Transfer of the chromosomally encoded tetracycline resistance gene tet(M) from marine bacteria to Escherichia coli and Enterococcus faecalis

Genomics Revealed Novel Chromosomal Integration of Antimicrobial Resistance Cluster tet(B), sul2, blaTEM-1B, aph(3″)-Ib, and aph(6)-Id in Salmonella Typhimurium

Antimicrobial-resistant Salmonella has posed a huge threat to food safety and public health, and tetracycline is the commonly used antibiotic for treating salmonellosis. In this study, eight Salmonella Typhimurium isolates from diarrhea patients (n = 7) and clam (n = 1) exhibited high-level tetracycline resistance (minimum inhibitory concentration = 128 μg/mL), and these isolates were further resistant to ampicillin and sulfonamides, formatting the R-type ASuT (ampicillin, sulfonamides, and tetracycline). Then, these eight isolates were sequenced using PacBio platform, revealing the presence of tetracycline resistance gene tet(B), along with sulfonamide-resistance gene sul2, extended-spectrum-β-lactamase gene blaTEM-1B, and aminoglycoside resistance genes aph(3″)-Ib and aph(6)-Id on the chromosome, which was associated with R-type ASuT. Four types (A, B1, B2, and C) of genetic arrangement for chromosomally encoding tet(B) were found, inserted into fljBA operon. Type C (fljBA operon-tet(B)-sul2-blaTEM-1B-aph(3″)-Ib-aph(6)-Id-merACDEPTR) was the most common type and was accompanied by various insertion sequences (ISs) (IS26, IS1, and ISVsa5) and recombinases. Pairwise sequence alignment showed that type C arrangement likely resulted from stepwise acquisitions and rearrangements facilitated by the actions of ISs, followed by integration into the chromosome by prophages. Phylogenomic analysis showed that all eight Salmonella Typhimurium isolates from China in this study, along with a human-borne Salmonella Typhimurium isolate (DA34821) from Germany and a foodborne Salmonella Typhimurium isolate (CFSA629) from China, clustered into a single clade, sharing ≤67 SNPs, which suggested that clone spread occurred. These findings underline the emergence of R-type ASuT in Salmonella Typhimurium, which is attributed to the presence of an antimicrobial resistance gene cluster (tet(B), sul2, blaTEM-1B, aph(3″)-Ib, and aph(6)-Id) encoded on the chromosome.

Occurrence of Antibiotic-Resistant Bacteria in Urban Surface Water Sources in Bangladesh

Infections caused by antibiotic-resistant bacteria (ARB) result in an estimated 1.27 million human deaths annually worldwide. Surface waters are impacted by anthropogenic factors, which contribute to the emergence and spread of ARB in the aquatic environment. While research on antibiotic resistance in surface waters has increased recently in developing nations, including Bangladesh, especially in aquaculture, such studies are still limited in Bangladesh compared to developed nations. In this study, bacteria strains isolated from three rivers and two lakes in Khulna city, Bangladesh were characterized for their antibiotic resistance using disk diffusion method. Of the 106 bacterial isolates from 180 surface water samples, the majority exhibited resistance to Ciprofloxacin (75.0-87.5%) and Ceftriaxone (65.6-78.1%), while resistance to Ampicillin was comparatively lower (9.4-18.8%). Notably, the prevalence of ARB was observed to be higher during the wet seasons compared to the dry seasons. The 16S rRNA gene analysis showed that Shigella flexneri was the most dominant (17.9%) bacterium among the ARB cultured from surface waters, followed by Escherichia fergusonii (12.5%), Proteus mirabilis (10.7%), and Enterobacter quasiroggenkampii (8.9%). At the genus level, Enterobacter (23.5%), Shigella (20.6%), and Escherichia spp. (14.7%) were the most abundant among the ARB in both river and lake samples. The findings of this study highlight the prevalence of antimicrobial resistance in surface water sources and suggest the need for enhanced monitoring and improved disposal practices to mitigate potential public health risks.

