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Biomedical subjects

M Wootton

Publications and source records attributed to M Wootton.

At least 37 records · Page 2Linked to original sources
PubMed1999

B-cell antigens within normal and activated human T cells.

In this study we compared cell surface staining for human peripheral blood lymphocyte (PBL) CD antigens by flow cytometry, with staining obtained following permeabilization of PBL using the Cytoperm method (Serotec). Six CD antigens (CD20, CD21, CD22, CD32, CD35 and major histocompatibility complex class II antigen) normally found on the surface of B cells, were also found to be expressed within T cells. We also showed, by immunoelectron microscopy, that these inappropriately expressed ('occult') CD antigens are located within cytoplasmic vesicles or within the rough endoplasmic reticulum. Following in vitro activation of T cells a distinct increase in expression of all of these cytoplasmic antigens was observed but staining at the cell surface was, by comparison, weak. We therefore propose that up-regulation of various B-cell CD antigens occurs within the cytoplasm of T cells following activation and that these antigens may be synthesized and released into the fluid-phase as soluble immunoregulatory molecules.

Antigens, CD↗
PubMed1999

The antibacterial efficacy of levofloxacin and ciprofloxacin against Pseudomonas aeruginosa assessed by combining antibiotic exposure and bacterial susceptibility.

Ciprofloxacin has a four-fold greater in-vitro activity than levofloxacin against Pseudomonas aeruginosa, but levofloxacin has a four-fold higher area under the serum concentration-time curve (AUC) for an equivalent dose. It has been proposed that the AUC/MIC ratio is a general predictor of antibacterial efficacy for quinolones. Using an in-vitro kill curve technique, performed in quadruplicate, with nine antibiotic concentrations and three strains of P. aeruginosa with varying quinolone susceptibility, we constructed sigmoidal dose-response curves for AUC(0-6.5)/MIC and area under the bacterial kill curve (AUBKC) or AUC(0-24)/MIC and log change in viable count at 24 h (delta24). For levofloxacin the log AUC(0-6.5)/MIC ratio to produce 50% of the maximal effect was 0.74 +/- 0.13 (r2 = 0.9435) for levofloxacin and 0.82 +/- 0.06 (r2 = 0.7935) for ciprofloxacin. The log AUC(0-24)/MIC ratio to produce 50% maximal effect was 1.58 +/- 0.13 (r2 = 0.7788) for levofloxacin and 1.37 +/- 0.12 (r2 = 0.7207) for ciprofloxacin. An AUC(0-24)/MIC ratio of 125 produced 85.4% of the maximal response with levofloxacin and 81.5% with ciprofloxacin. These data suggest that levofloxacin and ciprofloxacin have equivalent activity against P. aeruginosa at equivalent AUC/MIC ratios.

Anti-Infective Agents↗
PubMed1999

In-vitro activity of HMR 3647 against Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and beta-haemolytic streptococci.

The in-vitro activity of HMR 3647 and seven comparators (azithromycin, clarithromycin, erythromycin A, roxithromycin, penicillin G, ciprofloxacin and levofloxacin) were tested against 207 Streptococcus pneumoniae and 200 beta-haemolytic streptococci. Ten comparators (azithromycin, clarithromycin, erythromycin A, roxithromycin, ampicillin, co-amoxiclav, cefuroxime, cefotaxime, ciprofloxacin and levofloxacin) were tested against 143 Haemophilus influenzae and 58 Moraxella catarrhalis. The MIC50 of HMR 3647 for S. pneumoniae was < or =0.008 mg/L, less than that for the macrolides or quinolones tested. Pneumococci with an erythromycin A MIC of 0.06 mg/L (n = 23) had an MIC50 of HMR 3647 < or =0.008 mg/L, whereas isolates with an erythromycin A MIC > or =1 mg/L (n = 34) had an MIC50 of HMR 3647 of 0.03 mg/L, a four-fold increase. In contrast, the difference in macrolide MIC50s for the two groups was > or =64-fold. The MIC50s foro beta-haemolytic streptococci, classified by Lancefield group, were in the range 0.015 to 0.06 mg/L for HMR 3647. H. influenzae were categorized into three groups according to cefuroxime MIC: <1 mg/L (n = 72); 2-4 mg/L (n = 29); and >4 mg/L (n = 42). The MIC50 of HMR 3647 increased two-fold with increasing cefuroxime MICs; beta-lactam MICs increased much more markedly. The MIC50 of HMR 3647 for M. catarrhalis was 0.03 mg/L. HMR 3647 has good activity against respiratory tract pathogens but in-vitro susceptibility is affected by erythromycin A susceptibility in S. pneumoniae and beta-haemolytic streptococci.

