First report of linezolid-resistant cfr-positive methicillin-resistant Staphylococcus aureus in humans in Portugal

Identification of potential inhibitors against Staphylococcus aureus shikimate dehydrogenase through virtual screening and susceptibility test

Staphylococcus aureus shikimate dehydrogenase (SaSDH) plays a crucial role in the growth of Staphylococcus aureus (S. aureus), but absent in mammals and therefore a potential target for antibacterial drugs to treat drug-resistant S. aureus infection. In this study, a 3D model of SaSDH was constructed by homology modelling and inhibitors of SaSDH were screened through virtual screening. (-)-Gallocatechin gallate and rhodiosin were identified as inhibitors with Kis of 2.47 μM and 73.38 μM, respectively. Molecular docking and isothermal titration calorimetry showed that both inhibitors interact with SaSDH with a KD of 44.65 μM for (-)-gallocatechin gallate and 16.45 μM for rhodiosin. Both inhibitors had antibacterial activity, showing MICs of 50 μg/mL for (-)-gallocatechin gallate and 250 μg/mL for rhodiosin against S. aureus. The current findings have the potential for identification of drugs to treat S. aureus infections by targeting SaSDH.

Antibiotic Resistance Genes, Virulence Factors, and Biofilm Formation in Coagulase-Negative Staphylococcus spp. Isolates from European Hakes (Merluccius merluccius, L.) Caught in the Northeast Atlantic Ocean

The indiscriminate use of antibiotics has contributed to the dissemination of multiresistant bacteria, which represents a public health concern. The aim of this work was to characterize 27 coagulase-negative staphylococci (CoNS) isolated from eight wild Northeast Atlantic hakes (Merluccius merluccius, L.) and taxonomically identified as Staphylococcus epidermidis (n = 16), Staphylococcus saprophyticus (n = 4), Staphylococcus hominis (n = 3), Staphylococcus pasteuri (n = 2), Staphylococcus edaphicus (n = 1), and Staphylococcus capitis (n = 1). Biofilm formation was evaluated with a microtiter assay, antibiotic susceptibility testing was performed using the disk diffusion method, and antibiotic resistance and virulence determinants were detected by PCR. Our results showed that all staphylococci produced biofilms and that 92.6% of the isolates were resistant to at least one antibiotic, mainly penicillin (88.8%), fusidic acid (40.7%), and erythromycin (37%). The penicillin resistance gene (blaZ) was detected in 66.6% (18) of the isolates, of which 10 also carried resistance genes to macrolides and lincosamides (mphC, msr(A/B), lnuA, or vgaA), 4 to fusidic acid (fusB), and 3 to trimethoprim-sulfamethoxazole (dfrA). At least one virulence gene (scn, hla, SCCmecIII, and/or SCCmecV) was detected in 48% of the isolates. This study suggests that wild European hake destined for human consumption could act as a vector of CoNS carrying antibiotic resistance genes and/or virulence factors.

cfr and fexA genes in methicillin-resistant Staphylococcus aureus from humans and livestock in the Netherlands

Background

Although the Netherlands is a country with a low endemic level of methicillin-resistant Staphylococcus aureus (MRSA), a national MRSA surveillance has been in place since 1989. In 2003 livestock emerged as a major reservoir of MRSA and currently livestock-associated MRSA (clonal complex CC398) make up 25% of all surveillance isolates. To assess possible transfer of resistant strains or resistance genes, MRSA obtained from humans and animals were characterized in detail.

Methods

The sequenced genomes of 6327 MRSA surveillance isolates from humans and from 332 CC398 isolates from livestock-related samples were analyzed and resistance genes were identified. Several isolates were subjected to long-read sequencing to reconstruct chromosomes and plasmids.

Results

Here we show the presence of the multi-resistance gene cfr in seven CC398 isolates obtained from humans and in one CC398 isolate from a pig-farm dust sample. Cfr induces resistance against five antibiotic classes, which is true for all but two isolates. The isolates are genetically unrelated, and in seven of the isolates cfr are located on distinct plasmids. The fexA gene is found in 3.9% surveillance isolates and in 7.5% of the samples from livestock. There is considerable sequence variation of fexA and geographic origin of the fexA alleles.

