[Impact of mass spectrometry by MALDI-TOF MS for the rapid identification of aerobic and anaerobic bacteria of clinical importance]. / Impacto de la espectrometría de masas por MALDI-TOF MS en la identificación rápida de bacterias aeróbicas y anaeróbicas de importancia clínica.

BACKGROUND: MALDI-TOF MS (Matrix Assisted Laser Desorption Ionization -Time of Flight Mass Spectrometry) technology, recently introduced in the microbiology laboratory has proven to be a precise and rapid method for bacterial identification. OBJECTIVE: To evaluate the performance, costs associated and turnaround time of MALDI-TOF in a routine laboratory. MATERIAL AND METHOD: Five hundred and sixty one clinical isolates (281 aerobes and 280 anaerobes) previously identified by conventional methods were evaluated. Discordances were resolved by means of 16S rRNA sequencing. RESULTS: MALDI-TOF identified 95, 7% of the aerobes isolates and 86, 4% of the anaerobes. The groups with better performance were the enterobacteriacea and Bacteroides spp with 95% and 100% identification at the species level. The error rate of MALDI-TOF and conventional methods compared to sequencing was 0, 39% and 9, 4% respectively. The costs associated were 8 times lower with a turnaround time of 6 hours. CONCLUSION: MALDI-TOF proved to be simple, precise and less expensive technology compared to the traditional methods.

Impacto de la espectrometría de masas por MALDI-TOF MS en la identificación rápida de bacterias aeróbicas y anaeróbicas de importancia clínica / Impact of mass spectrometry by MALDI-TOF MS for the rapid identification of aerobic and anaerobic bacteria of clinical importance

Background: MALDI-TOF MS (Matrix Assisted Laser Desorption Ionization -Time of Flight Mass Spectrometry) technology, recently introduced in the microbiology laboratory has proven to be a precise and rapid method for bacterial identification. Objective: To evaluate the performance, costs associated and turnaround time of MALDI-TOF in a routine laboratory. Material and Method: Five hundred and sixty one clinical isolates (281 aerobes and 280 anaerobes) previously identified by conventional methods were evaluated. Discordances were resolved by means of 16S rRNA sequencing. Results: MALDI-TOF identified 95, 7% of the aerobes isolates and 86, 4% of the anaerobes. The groups with better performance were the enterobacteriacea and Bacteroides spp with 95% and 100% identification at the species level. The error rate of MALDI-TOF and conventional methods compared to sequencing was 0, 39% and 9, 4% respectively. The costs associated were 8 times lower with a turnaround time of 6 hours. Conclusion: MALDI-TOF proved to be simple, precise and less expensive technology compared to the traditional methods.

Introducción: La tecnología MALDI-TOF MS (Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry) incorporada recientemente en el laboratorio de microbiología ha demostrando ser un método rápido y preciso para la identificación bacteriana. Objetivo: Evaluar el desempeño de MALDI-TOF para la identificación de aislados clínicos, comparar los costos asociados y el tiempo en la entrega de resultados en un laboratorio de rutina. Material y Método: Se evaluaron un total de 561 aislados de pacientes (281 aeróbicos y 280 anaeróbicos estrictos) identificados previamente por métodos convencionales, los que fueron identificados por MALDI-TOF. Las discordancias fueron resueltas mediante secuenciación del 16S ARNr. Resultados: MALDI-TOF identificó adecuadamente a 95,7% de los aislados aeróbi-cos y 86,4% de los anaeróbicos estrictos, observándose el mayor porcentajes de identificación a nivel de especie en los grupos de enterobacterias y Bacteroides spp (95 y 100% respectivamente). La tasa de error de MALDI-TOF y métodos convencionales vs secuenciación fue de 0,39 y 9,4%, respectivamente. El costo asociado por identificación fue ocho veces menor que el de los métodos tradicionales con una demora promedio de seis horas en la entrega de resultados. Conclusión: MALDI-TOF mostró ser una tecnología simple, precisa y de menor costo que los métodos tradicionales.

[Surveillance of carbapenem-resistant enterobacteria in stool cultures in a university hospital in Santiago, Chile]. / Vigilancia de enterobacterias productoras de carbapenemasas en cultivos rectales en un hospital universitario de Santiago, Chile.

BACKGROUND: Clinical cultures detect only one-third of colonized patients with carbapenem-resistant Enterobacteriaceae. Early identification and contact precautions implementation would help to interrupt transmission. In our hospital no carbapenemase-producing enterobacteria infections have been described. AIM: To perform stool surveillance cultures in patients hospitalized in critical care unit with the purpose to detect carbapenemase-producing Enterobacteriacea. MATERIAL AND METHODS: Rectal swabs were obtained of patients after five or more days of hospital stay, on a monthly basis from July to December 2011. Phenotypic assays (modified test Hodge and phenylboronic acid test) and polymerase chain reaction (PCR) searching for six carbapenemases of group A and B of Ambler's classification were performed. RESULTS: During this period, 241 surveillance rectal cultures were performed. Thirty eight enterobacteria isolated from 30 patients presented a decreased susceptibility to carbapenems by agar dilution method. All PCR were negative. CONCLUSION: We found that despite the significant number of resistant isolates, patients hospitalized in our institution are not colonized with carbapenemase-producing Enterobacteriaceae. We highlight the importance of screening before having the problem in place.

Porin alterations present in non-carbapenemase-producing Enterobacteriaceae with high and intermediate levels of carbapenem resistance in Chile.

The main goal of this work was to identify the mechanisms responsible for carbapenem resistance in 61 Chilean clinical isolates of Enterobacteriaceae (Enterobacter spp., Serratia marcescens, Morganella morganii, Escherichia coli and Klebsiella pneumoniae) with reduced susceptibility to at least one carbapenem (ertapenem, imipenem or meropenem). All of the isolates were analysed for the presence of carbapenemases, extended spectrum ß-lactamases (ESBLs), AmpC enzymes and outer-membrane proteins. None of the isolates exhibited carbapenemase activity nor did they have any of the carbapenemase genes that were screened for. Most of the 61 strains produced at least one ESBL and/or one AmpC enzyme and either lost their porins or had altered porins according to sequence analysis. The distribution of ESBLs and AmpC enzymes was different among the species studied. Resistance in K. pneumoniae and E. coli isolates was associated with ESBLs; in M. morganii isolates, resistance was attributed to overexpression of an AmpC enzyme; and in Enterobacter spp. isolates, resistance was associated with both types of enzymes. In K. pneumoniae isolates, porin integrity was more a determinant of carbapenem resistance than the presence of ESBLs, whereas in isolates of Enterobacter spp., M. morganii and S. marcescens, the presence of an overexpressed AmpC enzyme was associated with higher imipenem and meropenem MIC values. Therefore, carbapenem resistance in Chilean isolates is not due to true carbapenemases but rather to a combination of porin loss/alteration and ß-lactamase activity. The fact that carbapenemases were not detected in this study is unique, given that many countries in the region have already reported the presence of these enzymes.