Co-production of Tet(X) and MCR-1, two resistance enzymes by a single plasmid

Tigecycline and colistin are few of ‘last-resort’ antibiotic defences used in anti-infection therapies against carbapenem-resistant bacterial pathogens. The successive emergence of plasmid-borne tet(X) tigecycline resistance mechanism and mobile colistin resistance (mcr) determinant, renders them clinically useless. Here, we report that co-carriage of tet(X6) and mcr-1 gives co-resistance to both classes of antibiotics by a single plasmid in Escherichia coli. Tet(X6), the new tigecycline resistance enzyme is functionally defined. Both Tet(X6) and MCR-1 robustly interfere accumulation of antibiotic-induced reactive oxygen species (ROS). Unlike that mcr-1 exerts fitness cost in E. coli, tet(X6) does not. In the tet(X6)-positive strain that co-harbors mcr-1, tigecycline resistance is independently of colistin resistance caused by MCR-1-mediated lipid A remodelling, and vice versa. In general consistency with that of MCR-1, Tet(X6) leads to the failure of tigecycline treatment in the infection model of G. mellonella. Taken together, the co-production of Tet(X) and MCR-1 appears as a major clinic/public health concern.     

Two Different Tetracycline Resistance Mechanisms, Plasmid-Carried tet(L) and Chromosomally Located Transposon-Associated tet(M), Coexist in Lactobacillus sakei Rits 9

Lactobacillus sakei is extensively used as functional starter culture in fermented meat products. One of the safety criteria of a starter culture is the absence of potentially transferable antibiotic resistance determinants. However, tetracycline-resistant L. sakei strains have already been observed. In this paper, we show that tetracycline resistance in L. sakei Rits 9, a strain isolated from Italian Sola cheese made from raw milk, is mediated by a transposon-associated tet(M) gene coding for a ribosomal protection protein and a plasmid-carried tet(L) gene coding for a tetracycline efflux pump. pLS55, the 5-kb plasmid carrying the tet(L) gene, is highly similar to the pMA67 plasmid recently described for Paenibacillus larvae, a species pathogenic to honeybees. pLS55 could be transferred by electroporation into the laboratory strain L. sakei 23K. While the L. sakei 23K transformant containing pLS55 displayed an intermediate tetracycline resistance level (MIC, <32 μg/ml), L. sakei Rits 9, containing both tetracycline-resistant determinants, had a MIC of <256 μg/ml, suggesting that Tet L and Tet M confer different levels of resistance in L. sakei. Remarkably, in the absence of tetracycline, a basal expression of both genes was detected for L. sakei Rits 9. In addition, subinhibitory concentrations of tetracycline affected the expression patterns of tet(M) and tet(L) in different ways: the expression of tet(M) was induced only at high tetracycline concentrations, whereas the expression of tet(L) was up-regulated at lower concentrations. This is the first time that two different mechanisms conferring resistance to tetracycline are characterized for the same strain of a lactic acid bacterium.     

Detection of tetracycline and macrolide resistance determinants in enterococci of animal and environmental origin using multiplex PCR

An occurrence of resistance to tetracycline (TET) and erythromycin (ERY) was ascertained in 82 isolates of Enterococcus spp. of animal and environmental origin. Using E test, 33 isolates were resistant to TET and three isolates to ERY. Using polymerase chain reaction (PCR; single and multiplex), the TET determinants tet(M) and tet(L) were detected in 35 and 13 isolates, respectively. Twelve isolates carried both tet(M) and tet(L) genes. Eight isolates possessed ermB gene associated with ERY resistance. Multiplex PCR was shown to be a suitable method for simultaneous determination of all three resistance determinants that occurred most frequently in bacteria isolated from poultry. This study also demonstrates that gastrointestinal tract of broilers may be a reservoir of enterococci with acquired resistance to both TET and ERY that can be transferred to humans via food chain.     