Conclusions

The rare cfr and fexA resistance genes are found in MRSA from humans and animals in the Netherlands, but there is no evidence for spread of resistant strains or resistance plasmids. The proportion of cfr-positive MRSA is low, but its presence is worrying and should be closely monitored.

MRSA in Humans, Pets and Livestock in Portugal: Where We Came from and Where We Are Going

Over the years, molecular typing of methicillin-resistant S. aureus (MRSA) has allowed for the identification of endemic MRSA strains and pathogenic strains. After reaching a peak of predominance in a given geographic region, MRSA strains are usually replaced by a new strain. This process is called clonal replacement and is observed worldwide. The worldwide spread of hospital-associated MRSA (HA-MRSA), community-associated MRSA (CA-MRSA) and livestock-associated MRSA (LA-MRSA) clones over the last few decades has allowed this microorganism to be currently considered a pandemic. In Portugal, most HA-MRSA infections are associated with EMRSA-15 (S22-IV), New York/Japan (ST5-II) and Iberian (ST247-I) clones. Regarding the strains found in the community, many of them are frequently associated with the hospital environment, namely the Pediatric, Brazilian and Iberian clones. On the other hand, a strain that is typically found in animals, MRSA clonal complex (CC) 398, has been described in humans as colonizing and causing infections. The ST398 clone is found across all animal species, particularly in farm animals where the economic impact of LA-MRSA infections can have disastrous consequences for industries. In contrast, the EMRSA-15 clone seems to be more related to companion animals. The objective of this review is to better understand the MRSA epidemiology because it is, undoubtedly, an important public health concern that requires more attention, in order to achieve an effective response in all sectors.

Linezolid-resistance Staphylococcus aureus – Prevalence, Emerging Resistance Mechanisms, Challenges and Perspectives

Staphylococcus aureus, an opportunistic pathogen, can root several infections viz skin and tissue infections, bacteraemia, food poisoning, pneumonia, and many other clinical conditions with some variations of virulence factors. In treatment of infections, caused by this Gram-positive pathogen, several antibiotics are being used importantly Methicillin and Vancomycin. This pathogen has high capability of antibiotic resistance development and had evolved new strains such as Methicillin-resistant Staphylococcus aureus (MRSA), and Vancomycin-resistant Staphylococcus aureus (VRSA). Meta-analysis in Ethiopia showed that pooled prevalence of MRSA in environment, food, animal, and human was 54%, 77%, 15%, and 38% respectively (2022). Risk of MRSA isolates from burn ICU was 55 % higher (2018). In Bangladesh, 37.1% isolates from frozen meat chicken (2021) were identified as MRSA. This problem is being dealt with a novel drug called Linezolid which has been proved effective against both MRSA and VRSA. Exacerbating the situation, this pathogen has shown resistance against this unprecedented drug by means of a number of drug resistance mechanisms. Its prevalence has been reporting since the adoption of the drug, but with a minute ratio at one time/place to the very high percentage at another time/place. This inconsistent prevalence must not be ignored, and its surveillance should be augmented as antibiotic treatment is critical for fighting against microbial infections. This review highlights the worldwide reports in which Staphylococcus aureus of either wildtype or Methicillin or Vancomycin resistance that have shown resistance to Linezolid drug for the past 2 decades. At the same time where incidences of Linezolid Resistant Staphylococcus aureus (LRSA) indications are reporting, there is a call for comprehensive strategies to overcome this challenge of antibiotic resistance.

