Search PubMed⌕ Search

Biomedical subjects

L R Peterson

Publications and source records attributed to L R Peterson.

At least 19 recordsLinked to original sources
PubMed1992

Treatment of asymptomatic Clostridium difficile carriers (fecal excretors) with vancomycin or metronidazole. A randomized, placebo-controlled trial.

OBJECTIVE: To compare the efficacy of vancomycin and metronidazole for eradication of asymptomatic Clostridium difficile fecal excretion as a means of controlling nosocomial outbreaks of C. difficile diarrhea. DESIGN: Randomized, placebo-controlled, non-blinded trial. SETTING: Six hundred-bed regional referral Veterans Affairs Medical Center. PATIENTS: Thirty patients excreting C. difficile without diarrhea or abdominal symptoms. INTERVENTIONS: All patients were randomized to receive 10 days of oral vancomycin, 125 mg four times daily; metronidazole, 500 mg twice daily; or placebo, three times daily. MEASUREMENTS: Stool cultures were obtained during treatment and for 2 months after treatment. All C. difficile isolates were typed by restriction endonuclease analysis (REA). RESULTS: Clostridium difficile organisms were not detected during and immediately after treatment in 9 of 10 patients treated with vancomycin compared with 3 of 10 patients treated with metronidazole (P = 0.02) and 2 of 10 patients in the placebo group (P = 0.005). The fecal vancomycin concentration was 1406 +/- 1164 micrograms/g feces, but metronidazole was not detectable in 9 of 10 patients. Eight of the nine evaluable patients who had negative stool cultures after treatment with vancomycin began to excrete C. difficile again 20 +/- 8 days after completing treatment. Three of these patients received additional antibiotics before C. difficile excretion recurred, and five acquired new C. difficile REA strains. Four of six patients who received only vancomycin before C. difficile excretion recurred were culture-positive at the end of the study compared with one of nine patients who received only placebo (P = 0.047). CONCLUSIONS: Asymptomatic fecal excretion of C. difficile is transient in most patients, and treatment with metronidazole is not effective. Although treatment with vancomycin is temporarily effective, it is associated with a significantly higher rate of C. difficile carriage 2 months after treatment and is not recommended.

Aged↗
PubMed1992

Effect of yogurt on clindamycin-induced Clostridium difficile colitis in hamsters.

Yogurt exhibits in vitro bactericidal activity against a variety of pathogenic microorganisms, including Clostridium difficile. In the present studies, we tested whether yogurt ingestion could prevent or ameliorate antibiotic associated colitis in the clindamycin-treated hamster model. Male golden Syrian hamsters were given 5 mg/kg clindamycin subcutaneously 24 hr before and 6 hr following inoculation with 0.5 ml of less than 10, 10(3), 10(5), or 10(6) CFU/ml of C. difficile. Hamsters in the control group ingested chow and water ad libitum, whereas the experimental group ingested chow and a 1:1 (v/v) mixture of yogurt and water ad libitum, beginning 24 hr before the first injection of clindamycin and continuing throughout the course of the study. Animals were monitored for colonization with C. difficile, pathological evidence of colitis, and death. Mortality was 100% in yogurt-treated animals, and all animals showed histological changes of severe colitis. Fecal and intestinal segment cultures were positive for C. difficile in all animals. Thus, in the hamster model, we found no evidence to support the possible efficacy of yogurt in the prevention of C. difficile colitis.

Animals↗
PubMed1992

Acquisition of Clostridium difficile by hospitalized patients: evidence for colonized new admissions as a source of infection.

The frequency of introduction and spread of specific Clostridium difficile strains among hospitalized patients were assessed by serial cultures of patients admitted to a medical-surgical ward with endemic C. difficile-associated diarrhea. Stool cultures were obtained from 634 (94%) of 678 consecutive admissions to the ward (ward admissions), and all C. difficile isolates were typed by restriction endonuclease analysis. Sixty-five ward admissions introduced C. difficile to the ward, and 54 initially culture-negative admissions acquired C. difficile on the ward. Ward admissions hospitalized within the prior 30 days in the medical center were more likely to be culture-positive for C. difficile at admission to the study ward than those not previously hospitalized at the institution (16% vs. 7%, P less than .001). Nosocomial acquisition of a C. difficile strain was preceded by a documented introduction of that strain to the ward by another asymptomatic ward admission in 16 (84%) of 19 instances, suggesting that C. difficile-colonized new admissions are a major source of nosocomial C. difficile infections.

