Evaluation of an in-house MALDI-TOF MS rapid diagnostic method for direct identification of micro-organisms from blood cultures

Evaluation of the Zybio EXS3000 mass spectrometry in routine identification of Clinical isolates

The matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been widely applied in routine clinical microbiology laboratories as an efficient and reliable technique for diagnostic purpose. In this work, we evaluated the performance of the newly developed Zybio EXS3000 (Zybio Inc., China) in microbial identification and compared it with VITEK MS (bioMérieux, France). For this study, a total of 1340 isolates from various clinical specimens were collected. These isolates were analyzed simultaneously on both EXS3000 and VITEK MS. The inconsistent or unidentifiable data were further identified using the help of either 16S rRNA gene or ITS region sequencing. During the study, we observed that EXS3000 and VITEK MS provided positive confirmatory diagnostics for 95.0% and 96.5% of the isolates, respectively, which were consistent with the sequencing results. However, it is worth noting that the EXS3000 system needs to improve the identification performance of Candida albicans in the follow-up. There are no significant differences between the two devices in terms of microbial identification performance. The advantage of EXS3000 over VITEK MS is in its ability to perform in significantly lesser time period. In conclusion, the results of this investigation showed that EXS3000 can be used to identify microorganisms in clinical microbiology laboratories.

MALDI-TOF MS Indirect Beta-Lactamase Detection in Ampicillin-Resistant Haemophilus influenzae

Rapid identification of beta-lactamase-producing strains of Haemophilus influenzae plays key role in diagnostics in clinical microbiology. Therefore, the aim of this study was the rapid determination of beta-lactamase's presence in H. influenzae isolates via indirect detection of degradation ampicillin products using MALDI-TOF MS. H. influenzae isolates were subjected to antibiotic resistance testing using disk diffusion and MIC methodologies. Beta-lactamase activity was tested using MALDI-TOF MS, and results were compared to spectral analysis of alkaline hydrolysis. Resistant and susceptible strains of H. influenzae were distinguished, and strains with a high MIC level were identified as beta-lactamase-producing. Results indicate that MALDI-TOF mass spectrometry is also suitable for the rapid identification of beta-lactamase-producing H. influenzae. This observation and confirmation can accelerate identification of beta-lactamase strains of H. influenzae in clinical microbiology, which can have an impact on health in general.

Evaluation of a sterile, filter-based, in-house method for rapid direct bacterial identification and antimicrobial susceptibility testing using positive blood culture

This study aimed to assess the performance of our in-house method for rapid direct bacterial identification (ID) and antimicrobial susceptibility testing (AST) using a positive blood culture (BC) broth. For Gram-negative bacteria, 4 mL of BC broth was aspirated and passed through a Sartorius Minisart syringe filter with a pore size of 5 µm. The filtrate was then centrifuged and washed. A small volume of the pellet was used for ID, using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and for AST, using automated broth microdilution. For Gram-positive cocci, 4 mL of BC broth was passed through the Minisart syringe filter. Then, 4 mL of sterile distilled water was injected in the direction opposite to that of the filtration to collect the bacterial residue trapped in the filter. Compared with the conventional method performed with pure colonies on agar plates, 94.0% (234/249) were correctly identified using the in-house method, with rates of 91.4% (127/139) and 97.3% (107/110) for Gram-positive and Gram-negative isolates, respectively. Of 234 correctly identified isolates, 230 were assessed by AST. Categorical agreement and essential agreement were 93.3% and 94.5%, respectively, with a minor error rate of 3.8%, a major error rate of 3.4%, and a very major error rate of 1.6%. Our in-house preparation method showed good performance in rapid direct ID and AST using positive BC broths compared to the conventional method. This simple method can shorten the conventional turnaround time for ID and AST by at least 1 day, potentially contributing to better patient management.

24/7 workflow for bloodstream infection diagnostics in microbiology laboratories: the first step to improve clinical management

OBJECTIVES

We aimed to evaluate the impact of an uninterrupted workflow regarding blood cultures on turnaround time and antibiotic prescription.