Platanus hybrida’s Phenolic Profile, Antioxidant Power, and Antibacterial Activity against Methicillin-Resistant Staphylococcus aureus (MRSA)

Methicillin-resistant S. aureus (MRSA) are a threat to public health as they frequently reveal a multidrug-resistant pattern. Researchers all over the world are on an urgent hunt for new treatments to help fight infections before antibiotics become obsolete, and some natural alternatives, such as polyphenols, have already exhibited therapeutic properties. Therefore, this study aimed to determine the phenolic profile, antioxidant capacity, and antimicrobial activity against MRSA of the leaf, fruit, and stem bark extracts of Platanus hybrida. The polyphenols were extracted with a water/ethanol (20:80) mixture and the methodology included HPLC-DAD, DPPH, FRAP, and CuPRAC. To address this issue from a One Health perspective, the Kirby–Bauer disc diffusion method was performed against nine MRSA strains from three different sources (livestock, wild animals, and humans). Fourteen phenolics were identified and the leaf extract showed the highest phenolic content, followed by the fruit extract. The leaf extract also showed the highest antioxidant capacity while the fruit extract had the lowest antioxidant capacity. Both leaf and fruit extracts inhibited the growth of strains from all sources, while the stem bark extract did not inhibit the growth of human strains. This work highlights the complex chemical composition and the antioxidative and antimicrobial potential of extracts derived from P. hydrida.

Biofilm Formation of Multidrug-Resistant MRSA Strains Isolated from Different Types of Human Infections

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main pathogens causing chronic infections, mainly due to its capacity to form biofilms. However, the mechanisms underlying the biofilm formation of MRSA strains from different types of human infections are not fully understood. MRSA strains isolated from distinct human infections were characterized aiming to determine their biofilm-forming capacity, the biofilm resistance to conventional antibiotics and the prevalence of biofilm-related genes, including, icaA, icaB, icaC, icaD, fnbA, fnbB, clfA, clfB, cna, eno, ebpS, fib and bbp. Eighty-three clinical MRSA strains recovered from bacteremia episodes, osteomyelitis and diabetic foot ulcers were used. The biofilm-forming capacity was evaluated by the microtiter biofilm assay and the biofilm structure was analyzed via confocal scanning laser microscopy. The antimicrobial susceptibility of 24-h-old biofilms was assessed against three antibiotics and the biomass reduction was measured. The metabolic activity of biofilms was evaluated by the XTT assay. The presence of biofilm-related genes was investigated by whole-genome sequencing and by PCR. Despite different intensities, all strains showed the capacity to form biofilms. Most strains had also a large number of biofilm-related genes. However, strains isolated from osteomyelitis showed a lower capacity to form biofilms and also a lower prevalence of biofilm-associated genes. There was a significant reduction in the biofilm biomass of some strains tested against antibiotics. Our results provide important information on the biofilm-forming capacity of clinical MRSA strains, which may be essential to understand the influence of different types of infections on biofilm production and chronic infections.

Efficacy of dalbavancin against MRSA biofilms in a rat model of orthopaedic implant-associated infection

OBJECTIVES

The aim of this study was to evaluate the efficacy of dalbavancin against MRSA biofilm-related infection in orthopaedic implants in vivo.

METHODS

One MRSA strain isolated from human osteomyelitis was used to promote biofilm formation on the surface of screws. The implants were inserted in the proximal tibia under general anaesthesia. Thirty-nine Wistar rats were divided into three groups [control group (no treatment), Group 1 (7 days of treatment) and Group 2 (14 days of treatment)]; both treatment groups were administered dalbavancin intraperitoneally and euthanized after treatment. cfu of bacteria present in both the tibia and the implant were quantified. The infection severity was assessed by histopathology and scored from 0 (no infection) to 4 (severe infection).

RESULTS

The high number of cfu/g and cfu/mL present in the control group indicated a well-established infection. There was a significant reduction in cfu in rats treated with dalbavancin both in the tibia (2.8 × 105 cfu/g) and the implant (1.1 × 106 cfu/mL) in Group 1 (1.8 × 103 cfu/g and 2.4 × 105 cfu/mL, respectively) and in Group 2 (8.2 cfu/g and 8.2 × 103 cfu/mL, respectively). Most animals from the control group presented an infection scored as 3 (severe). At the end of the experiment, most rats from Groups 1 and 2 presented an infection scored as 2 (moderate) and 0 (no infection), respectively.

