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Biomedical subjects

R J Wallace

Publications and source records attributed to R J Wallace.

At least 109 records · Page 6Linked to original sources
PubMed1995

Adverse events associated with high-dose rifabutin in macrolide-containing regimens for the treatment of Mycobacterium avium complex lung disease.

We initiated a multidrug trial that included high-dose rifabutin for the treatment of pulmonary Mycobacterium avium complex (MAC) disease. Twenty-six patients received rifabutin (600 mg/d) in combination with ethambutol, streptomycin, and either clarithromycin (500 mg b.i.d.; 15 patients) or azithromycin (600 mg/d; 11 patients). Rifabutin-related adverse events occurred in 77% of patients. Fifty-eight percent of patients required a dosage adjustment or discontinuance of rifabutin therapy. The most common adverse event was a reduction in the mean total white blood cell (WBC) count, which decreased from 8,600 +/- 2,800/mm3 before treatment to 4,500 +/- 2,100/mm3 during treatment (P = .0001). Although all patients had some decrease in WBC count, only three patients (12%) required a dosage adjustment for this reason. Other common adverse events included gastrointestinal symptoms (nausea, vomiting, or diarrhea; 42%) and abnormal liver enzyme levels (12%). Eight of 11 patients (73%) with gastrointestinal symptoms, including one patient with abnormal liver enzyme levels, required a rifabutin-dosage adjustment. The most severe adverse events, always requiring an adjustment of therapy, were a diffuse polyarthralgia syndrome (19%) and anterior uveitis (8%). The latter toxicity has previously been reported to occur only in patients with AIDS and was seen only in patients who also were receiving clarithromycin. On the basis of the current findings, we recommend that rifabutin be used at a dose of 300 mg/d in multidrug regimens that include a macrolide for treatment of MAC lung disease.

Adult↗
PubMed1995

Reduced serum levels of clarithromycin in patients treated with multidrug regimens including rifampin or rifabutin for Mycobacterium avium-M. intracellulare infection.

The newer macrolides and rifamycins (rifabutin) are major advances for treatment or prophylaxis of disease due to Mycobacterium avium complex. Although rifampin and rifabutin are known to induce the hepatic cytochrome P-450 system, their impact on the metabolism of clarithromycin is unknown. Clarithromycin and its major metabolite, 14-OH clarithromycin, were measured in the sera of patients receiving 500 mg twice a day before and after the addition of antituberculous drugs, including 600 mg/day of rifampin or rifabutin. Mean serum levels of clarithromycin given as a single agent were 5.4 +/- 2.1 micrograms/mL. These decreased to 0.7 +/- 0.6 micrograms/mL in patients receiving rifampin and 2.0 +/- 1.5 micrograms/mL in those receiving rifabutin. Mean serum levels of 14-OH clarithromycin were similar in the 3 groups (1.8-1.9 micrograms/mL). Rifampin and (to a lesser degree) rifabutin appear to induce the metabolism of clarithromycin.

Clarithromycin↗
PubMed1995

Phylogeny of the Mycobacterium chelonae-like organism based on partial sequencing of the 16S rRNA gene and proposal of Mycobacterium mucogenicum sp. nov.

The Mycobacterium chelonae-like organism (MCLO) is a recently described member of the Mycobacterium fortuitum complex which causes posttraumatic skin infections and catheter sepsis. This taxon is a distinct group biochemically and has a unique mycolic acid profile as determined by high-performance liquid chromatography. Its phylogenetic relationships to other mycobacteria, however, have not been studied previously. We sequenced 1,062 bp of the 16S rRNA genes from three MCLO strains obtained from the American Type Culture Collection and compared our results with the sequences of previously described taxa of rapidly growing and slowly growing mycobacteria. Two biochemically typical strains (ATCC 49650T [T = type strain] and ATCC 49651) had identical sequences, while the sequence of a biochemically atypical strain (ATCC 49649) differed by 4 bp from the sequence of the two typical strains. The Hamming distances between these MCLO strains and related rapidly growing mycobacteria are comparable to the Hamming distances among taxa of rapidly growing mycobacteria established as species by DNA-DNA hybridization. We propose the name Mycobacterium mucogenicum sp. nov. for this new taxon because of the highly mucoid nature of most isolates on solid media.

