Biomedical subjects

J L Johnson

Publications and source records attributed to J L Johnson.

At least 127 records · Page 7Linked to original sources

PubMed1999

Forming the phosphate layer in reconstituted horse spleen ferritin and the role of phosphate in promoting core surface redox reactions.

Apo horse spleen ferritin (apo HoSF) was reconstituted to various core sizes (100-3500 Fe3+/HoSF) by depositing Fe(OH)3 within the hollow HoSF interior by air oxidation of Fe2+. Fe2+ and phosphate (Pi) were then added anaerobically at a 1:4 ratio, and both Fe2+ and Pi were incorporated into the HoSF cores. The resulting Pi layer consisted of Fe2+ and Pi at about a 1:3 ratio which is strongly attached to the reconstituted ferritin mineral core surface and is stable even after air oxidation of the bound Fe2+. The total amount of Fe2+ and Pi bound to the iron core surface increases as the core volume increases up to a maximum near 2500 iron atoms, above which the size of the Pi layer decreases with increasing core size. Mössbauer spectroscopic measurements of the Pi-reconstituted HoSF cores using 57Fe2+ show that 57Fe3+ is the major species present under anaerobic conditions. This result suggests that the incoming 57Fe2+ undergoes an internal redox reaction to form 57Fe3+ during the formation of the Pi layer. Addition of bipyridine removes the 57Fe3+ bound in the Pi layer as [57Fe(bipy)3]2+, showing that the bound 57Fe2+ has not undergone irreversible oxidation. This result is related to previous studies showing that 57Fe2+ bound to native core is reversibly oxidized under anaerobic conditions in native holo bacterial and HoSF ferritins. Attempts to bury the Pi layer of native or reconstituted HoSF by adding 1000 additional iron atoms were not successful, suggesting that after its formation, the Pi layer "floats" on the developing iron mineral core.

Animals↗

PubMed1999

Posthemorrhagic shock mesenteric lymph primes circulating neutrophils and provokes lung injury.

Mesenteric lymph has recently been invoked as an avenue for gut-derived factors that may result in distant organ injury following hemorrhagic shock. We demonstrate that posthemorrhagic shock mesenteric lymph primes neutrophils (PMNs) and causes lung injury. Methods. Mesenteric lymph was collected from Sprague-Dawley rats from their mesenteric lymph duct prior to, during, and following hemorrhagic shock (MAP 40 for 90 min). The rats were then resuscitated with shed blood plus lactated Ringers (2X shed blood) over 3 h. Lung leak was assessed by transudation of Evan's blue dye into the alveolus as measured by bronchoalveolar lavage. Isolated human PMNs were incubated with 1 and 10% lymph; priming was measured by the fMLP (1 microM)-stimulated production of superoxide and surface expression of CD11b determined by flow cytometry. Results. Mesenteric lymph flow increased significantly during resuscitation: preshock 144.4 microl/h, shock 44.5 microl/h, resuscitation 566.6 microl/h. Furthermore, diversion of this lymph abrogated lung injury as compared to rats without lymph diversion. Finally, mesenteric lymph from postshock animals primed PMNs for superoxide production (nearly three times control cells) as well as increased surface expression of CD11b (2-fold over control). Conclusion. Mesenteric lymph primes PMNs and causes lung injury following hemorrhagic shock. Mesenteric lymph provides a conduit for proinflammatory mediators that may participate in the pathogenesis of MOF.

Animals↗

PubMed1999

Redox reactivity of animal apoferritins and apoheteropolymers assembled from recombinant heavy and light human chain ferritins.

