Candidate biomarkers of antibiotic resistance for the monitoring of wastewater and the downstream environment

Urban wastewater treatment plants (UWTPs) are essential for reducing the pollutants load and protecting water bodies. However, wastewater catchment areas and UWTPs emit continuously antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs), with recognized impacts on the downstream environments. Recently, the European Commission recommended to monitor antibiotic resistance in UWTPs serving more than 100 000 population equivalents. Antibiotic resistance monitoring in environmental samples can be challenging. The expected complexity of these systems can jeopardize the interpretation capacity regarding, for instance, wastewater treatment efficiency, impacts of environmental contamination, or risks due to human exposure. Simplified monitoring frameworks will be essential for the successful implementation of analytical procedures, data analysis, and data sharing. This study aimed to test a set of biomarkers representative of ARG contamination, selected based on their frequent human association and, simultaneously, rare presence in pristine environments. In addition to the 16S rRNA gene, ten potential biomarkers (intI1, sul1, ermB, ermF, aph(3'')-Ib, qacEΔ1, uidA, mefC, tetX, and crAssphage) were monitored in DNA extracts (n = 116) from raw wastewater, activated sludge, treated wastewater, and surface water (upstream and downstream of UWTPs) samples collected in the Czech Republic, Denmark, Israel, the Netherlands, and Portugal. Each biomarker was sensitive enough to measure decreases (on average by up to 2.5 log-units gene copy/mL) from raw wastewater to surface water, with variations in the same order of magnitude as for the 16S rRNA gene. The use of the 10 biomarkers allowed the typing of water samples whose origin or quality could be predicted in a blind test. The results show that, based on appropriate biomarkers, qPCR can be used for a cost-effective and technically accessible approach to monitoring wastewater and the downstream environment.

Survival of clinical and environmental carbapenem-resistant Klebsiella pneumoniae ST147 in surface water

Carbapenem-resistant Klebsiella pneumoniae represents a healthcare threat, already disseminated in the environment. This study aimed to compare the behaviour of a clinical and an environmental K. pneumoniae strain (multilocus sequence type ST147) harbouring the gene blaKPC-3 in water. The abundance of the genes phoE (specific for K. pneumoniae) and blaKPC-3 was monitored by quantitative PCR in urban runoff water and sterile ultra-pure water microcosms, aiming to assess survival, blaKPC-3 persistence, and the effect of the native water microbiota. In sterile ultra-pure water, the abundance of cultivable K. pneumoniae and blaKPC-3 gene did not change over the incubation period (8 days). In contrast, in urban runoff, the K. pneumoniae and the genes phoE and blaKPC genes decreased by up to 3 log-units. These results suggest that K. pneumoniae were outcompeted by the native microbiota of the urban runoff water and that the decay of blaKPC-3 gene was due to host death, rather than to gene loss. The study highlights that although native microbiota is essential to hamper the persistence of non-native bacteria, carbapenemase producing K. pneumoniae can survive in urban runoff water for at least one week.

Microbiome and Resistome Profiles along a Sewage-Effluent-Reservoir Trajectory Underline the Role of Natural Attenuation in Wastewater Stabilization Reservoirs

Antibiotic-resistant bacteria and antibiotic resistance gene (ARGs) loads dissipate through sewage treatment plants to receiving aquatic environments, but the mechanisms that mitigate the spread of these ARGs are not well understood due to the complexity of full-scale systems and the difficulty of source tracking in downstream environments. To overcome this problem, we targeted a controlled experimental system comprising a semicommercial membrane-aerated bioreactor (MABR), whose effluents fed a 4,500-L polypropylene basin that mimicked effluent stabilization reservoirs and receiving aquatic ecosystems. We analyzed a large set of physicochemical measurements, concomitant with the cultivation of total and cefotaxime-resistant Escherichia coli, microbial community analyses, and quantitative PCR (qPCR)/digital droplet PCR (ddPCR) quantification of selected ARGs and mobile genetic elements (MGEs). The MABR removed most of the sewage-derived organic carbon and nitrogen, and simultaneously, E. coli, ARG, and MGE levels dropped by approximately 1.5- and 1.0-log unit mL-1, respectively. Similar levels of E. coli, ARGs, and MGEs were removed in the reservoir, but interestingly, unlike in the MABR, the relative abundance (normalized to 16S rRNA gene-inferred total bacterial abundance) of these genes also decreased. Microbial community analyses revealed the substantial shifts in bacterial and eukaryotic community composition in the reservoir relative to the MABR. Collectively, our observations lead us to conclude that the removal of ARGs in the MABR is mainly a consequence of treatment-facilitated biomass removal, whereas in the stabilization reservoir, mitigation is linked to natural attenuation associated with ecosystem functioning, which includes abiotic parameters, and the development of native microbiomes that prevent the establishment of wastewater-derived bacteria and associated ARGs. IMPORTANCE Wastewater treatment plants are sources of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs), which can contaminate receiving aquatic environments and contribute to antibiotic resistance. We focused on a controlled experimental system comprising a semicommercial membrane-aerated bioreactor (MABR) that treated raw sewage, whose effluents fed a 4,500-L polypropylene basin that mimicked effluent stabilization reservoirs. We evaluated ARB and ARG dynamics across the raw-sewage-MABR-effluent trajectory, concomitant with evaluation of microbial community composition and physicochemical parameters, in an attempt to identify mechanisms associated with ARB and ARG dissipation. We found that removal of ARB and ARGs in the MABR was primarily associated with bacterial death or sludge removal, whereas in the reservoir it was attributed to the inability of ARBs and associated ARGs to colonize the reservoir due to a dynamic and persistent microbial community. The study demonstrates the importance of ecosystem functioning in removing microbial contaminants from wastewater.

Insight into phylogenomic bias of blaVIM-2 or blaNDM-1 dissemination amongst carbapenem-resistant Pseudomonas aeruginosa

OBJECTIVES

Pseudomonas aeruginosa (P. aeruginosa) are ubiquitous opportunistic pathogens that combine intrinsic and acquired multidrug resistance phenotypes. Due to different types of acquired genes, carbapenem resistance has been expanding in this species. This study hypothesised that the spread of carbapenem resistance among P. aeruginosa is influenced by phylogenomic features, being distinct for different genes.

METHODS

To test this hypothesis, the genomes of P. aeruginosa harbouring blaVIM-2 or blaNDM-1 genes were compared. The blaVIM-2 gene was selected because, although frequent, it is almost restricted to this species and blaNDM-1 gene due to its wide interspecies distribution. A group of genomes harbouring the genes blaVIM-2 (n = 116) or blaNDM-1 (n = 27), available in GenBank, was characterised based on core phylogenomic analysis, functional categories in the accessory genome and mobile genetic elements flanking the selected genes.

RESULTS

Most blaVIM-2 gene hosts belonged to multilocus sequence types (ST) ST111 (n = 32 of 116) and ST233 (n = 27 of 116) and were reported in Europe (n = 75 of 116). The blaNDM-1 gene hosts were distributed by different STs (ST38, ST773, ST235, ST357 and ST654), frequently from Asia (n = 11 of 27). Significant differences in the prevalence of functional protein/enzyme annotations per number of accessory genomes were observed between blaVIM-2+ and blaNDM-1+. The blaVIM-2 gene was frequently inserted in the Tn402-like and Tn21 transposons family and rarely in IS6100, while blaNDM-1 gene was preferentially flanked by ISAba125 and bleMBL genes or associated with IS91 insertion sequence.

CONCLUSION

The hypothesis that carbapenem resistance gene acquisition is not random among phylogenomic lineages was confirmed, suggesting the importance of phylogeny in the dissemination of antibiotic resistance genes.

