones. The other 35% of isolates were minor variants of the major clones, unrelated minor clones, and unique isolates, many of which appeared to have arisen by horizontal gene transfer events.

Bacterial Proteins↗
PubMed1995

Electrophoretic variation in adenylate kinase of Neisseria meningitidis is due to inter- and intraspecies recombination.

In prokaryotic and eukaryotic organisms, the electrophoretic variation in housekeeping enzymes from natural populations is assumed to have arisen by the accumulation of stochastic predominantly neutral mutations. In the naturally transformable bacterium Neisseria meningitidis, we show that variation in the electrophoretic mobility of adenylate kinase is due to inter- and intraspecies recombination rather than mutation. The nucleotide sequences of the adenylate kinase gene (adk) from isolates that express the predominant slow electrophoretic variant were rather uniform, differing in sequence at an average of 1.1% of nucleotide sites. The adk sequences of rare isolates expressing the fast migrating variant were identical to each other but had a striking mosaic structure when compared to the adk genes from strains expressing the predominant variant. Thus the sequence from the fast variants was identical to those of typical slow variants in the first 158 bp of the gene but differed by 8.4% in the rest of the gene (nt 159-636). The fast electrophoretic variant appears to have arisen by the replacement of most of the meningococcal gene with the corresponding region from the adk gene of a closely related Neisseria species. The adk genes expressing the electrophoretic variant with intermediate mobility were perfect, or almost perfect, recombinants between the adk genes expressing the fast and slow variants. Recombination may, therefore, play a major role in the generation of electrophoretically detectable variation in housekeeping enzymes of some bacterial species.

Adenylate Kinase↗
PubMed1995

Genetics and molecular biology of beta-lactam-resistant pneumococci.

Penicillin-resistant pneumococci have been reported with increasing frequency in recent years. Isolates with high-level resistance are now found in many countries, and in some countries they constitute a substantial proportion of all isolates. A worrying development is the recent emergence of pneumococci with high-level resistance to third-generation cephalosporins. Resistance to beta-lactam antibiotics in pneumococci is due entirely to the development of altered forms of the high-molecular-weight penicillin-binding proteins (PBPs) that have decreased affinity for the antibiotics. High-level resistance to third-generation cephalosporins has occurred by the development of altered forms of PBP1a and 2x, whereas high-level penicillin resistance additionally requires alterations of PBP2b. Altered PBPs are encoded by mosaic genes that have emerged by recombinational events between the pbp genes of pneumococci and their homologs in closely related streptococcal species. Horizontal gene transfer, presumably mediated by genetic transformation, has also resulted in the dissemination of altered pbp genes, and possibly capsular biosynthetic genes, between different pneumococcal lineages to produce new resistant clones.

Aminoacyltransferases↗
PubMed1995

Sequence evolution of the porB gene of Neisseria gonorrhoeae and Neisseria meningitidis: evidence of positive Darwinian selection.

Protein 1 (PI) is a major porin of Neisseria gonorrhoeae and Neisseria meningitidis and is encoded by a single locus, porB. Alleles of the porB locus of N. gonorrhoeae are assigned to two homology groups, PI(A) and PI(B), on the basis of immunological and structural similarity. In a like manner, alleles of the porB locus of the closely related bacterium, N. meningitidis, are allocated into class 2 and class 3 homology groups. An individual strain of N. gonorrhoeae or N. meningitidis expresses either one or other of these porin homology groups but never both, and the antigenic reactions of these highly diverse outer membrane proteins form part of the N. gonorrhoeae and N. meningitidis serotyping schemes. A comparison of the number of synonymous and nonsynonymous substitutions per site between the two most divergent alleles of each of these four groups of porB alleles shows that PI(A) alleles have accumulated significantly more nonsynonymous substitutions per site than synonymous substitutions. In contrast the distribution of synonymous and nonsynonymous substitutions between alleles of class 2 and class 3 porins are not significantly different from random. We localize the regions of the PI(A) alleles with an excess of amino acid changes to the surface-exposed loops of these outer membrane proteins and suggest that positive Darwinian selection for diversity, driven by the human immune system, can most easily explain the allelic polymorphism and the pattern of synonymous and nonsynonymous substitutions.