Base Sequence↗
PubMed1995

PCR amplification and restriction endonuclease analysis of a 65-kilodalton heat shock protein gene sequence for taxonomic separation of rapidly growing mycobacteria.

A total of 129 reference and clinical strains of rapidly growing mycobacteria (RGM) belonging to 10 taxonomic groups were studied for restriction fragment length polymorphism patterns from a PCR-amplified 439-bp segment of the 65-kDa heat shock protein (HSP) gene. Of 24 endonucleases evaluated, restriction fragment length polymorphism patterns produced by HaeIII and BstEII and then by AciI and CfoI gave the best separation. Sixty percent of all RGM taxa studied were differentiated by HaeIII digests alone. Single unique patterns were observed with HaeIII and/or BstEII for Mycobacterium fortuitum (100%), M. chelonae (94%), M. abscessus (96%), M. smegmatis (100%), M. mucogenicum (formerly the M. chelonae-like organism) (100%), and the sorbitol-negative third biovariant of M. fortuitum (100%). Evidence is presented in support of two subgroups within M. peregrinum, M. smegmatis, and the unnamed third biovariant of M. fortuitum (sorbitol positive and sorbitol negative). PCR-based technology provides a rapid, accurate system for the identification of clinically important species of RGM which should be particularly useful for reference laboratories.

Bacterial Proteins↗
PubMed1995

DNA amplification and restriction endonuclease analysis for differentiation of 12 species and taxa of Nocardia, including recognition of four new taxa within the Nocardia asteroides complex.

Nineteen reference and 156 clinical strains of the genus Nocardia belonging to 12 taxonomic groups were studied for restriction fragment length polymorphism (RFLP) by using an amplified 439-bp segment of the 65-kDa heat shock protein gene. Of 30 restriction endonucleases, digestion with MspI and then digestion with BsaHI produced RFLP band patterns which separated all 12 groups except N. asteroides type IV from 6 of 12 N. transvalensis isolates and N. carnea from the N. asteroides type VI isolates. Commonly encountered species such as N. nova, N. farcinica, N. brasiliensis sensu stricto, and N. otitidiscaviarum were easily separated. Each taxon resulted in a single RFLP band pattern that included > or = 96% of all biochemically grouped isolates for 9 of 12 taxa with MspI and for 8 of 12 taxa with BsaHI. With the use of both patterns, only 6 of 175 (3.4%) isolates failed to fit the biochemically defined group patterns. These studies provide the first evidence for the separate identities of four antibiogram-defined (but currently unnamed) groups within the N. asteroides complex (types I, II, IV, and VI) and the presence of two subgroups within N. transvalensis. They also provide genotypic evidence for the separate identities of N. nova and N. farcinica. The lack of BstEII recognition sites in amplicons obtained from nocardiae provides a simple and rapid method for the differentiation of nocardiae from mycobacteria. DNA amplification with RFLP analysis is the first rapid method that distinguishes all clinically significant taxa and recognized species within the genus Nocardia.

Bacterial Typing Techniques↗
PubMed1995

New Nocardia taxon among isolates of Nocardia brasiliensis associated with invasive disease.

Nocardia brasiliensis, the second most frequently isolated aerobic actinomycete in the clinical laboratory, is usually associated with localized cutaneous infections. However, 22% of 238 N. brasiliensis isolates from the United States and 12% of 66 isolates from Queensland, Australia, which had been collected over a 17-year period, were associated with extracutaneous and/or disseminated diseases. Of the 62 invasive isolates, 37 (60%) were susceptible to ciprofloxacin and/or were susceptible to clarithromycin and resistant to minocycline, compared with only 6 (3%) of 242 localized cutaneous isolates. The 43 isolates with this susceptibility pattern appeared to define a new taxon. They were similar to Nocardia asteroides complex isolates clinically in proportions from persons with pulmonary (70%), central nervous system (23%), and/or disseminated diseases (37%) in the setting of corticosteroids (74%) or AIDS (14%). This putative new taxon differed from N. brasiliensis in the hydrolysis of adenine (92 versus 4%), beta-lactamase patterns on isoelectric focusing, and the presence of two early mycolic acid-ester peaks by high-performance liquid chromatography. Restriction analysis of a 439-bp fragment of the 65-kDa heat shock protein gene revealed that N. brasiliensis and the new taxon had different restriction patterns with 8 of the 11 enzymes tested. Screening of invasive isolates of N. brasiliensis for susceptibility to ciprofloxacin will identify most isolates of the new taxon, which likely represents a new Nocardia species.

