Fluoroquinolone Resistance in Bacteroides fragilis following Sparfloxacin Exposure

ABSTRACT In vitro pharmacodynamic studies investigating the antimicrobial properties of five fluoroquinolones, (trovafloxacin, sparfloxacin, clinafloxacin, levofloxacin, and ciprofloxacin) againstBacteroides fragilis ATCC 23745 were conducted. The times required to reduce the viable counts by 3 log units were as follows: clinafloxacin, 2.9 h; levofloxacin, 4.6 h; trovafloxacin, 6 h; and sparfloxacin, 10 h. Exposure to ciprofloxacin did not achieve a 3-log decrease in viable counts. The susceptibility ofB. fragilis was determined both prior to exposure and following 24 h of exposure to each of the five fluoroquinolones tested. The MICs of clinafloxacin, levofloxacin, trovafloxacin, sparfloxacin, ciprofloxacin, metronidazole, cefoxitin, chloramphenicol, and clindamycin were determined by the broth microdilution method. The MICs for B. fragilis preexposure were as follows: clinafloxacin, 0.25 μg/ml; trovafloxacin, 0.5 μg/ml; sparfloxacin, 2 μg/ml; levofloxacin, 2 μg/ml; and ciprofloxacin, 8 μg/ml. Similar pre- and postexposure MICs were obtained for cultures exposed to trovafloxacin, clinafloxacin, levofloxacin, and ciprofloxacin. However, following 24 h of exposure to sparfloxacin, a fluoroquinolone-resistant strain emerged. The MICs for this strain were as follows: clinafloxacin, 1 μg/ml; trovafloxacin, 4 μg/ml; sparfloxacin, 16 μg/ml; levofloxacin, 16 μg/ml; and ciprofloxacin, 32 μg/ml. No changes in the susceptibility of B. fragilispre- and postexposure to sparfloxacin were noted for metronidazole (MIC, 1 μg/ml), cefoxitin (MIC, 4 μg/ml), chloramphenicol (MIC, 4 μg/ml), and clindamycin (MIC, 0.06 μg/ml). Resistance remained stable as the organism was passaged on antibiotic-free agar for 10 consecutive days. Mutant B. fragilis strains with decreased susceptibility to clinafloxacin, trovafloxacin, sparfloxacin, levofloxacin, and ciprofloxacin were selected on brucella blood agar containing 8× the MIC of levofloxacin at a frequencies of 6.4 × 10−9, 4× the MICs of trovafloxacin and sparfloxacin at frequencies of 2.2 × 10−9 and 3.3 × 10−10, respectively, and 2× the MIC of clinafloxacin at a frequency of 5.5 × 10−11; no mutants were selected with ciprofloxacin. The susceptibilities of strains to trovafloxacin, levofloxacin, clinafloxacin, sparfloxacin, and ciprofloxacin before and after exposure to sparfloxacin were modestly affected by the presence of reserpine (20 μg/ml), an inhibitor of antibiotic efflux. The mechanism of fluoroquinolone resistance is being explored, but it is unlikely to be efflux due to a lack of cross-resistance to unrelated antimicrobial agents and to the fact that the MICs for strains before and after exposure to sparfloxacin are minimally affected by reserpine.

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Activity of Ceftazidime-Avibactam against Fluoroquinolone-Resistant Enterobacteriaceae and Pseudomonas aeruginosa

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.05136-14 ◽

2015 ◽

Vol 59 (6) ◽

pp. 3059-3065 ◽

Cited By ~ 14

Author(s):

C. Pitart ◽

F. Marco ◽

T. A. Keating ◽

W. W. Nichols ◽

J. Vila

Keyword(s):

