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Biomedical subjects

H F Chambers

Publications and source records attributed to H F Chambers.

At least 19 recordsLinked to original sources
PubMed2001

Chemokine receptor 2 serves an early and essential role in resistance to Mycobacterium tuberculosis.

Although the protective cellular immune response to Mycobacterium tuberculosis requires recruitment of macrophages and T lymphocytes to the site of infection, the signals that regulate this trafficking have not been defined. We investigated the role of C-C chemokine receptor 2 (CCR2)-dependent cell recruitment in the protective response to M. tuberculosis. CCR2(-/-) mice died early after infection and had 100-fold more bacteria in their lungs than did CCR2(+/+) mice. CCR2(-/-) mice exhibited an early defect in macrophage recruitment to the lung and a later defect in recruitment of dendritic cells and T cells to the lung. CCR2(-/-) mice also had fewer macrophages and dendritic cells recruited to the mediastinal lymph node (MLN) after infection. T cell migration through the MLN was similar in CCR2(-/-) and CCR2(+/+) mice. However, T cell priming was delayed in the MLNs of the CCR2(-/-) mice, and fewer CD4(+) and CD8(+) T cells primed to produce IFN-gamma accumulated in the lungs of the CCR2(-/-) mice. These data demonstrate that cellular responses mediated by activation of CCR2 are essential in the initial immune response and control of infection with M. tuberculosis.

Animals↗
PubMed2001

A proteolytic transmembrane signaling pathway and resistance to beta-lactams in staphylococci.

beta-Lactamase and penicillin-binding protein 2a mediate staphylococcal resistance to beta-lactam antibiotics, which are otherwise highly clinically effective. Production of these inducible proteins is regulated by a signal-transducing integral membrane protein and a transcriptional repressor. The signal transducer is a fusion protein with penicillin-binding and zinc metalloprotease domains. The signal for protein expression is transmitted by site-specific proteolytic cleavage of both the transducer, which autoactivates, and the repressor, which is inactivated, unblocking gene transcription. Compounds that disrupt this regulatory pathway could restore the activity of beta-lactam antibiotics against drug-resistant strains of staphylococci.

Amino Acid Motifs↗
PubMed2001

Identifying pulmonary tuberculosis in patients with negative sputum smear results.

BACKGROUND: Clinicians need to decide whether to begin empiric therapy for patients who are suspected of having tuberculosis (TB) but have negative sputum smear results. Culture results may take weeks, and delaying treatment may allow further transmission of disease. STUDY OBJECTIVE: To identify the clinical, demographic, and radiographic characteristics that identify smear-negative patients who have TB, and to create a TB prediction rule. DESIGN: Retrospective chart review. SETTING: University-affiliated public hospital in San Francisco, CA, between 1993 and 1998. PATIENTS: Forty-seven patients with TB and 141 control patients who were hospitalized with a suspicion of pulmonary TB; all had negative sputum smear results. MEASUREMENTS AND RESULTS: Demographic, clinical, and radiographic variables were determined by chart review. In multivariate analysis, a positive tuberculin skin test result (odds ratio [OR], 4.8; 95% confidence interval [CI], 2.0 to 11.9) was independently associated with an increased risk of a positive TB culture finding. A radiographic pattern not typical of pulmonary tuberculosis (OR, 0.3; 95% CI, 0.1 to 0.7) and expectoration with cough (OR, 0.3; 95% CI, 0.1 to 0.6) were predictive of a decreased risk. An interaction between HIV seropositivity and mediastinal lymphadenopathy on the chest radiograph was also associated with a positive TB culture result (OR, 7.2; 95% CI, 1.4 to 36.0). The TB prediction score (TPS) was created with widely ranging likelihood ratios that could affect the posterior probability of TB by 30-fold. CONCLUSION: The TPS put into context with the overall prevalence of TB in a given area may help clinicians decide if a patient with negative sputum smear results should start empiric antituberculous therapy or wait for culture results. These results need prospective validation.

Adult↗
PubMed1999

The role of glycopeptide antibiotics in the treatment of infective endocarditis.