Base Sequence↗
PubMed1995

Tuberculosis outbreak among healthcare workers in a community hospital.

Twenty-nine healthcare workers (HCW) were exposed to an active case of unrecognized drug-susceptible pulmonary tuberculosis in a community hospital for as long as 2 h in the emergency room and 10 h in a medical intensive care unit. Twelve of the 29 exposed HCW could not be evaluated for tuberculosis infection because 10 of them had a previously positive tuberculin skin test and two were lost to follow-up. Of the remaining 17 tuberculin skin test negative HCW, 13 (76%) either converted their skin test to positive (10 HCW) or developed active disease (three HCW) after exposure to the index case. The Mycobacterium tuberculosis isolates from the three HCW had identical DNA restriction fragment length polymorphism (RFLP) patterns when studied by pulsed field gel electrophoresis. This case of drug-susceptible tuberculosis was associated with unusually high rates of tuberculosis infection and disease in HCW. Prevention of similar occurrences in HCW may be difficult because of the short exposure time required for transmission of tuberculosis and the absence of consensus on optimal respiratory protective measures.

Adult↗
PubMed1995

Different strains of Saccharomyces cerevisiae differ in their effects on ruminal bacterial numbers in vitro and in sheep.

A ruminal simulation device (Rusitec) was used to compare the effects of Saccharomyces cerevisiae strains NCYC 240, NCYC 694, NCYC 1026, NCYC 1088, and Yea-Sacc (a commercial product containing S. cerevisiae) on ruminal fermentation. S. cerevisiae NCYC 240, NCYC 1088, NCYC 1026, and NCYC 694 were grown on malt extract at 30 degrees C in aerated fed-batch culture and harvested along with spent growth medium by freeze-drying. Each vessel received daily 20 g of a basal diet consisting of hay, barley, molasses, fishmeal, and a minerals/vitamins mixture at 500, 299.5, 100, 91, and 9.5 g/kg of DM, respectively. Yeast preparations (500 mg/d) were added along with the feed. S. cerevisiae NCYC 240, NCYC 1026, and Yea-Sacc stimulated total and cellulolytic bacterial numbers, whereas S. cerevisiae NCYC 694 and NCYC 1088 had no effect on the numbers of bacteria. The effects of S. cerevisiae NCYC 240, NCYC 1026, and Yea-Sacc on ruminal fermentation were further investigated in vivo using ruminally cannulated sheep fed 1.5 kg/d of the diet used in Rusitec, supplemented with 2 g/d of yeast culture. All treatments tended to stimulate total and cellulolytic bacterial numbers. However, the stimulation was only statistically significant for S. cerevisiae NCYC 1026 with total bacterial numbers and S. cerevisiae NCYC 240 with cellulolytic bacteria (P < .05). Increased bacterial numbers were associated with an increase in the rate of straw degradation in the rumen and a nonsignificant (P > .05) increase in the excretion of purine derivatives in the urine, measured as an index of microbial nitrogen leaving the rumen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Recent changes in taxonomy and disease manifestations of the rapidly growing mycobacteria.

Rapidly growing mycobacteria are a complex group of environmental organisms that cause human disease. Eight taxonomic groups of pathogens are recognized of which three, the Mycobacterium chelonae-like organism (MCLO) and the two Mycobacterium fortuitum third biovariant groups, have yet to receive names pending DNA-DNA homology studies. Clinical disease due to all eight taxons usually consists of skin or soft tissue infections following trauma. Nosocomial disease has become increasingly important, pseudoepidemics associated with contaminated automated endoscopic washing machines being the most recently described manifestation. The development of DNA fingerprinting technology, especially pulsed-field gel electrophoresis, has improved the possibilities of studying the epidemiology of these infections. Pulmonary disease, primarily due to Mycobacterium abscessus, and disseminated cutaneous disease due to Mycobacterium chelonae, have recently been characterized. Imipenem and the newer macrolide clarithromycin represent important new therapeutic agents active against these species. Other important therapeutic agents include amikacin and the newer quinolones, which have variable degrees of susceptibility within different taxonomic groups, necessitating susceptibility testing.