Effect of environmental factors on conjugative transfer of antibiotic resistance genes in aquatic settings

Antimicrobial-resistance genes (ARGs) are spread among bacteria by horizontal gene transfer, however, the effect of environmental factors on the dynamics of the ARG in water environments has not been very well understood. In this systematic review, we employed the regression tree algorithm to identify the environmental factors that facilitate/inhibit the transfer of ARGs via conjugation in planktonic/biofilm-formed bacterial cells based on the results of past relevant research. Escherichia coli strains were the most studied genus for conjugation experiments as donor/recipient in the intra-genera category. Conversely, Pseudomonas spp., Acinetobacter spp., and Salmonella spp. were studied primarily as recipients across inter-genera bacteria. The conjugation efficiency (ce) was found to be highly dependent on the incubation period. Some antibiotics, such as nitrofurantoin (at ≥0.2 µg ml-1) and kanamycin (at ≥9.5 mg l-1) as well as metallic compounds like mercury (II) chloride (HgCl2, ≥3 µmol l-1), and vanadium (III) chloride (VCl3, ≥50 µmol l-1) had enhancing effect on conjugation. The highest ce value (-0.90 log10) was achieved at 15°C-19°C, with linoleic acid concentrations <8 mg l-1, a recognized conjugation inhibitor. Identifying critical environmental factors affecting ARG dissemination in aquatic environments will accelerate strategies to control their proliferation and combat antibiotic resistance.

Chlorogenic acid attenuates tet (X)-mediated doxycycline resistance of Riemerella anatipestifer

Introduction

The increasing resistance of R. anatipestifer has posed a significant threat to the poultry industry in recent years. The tet gene is the primary determinant of tetracycline resistance in numerous bacteria, and the enzyme modification gene tet(X) is predominantly detected in tetracycline-resistant R. anatipestifer strains.

Methods

In this study, we evaluated the susceptibility of both the standard strain and clinical isolates of R. anatipestifer to doxycycline. And the expression levels of tet(X), tet(A), and tet(O) genes were detected. To assess drug susceptibility, shuttle plasmids were constructed to transfer the tet(X) gene into the standard strain of R. anatipestifer followed by treatment with chlorogenic acid.

Results and discussion

The results revealed that the minimum inhibitory concentration of doxycycline for the standard strain was 0.25μg/mL, whereas it exceeded 8μg/mL for the clinical isolates. Furthermore, there was a significant upregulation observed in expression levels of tet(X), tet(A), and tet(O) genes among induced strains. Interestingly, when transferring the tet(X) gene into the standard strain, its sensitivity to doxycycline decreased; however, MIC values for chlorogenic acid remained consistent between both standard and drug-resistant strains of R. anatipestifer. Moreover, we made a surprising discovery that screening passage with chlorogenic acid resulted in increased sensitivity of R. anatipestifer to doxycycline. Further analysis demonstrated a reversal in expression trends among three differentially expressed genes within induced drug resistance group after intervention with chlorogenic acid. The main objective behind this study is to investigate both killing effect exerted by chlorogenic acid on drug-resistant R. anatipestifer as well as its regulatory impact on drug resistance genes. This will provide novel insights and theoretical basis towards development of chlorogenic acid as a promising drug for treatment and control of drug resistance in R. anatipestifer.

Persistence of Marine Bacterial Plasmid in the House Fly (Musca domestica): Marine-Derived Antimicrobial Resistance Genes Have a Chance of Invading the Human Environment

The house fly is known to be a vector of antibiotic-resistant bacteria (ARB) in animal farms. It is also possible that the house fly contributes to the spread of ARB and antibiotic resistance genes (ARGs) among various environments. We hypothesized that ARB and ARGs present in marine fish and fishery food may gain access to humans via the house fly. We show herein that pAQU1, a marine bacterial ARG-bearing plasmid, persists in the house fly intestine for 5 days after fly ingestion of marine bacteria. In the case of Escherichia coli bearing the same plasmid, the persistence period exceeded 7 days. This interval is sufficient for transmission to human environments, meaning that the house fly is capable of serving as a vector of marine-derived ARGs. Time course monitoring of the house fly intestinal microflora showed that the initial microflora was occupied abundantly with Enterobacteriaceae. Experimentally ingested bacteria dominated the intestinal environment immediately following ingestion; however, after 72 h, the intestinal microflora recovered to resemble that observed at baseline, when diverse genera of Enterobacteriaceae were seen. Given that pAQU1 in marine bacteria and E. coli were detected in fly excrement (defined here as any combination of feces and regurgitated material) at 7 days post-bacterial ingestion, we hypothesize that the house fly may serve as a vector for transmission of ARGs from marine items and fish to humans via contamination with fly excrement.

