Dynamics and activity of an ammonia-oxidizing archaea bloom in South San Francisco Bay.

Transient or recurring blooms of ammonia-oxidizing archaea (AOA) have been reported in several estuarine and coastal environments, including recent observations of AOA blooms in South San Francisco Bay. Here, we measured nitrification rates, quantified AOA abundance, and analyzed both metagenomic and metatranscriptomic data to examine the dynamics and activity of nitrifying microorganisms over the course of an AOA bloom in South San Francisco Bay during the autumn of 2018 and seasonally throughout 2019. Nitrification rates were correlated with AOA abundance in quantitative polymerase chain reaction (PCR) data, and both increased several orders of magnitude between the autumn AOA bloom and spring and summer seasons. From bloom samples, we recovered an extremely abundant, high-quality Candidatus Nitrosomarinus catalina-like AOA metagenome-assembled genome that had high transcript abundance during the bloom and expressed >80% of genes in its genome. We also recovered a putative nitrite-oxidizing bacteria metagenome-assembled genome from within the Nitrospinaceae that was of much lower abundance and had lower transcript abundance than AOA. During the AOA bloom, we observed increased transcript abundance for nitrogen uptake and oxidative stress genes in non-nitrifier metagenome-assembled genomes. This study confirms AOA are not only abundant but also highly active during blooms oxidizing large amounts of ammonia to nitrite-a key intermediate in the microbial nitrogen cycle-and producing reactive compounds that may impact other members of the microbial community.

Community coalescence under variable hydrochemical conditions of the Chesapeake Bay shaped bacterial diversity and functional traits.

Community coalescence related to bacterial mixing events regulates community characteristics and affects the health of estuary ecosystems. At present, bacterial coalescence and its driving factors are still unclear. The present study used a dataset from the Chesapeake Bay (2017) to address how bacterial community coalescence in response to variable hydrochemistry in estuarine ecosystems. We determined that variable hydrochemistry promoted the deterioration of water quality. Temperature, orthophosphate, dissolved oxygen, chlorophyll a, Secchi disk depth, and dissolved organic phosphorus were the key environmental factors driving community coalescence. Bacteria with high tolerance to environmental change were the primary taxa accumulated in community coalescence, and the significance of deterministic processes to communities was revealed. Community coalescence was significantly correlated with the pathways of metabolism and organismal systems, and promoted the co-occurrence of antibiotic resistance and virulence factor genes. Briefly, community coalescence under variable hydrochemical conditions shaped bacterial diversity and functional traits, to optimise strategies for energy acquisition and lay the foundation for alleviating environmental pressures. However, potential pathogenic bacteria in community coalescence may be harmful to human health and environmental safety. The present study provides a scientific reference for ecological management of estuaries.

Spatiotemporal assessment of pathogenic Leptospira in subtropical coastal watersheds.

The World Health Organization classifies leptospirosis as a significant public health concern, predominantly affecting impoverished and unsanitary regions. By using the Pensacola Bay System as a case study, this study examines the underappreciated susceptibility of developed subtropical coastal ecosystems such as the Pensacola Bay System to neglected zoonotic pathogens such as Leptospira. We analyzed 132 water samples collected over 12 months from 44 distinct locations with high levels of Escherichia coli (>410 most probable number/100 mL). Fecal indicator bacteria (FIB) concentrations were assessed using IDEXX Colilert-18 and Enterolert-18, and an analysis of water physiochemical characteristics and rainfall intensity was conducted. The LipL32 gene was used as a quantitative polymerase chain reaction (qPCR) indicator to identify the distribution of Leptospira interrogans. The results revealed 12 instances of the presence of L. interrogans at sites with high FIB over various land cover and aquatic ecosystem types. Independent of specific rainfall events, a seasonal relationship between precipitation and elevated rates of fecal bacteria and leptospirosis was found. These findings highlight qPCR's utility in identifying pathogens in aquatic environments and the widespread conditions where it can be found in natural and developed areas.

