Escherichia coli Phylogenetic and Antimicrobial Pattern as an Indicator of Anthropogenic Impact on Threatened Freshwater Mussels.

Freshwater bivalves are widely used as accumulation indicators and monitoring tools for assessing contaminant effects on different levels of biological integration. This pilot study aimed to explore the phylogenetic diversity of Escherichia coli isolated from freshwater mussels (Margaritifera margaritifera and Potomida littoralis) and characterize their phenotypes and antibiotic resistance profiles. Samples were collected in the Rabaçal and Tua Rivers, in the Douro basin, Portugal-two sites representing different levels of anthropogenic contamination. Antimicrobial susceptibility testing was performed via the disk diffusion method with 21 antibiotics. Results showed that 31% of isolates were multidrug-resistant (MDR). Thus, freshwater mussels provide an effective and time-integrated approach for identifying/quantifying fecal indicators, including MDR bacteria. PCR-based assays were designed for assessing phylogenetic E. coli groups. Among the E. coli isolates, the highest prevalence (44%) was observed in group D or E, followed by group E or Clade I (25%), group A (19%), and group B1 (13%). E. coli isolated from M. margaritifera predominantly exhibited a higher prevalence of phylogroups D or E, whereas E. coli from P. littoralis showed associations with phylogroups E or clade I, B1, A, and D or E. Our results provide new insights into the phylogenetic diversity of E. coli in freshwater bivalves. Additionally, the findings highlight the possible linkage of phylogroups with the host species, the geographical location in the water stream, and human activity. Using E. coli as a bioindicator isolated from freshwater mussels helps us grasp how human activities affect the environment. This study has important implications for those interested in safeguarding water resources, especially in tackling antibiotic resistance in aquatic ecosystems.

An Overview of Cefiderocol's Therapeutic Potential and Underlying Resistance Mechanisms.

Antimicrobial resistance continues to increase globally and treatment of difficult-to-treat (DTT) infections, mostly associated with carbapenem-resistant (CR) Pseudomonas aeruginosa, CR Acinetobacter baumannii, and CR- and third-generation-cephalosporins-resistant Enterobacterales remains a challenge for the clinician. The recent approval of cefiderocol has broaden the armamentarium for the treatment of patients with DTT infections. Cefiderocol is a siderophore cephalosporin that has shown excellent antibacterial activity, in part due to its innovative way of cell permeation. It is relatively stable compared to most commonly found carbapenamases. However, some resistant mechanisms to cefiderocol have already been identified and reduced susceptibility has developed during patient treatment, highlighting that the clinical use of cefiderocol must be rational. In this review, we summarize the current available treatments against the former resistant bacteria, and we revise and discuss the mechanism of action of cefiderocol, underlying the biological function of siderophores, the therapeutic potential of cefiderocol, and the mechanisms of resistance reported so far.

The Acinetobacter baumannii website (Ab-web): a multidisciplinary knowledge hub, communication platform, and workspace.

Acinetobacter baumannii is a Gram-negative bacterium increasingly implicated in hospital-acquired infections and outbreaks. Effective prevention and control of such infections are commonly challenged by the frequent emergence of multidrug-resistant strains. Here we introduce Ab-web (https://www.acinetobacterbaumannii.no), the first online platform for sharing expertise on A. baumannii. Ab-web is a species-centric knowledge hub, initially with 10 articles organized into two main sections, 'Overview' and 'Topics', and three themes, 'epidemiology', 'antibiotic resistance', and 'virulence'. The 'workspace' section provides a spot for colleagues to collaborate, build, and manage joint projects. Ab-web is a community-driven initiative amenable to constructive feedback and new ideas.

Emergence of KPC-3- and OXA-181-producing ST13 and ST17 Klebsiella pneumoniae in Portugal: genomic insights on national and international dissemination.

