Showing papers by "Barbara E. Murray published in 1993"

Nosocomial outbreak due to Enterococcus faecium highly resistant to vancomycin, penicillin, and gentamicin.

Abstract: In October 1990, Enterococcus faecium that was highly resistant to glycopeptides, penicillins, and aminoglycosides was isolated from the peritoneal dialysis fluid from a patient in an intensive care unit. Over the following 6 months, multiresistant E. faecium organisms were isolated from cultures of blood, urine, or surgical wound specimens from eight additional patients. Surveillance cultures of groin and/or rectal swabs were positive for eight of 37 patients and four of 62 employees at risk. Restriction endonuclease digestion of chromosomal DNA from outbreak isolates was consistent with dissemination of a single strain throughout the intensive care unit. Strict infection control interventions contained the outbreak after several weeks. Review of patient charts suggested that renal insufficiency, length of hospital stay, duration of antibiotic treatment, and prior treatment with vancomycin were risks for infection due to multiresistant E. faecium. The emergence of multiple-drug-resistant enterococci presents serious infection control and therapeutic dilemmas.

Generation of restriction map of Enterococcus faecalis OG1 and investigation of growth requirements and regions encoding biosynthetic function.

Abstract: A defined synthetic medium was used to determine the amino acid requirements of Enterococcus faecalis OG1 and to demonstrate the absence of a requirement for exogenous purines or pyrimidines. Genomic libraries prepared from strain OG1 were transduced into Escherichia coli auxotrophic mutants, and cloned DNAs which complemented pyrC, pyrD, purF, purL, and guaAB mutations were identified. These and other cloned DNAs with known functions were localized on a restriction map of OG1 which was generated with SfiI (5 fragments), AscI (9 fragments), and NotI (15 fragments); the size of the OG1 chromosome was revised from a previous estimate of approximately 2,750 kb to 2,825 kb. The synthetic medium and the restriction map should be useful for studying enterococcal metabolic functions and the relationships between chromosomally encoded genes.

Comparison of ribotyping and pulsed-field gel electrophoresis for subspecies differentiation of strains of Enterococcus faecalis.

Abstract: Hybridization of EcoRI- and HindIII-digested chromosomal DNAs from 41 isolates of Enterococcus faecalis with probes for rRNA genes was performed (ribotyping). The ability of ribotyping to distinguish strains at the subspecies level was compared with results previously determined by pulsed-field gel electrophoresis (PFGE). With EcoRI, seven ribopatterns (usually differing by only one band) were found, while PFGE had previously shown 25 clearly different patterns plus six related variants. Digestion with HindIII generated a few additional patterns but still failed to differentiate some strains that had very different PFGE patterns. Ribotyping with BscI has also been reported to be inadequate for subspecies strain differentiation (L. M. Hall, B. Duke, M. Guiney, and R. Williams, J. Clin. Microbiol. 30:915-919, 1992). Although ribotyping with other restriction endonucleases may perform better in distinguishing different strains, at present PFGE appears to be superior for strain differentiation.

Typing of group B streptococci: comparison of pulsed-field gel electrophoresis and conventional electrophoresis.

Abstract: The SmaI restriction endonuclease digestion patterns of chromosomal DNAs from 35 group B streptococci were analyzed by pulsed-field gel electrophoresis (PFGE). Nineteen different patterns and four possible variants were identified. Twenty-four isolates were previously analyzed by conventional electrophoresis of HindIII-digested and/or BglII plus EcoRI double-digested chromosomal DNA. Although interpretations by both methods were essentially the same, PFGE identified as variants two isolates that were previously classified as the same isolate. More importantly, PFGE of the chromosomal DNA of group B streptococci digested with SmaI generated more easily defined patterns, since fewer and better separated bands were obtained, whereas digestion with HindIII or EcoRI plus BglII typically generated 100 or more bands. SalI digestion also yielded easily evaluable results, although the SalI fragments were somewhat smaller than those generated by SmaI. In our hands, PFGE patterns were more easily discerned and interpreted than were patterns previously generated by conventional electrophoresis. Images

Evaluation of the molecular epidemiology of an outbreak of multiply resistant Shigella sonnei in a day-care center by using pulsed-field gel electrophoresis and plasmid DNA analysis.

