Evaluation of MALDI-TOF mass spectrometry and MALDI BioTyper in comparison to 16S rDNA sequencing for the identification of bacteria isolated from Arctic sea water

Comparison of MALDI-TOF mass spectrometry and 16S rDNA sequencing for identification of environmental bacteria: a case study of cave mussel-associated culturable microorganisms

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is routinely used as a rapid and cost-effective method for pathogen identification in clinical settings. In comparison, its performance in other microbiological fields, such as environmental microbiology, is still being tested, although isolates of environmental microbes are essential for in-depth in vivo studies of their biology, including biotechnological applications. We investigated the applicability of MALDI-TOF MS for the identification of bacterial isolates from a highly oligotrophic environment - Dinaric Karst caves, which likely harbor specific microorganisms. We cultured bacteria from the shell surface of the endemic mussel Congeria jalzici, one of the three known cave mussels in the world that lives in the Dinaric karst underground. The bacterial isolates were obtained by swabbing the shell surface of mussels living in microhabitats with different amounts of water: 10 air-exposed mussels, 10 submerged mussels, and 10 mussels in the hygropetric zone. A collection of 87 pure culture isolates was obtained, mostly belonging to the phylum Bacillota (72%), followed by Pseudomonadota (16%), Actinomycetota (11%), and Bacteroidota (1%). We compared the results of MALDI-TOF MS identification (Bruker databases DB-5989 and version 11, v11) with the results of 16S rDNA-based phylogenetic analysis, a standard procedure for bacterial identification. Identification to the genus level based on 16S rDNA was possible for all isolates and clearly outperformed the results from MALDI-TOF MS, although the updated MALDI-TOF MS database v11 gave better results than the DB-5989 version (85% versus 62%). However, identification to the species-level by 16S rDNA sequencing was achieved for only 17% of isolates, compared with 14% and 40% for the MALDI-TOF MS databases DB-5989 and v11 database, respectively. In conclusion, our results suggest that continued enrichment of MALDI-TOF MS libraries will result with this method soon becoming a rapid, accurate, and efficient tool for assessing the diversity of culturable bacteria from different environmental niches.

A Single-Laboratory Performance Evaluation of MALDI-TOF MS in Rapid Identification of Staphylococcus aureus, Cronobacter sakazakii, Vibrio parahaemolyticus, and Some Closely Related Bacterial Species of Public Health Importance

BACKGROUND

Staphylococcus is a genus of Gram-positive bacteria, known to cause food poisoning and gastrointestinal illness in humans. Additionally, the emergence of methicillin-resistant S. aureus (MRSA) strains has caused a major health care burden worldwide. Cronobacter is a group of Gram-negative bacteria that can survive in extreme dry conditions. Cronobacter sakazakii is known to contaminate powdered infant formula and cause life-threatening infections in neonates. Vibrio is a genus of human-pathogenic Gram-negative bacteria that can cause foodborne illness by consuming undercooked or raw seafood. Vibrio parahaemolyticus can cause serious gastrointestinal disease in humans. Thus, rapid identification of Staphylococcus spp., Cronobacter spp., and Vibrio spp. is crucial for the source tracking of contaminated food, as well as to measure the transmission dynamics of these bacterial pathogens causing foodborne diseases and outbreaks.

OBJECTIVE

This single-laboratory performance evaluation study used the VITEK MS system to evaluate the potential of MALDI-TOF MS technology for rapid identification of S. aureus-like, C. sakazakii-like, and V. parahaemolyticus-like isolates of public health importance.

METHOD

A total of 226 isolates recovered from various food, environmental surveillance samples, and other sources were identified by bioMérieux VITEK 2 and VITEK MS systems as Staphylococcus spp., Cronobacter spp., and Vibrio spp. Five American Type Culture Collection (ATCC) reference Gram-positive and Gram-negative bacterial isolates were also tested to complete the study. In addition, for some Staphylococcus spp. isolates, whole genome sequencing (WGS) and DNA sequencing of 16S rRNA partial region were also performed for species identification.

RESULTS

The VITEK MS system was able to provide species identification to all 96 isolates of Staphylococcus spp. and to all 29 isolates of Vibrio spp. examined with a high confidence value (99.9%). Similarly, species identification was observed for the majority of spots (245 of 303) for the 101 Cronobacter spp. isolates (∼82.0%) with a high confidence value (99.9%), and genus level identification was noticed for the rest of the Cronobacter spp. isolates (18.0%; 58 of the 303 spots) analyzed. Species identification data generated by VITEK 2 system were comparable to data obtained by the VITEK MS system.

CONCLUSIONS

The VITEK MS system is a reliable high-throughput platform that can rapidly identify Staphylococcus, Vibrio, and Cronobacter to the genus level, as well as S. aureus, C. sakazakii, V. parahaemolyticus, and other closely related foodborne isolates and bacterial isolates from additional sources, in most cases.

HIGHLIGHTS

The VITEK MS system can be used in the rapid genus and species identification of human-pathogenic Staphylococcus spp., Cronobacter spp., and Vibrio spp. isolates.

