Search

BackgroundThe emergence of each novel SARS-CoV-2 variants of concern (VOCs) requires investigation of its potential impact on the performance of diagnostic tests in use, including Antigen-detecting rapid diagnostic tests (Ag-RDT). Although anecdotal reports have been circulating that the newly emerged Omicron variant is in principle detectable by Ag-RDTs, few data on sensitivity are available.MethodsWe have performed 1) analytical sensitivity testing with cultured virus in eight Ag-RDTs and 2) retrospective testing in duplicates with clinical samples from vaccinated individuals with Omicron (n=18) or Delta (n=17) breakthrough infection on seven Ag-RDTs.FindingsOverall, we have found large heterogenicity between Ag-RDTs for detecting Omicron. When using cultured virus, we observed a trend towards lower sensitivity for Omicron detection compared to earlier circulating SARS-CoV-2 and the other VOCs. When comparing performance for Delta and Omicron in a comparable set of clinical samples in seven Ag-RDTs, 124/252 (49.2%) of all test performed showed a positive result for Omicron compared to 156/238 (65.6%) for Delta samples. Sensitivity for both Omicron and Delta between Ag-RDTs was highly variable. Four out of seven Ag-RDTs showed significantly lower sensitivity (pInterpretationSensitivity for detecting Omicron is highly variable between Ag-RDTs, necessitating a careful consideration when using these tests to guide infection prevention measures. While analytical and retrospective testing may be a proxy and timely solution to generate performance data, it is not a replacement for clinical evaluations which are urgently needed. Biological and technical reasons for detection failure by some Ag-RDTs need to be further investigated.FundingThis work was supported by the Swiss National Science Foundation (grant numbers 196383, 196644 and 198412), the Fondation Ancrage Bienfaisance du Groupe Pictet, the Fondation Privée des Hôpiteaux Universitaires de Genève and FIND, the global alliance for diagnostics.

International audience; Among clinically relevant lineages of Staphylococcus aureus, the lineage or clonal complex 398 (CC398) is of particular interest. Strains from this lineage were only described as livestock colonizers until 2007. Progressively, cases of infection were reported in humans in contact with farm animals, and now, CC398 isolates are increasingly identified as the cause of severe infections even in patients without any contact with animals. These observations suggest that CC398 isolates have spread not only in the community but also in the hospital setting. In addition, several recent studies have reported that CC398 strains are evolving towards increased virulence and antibiotic resistance. Identification of the origin and emergence of this clonal complex could probably benefit future large-scale studies that aim to detect sources of contamination and infection. Current evidence indicates that the evolution of CC398 strains towards these phenotypes has been driven by the acquisition of prophages and other mobile genetic elements. In this short review, we summarize the main knowledge of this major lineage of S. aureus that has become predominant in the human clinic worldwide within a single decade.

Staphylococcus aureus est une bactérie commensale retrouvée chez environ 30 % des individus sains dont elle colonise la peau et la muqueuse nasale. Cependant, c’est également une bactérie pathogène opportuniste responsable d’infections diverses telles que orgelet, ostéomyélite, endocardite, ou encore septicémie en envahissant un grand nombre de tissus et d’organes. Cette bactérie est capable de s’adapter à des conditions hostiles et variées, telles que carence nutritive et stress osmotique, oxydant, ou thermique, ainsi qu’à la réponse immunitaire de l’hôte, car elle produit une grande diversité de facteurs de virulence. La synthèse de ces facteurs est finement régulée par des protéines et des ARN régulateurs majoritairement non codants, souvent désignés par l’abréviation sARN (dérivée de l’anglais, small RNA). Les facteurs de transcription et les systèmes à deux composants contrôlent l’expression des gènes impliqués non seulement dans le métabolisme, mais aussi dans la réponse au stress et la virulence [1]. Par exemple, la protéine du contrôle catabolique (carbon catabolite control protein A, CcpA) a un rôle essentiel dans le choix de la source carbonée en régulant le métabolisme central de la bactérie ainsi que la virulence [2, 3]. CcpA se fixe à une séquence promotrice spécifique appelée cre (catabolite-responsive element), qui est très conservée chez les bactéries à Gram positif [2]. Quant aux sARN, ils interagissent principalement avec leurs ARN messagers (ARNm) cibles. L’hybridation peut conduire à la stabilisation/ déstabilisation de l’ARNm ou à l’activation/répression de sa traduction [4]. Nous avons montré que la transcription du sARN RsaI (RNA Staphylococcus aureus I) est réprimée par CcpA en présence de glucose [5]. L’induction de la synthèse de RsaI signale que la concentration en glucose diminue dans le milieu extracellulaire et que la croissance des bactéries est ralentie. En interagissant avec ses ARNm cibles ou d’autres sARN, il permet à la population bactérienne de modifier son métabolisme lorsque la source carbonée primaire est consommée.