The Spatial-Temporal Effects of Bacterial Growth Substrates on Antibiotic Resistance Gene Spread in the Biofilm

Biofilm is considered as the hotspot of antibiotic resistance gene (ARG) dissemination. Bacterial growth substrates are important factors for biofilm formation, but its spatial-temporal effects on ARG spread in biofilm is still unclear. In this study, microfluidics combined with microscopic observation were used to reveal spatial-temporal effects of bacterial growth substrates on ARG transfer at real time. The initial horizontal gene transfer events were found to be independent of substrate levels. However, subsequent transfer processes varied greatly depending on the availability of growth substrates. The proportion of transconjugants was much higher (~12%) when observed in substrate-rich regions (under the channel) at 24 h, followed by an exponential decline, with the distance far from the channel. Furthermore, three-dimensional observation revealed that vertical gene transfer influenced by the concentrations of bacterial growth substrates was important for ARG spread in biofilm. The transfer frequency was 8.2 times higher in the high substrate concentration (50×) compared to low concentration (0.5×) in simulated sewage, underscoring the substantial impact of bacterial growth substrate variability on ARG dissemination. This study is helpful for in-depth understanding of ARG dissemination through biofilms and indicates that reducing pollutant emission is important for ARG control in the environment.

The Genetic and Phenotypic Diversity of Bacillus spp. from the Mariculture System in China and Their Potential Function against Pathogenic Vibrio

Bacillus spp. could be one of the most suitable substitutes for the control and prevention of aquatic diseases. The occurrence of species population, antimicrobial character, and virulence diversity in Bacillus spp. recovered from the mariculture system in China between 2009 and 2021 were investigated, screening for probiotic Bacillus strains with good biological safety that can inhibit Vibrio parahaemolyticus, V. alginolyticus, V. harveyi, V. owensii, V. campbellii. The results showed that 116 Bacillus isolates were divided into 24 species, and the top three species were B. subtilis (37/116), B. velezensis (28/116), and B. amyloliquefaciens (10/116). Among the 116 Bacillus isolates, 32.8% were effective against V. parahaemolyticus, 30.1% for V. alginolyticus, 60.3% for V. harveyi, 69.8% for V. owensii and 74.1% for V. campbellii. More than 62% of Bacillus isolates were susceptible to florfenicol, doxycycline and tetracycline, etc., and 26/116 Bacillus isolates were found to be multiple-antibiotic-resistant (MAR), with MARI values ranging from 0 to 0.06. Eighteen kinds of antibiotic resistance genes were tested; only tetB, blaTEM, and blaZ were detected. And 9 isolates in 2 Bacillus species were excluded by 6/10 kinds of Bacillus-related toxin gene (hblA, hblC, nheB, nheC, entFM, cykK). Bio-safety testing indicated that three kinds of probiotics were good probiotic candidates to prevent Vibriosis. These results provide comprehensive genetic diversity, potential risks, and probiotic characteristics of Bacillus in the mariculture system in China, and provide basic support for green and healthy development of aquatic industry.

An Integrative and Conjugative Element (ICE) Found in Shewanella halifaxensis Isolated from Marine Fish Intestine May Connect Genetic Materials between Human and Marine Environments

Integrative and conjugative elements (ICEs) play a role in the horizontal transfer of antibiotic resistance genes (ARGs). We herein report an ICE from Shewanella halifaxensis isolated from fish intestine with a similar structure to both a clinical bacterial ICE and marine bacterial plasmid. The ICE was designated ICEShaJpn1, a member of the SXT/R391 family of ICEs (SRIs). ICEShaJpn1 has a common core structure with SRIs of clinical and fish origins and an ARG cassette with the pAQU1 plasmid of Photobacterium damselae subsp. damselae, suggesting that the common core of SRIs is widely distributed and ARG cassettes are collected from regional bacteria.