BACKGROUND: Carbapenem-resistant Klebsiella pneumoniae (CRKP) strains are of particular concern, especially strains with mobilizable carbapenemase genes such as blaKPC, blaNDM or blaOXA-48, given that carbapenems are usually the last line drugs in the ß-lactam class and, resistance to this sub-class is associated with increased mortality and frequently co-occurs with resistance to other antimicrobial classes. OBJECTIVES: To characterize the genomic diversity and international dissemination of CRKP strains from tertiary care hospitals in Lisbon, Portugal. METHODS: Twenty CRKP isolates obtained from different patients were subjected to WGS for species confirmation, typing, drug resistance gene detection and phylogenetic reconstruction. Two additional genomic datasets were included for comparative purposes: 26 isolates (ST13, ST17 and ST231) from our collection and 64 internationally available genomic assemblies (ST13). RESULTS: By imposing a 21 SNP cut-off on pairwise comparisons we identified two genomic clusters (GCs): ST13/GC1 (n = 11), all bearing blaKPC-3, and ST17/GC2 (n = 4) harbouring blaOXA-181 and blaCTX-M-15 genes. The inclusion of the additional datasets allowed the expansion of GC1/ST13/KPC-3 to 23 isolates, all exclusively from Portugal, France and the Netherlands. The phylogenetic tree reinforced the importance of the GC1/KPC-3-producing clones along with their rapid emergence and expansion across these countries. The data obtained suggest that the ST13 branch emerged over a decade ago and only more recently did it underpin a stronger pulse of transmission in the studied population. CONCLUSIONS: This study identifies an emerging OXA-181/ST17-producing strain in Portugal and highlights the ongoing international dissemination of a KPC-3/ST13-producing clone from Portugal.

Role of Goats in the Epidemiology of Coxiella burnetii.

Since its first description in the late 1930s, Q fever has raised many questions. Coxiella burnetii, the causative agent, is a zoonotic pathogen affecting a wide range of hosts. This airborne organism leads to an obligate, intracellular lifecycle, during which it multiplies in the mononuclear cells of the immune system and in the trophoblasts of the placenta in pregnant females. Although some issues about C. burnetii and its pathogenesis in animals remain unclear, over the years, some experimental studies on Q fever have been conducted in goats given their excretion pattern. Goats play an important role in the epidemiology and economics of C. burnetii infections, also being the focus of several epidemiological studies. Additionally, variants of the agent implicated in human long-term disease have been found circulating in goats. The purpose of this review is to summarize the latest research on C. burnetii infection and the role played by goats in the transmission of the infection to humans.

Occurrence and seasonality of Campylobacter spp. in Portuguese dairy farms.

The growing idea that natural products are better for consumption is creating behaviors that can lead to food safety problems and an increase of healthcare costs. One of the trending products is raw milk, which in some countries is sold by vending machines outside dairy farms. Campylobacteriosis is the most common gastrointestinal infection in humans in the European Union since 2005. Several outbreaks have been associated with the consumption of raw milk contaminated with Campylobacter spp. In the present study, the occurrence and seasonality of Campylobacter spp. in raw cow's milk were determined. Other samples from the dairy farm environment were also analyzed to understand the possible routes of contamination. The study was conducted from November 2020 to September 2021 in randomly selected dairy farms located in northern Portugal. One liter of milk was collected from bulk cooling tanks transported to the laboratory and analyzed within 24 h. Campylobacter spp. detection and identification were performed using real-time PCR methodology and confirmation followed ISO standards. From 100 dairy farms evaluated, the occurrence of Campylobacter spp. was estimated at 4.0 % in raw cow's milk samples. In the samples from the environment of the farms, only contaminated fecal samples were found, corresponding to an occurrence of 4.2 %. Positivity was observed in summer months. The results of this study indicate the potential risk of campylobacteriosis after the consumption of raw milk. Consumers who seek raw milk for health reasons should be aware of the risk, especially if they belong to vulnerable groups. Moreover, it raises the question of how climate change will impact food safety, suggesting that routine surveillance for zoonotic pathogens should be implemented in dairy farms.

The Discovery of the Role of Outer Membrane Vesicles against Bacteria.

Gram-negative bacteria are intrinsically resistant to many commercialized antibiotics. The outer membrane (OM) of Gram-negative bacteria prevents the entry of such antibiotics. Outer membrane vesicles (OMV) are naturally released from the OM of Gram-negative bacteria for a range of purposes, including competition with other bacteria. OMV may carry, as part of the membrane or lumen, molecules with antibacterial activity. Such OMV can be exposed to and can fuse with the cell surface of different bacterial species. In this review we consider how OMV can be used as tools to deliver antimicrobial agents. This includes the characteristics of OMV production and how this process can be used to create the desired antibacterial activity of OMV.

Occurrence and Biological Cost of mcr-1-Carrying Plasmids Co-harbouring Beta-Lactamase Resistance Genes in Zoonotic Pathogens from Intensive Animal Production.