Diverse Tetracycline Resistant Bacteria and Resistance Genes from Coastal Waters of Jiaozhou Bay

Environmental microbiology investigation was carried out in Jiaozhou Bay to determine the source and distribution of tetracycline-resistant bacteria and their resistance mechanisms. At least 25 species or the equivalent molecular phylogenetic taxa in 16 genera of resistant bacteria could be identified based on 16S ribosomal deoxyribonucleic acid sequence analysis. Enterobacteriaceae, Pseudomonadaceae, and Vibrionaceae constituted the majority of the typical resistant isolates. Indigenous estuarine and marine Halomonadaceae, Pseudoalteromonadaceae, Rhodobacteraceae, and Shewanellaceae bacteria also harbored tetracycline resistance. All the six resistance determinants screened, tet(A)–(E) and tet(G), could be detected, and the predominant genes were tet(A), tet(B), and tet(G). Both anthropogenic activity-related and indigenous estuarine or coastal bacteria might contribute to the tet gene reservoir, and resistant bacteria and their molecular determinants may serve as bioindicators of coastal environmental quality. Our work probably is the first identification of tet(E) in Proteus, tet(G) in Acinetobacter, tet(C) and tet(D) in Halomonas, tet(D) and tet(G) in Shewanella, and tet(B), tet(C), tet(E), and tet(G) in Roseobacter. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The role of anaerobic digestion in controlling the release of tetracycline resistance genes and class 1 integrons from municipal wastewater treatment plants

In this study, the abilities of two anaerobic digestion processes used for sewage sludge stabilization were compared for their ability to reduce the quantities of three genes that encode resistance to tetracycline (tet(A), tet(O), and tet(X)) and one gene involved with integrons (intI1). A two-stage, thermophilic/mesophilic digestion process always resulted in significant decreases in the quantities of tet(X) and intI1, less frequently in decreases of tet(O), and no net decrease in tet(A). The thermophilic stage was primarily responsible for reducing the quantities of these genes, while the subsequent mesophilic stage sometimes caused a rebound in their quantities. In contrast, a conventional anaerobic digestion process rarely caused a significant decrease in the quantities of any of these genes, with significant increases occurring more frequently. Our results demonstrate that anaerobic thermophilic treatment was more efficient in reducing quantities of genes associated with the spread of antibiotic resistance compared to mesophilic digestion.     

The application of Tet repressor in prokaryotic gene regulation and expression

Inducible gene expression based upon Tet repressor (tet regulation) is a broadly applied tool in molecular genetics. In its original environment, Tet repressor (TetR) negatively controls tetracycline (tc) resistance in bacteria. In the presence of tc, TetR is induced and detaches from its cognate DNA sequence tetO, so that a tc antiporter protein is expressed. In this article, we provide a comprehensive overview about tet regulation in bacteria and illustrate the parameters of different regulatory architectures. While some of these set‐ups rely on natural tet‐control regions like those found on transposon Tn10, highly efficient variations of this system have recently been adapted to different Gram‐negative and Gram‐positive bacteria. Novel tet‐controllable artificial or hybrid promoters were employed for target gene expression. They are controlled by regulators expressed at different levels either in a constitutive or in an autoregulated manner. The resulting tet systems have been used for various purposes. We discuss integrative elements vested with tc‐sensitive promoters, as well as tet regulation in Gram‐negative and Gram‐positive bacteria for analytical purposes and for protein overproduction. Also the use of TetR as an in vivo biosensor for tetracyclines or as a regulatory device in synthetic biology constructs is outlined. Technical specifications underlying different regulatory set‐ups are highlighted, and finally recent developments concerning variations of TetR are presented, which may expand the use of prokaryotic tet systems in the future.     

