Comparison of agar diffusion methodologies for antimicrobial susceptibility testing of Pseudomonas aeruginosa isolates from cystic fibrosis patients

Staphylococcus aureus nasal colonization and susceptibility profile to antimicrobials in hemodialysis patients using a protocol of seven collections

BACKGROUND

Patients colonized with Staphylococcus aureus in their nasal passages have a higher risk of acquiring infection, especially if they are immunocompromised or have comorbidities such as chronic renal failure undergoing hemodialysis (HD).

OBJECTIVE

This study aimed to report the prevalence of nasal carriage of S. aureus among HD patients utilizing a seven-week sampling protocol and to assess the susceptibility of these isolates to various antimicrobial agents.

METHODS

Over seven consecutive weeks, nasal swab samples were collected from 47 HD patients, resulting in a total of 329 samples. The microorganisms were identified using biochemical methods and subjected to antimicrobial susceptibility testing via disk diffusion and microdilution techniques.

RESULTS

Out of all the patients analyzed, 25 individuals (53.19%) were found to be colonized by S. aureus, with 21 of them displaying intermittent colonization. Additionally, 38% showed positive results for S. aureus in only the 6th or 7th week of sampling. Within the 58 isolates, 17.2% (n=10) exhibited methicillin (oxacillin)-resistance and 25.86% (n=15) displayed elevated vancomycin MIC values (2 µg/ml). Based on the results, daptomycin and gentamicin were found to be effective treatment options. However, 31% of the isolates (n=18) exhibited a MIC of 1 µg/ml for daptomycin.

CONCLUSION

Over half of the patients were colonized by S. aureus, but mostly on an intermittent basis. The identification of oxacillin resistance and high vancomycin and daptomycin MICs serve as warnings for possible future complications in managing bacteremia caused by S. aureus in these patients.

[CF Lung Disease - a German S3 Guideline: Pseudomonas aeruginosa]

Cystic Fibrosis (CF) is the most common autosomal recessive genetic multisystemic disease. In Germany, it affects at least 8000 people. The disease is caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene leading to dysfunction of CFTR, a transmembrane chloride channel. This defect causes insufficient hydration of the airway epithelial lining fluid which leads to reduction of the mucociliary clearance.Even if highly effective, CFTR modulator therapy has been available for some years and people with CF are getting much older than before, recurrent and chronic infections of the airways as well as pulmonary exacerbations still occur. In adult CF life, Pseudomonas aeruginosa (PA) is the most relevant pathogen in colonisation and chronic infection of the lung, leading to further loss of lung function. There are many possibilities to treat PA-infection.This is a S3-clinical guideline which implements a definition for chronic PA-infection and demonstrates evidence-based diagnostic methods and medical treatment in order to give guidance for individual treatment options.

Diagnosis and Management of Cystic Fibrosis Exacerbations

With the improving survival of cystic fibrosis (CF) patients and the advent of highly effective cystic fibrosis transmembrane conductance regulator (CFTR) therapy, the clinical spectrum of this complex multisystem disease continues to evolve. One of the most important clinical events for patients with CF in the course of this disease is acute pulmonary exacerbation (PEx). Clinical and microbial epidemiology studies of CF PEx continue to provide important insight into the disease course, prognosis, and complications. This work has now led to several large-scale clinical trials designed to clarify the treatment paradigm for CF PEx. The primary goal of this review is to provide a summary and update of the pathophysiology, clinical and microbial epidemiology, outcome and treatment of CF PEx, biomarkers for exacerbation, and the impact of highly effective modulator therapy on these events moving forward.

AtbFinder Diagnostic Test System Improves Optimal Selection of Antibiotic Therapy in Persons with Cystic Fibrosis

Cystic fibrosis (CF) is characterized by mutations of CFTR that lead to increased viscous secretions, bacterial colonization, and recurrent infections. Chronic Pseudomonas aeruginosa infection in persons with CF is associated with progressive and accelerated lung function decline despite aggressive antibiotic treatment. We report the management of respiratory infections in persons with CF with antibiotic therapy that was based on the recommendations of AtbFinder, a novel, rapid, culture-based diagnostic test system that employs a novel paradigm of antibiotic selection. AtbFinder mimics bacterial interactions with antibiotics at concentrations that can be achieved in affected tissues or organs and models conditions of interbacterial interactions within polymicrobial biofilms. This open-label, single-arm, investigator-initiated clinical study was designed to identify the efficacy of antibiotics selected using AtbFinder in persons with CF. Microbiological and clinical parameters were assessed following the change of antibiotic therapy to antibiotics selected with AtbFinder between January 2016 and December 2018 and retrospectively compared with clinical data collected between January 2013 and December 2015. We enrolled 35 persons with CF (33 with chronic P. aeruginosa colonization). Antibiotics selected using AtbFinder resulted in clearance of P. aeruginosa in 81.8% of subsequent cultures, decreased pulmonary exacerbations from 1.21 per patient per annum to 0, and an increase in predicted percent predicted forced expiratory volume in 1 s up to 28.4% from baseline. The number of systemic antibiotic courses used in patients after switching to the AtbFinder-selected therapy was reduced from 355 to 178. These findings describe the superiority of antibiotic regimens selected with AtbFinder compared with routine antimicrobial susceptibility testing.

Evaluation of Antimicrobial Susceptibility Testing Methods for Burkholderia cenocepacia and Burkholderia multivorans Isolates from Cystic Fibrosis Patients

The Burkholderia cepacia complex (BCC) is known for causing serious lung infections in people with cystic fibrosis (CF). These infections can require lung transplantation, eligibility for which may be guided by antimicrobial susceptibility testing (AST). While the Clinical and Laboratory Standards Institute recommends AST for BCC, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) does not, due to poor method performance and correlation with clinical outcomes. Furthermore, limited data exist on the performance of automated AST methods for BCC. To address these issues, reproducibility and accuracy were evaluated for disk diffusion (DD), broth microdilution (BMD), and MicroScan WalkAway using 50 B. cenocepacia and 50 B. multivorans isolates collected from people with CF. The following drugs were evaluated in triplicate: chloramphenicol (CAM), ceftazidime (CAZ), meropenem (MEM), trimethoprim-sulfamethoxazole (TMP-SMX), minocycline (MIN), levofloxacin (LVX), ciprofloxacin (CIP), and piperacillin-tazobactam (PIP-TAZ). BMD reproducibility was ≥ 95% for MEM and MIN only, and MicroScan WalkAway reproducibility was similar to BMD. DD reproducibility was < 90% for all drugs tested when a 3 mm cut-off was applied. When comparing the accuracy of DD to BMD, only MEM met all acceptance criteria. TMP-SMX and LVX had high minor errors, CAZ had unacceptable very major errors (VME), and MIN, PIP-TAZ, and CIP had both unacceptable minor errors and VMEs. For MicroScan WalkAway, no drugs met acceptance criteria. Analyses also showed that errors were not attributed to one species. In general, our data agree with EUCAST recommendations.

Occurrence, antimicrobial susceptibility, and pathogenic factors of Pseudomonas aeruginosa in canine clinical samples

Background and Aim:

Pseudomonas aeruginosa is a relevant opportunistic and difficult to treat pathogen due to its widespread environmental diffusion, intrinsic resistance to many classes of antimicrobials, high ability to acquire additional resistance mechanisms, and wide range of pathogenic factors. The present study aimed to investigate the prevalence of P. aeruginosa in canine clinical samples, the antimicrobial susceptibility against antipseudomonal antibiotics, and the presence of extracellular pathogenic factors of the isolates, as well as their ability to produce biofilm.

