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1.  Antibiotic resistance among enterococci isolated from clinical specimens between 1953 and 1954. 
Two hundred twenty group D streptococci isolated from 1953 to 1954 from patients in the Washington, D.C., area were characterized. All were susceptible to ampicillin, vancomycin, and gentamicin; none produced beta-lactamase activity. High-level resistance to streptomycin was expressed by 117 strains, and 2 strains were resistant to >8 microg of chloramphenicol per ml. Three isolates were resistant to both erythromycin and lincomycin, and DNA from these hybridized to an ermAM probe. Of 118 strains resistant to tetracycline and minocycline, genomic DNA from 63 was examined for homology to tet(M), tet(O), and tet(S). DNA from 20 strains hybridized to tet(M), DNA from 37 strains hybridized to tet(S), and DNA from none of the strains hybridized to tet(O).
PMCID: PMC163967  PMID: 9210693
2.  Use of a novel mobilizable vector to inactivate the scrA gene of Streptococcus sobrinus by allelic replacement. 
Journal of Bacteriology  1995;177(17):5028-5034.
The virulence factors of the cariogenic bacterium Streptococcus sobrinus have been difficult to assess because of a lack of tools for the genetic manipulation of this organism. The construction of an Escherichia coli-Streptococcus shuttle vector, pDL289, that can be mobilized into S. sobrinus by the conjugative plasmid pAM beta 1 was described in a previous report. The vector contains pVA380-1 for replication and mobilization in streptococci, the pSC101 replicon for maintenance in E. coli, a kanamycin resistance marker that functions in both hosts, and the multiple cloning site and lacZ from pGEM7Zf(-). pDL289 is stable with or without selection in several species of Streptococcus. In this study, a derivative with a deletion in the minus origin of the pVA380-1 component of pDL289 was constructed. This derivative, pDL289 delta 202, was less stable than pDL289 in Streptococcus gordonii Challis, Streptococcus mutans, and S. sobrinus. Both pDL289 and pDL289 delta 202 were mobilizable by pAM beta 1 into S. sobrinus, with frequencies of 3 x 10(-6) and 1 x 10(-7) transconjugants per recipient CFU, respectively. The cloned scrA gene of S. sobrinus 6715-10 coding for the EIISuc of the sucrose-specific phosphoenolpyruvate phosphotransferase system was interrupted by the insertion of a streptococcal spectinomycin resistance gene active in E. coli and streptococci. The interrupted scrA gene was subcloned into both pDL289 and pDL289 delta 202. Each recombinant plasmid was introduced into the DL1 strain of S. gordonii Challis, which was then used as a recipient for the conjugative transfer of pAM beta 1. The latter plasmid was used to mobilize each recombinant plasmid from S. gordonii Challis DL1 to S. sobrinus 6715-10RF. Subsequently, recombinants derived from a double-crossover event were isolated on the basis of resistance to spectinomycin and susceptibility to kanamycin. Recombinational events were confirmed by Southern hybridization, and the inactivation of the EII Suc in double crossovers was confirmed by phosphotransferase system assays. This is the first report of allelic replacement in S. sobrinus.
PMCID: PMC177280  PMID: 7665480
3.  Transcriptional analysis of rolling circle replicating plasmid pVT736-1: evidence for replication control by antisense RNA. 
Journal of Bacteriology  1995;177(15):4474-4480.
Several plasmids have been described in Actinobacillus actinomycetemcomitans, a gram-negative coccobacillus. Recently, the nucleotide sequence of pVT736-1, a cryptic plasmid of A. actinomycetemcomitans VT736, was determined. This plasmid possesses all the features necessary for rolling circle replication. The present study involved a transcriptional analysis of pVT736-1. Results of Northern (RNA) blot analyses and primer extension studies indicated that the two open reading frames identified in pVT736-1 are each preceded by at least one promoter. Expression of these promoters varied with growth phase. In addition, an antisense RNA (Cop RNA) appeared to control the synthesis of the putative replication protein. To our knowledge, this is the first rolling circle replicating plasmid isolated from a gram-negative organism that has been subjected to such detailed analysis.
PMCID: PMC177199  PMID: 7543479
4.  Tetracycline-resistant Mycoplasma hominis strains contain streptococcal tetM sequences. 
Clinical isolates of Mycoplasma hominis resistant to high levels of tetracycline contained DNA sequences homologous to the streptococcal tetracycline determinant, tetM. In contrast, none of the susceptible M. hominis isolates tested carried this determinant. This is the first description of tetM in an unrelated genus and suggests the spread of tetM from Streptococcus spp. to Mycoplasma spp.