Enterococcal biofilm - a nidus for antibiotic resistance transfer?

Enterococci, important agents of hospital acquired infection, are listed on the WHO list of multi-drug resistant pathogens commonly encountered in hospital acquired infections are now of increasing importance, due to the development of strains resistant to multiple antibiotics. Enterococci are also important microorganisms in the environment and their presence is frequently used as an indicator of faecal pollution. Their success is related to their ability to survive within a broad range of habitats and the ease by which they acquire mobile genetic elements, including plasmids, from other bacteria. The enterococci are frequently present within a bacterial biofilm which provides stability and protection to the bacterial population along with an opportunity for a variety of bacterial interactions. Enterococci can accept extrachromosomal DNA both from within its own species and from other bacterial species and this is enhanced by the proximity of the donor and recipient strains. It is this exchange of genetic material that makes the role of biofilm such an important aspect of the success of enterococci. There remain many questions regarding the most suitable model systems to study enterococci in biofilm and regarding the transfer of genetic material including antibiotic resistance in these biofilms. This review focuses on some important aspects of biofilm in the context of horizontal gene transfer (HGT) in enterococci.

Contamination of antibiotics and sul and tet(M) genes in veterinary wastewater, river, and coastal sea in Thailand

Water systems in Southeast Asia accumulate antibiotics and antibiotic resistance genes (ARGs) from multiple origins, notably including human clinics and animal farms. To ascertain the fate of antibiotics and ARGs in natural water environments, we monitored the concentrations of these items in Thailand. Here, we show high concentrations of tetracyclines (72,156.9 ng/L) and lincomycin (23,968.0 ng/L) in pig farms, followed by nalidixic acid in city canals. The city canals and rivers contained diverse distributions of antibiotics and ARGs. Assessments of targeted ARGs, including sul1, sul2, sul3, and tet(M), showed that freshwater (pig farm wastewater, rivers, and canals) consistently contained these ARGs, but these genes were less abundant in seawater. Although sulfonamides were low concentrations (<170 ng/mL), sul1 and sul2 genes were abundant in freshwater (minimum 4.4 × 10^-3-maximum 1.0 × 10⁰ copies/16S), suggesting that sul genes have disseminated over a long period, despite cessation of use of this class of antibiotics. Ubiquitous distribution of sul genes in freshwater appeared to be independent of selection pressure. In contrast, water of the coastal sea in the monitored area was not contaminated by these antibiotics or ARGs. The density of Enterobacteriales was lower in seawater than in freshwater, suggesting that the number of ARG-possessing Enterobacteriales falls after entering seawater. From the pig farms, through rivers/canals, to the coastal sea, the occurrence of tetracyclines and tet(M) exhibited some correlation, although not a strong one. However, no correlations were found between concentrations of total antibiotics and ARGs, nor between sulfonamides and sul genes. This is the first comprehensive study showing Thai features of antibiotics and ARGs contaminations. The pig farm is hot spot of antibiotics and ARGs, and sul genes ubiquitously distribute in freshwater environments, which become less abundant in seawater.

Prevalence of Antibiotic-Resistant Bacteria ESKAPE among Healthy People Estimated by Monitoring of Municipal Wastewater

There is increasing attention toward factors that potentially contribute to antibiotic resistance (AR), as well as an interest in exploring the emergence and occurrence of antibiotic resistance bacteria (ARB). We monitored six ARBs that cause hospital outbreaks in wastewater influent to highlight the presence of these ARBs in the general population. We analyzed wastewater samples from a municipal wastewater treatment plant (MWWTP) and hospital wastewater (HW) for six species of ARB: Carbapenem-resistant Enterobacteria (CARBA), extended-spectrum β-lactamase producing Enterobacteria (ESBL), multidrug-resistant Acinetobacter (MDRA), multidrug-resistant Pseudomonas aeruginosa (MDRP), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococci (VRE). We registered a high percentage of ARBs in MWWTP samples (>66%) for all ARBs except for MDRP, indicating a high prevalence in the population. Percentages in HW samples were low (<78%), and no VRE was detected throughout the study. CARBA and ESBL were detected in all wastewater samples, whereas MDRA and MRSA had a high abundance. This result demonstrated the functionality of using raw wastewater at MWWTP to monitor the presence and extent of ARB in healthy populations. This kind of surveillance will contribute to strengthening the efforts toward reducing ARBs through the detection of ARBs to which the general population is exposed.