There are several sets of guidelines for the treatment of infective endocarditis, reflecting the need for differing treatment in various countries and times. This review considers the need for differing treatment modalities and in particular the utility of the glycopeptide antibiotics vancomycin and teicoplanin. Specific recommendations are offered as to when to consider the use of glycopeptides, appropriate dosage, length of treatment course and whether to use monotherapy or combined therapy. Used judiciously, the glycopeptides give results as good as can be achieved with other antimicrobial agents without exceptional toxicity. The potential of teicoplanin for use in the outpatient treatment of infective endocarditis is considered.

Anti-Bacterial Agents↗
PubMed1999

A randomized clinical trial of mupirocin in the eradication of Staphylococcus aureus nasal carriage in human immunodeficiency virus disease.

Seventy-six human immunodeficiency virus (HIV)-infected patients with Staphylococcus aureus nasal carriage were randomized to treatment groups receiving intranasal mupirocin or placebo twice daily for 5 days. Nasal cultures for S. aureus were obtained at 1, 2, 6, and 10 weeks after therapy. At 1 week, 88% of mupirocin-treated patients had negative nasal cultures compared with 8% in placebo patients (P<.001). The percentage of mupirocin-treated patients with persistently negative nasal cultures decreased over time (63%, 45%, and 29% at 2, 6, and 10 weeks, respectively) but remained significantly greater than the placebo group (3% at 2, 6, and 10 weeks). In mupirocin-treated patients, most (16/19) instances of nasal recolonization were with pretreatment strains (determined by means of by pulsed field gel electrophoresis); mupirocin resistance was not observed. Five days of treatment with mupirocin eliminated S. aureus nasal carriage in HIV-infected patients for several weeks; however, since the effect waned over time, intermittent dosing regimens should be considered for long-term eradication.

AIDS-Related Opportunistic Infections↗
PubMed1999

Penicillin-binding protein-mediated resistance in pneumococci and staphylococci.

Target alteration underlies resistance to beta-lactam antibiotics in both Staphylococcus species and Streptococcus pneumoniae. The penicillin-binding protein (PBP) targets in penicillin-resistant strains of S. pneumoniae are modified, low-binding-affinity versions of the native PBPs. Multiple PBP targets may be modified by transformation and homologous recombination with DNA from PBP genes of viridans streptococci. The level of resistance is determined by how many and to what extent targets are modified. In contrast, methicillin resistance in staphylococci is due to expression of PBP 2a, a novel, low-affinity PBP for which there is no homologue in methicillin-susceptible strains. PBP 2a is encoded by mecA, a highly conserved gene most likely acquired by a rare transposition from Staphylococcus sciuri or a closely related ancestor. Expression of resistance can be highly variable, but this seems not to be determined by PBP modifications. Several non-PBP factors are required for high-level resistance.

Amino Acid Sequence↗
PubMed1999

Efficacy of levofloxacin for experimental aortic-valve endocarditis in rabbits infected with viridans group streptococcus or Staphylococcus aureus.

Levofloxacin is among the more active fluoroquinolones against streptococci and staphylococci. It is effective against moderately severe infections caused by these organisms, but its efficacy in the treatment of bacteremia and serious infections such as endocarditis is not well defined. We compared the efficacy of levofloxacin to those of standard agents in the rabbit model of aortic-valve endocarditis caused by fluoroquinolone-susceptible strains including a penicillin-susceptible strain of Streptococcus sanguis, a penicillin-resistant strain of Streptococcus mitis, a methicillin-resistant strain of Staphylococcus aureus, and a methicillin-susceptible strain of S. aureus. Levofloxacin administered intramuscularly at dosages of 20 to 40 mg/kg of body weight twice daily (b.i.d.) was completely ineffective against the penicillin-susceptible strain, with mean vegetation titers after 3 days of therapy not statistically significantly different from those for controls. Levofloxacin was no more effective than penicillin against the penicillin-resistant strain. Levofloxacin administered for 4 days at a dosage of 20 mg/kg b.i.d. was at least as effective as vancomycin administered intravenously at a dosage of 25 mg/kg b.i. d. against the methicillin-resistant S. aureus strain and was as effective as nafcillin administered intramuscularly at 100 mg three times daily against the methicillin-susceptible strain. Emergence of resistance to levofloxacin in vitro was less likely to occur than resistance to ciprofloxacin, and resistance to levofloxacin was not observed in vivo. Levofloxacin-rifampin combinations were antagonistic in vitro and in vivo. Levofloxacin was highly effective as a single agent against experimental staphylococcal endocarditis but was surprisingly ineffective against streptococcal endocarditis, suggesting that it has a potential role as treatment for serious S. aureus but not viridans group streptococcal infections in humans.

