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Hiller CX, Schwaller C, Wurzbacher C, Drewes JE. Removal of antibiotic microbial resistance by micro- and ultrafiltration of secondary wastewater effluents at pilot scale. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 838:156052. [PMID: 35598662 DOI: 10.1016/j.scitotenv.2022.156052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 05/04/2022] [Accepted: 05/15/2022] [Indexed: 05/09/2023]
Abstract
Low-pressure membrane filtration was investigated at pilot scale with regard to its removal of antimicrobial resistance genes (ARGs) in conventional secondary treated wastewater plant effluents. While operating microfiltration (MF) and ultrafiltration (UF) membranes, key operational parameters for antimicrobial resistance (AMR) studies and key factors influencing AMR removal efficiencies of low-pressure membrane filtration processes were examined. The main factor for AMR removal was the pore size of the membrane. The formation of the fouling layer on capillary membranes had only a small additive effect on intra- and extrachromosomal ARG removal and a significant additive effect on mobile ARG removal. Using feeds with different ARGs abundances revealed that higher ARG abundance in the feed resulted in higher ARG abundance in the filtrate. Live-Dead cell counting in UF filtrate showed intact bacteria breaking through the UF membrane. Strong correlations between 16S rRNA genes (as surrogate for bacteria quantification) and the sul1 gene in UF filtrate indicated ARBs likely breaking through UF membranes.
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Affiliation(s)
- Christian X Hiller
- Chair of Urban Water Systems Engineering, Technical University of Munich, Germany
| | - Christoph Schwaller
- Chair of Urban Water Systems Engineering, Technical University of Munich, Germany
| | - Christian Wurzbacher
- Chair of Urban Water Systems Engineering, Technical University of Munich, Germany
| | - Jörg E Drewes
- Chair of Urban Water Systems Engineering, Technical University of Munich, Germany.
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Furukawa T, Mekata T, Amarasiri M, Sei K. Concentration and reduction efficiency of vancomycin-resistant heterotrophic bacteria and vanA and vanB genes in each wastewater treatment unit processes. J Glob Antimicrob Resist 2022; 30:340-347. [PMID: 35830952 DOI: 10.1016/j.jgar.2022.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 06/20/2022] [Accepted: 07/05/2022] [Indexed: 10/17/2022] Open
Abstract
OBJECTIVES This study elucidated the distribution and fate of vancomycin (VCM)-resistant heterotrophic bacteria (HTB) and resistance genes, vanA and vanB, during each treatment unit process of a wastewater treatment plant (WWTP). METHODS Several bacterial counts as well as copy numbers of vanA and vanB genes were determined in each wastewater and sludge. In addition, HTB strains isolated from wastewater and sludge were analyzed for VCM susceptibility. Then, the fate and reduction ratios of each bacterial counts, copy numbers of vanA and vanB genes, and the existence ratio of VCM-resistant HTB strains in the wastewater treatment unit process were evaluated. RESULTS VCM-resistant HTB were detected in all wastewater and sludge samples, and their existence ratio decreased along the treatment (92.9% in influent wastewater to 39.4% in chlorinated water). Notably, most of the HTB isolated from the influent wastewater were resistant to 8.0 µg/mL of VCM, strongly suggesting that a significant amount of ARB is flowing into the WWTP from urban areas through the sewerage system. The vanA and vanB genes were also detected in all wastewater and sludge, with high copy numbers (102-104 copies/mL) even in chlorinated water samples. CONCLUSIONS The results revealed that residual VCM-resistant HTB, and resistance genes, which could not be completely removed, were ubiquitously released into the aquatic environment. Furthermore, a high existence ratio of VCM-resistant HTB and high copy numbers of resistance genes were also detected in the sludge, indicating that they are constantly circulating in the wastewater treatment system via the returned sludge.
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Affiliation(s)
- Takashi Furukawa
- Laboratory of Environmental Hygiene, Department of Health Science, School of Allied Health Sciences, Kitasato University, 1-15-1, Kitasato, Sagamihara-Minami, 252-0373, Japan.
| | - Tohru Mekata
- Department of Veterinary Medicine, Faculty of Veterinary Medicine, Okayama University of Science, 1-3 Ikoinooka, Imabari, Ehime 794-8555, Japan.
| | - Mohan Amarasiri
- Laboratory of Environmental Hygiene, Department of Health Science, School of Allied Health Sciences, Kitasato University, 1-15-1, Kitasato, Sagamihara-Minami, 252-0373, Japan.
| | - Kazunari Sei
- Laboratory of Environmental Hygiene, Department of Health Science, School of Allied Health Sciences, Kitasato University, 1-15-1, Kitasato, Sagamihara-Minami, 252-0373, Japan.
