Phoenix System Research Articles

Consequences of switching from a fixed 2 : 1 ratio of amoxicillin/clavulanate (CLSI) to a fixed concentration of clavulanate (EUCAST) for susceptibility testing of Escherichia coli

The CLSI recommends a fixed 2 : 1 ratio of co-amoxiclav for broth microdilution susceptibility testing of Enterobacteriaceae, while EUCAST recommends a fixed 2 mg/L clavulanate concentration. The aims of this study were: (i) to determine the influence of a switch from CLSI to EUCAST methodology on Escherichia coli susceptibility rates; (ii) to compare susceptibility results obtained using EUCAST-compliant microdilution with those from disc diffusion and the Etest; and (iii) to evaluate the clinical outcome of patients with E. coli sepsis treated with co-amoxiclav in relation to the susceptibility results obtained using either method. Resistance rates were determined in three laboratories that switched from CLSI to EUCAST cards with the Phoenix system (Becton Dickinson) as well as in 17 laboratories that continued to use CLSI cards with the VITEK 2 system (bioMérieux). In one laboratory, isolates were simultaneously tested by both the Phoenix system and either disc diffusion (n = 471) or the Etest (n = 113). Medical and laboratory records were reviewed for E. coli sepsis patients treated with co-amoxiclav monotherapy. Only laboratories that switched methodology showed an increase in resistance rates - from 19% in 2010 to 31% in 2011 (P < 0.0001). All isolates that tested susceptible by microdilution were also susceptible by disc diffusion or the Etest, but of 326 isolates that tested resistant by microdilution, 43% and 59% tested susceptible by disc diffusion and the Etest, respectively. Among the 89 patients included there was a better correlation between clinical response and measured MICs using the Phoenix system than the Etest. EUCAST methodology resulted in higher co-amoxiclav E. coli resistance rates than CLSI methodology, but correlated better with clinical outcome. EUCAST-compliant microdilution and disc diffusion provided discrepant results.

Evaluation of Vancomycin Susceptibility Testing for Methicillin-Resistant Staphylococcus aureus: Comparison of Etest and Three Automated Testing Methods

We evaluated the ability of four commercial MIC testing systems (MicroScan, Vitek 2, Phoenix, and Etest) to detect vancomycin MIC values of ≤1 to ≥2 in 200 methicillin-resistant Staphylococcus aureus (MRSA) strains compared to the Clinical and Laboratory Standards Institute broth microdilution (BMD) reference methods. Compared to the BMD method, absolute agreement (0 ± dilution) was highest for the Phoenix system (66.2%) and the MicroScan turbidity method (61.8%), followed by the Vitek 2 system (54.3%). The Etest produced MIC values 1 to 2 dilutions higher than those produced by the BMD method (36.7% agreement). Of interest, the MicroScan system (prompt method) was more likely to overcall an MIC value of 1 mg/liter (74.1%), whereas the Phoenix (76%) and Vitek 2 (20%) systems had a tendency to undercall an MIC of 2 mg/liter. The ability to correctly identify vancomycin MIC values of 1 and 2 has clinical implications and requires further evaluation.

Bacteremia due to Brevundimonas vesicularis

In the original article on Brevundimonas vesicularis bacteremia, Zhang et al described the clinical characteristics and microbiological features of 22 patients with primary B. vesicularis bacteremia who were being treated in a medical center in southern Taiwan during 2006e2009. In this study, microbiological identification was performed with an API 20 NE system (bioMerieux, Marcy L’etoile, France) or Phoenix100 automated system (Becton, Dickinson, and Company, Sparks, MD, USA). However, there are some differences between commercial automated identification methods and 16s rRNA gene sequencing, as shown in another case series study conducted in Taiwan. Of the four strains identified as B. vesicularis by the Phoenix system, three were finally confirmed as Brevundimonas nasdae and one as Brevundimonas diminuta by the 16s rRNA gene sequencing. Again, four isolates were identified as B. diminuta or B. vesicularis by the VITEK 2 system (bioMerieux), which were finally confirmed as B. nasdae by 16s rRNA gene sequencing. Therefore, in addition to commercial identification methods, further identification by amolecularmethodmight