Animals↗
PubMed1998

A randomized comparison of the safety and efficacy of once-daily gentamicin or thrice-daily gentamicin in combination with ticarcillin-clavulanate.

PURPOSE: The primary purpose of the clinical trial was to assess the safety and efficacy of once-a-day compared with three-times-a-day gentamicin in patients with serious infections who had protocol-determined peak serum aminoglycoside concentrations. PATIENTS AND METHODS: A total of 249 hospitalized patients with suspected or proven serious infections were randomized in a 2:2:1 ratio to gentamicin given three times a day with ticarcillin-clavulanate (TC), gentamicin once a day with TC, or ticarcillin-clavulanate (TC) alone. The gentamicin once-a-day dosage for patients with estimated creatinine clearance values of > or =80 mL/min was 5.1 mg/kg. With lower creatinine clearance estimates, the mg/kg dosage of gentamicin was decreased, and the dosage intervals (once daily or three times a day) were maintained. Evaluability required documentation of achievement of protocol-defined peak serum gentamicin levels. RESULTS: Of the total 175 evaluable patients, there were no significant differences found between treatment regimens with respect to clinical or microbiologic efficacy. Bedside audiometry proved impractical due to the frequency of altered mental state in ill patients. Based on the traditional increase in serum creatinine values from baseline values, no differences in renal toxicity between the treatment groups was identified. When changes in renal function were reanalyzed based on maintaining, as opposed to worsening, of renal function, preservation of renal function was better in the gentamicin once-a-day patients as opposed to the gentamicin three-times-a-day patients, P <0.01. CONCLUSIONS: Gentamicin once a day plus TC, gentamicin three times a day plus TC, and TC alone had similar effects in seriously ill hospitalized patients. The incidence of nephrotoxicity was similar in the three treatment groups. Using a nonvalidated post-hoc analysis, renal function was better preserved in gentamicin once-a-day + TC and TC-only patients as opposed to gentamicin three-times-a-day + TC.

Adult↗
PubMed1998

Activity of amoxicillin/clavulanate in patients with tuberculosis.

Some beta-lactam antibiotics are active in vitro against Mycobacterium tuberculosis. There are anecdotal reports of successful treatment of tuberculosis caused by multiple-drug-resistant strains of M. tuberculosis with regimens that included amoxicillin/clavulanate. Reduction of M. tuberculosis in the sputum of patients with pulmonary tuberculosis during administration of amoxicillin/clavulanate was measured by a quantitative culture method to determine the activity in vivo. Patients were randomized to receive isoniazid, ofloxacin, or amoxicillin/clavulanate for 7 days. Isoniazid was the most effective agent, reducing M. tuberculosis after 2 days at a mean rate (+/- standard deviation) of 0.60 +/- 0.30 log10 cfu/mL per day, compared with 0.32 +/- 0.05 and 0.34 +/- 0.03 for ofloxacin and amoxicillin/clavulanate, respectively. The early bactericidal activity of amoxicillin/clavulanate was comparable to that reported for antituberculous agents other than isoniazid. Further studies of beta-lactam antibiotics with in vitro activity against M. tuberculosis are warranted to define their role in treatment of tuberculosis.

Adolescent↗
PubMed1998

Comparative efficacy of trovafloxacin in experimental endocarditis caused by ciprofloxacin-sensitive, methicillin-resistant Staphylococcus aureus.

The new fluoroquinolone trovafloxacin was tested against a ciprofloxacin-sensitive, methicillin-resistant Staphylococcus aureus strain in the rabbit model of endocarditis. Trovafloxacin was more effective than vancomycin (CFU/g of vegetation, 2.65 +/- 1.87 versus 4.54 +/- 2.80 [mean +/- standard deviation]; P < 0.05) or ampicillin-sulbactam plus rifampin (4.9 +/- 1.1 CFU/g). The addition of ampicillin-sulbactam to trovafloxacin tended to reduce titers further.