Materials and Methods:

Overall, 300 clinical specimens from dogs with pyoderma or abscesses (n=58), otitis (n=59), and suspected bladder infection (n=183) were analyzed by standard bacteriological methods. P. aeruginosa isolates were tested for their antimicrobial susceptibility by disk and gradient diffusion methods to determine the minimum inhibitory concentrations. The ability of the isolates to produce biofilm was investigated by a microtiter plate assay, while virulence genes coding for elastase (lasB), exotoxin A (toxA), alkaline protease (aprA), hemolytic phospholipase C (plcH), and exoenzyme S (ExoS) were detected by polymerase chain reaction method.

Results:

A total of 24 isolates of P. aeruginosa were found in clinical specimens (urine n=3, skin/soft tissue n=6, and ear canal n=15). No resistance was found to ceftazidime, gentamicin, aztreonam, and imipenem (IMI), while low levels of resistance were found to enrofloxacin (ENR) (4.2%) and piperacillin-tazobactam (8.3%). However, 41.7% and 29.2% of the isolates showed intermediate susceptibility to ENR and IMI, respectively. Disk and gradient diffusion methods showed high concordance. The majority of the isolates revealed a weak (33.3%) or intermediate (45.8%) ability to form biofilm, while the strong biofilm producers (20.8%) derived exclusively from the ear canal samples. All isolates (100%) were positive for lasB, aprA, and plcH genes, while exoS and toxA were amplified in 21 (87.5%) and 22 (91.7%) isolates, respectively.

Conclusion:

In the present study, P. aeruginosa isolates from canine clinical samples were characterized by low levels of antimicrobial resistance against antipseudomonal drugs. However, the high presence of isolates with intermediate susceptibility for some categories of antibiotics, including carbapenems which are not authorized for veterinary use, could represent an early warning signal. Moreover, the presence of isolates with strong ability to produce biofilm represents a challenge for the interpretation of the antimicrobial susceptibility profile. In addition, the high prevalence of the extracellular pathogenic factors was indicative of the potential virulence of the isolates.

Contemporary analysis of ETEST for antibiotic susceptibility and minimum inhibitory concentration agreement against Pseudomonas aeruginosa from patients with cystic fibrosis

Objectives

Cystic fibrosis (CF) acute pulmonary exacerbations are often caused by Pseudomonas aeruginosa, including multi-drug resistant strains. Optimal antibiotic therapy is required to return lung function and should be guided by in vitro susceptibility results. There are sparse data describing ETEST performance for CF isolates using contemporary isolates, methods and interpretation, as well as novel antibiotics, such as ceftazidime–avibactam and ceftolozane–tazobactam.

Methods

Pseudomonas aeruginosa (n = 105) isolated during pulmonary exacerbation from patients with CF were acquired from 3 US hospitals. Minimum inhibitory concentrations (MICs) were assessed by reference broth microdilution (BMD) and ETEST for aztreonam, cefepime, ceftazidime, ceftazidime–avibactam, ceftolozane–tazobactam, ciprofloxacin, levofloxacin, meropenem, piperacillin–tazobactam, and tobramycin. Broth microdilution was conducted in concordance with the Clinical and Laboratory Standards Institute M100. ETEST methodology reflected package insert recommendations. Performance of ETEST strips was evaluated using the Food and Drug Administration (FDA) and Susceptibility Testing Manufacturers Association (STMA) guidance.

Results

Of the 105 P. aeruginosa included, 46% had a mucoid phenotype. ETEST MICs typically read 0–1 dilution higher than BMD for all drugs. Categorical agreement and essential agreement ranged from 64 to 93% and 63 to 86%, respectively. The majority of observed errors were minor. A single very major error occurred with ceftazidime (4.2%). For ceftazidime–vibactam, 2 very major errors were observed and both were within essential agreement. Major errors occurred for aztreonam (3.3%), cefepime (9.4%), ceftazidime–avibactam (5.3%, adjusted 2.1%), ceftolozane–tazobactam (1%), meropenem (3.3%), piperacillin–tazobactam (2.9%), and tobramycin (1.5%).

Conclusions

ETEST methods performed conservatively for most antibiotics against this challenging collection of P. aeruginosa from patients with CF.

The accuracy of four commercial broth microdilution tests in the determination of the minimum inhibitory concentration of colistin

Colistin is considered as one of the last-resort antibiotics and reliable antimicrobial susceptibility testing is therefore crucial. The reference standard for AST according to EUCAST and CLSI is broth microdilution (BMD). However, BMD is labor intensive to perform. Commercial antimicrobial susceptibility tests derived from BMD method are available. We investigated the performance of four different commercial tests: Sensititre™, SensiTest™ Colistin, Micronaut MIC Strip Colistin and UMIC Colistin using 70 clinical isolates (half of them was deemed by VITEK2 as resistant), including isolates from cystic fibrosis patients and mcr-1 bearing isolates. We used two reference standards: BMD and composite MIC as determined by all four tests. Sensititre™ had essential agreement (EA, defined as minimum inhibitory concentration within ± 1 dilution) of 87% and 89% compared to BMD and composite reference standard, respectively. For SensiTest™, the EA's were 93% and 90%. For UMIC, 87% and 90%, and for Micronaut, 83% and 84%. All four tests demonstrated categorical agreement (CA) above 90%. CA for SensiTest™ and Micronaut was both 96%, UMIC 94%, and Sensititre™ 93%. All tests were reproducible as tested in two quality control isolates. In conclusion, in clinical isolates from a large referral center, the four commercial tests for determination of colistin minimum inhibitory concentrations showed acceptable performance.

Acute Pulmonary Exacerbations in Cystic Fibrosis

With the improving survival of cystic fibrosis (CF) patients and the advent of highly effective cystic fibrosis transmembrane conductance regulator therapy, the clinical spectrum of this complex multisystem disease continues to evolve. One of the most important clinical events for patients with CF in the course of this disease is an acute pulmonary exacerbation. Clinical and microbial epidemiology studies of CF pulmonary exacerbations continue to provide important insight into the disease course, prognosis, and complications. This work has now led to a number of large scale clinical trials with the goal of improving the treatment paradigm for CF pulmonary exacerbation. The primary goal of this review is to provide a summary of the pathophysiology, the clinical epidemiology, microbial epidemiology, outcome and the treatment of CF pulmonary exacerbation.

Defining antimicrobial resistance in cystic fibrosis

Antimicrobial resistance (AMR) can present significant challenges in the treatment of cystic fibrosis (CF) lung infections. In CF and other chronic diseases, AMR has a different profile and clinical consequences compared to acute infections and this requires different diagnostic and treatment approaches. This review defines AMR, explains how it occurs, describes the methods used to measure AMR as well as their limitations, and concludes with future directions for research and development in the area of AMR in CF.

Great phenotypic and genetic variation among successive chronic Pseudomonas aeruginosa from a cystic fibrosis patient

Background/Objectives

Different adapted Pseudomonas aeruginosa morphotypes are found during chronic infections. Relevant biological determinants in P. aeruginosa successively isolated from a cystic fibrosis (CF) patient were analyzed in this work to gain insight into P. aeruginosa heterogeneity during chronic infection.