Pseudomonas species prevalence, protein analysis, and antibiotic resistance: an evolving public health challenge

Psychrotrophic Pseudomonas is one of the significant microbes that lead to putrefaction in chilled meat. One of the biggest problems in the detection of Pseudomonas is that several species are seemingly identical. Currently, antibiotic resistance is one of the most significant challenges facing the world's health and food security. Therefore, this study was designed to apply an accurate technique for eliminating the identification discrepancy of Pseudomonas species and to study their resistance against various antimicrobials. A total of 320 chicken meat specimens were cultivated, and the isolated bacteria’ were phenotypically recognized. Protein analysis was carried out for cultured isolates via Microflex LT. The resistance of Pseudomonas isolates was recorded through Vitek® 2 AST-GN83 cards. Overall, 69 samples were identified as Pseudomonas spp. and included 18 Pseudomonas lundensis (P. lundensis), 16 Pseudomonas fragi (P. fragi), 13 Pseudomonas oryzihabitans (P. oryzihabitans), 10 Pseudomonas stutzeri (P. stutzeri), 5 Pseudomonas fluorescens (P. fluorescens), 4 Pseudomonas putida (P. putida), and 3 Pseudomonas aeruginosa (P. aeruginosa) isolates. Microflex LT identified all Pseudomonas isolates (100%) correctly with a score value ≥ 2.00. PCA positively discriminated the identified isolates into various groups. The antimicrobial resistance levels against Pseudomonas isolates were 81.16% for nitrofurantoin, 71% for ampicillin and ampicillin/sulbactam, 65.22% for cefuroxime and ceftriaxone, 55% for aztreonam, and 49.28% for ciprofloxacin. The susceptibilities were 100% for cefotaxime, 98.55% for ceftazidime, 94.20% for each piperacillin/tazobactam and cefepime, 91.3% for cefazolin. In conclusion, chicken meat was found to be contaminated with different Pseudomonas spp., with high incidence rates of P. lundensis. Microflex LT is a potent tool for distinguishing Pseudomonads at the species level.

Application of MALDI-TOF MS for identification of environmental bacteria: A review

Bacteria play a variety of roles in the environment. They maintain the balance in the ecosystem and provide different ecosystem services such as in biogeochemical cycling of nutrients, biodegradation of toxic pollutants, and others. Therefore, isolation and identification of different environmental bacteria are important to most environmental research. Due to the high cost and time associated with the conventional molecular techniques, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has gained considerable attention for routine identification of bacteria. This review aims to provide an overview of the application of MALDI-TOF MS in various environmental studies through bibliometric analysis and literature review. The bibliometric analysis helped to understand the time-variable application of MALDI-TOF MS in various environmental studies. The categorical literature review covers various environmental studies comprising areas like ecology, food microbiology, environmental biotechnology, agriculture, and plant sciences, which show the application of the technique for identification and characterization of pollutant-degrading, plant-associated, disease-causing, soil-beneficial, and other environmental bacteria. Further research should focus on bridging the gap between the phylogenetic identity of bacteria and their specific environmental functions or metabolic traits that can help in rapid advancements in environmental research, thereby, improving time and cost savings.

Rapid Cyanobacteria Species Identification with High Sensitivity Using Native Mass Spectrometry

Cyanobacteria have evolved over billions of years to adapt and survive in diverse climates. Environmentally, this presents a huge challenge because cyanobacteria can now rapidly form algae blooms that are detrimental to aquatic life. In addition, many cyanobacteria produce toxins, making them hazardous to animals and humans that they encounter. Rapid identification of cyanobacteria is essential to monitor and prevent toxic algae blooms. Here, we show for the first time how native mass spectrometry can quickly and precisely identify cyanobacteria from diverse aquatic environments. By monitoring phycobiliproteins, abundant protein complexes within cyanobacteria, simple, easy-to-understand mass spectral "fingerprints" were created that were unique to each species. Moreover, our method is 10-fold more sensitive than the current MALDI-TOF mass spectrometric methods, meaning that cyanobacteria can be monitored using this technology prior to bloom formation. Together, the data show great promise for the simultaneous detection and identification of co-existing cyanobacteria in situ.

Identification and Antibiotic Profiling of Wohlfahrtiimonas chitiniclastica, an Underestimated Human Pathogen

In the past 12 years, several case reports have clearly demonstrated that Wohlfahrtiimonas chitiniclastica is capable of causing sepsis and bacteremia in humans. However, since most clinicians are not familiar with this species, little is known about its pathogenicity and treatment options while it is as rare but underestimated human pathogen. Therefore, a larger strain collection is required so that methods can be identified that are most suitable to obtain rapid and reliable identification. Moreover, the antimicrobial resistance profile needs to be elucidated in order to explore possible treatment options. Over a period of 6 years, we therefore have collected a total of 14 W. chitiniclastica isolates in routine diagnostics, which now served as the basis for a comprehensive characterization with respect to identification and antibiotic profiling. We compared the accuracy and convenience of several identification techniques in which MALDI-TOF MS and sequencing of the 16S rRNA gene have proven to be suitable for identification of W. chitiniclastica. In addition, whole genome sequencing (WGS)-based digital DNA-DNA hybridization (dDDH) was used as a reference method for strain identification, and surprised with the detection of a novel W. chitiniclastica subspecies. A combination of in silico and in vitro analyses revealed a first insight into the antimicrobial resistance profile and the molecular basis of antimicrobial resistance. Based on our findings, trimethoprim/sulfamethoxazole, levofloxacin, and cephalosporins (e.g., ceftazidime) may be the best antibiotics to use in order to treat infections caused by W. chitiniclastica, while resistance to fosfomycin, amikacin and tobramycin is observed.