Pathogenic bacteria must rapidly adapt to ever‐changing environmental signals resulting in metabolism remodeling. The carbon catabolite repression, mediated by the catabolite control protein A (CcpA), is used to express genes involved in utilization and metabolism of the preferred carbon source. Here, we have identified RsaI as a CcpA‐repressed small non‐coding RNA that is inhibited by high glucose concentrations. When glucose is consumed, RsaI represses translation initiation of mRNAs encoding a permease of glucose uptake and the FN3K enzyme that protects proteins against damage caused by high glucose concentrations. RsaI also binds to the 3′ untranslated region of icaR mRNA encoding the transcriptional repressor of exopolysaccharide production and to sRNAs induced by the uptake of glucose‐6 phosphate or nitric oxide. Furthermore, RsaI expression is accompanied by a decreased transcription of genes involved in carbon catabolism pathway and an activation of genes involved in energy production, fermentation, and nitric oxide detoxification. This multifaceted RNA can be considered as a metabolic signature when glucose becomes scarce and growth is arrested., This work was supported by the Centre National de la Recherche Scientifique (CNRS) to [P.R.] and by the Agence Nationale de la Recherche (ANR, grant ANR‐16‐CE11‐0007‐01, RIBOSTAPH, to [P.R.]). It has also been published under the framework of the LABEX: ANR‐10‐LABX‐0036 NETRNA to [P.R.], a funding from the state managed by the French National Research Agency as part of the investments for the future program. The work is financed by a “Projet international de coopération scientifique” (PICS) No. PICS07507 between France and Spain to [I.C.]. D. Bronesky was supported by Fondation pour la Recherche Médicale (FDT20160435025). A. T‐A is financed by the Spanish Ministry of Economy and Competitiveness (BFU2014‐56698‐P) and the European Research Council Consolidator Grant (646869‐ReguloBac‐3UTR).

The intracellular redox environment of Staphylococcus aureus is mainly buffered by bacillithiol (BSH), a low molecular weight thiol. The identity of enzymes responsible for the recycling of oxidized bacillithiol disulfide (BSSB) to the reduced form (BSH) remains elusive. We examined YpdA, a putative bacillithiol reductase, for its role in maintaining intracellular redox homeostasis. The ypdA mutant showed increased levels of BSSB and a lower bacillithiol redox ratio vs. the isogenic parent, indicating a higher level of oxidative stress within the bacterial cytosol. We showed that YpdA consumed NAD(P)H; and YpdA protein levels were augmented in response to stress. Wild type strains overexpressing YpdA showed increased tolerance to oxidants and electrophilic agents. Importantly, YpdA overexpression in the parental strain caused an increase in BSH levels accompanied by a decrease in BSSB concentration in the presence of stress, resulting in an increase in bacillithiol redox ratio vs. the vector control. Additionally, the ypdA mutant exhibited decreased survival in human neutrophils (PMNs) as compared with the parent, while YpdA overexpression protected the resulting strain from oxidative stress in vitro and from killing by human neutrophils ex vivo. Taken together, these data present a new role for YpdA in Staphylococcus aureus physiology and virulence through the bacillithiol system.

