Similar MICs Research Articles

Activity of Retapamulin against Streptococcus pyogenes and Staphylococcus aureus Evaluated by Agar Dilution, Microdilution, E-Test, and Disk Diffusion Methodologies

The in vitro activity of retapamulin against 106 Staphylococcus aureus isolates and 109 Streptococcus pyogenes isolates was evaluated by the agar dilution, broth microdilution, E-test, and disk diffusion methodologies. Where possible, the tests were performed by using the CLSI methodology. The results of agar dilution, broth microdilution, and E-test (all with incubation in ambient air) for S. aureus yielded similar MICs, in the range of 0.03 to 0.25 microg/ml. These values corresponded to zone diameters between 25 and 33 mm by the use of a 2-microg retapamulin disk. Overall, 99% of the agar dilution results and 95% of E-test results for S. aureus were within +/-1 dilution of the microdilution results. For S. pyogenes, the MICs obtained by the agar and broth microdilution methods (both after incubation in ambient air) were in the range of 0.008 to 0.03 microg/ml, and E-test MICs (with incubation in ambient air) were 0.016 to 0.06 microg/ml. For S. pyogenes, 100% of the agar dilution MIC results were within +/-1 dilution of the broth microdilution results. E-test MICs (after incubation in ambient air) were within +/-1 and +/-2 dilutions of the broth microdilution results for 76% and 99% of the isolates, respectively. E-test MICs for S. pyogenes strains in CO(2) were up to 4 dilutions higher than those in ambient air. Therefore, it is recommended that when retapamulin MICs are determined by E-test, incubation be done in ambient air and not in CO(2), due to the adverse effect of CO(2) on the activity of this compound. Diffusion zones (with incubation in CO(2)) for S. pyogenes were 18 to 24 mm. Retapamulin MICs for all strains by all methods (with incubation in ambient air) were < or =0.25 microg/ml. These results demonstrate that S. pyogenes (including macrolide-resistant strains) and S. aureus (including methicillin-resistant and vancomycin-nonsusceptible strains) are inhibited by very low concentrations of retapamulin and that all four testing methods are satisfactory for use for susceptibility testing.

Involvement of the MexXY-OprM Efflux System in Emergence of Cefepime Resistance in Clinical Strains of Pseudomonas aeruginosa

Cefepime (FEP) and ceftazidime (CAZ) are potent beta-lactam antibiotics with similar MICs (1 to 2 mug/ml) for wild-type strains of Pseudomonas aeruginosa. However, recent epidemiological studies have highlighted the occurrence of isolates more resistant to FEP than to CAZ (FEPr/CAZs profile). We thus investigated the mechanisms conferring such a phenotype in 38 clonally unrelated strains collected in two French teaching hospitals. Most of the bacteria (n=32; 84%) appeared to stably overexpress the mexY gene, which codes for the RND transporter of the multidrug efflux system MexXY-OprM. MexXY up-regulation was the sole FEP resistance mechanism identified (n=12) or was associated with increased levels of pump MexAB-OprM (n=5) or MexJK (n=2), synthesis of secondary beta-lactamase PSE-1 (n=10), derepression of cephalosporinase AmpC (n=1), coexpression of both OXA-35 and MexJK (n=1), or production of both PSE-1 and MexAB-OprM (n=1). Down-regulation of the mexXY operon in seven selected strains by the plasmid-borne repressor gene mexZ decreased FEP resistance from two- to eightfold, thereby demonstrating the significant contribution of MexXY-OprM to the FEPr/CAZs phenotype. The six isolates of this series that exhibited wild-type levels of the mexY gene were found to produce beta-lactamase PSE-1 (n=1), OXA-35 (n=4), or both PSE-1 and OXA-35 (n=1). Altogether, these data provide evidence that MexXY-OprM plays a major role in the development of FEP resistance among clinical strains of P. aeruginosa.