Pseudomonas Aeruginosa ◽

Resistant Mutant ◽

Fluoroquinolone Resistance ◽

Cross Resistance ◽

Content Type ◽

E Coli ◽

Microdilution Method ◽

Broth Microdilution Method ◽

The Impact

ABSTRACTCeftazidime-avibactam and comparator antibiotics were tested by the broth microdilution method against 200Enterobacteriaceaeand 25Pseudomonas aeruginosastrains resistant to fluoroquinolones (including strains with the extended-spectrum β-lactamase [ESBL] phenotype and ceftazidime-resistant strains) collected from our institution. The MICs and mechanisms of resistance to fluoroquinolone were also studied. Ninety-nine percent of fluoroquinolone-resistantEnterobacteriaceaestrains were inhibited at a ceftazidime-avibactam MIC of ≤4 mg/liter (using the susceptible CLSI breakpoint for ceftazidime alone as a reference). Ceftazidime-avibactam was very active against ESBLEscherichia coli(MIC90of 0.25 mg/liter), ESBLKlebsiella pneumoniae(MIC90of 0.5 mg/liter), ceftazidime-resistant AmpC-producing species (MIC90of 1 mg/liter), non-ESBLE. coli(MIC90of ≤0.125 mg/liter), non-ESBLK. pneumoniae(MIC90of 0.25 mg/liter), and ceftazidime-nonresistant AmpC-producing species (MIC90of ≤0.5 mg/liter). Ninety-six percent of fluoroquinolone-resistantP. aeruginosastrains were inhibited at a ceftazidime-avibactam MIC of ≤8 mg/liter (using the susceptible CLSI breakpoint for ceftazidime alone as a reference), with a MIC90of 8 mg/liter. Additionally, fluoroquinolone-resistant mutants from each species tested were obtainedin vitrofrom two strains, one susceptible to ceftazidime and the other a β-lactamase producer with a high MIC against ceftazidime but susceptible to ceftazidime-avibactam. Thereby, the impact of fluoroquinolone resistance on the activity of ceftazidime-avibactam could be assessed. The MIC90values of ceftazidime-avibactam for the fluoroquinolone-resistant mutant strains ofEnterobacteriaceaeandP. aeruginosawere ≤4 mg/liter and ≤8 mg/liter, respectively. We conclude that the presence of fluoroquinolone resistance does not affectEnterobacteriaceaeandP. aeruginosasusceptibility to ceftazidime-avibactam; that is, there is no cross-resistance.

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Prevalence of Antimicrobial Resistance among Clinical Isolates of Bacteroides fragilis Group in Canada in 2010-2011: CANWARD Surveillance Study

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.05823-11 ◽

2011 ◽

Vol 56 (3) ◽

pp. 1247-1252 ◽

Cited By ~ 58

Author(s):

James A. Karlowsky ◽

Andrew J. Walkty ◽

Heather J. Adam ◽

Melanie R. Baxter ◽

Daryl J. Hoban ◽

...

Keyword(s):

Antimicrobial Agents ◽

Bacteroides Fragilis ◽

Clinical Isolates ◽

Surveillance Study ◽

Content Type ◽

Microdilution Method ◽

Broth Microdilution Method ◽

Amoxicillin Clavulanate ◽

Bacteroides Fragilis Group ◽

Bacteroides Ovatus

ABSTRACTClinical isolates of theBacteroides fragilisgroup (n= 387) were collected from patients attending nine Canadian hospitals in 2010-2011 and tested for susceptibility to 10 antimicrobial agents using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method.B. fragilis(59.9%),Bacteroides ovatus(16.3%), andBacteroides thetaiotaomicron(12.7%) accounted for ∼90% of isolates collected. Overall rates of percent susceptibility were as follows: 99.7%, metronidazole; 99.5%, piperacillin-tazobactam; 99.2%, imipenem; 97.7%, ertapenem; 92.0%, doripenem; 87.3%, amoxicillin-clavulanate; 80.9%, tigecycline; 65.9%, cefoxitin; 55.6%, moxifloxacin; and 52.2%, clindamycin. Percent susceptibility to cefoxitin, clindamycin, and moxifloxacin was lowest forB. thetaiotaomicron(n= 49, 24.5%),Parabacteroides distasonis/P. merdae(n= 11, 9.1%), andB. ovatus(n= 63, 31.8%), respectively. One isolate (B. thetaiotaomicron) was resistant to metronidazole, and two isolates (bothB. fragilis) were resistant to both piperacillin-tazobactam and imipenem. Since the last published surveillance study describing Canadian isolates ofB. fragilisgroup almost 20 years ago (A.-M. Bourgault et al., Antimicrob. Agents Chemother. 36:343–347, 1992), rates of resistance have increased for amoxicillin-clavulanate, from 0.8% (1992) to 6.2% (2010-2011), and for clindamycin, from 9% (1992) to 34.1% (2010-2011).