Comparison of Phoenix Automated System, API ID 32 Strep System and LightCycler Enterococcus MGRADE System in the Identification of Clinical Enterococcus Isolates

Enterococci which are part of the commensal flora of the human gastrointestinal and genitourinary tracts, are increasing in importance as the cause of hospital-acquired infections. Identification of Enterococcus spp. at the species level is of great importance, for appropriate treatment of patients, infection control and to supply epidemiological data. Conventional methods for the identification of enterococcus isolates at species level is difficult and time consuming. Correct identification of enterococcus isolates in clinical microbiology laboratory by conventional methods is replaced by semi-automated or automated identification and molecular methods. The aim of this study was to evaluate the performance of Phoenix automated system (BD Diagnostic Systems, USA), API Rapid ID 32 Strep System (bioMerieux, France) and Enterococcus MGRADE LightCycler kit (Roche Molecular Biochemicals, Germany) used in real-time polymerase chain reaction (Rt-PCR), for the species level identification of enterococcus strains isolated from clinical specimens. A total of 90 vancomycin susceptible enterococci isolated from different patients were identified by all of the three commercial systems, together with conventional methods. Of the strains, 59 were identified as E.faecalis, 28 were E.faecium, and one of each as E.raffinosus, E.hirae and E.casseliflavus with conventional methods. One E.faecalis strain identified by the conventional system was identified as E.faecium by Phoenix system and one E.faecium strain as E.durans. One E.raffinosus strain identifed by the conventional method was identified as E.avium by API. Conventionally identified four E.faecalis strains were determined to be E.faecium by Rt-PCR and one E.faecium, one E.raffinosus and one E.casseliflavus as E.faecalis. Accordingly, the consistency of Phoenix, API Rapid ID 32 Strep and LightCycler Enterococcus MGRADE systems with the conventional methods were detected as 97.8% (88/90), 98.9% (89/90), and 92.2% (83/90), respectively. In conclusion, all of those three commercial assays are appropriate methods to be used for the identification of enterococci at the species level in the routine clinical microbiology laboratories, due to their high compliance with the conventional method, and their ability to yield the results at the same day.

Species Identification of Bacteria and Fungi from Solid and Liquid Culture Media by MALDI-TOF Mass Spectrometry

Within the past years MALDI-TOF mass spectrometry has become a powerful tool for the species identification of cultured bacteria and fungi. In the present study, the implementation of MALDI-TOF mass spectrometry in a commercial high throughput laboratory is described. The impact of different growth conditions on the identification results was evaluated. Although slight differences in MALDI-TOF spectra of E. coli and S. aureus strains cultured on blood agar for various periods (5, 18, 24 and 48 hours) were noticed, reliable species identification was obtained for all periods. The same was true when E. coli and S. aureus strains were cultured for 18 hours on various solid media. Reliable identification was also achieved when fungi were cultured on solid and in liquid media (Sabouraud bouillon). Moreover, growth of fungi in bouillon resulted in accelerated identification. MALDI-TOF mass spectrometry also allowed reliable identification of microorganisms from positive blood culture samples. In total, 2,900 specimens (234 different species) predominantly derived from clinical samples were examined. Microorganisms were cultured on solid media, in blood culture bottles and in liquid Sabouraud bouillon. 98.6% (n=2,860) of the MALDI-TOF identification results matched those of conventional methods (e.g. Gram staining, carbohydrate degradation ability, Phoenix system) and 16S rDNA PCR product sequencing. Mismatches were mainly based on missing reference spectra in the database of the analysis system. The study was performed in 2009. Due to continuous improvement of the database, even higher accuracy would be achieved when performing the study nowadays. In summary, the use of MALDI-TOF mass spectrometry in a clinical high throughput environment leads to reliable results, even when various culture conditions are used, for instance bouillons for culture of fungi. MALDI-TOF mass spectrometry is a fast and robust identification system, which is on its way to become a new standard for the identification of microorganisms in high throughput laboratories.

Evaluation of microorganisms isolated from blood cultures and their susceptibility to antibiotics in two year period.