Methods

Seventeen P. aeruginosa isolates collected from a patient over a 3 year period were included, 5 small colony variants (SCV) and 12 mucoids. The following analyses were performed: Pulsed-Field-Gel-Electrophoresis (PFGE)/Multilocus- sequence-typing (MLST)/serotype, antimicrobial susceptibility, growth curves, capacity to form biofilm, pigment production, elastase activity, motility; presence/expression of virulence/quorum sensing genes, and identification of resistance mechanisms.

Results

All isolates had closely related PFGE patterns and belonged to ST412. Important phenotypic and genotypic differences were found. SCVs were more resistant to antimicrobials than mucoid isolates. AmpC hyperproduction and efflux pump activity were detected. Seven isolates contained two integrons and nine isolates only one integron. All SCVs showed the same OprD profile, while three different profiles were identified among mucoids. No amino acid changes were found in MutL and MutS. All isolates were slow-growing, generally produced high biofilm, had reduced their toxin expression and their quorum sensing, and showed low motility. Nevertheless, statistically significant differences were found among SCV and mucoid isolates. SCVs grew faster, presented higher biofilm formation and flicA expression; but produced less pyorubin and pyocyanin, showed lower elastase activity and rhlR, algD, and lasB expression than mucoid isolates.

Conclusion

These results help to understand the molecular behavior of chronic P. aeruginosa isolates in CF patients.

Evaluation of Biofilm Formation and Frequency of Multidrug-resistant and Extended Drug-resistant Strain in Pseudomonas aeruginosa Isolated from Burn Patients in Isfahan

Background:

Pseudomonas aeruginosa is a biofilm-forming bacterium which can result in serious health problems, particularly in burn patients. Biofilm has been assumed to protect the bacteria from environmental fluctuations such as antimicrobial agent. Mucoid strains generate extensive levels of the alginate exopolysaccharide, which is an important factor of its biofilm.

Materials and Methods:

Totally, 100 isolates of P. aeruginosa has been gathered from wound infections of burn patients. Polymerase chain reaction of exoA gene has been carried out to confirm the bacteriologic identification of isolates. The biofilm-forming capacity has been specified by capsule staining and microtiter plate test as qualitative and quantitative determination, respectively. Antimicrobial susceptibility of the isolates has been specified by disk diffusion method.

Results:

All the isolates carried the exoA gene. The antibiotic resistance was imipenem (90%); levofloxacin (93%); aztreonam (87%); piperacillin-tazobactam (85%); tobramycin (92%); polymyxin b (PB) (2%); and ceftazidime (CAZ) (32%). Totally, multidrug-resistant (MDR) and extended drug-resistant (XDR) isolates were 19% and 75%, respectively. Fortunately, pan drug-resistant (PDR) strain has not been observed. The assessment of biofilm formation has shown that 7% of the isolates were nonbiofilm (N), weak (W) 67%, moderate (M) 22%, and strong (S) 4%.

Conclusions:

As a result, the findings of this survey indicated that PB and CAZ were the most effective antibiotics against P. aeruginosa, which of course indicate a serious problem about the emergence of the PDR strains. There was no relationship between the patterns of biofilm production and antibiotic susceptibility, but high frequency of MDR/XDR and biofilm producer strains has been detected.

Interpreting carbapenem susceptibility testing results for Pseudomonas aeruginosa

OBJECTIVES

Carbapenems are among the most powerful antipseudomonal agents. Limited data is available on drug susceptibility testing by routine methods (disc diffusion and Etest) for meropenem and doripenem. We aimed to compare the in vitro activity of imipenem, meropenem, and doripenem against Pseudomonas aeruginosa.

METHODS

A total of 311 P. aeruginosa strains isolated from respiratory specimens in 170 patients who developed ventilator-associated pneumonia in two intensive care units were collected over a period of 31 months. The susceptibility of these isolates to imipenem, meropenem, and doripenem were determined by Etest and disc diffusion method.

RESULTS

Considering either all isolates or only the first isolates recovered per patient (311 and 170 respectively), the susceptibility rate for doripenem was higher than that for meropenem and imipenem. When MICs determined by Etest were converted into interpretative categories (S, I, R) using French (CA-SFM) guidelines, a poor correlation was observed for meropenem and doripenem. The percentages of correlation with the disc diffusion method were 90.6% and 89.7% for imipenem, 80.5% and 82.6% for meropenem, and 80.5% and 73.3% for doripenem, for the first isolates and all isolates, respectively. The rate of minor errors was as high as 17.7% and 16.1% for meropenem and 17.7% and 25.7% for doripenem for the first isolates and all isolates, respectively.

CONCLUSION

The accuracy of disc diffusion using CA-SFM guidelines appears unsatisfactory for all three carbapenems justifying guideline update for P. aeruginosa and carbapenems.

Use of Calgary and Microfluidic BioFlux Systems To Test the Activity of Fosfomycin and Tobramycin Alone and in Combination against Cystic Fibrosis Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is a major cause of morbidity and mortality in chronically infected cystic fibrosis patients. Novel in vitro biofilm models which reliably predict the therapeutic success of antimicrobial therapies against biofilm bacteria should be implemented. The activity of fosfomycin, tobramycin, and the fosfomycin-tobramycin combination against 6 susceptible P. aeruginosa strains isolated from respiratory samples from cystic fibrosis patients was tested by using two in vitro biofilm models: a closed system (Calgary device) and an open model based on microfluidics (BioFlux). All but one of the isolates formed biofilms. The fosfomycin and tobramycin minimal biofilm inhibitory concentrations (MBIC) were 1,024 to >1,024 μg/ml and 8 to 32 μg/ml, respectively. According to fractional inhibitory concentration analysis, the combination behaved synergistically against all the isolates except the P. aeruginosa ATCC 27853 strain. The dynamic formation of the biofilm was also studied with the BioFlux system, and the MIC and MBIC of each antibiotic were tested. For the combination, the lowest tobramycin concentration that was synergistic with fosfomycin was used. The captured images were analyzed by measuring the intensity of the colored pixels, which was proportional to the biofilm biomass. A statistically significant difference was found when the intensity of the inoculum was compared with the intensity of the microchannel in which the MBIC of tobramycin, fosfomycin, or their combination was used (P < 0.01) but not when the MIC was applied (P > 0.01). Fosfomycin-tobramycin was demonstrated to be synergistic against cystic fibrosis P. aeruginosa strains in the biofilm models when both the Calgary and the microfluidic BioFlux systems were tested. These results support the clinical use of this combination.

Susceptibility Testing for the Polymyxins: Two Steps Back, Three Steps Forward?

Optimizing and standardizing susceptibility testing for the polymyxins have become pressing issues, given the rise in multidrug-resistant Gram-negative bacilli. Recently, both the CLSI and EUCAST have recommended broth microdilution (BMD) (without polysorbate) as the reference method for polymyxin susceptibility testing. In this issue, K. L. Chew et al. (J Clin Microbiol 55:2609-2616, 2017, https://doi.org/10.1128/JCM.00268-17) compare the performances of three commercial BMD panels and the Etest to the reference, BMD, for polymyxin B and colistin, using 76 Enterobacteriaceae isolates (21 of which were mcr-1 positive). Although none of the commercial BMD panels strictly met FDA performance standards in this evaluation, possibly because of the small number isolates tested, the Sensititre panel achieved >90% categorical agreement for both polymyxin compounds. These results also reaffirm CLSI and EUCAST guidance that gradient diffusion testing, which had unacceptable error rates, should be abandoned. In a simulated analysis with lowered breakpoints (susceptible, ≤1 mg/liter; intermediate, 2 mg/liter; resistant, ≥4 mg/liter), error rates and agreement were improved across the various methods and the rate of detection of mcr-1-positive isolates improved. These observations, taken together with recent pharmacokinetic data on optimizing target attainment for the polymyxins, suggest that more-stringent (lower) breakpoints may be reasonable, although such an approach may be limited by the inherent reliability of current testing methodologies and a lack of robust clinical correlative data, which are sorely needed.