Animals↗
PubMed1998

The abilities of a Staphylococcus epidermidis wild-type strain and its slime-negative mutant to induce endocarditis in rabbits are comparable.

The abilities of a parent and mutant pair of Staphylococcus epidermidis strains, the slime-producing parent RP62A and its slime-negative mutant, to establish endocarditis in a rabbit model of aortic valve endocarditis and to accumulate and adhere to surfaces in vitro were compared. Vegetation titer and infection rate depended on the presence or absence of a catheter (P = 0.020) and on inoculum size (P < 0.001) but not on the infecting strain. The ability of the parent strain vis-à-vis its mutant to accumulate in vitro on surfaces as demonstrated in a slime test did not correlate with any enhancement in the development of endocarditis in the rabbit model. In vitro initial adherence rates were identical. Both isolates accumulated to the same reduced extent in vitro in the presence of serum, albumin, or gelatin. Adhesion was equally promoted by addition of fibronectin. These data suggest that the in vitro phenomenon of accumulation described as slime production in the absence of serum may not be an important virulence determinant in vivo.

Animals↗
PubMed1997

Cloning and sequence analysis of a class A beta-lactamase from Mycobacterium tuberculosis H37Ra.

A cosmid library from Mycobacterium tuberculosis H37Ra was introduced into Mycobacterium smegmatis, and eight recombinant clones with increased resistance to cefoxitin were identified. Isoelectric focusing detected an M. tuberculosis-derived beta-lactamase in one of these recombinant clones. A sequence analysis identified it as a class A beta-lactamase whose expression correlated with the increased resistance phenotype.

Amino Acid Sequence↗
PubMed1997

Methicillin resistance in staphylococci: molecular and biochemical basis and clinical implications.

Methicillin resistance in staphylococci is determined by mec, composed of 50 kb or more of DNA found only in methicillin-resistant strains. mec contains mecA, the gene for penicillin-binding protein 2a (PBP 2a); mecI and mecR1, regulatory genes controlling mecA expression; and numerous other elements and resistance determinants. A distinctive feature of methicillin resistance is its heterogeneous expression. Borderline resistance, a low-level type of resistance to methicillin exhibited by strains lacking mecA, is associated with modifications in native PBPs, beta-lactamase hyperproduction, or possibly a methicillinase. The resistance phenotype is influenced by numerous factors, including mec and beta-lactamase (bla) regulatory elements, fem factors, and yet to be identified chromosomal loci. The heterogeneous nature of methicillin resistance confounds susceptibility testing. Methodologies based on the detection of mecA are the most accurate. Vancomycin is the drug of choice for treatment of infection caused by methicillin-resistant strains. PBP 2a confers cross-resistance to most currently available beta-lactam antibiotics. Investigational agents that bind PBP 2a at low concentrations appear promising but have not been tested in humans. Alternatives to vancomycin are few due to the multiple drug resistances typical of methicillin-resistant staphylococci.

Anti-Bacterial Agents↗
PubMed1996

Atovaquone inhibits the glucuronidation and increases the plasma concentrations of zidovudine.

The pharmacokinetic interaction between atovaquone, a 1,4-hydroxynaphthoquinone, and zidovudine was examined in an open, randomized, three-phase crossover study in 14 patients infected with human immunodeficiency virus. Atovaquone (750 mg every 12 hours) and zidovudine (200 mg every 8 hours) were given orally alone and in combination. Atovaquone significantly increased the area under the zidovudine concentration-time curve (AUC) (1.82 +/- 0.62 micrograms.hr/ml versus 2.39 +/- 0.68 micrograms.hr/ml; p < 0.05) and decreased the oral clearance of zidovudine (2029 +/- 666 ml/min versus 1512 +/- 464 ml/min; p < 0.05). In contrast, atovaquone tended to decrease the AUC of zidovudine-glucuronide (7.31 +/- 1.51 micrograms.hr/ml versus 6.89 +/- 1.42 micrograms.hr/ml; p < 0.1) and significantly decreased the ratio of AUC zidovudine-glucuronide/AUC zidovudine (4.48 +/- 1.94 versus 3.12 +/- 1.1; p < 0.05). The maximum concentration of zidovudine-glucuronide was significantly lowered by atovaquone (5.7 +/- 1.5 versus 4.57 +/- 0.97 micrograms/ml; p < 0.05). Zidovudine had no effect on the pharmacokinetic disposition of atovaquone. Atovaquone appears to increase the AUC of zidovudine by inhibiting the glucuronidation of zidovudine.