Anti-Bacterial Agents↗
PubMed1999

Comparison of in-vitro pharmacodynamics of once and twice daily ciprofloxacin.

The pharmacodynamics of ciprofloxacin were explored in an in-vitro continuous bacterial culture model of infection, by simulating two oral dosing regimens; 0.5 g 12-hourly (bd) and 1 g 24-hourly (od). Three strains of Escherichia coli (ciprofloxacin MICs 0.03, 0.5 and 2 mg/L); two strains of Pseudomonas aeruginosa (MICs 0.09 and 1.5 mg/L), two strains of Staphylococcus aureus (MICs 0.12 and 1 mg/L) and two strains of Streptococcus pneumoniae (MICs 0.5 and 2 mg/L) were used. Three pharmacodynamic parameters, T > MIC, C(max)/MIC and AUC/MIC (T = time, C(max) = peak serum concentration, AUC = area under the curve), were compared with area under the bacterial-kill curve (AUBKC) (after transformation of the AUBKC) using a simple E(max) or sigmoidal E(max) model. AUBKC was taken to be the main antibacterial effect measure. The models were compared by inspection of residuals and Akaike information criterion. E(max) models adequately described the relationship between AUC/MIC and AUBKC and between C(max)/MIC and AUBKC, but not between T> MIC and AUBKC. All three pharmacodynamic parameters are related to each other but multiple regression analysis indicated that AUC/MIC was the best individual predictor of AUBKC. Despite this, comparison of od and bd regimens indicates some advantage to od in terms of early antibacterial effect. Serum concentration-time curve shape has some importance in determining antibacterial effect. These data indicate that for ciprofloxacin AUC/MIC ratio is not the sole determinant of antibacterial effect.

Anti-Infective Agents↗
PubMed1999

Expression and detection of hetero-vancomycin resistance in Staphylococcus aureus.

Isolates of Staphylococcus aureus resistant to vancomycin have been reported but appear to be extremely rare. However, isolates displaying hetero-resistance to vancomycin (hVRSA) are reportedly common in parts of Japan (9.3% of MRSA isolated from a group of university hospitals). We have investigated the reliability of the proposed method for detection of hetero-resistant isolates and the ability of clinical S. aureus isolates to express vancomycin resistance. The original method for identification of hVRSA was found to have poor reproducibility and may select for, rather than detect, vancomycin resistance. There appears to be a spectrum of heterogeneity in the expression of resistance to vancomycin among S. aureus. Until there is a clearer understanding of the mechanism and control of vancomycin resistance in S. aureus, and reliable tests are devised, the clinical relevance of different degrees of hetero-resistance cannot be assessed.

Anti-Bacterial Agents↗
PubMed1999

Exploration of the in-vitro pharmacodynamic activity of moxifloxacin for Staphylococcus aureus and Streptococci of lancefield groups A and G.

The serum concentrations associated with the oral administration of 400 mg moxifloxacin every 24 h over 48 h in man were simulated in an in-vitro dilutional, continuous bacterial culture model of infection. The initial inoculum was 5 x 10(7)-5 x 10(8) cfu/mL and all strains were tested on at least three occasions. Two strains of Staphylococcus aureus (one methicillin susceptible, the other resistant) with moxifloxacin MICs 0.14 mg/L and 0.06 mg/L and two strains of beta-haemolytic streptococci, Lancefield Group A, MIC 0. 16 mg/L and Group G, MIC 0.4 mg/L were used. In addition, two laboratory-generated mutants with raised moxifloxacin MICs were also employed: methicillin-sensitive S. aureus (MSSA) MIC 1.0 mg/L and Group A streptococcus MIC 1.8 mg/L. The antibacterial effect of moxifloxacin was judged by changes in viable count over time, and the area under the bacterial-kill curve (AUBKC) after 24 and 48 h. For S. aureus MIC 0.14 mg/L the AUBKC(24) (log cfu/mL.h) was 77.8 +/- 4.6 and AUBKC(48) 92.0 +/- 6.9. For its mutant, moxifloxacin MIC 1.0 mg/L, the AUBKC(24) was 116.1 +/- 15.6 and AUBKC(48) 211.9 +/- 23.1, indicating decreased killing. AUBKC(24) and AUBKC(48) values of 110.7 +/- 10.3 and 130.9 +/- 21.3, respectively, were noted for the MRSA strain. The Group A streptococcus, MIC 0.16 mg/L, had an AUBKC(24) of 91.4 +/- 19.4 and AUBKC(48) of 157.0 +/- 70.9. The mutant, MIC 1.8 mg/L, had an AUBKC(24) of 127.0 +/- 1.9 and AUBKC(48) of 205.1 +/- 6.4. Despite a lower MIC (0.4 mg/L) the single strain of Group G streptococcus tested was killed poorly, AUBKC(24) 139.9 +/- 3.6 and AUBKC(48) 252.3 +/- 18.6. The pharmacodynamic parameters AUC/MIC, T > MIC, (AUC > MIC)/MIC (AUC = area under the curve, T = time) and WAUC ((AUC/MIC) (T > MIC/100)) (WAUC = weighted area under the curve) were related to AUBKC(24) and AUBKC(48) using an inhibitory sigmoid E(max) model. T > MIC was poorly related to AUBKC (r = 0.36) while AUC/MIC, (AUC > MIC)/MIC and WAUC were strongly related to AUBKC(24) (r = 0.75-0.79) and AUBKC(48) (r = 0.78-0.84). The maximum antibacterial effect was achieved with an AUC/MIC ratio of 150-200. AUC-related pharmacodynamic parameters predicted antibacterial effect better than T > MIC.

