Minimizing the workup of blood culture contaminants: implementation and evaluation of a laboratory-based algorithm

An algorithm was implemented in the clinical microbiology laboratory to assess the clinical significance of organisms that are often considered contaminants (coagulase-negative staphylococci, aerobic and anaerobic diphtheroids, Micrococcus spp., Bacillus spp., and viridans group streptococci) when isolated from blood cultures. From 25 August 1999 through 30 April 2000, 12,374 blood cultures were submitted to the University of Iowa Clinical Microbiology Laboratory. Potential contaminants were recovered from 495 of 1,040 positive blood cultures. If one or more additional blood cultures were obtained within +/-48 h and all were negative, the isolate was considered a contaminant. Antimicrobial susceptibility testing (AST) of these probable contaminants was not performed unless requested. If no additional blood cultures were submitted or there were additional positive blood cultures (within +/-48 h), a pathology resident gathered patient clinical information and made a judgment regarding the isolate's significance. To evaluate the accuracy of these algorithm-based assignments, a nurse epidemiologist in approximately 60% of the cases performed a retrospective chart review. Agreement between the findings of the retrospective chart review and the automatic classification of the isolates with additional negative blood cultures as probable contaminants occurred among 85.8% of 225 isolates. In response to physician requests, AST had been performed on 15 of the 32 isolates with additional negative cultures considered significant by retrospective chart review. Agreement of pathology resident assignment with the retrospective chart review occurred among 74.6% of 71 isolates. The laboratory-based algorithm provided an acceptably accurate means for assessing the clinical significance of potential contaminants recovered from blood cultures.

In vitro activities of ravuconazole and voriconazole compared with those of four approved systemic antifungal agents against 6,970 clinical isolates of Candida spp

The in vitro activities of ravuconazole and voriconazole were compared with those of amphotericin B, flucytosine (5FC), itraconazole, and fluconazole against 6,970 isolates of Candida spp. obtained from over 200 medical centers worldwide. Both ravuconazole and voriconazole were very active against all Candida spp. (MIC at which 90% of the isolates tested are inhibited [MIC(90)], 0.25 microg/ml; 98% of MICs were < or 1 microg/ml); however, a decrease in the activities of both of these agents was noted among isolates that were susceptible-dose dependent (fluconazole MIC, 16 to 32 microg/ml) and resistant (MIC, > or = 64 microg/ml) to fluconazole. Candida albicans was the most susceptible species (MIC(90) of both ravuconazole and voriconazole, 0.03 microg/ml), and C. glabrata was the least susceptible species (MIC(90), 1 to 2 microg/ml). Ravuconazole and voriconazole were each more active in vitro than amphotericin B, 5FC, itraconazole, and fluconazole against all Candida spp. and were the only agents with good in vitro activity against C. krusei. These results provide further evidence for the spectrum and potency of ravuconazole and voriconazole against a large and geographically diverse collection of Candida spp.

Precision and accuracy of fluconazole susceptibility testing by broth microdilution, Etest, and disk diffusion methods

Interpretive agreements among the results of fluconazole broth microdilution tests, Etests, and disk diffusion tests were documented by evaluating 495 Candida spp. Microdilution reference test results were in agreement with 96% of the Etest results; most discrepancies were minor differences. Fluconazole resistance of Candida krusei strains often required a full 48 h of incubation in order to be observed by the standard method. For the disk diffusion tests that were performed on Mueller-Hinton agar with glucose and methylene blue, 97% of results were in agreement with those of the reference test, especially when zones of inhibition were measured after the first 24 h of incubation. Some Candida glabrata isolates failed to grow satisfactorily until a full 48 h of incubation was completed. Precision was determined by testing 50 selected isolates in triplicate in each of three laboratories. The reproducibility of results of disk diffusion tests was comparable to that of the reference method. With all procedures, determination of test results was particularly challenging with some strains, and new methods are needed in order to improve endpoint definition.

Clinical evaluation of a frozen commercially prepared microdilution panel for antifungal susceptibility testing of seven antifungal agents, including the new triazoles posaconazole, ravuconazole, and voriconazole

A commercially prepared frozen broth microdilution panel (Trek Diagnostic Systems, Westlake, Ohio) was compared with a reference microdilution panel for antifungal susceptibility testing of two quality control (QC) strains and 99 clinical isolates of Candida spp. The antifungal agents tested included amphotericin B, flucytosine, fluconazole, itraconazole, posaconazole, ravuconazole, and voriconazole. Microdilution testing was performed according to NCCLS recommendations. MIC endpoints were read visually after 48 h of incubation and were assessed independently for each microdilution panel. The MICs for the QC strains were within published limits for both the reference and Trek microdilution panels. Discrepancies among MIC endpoints of no more than 2 dilutions were used to calculate the percent agreement. Acceptable levels of agreement between the Trek and reference panels were observed for all antifungal agents tested against the 99 clinical isolates. The overall agreement for each antifungal agent ranged from 96% for ravuconazole to 100% for amphotericin B. The Trek microdilution panel appears to be a viable alternative to frozen microdilution panels prepared in-house.