Dissemination of Metallo-β-Lactamase-Producing Pseudomonas aeruginosa in Serbian Hospital Settings: Expansion of ST235 and ST654 Clones

This nationwide study aimed to investigate the molecular characteristics of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa in Serbia, underlying resistance mechanisms, the genetic context of detected MBL genes, and the clonal relationship between isolates harboring genes-encoding MBL. Overall, 320/5334 isolates collected from 2018 to 2021 were identified as P. aeruginosa. Carbapenem-resistant P. aeruginosa (CRPA) were screened for the presence of bla_VIM, bla_IMP, and bla_NDM, genes whereas MBL-positive isolates were tested for the presence of the bla_CTX-M-2, bla_PER, bla_TEM, bla_SHV, bla_VEB, and bla_GES. Multilocus sequence typing and phylogenomic analysis were performed for P. aeruginosa-producing MBL. The majority of the P. aeruginosa isolates were recovered from the lower respiratory tract (n = 120; 37.5%) and wound specimens (n = 108; 33.75%). CRPA isolates accounted for 43.1% (n = 138) of the tested isolates, 31 out of them being bla_NDM-1-positive (22.5%). The colistin resistance rate was 0.3%. MLST analysis revealed the occurrence of ST235 (n = 25) and ST654 (n = 6), mostly confined to Serbia. The distribution of beta-lactamase-encoding genes in these isolates suggested clonal dissemination and possible recombination: ST235/bla_NDM-1, ST235/bla_NDM-1/bla_PER-1, ST654/bla_NDM-1, ST654/bla_NDM-1/bla_PER-1, and ST654/bla_NDM-1/bla_GES-5. High-risk clones ST235 and ST654 identified for the first time in Serbia, are important vectors of acquired MBL and ESBL and their associated multidrug resistance phenotypes represent a cause for considerable concern.

In silico prediction of the enzymes involved in the degradation of the herbicide molinate by Gulosibacter molinativorax ON4T

Gulosibacter molinativorax ON4^T is the only known organism to produce molinate hydrolase (MolA), which catalyses the breakdown of the thiocarbamate herbicide into azepane-1-carboxylic acid (ACA) and ethanethiol. A combined genomic and transcriptomic strategy was used to fully characterize the strain ON4^T genome, particularly the molA genetic environment, to identify the potential genes encoding ACA degradation enzymes. Genomic data revealed that molA is the only catabolic gene of a novel composite transposon (Tn6311), located in a novel low copy number plasmid (pARLON1) harbouring a putative T4SS of the class FATA. pARLON1 had an ANI value of 88.2% with contig 18 from Agrococcus casei LMG 22410^T draft genome. Such results suggest that pARLON1 is related to genomic elements of other Actinobacteria, although Tn6311 was observed only in strain ON4^T. Furthermore, genomic and transcriptomic data demonstrated that the genes involved in ACA degradation are chromosomal. Based on their overexpression when growing in the presence of molinate, the enzymes potentially involved in the heterocyclic ring breakdown were predicted. Among these, the activity of a protein related to caprolactone hydrolase was demonstrated using heterologous expression. However, further studies are needed to confirm the role of the other putative enzymes.

Quality Control of Drinking Water in the City of Ilave, Region of Puno, Peru

The region of Puno, in Peru, is described as a region with some health conditions that may be associated with the water quality, such as a high index of anemia or cases of acute diarrhea in children. This study aimed at monitoring the drinking water quality of the city of Ilave, in Peru, and determining possible correlations between physical-chemical and microbiological parameters, and the water distribution conditions, such as the period of water availability. Physical-chemical parameters (turbidity, residual chlorine, temperature, conductivity, and pH), microbiological parameters (presence of coliforms), and heavy metals (Zn, Mn, Ni, Fe, and Cu) were determined. All the parameters quantified were within the maximum permissible limits according to Peruvian regulations, except for residual chlorine, which was, for all the treated water samples, below the recommended value of 0.5 mg/L. Coliforms that should be absent from drinking water were detected in all the household samples. These results demonstrate the need for the inclusion of additional steps of re-chlorination along the distribution system to guarantee the maintenance of residual levels of chlorine that assure the microbiological quality of water. The quality of the drinking water was not observed to correlate with the period of water availability.

Monitoring antibiotic resistance genes in wastewater environments: The challenges of filling a gap in the One-Health cycle

Antibiotic resistance (AR) is a global problem requiring international cooperation and coordinated action. Global monitoring must rely on methods available and comparable across nations to quantify AR occurrence and identify sources and reservoirs, as well as paths of AR dissemination. Numerous analytical tools that are gaining relevance in microbiology, have the potential to be applied to AR research. This review summarizes the state of the art of AR monitoring methods, considering distinct needs, objectives and available resources. Based on the overview of distinct approaches that are used or can be adapted to monitor AR, it is discussed the potential to establish reliable and useful monitoring schemes that can be implemented in distinct contexts. This discussion places the environmental monitoring within the One-Health approach, where two types of risk, dissemination across distinct environmental compartments, and transmission to humans, must be considered. The plethora of methodological approaches to monitor AR and the variable features of the monitored sites challenge the capacity of the scientific community and policy makers to reach a common understanding. However, the dialogue between different methods and the production of action-oriented data is a priority. The review aims to warm up this discussion.

The risk of transmitting antibiotic resistance through endophytic bacteria

Antibiotic resistance is a global human health threat distributed across humans, animals, plants, and the environment. Under the One-Health concept (humans, animals, and environment), the contamination of water bodies and soil by antibiotic-resistant bacteria cannot be dissociated from its potential transmission to humans. Edible plants can be colonized by a vast diversity of bacteria, representing an important link between the environment and humans in the One-Health triad. Based on multiple examples of bacterial groups that comprise endophytes reported in edible plants, and that have close phylogenetic proximity with human opportunistic pathogens, we argue that plants exposed to human-derived biological contamination may represent a path of transmission of antibiotic resistance to humans.

Effect of copper and zinc as sulfate or nitrate salts on soil microbiome dynamics and blaVIM-positive Pseudomonas aeruginosa survival

The exposure of soil to metals and to antibiotic resistant bacteria may lead to the progressive deterioration of soil quality. The persistence of antibiotic resistant bacteria or antibiotic resistance genes in soil can be influenced by the microbial community or by soil amendments with metal salts. This work assessed the effect of soil amendment with copper and zinc, as sulfate or nitrate salts, on the fate of a carbapenem-resistant (bla_VIM⁺) hospital effluent isolate of Pseudomonas aeruginosa (strain H1FC49) and on the variations of the microbial community composition. Microcosms with soil aged or not with copper and zinc salts (20 mM), and inoculated with P. aeruginosa H1FC49 were monitored at 0, 7, 14 and/or 30 days, for community composition (16S rRNA gene amplicon) and strain H1FC49 persistence. Data on culturable P. aeruginosa, quantitative PCR of the housekeeping gene ecf, and the presumably acquired genes bla_VIM⁺ and integrase (intI1), and community composition were interpreted based on descriptive statistics and multivariate analysis. P. aeruginosa and the presumably acquired genes, were quantifiable in soil for up to one month, in both metal-amended and non-amended soil. Metal amendments were associated with a significant decrease of bacterial community diversity and richness. The persistence of P. aeruginosa and acquired genes in soils, combined with the adverse effect of metals on the bacterial community, highlight the vulnerability of soil to both types of exogenous contamination.

Evolution of gentamicin and arsenite resistance acquisition in Ralstonia pickettii water isolates

Ralstonia pickettii are ubiquitous in water environments. Members of this species are frequently, but not always, resistant to both gentamicin and arsenite. Gentamicin and arsenite co-resistance and the putative molecular mechanisms were investigated. A group of 37 R. pickettii strains isolated from drinking water and hospital wastewater were characterized for gentamicin and arsenite resistance phenotypes, the number and size of plasmids, and screened for genetic elements associated with arsenite tolerance, Integrative and Conjugative Elements (ICEs), among other. The genomes of three representative strains were compared. Most gentamicin resistant (GR) isolates (32/33) were resistant to arsenite, and harbored ICE- and ars operon-related genes. These genetic elements were not detected in any of the five arsenite susceptible strains, regardless of the GR (n = 1) or gentamicin susceptibility (GS) (n = 4) phenotype. The comparison of the genomes of two GR (one resistant and one susceptible to arsenite) and one GS strains suggested that these phenotypes correspond to three phylogroups, distinguished by presence of some genes only in GR isolates, in addition to point mutations in functional genes. The presence of ICEs and ars operon-related genes suggest that arsenite resistance might have been acquired by GR lineages.

