Direct disk diffusion susceptibility testing from respiratory tract specimens: focus on Pseudomonas aeruginosa

ABSTRACTThe broth microdilution method for fosfomycin andPseudomonas aeruginosawas assessed and compared with the approved agar dilution method in 206 genetically unrelatedP. aeruginosaclinical isolates. Essential agreement between the two methods was 84%, and categorical agreement was 89.3%. Additionally, Etest and disk diffusion assays were performed. Results validate broth microdilution as a reliable susceptibility testing method for fosfomycin againstP. aeruginosa. Conversely, unacceptable concordance was established between Etest and disk diffusion results with agar dilution results.

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Detection and Susceptibility Testing of Hypermutable Pseudomonas aeruginosa Strains with the Etest and Disk Diffusion

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.48.7.2665-2672.2004 ◽

2004 ◽

Vol 48 (7) ◽

pp. 2665-2672 ◽

Cited By ~ 47

Author(s):

Maria D. Maciá ◽

Nuria Borrell ◽

José L. Pérez ◽

Antonio Oliver

Keyword(s):

Pseudomonas Aeruginosa ◽

Susceptibility Testing ◽

Resistant Mutant ◽

Inhibition Zone ◽

Disk Diffusion ◽

Strain Pao1 ◽

Resistance Development ◽

Standard Methods ◽

Inhibition Zones ◽

Derivative Strain

ABSTRACT Resistance development in Pseudomonas aeruginosa from chronically colonized cystic fibrosis (CF) patients has been linked to the presence of a high proportion of mismatch repair-deficient hypermutable strains. The detection of hypermutable strains by microbiology laboratories may be useful for establishing adequate antimicrobial therapies. In this work, we find that the Etest and disk diffusion can be used as simple methods for the detection and susceptibility testing of hypermutable P. aeruginosa isolates. Strain PAO1 and its hypermutable derivative strain PAOΔmutS were used to standardize the procedure, which was tested with 35 P. aeruginosa isolates from 21 CF patients. Mutation frequencies were estimated by standard methods, and 29% of the isolates were found to be hypermutable. MICs and inhibition zone diameters were determined for ceftazidime, imipenem, meropenem, ciprofloxacin, and tobramycin by using Etest strips and conventional disks, respectively. The presence (or absence) of resistant mutant subpopulations, as well as their relative numbers and the highest MICs for them (or smallest inhibition zone diameters), was recorded. The presence of resistant mutant subpopulations within the inhibition zones of three or more antibiotics clearly identified the strains as hypermutable (they were present in 10 of 10 hypermutable strains and 0 of 25 nonhypermutable strains) with both methods. Additionally, these methods allowed us to differentiate between dual effects of hypermutation in antibiotic resistance, namely, that (i) hypermutable isolates were substantially more resistant than nonhypermutable isolates and that (ii) the resistance of hypermutable isolates was dramatically increased by the presence of resistant mutant subpopulations. This differentiation may be relevant for the design of adequate treatments, since the second effect, in contrast to the first, may be overcome by antibiotic combinations.

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Comparison of Agar Diffusion Methodologies for Antimicrobial Susceptibility Testing of Pseudomonas aeruginosa Isolates from Cystic Fibrosis Patients

Journal of Clinical Microbiology ◽

10.1128/jcm.38.5.1818-1822.2000 ◽

2000 ◽

Vol 38 (5) ◽

pp. 1818-1822 ◽

Cited By ~ 42

Author(s):

Jane L. Burns ◽

Lisa Saiman ◽

Susan Whittier ◽

Davise Larone ◽

Jay Krzewinski ◽

...

Keyword(s):

Cystic Fibrosis ◽

Pseudomonas Aeruginosa ◽

Susceptibility Testing ◽

Correlation Coefficients ◽

Disk Diffusion ◽

Diffusion Method ◽

Broth Microdilution ◽

Disk Diffusion Method ◽

Agar Diffusion ◽

Broth Microdilution Method

Pseudomonas aeruginosa is the most common pathogen infecting the lungs of patients with cystic fibrosis (CF). Improved antimicrobial chemotherapy has significantly increased the life expectancy of these patients. However, accurate susceptibility testing of P. aeruginosa isolates from CF sputum may be difficult because the organisms are often mucoid and slow growing. This study of 597 CF isolates of P. aeruginosa examined the correlation of disk diffusion and Etest (AB BIODISK, Solna, Sweden) results with a reference broth microdilution method. The rates of interpretive errors for 12 commonly used antipseudomonal antimicrobials were determined. The disk diffusion method correlated well (zone diameter versus MIC) for all of the agents tested. However, for mucoid isolates, correlation coefficients (r values) for piperacillin, piperacillin-tazobactam, and meropenem were <0.80. The Etest correlation with reference broth microdilution results (MIC versus MIC) was acceptable for all of the agents tested, for both mucoid and nonmucoid isolates. Category interpretation errors were similar for the disk diffusion and Etest methods with 0.4 and 0.1%, respectively, very major errors (false susceptibility) and 1.1 and 2.2% major errors (false resistance). Overall, both agar diffusion methods appear to be broadly acceptable for routine clinical use in susceptibility testing of CF isolates of P. aeruginosa.