PMCID: PMC176326  PMID: 2994555
5.  Genetic, molecular, and functional analysis of Streptococcus faecalis R plasmid pJH1. 
Journal of Bacteriology  1983;155(3):1094-1104.
Streptococcus faecalis JH1 contains two conjugative plasmids, pJH1, an R plasmid that codes for resistance to kanamycin, streptomycin, erythromycin, and tetracycline, and pJH2, a hemolysin-bacteriocin plasmid. Strain JH1 was used as an antibiotic resistance donor in conjugation experiments with two plasmid-free S. faecalis recipient strains, JH2-2 and OG1-RF1. Plasmid pJH1 was purified from one transconjugant, DL77, and subjected to restriction endonuclease analyses. Five restriction enzymes, EcoRI, XbaI, BamHI, SalI, and XhoI, yielding 10, 9, 3, 2, and 2 fragments, respectively, were used to determine the size (80.7 kilobases) of pJH1 and to construct a restriction endonuclease map of the plasmid. Twenty-eight percent of the antibiotic-resistant transconjugants examined expressed only part of the resistance pattern (Kmr Smr Emr Tcr) associated with pJH1, that is, they were resistant to kanamycin, streptomycin, and erythromycin; to erythromycin and tetracycline; or to erythromycin or to tetracycline only. Most of these strains also produced hemolysin and bacteriocin, and several contained a hybrid plasmid consisting of pJH2 and specific segments of pJH1 DNA. Several of these hybrid plasmids, as well as a deletion derivative of pJH1 that coded for resistance to tetracycline but not to kanamycin, streptomycin, or erythromycin, were purified and used to confirm the arrangement of restriction endonuclease fragments on the pJH1 map and to locate the resistance determinants on this map.
PMCID: PMC217803  PMID: 6309740
6.  General Method for the Isolation of Plasmid Deoxyribonucleic Acid 
Journal of Bacteriology  1973;116(2):1064-1066.
Plasmid deoxyribonucleic acid (DNA) ranging from 5 × 106 to 65 × 106 daltons may be isolated from chromosomal DNA by the preferential precipitation of the higher-molecular-weight chromosomal DNA in the presence of sodium lauryl sulfate and a high concentration of NaCl.
PMCID: PMC285495  PMID: 4583233
7.  Sequence analysis of scrA and scrB from Streptococcus sobrinus 6715. 
Infection and Immunity  1993;61(6):2602-2610.
The complete nucleotide sequences of Streptococcus sobrinus 6715 scrA and scrB, which encode sucrose-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system and sucrose-6-phosphate hydrolase, respectively, have been determined. These two genes were transcribed divergently, and the initiation codons of the two open reading frames were 192 bp apart. The transcriptional initiation sites were determined by primer extension analysis, and the putative promoter regions of these two genes overlapped partially. The gene encoding enzyme IIScr, scrA, contained 1,896 nucleotides, and the molecular mass of the predicted protein was 66,529 Da. The hydropathy plot of the predicted amino acid sequence indicated that enzyme IIScr was a relatively hydrophobic protein. The gene encoding sucrose-6-phosphate hydrolase, scrB, contained 1,437 nucleotides. The molecular mass of the predicted protein was 54,501 Da, and the encoded enzyme was hydrophilic. The predicted amino acid sequences of the two open reading frames exhibited approximately 45 and 70% identity with those encoded by scrA and scrB, respectively, from Streptococcus mutans GS5. Homology also was observed between the N-terminal region of the S. sobrinus 6715 enzyme IIScr and other enzyme IIs specific for the glucopyranoside molecule, all of which generate glucopyranoside-6-phosphate during translocation and phosphorylation of the respective substrates. The sequence of the C-terminal domain of the S. sobrinus 6715 enzyme IIScr shared significant homology with enzyme IIIGlc from Escherichia coli and Salmonella typhimurium and with the C-terminal domain of enzyme IIBgl from E. coli, indicating that the two functional domains, enzyme IIScr and enzyme IIIScr, were covalently linked as a single polypeptide in S. sobrinus 6715. The deduced amino acid sequence of the gene product of S. sobrinus scrB shared strong homology with sucrase from Bacillus subtilis, Klebsiella pneumoniae, and Vibrio alginolyticus, suggesting conservation based on the physiological roles of these proteins.