Rapid and improved identification of drinking water bacteria using the Drinking Water Library, a dedicated MALDI-TOF MS database

According to the European Directives (UE) 2020/2184 and 2009/54/EC, which establishes the sanitary criteria for water intended for human consumption in Europe, water suitable for human consumption must be free of the bacterial indicators Escherichia coli, Clostridium perfringens and Enterococcus spp. Drinking water is also monitored for heterotrophic bacteria, which are not a human health risk, but can serve as an index of bacteriological water quality. Therefore, a rapid, accurate, and cost-effective method for the identification of these colonies would improve our understanding of the culturable bacteria of drinking water and facilitate the task of water management by treatment facilities. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is potentially such a method, although most of the currently available mass spectral libraries have been developed in a clinical setting and have limited environmental applicability. In this work, a MALDI-TOF MS drinking water library (DWL) was defined and developed by targeting bacteria present in water intended for human consumption. This database, made up of 319 different bacterial strains, can contribute to the routine microbiological control of either treated drinking water or mineral bottled water carried out by water treatment and distribution operators, offering a faster identification rate compared to a clinical sample-based library. The DWL, made up of 96 bacterial genera, 44 of which are not represented in the MALDI-TOF MS bacterial Bruker Daltonics (BDAL) database, was found to significantly improve the identification of bacteria present in drinking water.

Performance assessment of ASTA MicroIDSys, a new matrix assisted laser desorption ionization-time of flight mass spectrometry system, for identification of viridans group streptococci

The performance of the ASTA MicroIDSys system (ASTA, Suwon, South Korea), a new matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) system, was evaluated for the identification of viridans group streptococci (VGS) and compared with the results obtained with the Bruker Biotyper system (Bruker Daltonics, Hamburg, Germany). A total of 106 Streptococcus reference strains belonging to 24 species from the bacterial strain bank was analyzed using the two MALDI-TOF MS systems. Of the 106 reference strains tested, ASTA MicroIDSys and Bruker Biotyper correctly identified 84.9% and 81.1% at the species level, 100% and 97.2% at the group level and 100% and 98.1% at the genus level, respectively. The difference between the two systems was not statistically significant (P = 0.289). Out of 24 species, 13 species were accurately identified to the species level with 100% accurate identification rates with both systems. The accurate identification rates at the species level of ASTA MicroIDSys and Bruker Biotyper were 100% and 87.5% for the S. anginosus group; 78.4% and 73.5% for the S. mitis group; 91.7% and 91.7% for the S. mutans group; and 100% and 100% for the S. salivarius group, respectively. The ASTA MicroIDSys showed an identification performance equivalent to that of the Bruker Biotyper for VGS. Therefore, it would be useful for the identification of VGS strains in clinical microbiology laboratories. This article is protected by copyright. All rights reserved.

Microbial Reduction of Fumonisin B1 by the New Isolate Serratia marcescens 329-2

The mycotoxin fumonisin (FB) has become a major problem in maize products in southeastern Asia. Fumonisin can affect the health of humans and many animals. Fumonisin contamination can be reduced by detoxifying microbial enzyme. Screening of 95 potent natural sources resulted in 5.3% of samples yielding a total of five bacterial isolates that were a promising solution, reducing approximately 10.0-30.0% of fumonisin B1 (FB1). Serratia marcescens, one of the dominant degrading bacteria, was identified with Gram staining, 16S rRNA gene, and MALDI-TOF/TOF MS. Cell-free extract showed the highest fumonisin reduction rates, 30.3% in solution and 37.0% in maize. Crude proteins from bacterial cells were analyzed with a label-free quantification technique. The results showed that hydrolase enzymes and transferase enzymes that can cooperate in the fumonisin degradation process were highly expressed in comparison to their levels in a control. These studies have shown that S. marcescens 329-2 is a new potential bacterium for FB1 reduction, and the production of FB1-reducing enzymes should be further explored.

Identification of Potential Probiotics Producing Bacteriocins Active against Listeria monocytogenes by a Combination of Screening Tools

Listeria monocytogenes is an important food-borne pathogen and a serious concern to food industries. Bacteriocins are antimicrobial peptides produced naturally by a wide range of bacteria mostly belonging to the group of lactic acid bacteria (LAB), which also comprises many strains used as starter cultures or probiotic supplements. Consequently, multifunctional strains that produce bacteriocins are an attractive approach to combine a green-label approach for food preservation with an important probiotic trait. Here, a collection of bacterial isolates from raw cow's milk was typed by 16S rRNA gene sequencing and MALDI-Biotyping and supernatants were screened for the production of antimicrobial compounds. Screening was performed with live Listeria monocytogenes biosensors using a growth-dependent assay and pHluorin, a pH-dependent protein reporting membrane damage. Purification by cation exchange chromatography and further investigation of the active compounds in supernatants of two isolates belonging to the species Pediococcus acidilactici and Lactococcus garvieae suggest that their antimicrobial activity is related to heat-stable proteins/peptides that presumably belong to the class IIa bacteriocins. In conclusion, we present a pipeline of methods for high-throughput screening of strain libraries for potential starter cultures and probiotics producing antimicrobial compounds and their identification and analysis.

Comprehensive Profiling of Microbiologically Induced CaCO3 Precipitation by Ureolytic Bacillus Isolates from Alkaline Soils

Microbiologically induced CaCO3 precipitation (MICP) is a well-known bio-based solution with application in environmental, geotechnical, and civil engineering. The significance of the MICP has increased explorations of process efficiency and specificity via natural bacterial isolates. In this study, comprehensive profiling of five soil ureolytic Bacillus strains was performed through a newly formed procedure that involved six steps from selection and identification, through kinetic study, to the characterization of the obtained precipitates, for the first time. To shorten the whole selection procedure of 43 bioagents with the MICP potential, Standard Score Analysis was performed and five selected bacteria were identified as Bacillus muralis, B. lentus, B. simplex, B. firmus, and B. licheniformis by the MALDI-TOF mass spectrometry. Despite following the targeted activity, kinetic studies were included important aspects of ureolysis and the MICP such as cell concentration, pH profiling, and reduction in calcium ion concentration. At the final step, characterization of the obtained precipitates was performed using FTIR, XRD, Raman, DTA/TGA, and SEM analysis. Although all tested strains showed significant potential in terms of precipitation of calcite or calcite and vaterite phase, the main differences in the MICP behavior can be observed at the bacterial strain level. B. licheniformis showed favorable behavior compared to the reference Sporosarcina pasteurii DSM 33.