Relevance of multidrug-resistant Pseudomonas aeruginosa infections in cystic fibrosis

Multidrug-resistant (MDR) Pseudomonas aeruginosa is an important issue for physicians who take care of patients with cystic fibrosis (CF). Here, we review the latest research on how P. aeruginosa infection causes lung function to decline and how several factors contribute to the emergence of antibiotic resistance in P. aeruginosa strains and influence the course of the infection course. However, many aspects of the practical management of patients with CF infected with MDR P. aeruginosa are still to be established. Less is known about the exact role of susceptibility testing in clinical strategies for dealing with resistant infections, and there is an urgent need to find a tool to assist in choosing the best therapeutic strategy for MDR P. aeruginosa infection. One current perception is that the selection of antibiotic therapy according to antibiogram results is an important component of the decision-making process, but other patient factors, such as previous infection history and antibiotic courses, also need to be evaluated. On the basis of the known issues and the best current data on respiratory infections caused by MDR P. aeruginosa, this review provides practical suggestions to optimize the diagnostic and therapeutic management of patients with CF who are infected with these pathogens.

Microbiological diagnostic procedures for respiratory cystic fibrosis samples in Spain: towards standard of care practices

BACKGROUND

The microbiological procedures for cystic fibrosis (CF) samples of 17 participating Spanish centers were examined to verify their compliance with current international and national guidelines and to implement the best standards of care for microbiology practices. A 47-item questionnaire covering different CF microbiology aspects was sent to participant laboratories. Telephone interviews were performed when necessary. Data about samples processing for bacteria, mycobacteria and fungi were collected.

RESULTS

Gene sequencing (71%), MALDI-TOF (59%) or both (94%) were available for most laboratories. Susceptibility testing was performed by automated microdilution systems (94%) and manual diffusion methods (59%). However, a low use of selective media for Staphylococcus aureus (59%) and Burkholderia cepacia complex (71%), and of epidemiological typing methods (41%) was reported.

CONCLUSIONS

Most Spanish laboratories are in agreement with consensus guidelines for the processing of CF respiratory samples, but need to improve in the use of specific selective media and typing methods for epidemiologic studies.

Antimicrobial susceptibility differences among mucoid and non-mucoid Pseudomonas aeruginosa isolates

Pseudomonas aeruginosa is one of the most important opportunistic bacteria, causing a wide variety of infections particularly in immunocompromised patients. The extracellular glycocalyx is produced in copious amounts by mucoid strains of P. aeruginosa. Mucoid and non-mucoid P. aeruginosa strains show some differences in their antimicrobial susceptibility pattern. The aim of this study was to investigate the frequency of mucoid and non-mucoid types and their antimicrobial susceptibility patterns isolated from Milad and Mostafa Khomeini Hospital in Tehran, Iran.

One hundred P. aeruginosa isolates were collected which all were confirmed by conventional biochemical tests and PCR assay using specific primers for oprI and oprL lipoproteins. Mucoid and non-mucoid types of isolates were determined by culturing isolates on BHI agar containing Congo red and Muir mordant staining method. The susceptibility pattern of isolates against 23 different antibiotics was assessed using MIC sensititre susceptibility plates.

Fifty of 100 of isolates were mucoid type, of which 14 isolates were from Mostafa Khomeini Hospital. Frequency of mucoid type of P. aeruginosa in Mostafa Khomeini hospital (70%) was higher than that seen in Milad hospital (45%). The statistical analysis of MICs results showed significant differences in antimicrobial resistance among mucoid and non-mucoid types (non mucoid strains showed more resistance against tested antibiotics). This may be due to the tendency of some antibiotics to attach to extracellular glycocalyx of mucoid strains.

Culture-based diagnostic microbiology in cystic fibrosis: can we simplify the complexity?

Cystic fibrosis (CF) diagnostic microbiology has evolved from a focus on Staphylococcus aureus as primary pathogen to identification of the contribution of Pseudomonas aeruginosa and other non-fermenting gram negatives; studies of the lung microbiome have added new complexity. This review summarizes state-of-the art culture methods and makes recommendations for addition of non-culture based methods in the diagnostic laboratory. Plating on selective media is recommended, with organism identification by matrix assisted laser desorption-time of flight mass spectroscopy and real-time polymerase chain reaction (PCR) supplanting both biochemical identification and other less accurate and more time-consuming molecular methods. Conventional antibiotic susceptibility testing, possibly at less frequent intervals, remains the standard but more CF-relevant methods may arise in the future. There is a role for direct identification of organisms in clinical samples using quantitative real-time PCR, next generation sequencing, and metagenomic studies for the re-examination of samples that do not yield traditional CF pathogens.

Global fluoroquinolone resistance epidemiology and implictions for clinical use

This paper on the fluoroquinolone resistance epidemiology stratifies the data according to the different prescription patterns by either primary or tertiary caregivers and by indication. Global surveillance studies demonstrate that fluoroquinolone resistance rates increased in the past years in almost all bacterial species except S. pneumoniae and H. influenzae, causing community-acquired respiratory tract infections. However, 10 to 30% of these isolates harbored first-step mutations conferring low level fluoroquinolone resistance. Fluoroquinolone resistance increased in Enterobacteriaceae causing community acquired or healthcare associated urinary tract infections and intraabdominal infections, exceeding 50% in some parts of the world, particularly in Asia. One to two-thirds of Enterobacteriaceae producing extended spectrum β-lactamases were fluoroquinolone resistant too. Furthermore, fluoroquinolones select for methicillin resistance in Staphylococci. Neisseria gonorrhoeae acquired fluoroquinolone resistance rapidly; actual resistance rates are highly variable and can be as high as almost 100%, particularly in Asia, whereas resistance rates in Europe and North America range from <10% in rural areas to >30% in established sexual networks. In general, the continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some guidelines, for example, treatment of urinary tract, intra-abdominal, skin and skin structure infections, and traveller's diarrhea, or even precludes the use in indications like sexually transmitted diseases and enteric fever.