Alleles↗
PubMed1995

Resistance of Neisseria gonorrhoeae to antimicrobial hydrophobic agents is modulated by the mtrRCDE efflux system.

The mtr (multiple transferable resistance) system of Neisseria gonorrhoeae determines levels of gonococcal resistance to hydrophobic agents (HAs), including detergent-like fatty acids and bile salts that bathe certain mucosal surfaces. The genetic organization of the mtr system was determined and found to consist of the mtrR gene, which encodes a transcriptional regulator (MtrR), and three tandemly linked genes termed mtrCDE. The mtrCDE genes were organized in the same apparent transcriptional unit, upstream and divergent from the mtrR gene. The mtrCDE-encoded proteins of N. gonorrhoeae were analogous to a family of bacterial efflux/transport proteins, notably the MexABOprK proteins of Pseudomonas aeruginosa and the AcrAE and EnvCD proteins of Escherichia coli, that mediate resistance to drugs, dyes, and detergents. Inactivation of the mtrC gene resulted in loss of the MtrC lipoprotein and rendered gonococci hypersusceptible to structurally diverse HAs; this revealed the importance of the mtr system in determining HAR in gonococci. Further support for a role of the mtrCDE gene complex in determining levels of HAR in gonococci was evident when transformants bearing mutations in the mtrR gene were analysed. In this respect, missense and null mutations in the mtrR gene were found to result in increased levels of MtrC and HAR. However, high levels of MtrC and HAR, similar to those observed for clinical isolates, were associated with a single bp deletion in a 13 bp inverted repeat sequence that intervened the divergent mtrR and mtrC genes. We propose that the 13 bp inverted-repeat sequence represents a transcriptional control element that regulates expression of the mtrRCDE gene complex, thereby modulating levels of gonococcal susceptibility to HAs.

Amino Acid Sequence↗
PubMed1995

Opa-typing: a high-resolution tool for studying the epidemiology of gonorrhoea.

A single gonococcus possesses a family of 11 distinct and highly variable opa genes. The extensive variation and rapid evolution of the opa gene repertoire has been exploited to provide a high-resolution typing method for studies of the short-term transmission of gonorrhoea. The 11 opa genes are amplified with a single pair of primers by the polymerase chain reaction, digested with frequently-cutting restriction enzymes, and the fragments are fractionated on polyacrylamide to provide an opa-type. The method appeared to be highly discriminatory as the opa-types of gonococci, isolated world-wide over the last 30 years, were all different. Opa-typing discriminated between isolates of the same auxotype/serovar class. Similarly, there were 41 opa-types among 43 consecutive isolates from a sexually transmitted disease (STD) clinic. The two pairs of isolates from this clinic that gave the same opa-types were identical by other criteria and may have been from unsuspected sexual contacts. With one minor exception, identical opa-types were obtained from gonococci recovered from known sexual contacts. These results suggest that variation in the family of 11 opa genes evolves so rapidly that the opa-types of gonococci are distinguishable, unless the isolates are from sexual contacts or a short chain of disease transmission. The identification of gonococci with identical opa-types is therefore believed to be a good indicator that the individuals from which they were recovered were sexual partners, or part of a short chain of disease transmission.

Antigens, Bacterial↗
PubMed1995

Interspecies recombination in nature: a meningococcus that has acquired a gonococcal PIB porin.