The redox reactivities of air-oxidized apo horse spleen ferritin (HoSF) and apo rat liver ferritin (RaF) were examined by microcoulometry and reductive optical titrations. Microcoulometry on several independent lots of commercial HoSF revealed two distinct types of redox activity: one requiring 3-4 electrons and one requiring 6-7 electrons for full reduction of the protein shell. ApoRaF required 8-9 electrons to fully reduce the oxidized form. Reductive optical titrations confirmed the microcoulometric reduction stoichiometry and, in addition, showed that the spectra of both oxidized and reduced apoHoSF were distinct and possessed absorbances tailing into the visible region. The redox reactivity of both apoRaF and apoHoSF correlated with their H-subunit composition. Identical microcoulometric and optical experiments were conducted with recombinant apo human liver heavy (rHuHF) and light (rHuLF) ferritins, but neither was redox-active. These results suggest that the redox reactivity of native ferritins is due to their heteropolymeric nature. This was confirmed by mixing various proportions of rHuHF and rHuLF, dissociating the 24-mers into individual subunits with guanidine hydrochloride at pH 3.5, and renaturing to form heteropolymeric 24-mers. Microcoulometric measurements of these apoheteropolymers reassembled in vitro showed that they were redox-active like their native apoheteropolymer counterparts. The redox activity of these apoheteropolymers increased with H-subunit composition, reached a maximum near 12 H- and 12 L-subunits, and then declined to zero with increasing L-subunit composition. The decline in redox reactivity at high L-subunit concentrations indicates that both H- and L-subunits are involved in forming the observed redox centers. Apoheteropolymers formed from rHuLF and W93F (an H-chain mutant) were redox-inactive, suggesting that the conserved tryptophan is necessary for redox center formation.

Animals↗

PubMed1999

A K319N/E325Q double mutant of the lactose permease cotransports H+ with lactose. Implications for a proposed mechanism of H+/lactose symport.

In this study, we have examined the transport characteristics of the wild-type lactose permease, single mutants in which Lys-319 was changed to asparagine or alanine or Glu-325 was changed to glutamine or alanine, and the corresponding double mutant strains. The wild-type and Asn-319 mutant showed high levels of lactose uptake, with Km values of 0.42 and 1.30 mM and Vmax values of 102.6 and 48.3 nmol of lactose/min/mg of protein, respectively. The Asn-319/Gln-325 strain had a normal Km of 0.36 mM and a moderate Vmax of 18.5 nmol of lactose/min/mg of protein. By comparison, the single E325Q strain had a normal Km of 0.27 mM but a very defective Vmax of 1.3 nmol of lactose/min/mg of protein. A similar trend was observed among the alanine substitutions at these positions, although the Vmax values were lower for the Ala-319 mutations. When comparing the Vmax values between the single position 325 mutants with those of the double mutants, these results indicate that neutral 319 mutations substantially alleviate a defect in Vmax caused by neutral 325 mutations. With regard to H+/lactose coupling, the wild-type permease is normally coupled and can transport lactose against a gradient. The position 325 single mutants showed no evidence of H+ transport with lactose or thiodigalactoside (TDG) and were unable to facilitate uphill lactose transport. The single Asn-319 mutant and double Asn-319/Gln-325 mutant were able to transport H+ upon the addition of lactose or TDG. In addition, both of these strains catalyzed a sugar-dependent H+ leak that inhibited cell growth in the presence of TDG. These two strains were also defective in uphill transport, which may be related to their sugar-dependent leak pathway. Based on these and other results in the literature, a model is presented that describes how the interactions among several ionizable residues within the lactose permease act in a concerted manner to control H+/lactose coupling. In this model, Lys-319 and Glu-325 play a central role in governing the ability of the lactose permease to couple the transport of H+ and lactose.

Alanine↗

PubMed1999

Efficacy of bilateral prophylactic mastectomy in women with a family history of breast cancer.

