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Biomedical subjects

B E Murray

Publications and source records attributed to B E Murray.

At least 145 records · Page 8Linked to original sources
PubMed1988

Plasmids and pheromone response of the beta-lactamase producer Streptococcus (Enterococcus) faecalis HH22.

Streptococcus (Enterococcus) faecalis HH22 is a clinical isolate that produces beta-lactamase and is resistant to various other antimicrobial agents. In this study, HH22 was found to contain three conjugative plasmids and a conjugative transposon. pBEM10 encodes beta-lactamase, gentamicin resistance, and a response to the peptide pheromone cAD1; pAM323 encodes erythromycin resistance; and pAM324 encodes no known resistance. The latter two plasmids respond to pheromones designated cAM323 and cAM324 which are unrelated to other previously characterized pheromones. pBEM10 and pAM323 are the second and third examples of naturally occurring R plasmids that confer a sex pheromone response.

Conjugation, Genetic↗
PubMed1988

Restriction mapping and hybridization studies of a beta-lactamase-encoding fragment from Streptococcus (Enterococcus) faecalis.

A restriction map of a 5.1-kilobase EcoRI fragment encoding an enterococcal beta-lactamase was prepared and compared with the restriction map of a cloned staphylococcal beta-lactamase gene and with the published maps of several other staphylococcal beta-lactamase genes. Comparison and hybridization studies showed that there were identical restriction sites in the region of the bla structural gene but not in the region surrounding this gene.

DNA Restriction Enzymes↗
PubMed1988

Quantitative analysis and partial characterization of cytotoxin production by Salmonella strains.

The pathogenesis of the wide-spectrum human disease caused by Salmonella species is poorly understood. Cytotoxin production by other enteric pathogens has been increasingly investigated recently, and data are accumulating regarding the role of cytotoxins in enteric infections and hemolytic uremic syndrome. We studied the cytotoxic activity of 131 Salmonella strains of the major serotypes, including 94 strains of Salmonella enteritidis, 12 strains of Salmonella typhi, and 25 strains of Salmonella choleraesuis. Cytotoxicity was quantitatively determined in sonic extracts by a [3H]thymidine-labeled HeLa cell assay. All Salmonella strains examined showed some degree of cytotoxic activity. The geometric means +/- standard deviations of the amounts of cytotoxin produced (50% cytotoxic dose per milligram of bacterial protein) were 27 +/- 2 for S. typhi, 65 +/- 2 for S. enteritidis, and 117 +/- 2 for S. choleraesuis. Analysis of variance showed that the differences in cytotoxin production by the three species were significant (P less than 0.001). No significant differences were found between stool isolates and invasive strains of the same species. Neutralization studies showed that the cytotoxins produced by all Salmonella strains were immunologically distinct from Shiga toxin and the closely related Shiga-like toxins produced by Escherichia coli. DNA hybridization studies with DNA probes for Shiga-like toxins of types I and II showed no hybridization. In each species the cytotoxin was heat labile and sensitive to trypsin treatment, which indicated that its active component was probably protein in nature. Upon ultrafiltration with Amicon membranes and gel filtration chromatography, cytotoxic activity was found in the molecular weight range of 56,000 to 78,000. Our findings indicate that salmonellae produce cytotoxin(s) that may play a role in the manifestations of the various species.

Antibodies, Bacterial↗
PubMed1988

Lack of Shiga-like cytotoxin production by enteroinvasive Escherichia coli.

Enteroinvasive Escherichia coli has not been extensively studied for cytotoxin production. We evaluated 30 well-characterized enteroinvasive E. coli strains of all the known invasive serogroups from several geographic regions for their ability to produce Shiga-like cytotoxic activity assayed in a HeLa cell system. None of these strains produced cytotoxic activity that was neutralizable with antibody to Shiga-like toxin I or II.

Bacterial Toxins↗
PubMed1987

beta-Lactamase production in experimental endocarditis due to aminoglycoside-resistant Streptococcus faecalis.

We used a beta-lactamase-producing (beta L+) strain of Streptococcus faecalis that also had high levels of resistance to all aminoglycosides to induce experimental endocarditis in rats. The rats were treated for five or 10 days with procaine penicillin, vancomycin, gentamicin, rifampin, or ciprofloxacin (alone or in various combinations), or with penicillin plus clavulanic acid. The levels of penicillin in serum and vegetations declined rapidly in the beta L+-infected rats treated with procaine penicillin alone, unlike the sustained levels of penicillin in either beta L- -infected rats treated with procaine penicillin or beta L+-infected rats treated with penicillin plus clavulanic acid. For the beta L+-infected rats, the enterococcal counts in vegetations were significantly reduced (greater than 3 log10 cfu/g) only by vancomycin and by penicillin plus clavulanic acid. The efficacy of the latter regimen probably resulted from the inhibition of penicillin inactivation by clavulanic acid in vegetations infected with the beta L+ strain. Our in vivo findings document the biologic significance of beta-lactamase production.

Aminoglycosides↗
PubMed1987

Children with trimethoprim- and ampicillin-resistant fecal Escherichia coli in day care centers.

We conducted a cross-sectional study of 79 children attending seven day care centers in Houston, Texas, to detect fecal gram-negative bacilli resistant to trimethoprim (TMPr) and ampicillin (AMPr). Fifteen children (19%) were colonized with TMPr Escherichia coli; all but one strain were also resistant to sulfonamides. Most of the children with TMPr E. coli were clustered in center A, where 11 (37%) of 30 children were colonized; only four (8%) of 49 children in the other six centers were colonized with TMPr E. coli (P less than .005). The TMPr E. coli isolates from 10 of the 11 children in Center A had a similar antibiogram, which included resistance to sulfonamides, ampicillin, and streptomycin; eight had a similar total plasmid pattern, an observation suggesting spread within the day care center. Children colonized with AMPr E. coli were present in all centers, although a higher percentage of children in center A were colonized than in the other centers combined (70% vs. 35%; P less than .01).