The recent disappearance of a persistent Planktothrix bloom: Characterization of a regime shift in the phytoplankton of Sandusky Bay (USA).

Sandusky Bay is the drowned mouth of the Sandusky River in the southwestern portion of Lake Erie. The bay is a popular recreation location and a regional source for drinking water. Like the western basin of Lake Erie, Sandusky Bay is known for being host to summer cyanobacterial harmful algal blooms (cHABs) year after year, fueled by runoff from the predominantly agricultural watershed and internal loading of legacy nutrients (primarily phosphorus). Since at least 2003, Sandusky Bay has harbored a microcystin-producing bloom of Planktothrix agardhii, a species of filamentous cyanobacteria that thrives in low light conditions. Long-term sampling (2003-2018) of Sandusky Bay revealed regular Planktothrix-dominated blooms during the summer months, but in recent years (2019-2022), 16S rRNA gene community profiling revealed that Planktothrix has largely disappeared. From 2017-2022, microcystin decreased well below the World Health Organization (WHO) guidelines. Spring TN:TP ratios increased in years following dam removal, yet there were no statistically significant shifts in other physicochemical variables, such as water temperature and water clarity. With the exception of the high bloom of Planktothrix in 2018, there was no statistical difference in chlorophyll during all other years. Concurrent with the disappearance of Planktothrix, Cyanobium spp. have become the dominant cyanobacterial group. The appearance of other potential toxigenic genera (i.e., Aphanizomenon, Dolichospermum, Cylindrospermopsis) may motivate monitoring of new toxins of concern in Sandusky Bay. Here, we document the regime shift in the cyanobacterial community and propose evidence supporting the hypothesis that the decline in the Planktothrix bloom was linked to the removal of an upstream dam on the Sandusky River.

Structural properties and microbial diversity of the biofilm colonizing plastic substrates in Terra Nova Bay (Antarctica).

Microbial colonization on plastic polymers has been extensively explored, however the temporal dynamics of biofilm community in Antarctic environments are almost unknown. As a contribute to fill this knowledge gap, the structural characteristics and microbial diversity of the biofilm associated with polyvinyl chloride (PVC) and polyethylene (PE) panels submerged at 5 m of depth and collected after 3, 9 and 12 months were investigated in four coastal sites of the Ross Sea. Additional panels placed at 5 and 20 m were retrieved after 12 months. Chemical characterization was performed by FTIR-ATR and Raman (through Surface-Enhanced Raman Scattering, SERS) spectroscopy. Bacterial community composition was quantified at a single cell level by Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) and Confocal Laser Scanning Microscopy (CLSM); microbial diversity was assessed by 16S rRNA gene sequencing. This multidisciplinary approach has provided new insights into microbial community dynamics during biofouling process, shedding light on the biofilm diversity and temporal succession on plastic substrates in the Ross Sea. Significant differences between free-living and microbial biofilm communities were found, with a more consolidated and structured community composition on PVC compared to PE. Spectral features ascribable to tyrosine, polysaccharides, nucleic acids and lipids characterized the PVC-associated biofilms. Pseudomonadota (among Gamma-proteobacteria) and Alpha-proteobacteria dominated the microbial biofilm community. Interestingly, in Road Bay, close to the Italian "Mario Zucchelli" research station, the biofilm growth - already observed during summer season, after 3 months of submersion - continued afterwards leading to a massive microbial abundance at the end of winter (after 12 months). After 3 months, higher percentages of Gamma-proteobacteria in Road Bay than in the not-impacted site were found. These observations lead us to hypothesize that in this site microbial fouling developed during the first 3 months could serve as a starter pioneering community stimulating the successive growth during winter.

Interaction patterns and assembly mechanisms of dinoflagellates and diatoms in a coastal bay suffering from long-term eutrophication.