Tetracyclines and Tetracycline Resistance in Agricultural Soils: Microcosm and Field Studies

The influence of the use of antibiotics on the prevalence of resistance genes in the environment is still poorly understood. We studied the diversity of tetracycline and sulfonamide resistance genes as influenced by fertilization with pig manure in soil microcosms and at two field locations. Manure contained a high diversity of resistance genes, regardless of whether it stemmed from a farm operation with low or regular use of antibiotics. In the microcosm soils, the influence of fertilization with manure was clearly shown by an increase in the number of resistance genes in the soil after manuring. Spiking of the tetracycline compounds to the microcosms had only little additional impact on the diversity of resistance genes. Overall, the tetracycline resistance genes tet(T), tet(W), and tet(Z) were ubiquitous in soil and pig slurries, whereas tet(Y), tet(S), tet(C), tet(Q), and tet(H) were introduced to the microcosm soil by manuring. The diversity of tetracycline and sulfonamide [sul(1), sul(2), and sul(3)] resistance genes on a Swiss pasture was very high even before slurry amendment, although manure from intensive farming had not been applied in the previous years. The additional effect of manuring was small, with the tetracycline and sulfonamide resistance diversity staying at high levels for the complete growth season. At an agricultural field site in Germany, the diversity of tetracycline and sulfonamide resistance genes was considerably lower, possibly reflecting regional differences in gene diversity. This study shows that there is a considerable pool of resistance genes in soils. Although it is not possible to conclude whether this diversity is caused by the global spread of resistance genes after 50 years of tetracycline use or is due to the natural background in soil resistance genes, it highlights a role that environmental reservoirs might play in resistance gene capture.     

Fluorescence and Phosphorescence Study of Tet Repressor–Operator Interaction

Fluorescence and phosphorescence measurements have been carried out on single-p tryptophan (Trp 43 or Trp 75)-containing mutants of Tet repressor (Tet R). Tet R containing Trp 43, the residue localized in the DNA recognition helix of the repressor, has been used to observe the binding of Tet R to two 20-bp DNA sequences of tet O₁ and tet O₂ operators. Binding of Tet R to tet O₁ operator leads to a 78% decrease of the repressor fluorescence intensity, with an accompanying 20-nm blue shift of its fluorescence emission maximum to 330 nm. Upon binding of Tet R to tet O₂ operator, the Trp 43 fluorescence intensity is quenched by 60%, and a 10-nm shift of its emission maximum to 340 nm occurs. Solute fluorescence quenching studies, using acrylamide, performed at low ionic strength indicate that in both the complex of Tet R with the O₁ and that with the O₂ operator, Trp 43 is moderately buried, as indicated by a bimolecular rate quenching constant of about 1.8 × 10⁹ M^–1 sec^–1. In contrast to the Tet R–tet O₂ complex, the Stern–Volmer acrylamide quenching constant K _sv of the complex with tet O₁ operator changes from 7.5 M^–1 at 5 mM NaCl to 22 M^–1 at 200 mM NaCl, indicating different exposures of Trp 43 in the two complexes in solutions of higher ionic strength. Phosphorescence studies showed a 0–0 vibronic transition at 408 and 403 nm for Trp 43 and Trp 75, respectively. Upon binding of Tet R to the tet operators, we observed red shifts of 0–0 vibronic bands of Trp 43 to 413 and 412 nm for tet O₁ and tet O₂ operator, respectively, and the phosphorescence triplet lifetime of Trp 43 at 75 K was quenched from 6.0–5.5 to 3.5–3.3 sec. The thermal phosphorescence quenching profile ranged from –200°C to –20°C, and differed drastically for the two complexes, suggesting different dynamics of the microenvironment of the Trp 43 residue. The luminescence data for Trp 43 of Tet R suggest that the recognition helix of Tet R interacts in different fashions with the tet O₁ and tet O₂ operators.     