Bloodstream infections (BSIs) are a major cause of healthcare-associated morbidity and mortality. Analyses of the frequency of microorganisms isolated from blood cultures and antibiotic susceptibility can provide clinicians with relevant information for the empirical treatment of patients. The purpose of the study was to investigate to frequency of microorganisms isolated from blood cultures and their sensitivity to antimicrobial agents between January 2009 and December 2010 at the Training Hospital of Gulhane Military Medical Faculty. Blood cultures were processed by automatized BACTEC/9050 (Becton Dickinson, Maryland, USA). The observed growth of microorganisms in culture media was identified by conventional methods and PhoenixTM 100 automatized systems (BD Phoenix System, Beckton Dickinson, USA).Antimicrobial susceptibility tests were performed by Kirby-Bauer disc diffusion method and automatized systems (BD Phoenix System, Beckton Dickinson, USA) in accordance with the recommendations of Clinical and Laboratory Standarts Institute (CLSI). In the study period among the 6823 blood culture samples, 957 (14%) yielded positive results. Results of 600 (8.7%) blood culture samples evaluated as contamination. Of the 957 isolated microorganisms, 61.0% were Gram negative, 31.1% were Gram positive and 7.8% were yeast. E.coli was the most frequently isolated species (15.9%), followed by Klebsiella spp (15.4%) and Coagulase Negative Staphylococcus (CNS) (13.2%). Twenty eight percent% of S. aureus and 89% of CNS isolates were resistant to methicillin. Only one isolate (1.73%) was resistant to glycopeptides among Enterococcus spp. ESBL (Extended-spectrum beta lactamase) was detected in 36.8% of E.coli and 51.3% of Klebsiella spp. isolates.

Assessment of the Phoenix™ automated system and EUCAST breakpoints for antimicrobial susceptibility testing against isolates expressing clinically relevant resistance mechanisms

EUCAST breakpoint criteria are being adopted by automatic antimicrobial susceptibility testing systems. The accuracy of the Phoenix Automated System in combination with 2012 EUCAST breakpoints against recent clinical isolates was evaluated. A total of 697 isolates (349 Enterobacteriaceae, 113 Pseudomonas spp., 25 Acinetobacter baumannii, 11 Stenotrophomonas maltophilia, 95 Staphylococcus aureus, 6 coagulase negative staphylococci, 77 enterococci and 21 Streptococcus pneumoniae) with defined resistance phenotypes and well-characterized resistance mechanisms recovered in Spain (n = 343) and Italy (n = 354) were tested. Comparator antimicrobial susceptibility testing data were obtained following CLSI guidelines. Experimental agreement (EA), defined as MIC agreement ±1 log2 dilution, category agreement (CA) and relative discrepancies (minor (mD), major (MD) and very major discrepancies (VMD)) were determined. The overall EA and CA for all organism-antimicrobial agent combinations (n = 6.294) were 97.3% and 95.2%, respectively. mD, MD and VMD were 4.7%, 1.3% and 2.7%, all of them in agreement with the ISO (ISO20776–2:2007) acceptance criteria for assessment of susceptibility testing devices. VMD were mainly observed in amoxicillin-clavulanate and cefuroxime in Enterobacteriaceae and gentamicin in Pseudomonas aeruginosa, whereas MD were mainly observed in amoxicillin-clavulante in Enterobacteriaceae. mD were mainly observed in Enterobacteriaceae but distributed in different antimicrobials. For S. aureus and enterococci relative discrepancies were low. The Phoenix system showed accuracy assessment in accordance with the ISO standards when using EUCAST breakpoints. Inclusion of EUCAST criteria in automatic antimicrobial susceptibility testing systems will facilitate the implementation of EUCAST breakpoints in clinical microbiology laboratories.

Strategy for Rapid Identification and Antibiotic Susceptibility Testing of Gram-Negative Bacteria Directly Recovered from Positive Blood Cultures Using the Bruker MALDI Biotyper and the BD Phoenix System

Decreasing the time to species identification and antibiotic susceptibility determination of strains recovered from patients with bacteremia significantly decreases morbidity and mortality. Herein, we validated a method to identify Gram-negative bacteria directly from positive blood culture medium using the Bruker MALDI Biotyper and to rapidly perform susceptibility testing using the BD Phoenix.