Dinoflagellates and diatoms are highly prevalent and ecologically important phytoplankton in coastal waters, greatly contributing to primary productivity in marine ecosystems. Although their composition and diversity have been extensively elucidated in the open ocean, their interaction patterns and community assembly in long-term eutrophic coastal waters remain poorly understood. This investigation aimed to elucidate the seasonal successional patterns of dinoflagellates and diatoms by 18S rRNA gene amplicon sequencing in a semi-enclosed bay. The results revealed that dinoflagellate and diatom communities have pronounced seasonal succession patterns, which are primarily associated with temperature. Furthermore, the most prevalent species throughout the year were Heterocapsa rotundata and Skeletonema costatum. Moreover, the assembly of dinoflagellate and diatom communities was mainly dominated by stochastic processes, with drift being the major factor. The co-occurrence of dinoflagellates and diatoms showed seasonal patterns, with the highest interactions observed in autumn. In addition, interactions of Syndiniales with dinoflagellates and diatoms highlighted the roles of parasites in eutrophic conditions. Flavobacteriaceae and Rhodobacteraceae are the bacterial taxa that most frequently interacted with dinoflagellates and diatoms, with interactions between dinoflagellates and bacteria being more complex than those between diatoms and bacteria. Overall, this study provides results that deepen our understanding of the phytoplankton dynamics in coastal eutrophic waters.IMPORTANCEDinoflagellates and diatoms are major phytoplankton groups in coastal waters. The composition and diversity of dinoflagellates and diatoms in the open ocean have been well documented; however, it remains uncertain to what extent their adaptation to long-term eutrophic conditions influences their response to environmental disturbances. Here, we investigated the interactions and assembly processes of dinoflagellates and diatoms in a eutrophic bay throughout the whole year. Our findings revealed that interactions between dinoflagellates and diatoms are primarily shaped by seasonal transitions, while prolonged eutrophic conditions tend to amplify stochastic processes in community assembly. These findings provide novel perspectives on the influence of long-term eutrophication on phytoplankton dynamics within eutrophic waters.

A culture-independent approach, supervised machine learning, and the characterization of the microbial community composition of coastal areas across the Bay of Bengal and the Arabian Sea.

BACKGROUND: Coastal areas are subject to various anthropogenic and natural influences. In this study, we investigated and compared the characteristics of two coastal regions, Andhra Pradesh (AP) and Goa (GA), focusing on pollution, anthropogenic activities, and recreational impacts. We explored three main factors influencing the differences between these coastlines: The Bay of Bengal's shallower depth and lower salinity; upwelling phenomena due to the thermocline in the Arabian Sea; and high tides that can cause strong currents that transport pollutants and debris. RESULTS: The microbial diversity in GA was significantly higher than that in AP, which might be attributed to differences in temperature, soil type, and vegetation cover. 16S rRNA amplicon sequencing and bioinformatics analysis indicated the presence of diverse microbial phyla, including candidate phyla radiation (CPR). Statistical analysis, random forest regression, and supervised machine learning models classification confirm the diversity of the microbiome accurately. Furthermore, we have identified 450 cultures of heterotrophic, biotechnologically important bacteria. Some strains were identified as novel taxa based on 16S rRNA gene sequencing, showing promising potential for further study. CONCLUSION: Thus, our study provides valuable insights into the microbial diversity and pollution levels of coastal areas in AP and GA. These findings contribute to a better understanding of the impact of anthropogenic activities and climate variations on biology of coastal ecosystems and biodiversity.

Antibiotic resistance trends among Vibrio vulnificus and Vibrio parahaemolyticus isolated from the Chesapeake Bay, Maryland: a longitudinal study.

