Quality control limits for voriconazole disk susceptibility tests on Mueller-Hinton agar with glucose and methylene blue

An international collaborative study was performed in order to propose quality control limits for voriconazole disk diffusion tests on Mueller-Hinton agar with 2% glucose and 0.5 micro g of methylene blue per ml. The supplement may be added to the agar before autoclaving, or Mueller-Hinton agar plates may be flooded with a glucose-methylene blue solution. Replicate tests on both types of agar plates with 1- micro g voriconazole disks generated data to propose zone size limits for tests of Candida parapsilosis ATCC 22019 (28 to 37 mm), Candida albicans ATCC 90028 (31 to 42 mm), and Candida krusei ATCC 6258 (16 to 25 mm). Candida tropicalis ATCC 750 was not useful for this purpose.

Geographic variation in the susceptibilities of invasive isolates of Candida glabrata to seven systemically active antifungal agents: a global assessment from the ARTEMIS Antifungal Surveillance Program conducted in 2001 and 2002

We examined the susceptibilities to amphotericin B, flucytosine, fluconazole, posaconazole, ravuconazole, voriconazole, and caspofungin of 601 invasive isolates of Candida glabrata and grouped the isolates by geographic location: North America (331 isolates), Latin America (58 isolates), Europe (135 isolates), and Asia-Pacific (77 isolates). Caspofungin (MIC at which 90% of isolates tested are susceptible [MIC(90)], 0.12 microg/ml; 100% of strains are susceptible [S] at a MIC of Collapse

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MESH Headings

• Antifungal Agents/pharmacology
• Candida glabrata/drug effects
• Drug Resistance, Fungal
• Microbial Sensitivity Tests
• Time Factors

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Determination of fungicidal activities against yeasts and molds: lessons learned from bactericidal testing and the need for standardization

In certain unique clinical settings, the ability of the antimicrobial agent administered to kill the pathogen outright may be quite important. These situations invariably involve infection of a site not easily accessed by host defenses and/or of a structure with essential anatomic or physiologic function such as the heart (endocarditis), central nervous system (meningitis), or bone (osteomyelitis). Likewise, infections in immunosuppressed hosts, especially those who are neutropenic, are often thought to require microbicidal therapy. Proof of the cidal nature of an antimicrobial agent in vitro is tedious, complex, and fraught with error. Although several methods for assessing in vitro bactericidal activity have been standardized (NCCLS M26-A and M21-A), the clinical relevance of these determinations is questionable and the tests are performed infrequently in most laboratories. Most of the clinical data supporting the need for microbicidal therapy and testing have focused on bacterial infections. However, given the fact that most serious fungal infections occur in profoundly immunosuppressed individuals, it is generally assumed that a cidal regimen would be preferable in that setting as well. In view of this clinical concern and the perceived need to assess the fungicidal activity of a variety of agents, we considered that it would be useful to review what is known about the issues and problems in assessing bactericidal activity and the clinical utility of such measurements. Following this review, we discuss the issue of how one defines fungicidal activity in vitro and in vivo and how feasible it might be to determine the fungicidal activity of organism-drug combinations for purposes of both drug development and clinical care. Proposed methods for fungal time-kill determinations and minimal fungicidal concentration determinations are also discussed.

In vitro susceptibilities of rare Candida bloodstream isolates to ravuconazole and three comparative antifungal agents

We determined the in vitro susceptibilities of 643 strains of Candida spp., representing 13 species rarely isolated from blood, to ravuconazole as well as three licensed systemic antifungal agents (amphotericin B, fluconazole, and flucytosine). The organisms included 234 isolates of C. krusei, 102 isolates of C. guilliermondii, 103 isolates of C. lusitaniae, 18 isolates of C. famata, 29 isolates of C. kefyr, 20 isolates of C. pelliculosa, 13 isolates of C. rugosa, 101 isolates of C. dubliniensis, 4 isolates of C. inconspicua, 11 isolates of C. lipolytica, 1 isolate of C. sake, and 2 isolates of C. lambica and 5 isolates of C. zeylanoides. MIC determinations were made by the National Committee for Clinical Laboratory Standards reference broth microdilution method and Etest (amphotericin B). Ravuconazole demonstrated excellent activity (98% susceptible at MIC < or = 1 microg/mL) against all species with the exception of C. inconspicua (75% [3 of 4]). By comparison, decreased susceptibility to fluconazole and/or amphotericin B was observed among isolates of C. krusei, C. guilliermondii, C. famata, C. rugosa, C. inconspicua, and C. lambica. These findings illustrate the fact that many of the less common species of Candida exhibit decreased susceptibility to one or more of the established systemically active antifungal agents. Ravuconazole is clearly an "extended-spectrum" triazole with potent in vitro activity against these rare and potentially "emerging" opportunistic pathogens.