BACKGROUND: Options for women at high risk for breast cancer include surveillance, chemoprevention, and prophylactic mastectomy. The data on the outcomes for surveillance and prophylactic mastectomy are incomplete. METHODS: We conducted a retrospective study of all women with a family history of breast cancer who underwent bilateral prophylactic mastectomy at the Mayo Clinic between 1960 and 1993. The women were divided into two groups - high risk and moderate risk - on the basis of family history. A control study of the sisters of the high-risk probands and the Gail model were used to predict the number of breast cancers expected in these two groups in the absence of prophylactic mastectomy. RESULTS: We identified 639 women with a family history of breast cancer who had undergone bilateral prophylactic mastectomy: 214 at high risk and 425 at moderate risk. The median length of follow-up was 14 years. The median age at prophylactic mastectomy was 42 years. According to the Gall model, 37.4 breast cancers were expected in the moderate-risk group; 4 breast cancers occurred (reduction in risk, 89.5 percent; P<0.001). We compared the numbers of breast cancers among the 214 high-risk probands with the numbers among their 403 sisters who had not undergone prophylactic mastectomy. Of these sisters, 38.7 percent (156) had been given a diagnosis of breast cancer (115 cases were diagnosed before the respective proband's prophylactic mastectomy, 38 were diagnosed afterward, and the time of the diagnosis was unknown in 3 cases). By contrast, breast cancer was diagnosed in 1.4 percent (3 of 214) of the probands. Thus, prophylactic mastectomy was associated with a reduction in the incidence of breast cancer of at least 90 percent. CONCLUSIONS: In women with a high risk of breast cancer on the basis of family history, prophylactic mastectomy can significantly reduce the incidence of breast cancer.

Adolescent↗

PubMed1999

Psychiatric patients and treatments in 1997: findings from the American Psychiatric Practice Research Network.

Despite extensive studies on the epidemiology of mental disorders and advances in the treatment of these conditions, there is a paucity of detailed information concerning the characteristics of psychiatric patients and how treatments are administered in routine psychiatric practice. This 1997 observational study collected detailed information from 417 psychiatrists on the demographic, diagnostic, clinical, and treatment characteristics of a systematic sample of 1228 patients. Six hundred thirty-seven patients (51.9%) were women and the mean patient age was 41.9 years. The most common diagnostic category (53.7%) was mood disorders, followed by schizophrenia/psychotic disorders (14.6%), anxiety disorders (9.3%), and disorders of childhood (7.7%). Six hundred seventy-one patients (54.6%) had at least one comorbid Axis I condition and almost half (49.8%) had a history of psychiatric hospitalization. Patients received a mean of 2.0 psychotherapeutic medications, most commonly antidepressants (62.3%). Findings demonstrate that psychiatrists in routine practice treat a patient population with severe, complex conditions.

Adolescent↗

PubMed1999

Extracellular signal-related kinase 1/2 and p38 mitogen-activated protein kinase pathways serve opposite roles in neutrophil cytotoxicity.

BACKGROUND: Inflammatory stimuli rapidly activate mitogen-activated protein kinases (MAPKs) in neutrophils (PMNs). However, their role in cytotoxic function remains unknown. Elucidating the signals involved in release of cytotoxic agents from PMNs may provide new avenues for therapy in diseases of diminished or excessive PMN function. HYPOTHESIS: The p38 MAPK and extracellular signal-related kinase 1/2 (ERK1/2) modulate superoxide generation and elastase release in activated human PMNs. STUDY DESIGN: Isolated human PMNs were incubated with specific inhibitors of MAPK pathways, or vehicle control solution, before activation with the bacterial peptide f-Met-Leu-Phe. MAIN OUTCOME MEASURES: The rate of superoxide release from activated PMNs was measured by the superoxide dismutase-inhibitable reduction of cytochrome-c. Elastase release from PMNs was determined by cleavage of the substrate Ala-Ala-Pro-Val-pNA. RESULTS: Superoxide release from activated PMNs was inhibited by blockade of p38 MAPK activation but unaffected by blockade of ERK1/2. Conversely, elastase release was unaffected by p38 MAPK inhibition and increased by ERK1/2 inhibition. CONCLUSIONS: Activation of p38 MAPK promotes superoxide release from PMNs activated by f-Met-Leu-Phe. The ERK1/2 pathway may serve as a negative feedback mechanism for granule exocytosis.