Colistin is classified as a high-priority critical antimicrobial by the World Health Organization (WHO). A better understanding of the biological cost imposed by mcr-plasmids is paramount to comprehending their spread and may facilitate the decision about the ban of colistin in livestock. This study aimed to assess the prevalence of mcr and ESBL genes from 98 Escherichia coli and 142 Salmonella enterica isolates from food-producing animals and the impact of the mcr-1 acquisition on bacterial fitness. Only mcr-1 was identified by multiplex PCR (mcr-1 to mcr-10) in 15.3% of E. coli. Colistin MICs ranged between 8−32 mg/L. In four isolates, blaTEM-1, blaCTX-M-1, and blaCTX-M-15 co-existed with mcr-1. The IncH12, IncHI1, IncP, IncN, and IncI plasmids were transferred by conjugation to E. coli J53 at frequencies of 10−7 to 10−2 cells/recipient. Growth kinetics assays showed that transconjugants had a significantly lower growth rate than the recipient (p < 0.05), and transconjugants' average growth rate was higher in the absence than in the presence of colistin (1.66 versus 1.32 (p = 0.0003)). Serial transfer assay during 10 days demonstrated that plasmid retention ranged from complete loss to full retention. Overall, mcr-1-bearing plasmids impose a fitness cost, but the loss of plasmids is highly variable, suggesting that other factors beyond colistin pressure regulate the plasmid maintenance in a bacterial population, and colistin withdrawal will not completely lead to a decrease of mcr-1 levels.

Longitudinal Study Detects the Co-Carriage of ESBL and mcr-1 and -4 Genes in Escherichia coli Strains in a Portuguese Farrow-to-Finish Swine Herd.

Cephalosporins and polymyxins are employed in antimicrobial protocols to control and treat neonatal infections and post-weaning diarrhoea in swine operations. We conducted a longitudinal study to evaluate the colonization and transmission of antibiotic-resistant Escherichia coli in sows and their piglets in a farrow-to-finish operation, focusing on characterization of Extended Spectrum Beta-Lactamase (ESBL) and mcr genes, virulence traits and genetic relatedness. A total of 293 E. coli isolates were obtained from faecal samples collected in five time points. At birth blaCTX-M-1group cluster was detected in E. coli isolates from 9 sows and 49 piglets (73.41%), while in the following four' piglets sampling moments it was detected in 91.8%, 57.6%, 71.4% and 97.4%. The gene mcr-1 was detected in E. coli from one sow and from three piglets from different litters at birth and increased in the first weeks of piglet life (68.85%, 100%, 90% and 8.1%). A new mcr-4 allele, mcr-4.7, was identified in 3.28%, 28.57%, 7.5% of E. coli isolates. Most mcr-positive E. coli isolates (96,7%) carried blaCTX-M-1Group genes and 93,33% carried both mcr-4 and mcr-1. CTX-M-1 and CTX-M-32 were the most predominant ESBLs. Plasmids belonged to IncI1, IncF and IncN groups. Most isolates belong to phylogenetic group B1; PAI IV536 marker was detected in nine isolates. The strains were kept in the different stages of the piglets' life. The use of ceftiofur and colistin may explain the high prevalence and co-selection of blaCTX-M-1Group and mcr-1 and/or -4 genes, contributing to the maintenance of resistant and virulent isolates throughout the pig life cycle that may reach the food chain.

Multidrug-resistant Serratia rubidaea strains in the oral microbiota of healthy horses.

BACKGROUND: Many emergent pathogenic agents are cross-transmitted from animals to humans. Horses are considered as potential reservoirs of commensal, zoonotic, and multidrug-resistant bacteria. Equine bites could lead to infections caused by these agents, considering equine species as a public health concern. The more it is known about the equine oral microbiota the best secondary problems created by their commensal flora can be controlled. There are very few reports of Serratia rubidaea, a zoonotic and opportunistic bacterium, both in human and veterinary medicine. AIM: This study aimed to evaluate the Gram-negative microbiota of healthy equine oral cavities and their antimicrobial susceptibility. METHODS: During equine routine oral procedures, eight healthy horses were selected for this study, after discarding any abnormal dental conditions. Samples were collected from the subgingival space and gingival margin from the tooth 406 and both the identification and antimicrobial susceptibility test of Gram-negative bacteria were performed. RESULTS: This study reports the isolation of 32 Gram-negative agents, 27 of which were multidrug-resistant to the antimicrobial classes tested. High resistance rates were obtained to commonly used antimicrobial drugs, particularly macrolides and aminoglycosides as to carbapenems that are specific to human medicine. Two multi-drug resistance strains of S. rubidaea were found in the mouth of two healthy horses. CONCLUSION: Most Gram-negative isolates found in healthy horses were zoonotic and multi-drug resistant. This is a strong reason to consider the horse as an animal with a major place in the "One Health" concept. Equine clinicians should take precautions when working with horses' mouths. Antimicrobial sensitivity tests should be taken into consideration when finding the appropriate antimicrobial therapy protocol. To the authors' best knowledge, this is the first report about isolation of S. rubidaea from the mouth of the equine species.