PMCID: PMC280890  PMID: 8500898
8.  Genetic analysis of scrA and scrB from Streptococcus sobrinus 6715. 
Infection and Immunity  1992;60(9):3739-3746.
A DNA fragment containing scrA and scrB, which encode enzyme II of the phosphoenolpyruvate-dependent sucrose phosphotransferase system and sucrose-6-phosphate hydrolase, respectively, was isolated from a lambda gt10 genomic DNA library of Streptococcus sobrinus 6715. Both genes were located on a 4.2-kb DNA fragment which was maintained stably in Escherchia coli on low-copy-number vector pGB2. The recombinant E. coli clone expressed sucrose-hydrolytic activity on MacConkey agar base supplemented with raffinose or sucrose. Results from deletion analysis showed that the sucrose-metabolic activity was contained within a 3.5-kb region. The lactic acid bacterium Lactococcus lactis subsp. lactis LM0230, which is devoid of sucrose-metabolic activity, was used to study the enzyme activities encoded by scrA and scrB from S. sobrinus 6715. L. lactis transformants carrying the 4.2-kb S. sobrinus-derived DNA fragment on E. coli-Streptococcus shuttle vector pDL278 were able to grow at the expense of sucrose and exhibited enzyme II and sucrose-6-phosphate hydrolase activities. Results from hybridization studies and a comparison of the restriction endonuclease maps of the scrA- and scrB-containing chromosomal regions from S. mutans GS5 and S. sobrinus 6715 suggested considerable divergence.
PMCID: PMC257385  PMID: 1500184
9.  Characterization of two plasmids from Campylobacter jejuni isolates that carry the aphA-7 kanamycin resistance determinant. 
Two small plasmids of 11.5 and 9.5 kb, each carrying an aphA-7 kanamycin phosphotransferase gene, were studied. The MICs of kanamycin for the two human Campylobacter jejuni isolates harboring the plasmids were 10,000 and 5,000 micrograms/ml, while the MICs of amikacin were 32 and 8 micrograms/ml, respectively. The MICs of gentamicin and tobramycin were less than or equal to 2 micrograms/ml for both isolates. The restriction endonuclease maps of the plasmids were similar, with the larger plasmid showing two discrete regions of additional DNA. When the aphA-7 gene from each plasmid was cloned into pBR322, the aphA-7 gene expressed the kanamycin resistance phenotype in Escherichia coli. For transformants containing the cloned aphA-7 gene, kanamycin MICs were greater than or equal to 128 micrograms/ml. The aphA-7 gene was also subcloned from the plasmid pFKT4420 into the E. coli-Streptococcus shuttle vector pDL278 and was transformed into Streptococcus gordonii Challis. For streptococcal transformants containing the novel plasmid, kanamycin MICs were 4,000 micrograms/ml. In the presence of a tetracycline resistance plasmid, both small plasmids could be mobilized during conjugal matings to Campylobacter coli recipients.
PMCID: PMC189362  PMID: 1503433
10.  Transformation of Actinobacillus actinomycetemcomitans by electroporation, utilizing constructed shuttle plasmids. 
Infection and Immunity  1991;59(12):4621-4627.
Actinobacillus actinomycetemcomitans, a periodontal pathogen, has been strongly implicated in human periodontal disease. Advances in the molecular analysis of A. actinomycetemcomitans virulence factors have been limited due to the unavailability of systems for genetic transfer, transposon mutagenesis, and gene complementation. Slow progress can be traced almost exclusively to the lack of gene vector systems and methods for the introduction of DNA into A. actinomycetemcomitans. An electrotransformation system that allowed at least five strains of A. actinomycetemcomitans to be transformed with stable shuttle plasmids which efficiently replicated in both Escherichia coli and A. actinomycetemcomitans was developed. One plasmid, a potential shuttle vector designated pDL282, is 5.7 kb in size, has several unique restriction enzyme sites, and codes for resistance to spectinomycin and ampicillin. E. coli and A. actinomycetemcomitans were transformed with equal efficiencies of approximately 10(5) transformants per micrograms of DNA. Similar transformation efficiencies were obtained whether the plasmid DNA was isolated from A. actinomycetemcomitans or E. coli. In addition, frozen competent cells of A. actinomycetemcomitans yielded comparable efficiencies of transformation. Restriction enzyme analysis of pDL282 isolated after transformation confirmed the presence of intact donor plasmids. A plasmid isolated from A. pleuropneumoniae was also capable of transforming some isolates of A. actinomycetemcomitans, although generally at a lower frequency. The availability of these shuttle plasmids and an efficient transformation procedure should significantly facilitate the molecular analysis of virulence factors of A. actinomycetemcomitans.