Antibiotic residues in final effluents of European wastewater treatment plants and their impact on the aquatic environment

A comprehensive monitoring of a broad set of antibiotics in the final effluent of wastewater treatment plants (WWTPs) of 7 European countries (Portugal, Spain, Ireland, Cyprus, Germany, Finland, and Norway) was carried out in two consecutive years (2015 and 2016). This is the first study of this kind performed at an international level. Within the 53 antibiotics monitored 17 were detected at least once in the final effluent of the WWTPs, i.e.: ciprofloxacin, ofloxacin, enrofloxacin, orbifloxacin, azithromycin, clarithromycin, sulfapyridine, sulfamethoxazole, trimethoprim, nalidixic acid, pipemidic acid, oxolinic acid, cefalexin, clindamycin, metronidazole, ampicillin, and tetracycline. The countries exhibiting the highest effluent average concentrations of antibiotics were Ireland and the southern countries Portugal and Spain, whereas the northern countries (Norway, Finland and Germany) and Cyprus exhibited lower total concentration. The antibiotic occurrence data in the final effluents were used for the assessment of their impact on the aquatic environment. Both, environmental predicted no effect concentration (PNEC-ENVs) and the PNECs based on minimal inhibitory concentrations (PNEC-MICs) were considered for the evaluation of the impact on microbial communities in aquatic systems and on the evolution of antibiotic resistance, respectively. Based on this analysis, three compounds, ciprofloxacin, azithromycin and cefalexin are proposed as markers of antibiotic pollution, as they could occasionally pose a risk to the environment. Integrated studies like this are crucial to map the impact of antibiotic pollution and to provide the basis for designing water quality and environmental risk in regular water monitoring programs.

Persistence of wastewater antibiotic resistant bacteria and their genes in human fecal material

Domestic wastewater is a recognized source of antibiotic resistant bacteria and antibiotic resistance genes (ARB&ARGs), whose risk of transmission to humans cannot be ignored. The fitness of wastewater ARB in the complex fecal microbiota of a healthy human was investigated in feces-based microcosm assays (FMAs). FMAs were inoculated with two wastewater isolates, Escherichia coli strain A2FCC14 (MLST ST131) and Enterococcus faecium strain H1EV10 (MLST ST78), harboring the ARGs blaTEM, blaCTX, blaOXA-A and vanA, respectively. The FMAs, incubated in the presence or absence of oxygen or in the presence or absence of the antibiotics cefotaxime or vancomycin, were monitored based on cultivation, ARGs quantification and bacterial community analysis. The fecal bacterial community was dominated by members of the phyla Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria and Verrucomicrobia. The ARGs harbored by the wastewater isolates could be quantified after one week, in FMAs incubated under both aerobic and anaerobic conditions. These observations were not significantly different in FMAs incubated anaerobically, supplemented with sub-inhibitory concentrations of cefotaxime or vancomycin. The observation that ARGs of wastewater ARB persisted in presence of the human fecal microbiota for at least one week supports the hypothesis of a potential transmission to humans, a topic that deserves further investigation.

Betaproteobacteria are predominant in drinking water: are there reasons for concern?

Betaproteobacteria include some of the most abundant and ubiquitous bacterial genera that can be found in drinking water, including mineral water. The combination of physiology and ecology traits place some Betaproteobacteria in the list of potential, yet sometimes neglected, opportunistic pathogens that can be transmitted by water or aqueous solutions. Indeed, some drinking water Betaproteobacteria with intrinsic and sometimes acquired antibiotic resistance, harbouring virulence factors and often found in biofilm structures, can persist after water disinfection and reach the consumer. This literature review summarises and discusses the current knowledge about the occurrence and implications of Betaproteobacteria in drinking water. Although the sparse knowledge on the ecology and physiology of Betaproteobacteria thriving in tap or bottled natural mineral/spring drinking water (DW) is an evidence of this review, it is demonstrated that DW holds a high diversity of Betaproteobacteria, whose presence may not be innocuous. Frequently belonging to genera also found in humans, DW Betaproteobacteria are ubiquitous in different habitats, have the potential to resist antibiotics either due to intrinsic or acquired mechanisms, and hold different virulence factors. The combination of these factors places DW Betaproteobacteria in the list of candidates of emerging opportunistic pathogens. Improved bacterial identification of clinical isolates associated with opportunistic infections and additional genomic and physiological studies may contribute to elucidate the potential impact of these bacteria.

Neighbor urban wastewater treatment plants display distinct profiles of bacterial community and antibiotic resistance genes

Urban wastewater treatment plants (UWTPs) are among the major recipients of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs), and antibiotic residues in urban environments. Although during treatment, bacteria of human and animal origin are removed, some are able to survive, persisting in the final effluent. The occurrence of these bacteria, especially those harboring ARGs, may have a direct impact on the quality of the treated wastewater that is returned to the environment. In this study, we aimed to assess if the final effluent bacterial communities of three UWTPs (PT1, PT2, and PT3) located next to each other were distinct and if such differences were related with the antibiotic resistance profiles.It was observed that the bacterial community (16S rRNA gene Illumina sequencing) and load of selected ARGs of final effluent differed among the three UWTPs, irrespective of sampling time. Members of the families Aeromonadaceae, Campylobacteraceae, Veillonellaceae, [Weeksellaceae], and Porphyromonadaceae were observed to be positively correlated with some ARGs (bla_CTX-M, bla_OXA-A, bla_SHV) and intI1 (p < 0.05), while Intrasporangiaceae were observed to be negatively correlated. While Aeromonadaceae are recognized relevant ARG harbors, the other bacterial families may represent bacteria that co-exist with the ARG hosts, which may belong to minor bacterial groups omitted in the analyses. These findings suggest the importance of bacterial dynamics during treatment to the ARB&ARGs removal, a rationale that may contribute to design new strategies to apply in the UWTPs to prevent the spread of antibiotic resistance.

Antibiotic resistance in European wastewater treatment plants mirrors the pattern of clinical antibiotic resistance prevalence

Integrated antibiotic resistance (AR) surveillance is one of the objectives of the World Health Organization global action plan on antimicrobial resistance. Urban wastewater treatment plants (UWTPs) are among the most important receptors and sources of environmental AR. On the basis of the consistent observation of an increasing north-to-south clinical AR prevalence in Europe, this study compared the influent and final effluent of 12 UWTPs located in seven countries (Portugal, Spain, Ireland, Cyprus, Germany, Finland, and Norway). Using highly parallel quantitative polymerase chain reaction, we analyzed 229 resistance genes and 25 mobile genetic elements. This first trans-Europe surveillance showed that UWTP AR profiles mirror the AR gradient observed in clinics. Antibiotic use, environmental temperature, and UWTP size were important factors related with resistance persistence and spread in the environment. These results highlight the need to implement regular surveillance and control measures, which may need to be appropriate for the geographic regions.

A rationale for the high limits of quantification of antibiotic resistance genes in soil

The determination of values of abundance of antibiotic resistance genes (ARGs) per mass of soil is extremely useful to assess the potential impacts of relevant sources of antibiotic resistance, such as irrigation with treated wastewater or manure application. Culture-independent methods and, in particular, quantitative PCR (qPCR), have been regarded as suitable approaches for such a purpose. However, it is arguable if these methods are sensitive enough to measure ARGs abundance at levels that may represent a risk for environmental and human health. This study aimed at demonstrating the range of values of ARGs quantification that can be expected based on currently used procedures of DNA extraction and qPCR analyses. The demonstration was based on the use of soil samples spiked with known amounts of wastewater antibiotic resistant bacteria (ARB) (Enterococcus faecalis, Escherichia coli, Acinetobacter johnsonii, or Pseudomonas aeruginosa), harbouring known ARGs, and also on the calculation of expected values determined based on qPCR. The limits of quantification (LOQ) of the ARGs (vanA, qnrS, bla_TEM, bla_OXA, bla_IMP, bla_VIM) were observed to be approximately 4 log-units per gram of soil dry weight, irrespective of the type of soil tested. These values were close to the theoretical LOQ values calculated based on currently used DNA extraction methods and qPCR procedures. The observed LOQ values can be considered extremely high to perform an accurate assessment of the impacts of ARGs discharges in soils. A key message is that ARGs accumulation will be noticeable only at very high doses. The assessment of the impacts of ARGs discharges in soils, of associated risks of propagation and potential transmission to humans, must take into consideration this type of evidence, and avoid the simplistic assumption that no detection corresponds to risk absence.