Adult↗
PubMed1996

Burden of Mycobacterium tuberculosis in sputum samples can be reliably determined using a quantitative, non-radioactive polymerase chain reaction assay.

OBJECTIVE: To develop a rapid assay for quantitation of Mycobacterium tuberculosis in sputum samples using the competitive polymerase chain reaction (PCR) and a colorimetric microtiter well detection format. DESIGN: The assay relies on the co-amplification of a 419 base pair (bp) pab fragment of M. tuberculosis together with a target template (pab/tet) made by splicing a fragment of tet excised from pbr322 between the 5' and 3' ends of the pab fragment to create a 380 bp hybrid template amplified with the same primers but readily distinguishable using probes specific for either pab or tet. RESULTS: We demonstrate a good correlation between the results obtained using this assay and the results of quantitative culture. CONCLUSION: This assay provides quantitative information regarding M. tuberculosis burden in samples containing between 10(3) and 10(8) colony forming units/milliliter (CFU/ml).

Animals↗
PubMed1996

Treatment of Staphylococcus aureus catheter-related infection and infective endocarditis with granulocyte colony-stimulating factor in the experimental rabbit model.

The role of granulocyte colony-stimulating factor with and without antibiotics in the treatment of catheter-related infection and infective endocarditis caused by methicillin-susceptible Staphylococcus aureus was assessed in the experimental rabbit model. Granulocyte colony-stimulating factor stimulated leukocytosis in infected animals but did not increase the clearance of methicillin-susceptible S. aureus from peripheral blood, subcutaneous port catheters, intravascular cardiac catheters, or aortic valve vegetations.

Animals↗
PubMed1996

Gyrase mutations in laboratory-selected, fluoroquinolone-resistant mutants of Mycobacterium tuberculosis H37Ra.

To characterize mechanisms of resistance to fluoroquinolones by Mycobacterium tuberculosis, mutants of strain H37Ra were selected in vitro with ofloxacin. Their quinolone resistance-determining regions for gyrA and gyrB were amplified and sequenced to identify mutations in gyrase A or B. Three types of mutants were obtained: (i) one mutant (TKp1) had no mutations in gyrA or gyrB; (ii) mutants that had single missense mutations in gyrA, and (iii) mutants that had two missense mutations resulting in either two altered gyrase A residues or an altered residue in both gyrases A and B. The TKp1 mutant had slightly reduced levels of uptake of [14C]norfloxacin, which was associated with two- to fourfold increases in the MICs of ofloxacin, ciprofloxacin, and sparfloxacin. Gyrase mutations caused a much greater increase in the MICs of fluoroquinolones. For mutants with single gyrA mutations, the increases in the MICs were 4- to 16-fold, and for mutants with double gyrase mutations, the MICs were increased 32-fold or more compared with those for the parent. A gyrA mutation in TKp1 secondary mutants was associated with 32- to 128-fold increases in the MICs of ofloxacin and ciprofloxacin compared with the MICs for H37Ra and an eight-fold increase in the MIC of sparfloxacin. Sparfloxacin was the most active fluoroquinolone tested. No sparfloxacin-resistant single-step mutants were selected at concentrations of > 2.5 micrograms/ml, and high-level resistance (i.e., MIC, > and = 5 micrograms/ml) was associated with two gyrase mutations. Mutations in gyrB and possibly altered levels of intracellular accumulation of drug are two additional mechanisms that may be used by M. tuberculosis in the development of fluoroquinolone resistance. Because sparfloxacin is more active in vitro and selection of resistance appears to be less likely to occur, it may have important advantage over ofloxacin or ciprofloxacin for the treatment of tuberculosis.

Anti-Infective Agents↗