A vaginal isolate of Neisseria has been reported to resemble Neisseria meningitidis in biochemical characteristics but to react with serological reagents that are specific to the PI porin from Neisseria gonorrhoeae. We have confirmed that this isolate has the biochemical attributes of a meningococcus and have shown that it clusters among meningococcal isolates on a dendrogram based on isoenzyme variation within housekeeping enzymes from populations of N. meningitidis and N. gonorrhoeae. Furthermore, the sequences of the fbp and adk genes were typical of those of N. meningitidis and were distinct from those of N. gonorrhoeae. However, the porB gene was very similar to the por genes of N. gonorrhoeae isolates that express the PIB class of outer-membrane porin (differing from one gonococcal por allele at only a single nucleotide site), and was clearly distinct from the porB genes of N. meningitidis. The isolate therefore appears to be a typical meningococcus, except that its porB gene has been replaced with the por gene from a gonococcus.

Adenylate Kinase↗
PubMed1995

Genetic analysis of clinical isolates of Streptococcus pneumoniae with high-level resistance to expanded-spectrum cephalosporins.

Streptococcus pneumoniae CS109 and CS111 were isolated in the United States in 1991 and have high levels of resistance to expanded-spectrum cephalosporins (MICs of 8 and 32 micrograms of cefotaxime per ml, respectively). CS109, but not CS111, also showed high-level resistance to penicillin. As both strains expressed the serotype 23F capsule, were very closely related in overall genotype, and possessed identical or closely related mosaic pbp1a, pbp2x, and pbp2b genes, it is likely that they have arisen from a recent common ancestor. High-level resistance to expanded-spectrum cephalosporins was entirely due to alterations of penicillin-binding proteins (PBPs) 1a and 2x, since a mixture of the cloned pbp1a and pbp2x genes from the resistant strains could transform the susceptible strain R6 to the full level of cephalosporin resistance of the clinical isolates. Both PBP1a and PBP2x of these strains were more resistant to inhibition by cephalosporins than those of typical highly penicillin-resistant isolates. The pbp1a genes of CS109 and CS111 were identical in sequence, and the fourfold difference in their levels of resistance to cephalosporins was due to a Thr-550-->Ala substitution at the residue following the conserved Lys-Ser-Gly motif of PBP2x. This substitution was also the major cause of the 16-fold-lower resistance of CS111 to penicillin. The pbp2x gene of CS111, in an appropriate genetic background, could provide resistance to 16 micrograms of cefotaxime per ml but only to 0.12 microgram of benzylpenicillin per ml. Removal of the codon 550 mutation resulted in a pbp2x gene that provided resistance to 4 microgram of cefotaxime per ml and 4 microgram of benzylpenicillin per ml. The Thr-550-->Ala substitution in CS111 therefore appears to provide increased resistance to expanded-spectrum cephalosporins but a loss of resistance to penicillin.

Amino Acid Sequence↗
PubMed1994

Resistance to antibiotics mediated by target alterations.

The development of resistance to antibiotics by reductions in the affinities of their enzymatic targets occurs most rapidly for antibiotics that inactivate a single target and that are not analogs of substrate. In these cases of resistance (for example, resistance to rifampicin), numerous single amino acid substitutions may provide large decreases in the affinity of the target for the antibiotic, leading to clinically significant levels of resistance. Resistance due to target alterations should occur much more slowly for those antibiotics (penicillin, for example) that inactivate multiple targets irreversibly by acting as close analogs of substrate. Resistance to penicillin because of target changes has emerged, by unexpected mechanisms, only in a limited number of species. However, inactivating enzymes commonly provide resistance to antibiotics that, like penicillin, are derived from natural products, although such enzymes have not been found for synthetic antibiotics. Thus, the ideal antibiotic would be produced by rational design, rather than by the modification of a natural product.

4-Quinolones↗
PubMed1994

Cluster of an erythromycin-resistant variant of the Spanish multiply resistant 23F clone of Streptococcus pneumoniae in South Africa.

A multiply resistant serotype 23F pneumococcus was cultured from a 3-year-old child with otitis media and five carriers at the child's day-care centre in South Africa. Attempts to eradicate carriage with mupirocin failed. The strains were identical to the Spanish clone of multiply resistant pneumococci by serotype, antimicrobial susceptibility pattern, restriction analysis of the penicillin-binding protein 1A, 2B and 2X genes and by multilocus enzyme electrophoresis. The data suggest that this clone has acquired erythromycin resistance. A possible link between the index case and residence of a family member in Spain was found.