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Antimicrobial Testing of Selected Fluoroquinolones Against Pseudomonas aeruginosa Isolated From Canine Otitis

Journal of the American Animal Hospital Association ◽

10.5326/0430307 ◽

2007 ◽

Vol 43 (6) ◽

pp. 307-312 ◽

Cited By ~ 13

Author(s):

Lindsay McKay ◽

Crystal D. Schuman Rose ◽

Jennifer L. Matousek ◽

Lynn S. Schmeitzel ◽

Nicole M. Gibson ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Minimum Inhibitory Concentration ◽

Susceptibility Testing ◽

Inhibitory Concentration ◽

Disk Diffusion

A total of 100 Pseudomonas aeruginosa (P. aeruginosa) isolates were collected over a 1.5- year period from cases of canine otitis. Sensitivities to enrofloxacin, marbofloxacin, and orbifloxacin were determined using minimum inhibitory concentration testing (MICT). Isolates were also tested for sensitivities to enrofloxacin and marbofloxacin using disk-diffusion susceptibility testing (DDST). Isolates were significantly more sensitive to marbofloxacin than to enrofloxacin (z = −4.57; P<0.05) or orbifloxacin (z = −5.02; P<0.05). Agreement was 87% between MICT and DDST for marbofloxacin, with approximately equal numbers of overestimation and underestimation errors. Agreement was 74% between MICT and DDST for enrofloxacin, but DDST tended to overestimate the number of enrofloxacin-susceptible strains. These results suggest that marbofloxacin is more effective against P. aeruginosa than either enrofloxacin or orbifloxacin and that relying on DDST may lead to ineffective enrofloxacin treatment.

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Pseudomonas aeruginosa: Antimicrobial Susceptibility Testing and Agreement Between Disk Diffusion and E-Test Methods

International Journal of Infectious Diseases ◽

10.1016/j.ijid.2008.05.300 ◽

2008 ◽

Vol 12 ◽

pp. e120-e121

Author(s):

S.G. Pathmanathan ◽

N.A. Samat ◽

R. Mohamed

Keyword(s):

Pseudomonas Aeruginosa ◽

Antimicrobial Susceptibility ◽

Susceptibility Testing ◽

Test Methods ◽

Antimicrobial Susceptibility Testing ◽

Disk Diffusion

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Verification of Ceftazidime-Avibactam and Ceftolozane-Tazobactam Susceptibility Testing Methods against Carbapenem-Resistant Enterobacteriaceae and Pseudomonas aeruginosa

Journal of Clinical Microbiology ◽

10.1128/jcm.01093-17 ◽

2017 ◽

Vol 56 (2) ◽

Cited By ~ 15

Author(s):

Ryan K. Shields ◽

Cornelius J. Clancy ◽

A. William Pasculle ◽

Ellen G. Press ◽

Ghady Haidar ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Susceptibility Testing ◽

Multidrug Resistant ◽

Disk Diffusion ◽

Gram Negative Bacteria ◽

Test Results ◽

Content Type ◽

Carbapenem Resistant ◽

Bacteria Resistance ◽

Carbapenem Resistant Enterobacteriaceae

ABSTRACT Ceftazidime-avibactam and ceftolozane-tazobactam are newly approved agents for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. Resistance to both agents has been described clinically. Susceptibility testing on automated systems is unavailable for either agent. Our objective was to compare the disk diffusion and Etest methods to standard broth microdilution (BMD) methods for testing ceftazidime-avibactam and ceftolozane-tazobactam against a diverse collection of carbapenem-resistant Enterobacteriaceae (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRP) isolates, respectively. Among 74 ceftazidime-avibactam-susceptible and -resistant CRE isolates, BMD categorical agreement was higher with Etest (96%) than with disk diffusion (72%; P = 0.0003). Twenty-eight percent of ceftazidime-avibactam-susceptible CRE isolates were classified as resistant by disk diffusion. Results were comparable to those obtained with resistance defined genotypically. Among 72 ceftolozane-tazobactam-susceptible and -resistant CRP isolates, the levels of BMD categorical agreement with disk diffusion and Etest were 94% and 96%, respectively; the only errors identified were minor. Our findings demonstrate that Etest measurements of ceftazidime-avibactam and ceftolozane-tazobactam susceptibility correlate closely with standard BMD methods, suggesting a useful role clinically. On the other hand, disk diffusion measurements overcalled CRE resistance to ceftazidime-avibactam. A better understanding of ceftazidime-avibactam interpretive breakpoints is needed before disk diffusion is used routinely in the clinic. Until clinicians and microbiologists understand Etest and disk diffusion performance at their centers, test results should be interpreted cautiously.