Mechanisms of antimicrobial resistance and genetic relatedness among enterococci isolated from dogs and cats in the United States

Aims: In this study, mechanisms of antimicrobial resistance and genetic relatedness among resistant enterococci from dogs and cats in the United States were determined. Methods and Results: Enterococci resistant to chloramphenicol, ciprofloxacin, erythromycin, gentamicin, kanamycin, streptomycin, lincomycin, quinupristin/dalfopristin and tetracycline were screened for the presence of 15 antimicrobial resistance genes. Five tetracycline resistance genes [tet(M), tet(O), tet(L), tet(S) and tet(U)] were detected with tet(M) accounting for approx. 60% (130/216) of tetracycline resistance; erm(B) was also widely distributed among 96% (43/45) of the erythromycin‐resistant enterococci. Five aminoglycoside resistance genes were also detected among the kanamycin‐resistant isolates with the majority of isolates (25/36; 69%) containing aph(3′)‐IIIa. The bifunctional aminoglycoside resistance gene, aac(6′)‐Ie‐aph(2″)‐Ia, was detected in gentamicin‐resistant isolates and ant(6)‐Ia in streptomycin‐resistant isolates. The most common gene combination among enterococci from dogs (n = 11) was erm(B), aac(6′)‐Ie‐aph(2″)‐Ia, aph(3′)‐IIIa, tet(M), while tet(O), tet(L) were most common among cats (n = 18). Using pulsed‐field gel electrophoresis (PFGE), isolates clustered according to enterococcal species, source and antimicrobial gene content and indistinguishable patterns were observed for some isolates from dogs and cats. Conclusion: Enterococci from dogs and cats may be a source of antimicrobial resistance genes. Significance and Impact of the Study: Dogs and cats may act as reservoirs of antimicrobial resistance genes that can be transferred from pets to people. Although host‐specific ecovars of enterococcal species have been described, identical PFGE patterns suggest that enterococcal strains may be exchanged between these two animal species.     

Unraveling Antimicrobial Resistance Genes and Phenotype Patterns among Enterococcus faecalis Isolated from Retail Chicken Products in Japan

Multidrug-resistant enterococci are considered crucial drivers for the dissemination of antimicrobial resistance determinants within and beyond a genus. These organisms may pass numerous resistance determinants to other harmful pathogens, whose multiple resistances would cause adverse consequences. Therefore, an understanding of the coexistence epidemiology of resistance genes is critical, but such information remains limited. In this study, our first objective was to determine the prevalence of principal resistance phenotypes and genes among Enterococcus faecalis isolated from retail chicken domestic products collected throughout Japan. Subsequent analysis of these data by using an additive Bayesian network (ABN) model revealed the co-appearance patterns of resistance genes and identified the associations between resistance genes and phenotypes. The common phenotypes observed among E. faecalis isolated from the domestic products were the resistances to oxytetracycline (58.4%), dihydrostreptomycin (50.4%), and erythromycin (37.2%), and the gene tet(L) was detected in 46.0% of the isolates. The ABN model identified statistically significant associations between tet(L) and erm(B), tet(L) and ant(6)-Ia, ant(6)-Ia and aph(3’)-IIIa, and aph(3’)-IIIa and erm(B), which indicated that a multiple-resistance profile of tetracycline, erythromycin, streptomycin, and kanamycin is systematic rather than random. Conversely, the presence of tet(O) was only negatively associated with that of erm(B) and tet(M), which suggested that in the presence of tet(O), the aforementioned multiple resistance is unlikely to be observed. Such heterogeneity in linkages among genes that confer the same phenotypic resistance highlights the importance of incorporating genetic information when investigating the risk factors for the spread of resistance. The epidemiological factors that underlie the persistence of systematic multiple-resistance patterns warrant further investigations with appropriate adjustments for ecological and bacteriological factors.     