Cytotoxicity, Immunologic↗

PubMed1999

Disparities in the respiratory burst between human and rat neutrophils.

The importance of reactive oxygen species (ROS) in neutrophil (PMN)-mediated injury to host tissues has been strongly implicated in a number of animal models. Peculiarities of the laboratory rat PMN, including an apparent paucity of superoxide release, prompted us to examine disparities in the respiratory burst between human and rat PMNs. Using isolated PMNs, we examined oxygen consumption, superoxide release, nitrate/nitrite release, and dihydrorhodamine (DHR) oxidation in response to an array of soluble stimuli. Our findings confirm that intact rat PMNs release little superoxide in comparison to human PMNs when primed and activated by soluble stimuli. For example, PMA-activated human PMNs released superoxide at 10.1 +/- 2.7 times the rate of rat PMNs (P < 0.01). However, measurements of oxygen consumption, cell-associated oxidant production (by DHR oxidation) and release of superoxide from electroporated cells suggests that rat PMNs generate oxidants at rates equivalent to human PMNs but preferentially release them in an intracellular compartment. Implications for the study of PMN-mediated oxidant injury in animal models are discussed.

Animals↗

PubMed1999

Isolated sulfite oxidase deficiency: review of two cases in one family.

OBJECTIVE: The authors describe two cases of isolated sulfite oxidase deficiency found in one family. This is a rare autosomal-recessive disorder presenting at birth with seizures, severe neurologic disease, and ectopia lentis. It can be easily missed with metabolic screening; however, the finding of lens subluxation stresses the importance of ophthalmic assessment in making the diagnosis. DESIGN: Two observational case reports. INTERVENTION/METHODS: Ophthalmic assessment, biochemical assay for specific urinary and plasma metabolites, magnetic resonance imaging, and gene sequencing were used to make the diagnosis of the disease in the proband. The diagnosis was subsequently recognized in a previously affected sibling after the postmortem neuropathology was reviewed. Mutation analysis was performed on cultured fibroblasts from the proband to identify and categorize the specific mutation responsible for the disease in the family. From this, future prenatal detection of sulfite oxidase deficiency is possible. MAIN OUTCOME MEASURES: The diagnosis of sulfite oxidase deficiency was established in this family, enabling appropriate genetic counseling and recurrence risk estimation. RESULTS: Point mutations were found in both alleles of the sulfite oxidase gene in the proband. The first is a 623C-->A mutation, which predicts an A208D substitution, and the second is a 1109C-->A, which predicts an S370Y substitution. Both residues A208D and S370Y are critical for sulfite oxidase activity. CONCLUSIONS: Isolated sulfite oxidase deficiency is a rare heritable disease for which mutation analysis can allow accurate prenatal screening. It often is difficult to diagnose by clinical presentation alone, but the critical finding of lens subluxation accompanying seizures and diffuse neurologic disease in an infant should alert the physician to the diagnosis.

Alleles↗

PubMed1999

South Asian womens' views on the causes of breast cancer: images and explanations.

Using ethnoscience methods, interviews with 50 South Asian women living in Western Canada were conducted and analyzed to explore explanations and images of breast cancer. Embedded in the women's stories of breast cancer were distinctive, often vivid and fear-provoking images of abnormal growth. Explanations about the causes of breast cancer involved five domains of belief. The first domain was of a physical nature and centred on damage to the breast. A second domain of explanations, 'can catch it,' focused on the way this disease could be spread to others. Other women attributed breast cancer to the ways women could 'bring it upon yourself,' often linking a negative lifestyle with the development of cancer. Many women attributed cancer to being 'in the hands of others,' explaining the cancer was caused by careless words, curses or divine power. Finally, breast cancer was seen as something that could be passed down in the family. The taxonomy developed in this study provides a useful framework for understanding the explanations that might underlie women's health-seeking behaviours and for developing culturally suitable counseling strategies.