Pathogenic bacteria must rapidly adapt to ever-changing environmental signals or nutrient availability resulting in metabolism remodeling. The carbon catabolite repression represents a global regulatory system, allowing the bacteria to express genes involved in carbon utilization and metabolization of the preferred carbon source. InStaphylococcus aureus, regulation of catabolite repressing genes is mediated by the carbon catabolite protein A (CcpA). Here, we have identified a CcpA-dependent small non-coding RNA, RsaI that is inhibited by high glucose concentrations. RsaI represses the translation of mRNAs encoding a major permease of glucose uptake, the FN3K enzyme that protects proteins against damages caused by high glucose concentrations, and IcaR, the transcriptional repressor of exopolysaccharide production. Besides, RsaI regulates the activities of other sRNAs responding to the uptake of glucose-6 phosphate or NO. Finally, RsaI inhibits the expression of several enzymes involved in carbon catabolism pathway, and activates genes involved in energy production, fermentation and NO detoxification when the glucose concentration decreases. This multifunctional RNA provides a signature for a metabolic switch when glucose is scarce and growth is arrested.

Expression of virulence factors in Staphylococcus aureus is regulated by a wide range of transcriptional regulators, including proteins and small RNAs (sRNAs), at the level of transcription and/or translation. The sarA locus consists of three overlapping transcripts generated from three distinct promoters, all containing the sarA open reading frame (ORF). The 5′ untranslated regions (UTRs) of these transcripts contain three separate regions ∼711, 409, and 146 nucleotides (nt) upstream of the sarA translation start, the functions of which remain unknown. Recent transcriptome-sequencing (RNA-Seq) analysis and subsequent characterization indicated that two sRNAs, teg49 and teg48, are processed and likely produced from the sarA P3 and sarA P1 transcripts of the sarA locus, respectively. In this report, we utilized a variety of sarA promoter mutants and cshA and rnc mutants to ascertain the contributions of these factors to the generation of teg49. We also defined the transcriptional regulon of teg49, including virulence genes not regulated by SarA. Phenotypically, teg49 did not impact biofilm formation or affect overall SarA expression significantly. Comparative analyses of RNA-Seq data between the wild-type, teg49 mutant, and sarA mutant strains indicated that ∼133 genes are significantly upregulated while 97 are downregulated in a teg49 deletion mutant in a sarA -independent manner. An abscess model of skin infection indicated that the teg49 mutant exhibited a reduced bacterial load compared to the wild-type S. aureus . Overall, these results suggest that teg49 sRNA has a regulatory role in target gene regulation independent of SarA. The exact mechanism of this regulation is yet to be dissected.

Staphylococcus epidermidis is the leading cause of infections on indwelling medical devices worldwide. Intrinsic antibiotic resistance and vigorous biofilm production have rendered these infections difficult to treat and, in some cases, require the removal of the offending medical prosthesis. With the exception of two widely passaged isolates, RP62A and 1457, the pathogenesis of infections caused by clinical S. epidermidis strains is poorly understood due to the strong genetic barrier that precludes the efficient transformation of foreign DNA into clinical isolates. The difficulty in transforming clinical S. epidermidis isolates is primarily due to the type I and IV restriction-modification systems, which act as genetic barriers. Here, we show that efficient plasmid transformation of clinical S. epidermidis isolates from clonal complexes 2, 10, and 89 can be realized by employing a plasmid artificial modification (PAM) in Escherichia coli DC10B containing a Δ dcm mutation. This transformative technique should facilitate our ability to genetically modify clinical isolates of S. epidermidis and hence improve our understanding of their pathogenesis in human infections. IMPORTANCE Staphylococcus epidermidis is a source of considerable morbidity worldwide. The underlying mechanisms contributing to the commensal and pathogenic lifestyles of S. epidermidis are poorly understood. Genetic manipulations of clinically relevant strains of S. epidermidis are largely prohibited due to the presence of a strong restriction barrier. With the introductions of the tools presented here, genetic manipulation of clinically relevant S. epidermidis isolates has now become possible, thus improving our understanding of S. epidermidis as a pathogen.