Biofilms: hot spots of horizontal gene transfer (HGT) in aquatic environments, with a focus on a new HGT mechanism

Biofilms in water environments are thought to be hot spots for horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs). ARGs can be spread via HGT, though mechanisms are known and have been shown to depend on the environment, bacterial communities and mobile genetic elements. Classically, HGT mechanisms include conjugation, transformation and transduction; more recently, membrane vesicles (MVs) have been reported as DNA reservoirs implicated in interspecies HGT. Here, we review the current knowledge on the HGT mechanisms with a focus on the role of MVs and the methodological innovations in the HGT research.

Tetracycline Resistance Gene Profiles in Red Seabream (Pagrus major) Intestine and Rearing Water After Oxytetracycline Administration

Marine aquaculture fish and the environment are possible hot spots for the maintenance and spread of antibiotic resistance genes (ARGs). We here show the time courses of changes of six tetracycline resistance genes (tet) in fish rearing seawater and fish intestine in tank experiments. Experimental tanks were prepared as oxytetracycline (OTC) administration tanks and those without OTC. It was found that tet(B), tet(M), and tet(W) were dominant in seawater among the six tet genes. tet(B) and tet(M) abundances increased immediately after OTC administration, indicating that OTC served as a selective pressure to increase the proportion of tet-possessing bacteria. In contrast, the abundance of tet genes in the fish intestine did not differ between the with- and without-OTC administration groups, and clearly was not altered by OTC administration. Profile changing of tet in seawater and fish intestine did not synchronize. These observations suggested that the dynamics of intestinal tet-possessing bacteria do not directly reflect the environment, but reflect selection within the intestine.

Genetic and Phenotypic Characteristics of a Multi-strain Probiotic for Broilers

Bacteria isolated from different segments of the gastro-intestinal tract (GIT) of healthy free-range broilers were screened for probiotic properties. Six strains were selected and identified as Lactobacillus gallinarum, Lactobacillus johnsonii, Lactobacillus salivarius, Lactobacillus crispatus, Enterococcus faecalis and Bacillus amyloliquefaciens based on 16S rRNA, gyrB and recA gene sequence analyses. All six strains produced exopolysaccharides (EPS) and formed biofilms under conditions simulating the broiler GIT. Lactobacillus johnsonii DPN184 and L. salivarius DPN181 produced hydrogen peroxide, and L. crispatus DPN167 and E. faecalis DPN94 produced bile salt hydrolase (BSH) and phytase. Bacillus amyloliquefaciens DPN123 produced phytase, amylase, surfactin and iturin A1. No abnormalities were observed when broilers were fed the multi-strain combination, suggesting that it could be used as a probiotic.

Conjugative Gene Transfer between Nourished and Starved Cells of Photobacterium damselae ssp. damselae and Escherichia coli

Horizontal gene transfer (HGT) between bacteria with different habitats and nutritional requirements is important for the spread of antibiotic resistance genes (ARG). The objective of the present study was to clarify the effects of organic matter on HGT between nourished and starved bacteria. We demonstrated that conjugation ability is affected by the nutritional conditions of the cell and environment. A filter mating HGT experiment was performed using Photobacterium damselae ssp. damselae, strain 04Ya311, a marine-origin bacterium possessing the multidrug-resistance plasmid pAQU1, as the donor, and Escherichia coli as the recipient. The donor and recipient were both prepared as nutrient-rich cultured and starved cells. Filter mating was performed on agar plates with and without organic nutrients. The transcription of the plasmid-borne genes tet(M) and traI was quantitated under eutrophic and oligotrophic conditions. The donor P. damselae transferred the plasmid to E. coli at a transfer rate of 10⁻⁴ under oligotrophic and eutrophic conditions. However, when the donor was starved, HGT was not detected under oligotrophic conditions. The addition of organic matter to starved cells restored conjugative HGT even after 6 d of starvation. The transcription of traI was not detected in starved cells, but was restored upon the addition of organic matter. The HGT rate appears to be affected by the transcription of plasmid-associated genes. The present results suggest that the HGT rate is low in starved donors under oligotrophic conditions, but is restored by the addition of organic matter.