Persistence of Resistance to Erythromycin and Tetracycline in Swine Manure During Simulated Composting and Lagoon Treatments

The use of antimicrobials in food animal production leads to the development of antimicrobial resistance (AMR), and animal manure constitutes the largest reservoir of such AMR. In previous studies, composted swine manure was found to contain substantially lower abundance of AMR genes that encode resistance to tetracyclines (tet genes) and macrolide–lincosamide–streptogramin B (MLS_B) superfamily (erm genes), than manures that were treated by lagoons or biofilters. In this study, temporal changes in AMR carried by both cultivated and uncultivated bacteria present in swine manure during simulated composting and lagoon storage were analyzed. Treatments were designed to simulate the environmental conditions of composting (55°C with modest aeration) and lagoon storage (ambient temperature with modest aeration). As determined by selective plate counting, over a 48-day period, cultivated aerobic heterotrophic erythromycin-resistant bacteria and tetracycline-resistant bacteria decreased by more than 4 and 7 logs, respectively, in the simulated composting treatment while only 1 to 2 logs for both resistant bacterial groups in the simulated lagoon treatment. Among six classes each of erm and tet genes quantified by class-specific real-time PCR assays, the abundance of erm(A), erm(C), erm(F), erm(T), erm(X), tet(G), tet(M), tet(O), tet(T), and tet(W) declined marginally during the first 17 days, but dramatically thereafter within 31 days of the composting treatment. No appreciable reduction of any of the erm or tet genes analyzed was observed during the simulated lagoon treatment. Correlation analysis showed that most of the AMR gene classes had similar persistence pattern over the course of the treatments, though not all AMR genes were destructed at the same rate during the treatments.     

Antimicrobial resistance in faecal enterococci and Escherichia coli isolates recovered from Iberian wolf

The aim of this study was to report the antimicrobial resistance, the molecular mechanisms associated and the detection of virulence determinants within faecal Enterococcus spp. and Escherichia coli isolates of Iberian wolf. Enterococci (n = 227) and E. coli (n = 195) isolates were obtained from faecal samples of Iberian wolf (Canis lupus signatus). High rates of resistance were detected for tetracycline and erythromycin among the enterococci isolates, and most of resistant isolates harboured the tet(M) and/or tet(L) and erm(B) genes, respectively. The bla_TEM, tet(A) and/or tet(B), and aadA or strA‐strB genes were detected among most ampicillin‐, tetracycline‐ or streptomycin‐resistant E. coli isolates, respectively. E. coli isolates were ascribed to phylogroups A (n = 56), B1 (91), B2 (13) and D (35). The occurrence of resistant enterococci and E. coli isolates in the faecal flora of Iberian wolf, including the presence of resistant genes in integrons, and virulence determinants was showed in this study. Iberian wolf might act as reservoir of certain resistance genes that could be spread throughout the environment.

Significance and Impact of the Study

This study shows antimicrobial resistance in commensal bacteria from the free‐range, Portuguese, Iberian wolf population. The results indicate that the Iberian wolf could contribute to the spread of resistant bacteria throughout the environment. Additionally, in case of infection, an increased risk of therapeutic failure due to the presence of multiresistant bacteria may represent a health problem for this endangered species. Future studies must be performed to analyse the possible contamination of these animals through the environment and/or the food chain.     

The Transposon-Like Structure of IS26-Tetracycllne,and Kanamycin Resistance Determinant Derived from Transferable R Plasmid of Fish Pathogen,Pasteurella piscicida

Tetracycline (pp-tet), and kanamycin (pp-kan) resistance genes were cloned from a transferable R plasmid of fish pathogen Pasteurella piscicida, and complete nucleotide sequences were determined. The pp-tet was a class D Tet determinant constructed with the tetA resistance gene of 1,182 bp encoding a protein with a deduced molecular mass of 41 kDa and the tetR repressor gene of 654 bp encoding a product of 24 kDa. The pp-tet was highly homologous to the tet(D) of plasmid RA1 isolated from Aeromonas hydrophila with two nucleotide differences in the tetR, and of plasmid pIP173 from Salmonella ordonez with two nucleotide differences in the tetA. The pp-kan contained 813 bp encoding a 31 kDa protein of 271 amino acids, and was classified into type aph-Ic. It was identical to the aphA7 in the IAB operon of pBWH77, in which was originally found an isolate of Klebsiella pneumoniae, in its nucleotide sequences and hybrid promoter construction. The genes were connected by an insertion sequence IS 26 of 820 bp, and were flanked by repeated copies in direct orientation at the 3′ flanking region of the pp-tetA and in inverted orientation at the 3′ flanking region of the pp-kan. The genetic elements are organized like a complex transposon by close linkage of the IS 26 and the pp-tet and -kan.     