Antibiotics are often used to treat severe Vibrio infections, with third-generation cephalosporins and tetracyclines combined or fluoroquinolones alone being recommended by the US Centers for Disease Control and Prevention. Increases in antibiotic resistance of both environmental and clinical vibrios are of concern; however, limited longitudinal data have been generated among environmental isolates to inform how resistance patterns may be changing over time. Hence, we evaluated long-term trends in antibiotic resistance of vibrios isolated from Chesapeake Bay waters (Maryland) across two 3-year sampling periods (2009-2012 and 2019-2022). Vibrio parahaemolyticus (n = 134) and Vibrio vulnificus (n = 94) toxR-confirmed isolates were randomly selected from both sampling periods and tested for antimicrobial susceptibility against eight antibiotics using the Kirby-Bauer disk diffusion method. A high percentage (94%-96%) of V. parahaemolyticus isolates from both sampling periods were resistant to ampicillin and only 2%-6% of these isolates expressed intermediate resistance or resistance to third-generation cephalosporins, amikacin, tetracycline, and trimethoprim-sulfamethoxazole. Even lower percentages of resistant V. vulnificus isolates were observed and those were mostly recovered from 2009 to 2012, however, the presence of multiple virulence factors was observed. The frequency of multi-drug resistance was relatively low (6%-8%) but included resistance against antibiotics used to treat severe vibriosis in adults and children. All isolates were susceptible to ciprofloxacin, a fluoroquinolone, indicating its sustained efficacy as a first-line agent in the treatment of severe vibriosis. Overall, our data indicate that antibiotic resistance patterns among V. parahaemolyticus and V. vulnificus recovered from the lower Chesapeake Bay have remained relatively stable since 2009.IMPORTANCEVibrio spp. have historically been susceptible to most clinically relevant antibiotics; however, resistance and intermediate-resistance have been increasingly recorded in both environmental and clinical isolates. Our data showed that while the percentage of multi-drug resistance and resistance to antibiotics was relatively low and stable across time, some Vibrio isolates displayed resistance and intermediate resistance to antibiotics typically used to treat severe vibriosis (e.g., third-generation cephalosporins, tetracyclines, sulfamethoxazole-trimethoprim, and aminoglycosides). Also, given the high case fatality rates observed with Vibrio vulnificus infections, the presence of multiple virulence factors in the tested isolates is concerning. Nevertheless, the continued susceptibility of all tested isolates against ciprofloxacin, a fluoroquinolone, is indicative of its use as an effective first-line treatment of severe Vibrio spp. infections stemming from exposure to Chesapeake Bay waters or contaminated seafood ingestion.

Bioprospecting of extremophilic perchlorate-reducing bacteria: report of promising Bacillus spp. isolated from sediments of the bay of Cartagena, Colombia.

Three extremophile bacterial strains (BBCOL-009, BBCOL-014 and BBCOL-015), capable of degrading high concentrations of perchlorate at a range of pH (6.5 to 10.0), were isolated from Colombian Caribbean Coast sediments. Morphological features included Gram negative strain bacilli with sizes averaged of 1.75 × 0.95, 2.32 × 0.65 and 3.08 × 0.70 µm, respectively. The reported strains tolerate a wide range of pH (6.5 to 10.0); concentrations of NaCl (3.5 to 7.5% w/v) and KClO4- (250 to 10000 mg/L), reduction of KClO4- from 10 to 25%. LB broth with NaCl (3.5-30% w/v) and KClO4- (250-10000 mg/L) were used in independent trials to evaluate susceptibility to salinity and perchlorate, respectively. Isolates increased their biomass at 7.5 % (w/v) NaCl with optimal development at 3.5 % NaCl. Subsequently, ClO4- reduction was assessed using LB medium with 3.5% NaCl and 10000 mg/L ClO4-. BBCOL-009, BBCOL-014 and BBCOL-015 achieved 10%, 17%, and 25% reduction of ClO4-, respectively. The 16 S rRNA gene sequence grouped them as Bacillus flexus T6186-2, Bacillus marisflavi TF-11 (T), and Bacillus vietnamensis 15 - 1 (T) respectively, with < 97.5% homology. In addition, antimicrobial resistance to ertapenem, vancomycine, amoxicillin clavulanate, penicillin, and erythromycin was present in all the isolates, indicating their high adaptability to stressful environments. The isolated strains from marine sediments in Cartagena Bay, Colombia are suitable candidates to reduce perchlorate contamination in different environments. Although the primary focus of the study of perchlorate-reducing and resistant bacteria is in the ecological and agricultural realms, from an astrobiological perspective, perchlorate-resistant bacteria serve as models for astrobiological investigations.