Abstract: Outbreaks of diarrhea in child day-care centers (DCC) are common. This study was undertaken to evaluate the molecular epidemiology of an outbreak of diarrhea due to Shigella sonnei. This outbreak involved 25 of 52 (48%) DCC children and 14 of 132 (11%) teachers and household contacts. S. sonnei isolates from nine children and five contacts were characterized by antimicrobial susceptibility, plasmid content, plasmid DNA restriction fragment pattern, and pulsed-field gel electrophoresis (PFGE) of total genomic DNA; 33 isolates from Houston, Tex., Chicago, Ill., and Mexico City, Mexico, also were studied. All outbreak isolates were resistant to ampicillin and trimethoprim-sulfamethoxazole and shared five to six plasmids ranging from 3.3 to 70 MDa. A total of 8 of 12 temporally associated nonoutbreak Houston isolates had plasmid profiles and restriction fragment patterns similar to those of the outbreak strain, despite possessing different antibiotic susceptibility patterns. PFGE demonstrated identical DNA patterns among outbreak isolates and similar or identical patterns among temporally associated sporadic Houston isolates with plasmid profiles similar to that of the outbreak strain. All other nonoutbreak strains from Houston, Chicago, and Mexico had plasmid profiles, restriction fragment patterns, and PFGE patterns different from those of the outbreak strain. DCC outbreak isolates could be distinguished from most sporadic isolates by antimicrobial susceptibility testing, but plasmid analysis and PFGE could not differentiate common-source isolates from sporadic isolates in the same location during the same time period, indicating that isolates present in the community were genetically similar to those producing outbreaks in the DCC.

In vitro activity of azithromycin against bacterial enteric pathogens.

Abstract: The in vitro activity of azithromycin against enteric bacterial pathogens was determined by agar dilution. Azithromycin was highly active against Campylobacter spp. (MIC for 90% of strains tested [MIC90] = 0.125 micrograms/ml) and against enterotoxigenic, enterohemorrhagic, enteroinvasive, and enteropathogenic Escherichia coli (MIC90 = 2 micrograms/ml), Shigella spp. (MIC90 = 1 micrograms/ml), and Salmonella spp. (MIC90 = 4 micrograms/ml), including Salmonella typhi (MIC90 = 1 microgram/ml). On the basis of the in vitro activity of the drug against these organisms, clinical studies of azithromycin in enteric diseases should be considered; the high intracellular concentrations achieved by azithromycin may be particularly relevant for organisms like S. typhi, Campylobacter spp., and Shigella spp. which typically invade cells as part of their infectious process.

The nosocomial transmission of enterococci

Abstract: Enterococci have become a significant cause of nosocomial infections in the past two decades. Moreover, acquisition of new resistance traits such as aminoglycoside resistance, β-lactamase production, high-level resistance to penicillins due to penicillin-binding protein changes and glycopeptide resistance has dramatically limited therapeutic options for disease caused by these organisms. Although hospital-associated enterococcal infections were previously thought to be derived from endogenous flora, recent epidemiologic studies, assisted in some instances by the application of new molecular techniques, have identified both intra- and inter-hospital spread of strains of enterococci. These studies have indicated that person-to-person transmission via the hands of health care personnel may occur and have implicated inanimate objects as a possible source of enterococcal infection. It has also been shown that a major risk factor for nosocomial acquisition of enterococci is the use of antibiotics, presumably because enterococci are resistant to many of the commonly used antimicrobial regimens. With the information currently available, there can be little doubt that nosocomial infections due to enterococci will continue to be important in the future. Rapid identification of patients infected or colonized by multi-resistant enterococci, strict adherence to infection control practices, and prudent use of antibiotics all seem necessary to control and prevent nosocomial infections due to enterococci.

Genes involved in the regulation of beta-lactamase production in enterococci and staphylococci.

Abstract: In enterococci, the structural gene for beta-lactamase (blaZ) is identical to blaZ from Staphylococcus aureus. However, in the enterococci studied to date, beta-lactamase is produced constitutively, whereas in staphylococci it is often inducible. Recent reports have revealed the presence of two adjacent genes upstream of the staphylococcal blaZ thought to be the antirepressor (blaR1) and repressor (blaI) genes. In the present study, beta-lactamase expression mutants of the staphylococcal beta-lactamase plasmid pI524 were generated by transposon mutagenesis with the transposon Tn917. Tn917 insertions upstream of blaZ in either blaR1 or blaI resulted in constitutive beta-lactamase production, indicating that the repressor function is lost with insertion of Tn917 into either gene. This finding supports the concept that the staphylococcal beta-lactamase regulatory genes are encoded on a polycistronic mRNA. The corresponding region upstream of the enterococcal blaZ from Enterococcus faecalis HH22 was sequenced and compared with the staphylococcal blaR1 sequence. The two sequences were identical for 893 nucleotides, and then the sequences diverged completely. Therefore, in strain HH22, only 51% of the putative antirepressor gene is present and the repressor gene is also absent. In conclusion, constitutive beta-lactamase production in HH22 appears to be due to a lack of the regulatory genes blaR1 and blaI which regulate expression of blaZ in staphylococci.