PMCID: PMC259087  PMID: 1937823
11.  Cloning and nucleotide base sequence analysis of a spectinomycin adenyltransferase AAD(9) determinant from Enterococcus faecalis. 
Enterococcus faecalis LDR55, a human clinical isolate, is resistant to tetracycline (Tcr), erythromycin (Emr), and high levels (greater than 2,000 micrograms/ml) of spectinomycin (Spr) but not streptomycin. Filter matings between strain LDR55 and E. faecalis OG1-RF produced transconjugants with the following resistance phenotypes: Tcr Emr Spr, Tcr Emr, Tcr Spr, and Tcr only but never Emr or Spr only. The genetic determinant encoding resistance to spectinomycin was cloned in Streptococcus sanguis Challis from pDL55, a 26-kb plasmid harbored by a Tcr Spr transconjugant. Subcloning experiments yielded a 1.1-kb ClaI-NdeI fragment that encoded very high-level Spr in S. sanguis (10 mg/ml) and Escherichia coli (50 mg/ml). Cell extracts of cultures obtained from Spr strains expressed adenylating activity for spectinomycin but not for streptomycin, indicating that Spr was due to an AAD(9) activity. The nucleotide base sequence of the 1.1-kb ClaI-NdeI fragment contained a single 750-base open reading frame. The protein predicted from the open reading frame consisted of 250 amino acids and had a calculated size of approximately 28,000 daltons, similar to the size estimated from maxicell analysis (29,000 daltons). The deduced amino acid sequence of the streptococcal AAD(9) was compared with that of the AAD(9) encoded by staphylococcal transposon Tn554. The two proteins shared approximately 39% amino acid identity, which was expanded to 53% when conservative amino acid changes were included. When the streptococcal protein was compared with an AAD(3")(9) protein of E. coli, the degrees of identity were 27 and 47%, on the basis of actual amino acids and conservative replacements, respectively. The cloning and nucleotide base sequence analyses of the spectinomycin AAD(9) determinant from E. faecalis that results in high-level Spr when transferred to S. sanguis or E. coli are presented.
PMCID: PMC245272  PMID: 1659306
12.  Improved electroporation and cloning vector system for gram-positive bacteria. 
A protocol for transformation of intact Enterococcus faecalis cells by electroporation was developed through a systematic examination of the effects of changes in various parameters, including (i) growth conditions; (ii) composition of the electroporation solution; (iii) electroporation conditions, such as field strength and resistance; (iv) size, concentration, and purity of DNA used for transformation; and (v) conditions used to select for transformants. Key features of this protocol include the use of exponential-phase cells grown in inhibitory concentrations of glycine and the use of an acidic sucrose electroporation solution. Frequencies of greater than 2 x 10(5) transformants per microgram of plasmid DNA were obtained for E. faecalis cells, whereas various strains of streptococci and Bacillus anthracis were transformed at frequencies of 10(3) to 10(4) transformants per microgram of plasmid DNA with the same protocol. A novel Escherichia coli-Streptococcus and Enterococcus shuttle cloning vector, pDL276, was constructed for use in conjunction with the electroporation system. This vector features a multiple cloning site region flanked by E. coli transcription termination sequences, a relatively small size (less than 7 kb), and a kanamycin resistance determinant expressed in both gram-positive and gram-negative hosts. Various enterococcal and streptococcal DNA sequences were cloned in E. coli (including sequences that could not be cloned on other vectors) and were returned to the original host by electroporation. The vector and electroporation system was also used to clone directly into E. faecalis.
PMCID: PMC182867  PMID: 1905518
13.  Nucleotide sequence analysis of a type 1 fimbrial gene of Streptococcus sanguis FW213. 
Infection and Immunity  1989;57(11):3527-3533.