The bifidobacterial distribution in the microbiome of captive primates reflects parvorder and feed specialization of the host

Bifidobacteria, which commonly inhabit the primate gut, are beneficial contributors to host wellbeing. Anatomical differences and natural habitat allow an arrangement of primates into two main parvorders; New World monkeys (NWM) and Old World monkeys (OWM). The number of newly described bifidobacterial species is clearly elevated in NWM. This corresponds to our finding that bifidobacteria were the dominant group of cultivated gut anaerobes in NWM, while their numbers halved in OWM and were often replaced by Clostridiaceae with sarcina morphology. We examined an extended MALDI-TOF MS database as a potential identification tool for rapid screening of bifidobacterial distribution in captive primates. Bifidobacterial isolates of NWM were assigned mainly to species of primate origin, while OWM possessed typically multi-host bifidobacteria. Moreover, bifidobacterial counts reflected the feed specialization of captive primates decreasing from frugivore-insectivores, gummivore-insectivores, frugivore-folivores to frugivore-omnivores. Amplicon sequencing analysis supported this trend with regards to the inverse ratio of Actinobacteria and Firmicutes. In addition, a significantly higher diversity of the bacterial population in OWM was found. The evolution specialization of primates seems to be responsible for Bifidobacterium abundance and species occurrence. Balanced microbiota of captive primates could be supported by optimized prebiotic and probiotic stimulation based on the primate host.

Biological activity of bacteria isolated from wetland sediments collected from a conservation unit in the southern region of Brazil

Wetlands are ecosystems rich in biodiversity and their ecological importance is recognized worldwide. Sediment samples were subjected to physical-chemical analysis and organic carbon content varied from 3.0% to 4.8%, the clay between 32 and 40%, silt with 41% and 43%, sand coarse varied between 6 and 11% and fine sand between 7 and 16%. The nitrogen values ​​varied from 0.25% to 0.48%, the pH from 5.4 to 7.5 and the humidity ​​varied from 44 to 56%. The selected isolates were evaluated for enzymatic properties and 64% showed positive results for amylase, 16% for gelatinase, 37% for lipase, 91% for protease and 2.7% for inulinase. Six bacterial isolates were selected for the overlapping assay and Bacillus sp. sed 2.2 showed inhibitory activity against Corynebacterium fimi NCTC 7547, and the antimicrobial substance was partially purified. The characterization of the substance was carried and the substance was stable at 100° C for up to 10 minutes and sensitive to the enzymes papain and trypsin. This substance was active against some species of Listeria, including Listeria monocytogenes ATCC 7644. The microorganims obtained from sediment samples were important sources of bioactive compounds, including enzymes and peptides, being a source of bioactive compounds to be studied.

Modern Analytical Techniques for Detection of Bacteria in Surface and Wastewaters

Contamination of surface waters with pathogens as well as all diseases associated with such events are a significant concern worldwide. In recent decades, there has been a growing interest in developing analytical methods with good performance for the detection of this category of contaminants. The most important analytical methods applied for the determination of bacteria in waters are traditional ones (such as bacterial culturing methods, enzyme-linked immunoassay, polymerase chain reaction, and loop-mediated isothermal amplification) and advanced alternative methods (such as spectrometry, chromatography, capillary electrophoresis, surface-enhanced Raman scattering, and magnetic field-assisted and hyphenated techniques). In addition, optical and electrochemical sensors have gained much attention as essential alternatives for the conventional detection of bacteria. The large number of available methods have been materialized by many publications in this field aimed to ensure the control of water quality in water resources. This study represents a critical synthesis of the literature regarding the latest analytical methods covering comparative aspects of pathogen contamination of water resources. All these aspects are presented as representative examples, focusing on two important bacteria with essential implications on the health of the population, namely Pseudomonas aeruginosa and Escherichia coli.

Development of an inexpensive matrix-assisted laser desorption-time of flight mass spectrometry method for the identification of endophytes and rhizobacteria cultured from the microbiome associated with maize

Many endophytes and rhizobacteria associated with plants support the growth and health of their hosts. The vast majority of these potentially beneficial bacteria have yet to be characterized, in part because of the cost of identifying bacterial isolates. Matrix-assisted laser desorption-time of flight (MALDI-TOF) has enabled culturomic studies of host-associated microbiomes but analysis of mass spectra generated from plant-associated bacteria requires optimization. In this study, we aligned mass spectra generated from endophytes and rhizobacteria isolated from heritage and sweet varieties of Zea mays. Multiple iterations of alignment attempts identified a set of parameters that sorted 114 isolates into 60 coherent MALDI-TOF taxonomic units (MTUs). These MTUs corresponded to strains with practically identical (>99%) 16S rRNA gene sequences. Mass spectra were used to train a machine learning algorithm that classified 100% of the isolates into 60 MTUs. These MTUs provided >70% coverage of aerobic, heterotrophic bacteria readily cultured with nutrient rich media from the maize microbiome and allowed prediction of the total diversity recoverable with that particular cultivation method. Acidovorax sp., Pseudomonas sp. and Cellulosimicrobium sp. dominated the library generated from the rhizoplane. Relative to the sweet variety, the heritage variety c ontained a high number of MTUs. The ability to detect these differences in libraries, suggests a rapid and inexpensive method of describing the diversity of bacteria cultured from the endosphere and rhizosphere of maize.