Molecular diversity and transferability of the tetracycline resistance gene <Emphasis Type="Italic">tet</Emphasis>(M), carried on Tn<Emphasis Type="Italic">916-1545</Emphasis> family transposons,in enterococci from a total food chain

In the present study, 20 enterococci belonging to the species Enterococcus faecalis (12 strains), Enterococcus faecium (4), Enterococcus durans (2), Enterococcus hirae (1) and Enterococcus mundtii (1) and originating from a total production chain of swine meat commodities were analysed to investigate the diversity of their tetracycline resistance gene tet(M). PCR–RFLP and sequence analysis showed that the tet(M) gene of most strains can be correlated with the Tn916 transposon. Conversely, tet(M) of six E. faecalis and the E. hirae strain, all isolated from pig faecal samples, may be associated with previously undescribed members of the Tn916-1545 transposon family. In vitro filter conjugation trials showed the ability of 50% of the enterococcal strains, including E. mundtii, to transfer the tet(M) gene (and the associated Tn916 and new transposons) to E. faecalis or Listeria innocua recipient strains. tet(M) gene transfer to L. innocua recipient was also directly observed in meat food products. Collectively, these sequence and conjugation data indicate that various transposons can be responsible of the spread of tetracycline resistance in enterococci and validate the opinion that Enterococcus species are important sources of antibiotic resistance genes for potentially pathogenic bacteria occurring in the food chain. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phenotypic and genotypic bacterial antimicrobial resistance in liquid pig manure is variously associated with contents of tetracyclines and sulfonamides

Aims: Antibiotic residues as well as antibiotic‐resistant bacteria in environmental samples might pose a risk to human health. This study aimed to investigate the association between antibiotic residues and bacterial antimicrobial resistance in liquid pig manure used as fertilizer. Methods and Results: Concentrations of tetracyclines (TETs) and sulfonamides (SULs) were determined by liquid chromatography‐mass spectrometry in 305 pig manure samples; antibiotic contents were correlated to the phenotypic resistance of Escherichia coli (n = 613) and enterococci (n = 564) towards up to 24 antibiotics. In 121 samples, the concentration of the TET resistance genes tet(M), tet(O) and tet(B) was quantified by real‐time‐PCR. TETs were found in 54% of the samples. The median sum concentration of all investigated TETs in the positive samples was 0·73 mg kg^?1. SULs were found with a similar frequency (51%) and a median sum concentration of 0·15 mg kg^?1 in the positive samples. Associated with the detection of TETs and/or SULs, resistance rates were significantly elevated for several substances – some of them not used in farm animals, e.g. chloramphenicol and synercid. In addition, multiresistant isolates were found more often in samples containing antibiotics. Analysis of the resistance genes tet(M) and tet(O) already showed a significant increase in their concentrations – but not in tet(B) – in the lowest range of total TET concentration. Mean tet(M) concentrations increased by the factor of 4·5 in the TET concentration range of 0·1–1 mg kg^?1, compared to negative manure samples. Conclusions: Antibiotic contamination of manure seems to be associated with a variety of changes in bacterial resistance, calling for a prudent use of antibiotics in farm animals. Significance and Impact of the Study: This study provides an interdisciplinary approach to assess antimicrobial resistance by combining the microbiological analysis of bacterial resistance with high quality chemical analysis of antibiotic residues in a representative number of environmental samples.     