Epidemiology of candidemia: 3-year results from the emerging infections and the epidemiology of Iowa organisms study

Bloodstream infections due to Candida species cause significant morbidity and mortality. Surveillance for candidemia is necessary to detect trends in species distribution and antifungal resistance. We performed prospective surveillance for candidemia at 16 hospitals in the State of Iowa from 1 July 1998 through 30 June 2001. Using U.S. Census Bureau and Iowa Hospital Association data to estimate a population denominator, we calculated the annual incidence of candidemia in Iowa to be 6.0 per 100,000 of population. Candida albicans was the most common species detected, but 43% of candidemias were due to species other than C. albicans. Overall, only 3% of Candida species were resistant to fluconazole. However, Candida glabrata was the most commonly isolated species other than C. albicans and demonstrated some resistance to azoles (fluconazole MIC at which 90% of the isolates tested are inhibited, 32 microg/ml; 10% resistant, 10% susceptible dose dependent). C. glabrata was more commonly isolated from older patients (P = 0.02) and caused over 25% of candidemias among persons 65 years of age or older. The investigational triazoles posaconazole, ravuconazole, and voriconazole had excellent in vitro activity overall against Candida species. C. albicans is the most important cause of candidemia and remains highly susceptible to available antifungal agents. However, C. glabrata has emerged as an important and potentially antifungal resistant cause of candidemia, particularly among the elderly.

Antifungal activities of posaconazole, ravuconazole, and voriconazole compared to those of itraconazole and amphotericin B against 239 clinical isolates of Aspergillus spp. and other filamentous fungi: report from SENTRY Antimicrobial Surveillance Program, 2000

Posaconazole, ravuconazole, and voriconazole are new triazole derivatives that possess potent, broad-spectrum antifungal activity. We evaluated the in vitro activity of these investigational triazoles compared with that of itraconazole and amphotericin B against 239 clinical isolates of filamentous fungi from the SENTRY Program, including Aspergillus spp. (198 isolates), Fusarium spp. (7 isolates), Penicillium spp. (19 isolates), Rhizopus spp. (4 isolates), Mucor spp. (2 isolates), and miscellaneous species (9 isolates). The isolates were obtained from 16 different medical centers in the United States and Canada between January and December 2000. In vitro susceptibility testing was performed using the microdilution broth method outlined in the National Committee for Clinical Laboratory Standards M38-P document. Overall, posaconazole was the most active compound, inhibiting 94% of isolates at a MIC of < or = 1 microg/ml, followed by voriconazole (91%), amphotericin B (89%), ravuconazole (88%), and itraconazole (70%). All three new triazoles demonstrated excellent activity (MIC, < or = 1 microg/ml) against Aspergillus spp. (114 Aspergillus fumigatus, 22 Aspergillus niger, 13 Aspergillus flavus, 9 Aspergillus versicolor, 8 Aspergillus terreus, and 32 Aspergillus spp.): posaconazole (98%), voriconazole (98%), ravuconazole (92%), amphotericin B (89%), and itraconazole (72%). None of the triazoles were active against Fusarium spp. (MIC at which 50% of the isolates tested were inhibited [MIC(50)], >8 microg/ml) or Mucor spp. (MIC(50), >8 microg/ml). Posaconazole and ravuconazole were more active than voriconazole against Rhizopus spp. (MIC(50), 1 to 2 microg/ml versus >8 microg/ml, respectively). Based on these results, all three new triazoles exhibited promising activity against Aspergillus spp. and other less commonly encountered isolates of filamentous fungi. The clinical value of these in vitro data remains to be seen, and in vitro-in vivo correlation is needed for both new and established antifungal agents. Surveillance efforts should be expanded in order to monitor the spectrum of filamentous fungal pathogens and their in vitro susceptibility as these new antifungal agents are introduced into clinical use.