Stability of Mueller-Hinton agar supplemented with glucose and methylene blue for disk diffusion testing of fluconazole and voriconazole

The shelf life of Mueller-Hinton agar supplemented with 2% glucose and methylene blue (0.5 micro g/ml) (MH-GMB) prepared in the laboratory to test disk diffusion of voriconazole and fluconazole was assessed using quality control (QC) strains of Candida albicans ATCC 90028, Candida krusei ATCC 6258, and Candida parapsilosis ATCC 22019. MH-GMB agar plates were prepared as described in National Committee for Clinical Laboratory Standards document M44-P, and isolates were tested using 25- micro g fluconazole disks and 1- micro g voriconazole disks over a 36-day period. Zone diameters for fluconazole and voriconazole varied by no more than 4 mm over the study period, and 95 to 100% of results were within the established QC limits for the strains tested. Prepared MH-GMB agar plates provide acceptable performance for disk diffusion testing for at least 30 days when stored at 5 degrees C.

In vitro activities of voriconazole, posaconazole, and fluconazole against 4,169 clinical isolates of Candida spp. and Cryptococcus neoformans collected during 2001 and 2002 in the ARTEMIS global antifungal surveillance program

We examined the in vitro activities of voriconazole, posaconazole, and fluconazole against 3,932 isolates of Candida spp. and 237 isolates of Cryptococcus neoformans obtained from over 100 medical centers worldwide during 2001 and 2002. The MICs of the antifungal drugs were determined by broth microdilution tests performed according to the National Committee for Clinical Laboratory Standards (NCCLS) methods using RPMI 1640 as the test medium. Voriconazole and posaconazole were very active against Candida spp. (97-98% susceptible at MICs < or =1 microg/ml) and C. neoformans (98-100% susceptible at MICs < or =1 microg/mL). C. albicans (MIC90, 0.015-0.03 microg/ml) was the most susceptible species of Candida to both agents and C. glabrata (MIC90, 1-2 microg/mL) was the least susceptible. Both voriconazole and posaconazole were more active than fluconazole against all Candida spp. and C. neoformans. These results provide further evidence for the increased spectrum and potency of the new triazoles against a large and geographically diverse collection of opportunistic fungal pathogens.

Evaluation of the NCCLS M44-P Disk Diffusion Method for Determining Susceptibilities of 276 Clinical Isolates of Cryptococcus neoformans to Fluconazole

We evaluated the NCCLS M44-P fluconazole disk diffusion method in comparison with the NCCLS M27-A2 broth microdilution method for determining the susceptibility of 276 isolates of Cryptococcus neoformans . Disk diffusion testing was performed using Mueller-Hinton agar supplemented with 2% glucose and 0.5 μg of methylene blue/ml. Among the 276 isolates, 259 (93.8%) were susceptible, 16 (5.8%) were susceptible—dose dependent, and 1 (0.4%) was resistant to fluconazole as determined by the NCCLS broth microdilution method. The overall categorical agreement between the two methods was 86%, with 0% very major errors, 2% major errors, and 12% minor errors. The disk diffusion method using Mueller-Hinton agar supplemented with glucose and methylene blue appears to be a useful approach for determining the fluconazole susceptibility of C. neoformans.

Twelve years of fluconazole in clinical practice: global trends in species distribution and fluconazole susceptibility of bloodstream isolates of Candida