Adult↗

PubMed1999

Smoking relapse and early weaning among postpartum women: is there an association?

BACKGROUND: Smoking in the postpartum period may contribute to early weaning, although the nature and temporal aspect of the relationship are poorly understood. The objective of this study was to examine the association between early weaning and smoking relapse among women who stopped smoking during pregnancy. METHODS: A secondary analysis of data from a randomized controlled trial was conducted. The participants were 228 women who had stopped smoking for pregnancy, who participated in a smoking relapse prevention trial, and who breastfed. Women who relapsed to daily smoking postpartum were compared with those who remained abstinent or smoked occasionally. The dependent variable was breastfeeding for less than 26 weeks (early weaning). Potential covariates included intended duration of breastfeeding, parity, partner's smoking, nicotine dependence, emotional health, return to paid employment, and various sociodemographic variables. RESULTS: Approximately two-thirds (65.1%) of the women who relapsed to daily smoking weaned before 26 weeks compared with 33.8 percent of the women who remained abstinent or smoked occasionally. Controlling for intended duration of breastfeeding, education, and return to paid employment, women who resumed daily smoking were almost four times more likely to wean early than those who abstained or smoked occasionally. CONCLUSIONS: Early weaning may result from psychological or physiological changes associated with tobacco use. Smoking relapse prevention in the postpartum period may be one of the most effective interventions in ensuring that women who stop smoking for pregnancy remain stopped and breastfeed their babies for the recommended duration.

Adolescent↗

PubMed1999

The relationship between parental history and substance use severity in drug treatment patients.

The authors explored the relationship between the history of parental problematic alcohol and drug use and their adult children's alcohol and drug use disorders. Subjects were 347 admissions to an outpatient substance abuse program. There was a positive relationship between the number of parents affected by alcohol and/or drug problems and the percentage of probands with co-existing alcohol and drug use disorders for probands with alcohol use disorders but not for those with only drug abuse. Probands with two affected parents had significantly higher alcohol abuse scores and drug, family, and psychiatric composite test scores than those with a negative family history. This preliminary study indicates that the severity of a proband's substance use disorder may be influenced by parental substance use history.

Adult↗

PubMed1999

Apoptosis and T cell hyporesponsiveness in pulmonary tuberculosis.

Mycobacterium tuberculosis (MTB)-induced T cell responses are depressed in peripheral blood mononuclear cells of persons with newly diagnosed pulmonary tuberculosis (TB), and levels of interferon (IFN)-gamma remain low even after completion of antituberculous therapy. Loss of MTB-reactive T cells through apoptotic mechanisms could account for this prolonged T cell hyporesponsiveness. T cell apoptosis was studied in TB patients and healthy control subjects. Both spontaneous and MTB-induced apoptosis (in CD4 and non-CD4 T cells) from TB patients was increased when compared with healthy control subjects, whereas coculture with control antigen (candida) had no effect on T cell apoptosis in either group of study subjects. An inverse correlation existed between increased MTB-induced T cell apoptosis and IFN-gamma and interleukin (IL)-2 immunoreactivities. Successful antituberculous chemotherapy resulted in a 50% reduction in both spontaneous and MTB-induced apoptosis, which coincided with 3- and 8-fold increases in levels of MTB-stimulated IL-2 and IFN-gamma, respectively. These data indicate that apoptotic pathways are operant during active MTB infection and may contribute to deletion of MTB-reactive T cells and the immunopathogenesis of this disease.

Apoptosis↗

PubMed1999

Depressed T-cell interferon-gamma responses in pulmonary tuberculosis: analysis of underlying mechanisms and modulation with therapy.