Bacterial Typing Techniques↗
PubMed1992

Detection of gyrA gene mutations associated with ciprofloxacin resistance in methicillin-resistant Staphylococcus aureus: analysis by polymerase chain reaction and automated direct DNA sequencing.

A portion of the gyrA gene from amino acid codons 67 to 129 was sequenced in 34 methicillin-resistant Staphylococcus aureus strains (14 isolated in Minnesota, 10 isolated in Indiana, and 10 isolated in Tennessee). Twenty-eight of these strains were ciprofloxacin resistant. Sixteen of the strains contained a Ser----Leu mutation at codon 84; 3 contained strains a Ser----Ala mutation at codon 84; 3 strains contained two mutations, Ser----Leu at codon 84 and Ser----Pro at codon 85; and 6 strains contained a Glu----Lys mutation at codon 88. Six strains were wild type and ciprofloxacin susceptible. Several mutations from amino acid codons 84 through 88 can be associated with high-level quinolone resistance.

Base Sequence↗
PubMed1992

Tests for bactericidal effects of antimicrobial agents: technical performance and clinical relevance.

Bactericidal testing has been used for several decades as a guide for antimicrobial therapy of serious infections. Such testing is most frequently performed when bactericidal antimicrobial agent therapy is considered necessary (such as when treating infectious endocarditis or infection in an immunocompromised host). It has also been used to ensure that the infecting organism is killed by (not tolerant to) usually bactericidal compounds. However, few data are available to support the role of such tests in direct patient care. Several important variables affect the reproducibility of the test results; however, proposed reference methods are now available for performing the MBC test. With minor modifications, these can provide a standardized approach for laboratories that need to perform them. Currently, little evidence is available to support the routine use of such testing for the care of individual patients. However, testing of new (investigational) antimicrobial agents can be beneficial in determining their potential to provide bactericidal antimicrobial activity during clinical use. New methods to assess bactericidal activity are being developed, but as yet none have been rigorously tested in patient care settings; further, for most of these methods, little information is available as to which technical parameters affect their results. In clinical laboratories, all bactericidal tests must be performed with rigorously standardized techniques and adequate controls, bearing in mind the limitations of the currently available test procedures.

Animals↗
PubMed1992

Revision of standards for adjusting the cation content of Mueller-Hinton broth for testing susceptibility of Pseudomonas aeruginosa to aminoglycosides.

A multilaboratory study was undertaken to reassess the amount of calcium and magnesium that should be added to Mueller-Hinton broth when testing Pseudomonas aeruginosa against amikacin, gentamicin, isepamicin, netilmicin, and tobramycin. To achieve parity with agar dilution tests, cation-adjusted broth should contain 20 to 25 mg of calcium and 10 to 12.5 mg of magnesium per liter rather than the 50- and 25-mg/liter supplements recommended previously. For quality control of tests with contemporary media, MIC control limits should be adjusted by lowering the current MIC limits by at least 1 doubling-dilution interval.

Aminoglycosides↗
PubMed1992

Comparison of the VIDAS Clostridium difficile toxin A immunoassay with C. difficile culture and cytotoxin and latex tests.

The VIDAS Clostridium difficile toxin A immunoassay (CDA) is a new, automated, enzyme-linked fluorescent-antibody assay for detection of C. difficile toxin A antigen in stool specimens. Simultaneous, parallel testing was performed by using the VIDAS CDA, the Culturette brand CDT latex test for C. difficile antigens, and conventional laboratory cell culture tests for C. difficile, cytotoxicity and C. difficile culture. One hundred ninety-four consecutive fresh soft or liquid stool samples submitted for C. difficile testing between July and September 1990 were evaluated. Of the 194 samples tested, 19 (10%) were from 16 patients who met our case definition for C. difficile-associated disease. The in vitro tests were evaluated in relation to two forms of a clinical case definition. In one form, a positive culture for toxin-producing C. difficile or a positive cytotoxin result obtained directly from the stool specimen was required as laboratory evidence of C. difficile. In the other, a positive result of any of the four laboratory tests was accepted for the laboratory portion of the case definition. No significant difference between the sensitivity of the VIDAS CDA and that of the Culturette brand CDT latex test was found (48 to 58% sensitivity for the CDT latex test and 52 to 63% sensitivity for the VIDAS CDA compared with 93 to 100% sensitivity for culture and 70 to 100% sensitivity for cytotoxin testing). The performance of the VIDAS CDA, however, was hampered by a high percentage of tests (19%) which gave an uninterpretable result.