Emerging elevated mupirocin resistance rates among staphylococcal isolates in the SENTRY Antimicrobial Surveillance Program (2000): correlations of results from disk diffusion, Etest and reference dilution methods

Staphylococci cause one-third of all serious invasive infections in the SENTRY Antimicrobial Surveillance Program including bacteremias and lower respiratory tract infections. Staphylococci are also commensals of the skin and nasal passages; therefore, topical agents active against these organisms are valuable in preventing infections or transfer of the organisms between patients and/or health care workers. Mupirocin is a potent topical anti-staphylococcal compound, but its effectiveness has been compromised by emerging resistance. In early 2000, the SENTRY Program detected 302 mupirocin-resistant isolates (131 Staphylococcus aureus, and 171 coagulase-negative staphylococci [CoNS]) from the United States (19/25 medical centers), Canada (4/5), Latin America (3/9) and Europe (7/18). One hundred sixty-eight mupirocin-resistant and 59 susceptible isolates were tested further by reference MIC, Etest (AB BIODISK, Solna, Sweden) and disk diffusion (5-microg) methods. Mupirocin resistance rates for blood stream infections varied by geographic area: for S. aureus from 1.9 to 5.6%, and for CoNS from 12.8 to 39.9%. Using elevated mupirocin MIC results, two resistant populations were noted: low-level resistance at 8-128 microg/mL and high-level resistance at > or = 1024 microg/mL. Acceptable correlation was observed between Etest and disk diffusion results (r = 0.84) without serious intermethod interpretive errors. High-level resistant isolates had heavy growth with no visible zone around the disk; low-level resistant isolates produced hazy zones of inhibition, and susceptible strains had clear zones of inhibition at > or = 17 mm. As mupirocin resistance can be plasmid-mediated, the prudent and appropriate use of this topical agent is important to minimize the ongoing development of resistance. Local surveillance for emerging mupirocin resistance appears warranted particularly in the United States and Canada, pragmatically using a disk diffusion test screening. Where more precise data are needed, the Etest is a very accurate method for distinguishing mupirocin low-level from high-level resistance patterns.

Trends in antifungal susceptibility of Candida spp. isolated from pediatric and adult patients with bloodstream infections: SENTRY Antimicrobial Surveillance Program, 1997 to 2000

From 1 January 1997 through 31 December 2000, 2,047 bloodstream infections (BSIs) due to Candida spp. were reported from hospitals in the United States, Canada, Latin America, and Europe participating in the SENTRY Antifungal Surveillance Program. Among individuals in four age groups (< or =1, 2 to 15, 16 to 64, and > or =65 years) Candida albicans was the most common species, causing 60, 55, 55, and 50% of infections, respectively. C. glabrata caused 17 to 23% of BSIs in those ages 16 to 64 and > or = 65 years, whereas it caused only 3% of BSIs in the individuals in the two younger age groups (P < 0.001). C. parapsilosis (which caused 21 to 24% of BSIs) and C. tropicalis (which caused 7 to 10% of BSIs) were more common than C. glabrata in individuals ages < or =1 year and 2 to 15 years. Isolates of Candida spp. showed a trend of decreasing susceptibility to fluconazole, itraconazole, and amphotericin B with increasing patient age (P < or = 0.01). None of the C. glabrata isolates from individuals < or =1 year old were resistant to fluconazole, whereas they made up 5 to 9% of isolates from individuals ages 16 to 64 and > or =65 years. Isolates of C. tropicalis from patients < or =1 year old were more susceptible to flucytosine (MIC at which 90% of isolates are inhibited [MIC(90)], 0.5 microg/ml; 0% resistant isolates) than those from patients > or =65 years old (MIC(90), 32 microg/ml; 11% resistant isolates). The investigational triazoles posaconazole, ravuconazole, and voriconazole were all highly active against all species of Candida from individuals in all age groups. These data demonstrate differences in the species distributions of pathogens and differences in antifungal resistance among isolates from individuals in the pediatric and adult age groups. Ongoing surveillance will enhance efforts to limit the extent of antifungal resistance in individuals in various age groups.

The molecular epidemiology of penicillin-resistant Streptococcus pneumoniae in the United States, 1994-2000

The genetic relatedness of 672 penicillin-resistant isolates of Streptococcus pneumoniae (PRSP) recovered during national surveillance studies conducted in the United States during the periods of 1994-1995, 1997-1998, and 1999-2000 was determined by use of pulsed-field gel electrophoresis (PFGE). Overall, 104 different PFGE types were elucidated. For all study periods combined, the 12 most prevalent PFGE types included >75% of all isolates, and 5 types were closely related to widespread clones (Spain(23F)-1, France(9V)-3, Spain(6B)-2, Tennessee(23F)-4, and Taiwan(19F)-14). From 1994-1995 to 1999-2000, 3 major PFGE types (not closely related to 16 recognized clones) increased in prevalence. Multidrug resistance was identified among 96%-100% of the isolates in 9 of 12 predominant PFGE types. The prevalence of erythromycin resistance increased within 4 major PFGE types. These observations support the hypothesis that the dominant factor in the emergence of PRSP in the United States during the 1990s has been human-to-human spread of relatively few clonal groups that harbor resistance determinants to multiple classes of antibiotics.