Analysis of the Prevalence of Tetracycline Resistance Genes in Clinical Isolates ofEnterococcus faecalisandEnterococcus faeciumin a Japanese Hospital

Prevalence of seven tetracycline resistance (TC(R)) genes--tet(L), tet(M), tet(K), tet(O), tet(S), tet(T), and tet(U)--which are known to be distributed to gram-positive cocci was analyzed for 224 Enterococcus faecalis and 46 Enterococcus faecium clinical isolates obtained in a Japanese hospital. Any of the TC(R) genes was detected in 75.9% of all the enterococcal strains. The tet(M) was detected at highest rates in both E. faecalis (75.0%) and E. faecium (69.6%), followed by tet(L), which was harbored in 6.7% of E. faecalis isolates and 30.4% of E. faecium isolates. The tet(O), tet(S), and tet(T) were detected in E. faecalis at low frequencies mostly associated with tet(M), while tet(K) and tet(U) were not detected. Nucleotide sequences of tet(S) from E. faecalis strains were identical to that reported in Listeria monocytogenes. Sequences of tet(O) from two E. faecalis strains were almost identical to each other and also to those from Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus mutans, Campylobacter jejuni, and Campylobacter coli, although minor sequence divergence was observed. The tet(T), which had been reported only in Streptococcus pyogenes, was found in five E. faecalis strains. Sequence of the enterococcal tet(T) differed from that of S. pyogenes by only four nucleotides (four amino acids) and showed high sequence identity (99.8%, amino acid level). Enterococcal strains with any one TC(R) gene or those with two TC(R) genes showed generally similar MICs of tetracyclines, and no evident difference in resistance level was observed.

Clinical Pharmacokinetics of the Diastereomers of Arteether in Healthy Volunteers

To evaluate the pharmacokinetics of alpha- and beta-diastereomers of arteether in healthy male volunteers. The study was a single-centre clinical pharmacokinetic trial in healthy male subjects. A group comprising 13 subjects aged 25-50 years received a single intramuscular 150 mg individual dose of the arteether formulation containing alpha- and beta-isomers in a 30:70 ratio. Serial blood samples collected over a period of 0-192 hours were analysed by high-performance liquid chromatography-electrospray ionisation/tandem mass spectrometry and the plasma concentrations were subjected to compartmental and noncompartmental analyses. Pharmacodynamic parameters such as area under the inhibitory curve, ratio of area under the concentration-time curve to minimum inhibitory concentration (AUC/MIC), maximum plasma concentration to MIC (Cmax/MIC) and time that plasma concentration exceeds the MIC (T>MIC) were calculated in vitro in four strains of Plasmodium falciparum to evaluate the in vivo effectiveness of the proposed dosage regimen. There were no adverse effects observed during the study. The extent of metabolism of arteether to dihydroartemisinin (DHA) was low (approximately 5%) so as to be therapeutically nonsignificant. The pharmacokinetic profiles of the arteether diastereomers were different, and the maximum plasma concentrations of alpha- and beta-isomers were reached at 4.77+/-1.21 hours and 6.96+/-1.62 hours, respectively, after which they showed biphasic decline with apparent terminal elimination half-lives of 13.24+/-1.08 hours and 30.17+/-2.44 hours, respectively. The plasma and renal clearances, as well as whole blood to plasma partition ratios of the isomers, were comparable, while the apparent volume of distribution during terminal phase of the beta-isomer was approximately 3-fold higher than that of the alpha-isomer. In vitro erythrocyte culture experiments with four strains of P. falciparum showed similar MICs for both isomers of arteether. The highest observed MIC of 8 microg/L was selected for estimating the pharmacokinetic and pharmacodynamic parameters, which showed excellent correlation with published data on the clinical efficacy of arteether. The pharmacokinetics of arteether isomers demonstrated stereoselectivity, which was reflected mainly in the volume of distribution and the terminal elimination half-life. The alpha- and beta-isomers of arteether appeared to compliment each other pharmacokinetically, with the alpha-isomer providing comparatively rapid and higher plasma concentrations resulting in immediate reduction in percentage parasitaemia, while the beta-isomer, with its longer terminal elimination half-life, mean residence time and sustained plasma concentrations, maintained the activity for longer periods. The extent of metabolic conversion of arteether to DHA was minimal, so as to have any therapeutic or toxic significance.