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Review of Antimicrobial Resistance in Wastewater in Japan: Current Challenges and Future Perspectives. Antibiotics (Basel) 2022; 11:antibiotics11070849. [PMID: 35884103 PMCID: PMC9312076 DOI: 10.3390/antibiotics11070849] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 06/14/2022] [Accepted: 06/22/2022] [Indexed: 12/18/2022] Open
Abstract
Antimicrobial resistance (AMR) circulates through humans, animals, and the environments, requiring a One Health approach. Recently, urban sewage has increasingly been suggested as a hotspot for AMR even in high-income countries (HICs), where the water sanitation and hygiene infrastructure are well-developed. To understand the current status of AMR in wastewater in a HIC, we reviewed the epidemiological studies on AMR in the sewage environment in Japan from the published literature. Our review showed that a wide variety of clinically important antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs), and antimicrobial residues are present in human wastewater in Japan. Their concentrations are lower than in low- and middle-income countries (LMICs) and are further reduced by sewage treatment plants (STPs) before discharge. Nevertheless, the remaining ARB and ARGs could be an important source of AMR contamination in river water. Furthermore, hospital effluence may be an important reservoir of clinically important ARB. The high concentration of antimicrobial agents commonly prescribed in Japan may contribute to the selection and dissemination of AMR within wastewater. Our review shows the importance of both monitoring for AMR and antimicrobials in human wastewater and efforts to reduce their contamination load in wastewater.
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Furukawa T, Ueno T, Matsumura M, Amarasiri M, Sei K. Inactivation of antibiotic resistant bacteria and their resistance genes in sewage by applying pulsed electric fields. JOURNAL OF HAZARDOUS MATERIALS 2022; 424:127382. [PMID: 34879573 DOI: 10.1016/j.jhazmat.2021.127382] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 08/23/2021] [Accepted: 09/27/2021] [Indexed: 06/13/2023]
Abstract
We evaluated the suitability of pulsed electric field (PEF) technology as a new disinfection option in the sewage treatment plants (STPs) that can inactivate antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). It was shown that PEF applied disinfection could inactivate not only vancomycin-resistant enterococci (VRE), but also vanA resistance gene. Cultivable VRE could be effectively inactivated by PEF applied disinfection, and were reduced to below the detection limit (log reduction value of VRE > 5 log). Although the vanA also showed a reduction of more than 4 log, it remained in the order of 105 copies/mL, suggesting that ARGs are more difficult to be inactivated than ARB in PEF applied disinfection. Among parameters in each applying condition verified in this study, the initial voltage was found to be the most important for inactivation of ARB and ARGs. Furthermore, frequency was a parameter that affects the increase or decrease of the duration time, and it was suggested that the treatment time could be shortened by increasing the frequency. Our results strongly suggested that PEF applied disinfection may be a new disinfection technology option for STPs that contributes to the control of ARB and ARGs contamination in the aquatic environments.
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Affiliation(s)
- Takashi Furukawa
- Laboratory of Environmental Hygiene, Department of Health Science, School of Allied Health Sciences, Kitasato University, 1-15-1, Kitasato, Sagamihara, Minami 252-0373, Japan.