We determined the species distribution and in-vitro susceptibility of 6082 bloodstream infection (BSI) isolates of Candida spp. collected from 250 medical centres in 32 nations over a 10-year period from 1992 through 2001. The species included 3401 C. albicans, 984 C. glabrata, 796 C. parapsilosis, 585 C. tropicalis, 153 C. krusei, 67 C. lusitaniae, 48 C. guilliermondii, 10 C. famata, 10 C. kefyr, six C. pelliculosa, five C. rugosa, four C. lipolytica, three C. dubliniensis, three C. inconspicua, two C. sake and one isolate each of C. lambica, C. norvegensis and C. zeylanoides. Minimum inhibitory concentration determinations were made using the National Committee for Clinical Laboratory Standards reference broth microdilution method. Variation in the rank order and frequency of the different species of Candida was observed over time and by geographic area. The proportion of BSI due to C. albicans and C. glabrata increased and C. parapsilosis decreased over time in Canada, the USA and Europe. C. glabrata was an infrequent cause of BSI in Latin America and the Asia-Pacific region. Very little variation in fluconazole susceptibility was observed among isolates of C. albicans, C. tropicalis and C. parapsilosis. These species accounted for 78% of all BSI and remained highly susceptible (91-100% susceptible) to fluconazole from 1992 to 2001 irrespective of geographic origin. The prevalence of fluconazole resistance among C. glabrata isolates was variable both over time and among the various countries and regions. Resistance to fluconazole among C. glabrata isolates was greatest in the USA and varied by US census region (range 0-23%). These observations are generally encouraging relative to the sustained usefulness of fluconazole as a systemically active antifungal agent for the treatment of candida BSI.

Exophiala oligosperma causing olecranon bursitis

A 62-year-old male with a history of Wegener's granulomatosis and immunosuppressive therapy presented with chronic olecranon bursitis. A black velvety mould with brown septate hyphae and tapered annellides was isolated from a left elbow bursa aspirate and was identified as an Exophiala species. Internal transcribed sequence rRNA sequencing showed the isolate to be identical to Exophiala oligosperma. The patient was successfully treated with aspiration and intrabursal amphotericin B.

Activities of caspofungin, itraconazole, posaconazole, ravuconazole, voriconazole, and amphotericin B against 448 recent clinical isolates of filamentous fungi

We examined the in vitro activity of caspofungin, posaconazole, voriconazole, ravuconazole, itraconazole, and amphotericin B against 448 recent clinical mold isolates. The endpoint for reading caspofungin was the minimum effective concentration (MEC). Among the triazoles, posaconazole was most active, inhibiting 95% of isolates at <or=1 microg/ml, followed by ravuconazole (91%), voriconazole (90%), and itraconazole (79%). Caspofungin and amphotericin B inhibited 93% and 89% of isolates at <or=1 microg/ml, respectively, with caspofungin demonstrating an MEC 90 of 0.12 microg/ml. All three new triazoles and caspofungin inhibited >95% of Aspergillus spp. at <or=1 microg/ml compared to 83% for itraconazole and 91% for amphotericin B. Amphotericin B inhibited only 38% of Aspergillus terreus isolates at <or=1 microg/ml, whereas the three new triazoles and caspofungin inhibited all A. terreus at <or=0.5 microg/ml. The new triazoles and caspofungin have excellent in vitro activity against a very large collection of recent clinical isolates of Aspergillus spp., and some in vitro activity against selected other filamentous fungi.

Antimicrobial activity against strains of Escherichia coli and Klebsiella spp. with resistance phenotypes consistent with an extended-spectrum beta-lactamase in Europe

Extended-spectrum beta-lactamases (ESBLs) have continued to evolve after their initial detection in Europe nearly two decades ago. The summary results from the MYSTIC Program (31 medical centers) were utilized to assess the extent of ESBL occurrence in Europe from 1997 to 2000. ESBL phenotype rates in Klebsiella spp. (32.8%) and Escherichia coli (14.4%) were generally stable, but extensive hospital-to-hospital and unit-to-unit variations were noted. The highest ESBL rates were found in eastern Europe (including Turkey) and in intensive care unit patient populations. Carbapenems remained active against the ESBL-producing strains (meropenem MIC90, 0.25-1 mg/L), while some other agents, such as aminoglycosides, fluoroquinolones, and piperacillin-tazobactam, were significantly less effective. International surveillance initiatives should be maintained to monitor future progression of this important resistance.