Comparison of Etest, chequerboard dilution and time-kill studies for the detection of synergy or antagonism between antifungal agents tested against Candida species

Currently, there is considerable debate regarding the best in vitro method for testing antifungal combinations against Candida spp. In this study, we compared the results obtained by chequerboard dilution, time-kill studies and Etest for several antifungal combinations against Candida spp. Three Candida albicans isolates (fluconazole MICs of 1.0, 32 and >256 mg/L) and three non-albicans Candida isolates (C. glabrata, C. tropicalis and C. krusei) were tested in RPMI 1640 medium. By chequerboard testing, the majority of antifungal combinations were found to be indifferent. Notably, antagonism was identified by time-kill studies and by Etest for combinations of amphotericin B-fluconazole, but it was not detected by the chequerboard method. Pre-exposure of isolates to fluconazole did not affect results of the Etest or chequerboard method, but it did increase the frequency of antagonism noted by time-kill methods. This study indicates that chequerboard dilution testing in RPMI medium may not reliably detect the attenuation of amphotericin B activity. Of the three methods, Etest was the simplest to use and yielded reproducible results for testing antifungal combinations.

Comparative antimicrobial spectrum and activity of BMS284756 (T-3811; a desfluoroquinolone) tested against an international collection of staphylococci and enterococci, including in vitro test development and intermethod comparisons

The study was initiated to determine the in vitro activity and MIC/disk test comparisons of BMS284756, a new des-fluoro(6)-quinolone, against isolates of staphylococci and enterococci from the SENTRY Antimicrobial Surveillance Program, 2000. Isolates were tested by reference broth microdilution and standardized disk diffusion methods. Against 3,789 strains of gram-positive cocci from the SENTRY Program (2000), the BMS284756 MIC90 and percentage susceptible at < or = 2 and < or = 4 microg/ml were: Staphylococcus aureus (4 microg/ml; 89.3 and 97.1%), coagulase-negative staphylococci (CoNS; 4 microg/ml; 86.1 and 96.0%) and enterococci (> 4 microg/ml; 62.0 and 76.2%). Also tested were selected staphylococci (300 strains) and enterococci (102 strains) by two standardized methods. The activity of BMS284756 was highly correlated with oxacillin resistance among staphylococci. Oxacillin-susceptible staphylococci were all inhibited by BMS284756 at < or = 0.5 microg/ml, whereas oxacillin-resistant strains required inhibitory concentrations of > or = 1 microg/ml. Excellent correlation was observed between the MIC and 5-microg disk zone diameter for staphylococci and enterococci (r=0.91 to 0.93). Among vancomycin-susceptible enterococci, 67% of Enterococcus faecalis, 25% of E. faecium, and 76% of other Enterococcus spp. isolates were inhibited by BMS284756 at < or = 2 microg/ml. All vancomycin-resistant enterococci (VRE; 11 E. faecalis and 15 E. faecium) were inhibited by > or = 2 microg/ml of BMS284756. Among the non-VRE, non-faecium enterococcal isolates (n=64), 62% were inhibited by < or = 0.5 microg/ml. BMS284756 showed excellent activity against oxacillin-susceptible staphylococci and moderate activity against enterococci other than VRE and E. faecium. Acceptable correlations were observed between MIC and disk test results for both tested genus groups.

Frequency of pathogen occurrence and antimicrobial susceptibility among community-acquired respiratory tract infections in the respiratory surveillance program study: microbiology from the medical office practice environment