Bacterial lineages putatively associated with the dissemination of antibiotic resistance genes in a full-scale urban wastewater treatment plant

Urban wastewater treatment plants (UWTPs) are reservoirs of antibiotic resistance. Wastewater treatment changes the bacterial community and inevitably impacts the fate of antibiotic resistant bacteria and antibiotic resistance genes (ARGs). Some bacterial groups are major carriers of ARGs and hence, their elimination during wastewater treatment may contribute to increasing resistance removal efficiency. This study, conducted at a full-scale UWTP, evaluated variations in the bacterial community and ARGs loads and explored possible associations among them. With that aim, the bacterial community composition (16S rRNA gene Illumina sequencing) and ARGs abundance (real-time PCR) were characterized in samples of raw wastewater (RWW), secondary effluent (sTWW), after UV disinfection (tTWW), and after a period of 3 days storage to monitoring possible bacterial regrowth (tTWW-RE). Culturable enterobacteria were also enumerated. Secondary treatment was associated with the most dramatic bacterial community variations and coincided with reductions of ~2 log-units in the ARGs abundance. In contrast, no significant changes in the bacterial community composition and ARGs abundance were observed after UV disinfection of sTWW. Nevertheless, after UV treatment, viability losses were indicated ~2 log-units reductions of culturable enterobacteria. The analysed ARGs (qnrS, bla_CTX-M, bla_OXA-A, bla_TEM, bla_SHV, sul1, sul2, and intI1) were strongly correlated with taxa more abundant in RWW than in the other types of water, and which associated with humans and animals, such as members of the families Campylobacteraceae, Comamonadaceae, Aeromonadaceae, Moraxellaceae, and Bacteroidaceae. Further knowledge of the dynamics of the bacterial community during wastewater treatment and its relationship with ARGs variations may contribute with information useful for wastewater treatment optimization, aiming at a more effective resistance control.

Antibiotic resistance in wastewater treatment plants: Tackling the black box

Wastewater is among the most important reservoirs of antibiotic resistance in urban environments. The abundance of carbon sources and other nutrients, a variety of possible electron acceptors such as oxygen or nitrate, the presence of particles onto which bacteria can adsorb, or a fairly stable pH and temperature are examples of conditions favouring the remarkable diversity of microorganisms in this peculiar habitat. The wastewater microbiome brings together bacteria of environmental, human and animal origins, many harbouring antibiotic resistance genes (ARGs). Although numerous factors contribute, mostly in a complex interplay, for shaping this microbiome, the effect of specific potential selective pressures such as antimicrobial residues or metals, is supposedly determinant to dictate the fate of antibiotic resistant bacteria (ARB) and ARGs during wastewater treatment. This paper aims to enrich the discussion on the ecology of ARB&ARGs in urban wastewater treatment plants (UWTPs), intending to serve as a guide for wastewater engineers or other professionals, who may be interested in studying or optimizing the wastewater treatment for the removal of ARB&ARGs. Fitting this aim, the paper overviews and discusses: i) aspects of the complexity of the wastewater system and/or treatment that may affect the fate of ARB&ARGs; ii) methods that can be used to explore the resistome, meaning the whole ARB&ARGs, in wastewater habitats; and iii) some frequently asked questions for which are proposed addressing modes. The paper aims at contributing to explore how ARB&ARGs behave in UWTPs having in mind that each plant is a unique system that will probably need a specific procedure to maximize ARB&ARGs removal.

Oryzisolibacter propanilivorax gen. nov., sp. nov., a propanil-degrading bacterium

Strain EPL6^T, a Gram-negative, motile, short rod was isolated from a propanil and 3,4-dichloroaniline enrichment culture produced from rice paddy soil. Based on the analyses of the 16S rRNA gene sequence, strain EPL6^T was observed to be a member of the family Comamonadaceae, sharing the highest pairwise identity with type strains of the species Alicycliphilus denitrificans K601^T (96.8 %) and Melaminivora alkalimesophila CY1^T (96.8 %). Strain EPL6^T was able to grow in a temperature range of 15-37 °C, pH 6-9 and in the presence of up to 4 % (w/v) NaCl and tested positive for catalase and oxidase reactions. The major respiratory quinone was Q8. The genomic DNA had a G+C content of 69.4±0.9 mol%. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol, and the major fatty acid methyl esters comprised C16 : 0, C18 : 1ω7c and summed feature 3 (C16 : 1ω7c/iso-C15 : 0 2-OH). Comparison of the genome sequence of strain EPL6^T and of its closest neighbours, Melaminivora alkalimesophila CY1^T and Alicycliphilus denitrificans K601^T, yielded values of ANI ≤84.1 % and of AAI ≤80.3 %. Therefore, the genetic, phylogenetic, phenotypic and chemotaxonomic characteristics support the classification of this organism into a new taxon. Considering the genetic divergence of strain EPL6^T from the type strains of the closest species, which belong to distinct genera, we propose a new genus within the family Comamonadaceae, named Oryzisolibacter propanilivorax gen. nov., sp. nov., represented by the isolate EPL6^T as the type strain of the species (=LMG 28427^T=CECT 8927^T).

Ubiquitous and persistent Proteobacteria and other Gram-negative bacteria in drinking water

Drinking water comprises a complex microbiota, in part shaped by the disinfection and distribution systems. Gram-negative bacteria, mainly members of the phylum Proteobacteria, represent the most frequent bacteria in drinking water, and their ubiquity and physiological versatility raises questions about possible implications in human health. The first step to address this concern is the identification and characterization of such bacteria that is the first objective of this study, aiming at identifying ubiquitous or persistent Gram-negative bacteria, Proteobacteria or members of other phyla, isolated from tap water or from its source. >1000 bacterial isolates were characterized and identified, and a selected group (n=68) was further analyzed for the minimum inhibitory concentrations (MIC) to antibiotics (amoxicillin and gentamicin) and metals (copper and arsenite). Total DNA extracts of tap water were examined for the presence of putatively acquired antibiotic resistance or related genes (intI1, bla_TEM, qnrS and sul1). The ubiquitous tap water genera comprised Proteobacteria of the class Alpha- (Blastomonas, Brevundimonas, Methylobacterium, Sphingobium, Sphingomonas), Beta- (Acidovorax, Ralstonia) and Gamma- (Acinetobacter and Pseudomonas). Persistent species were members of genera such as Aeromonas, Enterobacter or Dechloromonas. Ralstonia spp. showed the highest MIC values to gentamicin and Acinetobacter spp. to arsenite. The genes intI1, bla_TEM or sul1 were detected, at densities lower than 2.3×10⁵copies/L, 2.4×10⁴copies/L and 4.6×10²copies/L, respectively, in most tap water samples. The presence of some bacterial groups, in particular of Beta- or Gammaproteobacteria (e.g. Ralstonia, Acinetobacter, Pseudomonas) in drinking water may deserve attention given their potential as reservoirs or carriers of resistance or as opportunistic pathogens.

Development of an automatic identification algorithm for antibiogram analysis

Routinely, diagnostic and microbiology laboratories perform antibiogram analysis which can present some difficulties leading to misreadings and intra and inter-reader deviations. An Automatic Identification Algorithm (AIA) has been proposed as a solution to overcome some issues associated with the disc diffusion method, which is the main goal of this work. AIA allows automatic scanning of inhibition zones obtained by antibiograms. More than 60 environmental isolates were tested using susceptibility tests which were performed for 12 different antibiotics for a total of 756 readings. Plate images were acquired and classified as standard or oddity. The inhibition zones were measured using the AIA and results were compared with reference method (human reading), using weighted kappa index and statistical analysis to evaluate, respectively, inter-reader agreement and correlation between AIA-based and human-based reading. Agreements were observed in 88% cases and 89% of the tests showed no difference or a <4mm difference between AIA and human analysis, exhibiting a correlation index of 0.85 for all images, 0.90 for standards and 0.80 for oddities with no significant difference between automatic and manual method. AIA resolved some reading problems such as overlapping inhibition zones, imperfect microorganism seeding, non-homogeneity of the circumference, partial action of the antimicrobial, and formation of a second halo of inhibition. Furthermore, AIA proved to overcome some of the limitations observed in other automatic methods. Therefore, AIA may be a practical tool for automated reading of antibiograms in diagnostic and microbiology laboratories.