A structural gene for type 1 fimbriae of Streptococcus sanguis FW213 was located within a 6-kilobase fragment cloned in Escherichia coli. A 1.6-kilobase internal fragment contains an open reading frame of 927 bases coding for an immunoreactive peptide of 34,349 daltons, which corresponds in size with an observed cytoplasmic form of fimbrial peptide (P. M. Fives-Taylor, F. L. Macrina, T. J. Pritchard, and S. J. Peene, Infect. Immun. 55:123-128, 1987). Disruption of the reading frame by insertional mutagenesis results in loss of immunoreactivity. Consensus sequences for initiation of transcription and translation were identified 5' to the coding region. Transcription terminator-like sequences were found downstream of the coding region. The deduced amino acid sequence of the cloned fimbrial peptide shows a strongly hydrophobic signal sequence at the amino terminus. The carboxyl-terminal region does not include a hydrophobic membrane anchor sequence such as has been reported for other gram-positive surface structures. A hydrophobic region of 12 to 14 amino acids downstream from the putative signal sequence cleavage site exhibits homology with the Streptococcus pyogenes type 6 M protein repetitive region A (S. K. Hollingshead, V. A. Fischetti, and J. R. Scott, J. Biol. Chem., 261:1677-1686, 1986). Functional homology at the level of protein secondary structure with Actinomyces viscosus T14V type 1 fimbriae (M. K. Yeung, B. M. Chassy, and J. O. Cisar, J. Bacteriol., 169:1678-1683, 1987) is proposed.
PMCID: PMC259863  PMID: 2572555
14.  Nucleotide sequence analysis of tetracycline resistance gene tetO from Streptococcus mutans DL5. 
Journal of Bacteriology  1988;170(8):3618-3626.
Streptococcus mutans DL5, isolated from the dental plaque of a pig, was resistant to high levels of streptomycin (Sm, 20 mg/ml), erythromycin (Em, 1 mg/ml), and tetracycline (Tc, greater than 100 micrograms/ml), but contained no detectable plasmid DNA. The Smr and Emr determinants were cloned from cellular DNA on the self-replicating 5-kilobase-pair (kbp) EcoRI fragment of pAM beta 1 and the 4.2-kbp cryptic plasmid pVA380-1, respectively, by transformation of Streptococcus sanguis Challis. Helper plasmid cloning, with a Challis host containing pVA380-1, was required to clone the Tcr determinant of strain DL5 on this vector. A single-colony isolate of the original Tcr clone contained a hybrid plasmid, pDL421, composed of 2.6 kbp of vector DNA and 11.4 kbp of S. mutans DNA. Plasmid pDL421 did not hybridize to plasmids containing the streptococcal Tcr determinants tetL, tetM, and tetN. A shortened derivative of this hybrid plasmid, pDL422, missing a 4.9-kbp HincII fragment from the S. mutans DNA but still encoding Tcr, was obtained by subcloning in S. sanguis Challis. The Tcr gene was located in a 1,917-base-pair open reading frame (ORF) corresponding to a 72-kilodalton protein. The ORF exhibited 99.4% sequence identity with the 1,917-base-pair tetO gene from a strain of Campylobacter coli (W. Sougakoff, B. Papadopoulou, P. Nordmann, and P. Courvalin, FEMS Microbiol. Lett. 44:153-160, 1987). A 1.67-kbp NdeI fragment, internal to the ORF from strain DL5, as well as pDL421 hybridized under stringent conditions to DNA from 10 of 10 Tcr strains of C. coli and Campylobacter jejuni from human and animal sources, but not to DNA from Tcs isolates of these two species.
PMCID: PMC211336  PMID: 2841293
15.  Transposon Tn916 mutagenesis in Bacillus anthracis. 
Infection and Immunity  1988;56(1):176-181.
Mutagenesis of Bacillus anthracis by the streptococcal tetracycline resistance transposon Tn916 is described. Tn916 was transferred from Streptococcus faecalis DS16C1 to B. anthracis VNR-1 by conjugation in a standard filter mating procedure. Tetracycline-resistant (Tcr) transconjugants were obtained at a frequency of 1.6 X 10(-8) per donor CFU. When donor and recipient cells were treated with nafcillin before conjugation, the frequency was increased nearly 10-fold. Nafcillin pretreatment of donor and recipient strains was used in all subsequent conjugation experiments. S.faecalis CG110, containing multiple chromosomal insertions of Tn916, transferred the transposon to B. anthracis VNR-1 at a frequency of 9.3 x 10(-5). A Tcr B. anthracis transconjugant, strain VNR-1-tet-1, transferred Tn916 to B. anthracis UM23-1 and Bacillus subtilis BST1 at frequencies of 2.1 x 10(-4) and 5.8 X 10(-6), respectively. The transfer of Tn916 occurred only on membrane filters, since no Tcr transconjugants were obtained when strains VNR-1-tet-1 and UM23-1 were mixed and incubated in broth culture. The presence of the Tn916-associated tetM gene in Tcr B. anthracis and B. subtilis transconjugants was confirmed in hybridization experiments by using a 5-kilobase-pair DNA fragment containing the tetM gene as a probe. Of 3,000 B. anthracis UM23-1 Tcr transconjugants tested, 21 were phenylalanine auxotrophs and 2 were auxotrophic for phenylalanine, tyrosine, and tryptophan.