Antimicrobial susceptibility and synergy studies of cystic fibrosis sputum by direct sputum sensitivity testing

Standard disc diffusion antimicrobial susceptibility testing (C+S) on individual Pseudomonas aeruginosa colonial morphotypes cultured from cystic fibrosis (CF) sputum has questionable clinical relevance. Direct sputum sensitivity testing (DSST) is a whole-sputum susceptibility test that removes bias associated with selecting individual colonial morphotypes. We sought to determine whether, in principle, the results from DSST support the possibility of improved clinical relevance compared with C+S. Individual (DSSTi) and combination (DSST) susceptibility to gentamicin, tobramycin, ceftazidime and meropenem were determined on 130 sputum samples referred from CF subjects with antibiotic-resistant chronic Gram-negative endobronchial infection. DSSTi and concurrent C+S were compared for categorical susceptibility, synergistic combinations were evaluated and the combination DSST efficacy index (DEI) calculated. Meropenem and tobramycin were the most active individual antibiotics by DSSTi on 89 P. aeruginosa-predominant samples, with 62 % of samples sensitive to each. C+S and DSSTi showed poor agreement (κ ranging from 0.02 to 0.6), discordance ranging from 20 % (meropenem) to 49 % (tobramycin), with DSSTi demonstrating both increased susceptibility and increased resistance. The combination that most frequently had the highest DEI was tobramycin + meropenem, occurring in 76 % of samples. DSSTi appears to be reproducible, yields different antimicrobial susceptibility results from C+S without simply identifying the most resistant isolates and DSST identifies the most effective in vitro antibiotic combinations, providing preliminary proof of concept of the potentially improved clinical relevance of whole-sputum testing. Future studies will determine whether these potential theoretical advantages translate into clinical benefits.

Management of refractory Pseudomonas aeruginosa infection in cystic fibrosis

Cystic fibrosis (CF) is the most common life-limiting inherited disease in Caucasian populations. The main cause of death in CF patients is respiratory failure resulting from chronic pulmonary infection. Pseudomonas aeruginosa is the most prevalent organism in the airway colonization of CF patients, and its persistence in the airways has been related to greater morbidity with a more rapid deterioration in lung function. P. aeruginosa has enormous genetic and metabolic flexibility that allows it to adapt and persist within the airways of CF patients, and it has the ability to easily acquire antimicrobial resistance. For these reasons, the management of infections and chronic colonization by P. aeruginosa remains a challenge for physicians. This article reviews the current and future antibacterial chemotherapy options for respiratory pseudomonal infection in CF patients.

Bioautography detection in thin-layer chromatography

Bioautography is a microbial detection method hyphenated with planar chromatography techniques. It is based mainly on antimicrobial or antifungal properties of analyzed substances. The review discusses three versions of bioautography, i.e. contact, immersion and direct bioautography. The more concern is given to the last one. Many applications are quoted, not only for testing various groups of compounds, but also for investigating biochemical processes and factors influencing bacterial growth. Additionally, related methods, which can be included into direct bioautography, are discussed. The most promising among them seems to be TLC-bioluminescence screening.

Colistin susceptibility testing: evaluation of reliability for cystic fibrosis isolates of Pseudomonas aeruginosa and Stenotrophomonas maltophilia

OBJECTIVES

Antibiotic susceptibility methods that are commonly used to test bacterial isolates from patients with cystic fibrosis are of uncertain reliability for the polymyxins. To assess the reliability of four standard testing methods, this pilot study used a challenge set that included polymyxin-resistant isolates of Pseudomonas aeruginosa and Stenotrophomonas maltophilia.

METHODS

Twenty-five P. aeruginosa and 12 S. maltophilia isolates were tested for susceptibility to colistin (polymyxin E). Repeatability (concordance of replicates performed concurrently), reproducibility (concordance of replicates performed over time) and comparability (concordance of different methods) of agar dilution, broth microdilution, Etest and disc diffusion were assessed through the use of descriptive statistics and scatterplot analyses.

RESULTS

All four methods displayed excellent repeatability (overall concordance rate of 99%). However, analysis of reproducibility revealed substantially lower rates of concordance (74% for agar dilution, 84% for broth microdilution and Etest, and 91% for disc diffusion). In addition, comparability to agar dilution of the three other methods was generally poor, with overall rates of very major error ranging from 12% for broth microdilution to 18% for Etest and disc diffusion.

CONCLUSIONS

Compared with agar dilution, other susceptibility testing methods give high rates of apparent false polymyxin susceptibility for cystic fibrosis isolates of P. aeruginosa and S. maltophilia. Prospective study of the correlation between in vitro susceptibility and clinical response is needed to clarify whether these discrepancies reflect oversensitivity of the agar dilution method or insensitivity of the other methods.

Detection of carbapenem resistance in clinical mucoid Pseudomonas aeruginosa isolates

Of 19 isolates of mucoid Pseudomonas aeruginosa, 2 isolates showed imipenem resistance conferred by reduced OprD production. Imipenem resistance was detected by the MicroScan broth microdilution and Etest methods, but minimum inhibitory concentrations could not be determined by the Vitek system for an isolate. In cases where susceptibility cannot be determined by the broth microdilution methods, Etest results would be valuable for effective treatment.

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. As resistance continues to emerge among a wide range of clinically relevant bacteria, the complexity of this communication increases. This updated version provides an overview of the important susceptibility concerns for most commonly isolated bacterial pathogens.

Validation of Vitek 2 nonfermenting gram-negative cards and Vitek 2 version 4.02 software for identification and antimicrobial susceptibility testing of nonfermenting gram-negative rods from patients with cystic fibrosis

Accurate identification and antimicrobial susceptibility testing (AST) of nonfermenters from cystic fibrosis patients are essential for appropriate antimicrobial treatment. This study examined the ability of the newly designed Vitek 2 nonfermenting gram-negative card (NGNC) (new gram-negative identification card; bioMérieux, Marcy-l'Etoile, France) to identify nonfermenting gram-negative rods from cystic fibrosis patients in comparison to reference methods and the accuracy of the new Vitek 2 version 4.02 software for AST compared to the broth microdilution method. Two hundred twenty-four strains for identification and 138 strains for AST were investigated. The Vitek 2 NGNC identified 211 (94.1%) of the nonfermenters correctly. Among morphologically atypical microorganisms, five strains were misidentified and eight strains were determined with low discrimination, requiring additional tests which raised the correct identification rate to 97.8%. Regarding AST, the overall essential agreement of Vitek 2 was 97.6%, and the overall categorical agreement was 92.9%. Minor errors were found in 5.1% of strains, and major and very major errors were found in 1.6% and 0.3% of strains, respectively. In conclusion, the Vitek NGNC appears to be a reliable method for identification of morphologically typical nonfermenters and is an improvement over the API NE system and the Vitek 2 GNC database version 4.01. However, classification in morphologically atypical nonfermenters must be interpreted with care to avoid misidentification. Moreover, the new Vitek 2 version 4.02 software showed good results for AST and is suitable for routine clinical use. More work is needed for the reliable testing of strains whose MICs are close to the breakpoints.

Antimicrobial susceptibility of clinical isolates of Pseudomonas aeruginosa from a Malaysian Hospital

Ongoing surveillance of Pseudomonas aeruginosa resistance against antimicrobial agents is fundamental to monitor trends in susceptibility patterns and to appropriately guide clinicians in choosing empirical or directed therapy. The in vitro activity level of eight antimicrobial drugs was assessed against 97 clinical isolates of P. aeruginosa collected consecutively for three months in 2007 from a Malaysian hospital. Antimicrobial susceptibility was determined using the E-test method in addition to the hospital's routine diagnostic testing by the disk diffusion method. Respiratory and wound swab isolates were the most frequently encountered isolates. The E-test and disk diffusion methods showed high concordance in determining the in vitro activity of the antimicrobial agents against the E isolates. Piperacillin-tazobactam was the most active antimicrobial agent with 91.8% susceptibility, followed by the aminoglycosides (amikacin, 86.6% and gentamicin, 84.5%), the quinolone (ciprofloxacin, 83.5%) and the beta-lactams (cefepime, 80.4%, ceftazidime, 80.4%, imipenem, 79.4% and meropenem, 77.3%). Incidence of multidrug resistance was 19.6% (19 out of 97 isolates). Periodic antibiotic resistance surveillance is fundamental to monitor changes in susceptibility patterns in a hospital setting.