METHODS

Monomicrobial episodes of bacteremia were retrospectively evaluated before and after a continuous 24/7 workflow was implemented in our clinical microbiology laboratory (pre- and post-intervention periods; PREIP and POSTIP). Primary outcome was the time from specimen collection to the first change in antibiotic therapy. Secondary outcomes included the time from specimen collection to effective antibiotic therapy and to antibiotic susceptibility testing results (or turnaround time), as well as hospital length of stay and all-cause mortality at 30 days.

RESULTS

A total of 548 episodes of bacteremia were included in the final analysis. There was no difference in PREIP and POSTIP regarding patient characteristics and causative bacteria. In POSTIP, the mean time to the first change in antibiotic therapy was reduced by 10.4 h (p<0.001). The time to effective antibiotic therapy and the turnaround time were respectively reduced by 4.8 h (p<0.001) and 5.1 h (p=0.006) in POSTIP. There was no difference in mean hospital length of stay or mortality between the two groups.

CONCLUSIONS

Around the clock processing of blood cultures allows for a reduction in turnaround time, which in turn reduces the delay until effective antibiotic therapy prescription.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in the diagnosis of microorganisms

Microbiology culture is the gold standard method for identifying microorganisms. This identification protocol takes several days to complete. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a technique that can identify different microorganisms quickly and accurately. The objective of this work was to evaluate the use of MALDI-TOF MS in the routine of clinical laboratories to identify microorganisms and to identify their resistance to antimicrobials. This study evaluated the relevance of the MALDI-TOF MS technique for microbiological diagnosis through a literature review. The authors found that MALDI-TOF MS can identify bacteria, fungi, viruses and parasites, even in blood cultures, and also serves to assess antimicrobial resistance. Thus, MALDI-TOF MS can become an indispensable tool in laboratory diagnosis.

Direct Quantitative Immunochemical Analysis of Autoinducer Peptide IV for Diagnosing and Stratifying Staphylococcus aureus Infections

An immunochemical strategy to detect and quantify AIP-IV, the quorum sensing (QS) signaling molecule produced by Staphylococcus aureus agr type IV, is reported here for the first time. Theoretical calculations and molecular modeling studies have assisted on the design and synthesis of a suitable peptide hapten (AIPIVS), allowing to obtain high avidity and specific antibodies toward this peptide despite its low molecular weight. The ELISA developed achieves an IC₅₀ value of 2.80 ± 0.17 and an LOD of 0.19 ± 0.06 nM in complex media such as 1/2 Tryptic Soy Broth. Recognition of other S. aureus AIPs (I-III) is negligible (cross-reactivity below 0.001%), regardless of the structural similarities. A pilot study with a set of clinical isolates from patients with airways infection or colonization demonstrates the potential of this ELISA to perform biomedical investigations related to the role of QS in pathogenesis and the association between dysfunctional agr or the agr type with unfavorable clinical outcomes. The AIP-IV levels could be quantified in the low nanomolar range in less than 1 h after inoculating agr IV-genotyped isolates in the culture broth, while those genotyped as I-III did not show any immunoreactivity after a 48 h growth, pointing to the possibility to use this technology for phenotyping S. aureus. The research strategy here reported can be extended to the rest of the AIP types of S. aureus, allowing the development of powerful multiplexed chips or point-of-care (PoC) diagnostic devices to unequivocally identify its presence and its agr type on samples from infected patients.