Evaluation of the Etest and disk diffusion methods for determining susceptibilities of 235 bloodstream isolates of Candida glabrata to fluconazole and voriconazole

The performances of the Etest and the disk diffusion methods for testing of the susceptibilities of 235 Candida glabrata isolates to fluconazole and voriconazole were compared with that of the National Committee for Clinical Laboratory Standards (NCCLS) approved standard broth microdilution (BMD) method. The NCCLS method used RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. Etest MICs were determined with RPMI 1640 agar containing 2% glucose (RPG agar) and with Mueller-Hinton agar containing 2% glucose and 0.5 microg of methylene blue per ml (MBE agar) and were read after incubation for 48 h at 35 degrees C. Disk diffusion testing was performed with MBE agar, 25-microg fluconazole disks, and 1- microg voriconazole disks and by incubation at 35 degrees C for 24 h. Overall agreements between the Etest and the BMD MICs obtained with RPG and MBE agars were 91 and 96%, respectively, for fluconazole and 93 and 95%, respectively, for voriconazole. Categorical agreements between the agar-based methods and BMD were 52.3 to 64.7% with fluconazole and 94.8 to 97.4% with voriconazole. The vast majority of the discrepancies by the disk diffusion and Etest methods with fluconazole were minor errors. The agar-based methods performed well in identifying isolates with resistance to fluconazole and decreased susceptibility to voriconazole.

Variation in susceptibility of bloodstream isolates of Candida glabrata to fluconazole according to patient age and geographic location

We examined the susceptibilities to fluconazole of 559 bloodstream infection isolates of Candida glabrata and grouped the isolates by patient age and geographic location within the United States. Susceptibility of C. glabrata to fluconazole was lowest in the Pacific (44%) and East South Central (47%) regions and was highest in the West South Central region (82%) (regions are as designated by the U.S. Bureau of the Census). Isolates from pediatric patients were virtually all susceptible to fluconazole, whereas the highest frequency of resistance was observed in isolates from patients 16 to 64 years of age.

Activities of fluconazole and voriconazole against 1,586 recent clinical isolates of Candida species determined by Broth microdilution, disk diffusion, and Etest methods: report from the ARTEMIS Global Antifungal Susceptibility Program, 2001

The ARTEMIS Global Antifungal Susceptibility Program (ARTEMIS Program) was initiated in 2001 to provide focused surveillance of the activities of fluconazole and voriconazole against Candida spp. isolated from blood and other normally sterile sites. A total of 1,586 episodes of infection were detected at 61 international study sites. Overall, 57.7% of the infections were due to Candida albicans, followed by C. glabrata (14.8%), C. parapsilosis (12.5%), C. tropicalis (9.4%), C. krusei (2.7%), and C. lusitaniae (1.5%). Isolates of C. albicans, C. parapsilosis, and C. tropicalis were all highly susceptible to fluconazole (for 99% of the isolates the MICs were Collapse

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MESH Headings

• Antifungal Agents/pharmacology
• Candida/classification
• Candida/drug effects
• Candida/isolation & purification
• Candidiasis/microbiology
• Drug Resistance, Fungal
• Fluconazole/pharmacology
• Humans
• Microbial Sensitivity Tests/methods
• Population Surveillance
• Pyrimidines/pharmacology
• Triazoles/pharmacology
• Voriconazole

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In vitro susceptibility testing of filamentous fungi: comparison of Etest and reference M38-A microdilution methods for determining posaconazole MICs

The performance of the Etest for posaconazole susceptibility testing of 72 isolates of filamentous fungi was assessed in comparison with the National Committee for Clinical Laboratory Standards (NCCLS) approved standard broth microdilution method (M38-A). The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48h at 35 degrees C. Etest MICs were determined with RPMI agar containing 2% glucose and were read after incubation for 48h at 35 degrees C. The isolates included Aspergillus fumigatus, A. flavus, A. nidulans, A. niger, A. versicolor, A. oryzae, A. terreus, Cladosporium spp., Curvularia sp., Exophiala sp., Fusarium spp., Paecilomyces spp., Pithomyces sp., Penicillium spp. and Scedosporium apiospermum. Overall agreement between Etest and microdilution MICs was 84% for Aspergillus spp. and 100% for the less common opportunistic molds, with the exception of Penicillium spp. (67%). Where a discrepancy was observed between Etest and the reference method, the Etest tended to give lower values. The Etest method using RPMI agar appears to be a useful method for determining posaconazole susceptibilities of filamentous fungi.