Manure as a Potential Hotspot for Antibiotic Resistance Dissemination by Horizontal Gene Transfer Events.

The increasing demand for animal-derived foods has led to intensive and large-scale livestock production with the consequent formation of large amounts of manure. Livestock manure is widely used in agricultural practices as soil fertilizer worldwide. However, several antibiotic residues, antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria are frequently detected in manure and manure-amended soils. This review explores the role of manure in the persistence and dissemination of ARGs in the environment, analyzes the procedures used to decrease antimicrobial resistance in manure and the potential impact of manure application in public health. We highlight that manure shows unique features as a hotspot for antimicrobial gene dissemination by horizontal transfer events: richness in nutrients, a high abundance and diversity of bacteria populations and antibiotic residues that may exert a selective pressure on bacteria and trigger gene mobilization; reduction methodologies are able to reduce the concentrations of some, but not all, antimicrobials and microorganisms. Conjugation events are often seen in the manure environment, even after composting. Antibiotic resistance is considered a growing threat to human, animal and environmental health. Therefore, it is crucial to reduce the amount of antimicrobials and the load of antimicrobial resistant bacteria that end up in soil.

Synthesis of Iron(II)-N-Heterocyclic Carbene Complexes: Paving the Way for a New Class of Antibiotics.

The synthesis and structural modulation of five pro-ligand salts was achieved using alternative sustainable synthetic strategies, the use of microwaves being the method of choice, with an 81% yield and an E factor of 43 for 3d. After complexation with Fe3(CO)12 by direct reaction with the appropriate pro-ligands at 130 °C, a set of iron(II) N-heterocyclic carbene (NHC) complexes were isolated and fully characterized (via 1H and 13C NMR and IR spectroscopy and elemental analysis). The antibacterial activities of the iron(II)-NHC complexes were tested against standard World Health Organization priority bacterial strains: Staphylococcus aureus ATCC 29213 and Escherichia coli ATCC 25922. The results showed a significant effect of the Fe(II)-NHC side-chain on the antibacterial activity against both Gram-negative and Gram-positive bacteria. Among all compounds, the most lipophilic iron complex, 3b, was found to be the most active one, with a minimum inhibitory concentration of 8 µg/mL. Pioneering mechanistic studies suggested an alternative mechanism of action (OH· formation), which opens the way for the development of a new class of antibiotics.

Seaweed Phenolics: From Extraction to Applications.

Seaweeds have attracted high interest in recent years due to their chemical and bioactive properties to find new molecules with valuable applications for humankind. Phenolic compounds are the group of metabolites with the most structural variation and the highest content in seaweeds. The most researched seaweed polyphenol class is the phlorotannins, which are specifically synthesized by brown seaweeds, but there are other polyphenolic compounds, such as bromophenols, flavonoids, phenolic terpenoids, and mycosporine-like amino acids. The compounds already discovered and characterized demonstrate a full range of bioactivities and potential future applications in various industrial sectors. This review focuses on the extraction, purification, and future applications of seaweed phenolic compounds based on the bioactive properties described in the literature. It also intends to provide a comprehensive insight into the phenolic compounds in seaweed.

Antibacterial Photodynamic Inactivation of Antibiotic-Resistant Bacteria and Biofilms with Nanomolar Photosensitizer Concentrations.

Gram-negative bacteria and bacteria in biofilms are very difficult to eradicate and are the most antibiotic-resistant bacteria. Therapeutic alternatives less susceptible to mechanisms of resistance are urgently needed to respond to an alarming increase of resistant nosocomial infections. Antibacterial photodynamic inactivation (PDI) generates oxidative stress that triggers multiple cell death mechanisms that are more difficult to counteract by bacteria. We explore PDI of multidrug-resistant bacterial strains collected from patients and show how positive charge distribution in the photosensitizer drug impacts the efficacy of inactivation. We demonstrate the relevance of size for drug diffusion in biofilms. The designed meso-imidazolyl porphyrins of small size with positive charges surrounding the macrocycle enabled the inactivation of bacteria in biofilms by 6.9 log units at 5 nM photosensitizer concentration and 5 J cm-2, which offers new opportunities to treat biofilm infections.