Direct Rapid Identification from Positive Blood Cultures by MALDI-TOF MS: Specific Focus on Turnaround Times

Early availability of pathogen identification in bloodstream infections has critical importance in patients' management. This study investigated the accuracy and feasibility of the direct rapid identification (RID) method from positive blood cultures (BCs) by MALDI-TOF MS and its impact on the turnaround time (TAT) compared to the short-term incubation routine identification (SIRID) method. Pellets prepared from 328 BCs using a serum separator tube in the RID method and colonies on agar plates in the SIRID method were identified with MALDI Biotyper. BCs on weekdays from 6 a.m. to 4 p.m. were defined as the daytime signal group (DSG); BCs from 4 p.m. to 6 a.m. were defined as the night signal group (NSG). Comparison between the two methods was performed with 310 monomicrobial BCs. Two hundred ninety-five (95.2%) monomicrobial BCs yielded an identification result with the RID method. Of the 295 BCs, 289 (97.9%) were identified correctly at the species level, 4 (1.4%) were at the genus level, and 2 (0.7%) were misidentified. In the RID method, at score cutoff values of 1.2, 1.3, 1.4 and 1.5, the rates of correct identifications at the species level were 97.9%, 98.9%, 99.3%, and 100%, respectively. The mean TAT in the DSG was significantly lower (P < 0.001) in the RID method (mean: 2.86 h; 95% CI: 2.65 to 3.07) compared to the SIRID method (mean: 19.49 h; 95% CI: 18.08 to 20.89). Correct identification rates at the species level were 100% in Gram-negative bacteria, 88.9% in Gram-positive bacteria, and 93.2% of all BCs isolates with the RID method. The TAT was improved remarkably in DSG, which might contribute to empirical antibiotic therapies of patients.

IMPORTANCE Using MALDI-TOF MS directly from BCs reduces the time required for pathogen identification, and the TATs for final identification have been compared with overnight incubation from solid media in previous studies. However, identification from a short incubation of agar plates has been increasingly accepted and successfully implemented in routine laboratories, but there is no data comparing direct MALDI-TOF MS with the short-term incubated agar plates. Our study showed that the TAT improved remarkably by applying a RID method by MALDI-TOF MS twice a day periodically when compared to the SIRID method.

Development of an In-House Rapid Antimicrobial Susceptibility Testing Protocol for Positive Blood Culture and Its Implementation in Routine Microbiology Laboratories

Bloodstream infections (BSI) are associated with high morbidity and mortality and remain a leading cause of death. Blood culture (BC) including the identification and the antimicrobial susceptibility testing of the causative microorganisms should be performed as soon as possible. In this study, we developed an in-house rapid antimicrobial susceptibility testing (rAST) protocol for positive BC. First, the rAST was performed in the simulated positive BC of standard strains (Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Pseudomonas aeruginosa ATCC 27853) at three different times to assess the reproducibility and operability by dispensing four drops of BC broth onto a Mueller–Hinton agar plate after a positive signal. Furthermore, the rAST was performed in clinical positive BCs. The results of rAST at 4, 6, 8, and 18 h of incubation were compared with results of the standard 16- to 20-h disk diffusion method, and the preliminary breakpoints of the rAST method were established according to the inhibition diameter of sensitive strains and resistant strains. Finally, the rAST was performed in the simulated positive BC of clinical strains to evaluate the availability of the preliminary breakpoints. The rAST results of standard strains were distributed evenly at three different times. Among the 202 clinical strains used to establish the preliminary breakpoints, the number of zone diameters that could be read and interpreted (60, 87, 98, and 100%) increased with incubation time (4, 6, 8, and 18 h), and the categorical agreement was acceptable, with total error rates of 3.0, 2.3, 2.1, and 1.3% at 4, 6, 8, and 18 h of incubation, respectively. In conclusion, the in-house rAST protocol for positive BC can be implemented in routine laboratories. It provides reliable antimicrobial susceptibility testing results for BSI pathogens after 4–6 h of incubation.

Comparison of Autof ms1000 and Bruker Biotyper MALDI-TOF MS Platforms for Routine Identification of Clinical Microorganisms