Background It has been suggested that prophages in the ST398 S. aureus clone are responsible for expanding ST398's spectrum of action and increasing its ability to cause human infections. We carried out the first characterization of the various prophages carried by 76 ST398 bloodstream infection (BSI) isolates obtained over 9 years of observation. Results Whole-genome sequencing of 22 representative isolates showed (1) the presence of the φ3-prophage and diverse genetic features typical of animal-associated isolates (i.e., SCCmec XI element, Tn916 transposon and non φ3-prophages) in a majority of BSI isolates, (2) one BSI isolate devoid of the φ3-prophage but otherwise similar to an animal-infecting isolate, (3) 35 prophages carrying numerous genes previously associated with virulence or immune evasion in animal models of staphylococcal infections. The analysis of prophage content in all 76 BSI isolates showed an increasing prevalence of polylysogeny over time. Overall, over the course of the last 10 years, the BSI isolates appear to have acquired increasing numbers of genetic features previously shown to contribute to bacterial adaptation and virulence in animal models of staphylococcal infections. Conclusions We hypothesize that lysogeny has played a significant role in increasing the ability of the ST398 clone to cause infections in humans. Our findings highlight the risk that the ST398 lineage will increase its threat to public health by continuing to acquire virulence and/or multiple antibiotic-resistance genes from hospital-associated clones of Staphylococcus aureus. Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-3516-x) contains supplementary material, which is available to authorized users.

DEAD-box RNA helicases are present in almost all living organisms and participate in various processes of RNA metabolism. Bacterial proteins of this large family were shown to be required for translation initiation, ribosome biogenesis and RNA decay. The latter is primordial for rapid adaptation to changing environmental conditions. In particular, the RhlB RNA helicase from E. coli was shown to assist the bacterial degradosome machinery. Recently, the CshA DEAD-box proteins from Bacillus subtilis and Staphylococcus aureus were shown to interact with proteins that are believed to form the degradosome. S. aureus can cause life-threatening disease, with particular concern focusing on biofilm formation on catheters and prosthetic devices, since in this form the bacteria are almost impossible to eradicate both by the immune system and antibiotic treatment. This persistent state relies on the expression of surface encoded proteins that allow attachment to various surfaces, and contrasts with the dispersal mode of growth that relies on the secretion of proteins such as hemolysins and proteases. The switch between these two states is mainly mediated by the Staphylococcal cell density sensing system encoded by agr. We show that inactivation of the cshA DEAD-box gene results in dysregulation of biofilm formation and hemolysis through modulation of agr mRNA stability. Importantly, inactivation of the agrA gene in the cshA mutant background reverses the defect, indicating that cshA is genetically upstream of agr and that a delicate balance of agr mRNA abundance mediated through stability control by CshA is critical for proper expression of virulence factors.

A gene encoding a putative DNA helicase from Staphylococcus aureus USA300 was cloned and expressed in Escherichia coli. The protein was purified to over 90% purity by chromatography. The purified enzyme, SauUSI, predominantly cleaves modified DNA containing 5mC and 5-hydroxymethylcytosine. Cleavage of 5mC-modified plasmids indicated that the sites S5mCNGS (S = C or G) are preferentially digested. The endonuclease activity requires the presence of adenosine triphosphate (ATP) or dATP whereas the non-hydrolyzable γ-S-ATP does not support activity. SauUSI activity was inhibited by ethylenediaminetetraacetic acid. It is most active in Mg(++) buffers. No companion methylase gene was found near the SauUSI restriction gene. The absence of a cognate methylase and cleavage of modified DNA indicate that SauUSI belongs to type IV restriction endonucleases, a group that includes EcoK McrBC and Mrr. SauUSI belongs to a family of highly similar homologs found in other sequenced S. aureus, S. epidermidis and S. carnosus genomes. More distant SauUSI orthologs can be found in over 150 sequenced bacterial/archaea genomes. Finally, we demonstrated the biological function of the type IV REase in restricting 5mC-modified plasmid DNA by transformation into clinical S. aureus strain SA564, and in restricting phage λ infection when the endonuclease is expressed in E. coli.