Performance of Vitek 2 in antimicrobial susceptibility testing of Pseudomonas aeruginosa isolates with different mechanisms of beta-lactam resistance

A total of 78 isolates of Pseudomonas aeruginosa grouped according to the phenotype for ceftazidime and imipenem susceptibility/resistance were used to assess the accuracy of the Vitek 2 system in antimicrobial susceptibility testing. Comparisons were made with a MIC gradient test for piperacillin-tazobactam, ceftazidime, aztreonam, imipenem, meropenem, gentamicin, and ciprofloxacin. For the total of 546 isolate-antimicrobial combinations tested, the category agreement was 83.6%, with 2.0, 1.6, and 12.8% very major, major, and minor errors, respectively. Vitek 2 accuracy was influenced differently by the mechanism responsible for resistance, and interpretation of the results in relation to phenotype could improve the performance of the system.

[Various typing methods of Pseudomonas aeruginosa strains isolated from cystic fibrosis patients]

Typing methods are essential to understand the epidemiology of bacterial infections. Strain typing is important for the detection of sources or routes of infections, identification between endemic and epidemic strains and prevention of transmission between patients. Some Pseudomonas aeruginosa cystic-fibrosis strains could not be typed with conventional typing methods. Due to the diverse phenotypic nature of P. aeruginosa, phenotyping methods are not discriminatory enough to identify strains belonging to the same genotype. Thus, molecular typing methods are required. These methods should be applied when data from phenotypic typing analysis becomes ambiguous, such as in cystic fibrosis. Molecular typing methods, developed over the past decade, are highly discriminatory in capacity and reproducibility. However, they are more likely applied in specialized laboratories since they are expensive and increase the workload. A reliable and low-cost typing system is required for better defining the epidemiology of this pathogen and designing more rational policies of infection control. Comparison between typing methods will pinpoint the limits and effectiveness of each method and will improve in turn the choice of a nonspecialized laboratory in terms of simplicity, time and cost.

Genome-scale metabolic network analysis of the opportunistic pathogen Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is a major life-threatening opportunistic pathogen that commonly infects immunocompromised patients. This bacterium owes its success as a pathogen largely to its metabolic versatility and flexibility. A thorough understanding of P. aeruginosa's metabolism is thus pivotal for the design of effective intervention strategies. Here we aim to provide, through systems analysis, a basis for the characterization of the genome-scale properties of this pathogen's versatile metabolic network. To this end, we reconstructed a genome-scale metabolic network of Pseudomonas aeruginosa PAO1. This reconstruction accounts for 1,056 genes (19% of the genome), 1,030 proteins, and 883 reactions. Flux balance analysis was used to identify key features of P. aeruginosa metabolism, such as growth yield, under defined conditions and with defined knowledge gaps within the network. BIOLOG substrate oxidation data were used in model expansion, and a genome-scale transposon knockout set was compared against in silico knockout predictions to validate the model. Ultimately, this genome-scale model provides a basic modeling framework with which to explore the metabolism of P. aeruginosa in the context of its environmental and genetic constraints, thereby contributing to a more thorough understanding of the genotype-phenotype relationships in this resourceful and dangerous pathogen.

A German external quality survey of diagnostic microbiology of respiratory tract infections in patients with cystic fibrosis

BACKGROUND

The goal of this pilot study was to design an external quality assessment (EQA) scheme for German cystic fibrosis (CF) clinical microbiology laboratories. Therefore, a multicentre study of 18 German CF laboratories was performed to evaluate their proficiency in analyzing CF respiratory secretions.

METHODS

Simulated clinical specimens containing a set of four frequent CF pathogens, namely two Pseudomonas aeruginosa strains differing in morphotype (mucoid versus non-mucoid) and resistotype, one Staphylococcus aureus strain and one Burkholderia multivorans strain, were distributed to each laboratory. Isolation, identification and antimicrobial susceptibility testing (AST) of any bacterial pathogen present and completion of a questionnaire about applied microbiological protocols were requested.

RESULTS

Three of four strains were isolated and identified correctly by almost all laboratories. B. multivorans was once misidentified as Burkholderia cenocepacia. Fourteen laboratories failed to detect the second multidrug resistant P. aeruginosa isolate. AST errors occurred most often for P. aeruginosa 2 followed by B. multivorans, P. aeruginosa 1 and S. aureus. Evaluation of the questionnaires revealed major differences in cultivation and identification techniques applied by the participating laboratories.

CONCLUSIONS

A periodical EQA programme for German CF laboratories and standardized microbiological procedures seem to be necessary to advance diagnostic microbiology employed on CF respiratory tract specimens and may help to improve anti-infective treatment and infection control practices for CF patients.

Exacerbations in cystic fibrosis. 1: Epidemiology and pathogenesis

With the improving survival of patients with cystic fibrosis (CF), the clinical spectrum of this complex multisystem disease continues to evolve. One of the most important clinical events for patients with CF in the course of this disease is an acute pulmonary exacerbation. Clinical and microbial epidemiology studies of CF pulmonary exacerbations continue to provide important insight into the course, prognosis and complications of the disease. This review provides a summary of the pathophysiology, clinical epidemiology and microbial epidemiology of a CF pulmonary exacerbation.

Evaluation of the E test for the assessment of synergy of antibiotic combinations against multiresistant Pseudomonas aeruginosa isolates from cystic fibrosis patients

The determination of synergistic effects of antimicrobial drug combinations can lead to improved therapeutic options in the antibiotic treatment of cystic fibrosis patients who are chronically infected with multiresistant Pseudomonas aeruginosa isolates. The aim of this study was to evaluate the performance of the E test versus the standard agar dilution checkerboard susceptibility test in the assessment of synergy and, in addition, to determine the activity of two antimicrobial combinations against 163 multiresistant P. aeruginosa isolates from cystic fibrosis patients. The agreement between the checkerboard method and the E test was excellent (>90%) for nonmucoid as well as mucoid isolates from cystic fibrosis patients. The rate of synergy was higher for the antibiotic combination of ceftazidime and tobramycin (28.8% of the cystic fibrosis strains) than for the combination of meropenem and tobramycin (19.0%). However, the probability of synergy for the second antibiotic combination increased significantly when the synergy of the first antibiotic combination had already been demonstrated (Fischer's exact test, p=0.049). The results show that the E test is a valuable and practical method for routine microbiological diagnostics and can aid in the selection of improved antibiotic options in the treatment of cystic fibrosis patients chronically infected with P. aeruginosa.

Accuracies of beta-lactam susceptibility test results for Pseudomonas aeruginosa with four automated systems (BD Phoenix, MicroScan WalkAway, Vitek, and Vitek 2)

Contemporary clinical isolates and challenge strains of Pseudomonas aeruginosa were tested by four automated susceptibility testing systems (BD Phoenix, MicroScan WalkAway, Vitek, and Vitek 2; two laboratories with each) against six broad-spectrum beta-lactams, and the results were compared to reference broth microdilution (BMD) and to consensus results from three validated methods (BMD, Etest [AB Biodisk, Solna, Sweden], and disk diffusion). Unacceptable levels of error (minor, major, and very major) were detected, some with systematic biases toward false susceptibility (piperacillin-tazobactam and imipenem) and others toward false resistance (aztreonam, cefepime, and ceftazidime). We encourage corrective action by the system manufacturers to address test biases, and we suggest that clinical laboratories using automated systems should consider accurate alternative methods for routine use.