In vitro activities of caspofungin compared with those of fluconazole and itraconazole against 3,959 clinical isolates of Candida spp., including 157 fluconazole-resistant isolates

Caspofungin is an echinocandin antifungal agent with broad-spectrum activity against Candida and Aspergillus spp. The in vitro activities of caspofungin against 3,959 isolates of Candida spp. obtained from over 95 different medical centers worldwide were compared with those of fluconazole and itraconazole. The MICs of the antifungal drugs were determined by broth microdilution tests performed according to the NCCLS method using RPMI 1640 as the test medium. Caspofungin was very active against Candida spp. (MIC at which 90% of the isolates were inhibited [MIC(90)], 1 micro g/ml; 96% of MICs were < or =2 micro g/ml). Candida albicans, C. dubliniensis, C. tropicalis, and C. glabrata were the most susceptible species of Candida (MIC(90), 0.25 to 0.5 micro g/ml), and C. guilliermondii was the least susceptible (MIC(90), >8 micro g/ml). Caspofungin was very active against Candida spp., exhibiting high-level resistance to fluconazole and itraconazole (99% of MICs were < or =1 micro g/ml). These results provide further evidence for the spectrum and potency of caspofungin activity against a large and geographically diverse collection of clinically important isolates of Candida spp.

In vitro susceptibility testing of Aspergillus spp.: comparison of Etest and reference microdilution methods for determining voriconazole and itraconazole MICs

The performance of the Etest for voriconazole and for itraconazole susceptibility testing of 376 isolates of Aspergillus spp. was assessed in comparison with the National Committee for Clinical Laboratory Standards (NCCLS) proposed standard microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. Etest MICs were determined with RPMI agar containing 2% glucose and were read after incubation for 48 h at 35 degrees C. The isolates included A. fumigatus, A. flavus, A. niger, A. terreus, A. versicolor, A. glaucus, A. nidulans, A. ustus, and A. sydowii. Overall agreement percentages between the Etest and microdilution MICs were 97.6% for voriconazole and 95.8% for itraconazole. Where a discrepancy was observed between Etest and the reference method, the Etest tended to give lower values with voriconazole and higher values with itraconazole. The Etest method using RPMI agar appears to be a useful method for determining the voriconazole and itraconazole susceptibilities of Aspergillus spp.

Evaluation of Etest method for determining fluconazole and voriconazole MICs for 279 clinical isolates of Candida species infrequently isolated from blood

The performance of Etest in fluconazole and voriconazole testing of 279 isolates of uncommon Candida spp. was assessed in comparison with the National Committee for Clinical Laboratory Standards (NCCLS)-approved standard broth microdilution (BMD) method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. Etest MICs were determined with RPMI agar containing 2% glucose and were read after incubation for 48 h at 35 degrees C. The isolates include Candida krusei, C. lusitaniae, C. guilliermondii, C. kefyr, C. rugosa, C. lipolytica, C. pelliculosa, C. dubliniensis, C. famata, C. zeylanoides, C. inconspicua, and C. norvegensis. Overall agreement between Etest and BMD MICs was 96% for fluconazole and 95% for voriconazole. Where a discrepancy was observed between Etest and the reference method, the Etest tended to give lower values with both fluconazole and voriconazole. The Etest method using RPMI agar appears to be a useful method for determining fluconazole and voriconazole susceptibilities of uncommon species of Candida.

In vitro activities of voriconazole, posaconazole, and four licensed systemic antifungal agents against Candida species infrequently isolated from blood

We determined the in vitro susceptibilities of 314 strains of Candida spp., representing 13 species rarely isolated from blood, to posaconazole and voriconazole as well as four licensed systemic antifungal agents (amphotericin B, flucytosine, fluconazole, and itraconazole). The organisms included 153 isolates of C. krusei, 67 isolates of C. lusitaniae, 48 isolates of C. guilliermondii, 10 isolates of C. famata, 10 isolates of C. kefyr, 6 isolates of C. pelliculosa, 5 isolates of C. rugosa, 4 isolates of C. lipolytica, 3 isolates of C. dubliniensis, 3 isolates of C. inconspicua, 2 isolates of C. sake, and 1 isolate each of C. lambica, C. norvegensis, and C. zeylanoides. MIC determinations were made by the National Committee for Clinical Laboratory Standards reference broth microdilution method and Etest (amphotericin B). Resistance to both amphotericin B and fluconazole was observed in strains of C. krusei, C. lusitaniae, C. guilliermondii, C. inconspicua, and C. sake. Resistance to amphotericin B, but not to fluconazole, was also observed among isolates of C. kefyr and C. rugosa. Posaconazole and voriconazole were active (MIC, < or = 1 micro g/ml) against 94 to 100% of these isolates. In contrast to the more common species of Candida causing bloodstream infection, these rare species appear to be less susceptible to the currently licensed systemic antifungal agents, with the exception of voriconazole. Continued surveillance will be necessary to detect the emergence of these species as more prevalent, resistant pathogens. The new triazoles appear to offer acceptable coverage of uncommon Candida sp. bloodstream infections.