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is widely used in clinical microbiology laboratories because it is cost-effective, reliable, and fast. This study is aimed at comparing the identification performance of the recently developed Autof ms1000 (Autobio, China) with that of the Bruker Biotyper (Bruker Daltonics, Germany). From January to June 2020, 205 preserved strains and 302 clinical isolates were used for comparison. Bacteria were tested with duplicates of the direct transfer method, and formic acid extraction was performed if the results were not at the species level. Fungi were tested with formic acid extraction followed by ethanol extraction methods. 16S rRNA or ITS region sequence analysis was performed on isolates that could not be identified by any of the instruments and on isolates that showed inconsistent results. The time to result of each instrument was also compared. Among preserved strains, species-level identification results were obtained in 202 (98.5%) strains by the Autof ms1000 and 200 (97.6%) strains by the Bruker Biotyper. Correct identification at the species/complex level was obtained for 200 (97.6%) strains by the Autof ms1000 and for 199 (97.1%) strains by the Bruker Biotyper. Among clinical isolates, species-level identification results were obtained in 301 (99.7%) strains and 300 (99.3%) strains by the Autof ms1000 and Bruker Biotyper, respectively. Correct identification at the species/complex level was achieved for 299 (99.0%) strains by the Autof ms1000 and for 300 (99.3%) strains by the Bruker Biotyper. The time to analyze 96 spots was approximately 14 min for the Autof ms1000 and approximately 27 min for the Bruker Biotyper. The two instruments showed comparable performance for the routine identification of clinical microorganisms. In addition, the Autof ms1000 has a short test time, making it convenient for use in clinical microbiology laboratories.

Advances in rapid diagnostics for bloodstream infections

Septicemia from bloodstream infections (BSI) is the second largest cause of inpatient mortality and the single most expensive condition for US hospitals to manage. There has been an explosive development of commercial diagnostic systems to accelerate the identification and antimicrobial susceptibility testing (AST) of causative pathogens. Despite adoption of advanced technologies like matrix-assisted laser desorption imaging-time-of-flight mass spectrometry and multiplex polymerase chain reaction for rapid identification, clinical impact has been variable, in part due to the persistent need for conventional AST as well as prescriber understanding of these rapidly evolving platforms. Newer technologies are expanding on rapid detection of genotypic determinants of resistance, but only recently has rapid phenotypic AST been available. Yet, improved outcomes with rapid diagnostic platforms are still most evident in conjunction with active antimicrobial stewardship. This review will outline key advancements in rapid diagnostics for BSI and the role of antimicrobial stewardship in this new era.

Staphylococcus argenteus: An emerging subclinical bovine mastitis pathogen in Thailand

Background and Aim:

Staphylococcus argenteus is an emerging species of the Staphylococcus aureus complex. It has usually been misidentified as S. aureus by conventional methods and its characteristics. S. argenteus is potentially emerging in both humans and animals with an increasing global distribution. This study aimed to differentiate and identify S. argenteus from S. aureus collected and isolated from milk samples of subclinical bovine mastitis cases in Maha Sarakham Province, Northeastern Thailand.

Materials and Methods:

Forty-two isolates of S. aureus were studied from 132 individual milk samples collected from subclinical bovine mastitis cases of 15 dairy farms in three districts of Maha Sarakham, Thailand. The identification was confirmed by conventional and immune-agglutination methods. Fifteen representative isolates which were suspected as being S. argenteus were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

Results:

The result from MALDI-TOF MS confirmed that seven from 15 isolates were S. argenteus and eight isolates were S. aureus.

Conclusion:

This study indicated that MALDI-TOF MS used as an identification and classification method could accurately differentiate the novel species, S. argenteus, from the S. aureus complex which is usually misdiagnosed. In addition, the identification of S. argenteus seems to be very limited in technical difficulty despite the fact that it may be the important causative pathogen in bovine mastitis as well as a pathogenic bacterium in food and milk. Therefore, it is essential for both bovine medicine and veterinary public health to emphasize and recognize this bacterial pathogen as an emerging disease of staphylococcal bacteria that there is a need for further study of S. argenteus infections.

Application of MALDI-TOF MS to rapid identification of anaerobic bacteria

BACKGROUND

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been rapidly developed and widely used as an analytical technique in clinical laboratories with high accuracy in microorganism identification.

OBJECTIVE

To validate the efficacy of MALDI-TOF MS in identification of clinical pathogenic anaerobes.