Hydromonas duriensis gen. nov., sp. nov., isolated from freshwater

An aerobic, Gram-stain-negative rod, designated strain A2P5T, was isolated from the Douro river, in Porto, Portugal. Cells were catalase- and oxidase-positive. Growth occurred at 15–30 °C, at pH 6–8 and in the presence of 1 % (w/v) NaCl. The major respiratory quinone was Q8, the genomic DNA had a G+C content of 47 ± 1 mol%, and phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol were amongst the major polar lipids. On the basis of 16S rRNA gene sequence analysis, strain A2P5T was observed to be a member of the family Burkholderiaceae, but could not be identified as a member of any validly named genus. The low levels of 16S rRNA gene sequence similarity to other recognized taxa ( < 91 %), together with the comparative analysis of phenotypic and chemotaxonomic characteristics, supported the proposal of a novel species of a new genus within the family Burkholderiaceae. The name Hydromonas duriensis gen. nov., sp. nov. is proposed. The type strain of Hydromonas duriensis is A2P5T ( = LMG 28428T = CCUG 66137T).

Multidrug Resistance in Quinolone-Resistant Gram-Negative Bacteria Isolated from Hospital Effluent and the Municipal Wastewater Treatment Plant

This study is aimed to assess if hospital effluents represent an important supplier of multidrug-resistant (MDR) Gram-negative bacteria that, being discharged in the municipal collector, may be disseminated in the environment and bypassed in water quality control systems. From a set of 101 non-Escherichia coli Gram-negative bacteria with reduced susceptibility to quinolones, was selected a group of isolates comprised by those with the highest indices of MDR (defined as nonsusceptibility to at least one agent in six or more antimicrobial categories, MDR ≥6) or resistance to meropenem or ceftazidime (n = 25). The isolates were identified and characterized for antibiotic resistance phenotype, plasmid-mediated quinolone resistance (PMQR) genes, and other genetic elements and conjugative capacity. The isolates with highest MDR indices were mainly from hospital effluent and comprised ubiquitous bacterial groups of the class Gammaproteobacteria, of the genera Aeromonas, Acinetobacter, Citrobacter, Enterobacter, Klebsiella, and Pseudomonas, and of the class Flavobacteriia, of the genera Chryseobacterium and Myroides. In this group of 25 strains, 19 identified as Gammaproteobacteria harbored at least one PMQR gene (aac(6')-Ib-cr, qnrB, qnrS, or oqxAB) or a class 1 integron gene cassette encoding aminoglycoside, sulfonamide, or carbapenem resistance. Most of the E. coli J53 transconjugants with acquired antibiotic resistance resulted from conjugation with Enterobacteriaceae. These transconjugants demonstrated acquired resistance to a maximum of five classes of antibiotics, one or more PMQR genes and/or a class 1 integron gene cassette. This study shows that ubiquitous bacteria, other than those monitored in water quality controls, are important vectors of antibiotic resistance and can be disseminated from hospital effluent to aquatic environments. This information is relevant to support management options aiming at the control of this public health problem.

Assessment of copper and zinc salts as selectors of antibiotic resistance in Gram-negative bacteria

Some metals are nowadays considered environmental pollutants. Although some, like Cu and Zn, are essential for microorganisms, at high concentrations they can be toxic or exert selective pressures on bacteria. This study aimed to assess the potential of Cu or Zn as selectors of specific bacterial populations thriving in wastewater. Populations of Escherichia coli recovered on metal-free and metal-supplemented culture medium were compared based on antibiotic resistance phenotype and other traits. In addition, the bacterial groups enriched after successive transfers in metal-supplemented culture medium were identified. At a concentration of 1mM, Zn produced a stronger inhibitory effect than Cu on the culturability of Enterobacteriaceae. It was suggested that Zn selected populations with increased resistance prevalence to sulfamethoxazole or ciprofloxacin. In non-selective culture media, Zn or Cu selected for mono-species populations of ubiquitous Betaproteobacteria and Flavobacteriia, such as Ralstonia pickettii or Elizabethkingia anophelis, yielding multidrug resistance profiles including resistance against carbapenems and third generation cephalosporins, confirming the potential of Cu or Zn as selectors of antibiotic resistant bacteria.

Wastewater reuse in irrigation: a microbiological perspective on implications in soil fertility and human and environmental health

The reuse of treated wastewater, in particular for irrigation, is an increasingly common practice, encouraged by governments and official entities worldwide. Irrigation with wastewater may have implications at two different levels: alter the physicochemical and microbiological properties of the soil and/or introduce and contribute to the accumulation of chemical and biological contaminants in soil. The first may affect soil productivity and fertility; the second may pose serious risks to the human and environmental health. The sustainable wastewater reuse in agriculture should prevent both types of effects, requiring a holistic and integrated risk assessment. In this article we critically review possible effects of irrigation with treated wastewater, with special emphasis on soil microbiota. The maintenance of a rich and diversified autochthonous soil microbiota and the use of treated wastewater with minimal levels of potential soil contaminants are proposed as sine qua non conditions to achieve a sustainable wastewater reuse for irrigation.

Bacterial diversity and antibiotic resistance in water habitats: searching the links with the human microbiome

Water is one of the most important bacterial habitats on Earth. As such, water represents also a major way of dissemination of bacteria between different environmental compartments. Human activities led to the creation of the so-called urban water cycle, comprising different sectors (waste, surface, drinking water), among which bacteria can hypothetically be exchanged. Therefore, bacteria can be mobilized between unclean water habitats (e.g. wastewater) and clean or pristine water environments (e.g. disinfected and spring drinking water) and eventually reach humans. In addition, bacteria can also transfer mobile genetic elements between different water types, other environments (e.g. soil) and humans. These processes may involve antibiotic resistant bacteria and antibiotic resistance genes. In this review, the hypothesis that some bacteria may share different water compartments and be also hosted by humans is discussed based on the comparison of the bacterial diversity in different types of water and with the human-associated microbiome. The role of such bacteria as potential disseminators of antibiotic resistance and the inference that currently only a small fraction of the clinically relevant antibiotic resistome may be known is discussed.

Genotypic diversity and antibiotic resistance in Sphingomonadaceae isolated from hospital tap water

The aim of this study was to infer about the modes and extent of dispersion of Sphingomonadaceae via tap water. Sphingomonadaceae isolated from tap water samples in different places of a hospital were compared, based on intra-species genetic variability and antibiotic resistance phenotypes. These isolates were also compared with others isolated before from houses and dental chairs, served by the same municipal water supply system. Sphingomonadaceae from hospital tap water comprised members of the genera Sphingomonas, Sphingobium, Novosphingobium and Blastomonas. In general, distinct genotypes of Sphingomonadaceae were detected in different hospital areas and in tap water outside the hospital, suggesting these bacteria are not persistent or widespread in the urban water distribution system. Possible intrinsic antibiotic resistance, observed in most or all members of the family or of a genus, was observed for colistin in Sphingomonadaceae, aminoglycosides in the genus Blastomonas and beta-lactams in the genus Sphingobium. Possible acquired resistance phenotypes, not common to all members of a given species, comprised fluoroquinolones, cephalosporins and sulphonamides. Although the potential of Sphingomonadaceae as opportunistic pathogens may be low, the capacity of these bacteria to thrive in water supply systems, combined with the intrinsic or acquired antibiotic resistance, may raise the risk associated with their occurrence in hospital tap water.

Patulibacter medicamentivorans sp. nov., isolated from activated sludge of a wastewater treatment plant

A Gram-positive, aerobic, non-motile, non-endospore-forming rod-shaped bacterium with ibuprofen-degrading capacity, designated strain I11(T), was isolated from activated sludge from a wastewater treatment plant. The major respiratory quinone was demethylmenaquinone DMK-7, C18 : 1 cis9 was the predominant fatty acid, phosphatidylglycerol was the predominant polar lipid, the cell wall contained meso-diaminopimelic acid as the diagnostic diamino acid and the G+C content of the genomic DNA was 74.1 mol%. On the basis of 16S rRNA gene sequence analysis, the closest phylogenetic neighbours of strain I11(T) were Patulibacter ginsengiterrae CECT 7603(T) (96.8 % similarity), Patulibacter minatonensis DSM 18081(T) (96.6 %) and Patulibacter americanus DSM 16676(T) (96.6 %). Phenotypic characterization supports the inclusion of strain I11(T) within the genus Patulibacter (phylum Actinobacteria). However, distinctive features and 16S rRNA gene sequence analysis suggest that is represents a novel species, for which the name Patulibacter medicamentivorans sp. nov. is proposed. The type strain is I11(T) ( = DSM 25962(T) = CECT 8141(T)).