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Lower Respiratory Tract Pathogens and Their Antimicrobial Susceptibility Pattern: A 5-Year Study

Antibiotics ◽

10.3390/antibiotics10070851 ◽

2021 ◽

Vol 10 (7) ◽

pp. 851

Author(s):

Biagio Santella ◽

Enrica Serretiello ◽

Anna De Filippis ◽

Folliero Veronica ◽

Domenico Iervolino ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Pseudomonas Aeruginosa ◽

Klebsiella Pneumoniae ◽

Respiratory Tract ◽

Antimicrobial Susceptibility ◽

Lower Respiratory Tract ◽

Susceptibility Testing ◽

Gram Negative Bacteria ◽

Susceptibility Pattern ◽

Gram Negative

Lower respiratory tract infections (LRTIs) are the most common infections in humans. It is estimated that 2.74 million deaths worldwide occur each year due to LRTIs. The aim of the study was to determine the frequency and antibiotic susceptibility pattern of microorganisms isolated from respiratory samples of patients with LRTIs. Between January 2015 and December 2019, a total of 7038 sputum and bronchoaspirate samples from suspected LRTI patients were collected. Among them, 2753 samples (39.1%) showed significant microbial growth on culture media. The LRTI rate was higher in patients with male gender (67.1%) and with age between 40–59 years (48.6%). The microorganism identification and antibiotic susceptibility testing were performed with Vitek 2. Out of 4278 isolates species, 3102 (72.5%) were Gram-negative bacteria, 1048 (24.5%) were Gram-positive bacteria, and 128 (3.0%) were Candida spp. Major microorganisms isolated were Acinetobacter baumannii (18.6%), Staphylococcus aureus (15.2%), Pseudomonas aeruginosa (14.2%), and Klebsiella pneumoniae (10.9%). In antimicrobial susceptibility testing, Staphylococcus aureus isolates were mostly resistant to Penicillin G (84.1%) and Oxacillin (48.1%), whereas they demonstrated maximum sensitivity to Tigecycline (100%) and Linezolid (99.5%). Among Gram-negative isolates, Acinetobacter baumannii showed maximum sensitivity to Colistin but was resistant to other antibiotics (95–99%). Klebsiella pneumoniae isolates were mostly resistant to Cefotaxime (72.7%) and sensitive to Gentamicin (54.3%), and Pseudomonas aeruginosa was resistant to Ciprofloxacin (40.3%) and sensitive to Amikacin (85.9%). Gram-negative bacteria represented the species most commonly isolated. A high rate of antimicrobial resistance was observed in this study. In conclusion, the correct identification of causative microorganisms and their susceptibility patterns to antibiotics is crucial for choosing targeted and effective antibiotic therapy in LRTIs, and to prevent the emergence of multidrug-resistant bacteria.

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Performance of Fully Automated Antimicrobial Disk Diffusion Susceptibility Testing Using Copan WASP Colibri coupled to Radian in-Line Carousel and Expert System

Journal of Clinical Microbiology ◽

10.1128/jcm.00777-21 ◽

2021 ◽

Author(s):

Abdessalam Cherkaoui ◽

Gesuele Renzi ◽

Nicolas Vuilleumier ◽

Jacques Schrenzel

Keyword(s):

Staphylococcus Aureus ◽

Pseudomonas Aeruginosa ◽

Expert System ◽

Enterococcus Faecalis ◽

Susceptibility Testing ◽

Disk Diffusion ◽

Clinical Samples ◽

Routine Laboratory ◽

Coagulase Negative Staphylococci ◽

Better Than

The purpose of the present study was to assess the agreement at the categorical level between the VITEK ® 2 system and the Colibri TM coupled to the Radian TM under real routine laboratory conditions. The 675 non-duplicate clinical strains included in this study (249 Enterobacterales-isolates, 198 Pseudomonas aeruginosa , 107 Staphylococcus aureus , 78 coagulase-negative staphylococci, 38 Enterococcus faecalis and 5 Enterococcus faecium ) were isolated from non-consecutive clinical samples referred to our laboratory between June and November 2020. In addition, 43 carbapenemase-producing Enterobacterales (CPE) formerly identified and stored in our laboratory were added to the panel, for a total of 718 strains. The overall categorical agreements between the two compared methods were 99.3% (4350/4380; 95% CI 99% - 99.5%); 98.6% (2147/2178; 95% CI 98.0% - 99.0%); 99.4% (1839/1850; 95% CI 98.9% - 99.7%); and 99.4% (342/344; 95% CI 97.9% - 99.8%) for Enterobacterales, P. aeruginosa , Staphylococcus spp. and Enterococcus spp. respectively. The most important cause of the very major errors encountered on the VITEK ® 2 for P. aeruginosa (62%, 13/21) was related to the presence of heteroresistant populations. Among the 43 CPE included in this study, one OXA-48-like, and one OXA-181-like were missed by the VITEK ® 2, even by rigorously applying the CPE screening cut-offs defined by EUCAST. The Colibri TM coupled to the Radian TM provide a fully automated solution for antimicrobial disk diffusion susceptibility testing with an accuracy that is equal to or better than that of the VITEK ® 2 system.

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