PMCID: PMC259253  PMID: 2826334
16.  Cloning and expression of a tetracycline resistance determinant from Campylobacter jejuni in Escherichia coli. 
The tetracycline resistance gene (tet) from the Campylobacter jejuni plasmid pFKT1025 was cloned into both pUC18 and pBR322 and was expressed when the chimeric plasmids were introduced into Escherichia coli. The location of the tet determinant on the chimeric plasmids was determined by BAL 31 deletion mapping within a 2.25-kilobase (kb) RsaI-HincII fragment. A protein of approximately 70 kilodaltons was consistently produced by E. coli maxicells harboring the cloned tet determinant. A 500-base-pair restriction fragment from within the 2.25-kb tet region was shown to hybridize only to DNA from tetracycline-resistant strains of C. jejuni and C. coli, but not to the DNA of organisms known to carry the streptococcal tetM determinant. No homology was noted between the DNA of 10 tetracycline-resistant isolates of campylobacter and the streptococcal tetL, tetM, or tetN determinants when tested under conditions of high stringency. However, homology was noted between a 5.0-kb HincII restriction fragment containing the tetM determinant and two C. jejuni tet R factors under conditions of reduced stringency.
PMCID: PMC174931  PMID: 2823694
17.  Molecular and genetic characterization of lactose-metabolic genes of Streptococcus cremoris. 
Journal of Bacteriology  1986;167(3):855-862.
Lac+ plasmid DNA from Streptococcus cremoris H2 was subcloned with an Escherichia coli vector on a 3.5-kilobase-pair PstI-AvaI fragment. Genetic analysis of the cloned DNA was possible because linear Lac+ DNA fragments were productive in the S. sanguis transformation system. Complementation of S. sanguis Lac-mutants showed that the 3.5-kilobase-pair fragment included the structural gene for 6-phospho-beta-D-galactosidase and either enzyme II-lac or factor III-lac of the lactose-specific phosphoenolpyruvate-dependent phosphotransferase system. Expression of the S. cremoris-like 40,000-dalton 6-phospho-beta-D-galactosidase in S. sanguis Lac+ transformants, rather than the 52,000-dalton wild-type S. sanguis enzyme, demonstrated the occurrence of gene replacement and not gene repair. The evidence supports chromosomal integration as the mechanism by which S. sanguis Lac- recipients are converted to a Lac+ phenotype after transformation with Lac+ DNA. Southern blot data suggest that the Lac+ DNA does not reside on a transposon, but that integration always occurs within a specific HincII fragment of the recipient chromosome. Hybridization experiments demonstrate homology between the S. cremoris Lac+ DNA and cellular DNA from Lac+ strains of Streptococcus lactis, S. mutans, S. faecalis, and S. sanguis.
PMCID: PMC215952  PMID: 3091581
18.  Broad geographical distribution of homologous erythromycin, kanamycin, and streptomycin resistance determinants among group D streptococci of human and animal origin. 
The Emr, Kmr, and Smr determinants of the Streptococcus faecalis R plasmid pJH1 were cloned in Streptococcus sanguis with a streptococcal plasmid vector, pVA380-1. Each cloned determinant was used as a probe in hybridization reactions with dot blots containing plasmid-enriched DNA from 91 group D streptococcal isolates resistant to erythromycin, kanamycin, and streptomycin; the isolates were obtained from animal and human sources in a variety of geographical locations. Nearly 70% of the strains contained DNA that hybridized to each of the three resistance determinants from pJH1. Five plasmids mediating resistance to erythromycin, kanamycin, and streptomycin were examined in more detail. These plasmids varied in size between 26 and 105 kilobase pairs (kbp) and exhibited very different EcoRI restriction patterns. However, each plasmid contained the resistance determinants on a single 13- to 20-kbp EcoRI fragment. Southern blot hybridizations and additional restriction endonuclease digests revealed extensive DNA sequence homology and virtually indistinguishable restriction endonuclease maps within a 9- to 11-kbp region of each plasmid which included the resistance determinants.
PMCID: PMC180439  PMID: 3010845
19.  Streptococcus faecalis R plasmid pJH1 contains a pAM alpha 1 delta 1-like replicon. 
Journal of Bacteriology  1985;164(2):626-632.