Bacterial diversity from the source to the tap: a comparative study based on 16S rRNA gene-DGGE and culture-dependent methods

This study aimed to assess the influence of water treatment and distribution on the bacterial communities with particular emphasis on tap water. Samples from the water treatment plant, the bulk supply distribution system and household taps, supplied by the same drinking water treatment plant, were analyzed using culture-dependent and culture-independent methods. Water treatment imposed alterations in the composition of the bacterial community, although this effect was more evident in the cultivable bacteria rather than among the total community assessed by 16S rRNA gene-denaturing gradient gel electrophoresis (DGGE) profiling. Water disinfection, mainly chlorination, promoted a reduction on bacterial diversity and cultivability, with a shift in the pattern of cultivable bacteria from predominantly Gram-negative to predominately Gram-positive and acid-fast. Downstream of the chlorination stages, tap water, in comparison with raw water, presented higher diversity indices and cultivability percentages. From the source to the tap, members of the Alpha-, Beta- and Gammaproteobacteria were the predominant lineages identified using 16S rRNA gene-DGGE analysis. Although with a lower coverage, the DGGE-based lineage identifications were in agreement with those found using 454-pyrosequencing analysis. Despite the effectiveness of water treatment to eliminate or inactivate most of the bacteria, Proteobacteria such as Acinetobacter, Bosea and Sphingomonadaceae may successfully colonize tap water.

Bottled mineral water as a potential source of antibiotic resistant bacteria

The antibiotic resistance phenotypes of the cultivable bacteria present in nine batches of two Portuguese and one French brands of commercially available mineral waters were examined. Most of the 238 isolates recovered on R2A, Pseudomonas Isolation agar or on these culture media supplemented with amoxicillin or ciprofloxacin, were identified (based on 16S rRNA gene sequence analysis) as Proteobacteria of the divisions Beta, Gamma and Alpha. Bacteria resistant to more than three distinct classes of antibiotics were detected in all the batches of the three water brands in counts up to 10² CFU/ml. In the whole set of isolates, it was observed resistance against all the 22 antimicrobials tested (ATB, bioMérieux and disc diffusion), with most of the bacteria showing resistance to three or more classes of antibiotics. Bacteria with the highest multi-resistance indices were members of the genera Variovorax, Bosea, Ralstonia, Curvibacter, Afipia and Pedobacter. Some of these bacteria are related with confirmed or suspected nosocomial agents. Presumable acquired resistance may be suggested by the observation of bacteria taxonomically related but isolated from different brands, exhibiting distinct antibiotic resistance profiles. Bottled mineral water was confirmed as a possible source of antibiotic resistant bacteria, with the potential to be transmitted to humans.

Diversity and antibiotic resistance in Pseudomonas spp. from drinking water

Pseudomonas spp. are common inhabitants of aquatic environments, including drinking water. Multi-antibiotic resistance in clinical isolates of P. aeruginosa is widely reported and deeply characterized. However, the information regarding other species and environmental isolates of this genus is scant. This study was designed based on the hypothesis that members of the genus Pseudomonas given their high prevalence, wide distribution in waters and genetic plasticity can be important reservoirs of antibiotic resistance in drinking water. With this aim, the diversity and antibiotic resistance phenotypes of Pseudomonas isolated from different drinking water sources were evaluated. The genotypic diversity analyses were based on six housekeeping genes (16S rRNA, rpoD, rpoB, gyrB, recA and ITS) and on pulsed field gel electrophoresis. Susceptibility to 21 antibiotics of eight classes was tested using the ATB PSE EU (08) and disk diffusion methods. Pseudomonas spp. were isolated from 14 of the 32 sampled sites. A total of 55 non-repetitive isolates were affiliated to twenty species. Although the same species were isolated from different sampling sites, identical genotypes were never observed in distinct types of water (water treatment plant/distribution system, tap water, cup fillers, biofilm, and mineral water). In general, the prevalence of antibiotic resistance was low and often the resistance patterns were related with the species and/or the strain genotype. Resistance to ticarcillin, ticarcillin with clavulanic acid, fosfomycin and cotrimoxazol were the most prevalent (69-84%). No resistance to piperacillin, levofloxacin, ciprofloxacin, tetracycline, gentamicin, tobramycin, amikacin, imipenem or meropenem was observed. This study demonstrates that Pseudomonas spp. are not so widespread in drinking water as commonly assumed. Nevertheless, it suggests that water Pseudomonas can spread acquired antibiotic resistance, preferentially via vertical transmission.

Comparison of ubiquitous antibiotic-resistant Enterobacteriaceae populations isolated from wastewaters, surface waters and drinking waters

This study aimed at assessing the role of ubiquitous (non-Escherichia coli) Enterobacteriaceae in the dissemination of antimicrobial resistance through the urban water cycle. Enterobacteriaceae isolated from a municipal wastewater treatment plant (111 isolates), urban water streams (33 isolates) and drinking water (123 isolates) were compared in terms of: (i) genera distribution, (ii) resistance to 12 antibiotics, and (iii) class 1 and class 2 integrons. The predominant bacterial genera were the same in the different types of water, although with a distinct pattern of species. The most prevalent resistance phenotypes were observed for amoxicillin, ticarcillin, cephalothin and sulphamethoxazole (24-59% in the three types of water). No resistance against ceftazidime or meropenem was observed. Resistance to cephalothin, amoxicillin and sulphamethoxazole was significantly more prevalent in drinking water, water streams and wastewater, respectively, than in the other types of water. It was possible to recognize antibiotic-resistance associations, namely for the pairs streptomycin-tetracycline (positive) and ticarcillin-cephalotin (negative). Class 1 and/or class 2 integrons with similar gene cassettes were detected in the three types of water. This study demonstrated that Enterobacteriaceae are important vehicles of antibiotic resistance, namely in drinking water.

Bacillus purgationiresistans sp. nov., isolated from a drinking-water treatment plant

A Gram-positive, aerobic, non-motile, endospore-forming rod, designated DS22T, was isolated from a drinking-water treatment plant. Cells were catalase- and oxidase-positive. Growth occurred at 15–37 °C, at pH 7–10 and with <8 % (w/v) NaCl (optimum growth: 30 °C, pH 7–8 and 1–3 % NaCl). The major respiratory quinone was menaquinone 7, the G+C content of the genomic DNA was 36.5 mol% and the cell wall contained meso-diaminopimelic acid. On the basis of 16S rRNA gene sequence analysis, strain DS22T was a member of the genus Bacillus. Its closest phylogenetic neighbours were Bacillus horneckiae NRRL B-59162T (98.5 % 16S rRNA gene sequence similarity), Bacillus oceanisediminis H2T (97.9 %), Bacillus infantis SMC 4352-1T (97.4 %), Bacillus firmus IAM 12464T (96.8 %) and Bacillus muralis LMG 20238T (96.8 %). DNA–DNA hybridization, and biochemical and physiological characterization allowed the differentiation of strain DS22T from its closest phylogenetic neighbours. The data supports the proposal of a novel species, Bacillus purgationiresistans sp. nov.; the type strain is DS22T ( = DSM 23494T = NRRL B-59432T = LMG 25783T).

Diversity and antibiotic resistance of Aeromonas spp. in drinking and waste water treatment plants

The taxonomic diversity and antibiotic resistance phenotypes of aeromonads were examined in samples from drinking and waste water treatment plants (surface, ground and disinfected water in a drinking water treatment plant, and raw and treated waste water) and tap water. Bacteria identification and intra-species variation were determined based on the analysis of the 16S rRNA, gyrB and cpn60 gene sequences. Resistance phenotypes were determined using the disc diffusion method. Aeromonas veronii prevailed in raw surface water, Aeromonas hydrophyla in ozonated water, and Aeromonas media and Aeromonas puntacta in waste water. No aeromonads were detected in ground water, after the chlorination tank or in tap water. Resistance to ceftazidime or meropenem was detected in isolates from the drinking water treatment plant and waste water isolates were intrinsically resistant to nalidixic acid. Most of the times, quinolone resistance was associated with the gyrA mutation in serine 83. The gene qnrS, but not the genes qnrA, B, C, D or qepA, was detected in both surface and waste water isolates. The gene aac(6')-ib-cr was detected in different waste water strains isolated in the presence of ciprofloxacin. Both quinolone resistance genes were detected only in the species A. media. This is the first study tracking antimicrobial resistance in aeromonads in drinking, tap and waste water and the importance of these bacteria as vectors of resistance in aquatic environments is discussed.