Continuing problems of antimicrobial resistance have prompted the initiation of several surveillance programs. Few, if any, of these programs focus on community-acquired respiratory tract infections seen in routine office-based practices. The Respiratory Surveillance Program (RESP; 1999-2000) in 674 community-based physician office practices in the United States determined the frequency of potential bacterial pathogens including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in patients diagnosed clinically with community-acquired pneumonia, acute exacerbations of chronic bronchitis, and sinusitis throughout all 9 US census/geographic regions. Susceptibility to the penicillins (ampicillin, penicillin), oral cephalosporins, fluoroquinolones (gatifloxacin, levofloxacin, ciprofloxacin), macrolides (erythromycin, azithromycin, clarithromycin), tetracycline, and trimethoprim/sulfamethoxazole was determined by reference methods. Patients were required to have a culturable focus of infection, and specimens were immediately sent to a reference laboratory. Among 22,689 total specimens (610 community-acquired pneumonia, 4,779 acute exacerbation of chronic bronchitis, 16,213 sinusitis, 1,087 other), H influenzae was the most commonly isolated organism from patients with community-acquired pneumonia (38%) and acute exacerbation of chronic bronchitis (35%) in all nine geographic regions. S pneumoniae was isolated in 18% of community-acquired pneumonia cases, 13% of acute exacerbation of chronic bronchitis cases, and 11% of sinusitis cases. M catarrhalis was most commonly isolated from the nasopharynx of patients with sinusitis (29%). High-level resistance to penicillin (2 microg/mL or greater; 16% overall) and the macrolides (32% to 35%) among S pneumoniae varied both with site of infection and with geographic region. The greatest resistance was observed among isolates from the nasopharynx of patients with sinusitis and from patients from the East South Central or South Atlantic regions of the United States. Although the susceptibility of H influenzae and M catarrhalis to the tested antimicrobials did not vary with the type of infection, beta-lactamase-mediated resistance to ampicillin among H influenzae ranged from 15% in New England to 32% in the East South Central region. The fluoroquinolones were highly active against these cultured isolates from community-acquired respiratory tract infection patients, with >99% of all S pneumoniae, H influenzae, and M catarrhalis strains susceptible to gatifloxacin (MIC(90), 0.5 microg/mL) and levofloxacin (MIC(90), 2 microg/mL). The extended-spectrum fluoroquinolones appear well suited for community-acquired respiratory tract infection therapy, including pathogens other than pneumococcus, H influenzae, and M catarrhalis.

Antifungal susceptibility testing. New technology and clinical applications

The state of the art for susceptibility testing of yeasts is comparable with that of bacteria. Standardized methods for performing antifungal susceptibility testing are reproducible, accurate, and available in clinical laboratories. The development of quality control limits and interpretive criteria for a limited number of antifungal agents provides a basis for the application of this testing in the clinical laboratory. A proficiency testing program is available as a quality assurance measure for laboratories and has documented steady improvement among laboratories using the NCCLS method. As with antibacterial agents, surveillance programs are now in place using reference quality testing methods to monitor antifungal resistance trends on a global scale. It is clear that antifungal susceptibility testing can predict outcome in several clinical situations. Susceptibility testing is most helpful in dealing with infection caused by non-albicans species of Candida, and susceptibility testing of azoles is increasingly important in the management of candidiasis in critically ill patients. Susceptibility testing also has been standardized for filamentous fungi that cause invasive infections. Studies are ongoing to further refine this approach and evaluate the in vivo correlation with the in vitro data for molds. Future efforts must be directed toward establishing and validating interpretive break-points for licensed antifungals such as amphotericin B, and for new antifungals that are not yet licensed. Finally, procedures must be optimized for testing non-Candida yeasts (e.g., C. neoformans) and molds.

Antioxidant enzyme expression in clinical isolates of Pseudomonas aeruginosa: identification of an atypical form of manganese superoxide dismutase

Expression of superoxide dismutases (FeSOD and MnSOD) and catalases by laboratory strains of Pseudomonas aeruginosa is modulated by exogenous factors. Whether clinical isolates behave similarly and whether antioxidant enzyme expression influences P. aeruginosa virulence remain unclear. Fifty-seven P. aeruginosa blood culture isolates, plus seven pairs of blood and local-site isolates, were examined for FeSOD, MnSOD, and catalase production in vitro. Under iron-replete growth conditions FeSOD and catalase activities were maximized. MnSOD was not detected. FeSOD and catalase activity decreased under iron-limited growth conditions, whereas MnSOD activity appeared. SOD and catalase activity did not change with site of isolation or by patient. MnSOD could not be expressed by one isolate due to a missense mutation in sodA that produced a premature stop codon. Eleven percent of the isolates expressed a novel, rapidly migrating MnSOD that was associated with missense mutations in the normal stop codon of sodA. We conclude that clinical P. aeruginosa isolates vary little in FeSOD and catalase expression. Some strains produce a newly described MnSOD variant, whereas one is deficient in MnSOD production. The absence of MnSOD expression in a P. aeruginosa strain causing invasive human disease indicates that MnSOD is probably not essential for P. aeruginosa virulence.