Adult↗
PubMed1994

Further evidence for the non-clonal population structure of Neisseria gonorrhoeae: extensive genetic diversity within isolates of the same electrophoretic type.

Analysis of data from multilocus enzyme electrophoresis has revealed that Neisseria gonorrhoeae populations are non-clonal. Fifteen percent of 227 isolates of N. gonorrhoeae had an identical multilocus genotype (ET1) and were recovered world-wide over a 26 year period. The recovery of isolates of identical multilocus genotype from geographically and temporally unassociated hosts is a common criterion of a clonal population structure. However, in a recombining (non-clonal) population, isolates with the same multilocus genotype can arise by the random association of the most common alleles in the population. Analysis of the variation in two further enzymes, in the restriction patterns obtained from the glutamine synthetase gene, and in the DNA fragments obtained using an arbitrarily primed polymerase chain reaction, was used to show that members of ET1 were almost as variable as randomly selected N. gonorrhoeae isolates. Unlike the situation in a strongly clonal species, the 26 ET1 isolates examined were increasingly sub-divided to give 19 distinguishable groups as variation at further loci was examined, and 24 distinguishable groups when auxotypes were also considered. We conclude that, as expected of a non-clonal population, the most commonly encountered N. gonorrhoeae multilocus genotype does not define a clone.

Bacterial Proteins↗
PubMed1994

Regulation of the permeability of the gonococcal cell envelope by the mtr system.

The mtrR gene of Neisseria gonorrhoeae controls the level of susceptibility to hydrophobic antibiotics and detergents. The mtrR gene was cloned and shown to encode a putative transcriptional repressor. The mtr region was homologous to the envCD and acrAB regions of Escherichia coli, which are also involved in susceptibility to hydrophobic compounds. A homologous repressor protein was encoded by a previously unrecognized open reading frame within both the envCD and acrAB regions. Deletion of mtrR resulted in increased resistance to antibiotics and detergents: the mtrR mutations in two penicillin-resistant clinical isolates resulted in a change of His-105 to Tyr. We propose that the mtrR repressor allows gonococci to regulate the permeability of its cell envelope in response to environmental signals, so that they can grow in the presence of toxic faecal lipids in the rectum as well as in the genital tract.

Amino Acid Sequence↗
PubMed1994

Interspecies recombination between the penA genes of Neisseria meningitidis and commensal Neisseria species during the emergence of penicillin resistance in N. meningitidis: natural events and laboratory simulation.

The penicillin-binding protein 2 genes (penA) of penicillin-resistant Neisseria meningitidis have a mosaic structure that has arisen by the introduction of regions from the penA genes of Neisseria flavescens or Neisseria cinerea. Chromosomal DNA from both N. cinerea and N. flavescens could transform a penicillin-susceptible isolate of N. meningitidis to increased resistance to penicillin. With N. flavescens DNA, transformation to resistance was accompanied by the introduction of the N. flavescens penA gene, providing a laboratory demonstration of the interspecies recombinational events that we believe underlie the development of penicillin resistance in many meningococci in nature. Surprisingly, with N. cinerea DNA, the penicillin-resistant transformants did not obtain the N. cinerea penA gene. However, the region of the penA gene derived from N. cinerea in N. meningitidis K196 contained an extra codon (Asp-345A) which was not found in any of the four N. cinerea isolates that we examined and which is known to result in a decrease in the affinity of PBP 2 in gonococci.

Bacterial Proteins↗
PubMed1993

Ecological separation and genetic isolation of Neisseria gonorrhoeae and Neisseria meningitidis.