| | - Takahisa Ueno
- Department of Electrical and Electronic Engineering, National Institute of Technology, Oita College, 1666 Maki, Oita 870-0152, Japan
| | - Mina Matsumura
- Laboratory of Environmental Hygiene, Department of Health Science, School of Allied Health Sciences, Kitasato University, 1-15-1, Kitasato, Sagamihara, Minami 252-0373, Japan
| | - Mohan Amarasiri
- Laboratory of Environmental Hygiene, Department of Health Science, School of Allied Health Sciences, Kitasato University, 1-15-1, Kitasato, Sagamihara, Minami 252-0373, Japan
| | - Kazunari Sei
- Laboratory of Environmental Hygiene, Department of Health Science, School of Allied Health Sciences, Kitasato University, 1-15-1, Kitasato, Sagamihara, Minami 252-0373, Japan
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Silva V, Caniça M, Capelo JL, Igrejas G, Poeta P. Diversity and genetic lineages of environmental staphylococci: a surface water overview. FEMS Microbiol Ecol 2021; 96:5909032. [PMID: 32949464 DOI: 10.1093/femsec/fiaa191] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 09/17/2020] [Indexed: 12/11/2022] Open
Abstract
Antimicrobial resistance in the environmental dimension is one of the greatest challenges and emerging threats. The presence of resistant bacteria and resistance genes in the environment, especially in aquatic systems, has been a matter of growing concern in the past decade. Monitoring the presence of antimicrobial resistance species, in this particular case, Staphylococcus spp., in natural water environments could lead to a better understanding of the epidemiology of staphylococci infections. Thus, the investigation of natural waters as a potential reservoir and vehicle for transmission of these bacteria is imperative. Only a few studies have investigated the prevalence, antimicrobial resistance and genetic lineages of staphylococci in natural waters. Those studies reported a high diversity of staphylococci species and lineages in surface waters. Methicillin-resistant S. aureus were relatively prevalent in surface waters and, as expected, often presented a multidrug-resistant profile. There was a high diversity of S. aureus lineages in surface waters. The presence of S. aureus CC8 and CC5 suggests a human origin. Among the coagulase-negative staphylococci, the most frequently found in natural waters was S. warneri and S. epidermidis. These studies are extremely important to estimate the contribution of the aquatic environment in the spread of pathogenic bacteria.
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Affiliation(s)
- Vanessa Silva
- Microbiology and Antibiotic Resistance Team (MicroART), Department of Veterinary Sciences, University of Trás-os-Montes and Alto Douro (UTAD), 5001-801 Vila Real, Portugal
- Department of Genetics and Biotechnology, Functional Genomics and Proteomics Unit, University of Trás-os-Montes and Alto Douro, 5001-801 Vila Real, Portugal
- Functional Genomics and Proteomics Unit, University of Trás-os-Montes and Alto Douro (UTAD), 5001-801 Vila Real, Portugal
- Associated Laboratory for Green Chemistry (LAQV-REQUIMTE), NOVA University of Lisbon, Lisboa, 2829-516 Caparica, Portugal
| | - Manuela Caniça
- National Reference Laboratory of Antibiotic Resistances and Healthcare Associated Infections (NRL-AMR/HAI), Department of Infectious Diseases, National Institute of Health Dr Ricardo Jorge, Av. Padre Cruz, 1649-016 Lisbon, Portugal
- Centre for the Studies of Animal Science, Institute of Agrarian and Agri-Food Sciences and Technologies, Oporto University, 4051-401 Oporto, Portugal
| | - José L Capelo
- BIOSCOPE Group, LAQV-REQUIMTE, Department of Chemistry, Faculty of Science and Technology, NOVA University of Lisbon, 2825-466 Almada, Portugal
- Proteomass Scientific Society, 2825-466 Costa de Caparica, Portugal
| | - Gilberto Igrejas
- Department of Genetics and Biotechnology, Functional Genomics and Proteomics Unit, University of Trás-os-Montes and Alto Douro, 5001-801 Vila Real, Portugal
- Functional Genomics and Proteomics Unit, University of Trás-os-Montes and Alto Douro (UTAD), 5001-801 Vila Real, Portugal
- Associated Laboratory for Green Chemistry (LAQV-REQUIMTE), NOVA University of Lisbon, Lisboa, 2829-516 Caparica, Portugal
| | - Patrícia Poeta
- Microbiology and Antibiotic Resistance Team (MicroART), Department of Veterinary Sciences, University of Trás-os-Montes and Alto Douro (UTAD), 5001-801 Vila Real, Portugal
- Associated Laboratory for Green Chemistry (LAQV-REQUIMTE), NOVA University of Lisbon, Lisboa, 2829-516 Caparica, Portugal
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Makowska N, Bresa K, Koczura R, Philips A, Nowis K, Mokracka J. Urban wastewater as a conduit for pathogenic Gram-positive bacteria and genes encoding resistance to β-lactams and glycopeptides. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 765:144176. [PMID: 33385807 DOI: 10.1016/j.scitotenv.2020.144176] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 11/19/2020] [Accepted: 11/23/2020] [Indexed: 06/12/2023]