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In vitro activity of antimicrobial agents with and without sulbactam, EDTA and sulbactam-EDTA on ESBLs-producing Escherichia coli isolated from healthy Tibetan yaks

10.21203/rs.3.rs-39215/v1 ◽

2020 ◽

Author(s):

Baoguang Liu ◽

Xiaoling Yuan ◽

Yiheng Chen ◽

Xiaoshen Li ◽

Ming Bai ◽

...

Keyword(s):

Escherichia Coli ◽

Nasal Swab ◽

Antimicrobial Agents ◽

Synergistic Effects ◽

E Coli ◽

Microdilution Method ◽

Broth Microdilution Method ◽

Third Generation Cephalosporins ◽

Enhance Activity

Abstract Background The spread of ESBLs-producing bacteria has been strikingly rapid in many regions of the world and it causes therapeutic difficulties in everyday practice. The aims of this study were to investigate the prevalence and susceptibilities of ESBLs-producing Escherichia coli isolates from healthy Tibetan yaks in China, to evaluate the activity of drug combinations on ESBLs-producing E. coli isolates. Methods From July 2018 to August 2019, a total of 750 nasal swab samples were tested for the presence of E. coli and ESBLs-producing strains. The MICs of 11 antimicrobial agents alone and combinations with sulbactam, EDTA or sulbactam-EDTA against 240 ESBLs-producing E.coli strains were determined by the broth microdilution method. Results Overall, 59.87% (n = 449) of the samples were positive for E. coli, 240 (53.45%) of 449 E. coli isolates were confirmed to be ESBLs-producing. The addition of sulbactam to the third generation cephalosporins, amikacin and fosfomycin for all isolates resulted in low MICs, increasing the level of susceptibility from 0, 0 and 0% to 50 ~ 87.5, 4.2 and 100% respectively. The addition of EDTA to fluoroquinolones, doxycycline, florfenicol, amikacin and fosfomycin, showed improved activities and resulted in low MICs, increasing the level of susceptibility from 0, 0, 8.3, 0 and 0% to 4.2 ~ 29.2, 33.3, 33.3, 66.7 and 45.8%, respectively. All other antibacterials (except fluoroquinolones, doxycycline and florfenicol), when combined with sulbactam-EDTA, were found to be more active than combinations only with sulbactam or with EDTA against most of isolates, with lower MIC50s and MIC90s. Conclusion In conclusion, ESBLs-producing E. coli isolates were widespread in healthy Tibetan yaks in China. ESBLs-producing E. coli isolates exhibited varying degrees of multidrug resistance. This study these findings suggested that sulbactam can enhance activity of β-lactams and some non-β-lactams of antimicrobial agents and had a synergistic effects with EDTA in improving activities of some families of antimicrobials.