BACKGROUND: Classifying bacteria into species is problematic. Most microbiologists consider species to be groups of isolates that share some arbitrary degree of relatedness of biochemical or molecular (such as DNA sequence) features and that, ideally, are clearly delineated from all other groups of isolates. The main problem in applying to bacteria a biological concept of species based on the ability or inability of their genes to recombine, is that recombination appears to be rare in bacteria in nature, as indicated by the strong linkage disequilibrium between alleles found in most bacterial populations. However, there are some naturally transformable bacteria in which assortative recombination appears to be so frequent that alleles are in, or close to, linkage equilibrium. For these recombining populations a biological concept of species might be applicable. RESULTS: Populations of Neisseria gonorrhoeae and Neisseria meningitidis from Spain were analysed by multilocus enzyme electrophoresis. The data indicate that assortative recombination occurs frequently within populations, but not between populations. Similarly, the sequences of two house-keeping genes show no evidence of intragenic recombination between N. gonorrhoeae and N. meningitidis. CONCLUSIONS: N. gonorrhoeae and N. meningitidis represent extremely closely related 'sexual' populations that appear to be genetically isolated in nature, and thus conform to the biological concept of species. The extreme uniformity of N. gonorrhoeae house-keeping genes suggests that this species may have arisen recently as a clone of N. meningitidis that could colonize the genital tract. Ecological isolation - of populations that can colonize the genital tract from those that can colonize the nasopharynx - may have been an important component in speciation, leading to a lower frequency of recombination between species than within species.

Journal Article↗
PubMed1993

Horizontal spread of an altered penicillin-binding protein 2B gene between Streptococcus pneumoniae and Streptococcus oralis.

The region encoding the transpeptidase domain of the penicillin-binding protein 2B (PBP 2B) gene of two penicillin-resistant clinical isolates of Streptococcus oralis was > 99.6% identical in nucleotide sequence to that of a penicillin-resistant serotype 6 isolate of Streptococcus pneumoniae. The downstream 849 base pairs of these genes were identical. Analysis of the data indicates that the PBP gene has probably been transferred from S. pneumoniae into S. oralis, rather than vice versa, and shows that one region of this resistance gene has been distributed horizontally both within S. pneumoniae and into two different viridans group streptococci.

Amino Acid Sequence↗
PubMed1993

How clonal are bacteria?

Data from multilocus enzyme electrophoresis of bacterial populations were analyzed using a statistical test designed to detect associations between genes at different loci. Some species (e.g., Salmonella) were found to be clonal at all levels of analysis. At the other extreme, Neisseria gonorrhoeae is panmictic, with random association between loci. Two intermediate types of population structure were also found. Neisseria meningitidis displays what we have called an "epidemic" structure. There is significant association between loci, but this arises only because of the recent, explosive, increase in particular electrophoretic types; when this effect is eliminated the population is found to be effectively panmictic. In contrast, linkage disequilibrium in a population of Rhizobium meliloti exists because the sample consisted of two genetically isolated divisions, often fixed for different alleles: within each division association between loci was almost random. The method of analysis is appropriate whenever there is doubt about the extent of genetic recombination between members of a population. To illustrate this we analyzed data on protozoan parasites and again found panmictic, epidemic, and clonal population structures.

Animals↗
PubMed1993

Deletion analysis of the essentiality of penicillin-binding proteins 1A, 2B and 2X of Streptococcus pneumoniae.

An internal fragment from each of the penicillin-binding protein (PBP) 1A, 2B and 2X genes of Streptococcus pneumoniae, which included the region encoding the active-site serine residue, was replaced by a fragment encoding spectinomycin resistance. The resulting constructs were tested for their ability to transform S. pneumoniae strain R6 to spectinomycin resistance. Spectinomycin-resistant transformants could not be obtained using either the inactivated PBP 2X or 2B genes, suggesting that deletion of either of these genes was a lethal event, but they were readily obtained using the inactivated PBP 1A gene. Analysis using the polymerase chain reaction confirmed that the latter transformants had replaced their chromosomal copy of the PBP 1A gene with the inactivated copy of the gene. Deletion of the PBP 1A gene was therefore tolerated under laboratory conditions and appeared to have little effect on growth or susceptibility to benzylpenicillin.

Bacterial Proteins↗