Antimicrobial resistance trends in medical centers using carbapenems: report of 1999 and 2000 results from the MYSTIC program (USA)

Trends in susceptibility to antimicrobials were assessed from United States participants using 4488 isolates in the MYSTIC Program, 1999 (10 centers) through 2000 (15 centers). Diverse types of hospitals (general service, university, cancer, federal, pediatric, cystic fibrosis) were enrolled from 13 states. In 2000, oxacillin-susceptible staphylococci were 100% susceptible to meropenem, imipenem, and cefepime; but only 88% of strains were susceptible to ceftazidime. Among Enterobacteriaceae, > or = 96% of Enterobacter spp., Citrobacter spp., and Serratia spp. were susceptible to meropenem, imipenem, and cefepime; but ceftazidime, ceftriaxone, and piperacillin/tazobactam had 5-20% resistance rates. Extended-spectrum beta-lactamase resistance rates in Klebsiella spp. and Escherichia coli (6-7% and 3-5%, respectively) were stable over 2 years. Acinetobacter spp. were 78-81% susceptible to carbapenems but only 63-72% susceptible to ciprofloxacin. Meropenem, tobramycin, and piperacillin/tazobactam were the most active against Pseudomonas aeruginosa, but ciprofloxacin inhibited only 74% in 2000. Overall, meropenem remained the most potent agent, especially against ceftazidime- or piperacillin/tazobactam-resistant strains.

Antimicrobial susceptibility testing of clinical isolates of Bordetella pertussis from northern California: report from the SENTRY Antimicrobial Surveillance Program

Reports of an increased clinical incidence of pertussis and the development of resistance by Bordetella pertussis to erythromycin prompted the collection and testing of recent clinical isolates from patients in northern California against a range of antimicrobial agents by the Etest (AB BIODISK, Solna, Sweden) method. All isolates were fully susceptible to all eight agents tested (MIC, <or=0.38 microg/ml), including newer fluoroquinolones, such as gatifloxacin (MIC of which 90% of the isolates tested are inhibited, 0.006 microg/ml), which may be used in cases of adolescent or adult pertussis. Continued surveillance of B. pertussis isolates appears to be a prudent practice.

Evaluation of Etest method for determining caspofungin (MK-0991) susceptibilities of 726 clinical isolates of Candida species

The performance of the Etest for testing the susceptibilities to caspofungin (MK-0991) of 726 isolates of Candida spp. was assessed against the National Committee for Clinical Laboratory Standards (NCCLS) microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. MICs were determined by Etest for all 726 isolates with RPMI agar containing 2% glucose (RPG) and were read after incubation for 48 h at 35 degrees C. The Candida isolates included Candida albicans (n = 486), Candida glabrata (n = 96), Candida tropicalis (n = 51), Candida parapsilosis (n = 47), Candida krusei (n = 11), Candida lusitaniae (n = 2), and Candida guilliermondii (n = 33). In addition, a subset of 314 isolates were also tested by Etest using Casitone agar (CAS) and antibiotic medium 3 agar (AM3). The Etest results obtained using RPG correlated well with reference MICs. Overall agreement was 94% with RPG, 82% with CAS, and 79% with AM3. When RPG was used, agreement ranged from 79% for C. parapsilosis to 100% for C. krusei, C. lusitaniae, and C. guilliermondii. When CAS was used, agreement ranged from 0% for C. lusitaniae to 100% for C. glabrata. With AM3, agreement ranged from 0% for C. lusitaniae to 100% for C. guilliermondii. All three media supported growth of each of the Candida species. Etest results were easy to read, with sharp zones of inhibition. In most instances (75%) where a discrepancy was observed between the Etest and the reference method, the Etest MIC was lower. The Etest method using RPG appears to be useful for determining caspofungin susceptibilities of Candida species.

Spectrum and activity of three contemporary fluoroquinolones tested against Pseudomonas aeruginosa isolates from urinary tract infections in the SENTRY Antimicrobial Surveillance Program (Europe and the Americas; 2000): more alike than different!

The spectrum and potency of ciprofloxacin, gatifloxacin and levofloxacin was compared to that of 10 other agents against urinary tract isolates of Pseudomonas aeruginosa among patients in the year 2000 SENTRY Antimicrobial Surveillance Program (Europe, Latin America, North America). Dramatic differences were observed between isolates in geographic areas with the most fluoroquinolone-resistant strains detected in Latin America (54.5% resistance) compared to resistance rates of 40.8-43.7% and 28.3-29.2% for Europe and North America, respectively. Overall, no significant differences were observed between the spectrums of these fluoroquinolones (37.1-38.8% resistance) for therapy of P. aeruginosa urinary tract infections in hospitalized patients. Generally, in this world wide sample, aminoglycosides, carbapenems (imipenem, meropenem), cefepime, and piperacillin with or without tazobactam possessed a wider range of activity and spectrum versus current P. aeruginosa clinical isolates.