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Susceptibility trends of ceftolozane/tazobactam and comparators when tested against European Gram-negative bacterial surveillance isolates collected during 2012–18

Journal of Antimicrobial Chemotherapy ◽

10.1093/jac/dkaa278 ◽

2020 ◽

Vol 75 (10) ◽

pp. 2907-2913 ◽

Cited By ~ 1

Author(s):

Helio S Sader ◽

Cecilia G Carvalhaes ◽

Leonard R Duncan ◽

Robert K Flamm ◽

Dee Shortridge

Keyword(s):

Eastern Europe ◽

Active Compound ◽

Western Europe ◽

Antimicrobial Agents ◽

Gram Negative Bacteria ◽

Gram Negative ◽

Microdilution Method ◽

Broth Microdilution Method ◽

Systemic Infections

Abstract Background The Program to Assess Ceftolozane/Tazobactam Susceptibility (PACTS) monitors the in vitro activity of ceftolozane/tazobactam and numerous antimicrobial agents against Gram-negative bacteria worldwide. Objectives To evaluate the activity of ceftolozane/tazobactam and resistance trends among Pseudomonas aeruginosa and Enterobacterales isolates in Europe between 2012 and 2018. Methods P. aeruginosa (7503) and Enterobacterales (30 582) isolates were collected from 53 medical centres in 26 countries in Europe and the Mediterranean region and tested for susceptibility by reference broth microdilution method in a central laboratory. MIC results were interpreted using EUCAST criteria. Results Ceftolozane/tazobactam was the most active compound tested against P. aeruginosa isolates after colistin, with overall susceptibility rates of 94.1% in Western Europe and 80.9% in Eastern Europe. Moreover, ceftolozane/tazobactam retained activity against 75.2% and 59.2% of meropenem-non-susceptible P. aeruginosa isolates in Western and Eastern Europe, respectively. Tobramycin was the third most active compound tested against P. aeruginosa, with susceptibility rates of 88.6% and 70.9% in Western and Eastern Europe, respectively. Ceftolozane/tazobactam was active against 94.5% of all Enterobacterales and 96.1% of meropenem-susceptible isolates from Western Europe. In Eastern Europe, ceftolozane/tazobactam was active against 79.4% of Enterobacterales overall and 86.2% of meropenem-susceptible isolates. Discussion Antimicrobial susceptibility rates for agents commonly used to treat serious systemic infections varied widely among nations and geographic regions and were generally lower in Eastern Europe compared with Western Europe. Ceftolozane/tazobactam demonstrated potent activity against P. aeruginosa, including MDR strains, and retained activity against most meropenem-susceptible Enterobacterales causing infection in European medical centres.

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In Vitro Activity of Eravacycline against Gram-Positive Bacteria Isolated in Clinical Laboratories Worldwide from 2013 to 2017

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01715-19 ◽

2019 ◽

Vol 64 (3) ◽

Cited By ~ 1

Author(s):

Ian Morrissey ◽

Stephen Hawser ◽

Sibylle H. Lob ◽

James A. Karlowsky ◽

Matteo Bassetti ◽

...

Keyword(s):

Antimicrobial Agents ◽

Clinical Isolates ◽

Gram Positive ◽

Content Type ◽

Gram Positive Bacteria ◽

Microdilution Method ◽

Clinical Laboratories ◽

Broth Microdilution Method ◽

Doubling Dilution

ABSTRACT Eravacycline is a novel, fully synthetic fluorocycline antibiotic being developed for the treatment of serious infections, including those caused by resistant Gram-positive pathogens. Here, we evaluated the in vitro activities of eravacycline and comparator antimicrobial agents against a recent global collection of frequently encountered clinical isolates of Gram-positive bacteria. The CLSI broth microdilution method was used to determine in vitro MIC data for isolates of Enterococcus spp. (n = 2,807), Staphylococcus spp. (n = 4,331), and Streptococcus spp. (n = 3,373) isolated primarily from respiratory, intra-abdominal, urinary, and skin specimens by clinical laboratories in 37 countries on three continents from 2013 to 2017. Susceptibilities were interpreted using both CLSI and EUCAST breakpoints. There were no substantive differences (a >1-doubling-dilution increase or decrease) in eravacycline MIC90 values for different species/organism groups over time or by region. Eravacycline showed MIC50 and MIC90 results of 0.06 and 0.12 μg/ml, respectively, when tested against Staphylococcus aureus, regardless of methicillin susceptibility. The MIC90 values of eravacycline for Staphylococcus epidermidis and Staphylococcus haemolyticus were equal (0.5 μg/ml). The eravacycline MIC90s for Enterococcus faecalis and Enterococcus faecium were 0.06 μg/ml and were within 1 doubling dilution regardless of the vancomycin susceptibility profile. Eravacycline exhibited MIC90 results of ≤0.06 μg/ml when tested against Streptococcus pneumoniae and beta-hemolytic and viridans group streptococcal isolates. In this surveillance study, eravacycline demonstrated potent in vitro activity against frequently isolated clinical isolates of Gram-positive bacteria (Enterococcus, Staphylococcus, and Streptococcus spp.), including isolates collected over a 5-year period (2013 to 2017), underscoring its potential benefit in the treatment of infections caused by common Gram-positive pathogens.