Candidimonas nitroreducens gen. nov., sp. nov. and Candidimonas humi sp. nov., isolated from sewage sludge compost

Two bacterial strains (SC-089T and SC-092T) isolated from sewage sludge compost were characterized by using a polyphasic approach. The isolates were Gram-negative short rods, catalase- and oxidase-positive, and showed good growth at 30 °C, at pH 7 and with 1 % (w/v) NaCl. Ubiquinone 8 was the major respiratory quinone, and phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol were amongst the major polar lipids. On the basis of 16S rRNA gene sequence analysis, the strains were observed to be members of the family Alcaligenaceae, but could not be identified as members of any validly described genus. The low levels of 16S rRNA gene sequence similarity to other recognized taxa, together with comparative analysis of phenotypic traits and chemotaxonomic markers, supported the proposal of a new genus within the family Alcaligenaceae, for which the name Candidimonas gen. nov. is proposed. Strains SC-089T and SC-092T, which shared 99.1 % 16S rRNA gene sequence similarity, could be differentiated at the phenotypic level, and DNA–DNA hybridization results supported their identification as representing distinct species. The names proposed for these novel species are Candidimonas nitroreducens sp. nov. (type strain, SC-089T = LMG 24812T = CCUG 55806T) and Candidimonas humi sp. nov. (type strain, SC-092T = LMG 24813T = CCUG 55807T).

Acinetobacter rudis sp. nov., isolated from raw milk and raw wastewater

Two bacterial strains, G30(T) and A1PC16, isolated respectively from raw milk and raw wastewater, were characterized using a polyphasic approach. Chemotaxonomic characterization supported the inclusion of these strains in the genus Acinetobacter, with Q-8 and Q-9 as the major respiratory quinones, genomic DNA G+C contents within the range observed for this genus (38-47 mol%) and C(16:0), C(18:1)ω9c and C(16:1)ω7c/iso-C(15:0) 2-OH as the predominant fatty acids. The observation of 16S rRNA gene sequence similarity lower than 97% with other Acinetobacter species with validly published names led to the hypothesis that these isolates could represent a novel species. This hypothesis was supported by comparative analysis of partial sequences of the genes rpoB and gyrB, which showed that strains G30(T) and A1PC16 did not cluster with any species with validly published names, forming a distinct lineage. DNA-DNA hybridizations confirmed that the two strains were members of the same species, which could be distinguished from their congeners by several phenotypic characteristics. On the basis of these arguments, it is proposed that strains G30(T) and A1PC16 represent a novel species, for which the name Acinetobacter rudis sp. nov. is proposed. The type strain is strain G30(T) (=LMG 26107(T) =CCUG 57889(T) =DSM 24031(T) =CECT 7818(T)).

Paenibacillus residui sp. nov., isolated from urban waste compost

Two bacterial strains, MC-246(T) and MC-247, were isolated from municipal urban waste compost and characterized by a polyphasic approach. Both isolates were Gram-stain-variable, endospore-forming rods that were catalase-, oxidase- and β-galactosidase-positive, and able to grow at 25-50°C and pH 7.0-9.0, with optimum growth at 37°C and pH 7. The predominant cellular fatty acids were anteiso-C₁₅:₀, iso-C₁₅:₀, iso-C₁₆: ₀, anteiso-C₁₇:₀ and iso-C₁₇:₀; the major respiratory quinone was menaquinone MK-7; the cell wall peptidoglycan was of type A1γ; and the DNA G+C content was 49 mol%. These characteristics, as well as data from 16S RNA gene sequence analysis, showed that these strains were affiliated with the genus Paenibacillus; the type strains of Paenibacillus ginsengarvi and Paenibacillus hodogayensis were among their closest neighbours (< 94.2 % sequence similarity). Nevertheless, the hypothesis that strains MC-246(T) and MC-247 could represent a novel species was supported by the low 16S rRNA gene sequence similarity values shared with other members of the genus Paenibacillus and by the observation of distinct biochemical and physiological traits. Strains MC-246(T) and MC-247 shared 99.6 % 16S rRNA gene sequence similarity and showed almost identical MALDI-TOF mass spectra, but could be distinguished at the phenotypic and genotypic level. However, DNA-DNA hybridization between strains MC-246(T) and MC-247 resulted in values above 70 % indicating that both organisms represent a single species, for which the name Paenibacillus residui sp. nov. is proposed; the type strain is MC-246(T) (=DSM 22072(T) =CCUG 57263(T)).

Shinella fusca sp. nov., isolated from domestic waste compost

A bacterium, designated strain DC-196(T), isolated from kitchen refuse compost was analysed by using a polyphasic approach. Strain DC-196(T) was characterized as a Gram-negative short rod that was catalase- and oxidase-positive, and able to grow at 10-40 degrees C, pH 6-9 and in NaCl concentrations as high as 3 %. Chemotaxonomically, C(18 : 1) was observed to be the predominant cellular fatty acid and ubiquinone 10 (Q10) was the predominant respiratory quinone. The G+C content of the genomic DNA was determined to be 66 mol%. On the basis of the genotypic, phenotypic and chemotaxonomic characteristics, strain DC-196(T) was assigned to the genus Shinella, although with distinctive features. At the time of writing, 16S rRNA gene sequence similarities of 97.6-96.8 % and the low DNA-DNA hybridization values of 38.2-32.2 % with the type strains of the three recognized Shinella species confirmed that strain DC-196(T) represents a novel species of the genus, for which the name Shinella fusca sp. nov. is proposed (type strain DC-196(T)=CCUG 55808(T)=LMG 24714(T)).

Sphingobium vermicomposti sp. nov., isolated from vermicompost

Strain VC-230(T) was isolated from homemade vermicompost produced from kitchen waste. The isolate was a Gram-negative-staining, catalase- and oxidase-positive, motile rod-shaped bacterium able to grow at 15-37 degrees C and pH 6-8. On the basis of 16S rRNA gene sequence analysis, strain VC-230(T) was determined to belong to the family Sphingomonadaceae by its clustering with type strains of the genus Sphingobium, with Sphingobium chlorophenolicum ATCC 33790(T) (97.7 %) and Sphingobium herbicidovorans DSM 11019(T) (97.4 %) as its closest neighbours. The polar lipid pattern, the presence of spermidine and ubiquinone 10, the predominance of the cellular fatty acids C(18 : 1)omega7c/9t/12t, C(16 : 1)omega7c and C(16 : 0) and the G+C content of the genomic DNA supported the affiliation of this organism to the genus Sphingobium. The phylogenetic, chemotaxonomic, phenotypic and DNA-DNA hybridization analyses verify that strain VC-230(T) represents a novel species, for which the name Sphingobium vermicomposti sp. nov. is proposed. The type strain is VC-230(T) (=CCUG 55809(T) =DSM 21299(T)).

Microbacterium invictum sp. nov., isolated from homemade compost

Strain DC-200T was isolated from homemade compost produced from kitchen refuse and characterized using a polyphasic approach. The isolate was a Gram-positive motile short rod, facultatively aerobic, catalase-positive and oxidase-negative, and was able to grow at 10-37 degrees C, pH 6.0-9.5 and with up to 5% of NaCl. The peptidoglycan was of the type B1 alpha and the muramic acid residues were glycolylated. The major fatty acids were anteiso-C15:0 and anteiso-C17:0. The predominant respiratory menaquinones were MK-11 and MK-12. The G+C content of the genomic DNA was 70 mol%. Based on the analysis of the 16S rRNA gene sequence, the closest phylogenetic neighbours of strain DC-200T were Microbacterium lacus A5E-52T (98.7%) and Microbacterium aoyamense KV-492T (98.2%). The phenetic characterization of the isolate supports its inclusion within the genus Microbacterium; however, its distinctive phenotypic features and the results from the 16S rRNA gene sequence analysis and the DNA-DNA hybridization study suggest that the isolate represents a novel species. The name Microbacterium invictum sp. nov. is proposed. The type strain is DC-200T (=DSM 19600T=LMG 24557T).

