Rapid and sensitive detection of carbapenemase activity in Acinetobacter baumannii using superficially porous liquid chromatography-tandem mass spectrometry

One System for All: Is Mass Spectrometry a Future Alternative for Conventional Antibiotic Susceptibility Testing?

The two main pillars of clinical microbiological diagnostics are the identification of potentially pathogenic microorganisms from patient samples and the testing for antibiotic susceptibility (AST) to allow efficient treatment with active antimicrobial agents. While routine microbial species identification is increasingly performed with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), routine AST still largely relies on conventional and molecular techniques such as broth microdilution or disk and gradient diffusion tests, PCR and automated variants thereof. However, shortly after the introduction of MALDI-TOF MS based routine identification, first attempts to perform AST on the same instruments were reported. Today, a number of different approaches to perform AST with MALDI-TOF MS and other MS techniques have been proposed, some restricted to particular microbial taxa and resistance mechanisms while others being more generic. Further, while some of the methods are in a stage of proof of principles, others are already commercialized. In this review we discuss the different principal approaches of mass spectrometry based AST and evaluate the advantages and disadvantages compared to conventional and molecular techniques. At present, the possibility that MS will soon become a routine tool for AST seems unlikely – still, the same was true for routine microbial identification a mere 15 years ago.

Blue light irradiation triggers the antimicrobial potential of ZnO nanoparticles on drug-resistant Acinetobacter baumannii

Photodynamic inactivation (PDI) is a non-invasive and safe therapeutic method for microbial infections. Bacterial antibiotic resistance is caused by antibiotics abuse. Drug-resistant Acinetobacter spp. is a serious problem in hospitals around the world. These pathogens from nosocomial infections have high mortality rates in frailer people, and Acinetobacter spp. is commonly found in immunocompromised patients. Visible light is safer than ultraviolet light (UV) for PDI of nosocomial pathogens with mammalian cells. Zinc oxide nanoparticles (ZnO-NPs) were used in this study as an antimicrobial agent and a photosensitizer. ZnO is recognized as safe and has extensive usage in food additives, medical and cosmetic products. In this study, we used 0.125 mg/ml ZnO-NPs combined with 10.8 J/cm² blue light (BL) on Acinetobacter baumannii (A. baumannii) that could significantly reduce microbial survival. However, individual exposure to ZnO-NPs does not affect the viability of A. baumannii. BL irradiation could trigger the antimicrobial ability of ZnO nanoparticles on A. baumannii. The mechanism of photocatalytic ZnO-NPs treatment for sterilization occurs through bacterial membrane disruptions. Otherwise, the photocatalytic ZnO-NPs treatment showed high microbial eradication in nosocomial pathogens, including colistin-resistant and imipenem-resistant A. baumannii and Klebsiella pneumoniae. Based on our results, the photocatalytic ZnO-NPs treatment could support hygiene control and clinical therapies without antibiotics to nosocomial bacterial infections.

Emergence of carbapenem-resistant Acinetobacter baumannii ST787 in clinical isolates from blood in a tertiary teaching hospital in Northern Taiwan

BACKGROUND/PURPOSE

The purpose of this study is to investigate the predominant clones of carbapenem-resistant Acinetobacter baumannii (CRAB) in our hospital in Taiwan by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) technique.

METHODS

We collected 108 non-duplicate A. baumannii clinical blood isolates from January 2012 to December 2013 in MacKay Memorial Hospital. PFGE and MLST were used for typing the A. baumannii isolates and for investigation of the predominant clones. Bacteria isolates were screened by polymerase chain reaction for the presence of the carbapenemase-encoding genes.

RESULTS

All 108 isolates were classified as 33 pulsotypes by PFGE. The predominant clones were pulsotype 10 (12.04%) in 2012 and pulsotype 8 (16.67%) in 2013, respectively. The 31 predominant pulsotype isolates were typed by MLST, and ST787 (54.84%) and ST455 (45.16%) were identified. All isolates carried bla_OXA-51-like genes, and bla_OXA-23-like genes was founded in 101 isolates (93.52%). Other identified resistance genes included bla_OXA-24-like and bla_OXA-IMP.

CONCLUSION

To the best of our knowledge, this study is the first to describe the microbiological characteristics of CRAB ST787, which carried high genetic resistance to carbapenem, but remained susceptible to colistin. CRAB ST787 was the predominant clone in our hospital in the study period.