CONCLUSIONS

Although there was a marked decrease in cfu number, signs of biofilm-induced infection prevailed after 14 days of treatment. Further studies should be carried out to evaluate the potential of dalbavancin in the treatment of bone and orthopaedic implant-associated MRSA infections.

Antimicrobial Resistance and Genetic Lineages of Staphylococcus aureus from Wild Rodents: First Report of mecC-Positive Methicillin-Resistant S. aureus (MRSA) in Portugal

The frequent carriage of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), by wild animals along with its zoonotic potential poses a public health problem. Furthermore, the repeated detection of the mecA gene homologue, mecC, in wildlife raises the question whether these animals may be a reservoir for mecC-MRSA. Thus, we aimed to isolate S. aureus and MRSA from wild rodents living in port areas and to characterize their antimicrobial resistance and genetic lineages. Mouth and rectal swab samples were recovered from 204 wild rodents. The samples were incubated in BHI broth with 6.5% of NaCl and after 24 h at 37 °C the inoculum was seeded onto Baird-Parker agar, Mannitol Salt agar and ORSAB (supplemented with 2 mg/L of oxacillin) plates. Species identification was confirmed by MALDI-TOF MS. The antimicrobial susceptibility testing was performed by the Kirby-Bauer disc diffusion method against 14 antibiotics. The presence of virulence and resistance genes was performed by PCR. The immune evasion cluster (IEC) system was investigated in all S. aureus. All isolates were characterized by MLST, spa- and agr typing. From 204 samples, 38 S. aureus were isolated of which six MRSA were detected. Among the six MRSA isolates, three harbored the mecC gene and the other three, the mecA gene. All mecC-MRSA isolates were ascribed to sequence type (ST) 1945 (which belongs to CC130) and spa-type t1535 whereas the mecA isolates belonged to ST22 and ST36 and spa-types t747 and t018. Twenty-five S. aureus were susceptible to all antibiotics tested. S. aureus isolates were ascribed to 11 MLST and 12 spa-types. S. aureus presents a great diversity of genetic lineages in wild rodents. This is the first report of mecC-MRSA in Portugal.

Anti-biofilm activity of dalbavancin against methicillin-resistant Staphylococcus aureus (MRSA) isolated from human bone infection

The presence of methicillin-resistant Staphylococcus aureus (MRSA) in bone infections difficults its treatment and is a sign of concern. The aim of this study was to evaluate in vitro activity of dalbavancin on pre-established adhered cells and 24 h old biofilms of MRSA strains isolated from a human bone infection. Thirty-three MRSA were isolated from osteomyelitis episodes. The antimicrobial susceptibility of these strains was assessed by the Kirby-Bauer disc diffusion method and the presence of resistance genes was screened by PCR. MRSA planktonic minimum inhibitory concentration and minimum bactericidal concentration were assessed. Minimum biofilm eradication concentration (MBEC) was performed by the microtiter biofilm formation assay. All 33 MRSA strains were classified as multidrug-resistant strains and susceptible to dalbavancin. Dalbavancin inhibited the growth of 54.6% and 52% of strains at the concentrations of 0.05 µg/mL and 1 µg/mL, respectively. The MBEC values up to 0.4 µg/mL demonstrated that dalbavancin was active against most strains in pre-established adhered cells and 24 h old biofilms. The current results show that dalbavancin is active against adhered cells and biofilms in vitro, suggesting that this antimicrobial agent may be an option for the treatment of bone infections caused by MRSA.

Clonal Diversity and Antimicrobial Resistance of Methicillin-Resistant Staphylococcus pseudintermedius Isolated from Canine Pyoderma