Exploring changes in microplastic-associated bacterial communities with time, location, and polymer type in Liusha Bay, China.

Microplastics have become a widespread concern within marine environments and are particularly evident in aquaculture regions that are characterized by plastic accumulation. This study employed 16 S rDNA sequencing to investigate the dynamic succession of microbial communities colonizing polyvinyl chloride (PVC), polystyrene (PS), and polyamide (PA) microplastics in seawater, when subjected to varying exposure durations in the Liusha Bay aquaculture region. Results revealed that the composition of microplastics microbial communities varied remarkably across geographical locations and exposure times. With an increase in exposure duration, both the diversity and richness of bacterial communities colonizing microplastics significantly increased, microbial communities show adaptations to the plastisphere. The type of microplastics had a significant effect on the community structure characteristicsof bacteria attached to their surfaces, with inconsistent trends in the relative abundance of different genera on different substrates. Notably, microplastic surfaces harbored a significant abundance of hydrocarbon-degrading bacteria, exemplified by Erythrobacter. These findings underscore the potential of microplastics as unique microbial niches. Meanwhile, long-term exposure experiments also offer the possibility of screening for plastic-degrading bacteria. In addition, the presence of the pathogenic bacterium Vibrio was detected in all microplastic samples, implying that microplastics could serve as carriers for pathogenic dissemination. This underscores the urgency of addressing the risk posed by the proliferation of harmful bacteria on microplastic surfaces. Overall, this study enhances our understanding of microbial community dynamics on microplastics under diverse conditions. It contributes to the broader comprehension of plastisphere microbial ecosystems in the marine environment, thereby addressing critical environmental implications.

Planktonic eukaryotes in the Chesapeake Bay: contrasting responses of abundant and rare taxa to estuarine gradients.

Phytoplankton are important drivers of aquatic ecosystem function and environmental health. Their community compositions and distributions are directly impacted by environmental processes and human activities, including in the largest estuary in North America, the Chesapeake Bay. It is crucial to uncover how planktonic eukaryotes play fundamental roles as primary producers and trophic links and sustain estuarine ecosystems. In this study, we investigated the detailed community structure and spatiotemporal variations of planktonic eukaryotes in the Chesapeake Bay across space and time for three consecutive years. A clear seasonal and spatial shift of total, abundant, and rare planktonic eukaryotes was evident, and the pattern recurred interannually. Multiple harmful algal species have been identified in the Bay with varied distribution patterns, such as Karlodinium, Heterosigma akashiwo, Protoperidinium sp., etc. Compared to abundant taxa, rare subcommunities were more sensitive to environmental disturbance in terms of richness, diversity, and distribution. The combined effects of temporal variation (13.3%), nutrient availability (10.0%), and spatial gradients (8.8%) structured the distribution of eukaryotic microbial communities in the Bay. Similar spatiotemporal patterns between planktonic prokaryotes and eukaryotes suggest common mechanisms of adjustment, replacement, and species interaction for planktonic microbiomes under strong estuarine gradients. To our best knowledge, this work represents the first systematic study on planktonic eukaryotes in the Bay. A comprehensive view of the distribution of planktonic microbiomes and their interactions with environmental processes is critical in understanding the underlying microbial mechanisms involved in maintaining the stability, function, and environmental health of estuarine ecosystems. IMPORTANCE: Deep sequencing analysis of planktonic eukaryotes in the Chesapeake Bay reveals high community diversity with many newly recognized phytoplankton taxa. The Chesapeake Bay planktonic eukaryotes show distinct seasonal and spatial variability, with recurring annual patterns of total, abundant, and rare groups. Rare taxa mainly contribute to eukaryotic diversity compared to abundant groups, and they are more sensitive to spatiotemporal variations and environmental filtering. Temporal variations, nutrient availability, and spatial gradients significantly affect the distribution of eukaryotic microbial communities. Similar spatiotemporal patterns in prokaryotes and eukaryotes suggest common mechanisms of adjustment, substitution, and species interactions in planktonic microbiomes under strong estuarine gradients. Interannually recurring patterns demonstrate that diverse eukaryotic taxa have well adapted to the estuarine environment with a long residence time. Further investigations of how human activities impact estuarine planktonic eukaryotes are critical in understanding their essential ecosystem roles and in maintaining environmental safety and public health.