Intestinal cytotoxicity induced by Escherichia coli is fully prevented by red wine polyphenol extract: Mechanistic insights in epithelial cells.

Gastrointestinal infections are considered a serious public health problem in view of their high incidence and the increasing antibiotic resistance of the microorganisms involved in their pathogenesis, namely Escherichia coli. Consequently, finding new ways to prevent and/or threat these infections is urgent. In this study we investigated whether a well-characterised polyphenolic red wine extract is able to inhibit the cytotoxic effects induced by a clinical pathogenic Escherichia coli strain (E. coli 270) against HT-29 colon epithelial cells. Firstly, we provide evidences showing that the E. coli strain triggered the death of the intestinal epithelial cells through the production and release of a toxin. Then we support that, in a concentration dependent way, RWE through both, a direct interaction with bacterial exotoxin and the epithelial cells, prevented the action of the toxin on the cells, significantly reducing cell death. This intends to constitute a position paper as detailed mechanisms for the inhibition of E. coli-induced toxicity by polyphenols are yet to be completely unraveled. However, considering that the amount of red wine polyphenols used can be easily achieved in a normal diet, this study suggests that RWE may provide a readily available dietary product with potential benefit for the prevention and/or treatment of intestinal infections induced by intestinal pathogenic bacteria and may open new therapeutic avenues for the development of potential natural antimicrobial agents.

CRISPR-Cas: Converting A Bacterial Defence Mechanism into A State-of-the-Art Genetic Manipulation Tool.

Bacteriophages are pervasive viruses that infect bacteria, relying on their genetic machinery to replicate. In order to protect themselves from this kind of invader, bacteria developed an ingenious adaptive defence system, clustered regularly interspaced short palindromic repeats (CRISPR). Researchers soon realised that a specific type of CRISPR system, CRISPR-Cas9, could be modified into a simple and efficient genetic engineering technology, with several improvements over currently used systems. This discovery set in motion a revolution in genetics, with new and improved CRISPR systems being used in plenty of in vitro and in vivo experiments in recent years. This review illustrates the mechanisms behind CRISPR-Cas systems as a means of bacterial immunity against phage invasion and how these systems were engineered to originate new genetic manipulation tools. Newfound CRISPR-Cas technologies and the up-and-coming applications of these systems on healthcare and other fields of science are also discussed.

Plasmid-Mediated Colistin Resistance in Salmonella enterica: A Review.

Colistin is widely used in food-animal production. Salmonella enterica is a zoonotic pathogen, which can pass from animal to human microbiota through the consumption of contaminated food, and cause disease, often severe, especially in young children, elderly and immunocompromised individuals. Recently, plasmid-mediated colistin resistance was recognised; mcr-like genes are being identified worldwide. Colistin is not an antibiotic used to treat Salmonella infections, but has been increasingly used as one of the last treatment options for carbapenem resistant Enterobacteria in human infections. The finding of mobilizable mcr-like genes became a global concern due to the possibility of horizontal transfer of the plasmid that often carry resistance determinants to beta-lactams and/or quinolones. An understanding of the origin and dissemination of mcr-like genes in zoonotic pathogens such as S. enterica will facilitate the management of colistin use and target interventions to prevent further spread. The main objective of this review was to collect epidemiological data about mobilized colistin resistance in S. enterica, describing the mcr variants, identified serovars, origin of the isolate, country and other resistance genes located in the same genetic platform.

Multidrug-Resistant Salmonella enterica Isolated from Food Animal and Foodstuff May Also Be Less Susceptible to Heavy Metals.