Occurrence and Persistence of Erythromycin Resistance Genes (erm) and Tetracycline Resistance Genes (tet) in Waste Treatment Systems on Swine Farms

Animal manure from modern animal agriculture constitutes the single largest source of antibiotic resistance (AR) owing to the use of large quantities of antibiotics. After animal manure enters the environment, the AR disseminates into the environment and can pose a potentially serious threat to the health and well-being of both humans and animals. In this study, we evaluated the efficiency of three different on-farm waste treatment systems in reducing AR. Three classes of erythromycin resistance genes (erm) genes (B, F, and X) conferring resistances to macrolide–lincosamides–streptogramin B (MLS_B) and one class of tetracycline resistance genes (tet) gene (G) conferring resistance to tetracyclines were used as models. Real-time polymerase chain reaction assays were used to determine the reservoir sizes of these AR genes present in the entire microbiome. These classes of AR genes varied considerably in abundance, with erm(B) being more predominant than erm(F), erm(X), and tet(G). These AR genes also varied in persistence in different waste treatment systems. Aerobic biofiltration reduced erm(X) more effectively than other AR genes, while mesophilic anaerobic digestion and lagoon storage did not appreciably reduce any of these AR genes. Unlike chemical pollutants, some AR genes could increase after reduction in a preceding stage of the treatment processes. Season might also affect the persistence of AR. These results indicate that AR arising from swine-feeding operations can survive typical swine waste treatment processes and thus treatments that are more effective in destructing AR on farms are required.     

Prevalence of tetracycline resistance genes in Greek seawater habitats

The presence of selected tetracycline resistance (Tc^R) genes was studied in different Greek seawater habitats, originated from wastewater treatment facilities, fishfarm, and coastal environments. The methods employed included assessment of the presence of twelve gene clusters by PCR, followed by hybridization with specific probes, in habitat extracted DNA, Tc^R bacteria, and exogenous isolated plasmids conferring Tc^R. The direct DNA-based analysis showed that tet(A) and tet(K) genes were detected in all habitats, whilst tet(C) and tet(E) were present in fishfarm and wastewater effluent samples and tet(M) was detected in fish-farm and coastal samples. Resistance genes tet(h), tet(C), tet(K), and tet(M) were detected in 60 of the 89 isolates screened. These isolates were identified by fatty acid methyl ester analysis (FAME) as Stenotrophomonas, Acinetobacter, Pseudomonas, Bacillus, and Staphylococcus strains. The presence of the Tc^R genes in 15% of the bacterial isolates coincided with the presence of IncP plasmids. A habitat-specific dissemination of IncP alpha plasmids in wastewater effluent isolates and of IncP beta plasmids in fishfarm isolates was observed. Exogenous isolation demonstrated the presence of plasmids harbouring Tc^R genes in all the habitats tested. Plasmids were shown to carry tet(h), tet(C), tet(E), and tet(K) genes. It is concluded that Tc^R genes are widespread in the seawater habitats studied and often occur on broad host range plasmids that seem to be well disseminated in the bacterial communities.     

Tetracycline resistance genes acquired at birth

Newborns acquire their first microbiota at birth. Maternal vaginal or skin bacteria colonize newborns delivered vaginally or by C-section, respectively (Dominguez-Bello et al. 2010 #884). We aimed to determine differences in the presence of four tetracycline (tet) resistance genes, in the microbes of ten newborns and in the mouth and vagina of their mothers, at the time of birth. DNA was amplified by PCR with primers specific for [tet(M), tet(O), tet(Q), and tet(W)]. Maternal vaginas harbored all four tet resistance genes, but most commonly tet(M) and tet(O) (63 and 38 %, respectively). Genes coding for tet resistance differed by birth mode, with 50 % of vaginally delivered babies had tet(M) and tet(O) and 16 and 13 % of infants born by C-section had tet(O) and tet(W), respectively. Newborns acquire antibiotic resistance genes at birth, and the resistance gene profile varies by mode of delivery.