Characterization of heteroresistance to fluconazole among clinical isolates of Cryptococcus neoformans

Strains of Cryptococcus neoformans expressing heteroresistance to fluconazole have been described previously. The present study was conducted to investigate the prevalence of heteroresistance among clinical isolates of C. neoformans and to characterize the heteroresistant phenotypes. A total of 107 clinical isolates of C. neoformans for which the MICs of fluconazole ranged from 0.25 to 32 microg/ml were selected. The isolates were chosen to represent a broad geographic distribution. Of the 107 C. neoformans isolates tested, 4 grew on medium containing fluconazole at concentrations that were four to eight times higher than the MICs for each strain. A fifth isolate, for which the fluconazole MIC was 32 microg/ml, grew on agar with 64 microg of fluconazole per ml. These five isolates (4.7% of the total number) were confirmed to exhibit heteroresistant compositions by population analysis. The degree and frequency of resistance varied among the isolates. Stepwise selection by exposure to fluconazole resulted in subclones of all five strains for which the fluconazole MIC was >64 microg/ml. Subclones of three strains demonstrated a homogeneous population of resistant cells on medium containing 64 microg of fluconazole/ml. The resistance was sensitive to incubation temperature, that is, heteroresistance was demonstrable only at 30 degrees C by agar-based tests, and was reversible through serial transfers on fluconazole-free medium over a period of 8 days. These results suggest that the fluconazole-heteroresistant phenotype of C. neoformans exists in a significant proportion of clinical isolates and that fluconazole resistance can be developed by selection from heteroresistant clones and induction by exposure to fluconazole.

Evaluation of Etest method for determining voriconazole and amphotericin B MICs for 162 clinical isolates of Cryptococcus neoformans

The performance of the Etest for voriconazole and amphotericin B susceptibility testing of 162 isolates of Cryptococcus neoformans was assessed against the National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 72 h at 35 degrees C. MICs were determined by Etest for all 162 isolates with RPMI 1640 agar containing 2% glucose (RPG agar) and were read after incubation for 72 h at 35 degrees C. The Etest results for both voriconazole and amphotericin B correlated well with reference MICs. Agreement was 94% for voriconazole and 99% for amphotericin B. When discrepancy was noted between the results obtained by Etest and broth microdilution for voriconazole, the Etest generally provided a higher MIC. The Etest method using RPG agar appears to be a useful method for determining the susceptibility of C. neoformans to voriconazole and amphotericin B.

Age-related trends in pathogen frequency and antimicrobial susceptibility of bloodstream isolates in North America: SENTRY Antimicrobial Surveillance Program, 1997-2000

We report age-related trends in pathogen frequency and antimicrobial susceptibility from 25,745 bloodstream infections (BSI) due to bacterial pathogens reported from medical centres participating in the North American SENTRY Antimicrobial Surveillance Program between January 1997 and September 2000. Staphylococcus aureus, Escherichia coli and coagulase-negative staphylococci (CoNS) were the most common pathogens, together accounting for 55% of all BSI pathogens during this time period. Among nosocomial BSI, CoNS were the most frequently isolated pathogens in infants less than 1 year of age, but S. aureus increased in frequency with increasing age. Among community-onset BSI pathogens, Streptococcus pneumoniae was the most frequently reported pathogen causing BSI in patients aged 1-5, S. aureus among those aged 6-64, and E. coli predominated at the extremes of age (less than 1 year and > or = 65 years of age). Among key organism: antimicrobial agent combinations evaluated, oxacillin resistance in S. aureus increased with increasing age; conversely, oxacillin resistance among CoNS was highest among children 5 years of age or younger. Penicillin resistance among S. pneumoniae BSI was highest in children younger than 5 years, while vancomycin resistance among Enterococcus spp. predominated among nosocomial BSI in patients over 50 years of age. Important age-related differences exist in species distribution and antimicrobial susceptibility of pathogens causing BSI. This information should be helpful for clinicians as they consider empirical antimicrobial therapy for patients with suspected BSI across the age continuum.