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In vitro effectiveness of antimicrobial properties of propolis and chlorhexidine on oral pathogens: A comparative study

Biosis:Biological Systems ◽

10.37819/biosis.001.03.0062 ◽

2020 ◽

Vol 1 (3) ◽

pp. 116-125

Author(s):

Hadis Tavafi ◽

Maryam- sadat Sadrzadeh-Afshar ◽

Soroush Niroomand

Keyword(s):

Periodontal Disease ◽

Antimicrobial Properties ◽

Bacterial Strains ◽

Microdilution Method ◽

Broth Microdilution Method ◽

Microbial Strains ◽

Bacteria And Fungi ◽

Antibacterial And Antifungal ◽

Oral Conditions

Periodontal disease is one of the most prevalent infectious oral conditions in the present century, and it is necessary to conduct research to find a solution to overcome these diseases. A variety of microbial strains of bacteria and fungi are involved in the pathogenesis of periodontal disease. The use of chemical agents such as mouthwashes is one of the strategies to control these diseases. The purpose of the present study was to compare the antimicrobial effects of propolis and chlorhexidine gluconate (CHX) on the bacterial strains of Streptococcus mutans, Streptococcus pyogenes, Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and the yeast strain of Candida albicans using the broth microdilution method. The results showed the inhibitory and microbicidal activities of the two substances against the tested microbial strains. The antibacterial and antifungal effects of CHX were more effective reported in this study than that of propolis against the studied pathogens. The results of this study also indicated that the propolis was less effective in inhibiting bacterial growth than the CHX. In addition, the combination of these two solutions had a synergistic effect on inhibition of other studied strains, with the exception of C. albicans and S. aureus. There is a need for further research on strains isolated from oral biofilm to achieve complementary results.

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Multicenter Survey of the Changing In Vitro Antimicrobial Susceptibilities of Clinical Isolates of Bacteroides fragilis Group, Prevotella, Fusobacterium, Porphyromonas, and PeptostreptococcusSpecies

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.45.4.1238-1243.2001 ◽

2001 ◽

Vol 45 (4) ◽

pp. 1238-1243 ◽

Cited By ~ 138

Author(s):

Kenneth E. Aldridge ◽

Deborah Ashcraft ◽

Karl Cambre ◽

Carl L. Pierson ◽

Stephen G. Jenkins ◽

...

Keyword(s):