Staphylococcus aureus is an versatile pathogen that can cause life-threatening infections. Depending on the clinical setting, up to 50% of S. aureus infections are caused by methicillin-resistant strains (MRSA) that in most cases are resistant to many other antibiotics, making treatment difficult. The emergence of community-acquired MRSA drastically changed the picture by increasing the risk of MRSA infections. Horizontal transfer of genes encoding for antibiotic resistance or virulence factors is a major concern of multidrug-resistant S. aureus infections and epidemiology. We identified and characterized a type III-like restriction system present in clinical S. aureus strains that prevents transformation with DNA from other bacterial species. Interestingly, our analysis revealed that some clinical MRSA strains are deficient in this restriction system, and thus are hypersusceptible to the horizontal transfer of DNA from other species, such as Escherichia coli , and could easily acquire a vancomycin-resistance gene from enterococci. Inactivation of this restriction system dramatically increases the transformation efficiency of clinical S. aureus strains, opening the field of molecular genetic manipulation of these strains using DNA of exogenous origin.

The toxin MazF sa in Staphylococcus aureus is a sequence-specific endoribonuclease that cleaves the majority of the mRNAs in vivo but spares many essential mRNAs (e.g., secY mRNA) and, surprisingly, an mRNA encoding a regulatory protein (i.e., sarA mRNA). We hypothesize that some mRNAs may be protected by RNA-binding protein(s) from degradation by MazF sa . Using heparin-Sepharose-enriched fractions that hybridized to sarA mRNA on Northwestern blots, we identified among multiple proteins the DEAD box RNA helicase CshA (NWMN_1985 or SA1885) by mass spectroscopy. Purified CshA exhibits typical RNA helicase activities, as exemplified by RNA-dependent ATPase activity and unwinding of the DNA-RNA duplex. A severe growth defect was observed in the cshA mutant compared with the parent when grown at 25°C but not at 37°C. Activation of MazF sa in the cshA mutant resulted in lower CFU per milliliter accompanied by a precipitous drop in viability (∼40%) compared to those of the parent and complemented strains. NanoString analysis reveals diminished expression of a small number of mRNAs and 22 small RNAs (sRNAs) in the cshA mutant versus the parent upon MazF sa induction, thus implying protection of these RNAs by CshA. In the case of the sRNA teg049 within the sarA locus, we showed that the protective effect was likely due to transcript stability as revealed by reduced half-life in the cshA mutant versus the parent. Accordingly, CshA likely stabilizes selective mRNAs and sRNAs in vivo and as a result enhances S. aureus survival upon MazF sa induction during stress.

International audience; Until recently, Staphylococcus aureus from clonal complex (CC)398 were mostly described as colonizing asymptomatic raised pigs and pig-farmers. Currently, the epidemiology of the CC398 lineage is becoming more complex. CC398 human-adapted isolates are increasingly being identified in bloodstream infections in humans living in animal-free environments. In addition, CC398 isolates are increasingly responsible for invasive infections in various animals. CC398 isolates that colonize asymptomatic pigs and the isolates that infect humans living in animal-free environments (human-adapted isolates) both lack several clinically important S. aureus-associated virulence factors but differ on the basis of their prophage content. Recent findings have provided insight into the influence of a φMR11-like helper prophage on the ability of CC398 isolates to infect humans. To assess the recent spread of the CC398 lineage to various animal species and to investigate the links between the φMR11-like prophage and the emergence of CC398 isolates infecting animals, we studied 277 isolates causing infections in unrelated animals. The prevalence of CC398 isolates increased significantly between 2007 and 2013 (p < 0.001); 31.8% of the animal isolates harbored the φMR11-like prophage. High-density DNA microarray experiments with 37 representative infected-animal isolates positive for φMR11-like DNA established that most infected-animal isolates carried many genetic elements related to antimicrobial resistance and virulence genes, and a φ3 prophage encoding immune-modulating proteins and associated with animal-to-human jumps. Our findings suggest recent clonal expansion and dissemination of a new subpopulation of CC398 isolates, responsible for invasive infections in various animals, with a considerable potential to colonize and infect humans, probably greater than that of human-adapted CC398 isolates, justifying active surveillance.

Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia (positive blood cultures after ≥7 days) represents a challenging subset of invasive MRSA infections. The comparison of genome sequences of persistent (300-169) and resolving (301-188) MRSA bacteremia isolates with similar genetic background (sequence type 45 [ST45]) will help us to better understand underlying mechanisms of persistent MRSA bacteremia.

Supplementary data (ANNEX); International audience; Staphylococcus aureus clonal complex 398 is a livestock-associated pathogen that poses a worldwide threat because of its ability to colonize and infect both humans and animals. We used high-resolution whole-genome microarrays, prophage profiling, immune evasion cluster characterization and whole-genome sequencing to investigate the roles of prophages in the emerging human-adapted subpopulation of CC398 that has been associated with invasive infections in humans living in animal-free environments. We characterized one phage and two prophages specifically harbored by CC398 isolates belonging to the emerging subpopulation. We introduced the phage into permissive prophage-free isolates. We investigated the effects of lysogeny on the host ability to resist further phage infection and transformation, to acquire the capacity to invade human cells, and to express virulence factors encoded by prophages. We report evidence of a defective ϕMR11-like helper prophage, named StauST398-5pro, specifically associated with the emerging non-LA CC398 subpopulation. StauST398-5pro confers substantial protection against horizontal genetic transfer to its host. It interacts with a human-associated β-converting prophage encoding immune-modulating proteins such that virulence genes are expressed during stress situations. Our findings provide insight into the role of phages in the expression of virulence and in the spread of genetic information among new host-adapted S. aureus isolates. We demonstrate that functional prophage elements can condition host specificity and confer new virulence traits on emerging intra-species clones of bacteria.

Sequence type 398 (ST398) Staphylococcus aureus was originally reported in livestock. We announce the complete genome sequence of an ST398 methicillin-susceptible S. aureus strain of animal origin, S123. The genome sequence reveals a wild-type genome that probably corresponds to an ancestral clone .

Sequence type 398 (ST398) Staphylococcus aureus was originally associated with animal infection. We announce the complete genome sequences of two ST398 methicillin-susceptible S. aureus strains of human origin, S94 and S100. The genome sequences assist in the characterization of interesting ST398 features related to host specificities .

Staphylococcus aureus is a major human pathogen responsible for a wide diversity of infections ranging from localized to life threatening diseases. From 1961 and the emergence of methicillin-resistant S. aureus (MRSA), this bacterium has shown a particular capacity to survive and adapt to drastic environmental changes and since the beginning of the 1990s it has spread worldwide. Until recently, S. aureus was considered as the prototype of a nosocomial pathogen but it has now been recognized as an agent responsible for outbreaks in the community. Several recent reports suggest that the epidemiology of MRSA is changing. Understanding of pathogenicity, virulence and emergence of epidemic clones within MRSA populations is not clearly defined, despite several attempts to identify common molecular features between strains that share similar epidemiological and/or virulence behavior. These studies included: pattern profiling of bacterial adhesins, analysis of clonal complex groups, molecular genotyping and enterotoxin content analysis. To date, all approaches failed to find a correlation between molecular determinants and clinical outcomes. We hypothesize that the capacity of the bacterium to become more invasive or virulent is determined by genetics. The utilization of massively parallel methods of analysis is therefore ideal to study the contribution of genetics. Therefore, this article focuses on the entire genome including coding sequences as well as noncoding sequences. This high resolution approach allows the monitoring micro- and macroevolution of MRSA and identification of specific genomic markers of evolution of invasive or highly virulent phenotypes.