Cross Infection↗
PubMed1994

Rifampin-resistant Mycobacterium kansasii.

We identified 36 rifampin-resistant Mycobacterium kansasii isolates, including 17 (4%) of 464 isolates recovered in Texas between 1989 and 1992. Of 29 patients infected with rifampin-resistant M. kansasii whose history of medication was known, 90% had previously received rifampin, and 58% of these patients had been treated with one or two effective drugs. Thirty-two percent of rifampin-resistant isolates recovered since 1989 were from patients who were seropositive for human immunodeficiency virus (HIV) infection. Twenty courses of therapy with a four-drug regimen determined on the basis of in vitro susceptibilities were administered to 16 patients from whom rifampin-resistant isolates were recovered; the therapy did not include surgery. Sputum cultures converted to negative as the result of 90% of treatments (time to conversion: mean, 11 weeks; range, 4-20 weeks). Bacteriologic relapses occurred in four of five patients who withdrew from therapy after being culture negative for < or = 6 months of therapy and in one of 12 patients who were culture negative for at least 12 months of therapy (mean, 16.3 months). This study suggests that the prognosis for cure of infection due to rifampin-resistant M. kansasii with chemotherapy alone is excellent, although the number of cases appears to be increasing, in part because of the HIV disease epidemic.

Adult↗
PubMed1994

Identification of mutations in 23S rRNA gene of clarithromycin-resistant Mycobacterium intracellulare.

Clarithromycin is a potent macrolide that has been used for treating infections with nontuberculous mycobacteria. Pairs of susceptible and resistant Mycobacterium intracellulare strains were obtained from patients with chronic pulmonary M. intracellulare infections undergoing monotherapy with clarithromycin. Nucleotide sequence comparisons of the peptidyltransferase region in 23S rRNAs from parental and resistant strains revealed that in three of six resistant strains, for which the MIC was > 32 micrograms/ml, a single base was mutated (Escherichia coli equivalent, A-2058-->G, C, or U). As the modification of adenine 2058 by dimethylation is a frequent cause of macrolide resistance in a variety of different bacteria, we suggest that mutation of A-2058 confers acquired resistance to clarithromycin in M. intracellulare.

Base Sequence↗
PubMed1994

Tetracycline resistance determinants in Mycobacterium and Streptomyces species.

Two of seven tetracycline-resistant (Tcr) Mycobacterium fortuitum group isolates and six Tcr clinical Streptomyces isolates carried gram-positive Tcr determinants (Tet K and Tet L) and Streptomyces resistance determinants (Otr A, Otr B, and Otr C). This represents the first documentation of the acquisition by mycobacteria of determinants coding for antibiotic resistance and suggests the potential for the spread of antibiotic resistance determinants within mycobacterial species.

Base Sequence↗
PubMed1994

Influence of Yucca shidigera extract on ruminal ammonia concentrations and ruminal microorganisms.

An extract of the desert plant Yucca shidigera was assessed for its possible benefit in ruminal fermentation. The extract bound ammonia in aqueous solution when concentrations of ammonia were low (up to 0.4 mM) and when the extract was added at a high concentration to the sample (20%, vol/vol). The apparent ammonia-binding capability was retained after autoclaving and was decreased slightly following dialysis. Acid-precipitated extract was inactive. No evidence of substantial ammonia binding was found at higher ammonia concentrations (up to 30 mM). When Y. shidigera extract (1%, vol/vol) was added to strained rumen fluid in vitro, a small (6%) but significant (P < 0.05) decrease in ammonia concentration occurred, apparently because of decreased proteolysis. Inclusion of Y. shidigera extract (1%, vol/vol) in the growth medium of the rumen bacterium Streptococcus bovis ES1 extended its lag phase, while growth of Butyrivibrio fibrisolvens SH13 was abolished. The growth of Prevotella (Bacteroides) ruminicola B(1)4 was stimulated, and that of Selenomonas ruminantium Z108 was unaffected. Protozoal activity, as measured by the breakdown of 14C-leucine-labelled S. ruminantium in rumen fluid incubated in vitro, was abolished by the addition of 1% extract. The antimicrobial activities were unaffected by precipitating tannins with polyvinylpyrrolidone, but a butanol extract, containing the saponin fraction, retained its antibacterial and antiprotozoal effects. Saponins from other sources were less effective against protozoa than Y. shidigera saponins. Y. shidigera extract, therefore, appears unlikely to influence ammonia concentration in the rumen directly, but its saponins have antimicrobial properties, particularly in suppressing ciliate protozoa, which may prove beneficial to ruminal fermentation and may lead indirectly to lower ruminal ammonia concentrations.