Abstract
The emergence and spread of clinical pathogens, antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment pose a direct threat to human and animal health worldwide. In this study, we analyzed qualitatively and quantitatively urban sewage resistome for the occurrence of genes encoding resistance to β-lactams and glycopeptides in the genomes of culturable bacteria, as well as in the wastewater metagenome of the Central Wastewater Treatment Plant in Koziegłowy (Poland). Moreover, we estimated the presence of pathogenic Gram-positive bacteria in wastewater based on analysis of species-specific virulence genes in the wastewater metagenome. The results show that the final effluent contains alarm pathogens with particularly dangerous mechanisms of antibiotic resistance, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). We also noticed that during the wastewater treatment, there is an increase in the frequency of MRSA and VRE. Furthermore, the results prove the effective removal of vanA, but at the same time show that wastewater treatment increases the relative abundance of mecA and virulence genes (groES and sec), indicating the presence of clinical pathogens E. faecalis and S. aureus in the effluent released to surface waters. We also observed an increase in the relative abundance of mecA and vanA genes already in the aeration tank, which suggests accumulation of contaminants affecting enhanced selection and HGT processes in the activated sludge. Moreover, we found a relation between the taxonomic composition and the copy number of ARGs as well as the presence of pathogens at various stages of wastewater treatment. The presence of clinically relevant pathogens, ARB, including multi-resistant bacteria, and ARGs in the effluent indicates that wastewater treatment plant play a key role in the existence of pathogens and antimicrobial resistance spreading pathway in the environment and human communities, which is a direct threat to public health and environmental protection.
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Affiliation(s)
- Nicoletta Makowska
- Department of Microbiology, Faculty of Biology, Adam Mickiewicz University in Poznań, Poznań, Poland; Department of Molecular Genetics, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznań, Poland
| | - Katarzyna Bresa
- Department of Microbiology, Faculty of Biology, Adam Mickiewicz University in Poznań, Poznań, Poland
| | - Ryszard Koczura
- Department of Microbiology, Faculty of Biology, Adam Mickiewicz University in Poznań, Poznań, Poland
| | - Anna Philips
- European Center for Bioinformatics and Genomics, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznań, Poland
| | - Katarzyna Nowis
- European Center for Bioinformatics and Genomics, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznań, Poland
| | - Joanna Mokracka
- Department of Microbiology, Faculty of Biology, Adam Mickiewicz University in Poznań, Poznań, Poland.
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Basode VK, Abdulhaq A, Alamoudi MUA, Tohari HM, Quhal WA, Madkhali AM, Hobani YH, Hershan AA. Prevalence of a carbapenem-resistance gene (KPC), vancomycin-resistance genes (van A/B) and a methicillin-resistance gene (mecA) in hospital and municipal sewage in a southwestern province of Saudi Arabia. BMC Res Notes 2018; 11:30. [PMID: 29335025 PMCID: PMC5769418 DOI: 10.1186/s13104-018-3167-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2017] [Accepted: 01/12/2018] [Indexed: 11/10/2022] Open
Abstract
Objective According to the World Health Organization, the increasing antibiotic resistance of pathogens is one of the most important threats to human health. Prevalence of a carbapenem-resistance gene (KPC), vancomycin-resistance genes (van A/B) and a methicillin-resistance gene (mecA) in hospital and municipal sewages will be potential threat to public health. Results Vancomycin-resistance genes were detected in the sewage of community tank-II, sewage tank of the tertiary and general hospital. Carbapenem-resistance gene was detected in sewage of community tank-II and sewage from tertiary hospital. Methicillin-resistance gene was detected in sewage of community tank-II, sewage from a fish market sewage tank and sewage from an animal slaughter house sewage tank. The detection of a KPC, van A/B and a mecA in sewages will help further the process to take the appropriate measures to prevent the spread of such bacteria in the environment.
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Affiliation(s)
- Vinod Kumar Basode
- Unit of Medical Microbiology, Department of Medical Lab Technology, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia.