Synthesis of pure stereoisomers of benzo[ b]thienyl dehydrophenylalanines by Suzuki cross-coupling. Preliminary studies of antimicrobial activity

Several benzo[ b]thienyldehydrophenylalanines were synthesized from pure stereoisomers of the methyl ester of N-( tert-butoxycarbonyl)-β-bromodehydrophenylalanine as an extension of our previously reported method for the synthesis of dehydrotryptophan analogues to dehydrophenylalanine derivatives. The latter were obtained in high yields by N-deprotection and bromination of N, N-bis-( tert-butoxycarbonyl)-( Z)-dehydrophenylalanine using TFA and NBS. This was carried out in two steps or in a one pot procedure resulting in different E/ Z ratios. These compounds were coupled under Suzuki cross-coupling conditions [Pd(PPh 3) 4, Na 2CO 3, DME/H 2O] with several boronic benzo[ b]thienyl acids in good to high yields maintaining the stereochemistry of the starting materials. The best yields were obtained when the boronic acid was in position 7 of the benzo[ b]thiophene and with the E isomer of the brominated dehydrophenylalanine. In some cases it was possible to increase the lower yields by changing the Pd source to PdCl 2(PPh 3) 2. A model dipeptide was prepared coupling a benzo[ b]thienyldehydrophenylalanine with the methyl ester of alanine. Preliminary antimicrobial studies were performed with both isomers of one of the β, β-diaryldehydroalanines obtained. The results show that the compounds are selective and very active (very low MICs) against Gram positive bacteria ( B. cereus and B. subtilis) the Z-isomer being more active. The compounds are also active against Candida albicans presenting similar MICs.

Activité in vitro du cefpodoxime sur Streptococcus pneumoniae : dernières données françaises et revue de la littérature

The objective of this study was to evaluate the in vitro activity of cefpodoxime (CPD) against S. pneumoniae (SP) strains isolated in France during 2002. Forty two hospital centers participated in the study. Strains were isolated from respiratory tract infections. Each center included each month the first five strains of SP that were clinically significant and non redundant. In total, 965 strains of SP were collected. MICs were determined by microdilution method in a central laboratory. 45,8%, 19,7% and 34,5% of the strains were susceptible (S), intermediate (I) and resistant (R) to penicillin (PEN) respectively. 49,7%, 3,7% and 46,6% were S, I and R to macrolides respectively. The MICs 50/90 (mg/L) of CPD were follows: all strains (n=965): 0,25/4; PEN-S strains (n=442): 0,03/0.12; PEN-I strains (n=190): 1/2; PEN-R strains (n=333): 4/4. In comparison with studies performed in France during the last 10 years, the in vitro activity of CPD appears to be stable, with similar MICs against PEN-S, PEN-I and PEN-R strains.

Antimicrobial Activity of Hydrophobic Xanthones from Cudrania cochinchinensis against Bacillus subtilis and Methicillin‐Resistant Staphylococcus aureus

Ten xanthones with one or two isoprenoid groups and a prenylated benzophenone isolated from roots of Cudrania cochinchinensis (Moraceae) were tested for their antimicrobial activities against Bacillus subtilis and methicillin-resistant Staphylococcus aureus (MRSA). Among these compounds, gerontoxanthone H exhibited considerable antibacterial activity against B. subtilis (MIC = 1.56 microg/ml). Four xanthones, gerontoxanthone I, toxyloxanthone C, cudraxanthone S, and 1,3,7-trihydroxy-2-prenylxanthone, showed weak antibacterial activity against the bacterium (MICs = 3.13-6.25 microg/ml). These compounds also exhibited similar MIC values against methicillin-sensitive S. aureus, MRSAs, and Micrococcus luteus.