The emergence of methicillin-resistant Staphylococcus pseudintermedius (MRSP) antimicrobial resistance and epidemic genetic lineages is posing a challenge in veterinary medicine due to the limited therapeutical options. MRSP has been identified as an important canine pyoderma pathogen. Thus, we aimed to characterize the antimicrobial resistance and clonal lineages of MRSP isolated from canine cutaneous pyoderma. Thirty-one MRSP isolates recovered from pyoderma were further characterized. The antimicrobial susceptibility testing of the isolates was performed by the Kirby-Bauer disc diffusion method against 14 antimicrobial agents. The presence of antimicrobial and virulence genes was carried out by PCR. Multilocus sequence typing was performed in all isolates. All strains had a multidrug-resistant profile showing resistance mainly to penicillin, macrolides and lincosamides, aminoglycosides, tetracycline and trimethoprim-sulfamethoxazole, which was encoded by the blaZ, ermB, msr(A/B), aac(6')-Ie-aph(2'')-Ia, aph(3')-IIIa, ant(4')-Ia, tetM, tetK and dfrG genes. All isolates harbored the lukS-I/lukF-I virulence factors. Isolates were ascribed to nine previously described sequence types (STs): ST123, ST339, ST727, ST71, ST537, ST45, ST1029, ST118 and ST1468; and to five STs first described in this study: ST2024, ST2025, ST2026, ST2027 and ST2028. In this study, most isolates belonged to ST123 (n = 16), which belongs to CC71 and is the most common clone in Europe. All isolates were multidrug-resistant, which may impose a serious threat to animal health.

Diversity of methicillin-resistant staphylococci among wild Lepus granatensis: first detection of mecA-MRSA in hares

MRSA in humans, pets and livestock have been widely investigated, nevertheless, there is still little information of MRSA in wild animals. Therefore, this study aimed to investigate the occurrence and antimicrobial resistance profiles of methicillin-resistant staphylococci (MRS) in wild Iberian hares and to characterize their genetic lineages. Samples from 83 wild hares (Lepus granatensis) were collected during the hunting season. Isolation of MRS was accomplish using Oxacillin Resistant Screening Agar medium with 2 mg/L of oxacillin. The susceptibility of the isolates was tested by the Kirby-Bauer disc diffusion method. The presence of resistance and virulence genes was studied by PCR. S. aureus strains were further characterized by multilocus sequence typing, agr, spa and SCCmec typing. From the 83 samples, 12 (14.45%) coagulase-negative staphylococci and 3 (3.6%) MRSA strains were isolated. Nine coagulase-negative isolates showed resistance to at least one antibiotic. One MRSA isolate showed a multidrug-resistant profile with resistances to ß-lactams, aminoglycosides, macrolides and lincosamides. All MRSA strains were ascribed to ST2855, t1190 and SCCmec type III. The frequency of MRSA strains in wild hares was low, nevertheless, the presence of MRSA in game animals is considered a public health problem and may represent a route of transmission between animals and humans.

High Efficacy of Ozonated Oils on the Removal of Biofilms Produced by Methicillin-Resistant Staphylococcus aureus (MRSA) from Infected Diabetic Foot Ulcers

Ozone has a high wound healing capacity and antibacterial properties and can be used as a complementary treatment in infections. Methicillin-resistant S. aureus (MRSA) is the most common pathogen found in infected diabetic foot ulcers. Most of MRSA are resistant to several classes of antibiotics and, therefore, there is a need for new, effective, and well-tolerated agents. Thus, we aimed evaluate the antimicrobial and antibiofilm potentials of ozonated vegetable oils against MRSA strains isolated from diabetic foot ulcers. Six ozonated oils were produced with concentrations of ozone ranging from 0.53 to 17 mg of ozone/g of oil. The peroxide values were determined for each oil. Ozonated oils content on fatty acid was determined by gas chromatography equipped with a flame ionization detector. The antimicrobial susceptibility testing was performed by the Kirby–Bauer disk diffusion method and the effect of ozonated oils on biofilm formation ability and on established biofilms was investigated. In general, the content in identified unsaturated fatty acid in oils decreased with the increase of ozonation time and, consequently, the peroxide value increased. Most bacterial strains were inhibited by ozonated oil at a concentration of 4.24 mg/g. Ozonated oils had moderate to high ability to remove adhered cells and showed a high capacity to eradicate 24 h old biofilms. Our results show promising use of ozonated oils on the treatment of infections, in particular those caused by multidrug-resistant MRSA strains.