METHODS

Twenty-eight studies covering 6685 strains of anaerobic bacteria were included in this meta-analysis. Fixed-effects models based on the P-value and the I-squared were used for meta-analysis to consider the possibility of heterogeneity between studies. Statistical analyses were performed by using STATA 12.0.

RESULTS

The identification accuracy of MALDI-TOF MS was 84% for species (I² = 98.0%, P < 0.1), and 92% for genus (I² = 96.6%, P < 0.1). Thereinto, the identification accuracy of Bacteroides was the highest at 96% with a 95% CI of 95-97%, followed by Lactobacillus spp., Parabacteroides spp., Clostridium spp., Propionibacterium spp., Prevotella spp., Veillonella spp. and Peptostreptococcus spp., and their correct identification rates were all above 90%, while the accuracy of rare anaerobic bacteria was relatively low. Meanwhile, the overall capabilities of two MALDI-TOF MS systems were different. The identification accuracy rate was 90% for VITEK MS vs. 86% for MALDI biotyper system.

CONCLUSIONS

Our research showed that MALDI-TOF-MS was satisfactory in genus identification of clinical pathogenic anaerobic bacteria. However, this method still suffers from different drawbacks in precise identification of rare anaerobe and species levels of common anaerobic bacteria.

Prevalence and dissemination risk of antimicrobial-resistant Enterobacteriaceae from shared bikes in Beijing, China

Bike-sharing as a common public transportation has been booming in China in recent years. Previous studies showed that the surfaces of public transport can act as reservoirs of antimicrobial-resistant (AR) bacteria, but AR bacterial contamination of shared bikes has not been investigated. Otherwise, the AR-Enterobacteriaceae is considered as a global health threat for humans. Herein, we aimed to investigate the prevalence of AR Enterobacteriaceae on shared bikes and examine correlations between AR Enterobacteriaceae from shared bikes and public buildings around Metro stations in Beijing. We collected 2117 samples from shared bikes at 240 Metro stations in Beijing. A total of 444 non-duplicate Enterobacteriaceae were isolated from 418 samples at 166 stations. The isolates exhibited low rates of resistance (0.5%-6.3%) to all antimicrobial agents except sulfamethoxazole-trimethoprim (31.5%). Three ceftazidime-resistant E. coli isolates were positive for bla_CTX-M-199 and two of them were positive for carbapenemase-producing gene bla_NDM-5. Multivariable logistic regression model revealed that variable "secondary/tertiary non-profit hospital nearby" was significantly (p < 0.05) associated with isolation of AR Enterobacteriaceae from the shared bikes around the Metro stations. Low AR rates of Enterobacteriaceae observed in this study suggested the risk of dissemination of AR-Enterobacteriaceae via shared bikes is limited. However, we identified hospitals as a risk factor for the dissemination of AR Enterobacteriaceae among shared bike users. More attention should be paid to both comprehensive hygiene managements in the surrounding environment of hospitals and the increasing of public awareness on the personal hygienic habits.

An update on the routine application of MALDI-TOF MS in clinical microbiology

Introduction: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has entered clinical diagnostics and is today a generally accepted and integral part of the workflow for microbial identification. MALDI-TOF MS identification systems received approval from national and international institutions, such as the USA-FDA, and are continuously improved and adopted to other fields like veterinary and industrial microbiology. The question is whether MALDI-TOF MS also has the potential to replace other conventional and molecular techniques operated in routine diagnostic laboratories. Areas covered: We give an overview of new advancements of mass spectral analysis in the context of microbial diagnostics. In particular, the expansion of databases to increase the range of readily identifiable bacteria and fungi, the refined discrimination of species complexes, subspecies, and types, the testing for antibiotic resistance or susceptibility, progress in sample preparation including automation, and applications of other mass spectrometry techniques are discussed. Expert opinion: Although many new approaches of MALDI-TOF MS are still in the stage of proof of principle, it is expectable that MALDI-TOF MS will expand its role in the clinical microbiology laboratory of the future. New databases, instruments and analytical software modules will continue to be developed to further improve diagnostic efficacy.