Immunological and clinical profiles were evaluated in 2 groups: human immunodeficiency virus (HIV)-uninfected and HIV-infected patients, with newly diagnosed pulmonary tuberculosis (TB), and tuberculin-skin-test-reactive healthy control subjects. HIV-uninfected patients with TB were also followed up longitudinally during and after chemotherapy. At the time of diagnosis, purified protein derivative (PPD)-stimulated production of interferon (IFN)-gamma by peripheral blood mononuclear cells from TB patients was depressed, compared with that of healthy control subjects, whereas levels of transforming growth factor (TGF)-beta and interleukin (IL)-10 were increased. In longitudinal studies, PPD stimulated production of IL-10 and TGF-beta returned to baseline by 3 months, whereas IFN-gamma production remained depressed for at least 12 months. These data indicate that the immunosuppression of TB is not only immediate and apparently dependent (at least in part) on immunosuppressive cytokines early during the course of Mycobacterium TB infection but is also long lasting, presumably relating to a primary abnormality in T-cell function.

Adolescent↗

PubMed1999

Circulating postinjury neutrophils are primed for the release of proinflammatory cytokines.

BACKGROUND: Postinjury neutrophil (PMN) priming identifies the injured patient at risk for the subsequent development of multiple organ failure (MOF). PMN priming has previously been shown to cause enhanced release of proteases and superoxide. PMNs, however, are a rich source of proinflammatory cytokines, such as interleukin (IL)-8 and tumor necrosis factor (TNF), which have been implicated in the development of MOF. PMNs also make IL-1ra, which is an anti-inflammatory cytokine that inhibits IL-1. It is our hypothesis that postinjury PMNs are primed for increased stimulated release of the proinflammatory cytokines IL-8 and TNF but not the anti-inflammatory cytokine IL-1ra. METHODS: Twelve trauma patients with a mean Injury Severity Score of 24 (+/-4.6) and 10 elective surgical patients were studied. Postinjury PMNs were isolated from blood obtained at presentation (within 2 hours after injury) and 24 hours after trauma. PMNs from elective surgical patients were obtained preoperatively, immediately postoperatively, and at 24 hours. The PMNs were stimulated with platelet-activating factor (200 nM)/N-formyl-methionyl-leucyl-phenylalanine (1 micromol/L) or lipopolysaccharide (100 ng/mL) incubated for 24 hours in RPMI-1640, and release of IL-8, TNF, and IL-1ra were measured. RESULTS: Postinjury PMNs were primed for both platelet-activating factor/N-formyl-methionyl-leucyl-phenylalanine-stimulated and lipopolysaccharide-stimulated IL-8 and TNF release at 2 hours after injury (fourfold increase of IL-8 release and fivefold increase of TNF release), whereas elective surgical patients demonstrated no priming. In contrast, postinjury patients were not primed for increased release of the counterinflammatory cytokine IL-1ra, suggesting a specific postinjury up-regulation of IL-8 and TNF. CONCLUSION: After injury, PMNs are primed for proinflammatory cytokine release in addition to superoxide and elastase. This augmented release of IL-8 and TNF may be involved in the subsequent development of organ dysfunction and ultimately MOF.

Adult↗

PubMed1999

Postinjury suppression of human neutrophil cytokine production results from the stabilization of inhibitory kappaB.