Direct inoculation method using BacT/ALERT 3D and BD Phoenix System allows rapid and accurate identification and susceptibility testing for both Gram-positive cocci and Gram-negative rods in aerobic blood cultures

This study describes a direct inoculation method using the automated BacT/ALERT 3D and the BD Phoenix System in combination for identification and susceptibility testing of isolates from positive blood cultures. Organism identification and susceptibility results were compared with the conventional method for 211 positive aerobic blood cultures. Of 110 Gram-positive cocci (GPCs), 98 (89.1%) isolates were correctly identified to the species level. Of 101 Gram-negative rods (GNRs), 98 (97.0%) isolates were correctly identified to the species level. The overall categorical agreement in antimicrobial susceptibility testing among the 110 GPCs was 92.7%, with 0.04% very major and 0.7% major error rates. The overall categorical agreement among 78 isolates of enterobacteria and 23 isolates of nonfermenters in GNRs was 99.5% and 91.1%, respectively, with no major errors identified. We conclude that, compared with previously reported direct inoculation methods, our method is superior in identification and susceptibility testing of GPCs.

Comparison of an automated system with four phenotypic methods for the detection of methicillin-resistant Staphylococcus aureus

Correct and rapid detection of methicillin resistance in Staphylococcus aureus is very important for treatment of infected patients. Detection of the mecA gene or PBP2a by polymerase chain reaction (PCR) is considered the gold standard for determination of methicillin resistance in staphylococci. In most clinical laboratories, phenotypic methods are used for the detection of methicillin resistance in S. aureus because PCR is not suitable for routine usage. In this study, we aimed to compare different phenotypic methods: disk diffusion, agar screening, latex agglutination and an automated system employed to establish the presence of methicillin-resistant S. aureus (MRSA). Presence of the mecA gene via PCR was used as the marker for MRSA positivity. Afterward, 214 samples were analyzed for methicillin resistance via oxacillin or cefoxitin disk diffusions, oxacillin agar screening, MRSA latex agglutination and the automated BD Phoenix system. Sensitivity, specificity, negative and positive predictive values of these phenotypic methods were evaluated. In the detection of MRSA, the cefoxitin disk-diffusion method was found to be more useful than oxacillin disk diffusion. The automated MRSA strain-detection system was found to be more successful than the other phenotypic methods. These results showed that the automated system could be used safely for routine MRSA detection. Key words: Phoenix, cefoxitin disk diffusion, mecA, oxacillin, methicillin-resistantStaphylococcus aureus, latex agglutination.

Infection Agents Detected with Wound Culture in Patients with Diabetic Foot who will Undergo Hyperbaric Oxygen Treatment

AIM: We aimed to obtain the knowledge of appropriate antibiotic therapy and to make a contribution to improving treatment efficacy by conducting a microbiological study of diabetic foot ulcers. METHOD: 30 patients (18 male and 12 female) with diabetic foot ulcer applying to our center for hyperbaric oxygen (HBO) treatment in 2010 were enrolled in this study. The wounds were graded according to Meggitt-Wagner classification system. Wound cultures were obtained before starting antibiotic therapy and HBO treatment. Phoenix system (Becton Dickinson, USA) and Kirby-Bauer disk diffusion antibiotic sensitivity testing were used in order to detect the antimicrobial susceptibility of the infection agents. The number of HBO sessions, glycemic control and treatment results were assessed. RESULTS: Mean age of the patients was 61.3 years (range: 35-83). 24 patients had a good glycemic control and 6 patients had not. The patients were given 5 to 55 HBO sessions (mean: 20). Of the 30 patients 19 (63.33%) recovered from the infection but 11 (36.67%) have not responded to the treatment. 14 different infectious agents were detected in diabetic foot ulcers we examined. Gram-positive agents were isolated in 12 (40%) out of 30 wound cultures and gram-negative agents were isolated in 18 (60%) wound culture. Pseudomonas aeruginosa was predominantly isolated and the other agents isolated were enterococcus faecalis, klebsiella pneumoniae, staphylococcus aureus and escherichia coli. CONCLUSION: The outcomes can not represent the general population rates due to the restriction factors. They give only an idea about the probability of infectious agent spectrum in diabetic foot ulcers and their antibiotic susceptibility. We want to attract attention to the fact that although pseudomonas aeruginosa infections are mostly encountered in hospital, they can also be acquired from the community and it will be useful to develop appropriate antibiotic policies and treatment protocols.