| | - Ahmed Abdulhaq
- Unit of Medical Microbiology, Department of Medical Lab Technology, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia.,Deanship of Scientific Affairs and Research, Jazan University, Jazan, Saudi Arabia
| | - Mohammed Uthman A Alamoudi
- Unit of Medical Microbiology, Department of Medical Lab Technology, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia
| | - Hassan Mohammad Tohari
- Unit of Medical Microbiology, Department of Medical Lab Technology, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia
| | - Waleed Ali Quhal
- Unit of Medical Microbiology, Department of Medical Lab Technology, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia
| | - Aymen Mohammed Madkhali
- Unit of Medical Microbiology, Department of Medical Lab Technology, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia
| | - Yahya Hasan Hobani
- Unit of Medical Molecular Biology and Genetics, Department of Medical Lab Technology, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia
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Inactivation Effect of Antibiotic-Resistant Gene Using Chlorine Disinfection. WATER 2017. [DOI: 10.3390/w9070547] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Vancomycin-Resistant Enterococci and Bacterial Community Structure following a Sewage Spill into an Aquatic Environment. Appl Environ Microbiol 2016; 82:5653-60. [PMID: 27422829 DOI: 10.1128/aem.01927-16] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 07/05/2016] [Indexed: 12/22/2022] Open
Abstract
UNLABELLED Sewage spills can release antibiotic-resistant bacteria into surface waters, contributing to environmental reservoirs and potentially impacting human health. Vancomycin-resistant enterococci (VRE) are nosocomial pathogens that have been detected in environmental habitats, including soil, water, and beach sands, as well as wildlife feces. However, VRE harboring vanA genes that confer high-level resistance have infrequently been found outside clinical settings in the United States. This study found culturable Enterococcus faecium harboring the vanA gene in water and sediment for up to 3 days after a sewage spill, and the quantitative PCR (qPCR) signal for vanA persisted for an additional week. Culturable levels of enterococci in water exceeded recreational water guidelines for 2 weeks following the spill, declining about five orders of magnitude in sediments and two orders of magnitude in the water column over 6 weeks. Analysis of bacterial taxa via 16S rRNA gene sequencing showed changes in community structure through time following the sewage spill in sediment and water. The spread of opportunistic pathogens harboring high-level vancomycin resistance genes beyond hospitals and into the broader community and associated habitats is a potential threat to public health, requiring further studies that examine the persistence, occurrence, and survival of VRE in different environmental matrices. IMPORTANCE Vancomycin-resistant enterococci (VRE) are harmful bacteria that are resistant to the powerful antibiotic vancomycin, which is used as a last resort against many infections. This study followed the release of VRE in a major sewage spill and their persistence over time. Such events can act as a means of spreading vancomycin-resistant bacteria in the environment, which can eventually impact human health.
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Dinarelli S, Girasole M, Kasas S, Longo G. Nanotools and molecular techniques to rapidly identify and fight bacterial infections. J Microbiol Methods 2016; 138:72-81. [PMID: 26806415 DOI: 10.1016/j.mimet.2016.01.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 01/13/2016] [Accepted: 01/13/2016] [Indexed: 12/22/2022]
Abstract
Reducing the emergence and spread of antibiotic-resistant bacteria is one of the major healthcare issues of our century. In addition to the increased mortality, infections caused by multi-resistant bacteria drastically enhance the healthcare costs, mainly because of the longer duration of illness and treatment. While in the last 20years, bacterial identification has been revolutionized by the introduction of new molecular techniques, the current phenotypic techniques to determine the susceptibilities of common Gram-positive and Gram-negative bacteria require at least two days from collection of clinical samples. Therefore, there is an urgent need for the development of new technologies to determine rapidly drug susceptibility in bacteria and to achieve faster diagnoses. These techniques would also lead to a better understanding of the mechanisms that lead to the insurgence of the resistance, greatly helping the quest for new antibacterial systems and drugs. In this review, we describe some of the tools most currently used in clinical and microbiological research to study bacteria and to address the challenge of infections. We discuss the most interesting advancements in the molecular susceptibility testing systems, with a particular focus on the many applications of the MALDI-TOF MS system. In the field of the phenotypic characterization protocols, we detail some of the most promising semi-automated commercial systems and we focus on some emerging developments in the field of nanomechanical sensors, which constitute a step towards the development of rapid and affordable point-of-care testing devices and techniques. While there is still no innovative technique that is capable of completely substituting for the conventional protocols and clinical practices, many exciting new experimental setups and tools could constitute the basis of the standard testing package of future microbiological tests.
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Affiliation(s)
- S Dinarelli
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Rome, Italy
| | - M Girasole
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Rome, Italy
| | - S Kasas
- Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Physique de la Matière Vivante, Lausanne, Switzerland; Département des Neurosciences Fondamentales, Université de Lausanne, Lausanne, Switzerland
| | - G Longo
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Rome, Italy.
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