Bacterial Toxins↗
PubMed1991

A general ampC active site oligonucleotide probe for gram-negative rods.

We have developed a 33 mer probe that hybridizes to the serine active site of the chromosomal ampC beta-lactamase gene of Pseudomonas aeruginosa and the Enterobacteriaceae. We tested this probe against a variety of Enterobacteriaceae, and a series of 23 P. aeruginosa by dot-blots and selected Southern blots. This probe is an alternative or supplement to enzyme studies for characterizing the class of a Gram-negative rod's beta-lactamase and is a useful tool for studies of Pseudomonas beta-lactamase regulation.

Base Sequence↗
PubMed1991

An evaluation of three commercial fecal transport systems for the recovery of enteric pathogens.

Twenty-five isolates, including six strains of Shigella species, six strains of Salmonella species, five strains of Yersinia enterocolitica, six strains of Campylobacter jejuni, and two strains of Vibrio parahaemolyticus, were inoculated at a concentration of 1.5 x 10(4) colony-forming units/mL into the following transport systems: Fekal Enteric Plus (Trend Scientific, Inc., St. Paul, MN), Cary Blair Transport Medium (Remel, Inc., Lenexa, KS), and Para-Pak C & S (Meridian Diagnostics, Inc., Cincinnati, OH). The Fekal Enteric Plus system showed a greater than or equal to 50% recovery of the original bacterial inoculum after 96 hours for all Salmonella, Shigella, and Yersinia strains tested and after as long as 72 hours for Vibrio strains. The Cary Blair Transport System showed greater than or equal to 50% recovery of the initial inoculum at 96 hours for five of six Salmonella strains, four of six Shigella strains, all Yersinia strains, and one of two Vibrio strains. With the use of the Para-Pak C & S, greater than or equal to 50% recovery of the original inoculum after 96 h was demonstrated for five of six Salmonella strains, four of six Shigella strains, all Yersinia strains, and one of two Vibrio strains. All three systems did not demonstrate even 10% recovery of the initial C. jejuni inoculum at 24 hours when held at room temperature.

Bacteriological Techniques↗
PubMed1991

The slide centrifuge gram stain as a urine screening method.

A slide centrifuge Gram stain procedure was performed to screen for bacteriuria 4161 urine specimens submitted in urine preservative tubes for routine culture. For slide centrifuge Gram staining, each urine sample was mixed well. Thereafter, 0.2 mL of each sample was placed, using a pipette, into a slide centrifuge chamber and centrifuged at 2,000 rpm for 5 minutes. The slides were heat fixed, Gram stained, and read by laboratory personnel who scanned 12 consecutive oil-immersion fields using a set pattern. The presence of the same organism in six or more fields was defined as a positive urine screen. Urine samples were cultured using a 0.001-mL loop and a comparison of culture growth with slide centrifuge screening was made. When growth of 100,000 or more colony-forming units per milliliter (CFU/mL) was the reference for comparison, the screen had a sensitivity rate of 98%, a specificity rate of 90%, a negative predictive value of 99%, and a positive predictive value of 65%. When a lower colony count of 10,000 or more CFU/mL was the reference for comparison, the screen had a sensitivity rate of 88%, a specificity rate of 95%, a negative predictive value of 96%, and a positive predictive value of 84%. The slide centrifuge Gram stain is a very sensitive screening method to detect bacteriuria in an adult male population.

Adult↗
PubMed1991

gyrA mutations in ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus from Indiana, Minnesota, and Tennessee.