Antimicrobial Agents ◽

Bacteroides Fragilis ◽

Penicillin G ◽

Individual Species ◽

Highly Active ◽

Antimicrobial Susceptibilities ◽

Broth Microdilution Method ◽

Multicenter Survey ◽

Resistance Rates

ABSTRACT In vitro surveys of antimicrobial resistance among clinically important anaerobes are an important source of information that can be used for clinical decisions in the choice of empiric antimicrobial therapy. This study surveyed the susceptibilities of 556 clinical anaerobic isolates from four large medical centers using a broth microdilution method. Piperacillin-tazobactam was the only antimicrobial agent to which all the isolates were susceptible. Similarly, imipenem, meropenem, and metronidazole were highly active (resistance, <0.5%), whereas the lowest susceptibility rates were noted for penicillin G, ciprofloxacin, and clindamycin. For most antibiotics, blood isolates were less susceptible than isolates from intra-abdominal, obstetric-gynecologic, and other sources. All isolates of the Bacteroides fragilis group were susceptible to piperacillin-tazobactam and metronidazole, while resistance to imipenem and meropenem was low (<2%). For these same isolates, resistance rates (intermediate and resistant MICs) to ampicillin-sulbactam, cefoxitin, trovafloxacin, and clindamycin were 11, 8, 7, and 29%, respectively. Among the individual species of the B. fragilis group, the highest resistance rates were noted among the following organism-drug combinations: for clindamycin,Bacteroides distasonis and Bacteroides ovatus; for cefoxitin, Bacteroides thetaiotaomicron, B. distasonis, and Bacteroides uniformis; for ampicillin-sulbactam,B. distasonis, B. ovatus, and B. uniformis; and for trovafloxacin, Bacteroides vulgatus. For the carbapenens, imipenem resistance was noted among B. fragilis and meropenem resistance was seen among B. fragilis, B. vulgatus, and B. uniformis. With few exceptions all antimicrobial agents were highly active against isolates of Prevotella, Fusobacterium, Porphyromonas, andPeptostreptococcus. These data further establish and confirm that clinically important anaerobes can vary widely in their antimicrobial susceptibilities. Fortunately most antimicrobial agents were active against the test isolates. However, concern is warranted for what appears to be a significant increases in resistance to ampicillin-sulbactam and clindamycin.

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In VitroActivity of Plazomicin against Gram-Negative and Gram-Positive Bacterial Pathogens Isolated from Patients in Canadian Hospitals from 2013 to 2017 as Part of the CANWARD Surveillance Study

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02068-18 ◽

2018 ◽

Vol 63 (1) ◽

Cited By ~ 6

Author(s):

Andrew Walkty ◽

James A. Karlowsky ◽

Melanie R. Baxter ◽

Heather J. Adam ◽

George G. Zhanel

Keyword(s):

Antimicrobial Agents ◽

Bacterial Pathogens ◽

Multidrug Resistant ◽

Surveillance Study ◽

Gram Positive ◽

Gram Negative ◽

Content Type ◽

Microdilution Method ◽

Broth Microdilution Method

ABSTRACTThe Clinical and Laboratory Standards Institute (CLSI) broth microdilution method was used to evaluate thein vitroactivities of plazomicin and comparator antimicrobial agents against 7,712 Gram-negative and 4,481 Gram-positive bacterial pathogens obtained from 2013 to 2017 from patients in Canadian hospitals as part of the CANWARD Surveillance Study. Plazomicin demonstrated potentin vitroactivity againstEnterobacteriaceae(MIC90≤ 1 µg/ml for all species tested exceptProteus mirabilisandMorganella morganii), including aminoglycoside-nonsusceptible, extended-spectrum β-lactamase (ESBL)-positive, and multidrug-resistant (MDR) isolates. Plazomicin was equally active against methicillin-susceptible and methicillin-resistant isolates ofStaphylococcus aureus.

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Susceptibility of bacteria of the Enterococcus genus isolated on Lithuanian poultry farms

Veterinární Medicína ◽

10.17221/44/2009-vetmed ◽

2010 ◽

Vol 54 (No. 12) ◽

pp. 583-588 ◽

Cited By ~ 5

Author(s):

M. Ruzauskas ◽

R. Siugzdiniene ◽

V. Spakauskas ◽

J. Povilonis ◽

V. Seputiene ◽

...