Identification, antibiotic resistance, and virulence profiling of Aeromonas and Pseudomonas species from wastewater and surface water

Aquatic environments are hotspots for the spread of antibiotic-resistant bacteria and genes due to pollution caused mainly by anthropogenic activities. The aim of this study was to evaluate the impact of wastewater effluents, informal settlements, hospital, and veterinary clinic discharges on the occurrence, antibiotic resistance profile and virulence signatures of Aeromonas spp. and Pseudomonas spp. isolated from surface water and wastewater. High counts of Aeromonas spp. (2.5 (± 0.8) - 3.3 (± 0.4) log₁₀ CFU mL^-1) and Pseudomonas spp. (0.6 (± 1.0) - 1.8 (± 1.0) log₁₀ CFU mL^-1) were obtained. Polymerase chain reaction (PCR) and MALDI-TOF characterization identified four species of Aeromonas and five of Pseudomonas. The isolates displayed resistance to 3 or more antibiotics (71% of Aeromonas and 94% of Pseudomonas). Aeromonas spp. showed significant association with the antibiotic meropenem (χ² = 3.993, P < 0.05). The virulence gene aer in Aeromonas was found to be positively associated with the antibiotic resistance gene blaOXA (χ² = 6.657, P < 0.05) and the antibiotic ceftazidime (χ² = 7.537, P < 0.05). Aeromonas recovered from both wastewater and surface water displayed high resistance to ampicillin and had higher multiple antibiotic resistance (MAR) indices close to the hospital. Pseudomonas isolates on the other hand exhibited low resistance to carbapenems but very high resistance to the third-generation cephalosporins and cefixime. The results showed that some of the Pseudomonas spp. and Aeromonas spp. isolates were extended-spectrum β-lactamase producing bacteria. In conclusion, the strong association between virulence genes and antibiotic resistance in the isolates shows the potential health risk to communities through direct and indirect exposure to the water.

Evaluation of the matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) system in the detection of mastitis pathogens from bovine milk samples

MALDI-TOF is a chemistry analytical tool that has recently been deployed in the identification of microorganisms isolated from nosocomial environments. Its use in diagnostics has been extremely advantageous in terms of cost effectiveness, sample preparation easiness, turn-around time and result analysis accessibility. In the dairy industry, where mastitis causes great financial losses, a rapid diagnostic method such as MALDI-TOF could assist in the control and prevention program of mastitis, in addition to the sanitation and safety level of the dairy farms and processing facility. However, the diagnostic strengths and limitations of this test method require further understanding. In the present study, we prospectively compared MALDI-TOF MS to conventional 16S rDNA sequencing method for the identification of pathogens recovered from milk associated with clinical and subclinical bovine mastitis cases. Initially, 810 bacterial isolates were collected from raw milk samples over a period of three months. However, only the isolates (481) having both 16S rDNA sequencing and MALDI-TOF identification were included in the final phase of the study. Among the 481 milk isolates, a total of 26 genera (12 g-postive and 14 g-negative), including 71 different species, were taxonomically charecterized by 16S rDNA at the species level. Comparatively, MALDI-TOF identified 17 genera (9 g-positive and 8 g-negative) and 33 differernt species. Overall, 445 (93%) were putatively identified to the genus level by MALDI-TOF MS and 355 (74%) were identified to the species level, but no reliable identification was obtained for 16 (3.3%), and 20 (4.2%) discordant results were identified. Future studies may help to overcome the limitations of the MALDI database and additional sample preparation steps might help to reduce the number of discordances in identification. In conclusion, our results show that MALDI-TOF MS is a fast and reliable technique which has the potential to replace conventional identification methods for common mastitis pathogens, routinely isolated from raw milk. Thus it's adoption will strengthen the capacity, quality, and possibly the scope of diagnostic services to support the dairy industry.

Mass spectrometry-based identification of bacteria isolated from industrially contaminated site in Salamanca (Mexico) and evaluation of their potential for DDT degradation

Longstanding industrial deposits of 1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene (DDT) impose environmental threat in Salamanca city, located in central Mexico. Native bacteria from this location were isolated and identified, and their potential utility for DDT biodegradation was examined. Twenty-five isolates were obtained, and cell lysates were analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) with Biotyper^TR; twenty-one organisms were identified at species level, and the other four were assigned to genus. The most abundant species corresponded to Bacillus (44%) and Pseudomonas genera (20%). Eight bacteria could grow in the presence of 200 mg/L of DDT. Two-week exposure of Lysinibacillus fusiformis, Bacillus mycoides, Bacillus pumilus, and Bacillus cereus to DDT 50 mg/L and 200 mg/L, caused percentage pesticide degradation in the range 41-48% and 26-31%, respectively. Other four bacteria presented lower degradation rates. Gas chromatography-mass spectrometry (GC-MS) analysis of the spent media revealed that eight isolates assisted the conversion of DDT, DDD (1,1-dichloro-2,2-bis-(4-chlorophenyl)ethane), and DDE (1,1-dichloro-2,2-bis-(4-chlorophenyl)ethylene) to DDMU (1,1-(2-chloro-1,1-ethenediyl)-bis-(4-chlorobenzene)); however, DDNU (2,2-bis(4-chlorophenyl)ethylene), DBP (4,4'-dichlorobenzophenone(bis(4-chlorophenyl)methanone)) and DBH (bis(4-chlorophenyl)methanol) were found only for L. fusiformis, B. mycoides, B. cereus, B. marisflavi, and B. megaterium. Within the context of DDT biodegradation, the first three were the most promising isolates and further studies will be aimed at setting the experimental conditions for efficient mineralization of DDT congeners.