Occurrence of sul and tet(M) genes in bacterial community in Japanese marine aquaculture environment throughout the year: Profile comparison with Taiwanese and Finnish aquaculture waters

The use of antibiotics in aquaculture causes selection pressure for antibiotic-resistant bacteria (ARB). Antibiotic resistance genes (ARGs) may persist in ARB and the environment for long time even after stopping drug administration. Here we show monthly differences in the occurrences of genes conferring resistance to sulfonamides (i.e. sul1, sul2, sul3), and tetracyclines (tet(M)) in Japanese aquaculture seawater accompanied by records of drug administration. sul2 was found to persist throughout the year, whereas the occurrences of sul1, sul3, and tet(M) changed month-to-month. sul3 and tet(M) were detected in natural bacterial assemblages in May and July, but not in colony-forming bacteria, thus suggesting that the sul3 was harbored by the non-culturable fraction of the bacterial community. Comparison of results from Taiwanese, Japanese, and Finnish aquaculture waters reveals that the profile of sul genes and tet(M) in Taiwan resembles that in Japan, but is distinct from that in Finland. To our knowledge, this work represents the first report to use the same method to compare the dynamics of sul genes and tet(M) in aquaculture seawater in different countries.

Tetracycline resistance gene tet(M) of a marine bacterial strain is not accumulated in bivalves from seawater in clam tank experiment and mussel monitoring

Antibiotic resistance genes (ARGs) are found in marine as well as terrestrial bacteria. Bivalves are known to accumulate chemical pollutants and pathogenic microbes, however, the fate of ARGs in bivalves after the intake of ARG-possessing bacteria is not known. Here we show that the copy number of oxytetracycline resistance gene tet(M) increased rapidly in the clam digestive tract by filtering water, then remained constant over 96h in a tank experiment even with the addition of tet(M)-possessing bacteria every 24h. >99.9% of the added tet(M) was decomposed, reaching a balanced state. Environmental sampling of mussel digestive tract and seawater supported the hypothesis that tet(M) was decomposed in bivalves as tet(M) was present in seawater from April to October at a concentration of 10^-5 to 10^-6 copies/16S, whereas tet(M) in mussels was mostly below the detection limit. Two (April) and three (July and October) individual mussels were positive for tet(M) with a concentration equivalent to that of seawater. We therefore conclude that bivalves do not accumulate tet(M) from seawater.

Various Profiles of tet Genes Addition to tet(X) in Riemerella anatipestifer Isolates From Ducks in China

To investigate tetracycline resistance and resistant genotype in Riemerella anatipestifer, the tetracycline susceptibility of 212 R. anatipestifer isolates from China between 2011 and 2017 was tested. The results showed that 192 of 212 (90.6%) R. anatipestifer isolates exhibited resistance to tetracycline (the MICs ranged from 4 to 256 μg/ml). The results of PCR detection showed that, 170 of 212 (80.2%) R. anatipestifer isolates possessed the tet(X) gene. Other genes, including tet(A), tet(M), tet(Q), tet(O), tet(B), and tet(O/W/32/O), were found at frequencies of 20.8, 4.7, 1.4, 0.9, 0.9, and 0.5%, respectively. However, tet(C), tet(E), tet(G), tet(K), and tet(W) were not detected in any isolate. In these tet gene positive strains, 31 (14.6%), 2 (0.9%), 5 (2.4%), 1 (0.5%), 3 (1.4%) were detected containing tet(A)/tet(X), tet(M)/tet(O), tet(M)/tet(X), tet(O)/tet(X), and tet(Q)/tet(X) simultaneously, respectively. One isolates, R131, unexpectedly contained three tet genes, i.e., tet(M), tet(O), and tet(X). Sequence analysis of the tet gene ORFs cloned from R. anatipestifer isolates confirmed that tet(A), tet(B), tet(M), tet(O), tet(Q) and an unusual mosaic tet gene tet(O/W/32/O) were present in R. anatipestifer. The MIC results of R. anatipestifer ATCC 11845 transconjugants carrying tet(A), tet(B), tet(M), tet(O), tet(O/W/32/O), tet(Q), and tet(X) genes exhibited tetracycline resistance with MIC values ranging from 4 to 64 μg/ml. Additionally, the tet(X) gene could transfer into susceptible strain via natural transformation (transformation frequencies of ~10⁻⁶). In conclusion, the tet(A), tet(B), tet(M), tet(O), tet(O/W/32/O), tet(Q), and tet(X) genes were found and conferred tetracycline resistance in R. anatipestifer isolates. Moreover, the tet(X) is the main mechanism of tetracycline resistance in R. anatipestifer isolates. To our knowledge, this is the first report of tet(A), tet(B), tet(M), tet(O), tet(Q), and mosaic gene tet(O/W/32/O) in R. anatipestifer.