UNLABELLED: Postinjury neutrophil (PMN) dysfunction is a well recognized event that may be responsible for increased infections. PMN cytokine production is an important component of their bactericidal capacity. When PMNs are stimulated, inhibitory factor kappaB (IkappaB) is degraded, allowing nuclear factor kappaB (NFkappaB) to translocate to the nucleus and promotes genes for the transcription of the interleukin-8 (IL-8) and tumor necrosis factor (TNF) genes. We hypothesize that similar to their late postinjury depressed superoxide production, postinjury PMNs manifest suppressed cytokine production, which is mediated by stabilization of IkappaB levels. METHODS: Twelve severely injured patients with an injury severity score (ISS) of 24 (+/-4.6) were studied as well as 10 elective surgical patients as a control. PMNs were isolated and incubated for 24 h in RPMI. PMNs were stimulated with lipopolysaccharide (LPS; 100 ng) or PAF (200 nm) and fMLP (1 microM) and release of IL-8, TNF, and interleukin-1 receptor antagonist (IL-1ra) were measured. Postinjury PMNs were also stimulated with LPS (100 ng), and IkappaB breakdown was measured at 0, 30, and 60 min using gel electrophoresis. RESULTS: Postinjury PMNs displayed a significant suppression of both IL-8 and TNF on postinjury Days 1-3, while the release of IL-1ra was preserved throughout the entire study period. In contrast, elective surgical patients demonstrated no decrease in IL-8 or TNF. Furthermore, IkappaB levels were preserved in the postinjury PMNs as compared with normal control PMNs. CONCLUSION: Postinjury PMNs have a suppressed release of both IL-8 and TNF following injury that did not occur in elective surgical patients. Furthermore, the NFkappaB/IkappaB-independent IL-1ra did not show suppression of release. In addition, stabilization of IkappaB following severe injury leads to decreased PMN IL-8 and TNF production. This genetic reprogramming may help explain PMN dysfunction and subsequent infections seen in severely injured patients.

Adult↗

PubMed1999

Pulmonary tuberculosis.

Pulmonary tuberculosis is a major cause of morbidity and mortality worldwide, resulting in the greatest number of deaths due to any one single infectious agent. This trend is due, at least in part, to increasing numbers of individuals co-infected with HIV and Mycobacterium tuberculosis (MTB). Concerted efforts between the World Health Organization and other agencies, therefore, are underway to improve tuberculosis control worldwide. These include basic research in tuberculosis diagnostics and vaccine development, institution of preventive therapy in individuals dually infected with HIV and MTB, and directly observed short-course antituberculous therapy in developing countries with a high prevalence of MTB infection. Further, newer, longer-acting antituberculous therapeutic agents such as rifapentine, which allow twice-weekly dosing in the continuation phase of anti-MTB therapy, have recently been released and are undergoing clinical trials. This review provides a synopsis of recent developments in these areas and serves as a reference source for interested readers.

Antitubercular Agents↗

PubMed1999

Drug tolerance in Mycobacterium tuberculosis.

Although Mycobacterium tuberculosis is eradicated rapidly during therapy in some patients with pulmonary tuberculosis, it can persist for many months in others. This study examined the relationship between mycobacterial drug tolerance (delayed killing in vitro), persistence, and relapse. It was performed with 39 fully drug-susceptible isolates from a prospective trial of standard short-course antituberculous therapy with sputum smear-positive, human immunodeficiency virus-uninfected subjects with pulmonary tuberculosis in Brazil and Uganda. The rate of killing in vitro was determined by monitoring the growth index (GI) in BACTEC 12B medium after addition of drug to established cultures and was measured as the number of days required for 99% sterilization. Drugs differed significantly in bactericidal activity, in the following order from greatest to least, rifampin > isoniazid-ethambutol > ethambutol (P < 0.001). Isolates from subjects who had relapses (n = 2) or in whom persistence was prolonged (n = 1) were significantly more tolerant of isoniazid-ethambutol and rifampin than isolates from other subjects (P < 0.01). More generally, the duration of persistence during therapy was predicted by strain tolerance to isoniazid and rifampin (P = 0.012 and 0.026, respectively). Tolerance to isoniazid-ethambutol and tolerance to rifampin were highly correlated (P < 0.001). Tolerant isolates did not differ from others with respect to the MIC of isoniazid; the rate of killing of a tolerant isolate by isoniazid-ethambutol was not increased at higher drug concentrations. These observations suggest that tolerance may not be due to drug-specific mechanisms. Tolerance was of the phenotypic type, although increased tolerance appeared to emerge after prolonged drug exposure in vivo. This study suggests that drug tolerance may be an important determinant of the outcome of therapy for tuberculosis.

Antitubercular Agents↗