Anti-Infective Agents↗
PubMed1999

Activity of moxifloxacin, administered once a day, against Streptococcus pneumoniae in an in vitro pharmacodynamic model of infection.

The antibacterial effect of moxifloxacin was studied by using an in vitro pharmacodynamic model of infection with dosing simulations of 400 mg every 24 h for 48 h. Streptococcus pneumoniae was tested by using four wild-type strains for which the moxifloxacin MICs were 0. 008, 0.12, 0.14, and 3.6 mg/liter. In addition, two isogenic mutants, generated from the strains for which the moxifloxacin MICs were </=0.12 mg/liter and for which the MICs were 1.0 and 1.6 mg/liter, were also used. Antibacterial efficacy was measured by the following indices: log change in viable count at 12, 24, 36, and 48 h; area under the bacterial kill curve (AUBKC); and time to kill 99.9% of the initial inoculum. With the three strains for which the moxifloxacin MICs were </=0.14 mg/liter, there was a marked reduction in viable count over 12 to 36 h; in contrast, with strains for which the MICs were >/=1.0 mg/liter, little killing occurred over 48 h. A sigmoid dose-response model indicated that the area under the curve/MIC ratio was strongly related to the log change in viable count at 24 and 48 h and to the AUBKC. These data indicate that moxifloxacin may have a role in management of S. pneumoniae infection.

Anti-Infective Agents↗
PubMed1999

Interactions between methicillin and vancomycin in methicillin-resistant Staphylococcus aureus strains displaying different phenotypes of vancomycin susceptibility.

Vancomycin-sensitive, -intermediate, and -heterointermediate methicillin-resistant Staphylococcus aureus isolates were tested by using E-tests to explore the interaction of methicillin and vancomycin. For the vancomycin-intermediate and -heterointermediate strains both drugs showed antagonism at concentrations below their MICs but synergy at methicillin concentrations near the MIC. This property could be used to screen for heterointermediate S. aureus strains.

Anti-Bacterial Agents↗
PubMed1998

In vitro activities of Y-688, a new 7-substituted fluoroquinolone, against anaerobic bacteria.

The in vitro activities of Y-688, a new 7-substituted fluoroquinolone derivative, against 317 nonduplicate anaerobic isolates were determined. Eighty-five percent of the Bacteroides fragilis group (n = 89) were inhibited by < or = 2 mg of Y-688 per liter, while 78, 100, 89, and 98% of gram-negative bacilli (n = 135), gram-positive cocci (n = 59), and non-spore-forming (n = 58) and spore-forming (n = 51) gram-positive bacilli, respectively, were inhibited by < or = 1 mg of Y-688 per liter.

Anti-Infective Agents↗
PubMed1997

Bay 12-8039, a new 8-methoxy-quinolone: comparative in-vitro activity with nine other antimicrobials against anaerobic bacteria.

The in-vitro activity of a new 8-methoxy-quinolone, Bay 12-8039, was assessed against 218 anaerobic bacteria. Ninety-eight per cent of strains belonging to the Bacteroides fragilis group (n = 65) were inhibited by < or = 2 mg/L of Bay 12-8039 whereas 97%, 94%, 94% and 100%, respectively, of Gram-negative bacilli (n = 93), non-sporing Gram-positive bacilli (n = 36), endospore-forming Gram-positive bacilli (n = 34) and Gram-positive cocci (n = 45) were also inhibited by < or = 2 mg/L. Eighty-three per cent of all anaerobes tested were inhibited by < or = 1 mg/L Bay 12-8039 and 99.5% by < or = 4 mg/L. When compared with ciprofloxacin, clinafloxacin, ofloxacin and trovafloxacin, Bay 12-8039 was more active than ciprofloxacin and ofloxacin, equipotent to trovafloxacin but not as active as clinafloxacin.