Release and Constancy of an Antibiotic Resistance Gene in Seawater under Grazing Stress by Ciliates and Heterotrophic Nanoflagellates

Extracellular DNA (exDNA) is released from bacterial cells through various processes. The antibiotic resistance genes (ARGs) coded on exDNA may be horizontally transferred among bacterial communities by natural transformation. We quantitated the released/leaked tetracycline resistance gene, tet(M) over time under grazing stress by ciliates and heterotrophic nanoflagellates (HNFs), and found that extracellular tet(M) (ex-tetM) increased with bacterial grazing. Separate microcosms containing tet(M)-possessing bacteria with ciliates or HNFs were prepared. The copy number of ex-tetM in seawater in the ciliate microcosm rapidly increased until 3 d after the incubation, whereas that in the HNF microcosm showed a slower increase until 20 d. The copy number of ex-tetM was stable in both cases throughout the incubation period, suggesting that extracellular ARGs are preserved in the environment, even in the presence of grazers. Additionally, ARGs in bacterial cells were constant in the presence of grazers. These results suggest that ARGs are not rapidly extinguished in a marine environment under grazing stress.

Resistance to antimicrobial agents among enterococci isolated from fecal samples of wild marine species in the southern coast of Brazil

The purpose of this study was to evaluate species distribution, antimicrobial resistance profiles, and presence of resistance genes in enterococci isolated from fecal samples of wild marine species, including seabirds (n=12), sea turtles (n=8), and mammals (n=3) found alive or dead in southern coast of Brazil. Enterococci were classified based on phenotypic and genotypic characteristics, tested for antibiotic susceptibility, and the presence of tet(S), tet(M), tet(L), mrsC, and erm(B) genes by PCR. Enterococcus faecalis and Enterococcus faecium were the most common species. Single (37.09%), double (25.80%), and multiple (16.12%) antibiotic resistance patterns were observed. Resistance to rifampicin occurred most frequently. The msrC, tet(M), and/or tet(L) genes were detected in 60.15%, 73.07%, and 23.07% of the resistant strains, respectively. In conclusion, the presence of antibiotic resistant strains in these species could be related to food web interactions and aquatic pollutants or linked to environmental resistome.

Identification of a New Tetracycline Resistance Determinant tet47 from Fish Intestine

To better understand food safety risks, functional genomic analysis was conducted to identify undescribed antibiotic resistance genes in fish samples from an aquaculture fish farm in Ohio. A fosmid genomic library from pooled DNA of antibiotic-resistant isolates was used to screen for resistance genes against tetracycline (Tet). A new Tet-resistant determinant designated as tet 47 was identified, with the original hosts being Providencia spp. from fish intestine. The new gene was also found to confer Tet resistance in Escherichia coli. Fish and byproducts were shown to be possible carriers that may disseminate new, functional, and potentially transmissible antibiotic resistance determinants through food, feed, and environmental contacts.