Diarrhea Associated with Aeromonas Species in Children in Day Care Centers

Abstract: Outbreaks of diarrhea caused by enteropathogens have been reported in day care centers (DCC), but Aeromonas species have not been implicated. This study evaluated 381 children involved in 51 outbreaks in four DCC to determine the association of Aeromonas species with diarrhea and to characterize the isolates. The organism was identified in two outbreaks of diarrhea. In one, Aeromonas species were isolated from 6 (24%) of 25 children and in the other from 5 (21%) of 24 children. Seven other Aeromonas strains from children in DCC were studied. Fourteen (78%) of 18 were Aeromonas caviae and 15 were from children with diarrhea. Of the isolates, 75% did not have plasmids detected; all others had unique plasmid patterns. All strains had different DNA content. Twenty-two control isolates of Aeromonas from children with diarrhea in Mexico and Dallas had different chromosomal DNA patterns. Most Aeromonas infections were associated with symptoms. Chromosomal DNA patterns differentiated Aeromonas strains better than did plasmid DNA patterns. The outbreaks of diarrhea were unusual in that several different Aeromonas genospecies were involved in each outbreak.

Impact of the fluoroquinolones on gastrointestinal flora

Abstract: A number of studies have been performed to evaluate the effect of the fluoroquinolones on gastrointestinal flora The fluoroquinolones have only slight or no effect on the oropharyngeal flora, except when Neisseria, Haemophilus or Branhamella spp are present Studies have consistently shown that Gram-negative facultative bacteria of the lower intestinal flora are strongly suppressed during administration of these agents Total faecal anaerobes are generally unchanged The effect of the fluoroquinolones on Gram-positive bacteria is more variable with mild to moderate suppression reported with some agents In view of the high faecal concentrations of the fluoroquinolones, the general lack of effect on anaerobes is surprising; it may be attributable to the large number of microorganisms found in faeces and faecal binding of the fluoroquinolones Several recent studies suggest that the effects of some fluoroquinolones on faecal anaerobes and Gram-positive cocci may be more profound in certain patient populations such as bone marrow transplant recipients and patients undergoing gastrointestinal surgery Colonisation with yeasts and the emergence of resistant bacterial strains have been reported during or after fluoroquinolone administration in some studies Future studies will need to investigate the effect of the newer agents with greater activity against anaerobes and Gram-positive cocci on the gastrointestinal flora and to continue surveillance for resistant organisms

GenesInvolved intheRegulation of,B-Lactamase Production inEnterococci andStaphylococci

Abstract: Inenterococci, thestructural genefor13-lactamase (blaZ) isidentical toblaZfromStaphylococcus aureus. However, intheenterococci studied todate,3-lactamase isproduced constitutively, whereas instaphylococci itisoften inducible. Recent reports haverevealed thepresence oftwoadjacent genes upstream ofthe staphylococcal blaZthought tobetheantirepressor (blaRl) andrepressor (blal) genes. Inthepresent study, P-lactamase expression mutants ofthestaphylococcal -lactamase plasmid pI524 weregenerated bytransposonmutagenesis withthetransposon Tn917. Tn917insertions upstream ofblaZineither blaRI orblaIl resulted inconstitutive 13-lactamase production, indicating thattherepressor function islost withinsertion ofTn917 into either gene. Thisfinding supports theconcept thatthestaphylococcal 13-lactamase regulatory genes are encoded ona polycistronic mRNA.Thecorresponding region upstream oftheenterococcal blaZfrom Enterococcus faecalis HH22wassequenced andcompared withthestaphylococcal blaRi sequence. Thetwo sequences wereidentical for893nucleotides, andthenthesequences diverged completely. Therefore, instrain HH22,only51%oftheputative antirepressor geneispresent andtherepressor geneisalsoabsent. In conclusion, constitutive 13-lactamase production inHH22appears tobeduetoalackoftheregulatory genes blaRI andblaI whichregulate expression ofblaZinstaphylococci. Penicillinase production amonggram-positive bacteria is usually inducible; thatis, enzymelevels increase manyfold overbaseline levels uponexposure tobeta-lactam antibiotics. OfthemajorP-lactamase producers amonggram-positive organisms, namely, Bacillus, Staphylococcus, andEnterococcus spp., theBacillus induction mechanism hasbeen studied inthegreatest detail. Ithasbeenshownthrough DNA nucleotide sequence determination anddeletion analysis that,B-lactamase synthesis inBacillus lichenifonnis is under thecontrol ofarepressor (penI) andanantirepressor (penJ) (2-4). penIislocated 5'tothepromoter forthe