Nicole Marty

Performances of the Vitek MS Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry System for Rapid Identification of Bacteria in Routine Clinical Microbiology

ABSTRACT Rapid and cost-effective matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS)-based systems will replace conventional phenotypic methods for routine identification of bacteria. We report here the first evaluation of the new MALDI-TOF MS-based Vitek MS system in a large clinical microbiology laboratory. This system uses an original spectrum classifier algorithm and a specific database designed for the identification of clinically relevant species. We have tested 767 routine clinical isolates representative of 50 genera and 124 species. Vitek MS-based identifications were performed by means of a single deposit on a MALDI disposable target without any prior extraction step and compared with reference identifications obtained mainly with the VITEK2 phenotypic system; if the identifications were discordant, molecular techniques provided reference identifications. The Vitek MS system provided 96.2% correct identifications to the species level (86.7%), to the genus level (8.2%), or within a range of species belonging to different genera (1.3%). Conversely, 1.3% of isolates were misidentified and 2.5% were unidentified, partly because the species was not included in the database; a second deposit provided a successful identification for 0.8% of isolates unidentified with the first deposit. The Vitek MS system is a simple, convenient, and accurate method for routine bacterial identification with a single deposit, considering the high bacterial diversity studied and as evidenced by the low prevalence of species without correct identification. In addition to a second deposit in uncommon cases, expanding the spectral database is expected to further enhance performances.

Risk of emergence of Pseudomonas aeruginosa resistance to β-lactam antibiotics in intensive care units

Objective:The emergence of Pseudomonas aeruginosa resistance to antimicrobial drugs is frequent in intensive care units and may be correlated with the use of some specific drugs. The purpose of our study was to identify a relationship between the use of various β-lactam antibiotics and the emergence of resistance and to characterize the mechanism of resistance involved. Design:We conducted an open prospective study over a 3-yr period by including all patients in whom P. aeruginosa had been isolated from one or more specimens: bronchial aspiration, blood cultures, catheters, and urinary cultures. Setting:General intensive care unit. Patients:One hundred and thirty-two intensive care unit patients. Interventions:The antibiotics studied were amoxiclav, piperacillin-tazobactam, cefotaxime, ceftazidime, cefepim, and imipenem. The mechanisms of resistance studied were production of penicillinase or cephalosporinase, nonenzymatic mechanisms, and loss of porin OprD2. Analysis was performed using Cox proportional-hazard regression with time-dependant variables. Measurements and Main Results:Forty-two strains became resistant, 30 to one antibiotic, nine to two, and three to three, leading to the study of 57 resistant strains. Imipenem (hazard ratio 7.8; 95% confidence interval, 3.4–18.1), piperacillin-tazobactam (hazard ratio 3.9; 95% confidence interval, 1.3–11.9), and cefotaxim (hazard ratio 9.3; 95% confidence interval, 2.9–30.2) were strongly linked to the emergence of resistance. The use of imipenem (p < .0001) was associated with the loss of porin OprD2. Thirty-six strains from nine patients, assayed by pulsed-field gel electrophoresis, showed that for any one patient, all the strains were genetically related. Conclusions:Our results show that there is a high risk of the emergence of drug resistance during treatment with cefotaxime, imipenem, and piperacillin-tazobactam. This has to be taken into account in the therapeutic choice and in the patient’s surveillance.

Identification of Clinical Streptococcus pneumoniae Isolates among other Alpha and Nonhemolytic Streptococci by Use of the Vitek MS Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry System

ABSTRACT Discrimination between Streptococcus pneumoniae and its close relatives of the viridans group is a common difficulty in matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry-based identification. In the present study, the performances of the Vitek MS MALDI-TOF mass spectrometry system were assessed using 334 pneumococci, 166 other S. mitis group streptococci, 184 non-S. mitis group streptococci, and 19 related alpha- and nonhemolytic aerobic Gram-positive catalase-negative coccal isolates. Pneumococci had been identified by means of optochin susceptibility and bile solubility or serotyping, and other isolates mainly by use of RapidID32 Strep strips. In case of discordant or low-discrimination results, genotypic methods were used. The sensitivity of the Vitek MS for the identification of S. pneumoniae was 99.1%, since only three bile-insoluble isolates were misidentified as Streptococcus mitis/Streptococcus oralis. Conversely, two optochin-resistant pneumococci were correctly identified (specificity, 100%). Three Streptococcus pseudopneumoniae isolates were also correctly identified. Among nonpneumococcal isolates, 90.8% (n = 335) were correctly identified to the species or subspecies level and 2.4% (n = 9) at the group level. For the remaining 25 isolates, the Vitek MS proposed a bacterial species included in the list of possible species suggested by genotypic methods, except for 4 isolates which were not identified due to the absence of the species in the database. According to our study, the Vitek MS displays performance similar to that of the optochin susceptibility test for routine identification of pneumococcal isolates. Moreover, the Vitek MS is efficient for the identification of other viridans group streptococci and related isolates, provided that the species are included in the database.

Structural studies of the acidic exopolysaccharide produced by a mucoid strain of Burkholderia cepacia, isolated from cystic fibrosis.

The acidic exopolysaccharide produced by a mucoid strain of Burkholderia cepacia isolated from a cystic fibrosis patient, was purified by cetyltrimethylammonium bromide precipitation and/or anion-exchange chromatography. Based on the sugar composition and permethylation analyses, supported by GLC-MS and NMR spectroscopy analyses, the repeating-unit of the polysaccharide was established as -->3)-beta-D-Glcp-(1-->3)-[4,6-O-(1-carboxyethylidene)]-alpha-D-Gal p-(1-->.

Identification and clinical significance of Helcococcus kunzii in human samples

ABSTRACT From 2008 to 2013, 39 Helcococcus kunzii strains were collected from human clinical specimens (79% from foot ulcers), and 85% of the 39 patients were infected. Matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry and molecular methods accurately identified all isolates. This large study of clinical observations confirms the potential pathogenic role of H. kunzii.

Diagnostic bactériologique des infections chez les greffés

Resume Les bacteries sont les microorganismes les plus frequemment impliques dans les infections du patient transplante, le pronostic etant variable selon l’agent concerne et le contexte de survenue. Il existe deux cadres distincts qui exposent les malades a des risques relativement specifiques et entrainent des attitudes preventives differentes : la greffe de cellules souches hematopoietiques et les transplantations d’organes solides. Lors des greffes de cellules souches hematopoietiques, la neutropenie, la presence de voies veineuses centrales a demeure, et la survenue de maladie du greffon contre l’hote constituent les elements majeurs du risque d’infection bacterienne. L’evolution des regimes de conditionnement et des strategies de greffe vise a controler ce risque. Apres les transplantations d’organes solides, les infections bacteriennes surviennent principalement dans un contexte postoperatoire, favorisees par les dispositifs medicaux. L’amelioration des techniques chirurgicales joue un role decisif dans la maitrise de ces complications infectieuses. Quel que soit le type de greffe, les bacteries habituellement rencontrees sont des germes couramment isoles dans un environnement hospitalier. D’autres presentent un caractere opportuniste et leur pathogenicite depend etroitement de l’etat global d’immunodepression du patient, faisant du transplante un terrain particulierement fragile par rapport a ces bacteries. Dans tous les cas, la rapidite du diagnostic bacteriologique conditionne le pronostic du patient, dans la mesure ou l’antibiotherapie doit etre adaptee dans les meilleurs delais.