Mutational changes occurring at amino acid codons 84 and 85 located in the gyrA gene of methicillin-resistant Staphylococcus aureus (MRSA) were studied using radiolabeled oligonucleotide probes to examine the incidence of these ciprofloxacin resistance determinants in 30 MRSA isolates from Indiana, Minnesota, and Tennessee. Four separate oligonucleotide probes, one each corresponding to the wild-type sequence, a mutation at codon 84 (nucleotide 251), a mutation at codon 85 (nucleotide 253), and mutations at both, were used to examine the total genomic DNA from each of the 30 isolates, which had been restricted, electrophoresed, and Southern blotted. The probes indicated that 15 of the 28 ciprofloxacin-resistant isolates gave results consistent with a single mutation at codon 84. Four of the 28 ciprofloxacin-resistant strains had results consistent with a mutation at codon 84 and possibly at codon 85. The two ciprofloxacin-sensitive isolates from Tennessee showed homology with the wild-type probe sequence. Five isolates (4, Minnesota; 1, Tennessee) had no homology with any probe. By oligonucleotide probes, ciprofloxacin-resistant MRSA from diverse geographic regions contained similar gyrA mutations at codons 84 or 85 in 19 of 28 ciprofloxacin-resistant isolates.

Base Sequence↗
PubMed1991

Uptake of 3H-norfloxacin in methicillin-resistant Staphylococcus aureus.

To examine the possibility of a proton-motive efflux pump for quinolones in highly quinolone-resistant clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), we studied 3H-norfloxacin uptake in two quinolone-resistant and two quinolone-sensitive strains of MRSA whose gyrA region surrounding amino acid codons 84 and 85 had been sequenced. Two strains were related (one sensitive and one resistant) in that both were recovered from a single patient, one before (sensitive) and one after (resistant) ciprofloxacin therapy. Drug uptake was assessed in four separate experiments running triplicate bacterial suspensions with radiolabeled drug added at time = 0. Sampling was performed in 10 min increments up to 50 min by a vacuum filtration method. The ionic uncoupler, carbonyl cyanide m-chlorophenylhydrazone (CCCPH), was added at 40 min to test inhibition of a pump mechanism. The results demonstrated no statistically significant differences in uptake between the sensitive and resistant groups, and the uptake patterns were similar. CCCPH also induced an equivalent surge, or enhanced uptake among these strains, rendering an energy-dependent efflux pump an unlikely contributor to the high levels of resistance seen in our strains. Our findings support parallel studies done on these isolates that implicate mutational changes at amino acid codon 84 and/or codon 85 in the gyrA gene as an explanation for high-level quinolone resistance (MIC to ciprofloxacin greater than or equal to 16 mg/L) in MRSA.

Anti-Infective Agents↗
PubMed1991

Ciprofloxacin resistance in coagulase-positive and -negative staphylococci: role of mutations at serine 84 in the DNA gyrase A protein of Staphylococcus aureus and Staphylococcus epidermidis.

gyrA mutations in quinolone-resistant pathogenic isolates of Staphylococcus spp. have been detected by the direct HinfI digestion of polymerase chain reaction products. Homology among gyrA genes allowed rapid examination of both coagulase-positive and -negative isolates. DNA sequence analysis revealed that ciprofloxacin resistance in Staphylococcus epidermidis is associated with a novel Ser-84----Phe mutation in the DNA gyrase A protein, analogous to Ser-84----Leu changes observed in Staphylococcus aureus.

Anti-Infective Agents↗
PubMed1991

Aminoglycoside resistance and aminoglycoside usage: ten years of experience in one hospital.

For 10 years the 700-bed Minneapolis Veterans Affairs Medical Center has conducted a policy of carefully controlled aminoglycoside usage and monitoring of resistance of over 25,000 aerobic and facultative gram-negative bacillary isolates to the aminoglycosides. On two occasions during the 1980s, our experience of introducing amikacin at a high level of usage was associated with a significant reduction in resistance to gentamicin and tobramycin among gram-negative bacilli. Rapid reintroduction of gentamicin usage in 1982 after the first amikacin period was associated with a significant and rapid increase in gentamicin and tobramycin resistance. However, in 1986, gentamicin was again reintroduced to this institution at an initially modest level, and the percentage of usage of gentamicin was gradually increased over a 15-month period without a significant change in resistance to gentamicin, tobramycin, or amikacin while maintaining an overall 68% gentamicin usage and 30% amikacin usage. Aminoglycoside usage (measured as patient days) rose steadily from under 2,000 patient days per quarter in 1980 and 1981 to over 3,000 days per quarter in 1985. Since 1985, usage has declined to under 2,500 patient days per quarter in 1990. This usage rise and fall occurred during a steadily declining daily patient census that was 590 in 1980 and 465 in 1989. A move to a new hospital building in June 1988 was associated with an additional significant decline in resistance to all aminoglycosides (P less than 0.05), continuing a trend that was evident for the year preceding the move. Resistance to aminoglycoside antibiotics is now at the lowest level in 10 years at this institution, with only one gram-negative organism, Pseudomonas aeruginosa, that exhibits more than 5% resistance to gentamicin and no gram-negative species that are more than 5% resistant to amikacin and tobramycin.