In vitro activity of the new quinolone WCK 771 against staphylococci.

The activity of WCK 771, an experimental quinolone developed to overcome quinolone resistance in staphylococci and other bacteria, was determined against quinolone-susceptible and -resistant Staphylococcus aureus and S. epidermidis. WCK 771 MICs for 50 and 90% of the strains tested (MIC(50) and MIC(90), respectively) were 0.008 and 0.015 microg/ml for S. aureus (n = 43) and 0.015 and 0.03 microg/ml for S. epidermidis (n = 44) for quinolone-susceptible isolates, compared to ciprofloxacin values of 0.12 and 0.25 microg/ml and 0.25 and 0.5 microg/ml, respectively. Values for levofloxacin were 0.12 and 0.25 microg/ml and 0.12 and 0.25 microg/ml, those for clinafloxacin were 0.015 and 0.03 microg/ml and 0.015 and 0.03 microg/ml, those for moxifloxacin were 0.03 and 0.06 microg/ml and 0.06 and 0.12 microg/ml, and those for gatifloxacin were 0.06 and 0.12 microg/ml and 0.12 and 0.25 microg/ml, respectively. The WCK 771 MIC(50) and MIC(90), respectively, were 0.5 and 1 microg/ml for both species of staphylococci (n = 73 for S. aureus, n = 70 for S. epidermidis) for isolates highly resistant to ciprofloxacin (MIC(50) and MIC(90), >32 and >32 microg/ml, respectively). Values for levofloxacin were 8 and 32 microg/ml and 8 and 32 microg/ml, those for clinafloxacin were 1 and 2 microg/ml and 0.5 and 2 microg/ml, those for moxifloxacin 4 and >4 microg/ml and 4 and >4 microg/ml, and those for gatifloxacin were 4 and >4 microg/ml and 2 and >4 microg/ml, respectively. WCK 771 and clinafloxacin demonstrated MICs of 1 microg/ml against three vancomycin-intermediate strains. WCK 771 showed concentration-independent killing for up to 24 h at 2, 4, and 8 times the MICs against quinolone-resistant staphylococci and was also bactericidal after 8 h for high-density inocula (10(8) CFU/ml) of quinolone-resistant strains at 5 microg/ml, whereas moxifloxacin at 7.5 microg/ml was bacteriostatic. WCK 771 was not a substrate of the NorA efflux pump as evident from the similar MICs against both an efflux-positive and an efflux-negative strain. Overall, WCK 771 was the most potent quinolone tested against the staphylococci tested, regardless of quinolone susceptibility.

Detection of cefotaxime-resistant CTX-M-3 in clinical isolates ofSerratia marcescens

Strains of Serratia marcescens (isolated in a hospital during April and August 2000) resistant to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, streptomycin, tetracycline, and gentamicin were characterized. Out of a total of 34 clinical isolates 6 (17.6 %) exhibited the extended spectrum beta-lactamases (ESBL) resistance; they were also resistant to cefotaxime (minimum inhibitory concentration, MIC > or = 128 microg/mL) but susceptible to imipenem (MIC < or = 0.5 microg/mL). This multidrug resistance was shown to be transferred by a conjugative plasmid. Transconjugants revealed similar MIC profiles when compared to the parental strains. Isoelectric focusing revealed one major transferable beta-lactamase (pI 8.4) which was further identified as CTX-M-3 by PCR and gene sequencing. The presence of strains with this type of ESBL showed the evolution of bla genes and their dissemination among at least three species of the family Enterobacteriaceae isolated within a single hospital. The predominance of CTX-M type enzymes found in this area of Taiwan appeared to be similar to that described in Poland.