Production, optimization and characterization of partially purified anti-mycotic compound from marine soil derived streptomycetes originating at unexplored region of Bay of Bengal, India.

Sixty-eight morphologically distinct isolates of marine actinomycetes were derived from seashore, mangrove, and saltpan ecosystems located between the Palk Strait and Gulf of Mannar region, Bay of Bengal, Tamilnadu. Twenty-five (36.8%) isolates exhibited anti-mycotic activity against Candida albicans and Cryptococcus neoformans in preliminary screening, and 4 isolates with prominent activity were identified and designated at the genus level as Streptomyces sp. VPTS3-I, Streptomyces sp. VPTS3-2, Streptomyces sp. VPTSA1-4 and Streptomyces sp. VPTSA1-8. All the potential antagonistic isolates were further characterized with phenotypic and genotypic properties including 16S rRNA gene sequencing and identified species level as Streptomyces afghaniensis VPTS3-1, S. matensis VPTS3-2, S. tuirus VPTSA1-4 and S. griseus VPTSA1-8. In addition, the active fractions from the potential antagonistic streptomycetes were extracted with organic solvents by shake flask culture method and the anti-mycotic efficacies were evaluated. The optimization parameters for the production of the anti-mycotic compound were found to be pH between 7 and 8, the temperature at 30ᵒC, the salinity of 2%, incubation of 9 days, and starch and KNO3 as the suitable carbon and nitrogen sources respectively in starch casein medium.

Responses of attached bacterial communities to blooms of the swimming shelled pteropod Creseis acicula in Daya Bay, southern China.

The shelled pteropod Creseis acicula is a marine pelagic shellfish widely distributed from temperate to tropical seas around the world. From June to July 2020, a C. acicula bloom first happened in the Daya Bay, southern China, and its density reached the highest value (5600 ind. m-3) ever recorded around the world. However, few studies have investigated the responses of bacterial communities to the C. acicula bloom. In the present study, we examined the community profiles of three communities of bacteria including the free-living and particle-attached bacteria in the blooming and reference waters, and bacteria attached to the whole body and shell of C. acicula using a high-throughput sequencing method. The results indicated that the C. acicula bloom had a greater impact on particle-attached bacteria than free-living bacteria. Among the bloom-sensitive particle-attached bacteria, the predominant bacterial phyla were Pseudomonadota, Bacteroidota and Verrucomicrobiota in the blooming areas, whereas they were Actinomycetota and Planctomycetota in the reference areas. Specifically, fecal bacteria Haloferula and Halioglobus spp. were significantly enriched in the blooming waters and accumulated on C. acicula shells. Conversely, the significantly lower relative abundance of Nocardioides sp. in the blooming area and accumulated on the whole body of C. acicula indicated their attachment to particles consumed by C. acicula. Overall, our results suggested that the C. acicula bloom influenced marine bacteria, particularly particle-attached bacteria, by increasing (e.g. providing shells and feces) or decreasing (e.g. filter-feeding the suspended particles) the abundance of available substances.