Ampicillin Resistance↗
PubMed1987

Activity of LY146032 against Enterococci with and without high-level aminoglycoside resistance, including two penicillinase-producing strains.

We tested the activity of LY146032 (LY) against 57 strains of enterococci collected from Chile, Thailand, and the United States. Some of the strains were resistant to high levels of gentamicin or streptomycin (or both), and two produced beta-lactamase (Bla+). MICs of LY ranged from 0.5 to 8 micrograms/ml, and MBCs ranged from 1 to 64 micrograms/ml. In time-kill assays, a 2 to 3 log10 killing effect was observed with LY against two Bla+ strains of Streptococcus (Enterococcus) faecalis and against three strains that were highly resistant to streptomycin and gentamicin. Synergism was demonstrated with LY and streptomycin against a Bla+ strain lacking high-level streptomycin resistance. These in vitro results suggest that LY should be studied further for possible use in treatment of enterococcal infections.

Aminoglycosides↗
PubMed1987

Failure to demonstrate a consistent in vitro bactericidal effect of trimethoprim-sulfamethoxazole against enterococci.

Controversy exists as to the in vitro and in vivo activities of trimethoprim-sulfamethoxazole (TMP-SMX) against enterococci. In this study, we investigated the in vitro activity of TMP-SMX in the type of Mueller-Hinton broth previously reported to give the lowest MICs and MBCs with enterococci. In all instances, MICs were less than or equal to 0.5 microgram/ml. The majority of tests showed MBCs of greater than 32 micrograms/ml, although there was some effect from varying the inoculum and the length of incubation after subculturing. Minor differences were noted when tests were repeated and between the results from microdilution and macrodilution tests and those obtained by the time-kill method. These results, as well as other reports, suggest that TMP-SMX should not be considered a reliable bactericidal agent against enterococci.

Drug Combinations↗
PubMed1986

Comparison of two beta-lactamase-producing strains of Streptococcus faecalis.

A second strain of enterococcus (PA) producing beta-lactamase (Bla+ phenotype) was compared with the previously reported Bla+ enterococcus, strain HH22. As with the original strain, there was a marked inoculum effect when PA was tested with penicillin, ampicillin, and piperacillin; no difference was noted with methicillin, cephalothin, imipenem, or vancomycin; the difference with ticarcillin was intermediate. High-level gentamicin resistance (Gmr) transferred from PA to an enterococcal recipient strain at a frequency approximately 100-fold lower than for HH22; all Gmr transconjugants from both strains were Bla+, but only PA showed linkage of Gmr and Bla+ with transfer of resistance to streptomycin, tetracycline, and chloramphenicol. EcoRI digestion of plasmid DNA from Gmr Bla+ transconjugants showed no similarities between the two strains. A 5.1-kilobase EcoRI Bla+-encoding fragment derived from HH22 was cloned into an Escherichia coli cloning vector and shown to hybridize to a 10.2-kilobase EcoRI fragment derived from PA; both fragments hybridized to an 840-base-pair staphylococcal Bla+ gene probe. These data indicate that the penicillinases are similar but encoded on different or differently arranged plasmids. The fact that both are transferable emphasizes the potential for this new streptococcal resistance determinant to disseminate.

Anti-Bacterial Agents↗
PubMed1986

In vitro studies of plasmid-mediated penicillinase from Streptococcus faecalis suggest a staphylococcal origin.

A strain of Streptococcus faecalis with plasmid-mediated penicillinase production was studied further. Partially purified penicillinase from the S. faecalis strain hydrolyzed penicillin, ampicillin, and ureido-penicillins but not penicillinase-resistant semisynthetic penicillins, cephalosporins, or imipenem; hydrolysis was inhibited by clavulanic acid. Hydrolysis of a given antibiotic correlated with a marked increase in the minimal inhibitory concentration (MIC) of that drug when a high inoculum was used. As with most enterococci, the MICs of cephalosporins and penicillinase-resistant semisynthetic penicillins were too high for clinical usefulness, although these agents did not show an inoculum effect. Based upon hybridization under stringent conditions of plasmid DNA from the S. faecalis strain to cloned penicillinase genes from Staphylococcus aureus, it appears that these resistance determinants are highly homologous and suggests that this enzyme was introduced into streptococci from staphylococci.

Anti-Bacterial Agents↗
PubMed1985

Increasing resistance to trimethoprim-sulfamethoxazole among isolates of Escherichia coli in developing countries.

Resistance of Escherichia coli to trimethoprim (TMP)-sulfamethoxazole remains at 3%-8% at many medical centers within the United States. In this study a 44% resistance rate was observed among E. coli isolated at a pediatric hospital in Santiago, Chile, and a 40% resistance rate at a general teaching hospital in Bangkok, Thailand. Most isolates were from urinary tract infections and showed high-level resistance (minimal inhibitory concentration of TMP greater than 1,000 micrograms/ml). Nineteen of 35 isolates tested transferred resistance to TMP; most cotransferred resistance to streptomycin and sulfonamides. Dihydrofolate reductase type I was detected by gene probing in 14 of 35 strains. Subsequent investigations in Brazil, Honduras, and Costa Rica revealed that this high rate of resistance was not an isolated phenomenon.

Brazil↗