Streptococcus faecalis R plasmid pJH1 did not transform competent strains of Streptococcus sanguis. A hybrid plasmid, pDL310, consisting of virtually all of the S. faecalis hemolysin-bacteriocin plasmid pJH2 and a segment of pJH1 DNA that included the tetracycline resistance determinant, yielded tetracycline-resistant transformants at a frequency of less than 10(-8) transformants per CFU, when it was added to a competent culture of S. sanguis Wicky. Four of the transformants contained a 4.7-kilobase plasmid (pDL316) that transformed strain Wicky at a frequency of 8.6 X 10(-8). Restriction endonuclease digests, agarose gel electrophoresis, and Southern blot hybridizations indicated that pDL316 consisted entirely of pJH1-derived DNA. Additional restriction studies, Southern blot hybridizations, and heteroduplex analyses indicated that pDL316 was very closely related to 4.6-kilobase tetracycline resistance plasmid pAM alpha 1 delta 1, a derivative of 9.0-kilobase S. faecalis plasmid pAM alpha 1.
PMCID: PMC214298  PMID: 2997123
20.  Evidence for a disseminated erythromycin resistance determinant mediated by Tn917-like sequences among group D streptococci isolated from pigs, chickens, and humans. 
A total of 199 streptococci isolated from feces of healthy chickens, pigs, and beef cattle and 26 human clinical isolates were tested for resistance to kanamycin, streptomycin, tetracycline, erythromycin, and lincomycin. Of 66 isolates resistant to these antibiotics, 12 transferred one or more resistance traits by conjugation in broth. Erythromycin resistance (Emr) was transferred from 10 of the 12 successful donors. AvaI digests of plasmids isolated from Emr transconjugants derived from two human, two chicken, and one pig isolate contained three fragments similar in size to those produced from Tn3871, an Emr transposon. The three fragments from each of the five digests on Southern blots hybridized to radiolabeled Tn3871. Plasmid DNA from a transconjugant derived from a second pig isolate contained two of the three Tn3871-associated AvaI fragments. One of the AvaI fragments from each of the six plasmids hybridized with a radiolabeled probe containing a cloned AvaI fragment from Tn3871 that contained the Emr determinant. Transposition of the Emr trait was demonstrated for the plasmids derived from one human and one pig isolate. We concluded that extensive DNA homology existed between plasmids from streptococcal strains obtained from two human patients, two chickens, and two pigs and the Emr transposon Tn3871, which is very similar or identical to the well-characterized Emr transposon Tn917. The detection of Tn3871-like sequences in streptococcal isolates from Arkansas, Illinois, North Carolina, and Washington, D.C. indicates wide dissemination of Emr mediated by the same or closely related transposons.
PMCID: PMC180070  PMID: 2988428
21.  Disseminated tetracycline resistance in oral streptococci: implication of a conjugative transposon. 
Infection and Immunity  1984;45(1):13-17.
A DNA sequence specifying tetracycline resistance (Tcr) has been previously cloned from a clinical isolate of Streptococcus mutans designated U202 (J. A. Tobian and F. L. Macrina, J. Bacteriol. 152:215-222, 1982). We used this sequence as a molecular probe in studying the dissemination of Tcr among oral streptococcal species isolated from patients treated with tetracycline. Eleven strains (including S. sanguis I, S. sanguis II, S. mitis, and S. salivarius) from seven patients were examined by Southern blot analysis. Seven strains showed strong hybridization to the Tcr probe, two showed weak hybridization, and two did not display detectable hybridization. Based on previous characterization of the cloned sequence, our data suggest the dissemination of the tetM class of resistance determinants among these oral streptococci. One of the clinical S. sanguis I isolates studied was able to transfer its Tcr phenotype to other oral streptococci and to enteric streptococci in the absence of plasmid DNA. This transfer appeared to be conjugation-like on the basis of its insensitivity to DNase and its dependence on intimate cell-to-cell contact. Using the cloned Tcr sequence, we were able to study the progeny of the matings. Our data suggest that this resistance transfer element occupies a chromosomal location in streptococcal cells and that it strongly resembles the conjugative transposon Tn916 in its behavior.
PMCID: PMC263248  PMID: 6329954
22.  Streptococcus faecalis R plasmid pJH1 contains an erythromycin resistance transposon (Tn3871) similar to transposon Tn917. 
Journal of Bacteriology  1984;158(3):1172-1174.