Salmonella enterica is a foodborne pathogen showing increasing multidrug resistance (MDR). We characterized the antimicrobial resistance (AMR) genotype using microarrays in a panel of 105 nontyphoidal S. enterica isolated from food animals and foodstuff. Nineteen isolates were chosen on the basis of their MDR and virulence for determination of heavy metal susceptibilities and screened by polymerase chain reaction for heavy metal resistance genes. Whole-genome sequencing (WGS) was performed on three isolates carrying clinically important AMR genes and the cdtB toxin gene to detect other heavy metal resistance mechanisms, and conjugation assays were performed to evaluate transfer of AMR/toxin genes with heavy metal resistance genes. AMR genotyping results showed isolates harbored between 1 and 12 mobile AMR genes, with 58% being classified as MDR. The tested subset of isolates showed reduced susceptibility to zinc (78%), copper (68%), silver (63%), arsenic (47%), and tellurite (26%); phenotypes that could be attributed to zitB (n = 32%), pcoA/pcoD (n = 32%), tcrB (n = 16%), arsB (n = 16%), silA/silE (n = 42%), and terF (n = 26%) genes. WGS confirmed the presence of other heavy metal resistance genes such as copA, cusA, and czcD. Isolates often harbored multiple heavy metal resistance genes. Two strains (Sal25 and Sal368) were able to conjugate with Escherichia coli J53 at a relatively high frequency (∼10-4 colony-forming units per recipient). Transformants selected in the presence of copper harbored either an IncHI2 (J53/Sal25 transconjugant) or IncF (J53/Sal368 transconjugant) plasmid with decreased susceptibilities to tellurite, zinc, copper, cobalt, arsenic, lead, mercury, and silver. blaCTX-M-1 and mcr-1 genes were also transferred to one transconjugant, and tet(M) and blaTEM-1 genes to the other. This work shows the presence of a diversity of AMR genes in this zoonotic pathogen, and suggests that heavy metals may contribute to selection of clinically important ones through the food chain, such as the plasmid-mediated colistin resistance gene mcr-1.

Molecular characterization of carbapenemases of clinical Acinetobacter baumannii-calcoaceticus complex isolates from a University Hospital in Tunisia.

The aim of this study was to identify the carbapenemases from clinical carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex (CRABC) isolates and to assess their potential dissemination by conjugation and natural transformation. CRABC (n = 101) were collected consecutively from inpatients of the University Hospital of Monastir, Tunisia, from 2013 to 2016. Antimicrobial susceptibility was determined by the disk diffusion method and E-test. Carbapenemase-encoding genes were screened by PCR. Genotyping was performed by Pasteur MLST scheme. Isolates were resistant to all beta-lactams, fluoroquinolones and aminoglycosides while 80 and 90% were susceptible to tigecycline and colistin, respectively. Resistance and intermediate resistance to imipenem were 87 and 13%, respectively. The genes blaOXA-24-like, blaOXA-58-like, blaOXA-143-like, blaOXA-48-like, blaVIM, blaIMP, and blaKPC were not found. The blaOXA-51-like and blaOXA-23-like genes were present in 100 and 82.17% isolates, respectively. One isolate (< 1%) carried blaNDM-1 and blaOXA-51-like and belonged to Sequence Type 85 (ST85). Absence of transconjugants suggests a chromosomal location of NDM-1 determinant. The blaNDM-1 gene was inserted in a truncated form of Tn125, which may explain the absence of blaNDM-1 carrier-transformants. To our knowledge, this is the first report of the finding of NDM-positive A. baumannii in Tunisian territory. The study shows that despite the low prevalence and potential spread of NDM-1 enzyme among CRABC, continuous regional antimicrobial resistance surveillance and improved infection control measures are required in Tunisia to prevent further dissemination.

ISAba1 and Tn6168 acquisition by natural transformation leads to third-generation cephalosporins resistance in Acinetobacter baumannii.

Acinetobacter baumannii has intrinsic beta-lactamase genes, namely ampC and blaOXA-51-like, which are only strongly expressed when the ISAba1 insertion sequence is upstream the 5' end of the genes. A second ampC gene has also been identified in some clinical A. baumannii strains. The increased expression of these genes leads to resistance to beta-lactams, including third-generation cephalosporins and/or carbapenems. The aim of this work was to assess the involvement of natural transformation in the transfer of chromosomal ampC-associated mobile elements, and related changes in the resistance profile of recipient cells. Natural transformation assays with the naturally competent A. baumannii A118 clinical isolate as recipient cell and the multidrug resistant A. baumannii Ab51 clinical isolate as the source of donor DNA produced transformants. All tested transformants showed integration of the ISAba1 close to the ampC gene. In two transformants, the ISAba1 was acquired by transposition and inserted between the usual folE and the ampC genes. The remaining transformants acquired the ISAba1 adjacent to a second ampC gene, as part of Tn6168, likely by homologous recombination. Our study demonstrates that natural transformation can contribute to the widespread of beta-lactams resistance, and acquisition of non-resistant determinants can lead to changes in the susceptibility profile of A. baumannii strains.