Compliance of clinical microbiology laboratories in the United States with current recommendations for processing respiratory tract specimens from patients with cystic fibrosis

Respiratory tract specimens from patients with cystic fibrosis (CF) require unique processing by clinical microbiology laboratories to ensure detection of all potential pathogens. The present study sought to determine the compliance of microbiology laboratories in the United States with recently published recommendations for CF respiratory specimens. Microbiology laboratory protocols from 150 of 190 (79%) CF care sites were reviewed. Most described the use of selective media for Burkholderia cepacia complex (99%), Staphylococcus aureus (82%), and Haemophilus influenzae (89%) and identified the species of all gram-negative bacilli (87%). Only 52% delineated the use of agar diffusion assays for susceptibility testing of Pseudomonas aeruginosa. Standardizing laboratory practices will improve treatment, infection control, and our understanding of the changing epidemiology of CF microbiology.

Accuracy of three automated systems (MicroScan WalkAway, VITEK, and VITEK 2) for susceptibility testing of Pseudomonas aeruginosa against five broad-spectrum beta-lactam agents

One hundred recent clinical Pseudomonas aeruginosa isolates were used to assess the quantitative (MIC) and qualitative (susceptibility category) accuracies of the MicroScan WalkAway, VITEK, and VITEK 2 automated susceptibility test systems when five-broad spectrum beta-lactams, aztreonam, cefepime, ceftazidime, imipenem, and piperacillin-tazobactam, were tested. Isolates were selected so that the MICs for the isolates overrepresented the MICs near the breakpoints to assess precisely the agreement between the results obtained with the automated systems and the results obtained by the reference tests. The categorical and MIC results from the automated systems were compared to the consensus result of three reference methods: broth microdilution, agar dilution, and disk diffusion. The consensus categorical testing (susceptibility and resistance) rates were 47 and 27%, respectively, for aztreonam; 59 and 14%, respectively, for cefepime; 44 and 43%, respectively, for ceftazidime; 71 and 19%, respectively, for imipenem; and 50 and 50%, respectively, for piperacillin-tazobactam. All systems tested exhibited a high, unacceptable level of very major (false-susceptible) errors for piperacillin-tazobactam (19 to 27%). Major (false-resistant) error rates were generally acceptable (0 to 3%), but minor error rates were elevated (8 to 32%) for cefepime (VITEK 2 and VITEK) and for aztreonam (all three systems), leading to consistent trends toward false resistance. Manufacturer reevaluation of these automated systems for the testing of selected beta-lactams with current clinical isolates of P. aeruginosa that exhibit contemporary resistance mechanisms would be prudent to minimize the potential for serious reporting errors.

Antimicrobial therapy for pulmonary pathogenic colonisation and infection by Pseudomonas aeruginosa in cystic fibrosis patients

Pseudomonas aeruginosa colonisation has a negative effect on pulmonary function in cystic fibrosis patients. The organism can only be eradicated in the early stage of colonisation, while reduction of bacterial density is desirable during chronic colonisation or exacerbations. Monthly, or at least 3-monthly, microbiological culture is advisable for patients without previous evidence of P. aeruginosa colonisation. Cultures should be performed at least every 2-3 months in patients with well-established colonisation, and always during exacerbations or hospitalisations. Treatment of patients following the first isolation of P. aeruginosa, but with no clinical signs of colonisation, should be with oral ciprofloxacin (15-20 mg/kg twice-daily for 3-4 weeks) plus inhaled tobramycin or colistin (intravenous treatment with or without inhaled treatment can be used as an alternative), while patients with acute infection should be treated for 14-21 days with high doses of two intravenous antimicrobial agents, with or without an inhaled treatment during or at the end of the intravenous treatment. Maintenance treatment after development of chronic P. aeruginosa infection/colonisation (pathogenic colonisation) in stable patients (aged>6 years) should be with inhaled tobramycin (300 mg twice-daily) in 28-day cycles (on-off) or, as an alternative, colistin (1-3 million units twice-daily). Colistin is also a possible choice for patients aged<6 years. Treatment can be completed with oral ciprofloxacin (3-4 weeks every 3-4 months) for patients with mild pulmonary symptoms, or intravenously (every 3-4 months) for those with severe symptoms or isolates with ciprofloxacin resistance. Moderate and serious exacerbations can be treated with intravenous ceftazidime (50-70 mg/kg three-times-daily) or cefepime (50 mg/kg three-times-daily) plus tobramycin (5-10 mg/kg every 24 h) or amikacin (20-30 mg/kg every 24 h) for 2-3 weeks. Oral ciprofloxacin is recommended for patients with mild pulmonary disease. If multiresistant P. aeruginosa is isolated, antimicrobial agents that retain activity are recommended and epidemiological control measures should be established.

Use of Pseudomonas biofilm susceptibilities to assign simulated antibiotic regimens for cystic fibrosis airway infection

OBJECTIVES

Increasing evidence indicates that Pseudomonas aeruginosa grows as a biofilm in the lungs of cystic fibrosis (CF) patients. In contrast, the bacterial inoculum used in conventional susceptibility testing is composed of planktonic cells. As a prelude to a clinical trial of biofilm susceptibility testing in CF, simulated antibiotic regimens based on either biofilm or conventional susceptibility testing of CF patient isolates were compared.

PATIENTS AND METHODS

Biofilm and conventional susceptibilities were determined for P. aeruginosa isolate sets from 40 CF patients. An algorithm was used to assign simulated regimens of two anti-pseudomonal antibiotics for each patient/susceptibility method dataset. For agents with equivalent activity, the algorithm included a drug selection hierarchy, the rationale for which was suppression of chronic infection. Substitution of an alternative hierarchy, based on treatment of acute exacerbation, was used to evaluate the robustness of the regimen assignments.

RESULTS

For both drug-ranking schemes, all 40 simulated regimens based on conventional susceptibilities included a beta-lactam antibiotic. In contrast, based on biofilm testing, only 43% of chronic regimens and 65% of acute regimens included a beta-lactam. Moreover, the conventional and biofilm regimens assigned to individual patients were discordant, with only 20% and 40% of chronic and acute regimens, respectively, consisting of drugs in the same two mechanistic classes by both methods.

CONCLUSIONS

Biofilm susceptibility testing of CF P. aeruginosa isolate sets leads to different antibiotic assignments than conventional testing, with no single two-drug regimen predicted to provide optimal anti-biofilm activity against the majority of isolate sets.