Detection of multidrug-resistant Enterobacteriaceae isolated from river waters flowing to the Guanabara Bay and from clinical samples of hospitals in Rio de Janeiro, Brazil / Detección de enterobacterias multirresistentes aisladas en aguas de los ríos que desembocan en la bahía de Guanabara y en muestras de hospitales de Río de Janeiro, Brasil

Abstract Introduction: The use of antibiotics in humans, animal husbandry and veterinary activities induces selective pressure leading to the colonization and infection by resistant strains. Objective: We evaluated water samples collected from rivers of the Guanabara Bay, which have suffered minor and major environmental degradation, and clinical samples of hospital origin to detect evidence of the presence of resistance genes to aminoglycosides, beta-lactam antibiotics and fluoroquinolones in strains of Klebsiella pneumoniae subsp. pneumoniae, K. pneumoniae subsp. ozaenae and Escherichia coli. Materials and methods: For isolation of the water strains we employed culture media containing 32 μg/ml cephalotin and 8 μg/ml gentamicin. The strains from clinical materials were selected using culture media containing 8 μg/ml gentamicin. The strains were identified and subjected to antimicrobial susceptibility testing (AST), plasmid DNA extraction and polymerase chain reaction (PCR) to detect genes encoding enzymes modifying aminoglycosides (EMA), extended-spectrum beta-lactamases (ESBL) and plasmid mechanisms of quinolone resistance (PMQR). Results: The AST of the isolates recovered from water samples showed multidrug-resistance profiles similar to those found in isolates recovered from clinical materials. All isolates from water samples and 90% of the isolates from clinical samples showed at least one plasmid band. In the PCR assays, 7.4% of the isolates recovered from water samples and 20% of those from clinical materials showed amplification products for the three antimicrobial classes. Conclusion: We believe that the detection of microorganisms presenting genetic elements in environments such as water is necessary for the prevention and control of their dissemination with potential to infect humans and other animals in eventual contact with these environments.

Resumen Introducción. El uso de antibióticos en seres humanos, en la industria pecuaria y en las actividades veterinarias induce una presión selectiva que resulta en la colonización e infección con cepas resistentes. Objetivo. Determinar la presencia de genes de resistencia a aminoglucósidos, betalactámicos y fluoroquinolonas en cepas de Klebsiella pneumoniae subsp. pneumoniae, K. pneumoniae subsp. ozaenae y Escherichia coli, obtenidas de muestras de agua de los ríos que desembocan en la bahía de Guanabara y de muestras clínicas de hospitales de Río de Janeiro. Materiales y métodos. En la selección de las cepas resistentes obtenidas de las muestras de agua de los ríos, se emplearon medios de cultivo que contenían 32 μg/ml de cefalotina y 8 μg/ ml de gentamicina. En el caso de las muestras de especímenes clínicos, se usaron medios de cultivo que contenían 8 μg/ml de gentamicina. Las cepas se identificaron y se sometieron a pruebas de sensibilidad antimicrobiana, extracción de ADN plasmídico y pruebas de reacción en cadena de la polimerasa (PCR) para detectar los genes que codifican aquellas enzimas que modifican los aminoglucósidos, las betalactamasas de espectro extendido (BLEE) y los mecanismos de resistencia a las quinolonas mediados por plásmidos. Resultados. Se encontraron perfiles de resistencia a los antimicrobianos similares en los dos grupos. En todas las bacterias obtenidas de las muestras de agua y en 90 % de las muestras clínicas, se evidenciaron bandas de plásmidos asociados con la transferencia de genes de resistencia. En las pruebas de PCR, se obtuvieron productos de amplificación de los genes de resistencia para las tres clases de antimicrobianos analizados, en el 7,4 % de las bacterias recuperadas de las muestras de agua y en el 20 % de aquellas recuperadas de las muestras clínicas. Conclusión. La detección de microorganismos con elementos genéticos que confieren resistencia a los antibióticos en ambientes como el agua, es una estrategia necesaria para prevenir y controlar la diseminación de estos agentes patógenos con potencial para infectar a humanos y a otros animales en dichos ambientes.