Environmental Recovery of Nosocomial Bacteria in a Companion Animal Shelter Before and After Infection Control Procedures

While the effects of cleaning and disinfection practices on the reduction of environmental nosocomial bacteria are well-established in human and large animal veterinary hospitals, how animal movements within animal health care facilities influence environmental bacterial recovery is poorly understood. During three consecutive weeks, 155 electrostatic wipes were collected from the environment pre- and post-cleaning only or following disinfection from seven target locations within an animal shelter. All samples were cultured, and isolates were identified using a matrix-assisted laser desorption ionization-time of flight mass spectrometry. Social network analysis of animal movements during the sampling period was performed to estimate the level of connectivity of the seven target locations. The relationship between bacterial levels and connectivity estimates of the target locations were investigated using a negative binomial regression model with a random effect of sampling areas. Overall, our results indicate a significant reduction in the total bacterial contamination with disinfection when compared to cleaning only [Coefficient (Coef.) = -1.72, 95% Confidence Interval (CI) = -3.09, -0.34, P = 0.015]. Higher total bacterial contamination was significantly more likely in sampled areas with less animal movement connectivity (Coef. = -0.32, 95% CI = -0.49, -0.15, P ≤ 0.001). Pseudomonas aeruginosa and ampicillin resistant Enterobacteriaceae (Escherichia coli, Enterobacter spp. and Klebsiella spp.) were present in the animal holdings and in the shelters' veterinary clinic environment at all sampling times. Our findings demonstrate that cleaning followed by disinfection practices are effective at reducing environmental bacterial levels. Areas with less animal connectivity are more likely to have a higher bacterial contamination. These areas could represent environmental reservoirs for bacterial infection and should be targeted with effective cleaning and disinfection protocols.

MALDI-ToF MS: A Rapid Methodology for Identifying and Subtyping Listeria monocytogenes

Listeria monocytogenes is a major food-borne pathogen and causative agent of a fatal disease, listeriosis. Stringent regulatory guidelines and zero tolerance policy toward this bacterium necessitate rapid, accurate, and reliable methods of identification and subtyping. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS) has recently become a method of choice for routine identification of pathogens in clinical settings and has largely replaced biochemical assays. Identification relies on well-curated databases such as SARAMIS. Extensive use of SARAMIS to generate consensus mass spectra, in conjunction with statistical analysis, such as partial least square-discriminant analysis and hierarchical cluster analysis, is useful in subtyping bacteria. While MALDI-ToF MS has been extensively used for pathogen detection, its application in bacterial subtyping has been limited. The protocol describes a MALDI-ToF MS workflow as a single tool for simultaneous identification and subtyping of L. monocytogenes directly from solid culture medium.

Challenges in microbiological identification of aerobic bacteria isolated from the skin of reptiles

INTRODUCTION

Bacterial pathogens are often involved in dermatitis in reptiles. Exact identification of reptile-specific but otherwise uncommon bacterial species may be challenging. However, identification is crucial to evaluate the importance of the detected bacterial species.

OBJECTIVE

The aim of this study was to assess the number of aerobic bacterial isolates cultured from skin-derived samples of reptiles which were not reliably identified by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS), and to determine their identity.

MATERIAL AND METHODS

Routine bacterial diagnostics were performed on 235 skin samples, and 417 bacterial isolates were analysed by MALDI-TOF MS. The isolates were grouped into categories based on their first score: category I (≥ 2.00), category II (≥ 1.70 and < 2.00), and category III (< 1.70). Isolates from category III were further investigated by 16S rRNA gene sequencing and the following criteria were applied: query cover 100%, e-value rounded to 0.0 and sequence identity (%) > 98.00% for genus identification, and > 99.00% for species identification.

RESULTS

The majority of bacterial isolates were in category I (85.1%) or category II (8.4%). In category III (6.5%) results achieved at first by MALDI-TOF MS corresponded to the results of the molecular analysis in 8.0% of isolates at the species level and in 24.0% at the genus level. Bacterial isolates classified as category III were heterogenic in genus (e.g. Chryseobacterium, Devriesea, Pseudomonas, Staphylococcus, Uruburuella), and some have only been described in reptiles so far.

CONCLUSIONS

Most of the aerobic bacterial isolates cultured from reptile skin achieved high scores by MALDI-TOF MS. However, in the majority of category III isolates MALDI-TOF MS results were different from those of the molecular analysis. This strengthens the need to carefully examine low-scored results for plausibility and to be familiar with the occurrence and morphology of relevant reptile-specific bacterial species (e.g. Devriesea agamarum) as well as with the limits of the database used.