Threatening Problem of Stenotrophomonas maltophilia Producing Extended-Spectrum Beta-Lactamases: Prevalence and Automated Antibiotic Susceptibility Pattern

Background: Stenotrophomonas maltophilia (S. maltophilia) is one of the most common emerging multi-drug resistant organisms. It is associated with difficult detection, treatment, and increased mortality particularly among immune compromised and debilitated individuals. Objectives: To determine the prevalence and antibiotic susceptibility pattern of S. maltophilia as emerging problem from different clinical isolates. Methods: A cross sectional study was conducted on 14000 cases. The isolates of Gram negative bacilli were identified based on conventional microbiological procedures. Extended spectrum beta lactamases (ESBLs) producing S. maltophilia identification and antibiotic susceptibility was further confirmed using automated BD Phoenix system where the panel of Gram negative antibiotics was tested. Results: Out of 14000 reviewed cases, 2100 were proved to be culture positive. Among Gram negative isolates, 1.5% was proved to be S. maltophilia. One hundred fourteen of Gram negative isolates were proved to be ESBL producers. More than half of ESBL isolates were E-coli. S. maltophilia represents (8.77%) of total Gram negative ESBL producers, while ESBL producing S. maltophilia represent (83.33%) among the total number of S. maltophilia isolates. Half number of S. maltophilia isolates was obtained from blood. About 83 % of S. maltophilia isolates showed resistance to all Gram negative Panels of antibiotics, while 100% of isolates were sensitive to Trimethoprimsulfamethoxazole (TMP – SXT). 16.67% of isolates showed sensitivity to ciprofloxacin (CIP), ceftazidime (CAZ). Conclusion: ESBL producing S. maltophilia is frequently resistant to a wide range of commonly used antimicrobials. Routine sensitivity reporting is required to detect these threatening, multidrug resistant organisms. Trimethoprim-sulfamethoxazole (TMP – SXT) is recommended as the agent of choice for the treatment of S. maltophilia infections. Alternatively, fluoroquinolones and ceftazidime (CAZ) may be used.

Antibiotic Susceptibility Testing of Grown Blood Cultures by Combining Culture and Real-Time Polymerase Chain Reaction Is Rapid and Effective

BackgroundEarly administration of appropriate antibiotic therapy in bacteraemia patients dramatically reduces mortality. A new method for RApid Molecular Antibiotic Susceptibility Testing (RAMAST) that can be applied directly to positive blood cultures was developed and evaluated.Methodology/Principal FindingsGrowth curves and antibiotic susceptibility of blood culture isolates (Staphylococcus aureus, enterococci and (facultative) aerobic Gram-negative rods) were determined by incubating diluted blood cultures with and without antibiotics, followed by a quantitative universal 16S PCR to detect the presence or absence of growth. Testing 114 positive blood cultures, RAMAST showed an agreement with microbroth dilution of 96.7% for Gram-negative rods, with a minor error (false-susceptibility with a intermediate resistant strain) rate of 1.9%, a major error (false resistance) rate of 0.8% and a very major error (false susceptibility) rate of 0.6%. Agreement for S.aureus was 97.9%, with a very major error rate of 2.1%. Enterococcus species showed 95.0% agreement, with a major error rate of 5.0%. These agreements are comparable with those of the Phoenix system. Starting from a positive blood culture, the test was completed within 9 hours.Conclusions/SignificanceThis new rapid method for antibiotic susceptibility testing can potentially provide accurate results for most relevant bacteria commonly isolated from positive blood cultures in less time than routine methods.