The impact of a freshwater fish farm on the community of tetracycline-resistant bacteria and the structure of tetracycline resistance genes in river water

The aim of this study was to assess the impact of a fish farm on the structure of antibiotic resistant bacteria and antibiotic resistance genes in water of Drwęca River. Samples of upstream river waters; post-production waters and treated post-production waters from fish farm; as well as downstream river waters were monitored for tetracycline resistant bacteria, tetracycline resistant genes, basic physico-chemical parameters and tetracyclines concentration. The river waters was characterized by low levels of pollution, which was determined based on water temperature, pH and concentrations of dissolved oxygen and tetracycline antibiotics. Culture-dependent (heterotrophic plate counts, counts of bacteria resistant to oxytetracycline (OTC(R)) and doxycycline (DOX(R)), minimum inhibitory concentrations for oxytetracycline and doxycycline, multidrug resistance of OTC(R) and DOX(R), qualitative composition of OTC(R) and DOX(R), prevalence of tet genes in resistant isolates) and culture-independent surveys (quantity of tet gene copies) revealed no significant differences in the abundance of antibiotic-resistant bacteria and antibiotic resistance genes between the studied samples. The only way in which the fish farm influenced water quality in the Drwęca River was by increasing the diversity of tetracycline-resistance genes. However, it should also be noted that the bacteria of the genera Aeromonas sp. and Acinetobacter sp. were able to transfer 6 out of 13 tested tet genes into Escherichiacoli, which can promote the spread of antibiotic resistance in the environment.

Management options for reducing the release of antibiotics and antibiotic resistance genes to the environment

BACKGROUND

There is growing concern worldwide about the role of polluted soil and water environments in the development and dissemination of antibiotic resistance.

OBJECTIVE

Our aim in this study was to identify management options for reducing the spread of antibiotics and antibiotic-resistance determinants via environmental pathways, with the ultimate goal of extending the useful life span of antibiotics. We also examined incentives and disincentives for action.

METHODS

We focused on management options with respect to limiting agricultural sources; treatment of domestic, hospital, and industrial wastewater; and aquaculture.

DISCUSSION

We identified several options, such as nutrient management, runoff control, and infrastructure upgrades. Where appropriate, a cross-section of examples from various regions of the world is provided. The importance of monitoring and validating effectiveness of management strategies is also highlighted. Finally, we describe a case study in Sweden that illustrates the critical role of communication to engage stakeholders and promote action.

CONCLUSIONS

Environmental releases of antibiotics and antibiotic-resistant bacteria can in many cases be reduced at little or no cost. Some management options are synergistic with existing policies and goals. The anticipated benefit is an extended useful life span for current and future antibiotics. Although risk reductions are often difficult to quantify, the severity of accelerating worldwide morbidity and mortality rates associated with antibiotic resistance strongly indicate the need for action.

Novel conjugative transferable multiple drug resistance plasmid pAQU1 from Photobacterium damselae subsp. damselae isolated from marine aquaculture environment

The emergence of drug-resistant bacteria is a severe problem in aquaculture. The ability of drug resistance genes to transfer from a bacterial cell to another is thought to be responsible for the wide dissemination of these genes in the aquaculture environment; however, little is known about the gene transfer mechanisms in marine bacteria. In this study, we show that a tetracycline-resistant strain of Photobacterium damselae subsp. damselae, isolated from seawater at a coastal aquaculture site in Japan, harbors a novel multiple drug resistance plasmid. This plasmid named pAQU1 can be transferred to Escherichia coli by conjugation. Nucleotide sequencing showed that the plasmid was 204,052 base pairs and contained 235 predicted coding sequences. Annotation showed that pAQU1 did not have known repA, suggesting a new replicon, and contained seven drug resistance genes: bla(CARB-9)-like, floR, mph(A)-like, mef(A)-like, sul2, tet(M) and tet(B). The plasmid has a complete set of genes encoding the apparatus for the type IV secretion system with a unique duplication of traA. Phylogenetic analysis of the deduced amino acid sequence of relaxase encoded by traI in pAQU1 demonstrated that the conjugative transfer system of the plasmid belongs to MOB(H12), a sub-group of the MOB(H) plasmid family, closely related to the IncA/C type of plasmids and SXT/R391 widely distributed among species of Enterobacteriaceae and Vibrionaceae. Our data suggest that conjugative transfer is involved in horizontal gene transfer among marine bacteria and provide useful insights into the molecular basis for the dissemination of drug resistance genes among bacteria in the aquaculture environment.