Ammonia↗
PubMed1994

Initial clarithromycin monotherapy for Mycobacterium avium-intracellulare complex lung disease.

Sputum conversion rates in Mycobacterium avium-intracellulare (MAI) complex lung disease have ranged from only 50 to 80% despite the use of three to five antituberculosis agents. We initiated a prospective, open, noncomparative trial of initial clarithromycin monotherapy at 500 mg twice a day for 4 months in HIV-negative patients with MAI lung disease. The primary study end point was microbiologic improvement. Of 30 patients enrolled, 20 completed therapy. This latter group was predominantly male (60%), smokers (70%), older than 45 yr of age (90%), infected with Mycobacterium intracellulare (70%) and with bilateral disease (85%). Of 19 patients with pretreatment minimum inhibitory concentrations (MIC) for clarithromycin < 16 micrograms/ml, 58% became sputum-negative, and 21% showed significant reductions in sputum positivity. Heavily positive sputum cultures (> 200 colonies) were reduced from 30 to 47 samples pretherapy (64%) to three of 54 (6%) post-therapy (p < 0.0001); 18 of 19 patients (95%) showed an improvement in sputum cultures, chest radiographs, or both. Only two patients (7%) discontinued the drug because of adverse events. Only three (16%) of 19 isolates developed clarithromycin resistance (MIC > 32 micrograms/ml). Clarithromycin-susceptible and -resistant MAI isolates from the same patient had identical DNA large-restriction fragment patterns. Clarithromycin is the first single agent to be shown efficacious in the treatment of MAI lung disease.

Adult↗
PubMed1994

Ruminal microbiology, biotechnology, and ruminant nutrition: progress and problems.

Present methods for manipulating ruminal fermentation that involve microbial biotechnology include dietary ionophores, antibiotics, and microbial feed additives. Developments in recombinant DNA technology mean that future methods will have a much wider scope. It has been suggested that genetically engineered ruminal microorganisms will be used in future to improve ruminal fermentation. Several technical objectives must be achieved before that will be possible. First, methods for inserting foreign or modified genes into ruminal microorganisms and ensuring their efficient expression must be developed. Broad host range plasmids and transposons have been used successfully to introduce new DNA into ruminal bacteria, as have shuttle vectors constructed as chimeras of plasmids from ruminal species and Escherichia coli. Although so far only antibiotic resistance markers have been transferred, the prospects for introducing other genes into selected ruminal bacteria are excellent. Second, the expression of the gene product(s) should be known to be nutritionally useful in vivo. A few examples of this type of benefit have been demonstrated, and many more proposed, including polysaccharidases for improving fiber digestion, methods for improving the amino acid composition of ruminal bacteria, and breakdown of plant toxins. Third, the difficulty that has been examined least, yet may prove most difficult to overcome, is that mechanisms have to be found for introducing and maintaining the new strain in the mixed ruminal population. Factors governing the survival of new strains in vivo are ill-understood, and attempts to select in favor of added new organisms have so far been unsuccessful. Because of the last obstacle, it may be advantageous, at least in the short term, to use nonruminal organisms, such as Saccharomyces cerevisiae, rather than indigenous ruminal species as a vehicle for implementing the benefits of recombinant DNA technology to ruminal fermentation. Yeast is already in widespread use as a feed additive, so no enrichment is necessary; and its genetics are already well known. Alternatively, adding particular enzymes to the diet may achieve some of the objectives described above, with the advantage that the manipulation could be achieved without the release of a recombinant microorganism.

Animal Nutritional Physiological Phenomena↗