Topical antibacterial therapy for mycobacterial keratitis: Potential for surgical prophylaxis and treatment

Background: Mycobacterium chelonae and Mycobacterium fortuitum are the 2 most commonly implicated species of nontuberculous myoobacteria in cases of bacterial keratitis. Objectives: This article summarizes available data on the in vitro antibacterial activity against M chelonae or M fortuitum of 2 agents—amikacin and clarithromycin—that have been used in the treatment of bacterial keratitis. In addition, the article reviews the in vitro activity of 5 commercially available topical ocular fluoro-quinolones (in order of availability, ciprofloxacin, ofloxacin, levofloxacin, gatifloxacin, and moxifloxacin) that may have potential in the surgical prophylaxis and treatment of keratitis caused by M chelonae or M fortuitum. Methods: A search of the English-language literature indexed on the MEDLINE, Life Sciences, EMBASE, BIOSIS, and Pharmaprojects databases from 1966 to October 7, 2003, was conducted using the terms Mycobacterium chelonae, Mycobacterium fortuitum, bacterial keratitis, topical antibiotic therapy, ocular infection-mycobacteria, and LASIK infections. Data on the minimum concentrations at which 90% of isolates were inhibited (MIC 90s) were reviewed and compared. Results: In the literature reviewed, the MIC 90 against M fortuitum was from 1 to 16 μg/mL for amikacin, from ≤2 to ≥8 μg/mL for clarithromycin, from 0.1 to 1 μg/mL for ciprofloxacin, from 0.5 to 3.13 μg/mL for ofloxacin, and ≤2 μg/mL for levofloxacin. The results were similar against M chelonae. The fourth-generation fluoroquinolones—gatifloxacin and moxifloxacin—had similar MIC 90s against M fortuitum (both, 0.2 to 1 μg/mL); however, moxifloxacin had greater activity than gatifloxacin against M chelonae (minimum inhibitory concentration range: moxifloxacin, ≤1 to 1.6 μg/mL; gatifloxacin, 3.2 to 6.25 μg/mL). Conclusions: Topical fluoroquinolones may be beneficial for ocular surgical prophylaxis and for the treatment of keratitis caused by M chelonae or M fortuitum. Based on their reported MIC 90s, none of the antibacterials reviewed had greater in vitro activity than moxifloxacin. In addition, moxifloxacin had greater in vitro activity than gatifloxacin against M chelonae, one of the predominant nontuberculous mycobacterial species involved in bacterial keratitis. Pending the conduct of controlled clinical studies, these findings suggest that moxifloxacin may have utility in the prevention and treatment of atypical mycobacterial keratitis.

Mechanism of fluoroquinolone resistance is an important factor in determining the antimicrobial effect of gemifloxacin against Streptococcus pneumoniae in an in vitro pharmacokinetic model.

Antibacterial effect and emergence of resistance to gemifloxacin and levofloxacin were studied in an in vitro pharmacokinetic model of infection. A panel of Streptococcus pneumoniae strains with known mechanisms of resistance were used; two strains had no known resistance mechanism, two had efflux pumps, three had gyrA plus parC mutations, and one had only a parC mutation. Gemifloxacin MICs were in the range of 0.016 to 0.25 mg/liter, and levofloxacin MICs ranged from 1 to 16 mg/liter. Antimicrobial effect was measured by area under the bacterial-kill curve up to 72 h, and emergence of resistance was determined by population analysis profile before and during drug exposure. The area under the curve (AUC)/MIC ratios for gemifloxacin and levofloxacin were 35 to 544 and 3 to 48, respectively. As expected on the basis of these AUC/MIC ratio differences, antibacterial effect was much greater for gemifloxacin than levofloxacin. In the gemifloxacin simulations, mechanism of resistance as well as MIC determined the antibacterial effect, as indicated by gemifloxacin's greater effect against efflux strains compared to those with gyrA or parC mutations despite similar MICs. This was not true of levofloxacin. Emergence of resistance was not easily demonstrated with either agent, and mechanism of resistance did not have any impact on it.