OBJECTIVES: To search for plasmid-mediated qnr genes among waterborne environmental Aeromonas spp. recovered from Switzerland. METHODS: Isolates presenting MICs of nalidixic acid or ciprofloxacin > or = 1 mg/L were screened for qnr genes by a multiplex PCR approach followed by sequencing. Plasmids were transferred by transformation, and further analysis of the genetic structures surrounding the qnrS2 gene was carried out by PCR and sequencing. RESULTS: A qnrS2 gene was identified from a single Aeromonas allosaccharophila isolate (Lugano lake, Lugano), as part of a mobile insertion cassette located on a broad host range IncU-type plasmid. This plasmid co-harboured a class 1 integron containing the aac(6')-Ib-cr, bla(OXA-1), catB3 and arr-3 gene cassettes. CONCLUSIONS: These findings strengthen further the role of Aeromonas spp. as a reservoir of antimicrobial resistance determinants in the environment.

Aeromonas spp. are environmental reservoirs of resistance determinants to different classes of antibiotic molecules (1, 3, 7). Intrinsic resistance to β-lactams among this genus may arise from the expression of chromosomal β-lactamases and/or efflux pumps (5). Acquired β-lactamases conferring resistance to narrow-spectrum β-lactams, such as OXA-type enzymes and the penicillinases TEM-1 and SHV-1, have been identified in that genus as well as in a single report of the extended-spectrum β-lactamase (ESBL) TEM-24 (2, 4). The aim of this study was to evaluate the prevalence of ESBLs among Aeromonas sp. strains recovered from several rivers, lakes, and activated sludges from the southern part of the Swiss Alps. Water samples were collected between 2002 and 2005 from the rivers Ticino and Vedeggio, from the lakes Cadagno and Lugano, and from activated sludges, all located in the Tessin county of Switzerland. The water samples were plated and growing bacteria identified by conventional biochemical methods (API-NE system; bioMerieux, Marcy-l'Etoile, France). All of the 50 Aeromonas sp. strains recovered were tested for ESBL detection by a synergy test using disks of ticarcillin-clavulanic acid, ceftazidime, cefotaxime, and aztreonam. The susceptibility testing of isolates was performed using Etest strips (AB Biodisk, Solna, Sweden). A single isolate, A72, recovered from an activated sludge located in Bioggio, displayed an ESBL phenotype. This isolate was resistant to most β-lactams, except cephamycins and carbapenems (Table ​(Table1).1). PCR amplifications performed as described previously (9), using primers specific for ESBL-encoding genes, followed by sequencing identified the blaPER-1 gene. Genotyping of isolate A72, according to the results of gyrB sequencing (10), identified Aeromonas media, a waterborne species known to cause diarrhea in humans (6). TABLE 1. MICs of antimicrobial agents for Aeromonas media A72, E. coli J53 harboring natural plasmid p72, and E. coli reference strain J53 A 70-kb plasmid (pAM) harboring the blaPER-1 gene was transferred by conjugation into the Escherichia coli J53 recipient strain, using a selection made of ceftazidime (10 μg/ml) and sodium azide (100 μg/ml). Transconjugant E. coli J53(pAM) showed an antimicrobial susceptibility pattern mirroring that of A. media A72 (Table ​(Table11). PCR mapping performed as described previously (9) identified the blaPER-1 gene as part of a Tn1213 composite transposon, as previously found (9). In addition, this Tn1213 structure was bracketed by the aphA6 and strA genes (encoding resistance to aminoglycosides) of transposon Tn5393d, as already observed in an Alcaligenes faecalis clinical isolate producing PER-1 recovered from Italy. In that latter isolate, the Tn5393d transposon was inserted into a Tn501 backbone carrying a mercury resistance transposon (8) that was not identified in A. media A72 by PCR mapping. Our study constitutes the first identification of an ESBL-producing environmental Aeromonas sp. strain. The occurrence of blaPER-1 on a conjugative and broad-host-range plasmid, inside a genetic context similar to that described for an A. faecalis clinical isolate recovered in a neighboring country, may indicate that Aeromonas spp. may act as vehicles for spreading such an antibiotic resistance determinant. These findings also strengthen the role of Aeromonas spp. as reservoirs or vectors of antimicrobial resistance determinants of clinical relevance, as recently exemplified by the identification of the plasmid-mediated quinolone resistance qnrS2 gene in Aeromonas punctata and A. media from the Seine River, Paris, France (1).