Amikacin↗
PubMed1991

Evaluation of cycloserine-cefoxitin-fructose agar and cycloserine-cefoxitin-fructose broth for recovery of Clostridium difficile from environmental sites.

Cycloserine-cefoxitin-fructose agar (CCFA) and cycloserine-cefoxitin-fructose broth (CCFB) containing either 500 or 250 micrograms of cycloserine per ml were compared for efficacy in the isolation of Clostridium difficile from hospital ward environmental sites. A RODAC imprint technique was used to inoculate prereduced CCFA. Moistened swabs were used to inoculate prereduced CCFB from environmental sites immediately adjacent to the RODAC sample sites. CCFA (6% positive) was significantly more sensitive than CCFB (3% positive; P less than 0.005), regardless of the cycloserine concentration. When the CCFA cycloserine concentration was decreased from 500 to 250 micrograms/ml, the overall rate of positive cultures rose from 4 to 17%. Medium containing 500 micrograms of cycloserine per ml may be too inhibitory to isolate many moderately sensitive strains of C. difficile from environmental sites. Regardless of the cycloserine concentration, the CCFA RODAC imprint technique is superior to the CCFB method.

Agar↗
PubMed1991

Comparison of traditional gas chromatography (GC), headspace GC, and the microbial identification library GC system for the identification of Clostridium difficile.

Three gas chromatography (GC) methods were compared for the identification of 52 clinical Clostridium difficile isolates, as well as 17 non-C. difficile Clostridium isolates. Headspace GC and Microbial Identification System (MIS) GC, an automated system which utilizes a software library developed at the Virginia Polytechnic Institute to identify organisms based on the fatty acids extracted from the bacterial cell wall, were compared against the reference method of traditional GC. Headspace GC and MIS were of approximately equivalent accuracy in identifying the 52 C. difficile isolates (52 of 52 versus 51 of 52, respectively). However, 7 of 52 organisms required repeated sample preparation before an identification was achieved by the MIS method. Both systems effectively differentiated C. difficile from non-C. difficile clostridia, although the MIS method correctly identified only 9 of 17. We conclude that the headspace GC system is an accurate method of C. difficile identification, which requires only one-fifth of the sample preparation time of MIS GC and one-half of the sample preparation time of traditional GC.

Bacteriological Techniques↗
PubMed1991

Antimicrobial penetration into polymorphonuclear leukocytes and alveolar macrophages.

Infections caused by intracellular organisms often involve the lung and may be implicated in chronic disease. These intracellular bacteria may be protected from otherwise lethal concentrations of extracellular antimicrobials. Knowledge of the intracellular concentration of usual antimicrobials used to treat pneumonia may allow physicians to refine their initial choice of therapy. Lipid-insoluble antimicrobials, such as penicillin, cephalosporins, aminoglycosides, trimethoprim, and imipenem penetrate poorly into cells, if they penetrate at all. Isoniazid, tetracycline, and lincomycin have intermediate intracellular penetration, and chloramphenicol, rifampin, ethambutol, quinolones, and lincosamides, plus macrolides, are avidly concentrated. Nonetheless, to date it has been difficult to correlate intracellular concentrations of antimicrobials with cellular killing or clinical outcome. Information derived from a more standardized approach to the evaluation of antimicrobial agent intracellular penetration will be useful in improving the direct application of in vitro study results to the clinical care of patients with pneumonia.

Anti-Bacterial Agents↗