The R plasmid pJH1 contains a 5.1-kilobase transposon ( Tn3871 ) that mediates inducible resistance to erythromycin. Three AvaI digestion fragments from this transposon are identical in size to and homologous with three AvaI-derived fragments from the previously described erythromycin resistance transposon Tn917 . These three DNA fragments account for greater than 90% of both transposons.
PMCID: PMC215569  PMID: 6327631
23.  Physical and genetic analyses of streptococcal plasmid pAM beta 1 and cloning of its replication region. 
Journal of Bacteriology  1984;157(2):445-453.
Plasmid pAM beta 1, originally isolated from Streptococcus faecalis DS5, mediates resistance to the MLS (macrolide, lincosamide, and streptogramin B alpha) group of antibiotics. A restriction endonuclease map of the 26.5-kilobase (kb) pAM beta 1 molecule was constructed by using the enzymes AvaI, HpaII, EcoRI, PvuII, Kpn1, BstEII, HpaI, HhaI, and HindIII. A comparison of this map to those of four independently isolated deletion derivatives of pAM beta 1 located the MLS resistance determinant within a 2-kb DNA segment and at least one conjugative function within an 8-kb region. The 5.0-kb EcoRI-B fragment from pAM beta 1 was ligated onto the 4.0-kb Escherichia coli plasmid vector, pACKC1, and used to transform E. coli HB101. The 9.0-kb chimeric plasmid was then used to transform Streptococcus sanguis Challis with concurrent expression of the E. coli kanamycin resistance determinant. The 5.0-kb EcoRI-B fragment from pAM beta 1 was subsequently used as a vector to clone a streptomycin resistance determinant from a strain of Streptococcus mutans containing no detectable plasmid DNA. Subcloning experiments, using a HindIII partial digest of pAM beta 1 DNA, narrowed the replication region of this plasmid to a 2.95-kb fragment.
PMCID: PMC215268  PMID: 6319361
24.  Broad geographical distribution of a cytotoxin gene mediating beta-hemolysis and bacteriocin activity among Streptococcus faecalis strains. 
Infection and Immunity  1983;40(3):1015-1022.
Conjugative hemolysin-bacteriocin plasmids were isolated from Streptococcus faecalis var. zymogenes strains of diverse geographical origins. Cloned DNA fragments containing the hemolysin-bacteriocin gene(s) from one of these plasmids (pAD1) hybridized to two EcoRI fragments of identical size from each of the five plasmids examined. Results of hybridization experiments in which total plasmid DNA was used suggested that the plasmids shared extensive homology. Two of the plasmids, pAD1 from strain DS16 (Ann Arbor, Mich.) and pAM gamma 1 from strain DS5 (Miami, Fla.), were 100% homologous and had identical EcoRI restriction patterns (eight fragments each). There was no detectable homology between the plasmid-mediated hemolysin determinants of S. faecalis and DNA from other beta-hemolytic streptococci (Lancefield groups A, B, F, or H).
PMCID: PMC348152  PMID: 6303955
25.  Characterization of two tetracycline resistance determinants in Streptococcus faecalis JH1. 
Journal of Bacteriology  1982;150(2):835-843.
Streptococcus faecalis strain JH1 harbors two conjugative plasmids: pJH1, an R plasmid mediating resistance to kanamycin, streptomycin, gentamicin, erythromycin, and tetracycline, and pJH2, a hemolysin-bacteriocin plasmid. Studies of plasmid-cured derivatives of strain JH1 and of transconjugates obtained after mixed incubation of JH1 with the plasmid-free S. faecalis strain JH2-2 revealed the presence of two tetracycline resistance determinants in strain JH1. One determinant mediated constitutive resistance to 40 micrograms of tetracycline per ml and was associated with plasmid pJH1. The second determinant, either on the chromosome of strain JH1 or on an undetectable plasmid, was inducible by tetracycline and enabled the host strain, in the absence of pJH1, to grow in the presence of 80 micrograms of tetracycline per ml. One transconjugant, strain DL172, was resistant to 80 micrograms of tetracycline per ml, sensitive to kanamycin, streptomycin, and erythromycin, and hemolytic in the presence, but not in the absence, of tetracycline. A single plasmid, pDL172, from this strain consisted of plasmid pJH2 and a 17.8-kilobase segment of DNA homologous to total cell DNA from strain JH1 but did not contain plasmid pJH1. Whether the addition of heterologous DNA to plasmid pJH2 occurred by translocation of a 17.8-kilobase tetracycline resistance transposon or by classical recombination with pJH2 has not been determined.
PMCID: PMC216436  PMID: 6802800

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