Confirmation of extended-spectrum β-lactamase-producing Serratia marcescens: preliminary report from Taiwan

Although Serratia marcescens is a common cause of nosocomial infection in Taiwan, strains producing extended-spectrum β-lactamases (ESBLs) are rare. We detected four clinical isolates of S. marcescens from Taiwan that exhibited resistance to cefotaxime (MICs, > 256 μg/ml) and cefepime (MICs, ≥ 32 μg/ml), but were susceptible to imipenem and meropenem. Transconjugants revealed similar MIC profiles when compared to the parental strains. Isoelectric focusing revealed one major transferable β-lactamase (pI 8.4), which was further identified as CTX-M-3 by polymerase chain reaction and gene sequencing. An AmpC-like enzyme (pI 8.8) was not transferable. All four isolates had significant MIC reductions of ≥3 log 2 dilutions for cefepime in the presence of clavulanic acid, compatible with the presence of an ESBL (CTX-M-3). Clavulanate did not significantly reduce the cefotaxime MIC for one isolate that may co-produce high-level AmpC β-lactamase (pI 8.8). Since high-level AmpC expression has minimal effect on the activity of cefepime, isolates co-producing AmpC β-lactamase may be recognized as additional ESBL producers by using cefepime as an ESBL screening agent.

Susceptibility of bacterial isolates to gatifloxacin and ciprofloxacin from clinical trials 1997–1998

MICs of gatifloxacin and ciprofloxacin against 3482 pre-treatment, clinical trial isolates collected during 1997–1998 are reported. These data suggested that gatifloxacin was four- to eight-fold more active than ciprofloxacin against Gram-positive bacteria, with gatifloxacin MIC 90s≤0.33 mg/l against Staphylococcus aureus and Streptococcus pneumoniae, and ≤1.0 mg/l versus viridans streptococci and Enterococcus faecalis. Both quinolones had similar MIC 90s versus Enterobacteriaceae (generally ≤0.38 mg/l, except 0.7–0.8 mg/l for Citrobacter freundii) and Pseudomonas aeruginosa (∼8 mg/l). A total of 78% P. aeruginosa had gatifloxacin MICs ≤2 mg/l. Gatifloxacin was more active than ciprofloxacin against Acinetobacter species and non- P. aeruginosa pseudomonads. Both had exceptional activity versus Haemophilus spp, Moraxella catarrhalis and Neisseria gonorrhoeae. In summary, compared to ciprofloxacin, gatifloxacin had improved activity against Gram-positive bacteria and comparable activity against Gram-negative bacteria.

Activity of rifapentine and its metabolite 25-O-desacetylrifapentine compared with rifampicin and rifabutin against Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium bovis and M. bovis BCG.

The in vitro activity of rifapentine and its metabolite, 25-O:-desacetylrifapentine, as compared with that of rifampicin and rifabutin, was determined against Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium bovis and M. bovis BCG. MICs were determined radiometrically and by the 1% proportional method using Middlebrook 7H11 agar. The bactericidal effect of the drugs was determined in parallel at selected concentrations. For drugsusceptible isolates of M. tuberculosis, the Bactec MICs of rifapentine and 25-O:-desacetylrifapentine were 0.03-0.06 mg/L and 0. 125-0.25 mg/L, respectively. Similar MICs were obtained for M. africanum (0.03-0.125 and 0.125-0.50 mg/L, respectively), and M. bovis (0.063-0.25 and 0.125-1.0 mg/L, respectively), but MICs were considerably lower for M. bovis BCG (0.008-0.063 mg/L for rifapentine and 0.016-0.125 mg/L for its metabolite). In general, MICs determined using 7H11 agar medium were usually one or two dilutions higher than those obtained using Bactec broth. When compared with rifampicin and rifabutin, the inhibitory activity of rifapentine for drug-susceptible isolates was roughly equal to that of rifabutin, and the inhibitory activity of 25-O:-desacetylrifapentine was comparable to that of rifampicin; however, rifapentine was somewhat more bactericidal than rifabutin at equal concentrations. Clinical isolates of M. tuberculosis with a high degree of resistance to rifampicin (MIC >/= 32 mg/L) were also highly resistant to rifabutin, rifapentine and 25-O:-desacetylrifapentine, although the MICs of rifabutin in this case were somewhat lower than the MICs of rifapentine.