Novel specific peaks for differentiating the Lactobacillus plantarum group using matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Identifying the Lactobacillus plantarum group using conventional taxonomic methods such as biochemical analysis and 16S rRNA gene sequencing is inaccurate, expensive, and time-consuming. In this study, for the first time, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to identify the L. plantarum group and develop a classification method for species level differentiation with specific peaks based on mass spectra. Furthermore, from the mass spectra of 131 isolates aligned with the biotyper database, 131 isolates (100%) were correctly identified at the species level with a mean score of 2.316. However, commercial databases could not accurately differentiate some isolates of L. plantarum group species because the same colony was identified as different species with similar score values. Moreover, these two species showed a similar mass pattern in the main spectrum profiles-dendrogram and Principal component analysis clustering generated by the mass peak of the reference strains and isolates. Specific peaks to each species were investigated from the analyzed mass peak, and they clearly showed that three species could be differentiated. These peaks were verified by re-identifying 131 isolates, and it demonstrated 100% specificity and accuracy. Also, using a specific peak, isolates that were undifferentiated from the biotyper database were clearly identified as one species, similar to species-specific polymerase chain reaction. Our data demonstrate that the specific peaks accurately differentiate the L. plantarum group and enable high-resolution identification at the species level; this methodology can be used to rapidly and easily identify them and determine their nomenclature.

New Arctic Bacterial Isolates with Relevant Enzymatic Potential

Fragments of wood drifting in the vicinity of Spitzbergen were used for the isolation of microorganisms, carried out using atypical carbon sources: colloidal chitin, cellulose and carboxymethylcellulose, xylan, casein, tributrin and olive oil. Purified cultures were subjected to a three-step identification: with classical methods, using MALDI-TOF MS Biotyper whole-cell protein fingerprinting, and molecular analysis of 16S rDNA. Subsequently, a preliminary assessment of the enzymatic potential of isolates was carried out. As a result, cellulolytic activity was observed in more than 50% of the bacterial strains, exhibiting activity of 0.30–0.40 U/mL. Over 53% of the isolates demonstrated xylanolytic activity, of which the highest reached from 0.40 to 0.90 U. Polygalacturonase activity of 0.003–1.6 was also demonstrated in half of the bacterial strains studied. Proteolytic activity of isolates did not exceed 0.3 U. An important highlight was the ability of fluorescent dye production by certain strains, grown on skim milk-agar, but also on pure meat extract.

Mass Spectrometry: A Rosetta Stone to Learn How Fungi Interact and Talk

Fungi are a highly diverse group of heterotrophic organisms that play an important role in diverse ecological interactions, many of which are chemically mediated. Fungi have a very versatile metabolism, which allows them to synthesize a large number of still little-known chemical compounds, such as soluble compounds that are secreted into the medium and volatile compounds that are chemical mediators over short and long distances. Mass spectrometry (MS) is currently playing a dominant role in mycological studies, mainly due to its inherent sensitivity and rapid identification capabilities of different metabolites. Furthermore, MS has also been used as a reliable and accurate tool for fungi identification (i.e., biotyping). Here, we introduce the readers about fungal specialized metabolites, their role in ecological interactions and provide an overview on the MS-based techniques used in fungal studies. We particularly present the importance of sampling techniques, strategies to reduce false-positive identification and new MS-based analytical strategies that can be used in mycological studies, further expanding the use of MS in broader applications. Therefore, we foresee a bright future for mass spectrometry-based research in the field of mycology.

Rapid screening of marine bacterial symbionts using MALDI-TOF MS

Matrix-Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) is a rapid, cost-effective and high-throughput method for bacteria characterization. However, most previous studies focused on clinical isolates. In this study, we evaluated the use of MALDI-TOF MS as a rapid screening tool for marine bacterial symbionts. A set of 255 isolates from different marine sources (corals, sponge, fish and seawater) was analyzed using cell lysates to obtain a rapid grouping. Cluster analysis of mass spectra and 16S rRNA showed 18 groups, including Vibrio, Bacillus, Pseudovibrio, Alteromonas and Ruegeria. MALDI-TOF distance similarity scores ≥ 60% and ≥ 70% correspond to ≥ 98.7% 16S rRNA gene sequence similarity and ≥ 95% pyrH gene sequence similarity, respectively. MALDI-TOF MS is a useful tool for Vibrio species groups' identification.

Custom Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometric Database for Identification of Environmental Isolates of the Genus Burkholderia and Related Genera

Success of discovery programs for microbial natural products is dependent on quick and concise discrimination between isolates from diverse environments. However, laboratory isolation and identification of priority genera using current 16S rRNA PCR-based methods are both challenging and time-consuming. An emerging strategy for rapid isolate discrimination is protein fingerprinting via matrix-assisted laser desorption ionization (MALDI) mass spectrometry. Using our in-house environmental isolate repository, we have created a main spectral (MSP) library for the Bruker Biotyper MALDI mass spectrometer that contains 95 entries, including Burkholderia, Caballeronia, Paraburkholderia, and other environmentally related genera. The library creation required the acquisition of over 2,250 mass spectra, which were manually reviewed for quality control and consolidated into a single reference library using a commercial software platform. We tested the effectiveness of the reference library by analyzing 49 environmental isolate strains using two different sample preparation methods. Overall, this approach correctly identified all strains to the genus level provided that suitable reference spectra were present in the MSP library. In this study, we present a fast, accurate method for taxonomic assignment of environmentally derived bacteria from the order Burkholderiales, providing a valuable alternative to traditional PCR-based methods. The MSP library described in the manuscript is available for use.IMPORTANCE The Gram-negative proteobacterial order Burkholderiales has emerged as a promising source of novel natural products in recent years. This order includes the genus Burkholderia and the newly defined genera Caballeronia and Paraburkholderia However, development of this resource has been hampered by difficulties with rapid and selective isolation of Burkholderiales strains from the environment. Environmental metagenome sequencing has revealed that the potential for natural products is not evenly distributed throughout the microbial world. Thus, large but targeted microbial isolate libraries are needed to effectively explore the chemical potential of natural products. To study these organisms efficiently, methods to quickly identify isolates to the genus level are required. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is already used in clinical settings to reliably identify unknown bacterial pathogens. We have adapted similar methodology using the MALDI Biotyper instrument to rapidly identify environmental isolates of Burkholderia, Caballeronia, and Paraburkholderia for downstream natural product discovery.