Comparative evaluation of the Vitek-2 Compact and Phoenix systems for rapid identification and antibiotic susceptibility testing directly from blood cultures of Gram-negative and Gram-positive isolates

We performed a comparative evaluation of the Vitek-2 Compact and Phoenix systems for direct identification and antimicrobial susceptibility testing (AST) from positive blood culture bottles in comparison to the standard methods. Overall, 139 monomicrobial blood cultures, comprising 91 Gram-negative and 48 Gram-positive isolates, were studied. Altogether, 100% and 92.3% of the Gram-negative isolates and 75% and 43.75% of the Gram-positive isolates showed concordant identification between the direct and the standard methods with Vitek and Phoenix, respectively. AST categorical agreements of 98.7% and 99% in Gram-negative and of 96.2% and 99.5% in Gram-positive isolates with Vitek and Phoenix, respectively, were observed. In conclusion, direct inoculation procedures for Gram-negative isolates showed an excellent performance with both automated systems, while for identification of Gram-positive isolates they proved to be less reliable, although Vitek provided acceptable results. This approach contributes to reducing the turnaround time to result of blood cultures, with a positive impact on patient care.

Comparative Evaluation of Bruker Biotyper and BD Phoenix Systems for Identification of Bacterial Pathogens Associated with Urinary Tract Infections

The Bruker Biotyper and BD Phoenix systems were evaluated for identification of 1,024 bacterial urinary tract isolates. The Biotyper and Phoenix systems correctly identified 99.9% and 99.5% to the genus level and 99.1% and 98.5% to the species level, respectively. Both systems provide reliable results, and the Biotyper system offers a rapid tool for urine bacterial isolate identification.

Evaluation of a commercial microarray as a confirmation test for the presence of extended-spectrum β-lactamases in isolates from the routine clinical setting

Since the diagnostic characteristics of the Check-KPC ESBL microarray as a confirmation test on isolates obtained in a routine clinical setting have not been determined, we evaluated the microarray in a random selection of 346 clinical isolates with a positive ESBL screen test (MIC >1 mg/L for cefotaxime or ceftazidime or an ESBL alarm from the Phoenix or Vitek-2 expert system) collected from 31 clinical microbiology laboratories in the Netherlands in 2009. Using sequencing as the reference method the sensitivity of the microarray was 97% (237/245), the specificity 98% (97/99), the positive predictive value 99% (237/239) and the negative predictive value 92% (97/105).

Evaluation of Three Automated Systems for Susceptibility Testing of Enterobacteria Containing qnrB, qnrS, and/or aac(6′)-Ib-cr

The accuracy of the MicroScan WalkAway, BD Phoenix, and Vitek-2 systems for susceptibility testing of quinolones and aminoglycosides against 68 enterobacteria containing qnrB, qnrS, and/or aac(6 ')-Ib-cr was evaluated using reference microdilution. Overall, one very major error (0.09%), 6 major errors (0.52%), and 45 minor errors (3.89%) were noted.

Evaluation of direct inoculation of the BD PHOENIX system from positive BACTEC blood cultures for both Gram-positive cocci and Gram-negative rods

BackgroundRapid identification (ID) and antibiotic susceptibility testing (AST) of the causative micro-organism of bloodstream infections result in earlier targeting of antibiotic therapy.In order to obtain results of ID and AST up to 24 hours earlier, we evaluated the accuracy of direct inoculation of the Phoenix system from positive blood cultures (BACTEC) by using Serum Separator Tubes to harvest bacteria from positive blood cultures. Results were compared to those of standard Phoenix procedure. Discrepancies between the two methods were resolved by using the API system, E-test or microbroth dilution.ResultsID with the direct method was correct for 95.2% of all tested Enterobacteriaceae (n = 42) and 71.4% of Pseudomonas aeruginosa strains (n = 7).AST with the direct method showed a categorical agreement for Gram-negative rods (GNR) of 99.0%, with 0.7% minor errors, 0.3% very major errors and no major errors. All antibiotics showed an agreement of >95%.The direct method for AST of Staphylococcus (n = 81) and Enterococcus (n = 3) species showed a categorical agreement of 95.4%, with a minor error rate of 1.1%, a major error rate of 3.1% and a very major error rate of 0.4%. All antibiotics showed an agreement of >90%, except for trimethoprim-sulfamethoxazole and erythromycin.ConclusionsInoculation of Phoenix panels directly from positive blood cultures can be used to report reliable results of AST of GNR a day earlier, as well as ID-results of Enterobacteriaceae. For Staphylococcus and Enterococcus species, results of AST can also be reported a day earlier for all antibiotics, except for erythromycin and trimethoprim-sulfamethoxazole.