Antibiotic resistance in coagulase negative staphylococci isolated from wastewater and drinking water

This study reports the antibiotic resistance patterns of coagulase negative staphylococci (CNS) isolated from a drinking water treatment plant (WTP), a drinking water distribution network, responsible for supplying water to the consumers (WDN), and a wastewater treatment plant (WWTP), responsible for receiving and treating domestic residual effluents. Genotyping and the 16S rRNA gene sequence analysis demonstrated a higher diversity of species both in the WTP (6 species/19 isolates) and WWTP (12 species/47 isolates) than in the WDN (6 species/172 isolates). Staphylococcus pasteuri and Staphylococcus epidermidis prevailed in the WTP and WDN and Staphylococcus saprophyticus in the WWTP. Staphylococci with reduced susceptibility (resistance or intermediary phenotype) to beta-lactams, tetracycline, clindamycin and erythromycin were observed in all types of water and belonged to the three major species groups. The highest resistance rate was found against erythromycin, presumably due to the presence of the efflux pump encoded by the determinant msrA, detected in the majority of the resistant isolates. This study demonstrates that antibiotic resistant CNS may colonize different types of water, namely drinking water fulfilling all the quality standards.

Microbacterium luticocti sp. nov., isolated from sewage sludge compost

Strain SC-087B(T), isolated from sewage sludge compost during a study of bacterial diversity in composts, was characterized. The isolate was a Gram-positive, short rod that was motile, catalase- and oxidase-negative and able to grow at 27-45 degrees C, pH 5.5-9.7 and in up to 10 % NaCl. The peptidoglycan was of the B2beta type, containing the characteristic amino acids ornithine, homoserine and hydroxyglutamic acid. The muramic acid residues of the peptidoglycan were partially glycolylated. The major cell-wall sugar was mannose; traces of xylose were also detected. The predominant fatty acids, comprising more than 70 % of the total, were anteiso-C(17 : 0) and anteiso-C(15 : 0), the major respiratory quinone was menaquinone-12 (MK-12) and the G+C content of the genomic DNA was 72 mol%. Based on analysis of the 16S rRNA gene sequence, the closest phylogenetic neighbours of strain SC-087B(T) were members of the family Microbacteriaceae, showing sequence similarity values of around 96 % with members of the species Microbacterium barkeri (96.0 %), Microbacterium gubbeenense (95.6 %) and Microbacterium indicum (95.7 %). The chemotaxonomic and phenotypic traits analysed supported the inclusion of this strain within the genus Microbacterium and the proposal of a novel species. The name Microbacterium luticocti sp. nov. is proposed and the type strain is SC-087B(T) (=DSM 19459(T)=CCUG 54537(T)).

Diversity of bacterial isolates from commercial and homemade composts

The diversity of heterotrophic bacterial isolates of three commercial and two homemade composts was studied. The commercial composts were produced from poultry litter (PC), sewage sludge (SC), municipal solid waste (MC), and homemade composts (thermal compost [DC] and vermicompost [VC]) from food wastes. The taxonomic and physiological diversity of the heterotrophic culturable bacteria was assessed using phenotypic and genotypic characterization and the analysis of the partial 16S rRNA gene sequence. Composts DC and SC presented the higher genotypic diversity, as could be inferred from the number of distinct genotypic patterns observed, 28 and 21, respectively. Gram-positive bacteria, mainly Firmicutes, were predominant in all the composts. Some organisms related with taxa rarely reported in composts, as Rhodanobacter spathiphylli, Moraxella osloensis, Lysobacter, Corynebacterium, Pigmentiphaga kullae, and new taxa were also isolated. The highest relative proportion of isolates able to degrade starch was found in compost SC (> 70%), to degrade gelatine in compost DC (> 70%), to degrade Tween 80 in compost PC (> 90%), and to degrade poly-epsilon-caprolactones in compost DC (> 80%). Compost MC presented the lowest relative proportions of isolates able to degrade starch (< 25%), gelatine (< 20%), and poly-epsilon-caprolactone (< 40%). When compared with the others, the homemade composts presented higher relative proportions of Gram-positive isolates able to inhibit the target organisms Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, or Pseudomonas aeruginosa. In compost MC, none of the Gram-positive isolates was able to inhibit those targets.

Paenibacillus humicus sp. nov., isolated from poultry litter compost

Two bacterial strains, PC-142 and PC-147(T), isolated from poultry litter compost, were characterized with respect to their phenetic and phylogenetic characteristics. The isolates were endospore-forming rods that were reddish in colour after Gram staining. They were catalase- and oxidase-positive, were able to degrade starch and gelatin and grew at 15-40 degrees C and pH 5.5-10.0. The predominant fatty acids were anteiso-C(15 : 0), iso-C(15 : 0) and iso-C(16 : 0), the major respiratory quinone was menaquinone MK-7, the cell-wall peptidoglycan was of the A1gamma type and the G+C content of the DNA was 58 mol%. The 16S rRNA gene sequence analysis and phenetic characterization indicated that these organisms belong to the genus Paenibacillus, with Paenibacillus pasadenensis SAFN-007(T) as the closest phylogenetic neighbour (97.5 %). Strains PC-142, PC-147(T) and P. pasadenensis SAFN-007(T) represent a novel lineage within the genus Paenibacillus, characterized by a high DNA G+C content (58-63 mol%). The low levels of 16S rRNA gene sequence similarity with respect to other taxa with validly published names and the identification of distinctive phenetic features in the two isolates indicate that strains PC-142 and PC-147(T) represent a novel species of the genus Paenibacillus, for which the name Paenibacillus humicus sp. nov. is proposed. The type strain is PC-147(T) (=DSM 18784(T) =NBRC 102415(T) =LMG 23886(T)).

Pseudosphingobacterium domesticum gen. nov., sp. nov., isolated from home-made compost

A bacterial strain, DC-186(T), isolated from home-made compost, was characterized for its phenotypic and phylogenetic properties. The isolate was a Gram-negative rod that was able to grow at 15-36 degrees C and pH 5.5-8.0. Strain DC-186(T) was positive in tests for catalase, oxidase and beta-galactosidase activities and aesculin hydrolysis. The predominant fatty acids were the summed feature C(16 : 1)/iso-C(15 : 0) 2-OH (42 %) and iso-C(15 : 0) (26 %), the major respiratory quinone was menaquinone-7 and the genomic DNA G+C content was 42 mol%. 16S rRNA gene sequence analysis and phenetic characterization indicated that this organism belongs to the phylum Bacteroidetes and revealed its affiliation to the family Sphingobacteriaceae. Of recognized taxa, strain DC-186(T) was most closely related to Sphingobacterium daejeonense (90 % sequence similarity) based on 16S rRNA gene sequence analysis. The low 16S rRNA gene sequence similarity with other recognized taxa and the identification of distinctive phenetic features for this isolate support the definition of a new genus within the family Sphingobacteriaceae. The name Pseudosphingobacterium domesticum gen. nov., sp. nov. is proposed, with strain DC-186(T) (=CCUG 54353(T)=LMG 23837(T)) as the type strain.

Gulbenkiania mobilis gen. nov., sp. nov., isolated from treated municipal wastewater

A bacterial strain (E4FC31T) isolated from treated municipal wastewater was characterized phenotypically and phylogenetically. Cells were Gram-negative, curved rods with a polar flagellum. The isolate was catalase-, oxidase- and arginine dihydrolase-positive, and able to grow between 15 and 45 °C and between pH 5.5 and 9.0. The predominant fatty acids were C16 : 1/iso-C15 : 02-OH and C16 : 0, the major respiratory quinone was ubiquinone 8 and the G+C content of the genomic DNA was 63 mol%. 16S rRNA gene sequence analysis indicated that strain E4FC31Tbelonged to the classBetaproteobacteriaand was a member of the familyNeisseriaceae. Its closest phylogenetic neighbours wereAquitalea magnusoniiandChromobacterium violaceum(<94 % 16S rRNA gene sequence similarity). Phylogenetic analysis and phenotypic characteristics of strain E4FC31Tsuggest that it represents a novel species of a new genus, for which the nameGulbenkiania mobilisgen. nov., sp. nov. is proposed. The type strain ofGulbenkiania mobilisis E4FC31T(=DSM 18507T=LMG 23770T).