Trends in antifungal drug susceptibility of Cryptococcus neoformans isolates in the United States: 1992 to 1994 and 1996 to 1998

The antifungal drug susceptibilities of two collections of Cryptococcus neoformans isolates obtained through active laboratory-based surveillance from 1992 to 1994 (368 isolates) and 1996 to 1998 (364 isolates) were determined. The MICs of fluconazole, itraconazole, and flucytosine were determined by the National Committee for Clinical Laboratory Standards broth microdilution method; amphotericin B MICs were determined by the E-test. Our results showed that the MIC ranges, the MICs at which 50% of isolates are inhibited (MIC(50)s), and the MIC(90)s of these four antifungal agents did not change from 1992 to 1998. In addition, very small numbers of isolates showed elevated MICs suggestive of in vitro resistance. The MICs of amphotericin B were elevated (>or=2 microg/ml) for 2 isolates, and the MICs of flucytosine were elevated (>or=32 microg/ml) for 14 isolates. Among the azoles, the fluconazole MIC was elevated (>or=64 microg/ml) for 8 isolates and the itraconazole MIC (>or=1 microg/ml) was elevated for 45 isolates. Analysis of 172 serial isolates from 71 patients showed little change in the fluconazole MIC over time. For isolates from 58 patients (82% of serial cases) there was either no change or a twofold change in the fluconazole MIC. In contrast, for isolates from seven patients (12% of serial cases) the increase in the MIC was at least fourfold. For isolates from another patient there was a 32-fold decrease in the fluconazole MIC over a 1-month period. We conclude that in vitro resistance to antifungal agents remains uncommon in C. neoformans and has not significantly changed with time during the past decade.

Evaluation of Etest method for determining posaconazole MICs for 314 clinical isolates of Candida species

The performance of the Etest for posaconazole (SCH 56592) susceptibility testing of 314 isolates of Candida spp. was assessed against the National Committee for Clinical Laboratory Standards (NCCLS) microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. MICs were determined by Etest for all 314 isolates with RPMI agar containing 2% glucose (RPG agar) and were read after incubation for 48 h at 35 degrees C. The Candida isolates included C. albicans (n = 174), C. glabrata (n = 57), C. tropicalis (n = 31), C. parapsilosis (n = 39), C. krusei (n = 5), C. guilliermondii (n = 6), and C. lusitaniae (n = 2). The Etest results correlated well with reference MICs. Overall agreement was 95%, and agreements for individual species were as follows: C. krusei, 100%; C. albicans, 98%; C. tropicalis, 97%; C. glabrata, 93%; C. parapsilosis, 85%; C. guilliermondii, 83%; and C. lusitaniae, 50%. The problem of trailing end points was minimized with RPG agar, and good agreement with broth dilution MICs was obtained when discernible growth within an established ellipse was ignored. The Etest method using RPG agar appears to be a useful method for determining posaconazole susceptibilities of Candida species.

Antifungal susceptibility testing: practical aspects and current challenges

Development of standardized antifungal susceptibility testing methods has been the focus of intensive research for the last 15 years. Reference methods for yeasts (NCCLS M27-A) and molds (M38-P) are now available. The development of these methods provides researchers not only with standardized methods for testing but also with an understanding of the variables that affect interlaboratory reproducibility. With this knowledge, we have now moved into the phase of (i) demonstrating the clinical value (or lack thereof) of standardized methods, (ii) developing modifications to these reference methods that address specific problems, and (iii) developing reliable commercial test kits. Clinically relevant testing is now available for selected fungi and drugs: Candida spp. against fluconazole, itraconazole, flucytosine, and (perhaps) amphotericin B; Cryptococcus neoformans against (perhaps) fluconazole and amphotericin B; and Aspergillus spp. against (perhaps) itraconazole. Expanding the range of useful testing procedures is the current focus of research in this area.