Bactericidal activity of gemifloxacin and other quinolones against Streptococcus pneumoniae.

This study compared the bactericidal activity of gemifloxacin (SB-265805) and a panel of test quinolones against two ciprofloxacin-resistant pneumococcal strains (Streptococcus pneumoniae 502226 and 503244) and one ciprofloxacin-sensitive strain (S. pneumoniae C3LN4). Activities were compared by calculating the bactericidal index of these agents. Gemifloxacin was found to be the most bactericidal quinolone tested against these strains. This finding confirms previous data indicating the superior in vitro activity of gemifloxacin against pneumococci, including ciprofloxacin-resistant strains. Although both ciprofloxacin-resistant strains tested had similar quinolone MICs, they differed considerably in their susceptibility to the bactericidal action of these agents. S. pneumoniae 502226 was more readily killed by quinolones than S. pneumoniae 503244 but, as would be expected, both were less susceptible than the ciprofloxacin-sensitive strain. Of the quinolones tested, trovafloxacin showed disproportionally poor activity against the ciprofloxacin-resistant strains even though potent activity was present against the ciprofloxacin-sensitive strain. These data highlight the importance of assessing quinolone bactericidal activity in addition to the MIC when evaluating new members of this antimicrobial class.

Characterization of passage-selected vancomycin-resistant Staphylococcus aureus strains of diverse parental backgrounds.

A series of 12 Staphylococcus aureus strains of various genetic backgrounds, methicillin resistance levels, and autolytic activities were subjected to selection for the glycopeptide-intermediate S. aureus (GISA) susceptibility phenotype on increasing concentrations of vancomycin. Six strains acquired the phenotype rapidly, two did so slowly, and four failed to do so. The vancomycin MICs for the GISA strains ranged from 4 to 16 microg/ml, were stable to 20 nonselective passages, and expressed resistance homogeneously. Neither ease of acquisition of the GISA phenotype nor the MIC attained correlated with methicillin resistance hetero- versus homogeneity or autolytic deficiency or sufficiency. Oxacillin MICs were generally unchanged between parent and GISA strains, although the mec members of both isogenic methicillin-susceptible and methicillin-resistant pairs acquired the GISA phenotype more rapidly and to higher MICs than did their susceptible counterparts. Transmission electron microscopy revealed that the GISA strains appeared normal in the absence of vancomycin but had thickened and diffuse cell walls when grown with vancomycin at one-half the MIC. Common features among GISAs were reduced doubling times, decreased lysostaphin susceptibilities, and reduced whole-cell and zymographic autolytic activities in the absence of vancomycin. This, with surface hydrophobicity differences, indicated that even in the absence of vancomycin the GISA cell walls differed from those of the parents. Autolytic activities were further reduced by the inclusion of vancomycin in whole-cell and zymographic studies. The six least vancomycin-susceptible GISA strains exhibited an increased capacity to remove vancomycin from the medium versus their parent lines. This study suggests that while some elements of the GISA phenotype are strain specific, many are common to the phenotype although their expression is influenced by genetic background. GISA strains with similar glycopeptide MICs may express individual components of the phenotype to different extents.