Molecular epidemiology of extended-spectrum beta-lactamase-producing, fluoroquinolone-resistant isolates of Klebsiella pneumoniae in Taiwan

Strains of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) have emerged worldwide. Concomitant ciprofloxacin resistance with ESBL production in K. pneumoniae isolates would severely restrict treatment options. Among 39 (18.5%) of 211 ESBL-KP isolates resistant to ciprofloxacin (MIC, >/=4 micro g/ml), 37 (95%) were high level resistant (MIC, >/=16 micro g/ml). These isolates were also cross resistant to the newer fluoroquinolones, including levofloxacin, gatifloxacin, gemifloxacin, and garenoxacin (BMS 284756). Sitafloxacin was most active against these ciprofloxacin-resistant ESBL-KP isolates with MICs for 67% of the isolates being </=2 micro g/ml. The molecular epidemiology of these multiresistant isolates was investigated by automated ribotyping and pulsed-field gel electrophoresis (PFGE). Ribotyping identified 18 different strains among the 39 ciprofloxacin-resistant ESBL-KP isolates. The majority (67%) of these isolates were contained in six ribogroups which were further confirmed by PFGE. The distribution of the six major strains of ciprofloxacin-resistant ESBL-KP within Taiwan included one (ribogroup 255.3-PFGE type E) with a nationwide distribution and several institution-specific strains. Interhospital cooperation appears necessary, with strict infection control practices coupled with restriction of fluoroquinolone and extended-spectrum beta-lactam use to control both the major epidemic strain and the more diverse strains observed within individual institutions.

In vitro activities of 5-fluorocytosine against 8,803 clinical isolates of Candida spp.: global assessment of primary resistance using National Committee for Clinical Laboratory Standards susceptibility testing methods

We determined the in vitro activity of flucytosine (5-fluorocytosine [5FC]) against 8,803 clinical isolates of Candida spp. (18 species) obtained from more than 200 medical centers worldwide between 1992 and 2001. The MICs were determined by broth microdilution tests performed according to NCCLS guidelines by using RPMI 1640 as the test medium and the following interpretive breakpoints: susceptible (S), < or =4 micro g/ml; intermediate (I), 8 to 16 micro g/ml; resistant (R), > or =32 micro g/ml. 5FC was very active against the 8,803 Candida isolates (MIC(90), 1 micro g/ml), 95% S. A total of 99 to 100% of C. glabrata (MIC(90), 0.12 micro g/ml), C. parapsilosis (MIC(90), 0.25 micro g/ml), C. dubliniensis (MIC(90), 0.12 micro g/ml), C. guilliermondii (MIC(90), 0.5 micro g/ml), and C. kefyr (MIC(90), 1 micro g/ml) were susceptible to 5FC at the NCCLS breakpoint. C. albicans (MIC(90), 1 micro g/ml; 97% S) and C. tropicalis (MIC(90), 1 micro g/ml; 92% S) were only slightly less susceptible. In contrast, C. krusei was the least susceptible species: 5% S; MIC(90), 32 micro g/ml. Primary resistance to 5FC is very uncommon among Candida spp. (95% S, 2% I, and 3% R), with the exception of C. krusei (5% S, 67% I, and 28% R). The in vitro activity of 5FC, combined with previous data demonstrating a prolonged post-antifungal effect (2.5 to 4 h) and concentration-independent activity (optimized at 4x MIC), suggest that 5FC could be used in lower doses to reduce host toxicity while maintaining antifungal efficacy.

Antifungal susceptibility of South African oral yeast isolates from HIV/AIDS patients and healthy individuals

The in vitro antifungal susceptibility profile of 589 oral yeast isolates from HIV/AIDS patients and healthy South Africans was determined against amphotericin B, nystatin, 5-fluorocytosine (5-FC), clotrimazole, miconazole, ketoconazole, itraconazole and fluconazole. The broth microdilution method of the National Committee on Clinical Laboratory Standards was used and MIC(50) and MIC(90) determined. A 100% susceptibility to fluconazole was observed among the 466 isolates of Candida albicans. Among C. krusei, the second most common isolate, only 2.6% of isolates were susceptible to fluconazole and itraconazole. Despite the lack of previous exposure to antifungal agents, very little difference was observed in the antifungal profile between the South African isolates and isolates from the United States (U.S.), Canada and South America. South Africa has a particularly high incidence of HIV-infection and oral candidiasis is the most common oral complication in these patients. This study provides important baseline data as the isolates were collected prior to fluconazole being made freely available to HIV/AIDS patients attending government health clinics.