Evaluation of GeneXpert® system for detection of methicillin-resistant Staphyloccocus aureus in clinical samples

Infections caused by methicillin-resistant Staphyloccocus aureus strains (MRSA) have reached epidemic proportions globally, being the major cause of nosocomial infections. Rapid identification of MRSA in nasal swabs or in clinical samples is considered a useful strategy for control and treatment of these infections. GeneXpert system (Cepheid Europe,Vira-Solelch, Maurence-Scopont-France) can detect by real-time PCR in approximately one hour methicillin-resistant S. aureus or coagulase-negative staphylococci (CoNS) in clinical samples, in comparison with 24 hours for the culture or 48 hours for the antimicrobial susceptibility testing. In this study GeneXpert system was compared with traditional tests for MRSA detection in nasal swabs, bloodcultures and surgical wound swabs. Materials and methods. Eighteen nasal swabs, 23 blood-cultures and 13 surgical wound swabs were tested. The samples were cultured on blood-agar and mannitol-salt agar. Identification of isolates was carried out with traditional tests (Gram staining, catalase, coagulase) and automatic Phoenix system. Methicillin-susceptibility was evaluated according to 2010 CLSI guidelines. GeneXpert system was performed according to manufacturers instructions, by using the specific kits and methicillin-resistance was detected by amplification of the genic sequences spa, SCC e mecA. Results. The results showed a 100% accordance between GeneXpert system and traditional tests for detection of methicillin-resistant staphylococci. In particular, among 18 nasal swabs, no MRSA was detected, while 1 bloodculture (4.3%) and 4 surgical wound swabs (30.7%) were positive for MRSA. Conclusions. GeneXpert system allows a rapid detection of MRSA in clinical samples and shows the same sensitivity and specificity as traditional tests. Therefore, it represents a further effective diagnostic method for prevention and treatment of nosocomial infections due to methicillin-resistant staphylococci.

A Biosensor Platform for Rapid Antimicrobial Susceptibility Testing Directly From Clinical Samples

A significant barrier to efficient antibiotic management of infection is that the standard diagnostic methodologies do not provide results at the point of care. The delays between sample collection and bacterial culture and antibiotic susceptibility reporting have led to empirical use of antibiotics, contributing to the emergence of drug resistant pathogens. As a key step toward the development of a point of care device for determining the antibiotic susceptibility of urinary tract pathogens, we report on a biosensor based antimicrobial susceptibility test. For assay development bacteria were cultured with or without antibiotics, and growth was quantitated by determining viable counts and electrochemical biosensor measurement of bacterial 16S rRNA. To determine antibiotic susceptibility directly from patient samples, urine was cultured on antibiotic plates for 2.5 hours and growth was determined by electrochemical measurement of bacterial 16S rRNA. For assay validation 252 urine samples were collected from patients at the Spinal Cord Injury Service at Veterans Affairs Palo Alto Health Care System. The biosensor based antimicrobial susceptibility test was completed for samples containing gram-negative organisms. Pathogen identification and antibiotic susceptibility results were compared between our assay and standard microbiological analysis. A direct biosensor quantitation of bacterial 16S rRNA can be used to monitor bacterial growth for a biosensor based antimicrobial susceptibility test. Clinical validation of a biosensor based antimicrobial susceptibility test with patient urine samples demonstrated that this test was 94% accurate in 368 pathogen-antibiotic tests compared to standard microbiological analysis. This biosensor based antimicrobial susceptibility test, in concert with our previously described pathogen identification assay, can provide culture and susceptibility information directly from a urine sample within 3.5 hours.