In vitro activity of voriconazole against selected fungi

Fifty-nine isolates consisting of 14 genera and 33 species of ascomycetes, basidiomycetes, and zygomycetes were tested against amphotericin B, fluconazole, itraconazole and voriconazole using an in vitro modified macrobroth dilution procedure based upon the NCCLS M27-A standard method for yeasts. The triazoles voriconazole and itraconazole had similar MIC values, except for Acremonium alabamensis, A. strictum, Fusarium oxysporum, F. solani and Wangiella dermatitidis, which had substantially lower voriconazole MIC values. Voriconazole MIC values were lower than those for itraconazole for the 17 species of Trichosporon tested. Fluconazole had high MIC values, often greater than 128 microg ml-1.

Characterization of a novel SHV β-lactamase variant that resembles the SHV-5 enzyme

An SHV type beta-lactamase frequently found in enterobacteria isolated in Greek hospitals was analyzed. The enzyme (SHV-5a) conferred resistance to ceftazidime and aztreonam. The DNA sequence of the structural gene was determined. The deduced amino acid sequence showed that positions 70-73 were occupied by the active site tetrad Ser-Thr-Phe-Lys. As in SHV-5, Ser-238 and Lys-240 were present. However, one deletion (Gly-54) and three substitutions (Arg-140 for Ala, Asn-192 for Lys and Val-193 for Leu) differentiate SHV-5a beta-lactamase from SHV-5. Asn-192 and Val-193 have been reported to date only in the R974 plasmid-mediate SHV-1 beta-lactamase. Hydrolysis studies with SHV-5a and SHV-5 showed that the enzymes behaved similarly. Additional evidence that they are functionally indistinguishable was provided by the similar MICs of beta-lactams when the enzymes were expressed under isogenic conditions. The sequence differences, however, indicate that they are derived from different ancestors.

Characterization of a novel SHV β-lactamase variant that resembles the SHV-5 enzyme

An SHV type β-lactamase frequently found in enterobacteria isolated in Greek hospitals was analyzed. The enzyme (SHV-5a) conferred resistance to ceftazidime and aztreonam. The DNA sequence of the structural gene was determined. The deduced amino acid sequence showed that positions 70–73 were occupied by the active site tetrad Ser-Thr-Phe-Lys. As in SHV-5, Ser-238 and Lys-240 were present. However, one deletion (Gly-54) and three substitutions (Arg-140 for Ala, Asn-192 for Lys and Val-193 for Leu) differentiate SHV-5a β-lactamase from SHV-5. Asn-192 and Val-193 have been reported to date only in the R974 plasmid-mediated SHV-1 β-lactamase. Hydrolysis studies with SHV-5a and SHV-5 showed that the enzymes behaved similarly. Additional evidence that they were functionally indistinguishable was provided by the similar MICs of β-lactams when the enzymes were expressed under isogenic conditions. The sequence differences, however, indicate that they are derived from different ancestors.

Relation between surface activity and antibacterial activity of amine-fluorides

Amine-fluoride molecules consist of two functional groups - the organic amine, which is a surface active agent and the fluoride ion. Both ions are known to have antibacterial properties. Studies have suggested that there is a positive correlation between the antibacterial properties and the surface activity of various organic amines. The purpose of our study was to determine the antibacterial activity of the two functional groups of amine-fluoride molecules and its relationship to their surface activity. In this study, minimal inhibitory/bacteriocidic concentration (MIC/MBC) were determined for Streptococcus sobrinus 6715 at a range of pH between 5 and 7. Surface activity measurements were conducted using a surface tensiometer. Amine-fluorides were found to have similar MIC values to that of chlorhexidine digluconate at all tested pH values, thus showing high antibacterial activity against Streptococcus sobrinus 6715. The MIC values of amine-fluorides and amine-chlorides are similar, and are about 100 times lower than the MIC value of NaF. No synergistic effect was found between the fluoride and the organic amine. No correlation was found between the antibacterial properties and the surface activity of amine-fluorides. Therefore, we conclude that the antibacterial activity of amine-fluorides derives mainly from the cationic nature of the organic amine, and not from its properties as a surface active agent.