Comparison of the Vitek gram-positive susceptibility 106 card, the MRSA-Screen latex agglutination test, and mecA analysis for detecting oxacillin resistance in a geographically diverse collection of clinical isolates of coagulase-negative staphylococci

The Vitek automated susceptibility testing system with a modified gram-positive susceptibility (GPS) 106 card (bioMerieux Vitek, Inc., Hazelwood. Mo.) and a rapid slide latex agglutination test (MRSA-Screen test; Denka Seiken Co., Ltd., Tokyo, Japan) were evaluated for their abilities to detect oxacillin resistance in coagulase-negative staphylococci (CoNS). The reference broth microdilution method and the detection of the mecA gene by PCR ("gold standard" reference result) were used to compare the results obtained with the commercial products. A total of 123 clinical isolates consisting of eight species were selected from U.S. surveillance collections. Among the mecA-positive isolates (95 strains), 30 isolates were initially negative on the MRSA-Screen test read at 3 min. When the agglutination reaction was extended for 10 min, 26 of the 30 isolates became positive. For a different four isolates, the oxacillin MIC was < or =0.25 microg/ml on the Vitek GPS 106 card. Among the mecA-negative isolates (28 strains), for two Staphylococcus warneri, two S. lugdunensis, and two S. saprophyticus strains MICs were > or =0.5 microg/ml by the reference broth microdilution method. Four of these isolates were also categorized as resistant with the Vitek GPS 106 card and two isolates were positive by the MRSA-Screen test. Overall, the MRSA-Screen test, GPS 106 card, and reference broth microdilution method had sensitivities of 95.7 (result at 10 min), 95.7, and 100%, respectively, and specificities of 92.8, 85.7, and 78.5%, respectively. Although the MRSA-Screen test required a slight procedural modification, both commercial methods achieved a sensitivity and specificity at detecting oxacillin resistance in CoNS at a level that was acceptable for clinical laboratory use.

In vitro activities of posaconazole (Sch 56592) compared with those of itraconazole and fluconazole against 3,685 clinical isolates of Candida spp. and Cryptococcus neoformans

Posaconazole is a new investigational triazole with broad-spectrum antifungal activity. The in vitro activities of posaconazole were compared with those of itraconazole and fluconazole against 3,685 isolates of Candida spp. (3,312 isolates) and C. neoformans (373 isolates) obtained from over 70 different medical centers worldwide. The MICs of the antifungal drugs were determined by broth microdilution tests performed according to the National Committee for Clinical Laboratory Standards method using RPMI 1640 as the test medium. Posaconazole was very active against all Candida spp. (MIC at which 90% of the isolates were inhibited [MIC(90)], 0.5 microg/ml; 97% of MICs were < or =1 microg/ml) and C. neoformans (MIC(90), 0.5 microg/ml; 100% of MICs were < or =1 microg/ml). Candida albicans was the most susceptible species of Candida (MIC(90), 0.06 microg/ml), and Candida glabrata was the least susceptible (MIC(90), 4 microg/ml). Posaconazole was more active than itraconazole and fluconazole against all Candida spp. and C. neoformans. These results provide further evidence for the spectrum and potency of posaconazole against a large and geographically diverse collection of clinically important fungal pathogens.

Optimal susceptibility testing conditions for detection of azole resistance in Aspergillus spp.: NCCLS collaborative evaluation. National Committee for Clinical Laboratory Standards

The most important role of susceptibility testing is to identify potentially resistant isolates for the agent being evaluated. Standard testing guidelines recently have been proposed for antifungal susceptibility testing of filamentous fungi (molds). This collaborative (eight centers) study evaluated further newly proposed guidelines (NCCLS, proposed standard M38-P, 1998) and other testing conditions for antifungal susceptibility testing of Aspergillus spp. to itraconazole and three new triazoles, posaconazole (SCH56592), ravuconazole (BMS-207147), and voriconazole. MICs of itraconazole, posaconazole, ravuconazole, and voriconazole for 15 selected isolates of three species of Aspergillus (A. fumigatus, A. flavus, and A. terreus) with well documented in vitro, clinical, or animal data were determined in each center by using four medium formulations (standard RPMI-1640 [RPMI], RPMI with 2% dextrose, antibiotic medium 3 [M3], and M3 with 2% dextrose) and two criteria of MIC determination (complete [MIC-0s] and prominent [MIC-2s] growth inhibition) at 24, 48, and 72 h. The highest reproducibility (92 to 99%) was seen with the standard RPMI and M3 media. Moreover, the distinction between itraconazole-resistant (MICs of >8 microg/ml for clinically resistant strains) and -susceptible (MICs of 0.03 to 1 microg/ml) isolates, as well as between a voriconazole-resistant laboratory mutant and other isolates (voriconazole MICs of 2 to >8 versus 0.12 to 2 microg/ml), was more consistently evident with the standard RPMI medium and when MIC-0s were determined at 48 h. These results provide further refinement of the testing guidelines for susceptibility testing of Aspergillus spp. and warrant consideration for inclusion in the future NCCLS document M38-A.