Breakpoints for predicting Pseudomonas aeruginosa susceptibility to inhaled tobramycin in cystic fibrosis patients: use of high-range Etest strips

Inhaled administration of tobramycin assures high concentrations in cystic fibrotic lungs, improving the therapeutic ratio over that of parenteral tobramycin levels, particularly against Pseudomonas aeruginosa. Conventional Clinical and Laboratory Standards Institute (CLSI; formerly National Committee for Clinical Laboratory Standards) breakpoints only consider parenteral levels and do not take into account these high antimicrobial concentrations. The Spanish Antibiogram Committee (The MENSURA Group) has tentatively defined specific breakpoint values for inhaled tobramycin when testing P. aeruginosa isolates from cystic fibrosis (CF) patients (susceptible, < or =64 microg/ml; resistant, > or =128 microg/ml). The antimicrobial susceptibilities of 206 prospectively collected CF P. aeruginosa isolates were determined by the reference agar dilution method. For tobramycin, the performance of high range tobramycin Etest strips (AB Biodisk, Solna, Sweden) and conventional tobramycin disks were assessed with the same collection. Applying MENSURA proposed breakpoints, 95.1% of the strains were categorized as susceptible to tobramycin, either using agar dilution or Etest high-range strips (99% categorical agreement between both methods). With CLSI breakpoints, susceptibility rates decreased to 79.1 and 81.1% for agar dilution and Etest strips, respectively (83.5% categorical agreement). Minor, major, and very major errors for Etest strips (CLSI criteria) were 13.6, 1.2, and 14.8%, respectively. Upon applying the new proposed criteria for inhaled tobramycin, only one major and one very major error were observed with Etest strips. Whenever inhaled tobramycin is considered for therapy, we suggest that P. aeruginosa strains from CF patients categorized as intermediate or resistant to tobramycin according to the CLSI criteria should be retested with high-range Etest strips and recategorized using MENSURA interpretive criteria. CLSI breakpoints should still be followed when intravenous tobramycin is used in CF patients, particularly during the course of exacerbations.

Prospective evaluation of emerging bacteria in cystic fibrosis

BACKGROUND

Bacteria contribute considerably to the progression of lung disease in cystic fibrosis. In this prospective, multi-centre study, we aimed to evaluate the occurrence of emerging bacteria and the physicians' assessments of the clinical importance of these findings.

METHODS

Twelve CF centres (total number of patients: 1419) reported the detection of any Stenotrophomonas maltophilia, Burkholderia cepacia complex, MRSA, Alcaligenes xylosoxidans, Klebsiella species and Mycobacteria during an observation period of 6 months.

RESULTS

213 specimens with emerging bacteria were reported from 145 different patients. The proportion of patients with emerging bacteria differed between centres (3-38%, mean: 12.6%) and increased with age. The predominant bacterium was S. maltophilia (n=106 positive specimens), followed by Klebsiellae (n=36), B. cepacia complex (n=31), A. xylosoxidans (n=16), Mycobacteria (n=11), MRSA (n=11), and others (n=2). In many instances the same microorganisms had already been reported earlier, indicating intermittent or chronic colonisation. The clinical status was reported to be stable in 70% of patients, and antibiotic treatment was anticipated for 46% of positive specimens. Comparison of clinical data to age matched controls did not reveal any significant differences with regard to pulmonary and nutritional status prior to detection of emerging bacteria.

CONCLUSION

These data suggest a high variability between centres regarding the prevalence of emerging bacteria. Most patients maintained a stable clinical condition during the 6-month study period despite being colonised with emerging bacteria.

Antimicrobial use and Pseudomonas aeruginosa susceptibility profile in a cystic fibrosis centre

The susceptibility patterns of 1315 mucoid and non-mucoid Pseudomonas aeruginosa strains from 224 patients were determined along with antibiotic utilisation in a Cystic Fibrosis Centre from 1993 to 1997. Ceftazidime was the most active agent (86.0% sensitive isolates), followed by piperacillin-tazobactam (81.7%), aztreonam (80.3%), imipenem (80%), piperacillin (76.8%), tobramycin (76.5%), ciprofloxacin (73.7%), ticarcillin (72.4%), ticarcillin-clavulanic acid (70.2%), amikacin (69.5%), netilmicin (56.5%), meropenem (79%) and imipenem (75.5%). The most frequently used compounds were nebulized colistin (mean+/-S.D., 109+/-45 defined daily doses per 1000 patients per day), followed by ciprofloxacin (98+/-8), tobramycin (55+/-9), ceftazidime (31+/-8) and amikacin (55+/-9). The mean antibiotic consumption by our CF patients was 413+/-47 defined daily doses per 1000 patients per day. Trend testing showed a significant decline of susceptibility to aminoglycosides, imipenem and ciprofloxacin, while the susceptibility of P. aeruginosa to piperacillin and ceftazidime was stable.

An epidemiological study of the susceptibility and frequency of multiple-drug-resistant strains of Pseudomonas aeruginosa isolated at medical institutes nationwide in Japan

The susceptibility of 3233 strains of Pseudomonas aeruginosa, isolated primarily in 2001, as agents of infection at 37 medical institutes with various specialties in seven regions of Japan (ranging from Hokkaido to Kyushu/Okinawa), to 18 antipseudomonal agents known to be active against P. aeruginosa was evaluated, in accordance with the National Committee for Clinical Laboratory Standards (NCCLS) guidelines. Of the 18 antipseudomonal agents, including some combinations of beta-lactamase inhibitors and antibacterial agents, ciprofloxacin had the lowest minimum inhibitory concentration (MIC)(50) (0.25 microg/ml) against P. aeruginosa, followed by meropenem, with an MIC(50) of 0.5 microg/ml. The MIC(50) of 7 of the examined antibacterial agents (ceftazidime, cefozopran, imipenem, biapenem, gentamicin, tobramycin, and levofloxacin) was between 1 and 2 microg/ml. Among the antipseudomonal agents tested, tobramycin showed the lowest MIC(90) (2 microg/ml), which was not significantly different from its MIC(50) (1 microg/ml). The MIC(90) of the other antibacterial agents examined ranged from 8 to 64 microg/ml and more. The susceptibility of the 3233 strains to the 12 antibacterial agents covered by the NCCLS guidelines was determined according to the standard method of the NCCLS guidelines. The frequency of strains resistant to meropenem, gentamicin, or tobramycin was relatively low (7.5%-8.3%). The frequency of strains showing intermediate to severe resistance to tobramycin was particularly low (8.0%). The frequency of strains resistant to aztreonam, imipenem, or levofloxacin was 16.7%-19.0%, about twice as high as the frequency of strains resistant to tobramycin. The susceptibility pattern of the 3233 strains (isolated from seven regions of Japan) to five antibacterial agents (ceftazidime, piperacillin, imipenem, gentamicin, and ciprofloxacin) was evaluated in relation to the regions from which they were isolated. The MIC(50) values of these antibacterial agents did not differ significantly among the regions. However, the MIC(90) values of ceftazidime and gentamicin were higher for strains isolated from the Kansai region than for strains isolated from other regions. The MIC(90) of ciprofloxacin was higher for strains isolated from the Tohoku, Kansai, and Kyushu/Okinawa regions than for strains isolated from other regions. Of the 3233 strains, 89 were classified as multiple-drug-resistant (imipenem, gentamicin, and ciprofloxacin) strains. Of these 89 strains, 42 were isolated from urine, 17 from sputum or pharyngeal mucus, 13 from pus, 8 from blood, 1 from cerebrospinal fluid, and 8 from other specimens. The frequency of multiple-drug-resistant strains was higher among strains isolated from the Tohoku and Kansai regions than in strains isolated from other regions.

Detection and susceptibility testing of hypermutable Pseudomonas aeruginosa strains with the Etest and disk diffusion

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 PAODeltamutS 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.