The applicability of gene sequencing and MALDI-TOF to identify less common gram-negative rods (Advenella, Castellaniella, Kaistia, Pusillimonas and Sphingobacterium) from environmental isolates

Our aim was to identify less common non-fermenting gram-negative rods during the bioremediation process. Five genera were found: Advenella, Castellaniella, Kaistia, Pusillimonas and Sphingobacterium, for a total of 15 isolates. Therefore, we evaluated the applicability of four methods currently available for bacteria identification: (1) conventional biochemical methods, (2) the VITEK^®-2 system, (3) MALDI-TOF mass spectrometry and (4) 16S rRNA gene sequencing. The biochemical methods and the VITEK^®-2 system were reliable only for the Sphingobacterium isolate and solely at the genus level. Both MALDI-TOF mass spectrometry platforms (Bruker and VITEK^® MS) did not achieve reliable identification results for any of these genera. 16S rRNA gene sequencing identified eight isolates to the species level but not to the subspecies level, when applicable. The remaining seven isolates were reliably identified through 16S rRNA gene sequencing to the genus level only. Our findings suggest that the detection and identification of less common genera (and species) that appeared at certain moments during the bioremediation process can be a challenge to microbiologists considering the most used techniques. In addition, more studies are required to confirm our results.

Rapid dereplication of microbial isolates using matrix-assisted laser desorption ionization time-of-flight mass spectrometry: A mini-review

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MALDI-TOF MS is applicable as high-resolution and high-throughput tool.

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The classification and characterization of cultivable microorganisms is targeted.

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Advantageous are its simple sample preparation and short measurement time.

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It accelerates the dereplication of isolates from large-scale screening campaigns.

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Applications for studying microbial diversity and future trends are discussed.

Matrix-Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) has become one of the most popular methods for the rapid, cost-effective and accurate classification and characterization of cultivable microorganisms. Due to its simple sample preparation and short measurement time, MALDI-TOF MS is an excellent choice for the high-throughput study of microbial isolates from rhizospheres or plants grown under diverse environmental conditions. While clinical isolates have a higher identification rate than environmental isolates due to the focus of commercial mass spectral libraries on the former, no identification is necessary in the dereplication step of large environmental studies. The grouping of large sets of isolates according to their intact protein profiles can be performed without knowledge of their taxonomy. Thus, this method is easily applicable to environmental samples containing microorganisms from yet undescribed phylogenetic origins. The main strategies applied to achieve effective dereplication are, first, expanding existing mass spectral libraries and, second, using an additional statistical analysis step to group measured mass spectra and identify unique isolates. In this review, these aspects are addressed. It closes with a prospective view on how MALDI-TOF MS-based microbial characterisation can accelerate the exploitation of plant-associated microbiota.

Application of MALDI Biotyper System for Rapid Identification of Bacteria Isolated from a Fresh Produce Market

MALDI-TOF MS has revolutionized the identification of microorganisms and has become an indispensable part of routine diagnostics in the clinical microbiological laboratory. However, application of this technique in microbial surveillance outside of clinical settings is limited. In this study, we have evaluated the performance of a Bruker MALDI Biotyper System for the identification of bacteria isolated from the hand palms of fresh produce handlers and their surrounding environments in a wholesale fresh produce market in Doha, Qatar. The accuracy was verified against the results obtained by bacterial 16S rRNA gene sequencing. A total of 105 isolates were tested, of which 67 (64%) isolates were identified by MALDI-TOF MS and 101 isolates (96%) were identified by 16S rRNA gene sequencing, either at the genus level or species level. However, MALDI-TOF MS identified more isolates (41%) at the species level than 16S rRNA gene sequencing (28%). MALDI-TOF MS was particularly useful in the species level identification of Enterobacteriaceae. MALDI-TOF MS successfully identified most known human pathogens in a rapid and cost-effective manner but failed to identify a significant number of isolates that were of environmental origin, suggesting room for further expansion of the reference database.

Rapid and robust MALDI-TOF MS techniques for microbial identification: a brief overview of their diverse applications

in mass spectrometry have enabled the investigation of various biological systems by directly analyzing diverse sets of biomolecules (i.e., proteins, lipids, and carbohydrates), thus making a significant impact on the life sciences field. Over the past decade, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been widely utilized as a rapid and reliable method for the identification of microorganisms. MALDI-TOF MS has come into widespread use despite its relatively low resolving power (full width at half maximum, FWHM: < 5,000) and its incompatibility with tandem MS analysis, features with which other high-resolution mass spectrometers are equipped. Microbial identification is achieved by searching databases containing mass spectra of peptides and proteins extracted from microorganisms of interest, using scoring algorithms to match analyzed spectra with reference spectra. In this paper, we give a brief overview of the diverse applications of rapid and robust MALDI-TOF MS-based techniques for microbial identification in a variety of fields, such as clinical diagnosis and environmental and food monitoring. We also describe the fundamental principles of MALDI-TOF MS. The general specifications of the two major MS-based microbial identification systems available in the global market (BioTyper® and VITEK® MS Plus) and the distribution of these instruments in Republic of Korea are also discussed. The current review provides an understanding of this emerging microbial identification and classification technology and will help bacteriologists and cell biologists take advantage of this powerful technique.