Keyword(s):

Antimicrobial Agents ◽

Broth Microdilution ◽

Diagnostic Systems ◽

Microtitre Plate ◽

Predominant Species ◽

Microdilution Method ◽

Broth Microdilution Method ◽

Poultry Farms ◽

Clinical Breakpoints

The aim of this study was to test and analyse the antimicrobial susceptibility of Enterococcus isolates from Lithuanian poultry farms. Investigations were carried out during the years 2008–2009. The sampling sites, located all over the country, included eight poultry farms of large capacity. All samples were collected from broilers. Enterococcus spp. were isolated from intestines immediately after slaughtering. A total of 160 samples were collected, 20 samples from each farm. The MICs (Minimum Inhibitory Concentrations) of eleven antimicrobial agents were determined for each of the isolates using the broth microdilution method with specific microtitre plate panels (Trek Diagnostic Systems, Inc.). Susceptibility according to clinical breakpoints of chloramphenicol, linezolid, erythromycin, penicillin, quinupristin/dalfopristin, tetracycline, vancomycin, ciprofloxacin and nitrofurantoin was evaluated. One hundred and forty seven samples (92%) from a total of 160 tested samples were positive for Enterococcus spp., however, only 74 strains were selected as non-duplicate isolates. The most predominant species were identified as E. faecium (38%), E. faecalis (17.5%), E. gallinarum (12%) and E. casseliflavus (12%). The most frequent resistance properties were resistances to tetracycline (75.6%), erythromycin (56.8%) and ciprofloxacin (41.9%). No strains resistant to vancomycin and linezolid were found. High percentages of susceptibility to chloramphenicol (82.4%) and penicillin (71.6%) were also observed. A high MIC of tigecycline (≥ 1 mg/l) to 12.2% of enterococci was determined during this study. 44.6% of tested strains had a high MIC (≥ 64 mg/l) to tylosin. There was no significant correlation found between resistances of different species to different antimicrobial agents in vitro.

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In Vitro Activity of Daptomycin against Vancomycin-Resistant Enterococci of Various Van Types and Comparison of Susceptibility Testing Methods

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.47.12.3760-3763.2003 ◽

2003 ◽

Vol 47 (12) ◽

pp. 3760-3763 ◽

Cited By ~ 40

Author(s):

James H. Jorgensen ◽

Sharon A. Crawford ◽

Cynthia C. Kelly ◽

Jan E. Patterson

Keyword(s):

Antimicrobial Agents ◽

Calcium Content ◽

Test Strip ◽

Vitro Activity ◽

Disk Diffusion ◽

In Vitro Activity ◽

Microdilution Method ◽

Broth Microdilution Method ◽

Vancomycin Resistant

ABSTRACT The increasing prevalence of vancomycin-resistant enterococcal (VRE) infections and the limited number of antimicrobial agents for their treatment emphasize a need for new, more effective agents. In this study, the in vitro activity of daptomycin was determined against a collection of 156 VRE from seven different institutions. Van types were characterized by PCR, and pulsed-field gel electrophoresis was performed to exclude isolates with >85% relatedness by dendrogram. Included were 126 Enterococcus faecium (109 vanA, 17 vanB) isolates, 5 Enterococcus faecalis (3 vanA, 2 vanB) isolates, 2 Enterococcus avium (vanA) isolates, 1 Enterococcus durans (vanA) isolate, 10 Enterococcus gallinarum (vanC1) isolates, and 12 Enterococcus casseliflavus (vanC2) isolates. MICs of daptomycin and five additional agents were determined by the NCCLS broth microdilution method with Mueller-Hinton (MH) broth containing supplemental calcium. MICs were also determined using two investigational E-test strip formulations, and disk diffusion testing was performed by the standard NCCLS method. The MIC of daptomycin at which 50% of the isolates tested were inhibited for this isolate collection was 4 μg/ml, and the MIC at which 90% of the isolates tested were inhibited was 8 μg/ml. Two isolates of vanA E. faecium were resistant to linezolid, and one isolate was resistant to quinupristin-dalfopristin. MICs of daptomycin determined by the E test with and without added calcium varied by 8- to 16-fold, and disk diffusion zones varied by 3 to 6 mm according to the calcium content of the commercial MH agar lots used in the study. This study has shown daptomycin to have good activity against a diverse collection of contemporary VRE isolates. However, improved standardization of the calcium content of MH agar will be important for reliable testing of daptomycin by clinical laboratories using either the E test or disk diffusion methods.

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