Anti-Infective Agents↗
PubMed1996

A new time-kill method of assessing the relative efficacy of antimicrobial agents alone and in combination developed using a representative beta-lactam, aminoglycoside and fluoroquinolone.

A time-kill curve employing nine sampling times over 6 h was used to provide data which were then used to develop a theoretical (best-fit) curve. From the theoretical curve parameters describing the rate of kill (alpha), time from addition of antibiotic to initiation of killing (d) and a function of the degree of killing observed (Ym/Yo) were defined. The area-under-the-curve (AUC) was calculated from the theoretical curve. The variability of each parameter was assessed using a theoretical curve to fit the data from experiments done on three occasions and in triplicate. In terms of the parameters alpha, d, Ym/Yo and AUC, no synergy was demonstrated with combinations of piperacillin/tazobactam plus ciprofloxacin or gentamicin when compared with single antibiotics. The AUC represents the best summary parameter of a time-kill curve but should be supported by other parameters describing the best-fit curve.

Acinetobacter↗
PubMed1996

The in-vitro activity of trovafloxacin and nine other antimicrobials against 413 anaerobic bacteria.

The in-vitro activity of trovafloxacin and nine other antimicrobials was determined for 413 non copy anaerobic clinical isolates. Trovafloxacin was the most active quinolone tested with an MIC90 of 0.5 mg/L against Gram-positive cocci (n = 75); MIC90 of 4 mg/L against Gram-positive bacilli (n = 151); MIC90 of 0.5 mg/L for Gram-negative cocci (n = 12) and MIC90 of 1 mg/L for Gram-negative bacilli (n = 175). Overall the MIC90 of trovafloxacin was 1 mg/L which was equivalent to co-amoxiclav and one dilution higher than that of imipenem. The other seven comparators, including clindamycin and metronidazole, had higher MIC90 values than trovafloxacin. Trovafloxacin is likely to have clinically useful activity against anaerobes from human infection.

Anti-Bacterial Agents↗
PubMed1995

The bacterial DNA content of mouse organs in the Cornell model of dormant tuberculosis.

SETTING: The Cornell model of murine tuberculosis has proved useful for demonstrating and studying dormancy. However, it has not previously been used to investigate the molecular aspects of dormancy. OBJECTIVE: To obtain a profile of the amount of Mycobacterium tuberculosis DNA at various stages of the Cornell model. DESIGN: BALB/C mice were infected intravenously with 2.7 x 10(6) cfu M tuberculosis strain H37Rv; they were left for two weeks, treated for 14 weeks with isoniazid and pyrazinamide and left untreated for a further 14 weeks. Spleens and lungs at start of treatment and at 8, 12, 14, 18, 24 and 28 weeks thereafter were examined by culture, and DNA in tissue homogenates was quantitated by polymerase chain reaction (PCR) and dot blot hybridisation. RESULTS: Culture and quantitative PCR estimated initial bacillary content at about 10(7) per organ. Thereafter, organ cultures rapidly declined and were usually negative between 14 and 28 weeks. However, during this period quantitative PCR consistently estimated about 5.5 log10 bacilli equivalents in spleens and lungs. Dot blot hybridisation sensitive to about 10 ng bacillary DNA was usually positive pretreatment and occasionally during and after treatment, hence confirming the PCR results. CONCLUSIONS: There is persistence of significant quantities of M. tuberculosis DNA throughout the various stages of the model. This may represent dead bacilli, free DNA or dormant forms.

Animals↗
PubMed1995

A critical assessment of the agar dilution chequerboard technique for studying in-vitro antimicrobial interactions using a representative beta-lactam, aminoglycoside and fluoroquinolone.

The agar dilution chequerboard technique of studying antimicrobial interactions was assessed by testing a representative beta-lactam (piperacillin/tazobactam), aminoglycoside (gentamicin) and fluoroquinolone (ciprofloxacin) against themselves, that is piperacillin/tazobactam plus piperacillin/tazobactam, gentamicin plus gentamicin and ciprofloxacin plus ciprofloxacin. In addition, combinations of piperacillin/tazobactam plus gentamicin or ciprofloxacin were also tested against Enterobacteriaceae and Acinetobacter spp. in triplicate. The agar dilution chequerboard technique did not reliably show addition when agents were combined with themselves, and there was also considerable variation when beta-lactam plus aminoglycoside or fluoroquinolone combinations when tested in triplicate. These observations, and problems with the design of the method, indicate that the chequerboard technique should be used only with adequate controls and replication, and then interpreted with extreme caution; ideally, it should not be used as a method of assessing antimicrobial interactions.

Acinetobacter↗