Therapeutic potential of dalbavancin in a rat model of methicillin-resistant Staphylococcus aureus (MRSA)-osteomyelitis

Bacterial osteomyelitis is a major clinical challenge in human and veterinary patients. This infection is an infrequent but feared complication of orthopedic surgery and is mainly caused by methicillin-resistant Staphylococcus aureus (MRSA). The aim of this study was to evaluate the efficacy of dalbavancin (dosed for either 7 or 14 days) in an MRSA-osteomyelitis tibial bone model. A total of 39 rats were included in the study. All animals received an inoculum of a clinical strain of MRSA (10⁶ colony-forming units [CFU]) injected into the proximal tibia under general anesthesia. Dalbavancin was injected intraperitoneally for 7 or 14 days in 13 animals each; the remaining 13 animals received saline solution. After treatment, the animals were sacrificed. Infected tibiae were recovered for histological evaluation and microbiological analysis (MRSA count per gram of bone). Rats that received dalbavancin showed a statistically significant reduction of MRSA counts compared with the control group: median 0 CFU/g bone (14 days of dalbavancin) vs. 70 CFU/g bone (7 days of dalbavancin) and 1600 CFU/g bone (control). Histological evaluation showed typical signs of osteomyelitis in the control group, whereas there were no signs of bone infection in 92% of the rats that received 14 days of dalbavancin. According to this model, dalbavancin seems to have good efficacy for treating serious Gram-positive bone infections, including those caused by MRSA.

Livestock-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) in Purulent Subcutaneous Lesions of Farm Rabbits

Methicillin-resistant Staphylococcus aureus (MRSA) are one of the main pathogens associated with purulent infections. MRSA clonal complex 97 (CC97) has been identified in a wide diversity of livestock animals. Therefore, we aimed to investigate the antibiotic resistance profiles of MRSA strains isolated from purulent lesions of food-producing rabbits. Samples from purulent lesions of 66 rabbits were collected in a slaughterhouse in Portugal. Samples were seeded onto ORSAB plates with 2 mg/L of oxacillin for MRSA isolation. Susceptibility to antibiotics was tested by the disk diffusion method against 14 antimicrobial agents. The presence of resistance genes, virulence factors and the immune evasion cluster (IEC) system was studied by polymerase chain reaction. All isolates were characterized by multilocus sequence typing (MLST), agr and spa typing. From the 66 samples analyzed, 16 (24.2%) MRSA were detected. All strains were classified as multidrug-resistant as they were resistant to at least three classes of antibiotics. All isolates showed resistance to penicillin, erythromycin and clindamycin. Seven isolates were resistant to gentamicin and harbored the aac(6′)-Ie-aph (2″)-Ia gene. Resistance to tetracycline was detected in 10 isolates harboring the tet(K) gene. The IEC genes were detected in three isolates. MRSA strains belonged to CC97, CC1, CC5, CC15 or CC22. The isolates were assigned to six different spa types. In this study we found a moderate prevalence of multidrug-resistant MRSA strains in food-producing rabbits. This may represent concern for food safety and public health, since cross-contamination may occur, leading to the spread of MRSA and, eventually, the possibility of ingestion of contaminated meat.

Molecular Epidemiology of Staphylococcus aureus Lineages in Wild Animals in Europe: A Review

Staphylococcus aureus is an opportunist pathogen that is responsible for numerous types of infections. S. aureus is known for its ability to easily acquire antibiotic resistance determinants. Methicillin-resistant S. aureus (MRSA) is a leading cause of infections both in humans and animals and is usually associated with a multidrug-resistant profile. MRSA dissemination is increasing due to its capability of establishing new reservoirs and has been found in humans, animals and the environment. Despite the fact that the information on the incidence of MRSA in the environment and, in particular, in wild animals, is scarce, some studies have reported the presence of these strains among wildlife with no direct contact with antibiotics. This shows a possible transmission between species and, consequently, a public health concern. The aim of this review is to better understand the distribution, prevalence and molecular lineages of MRSA in European free-living animals.

Radezolid Is More Effective Than Linezolid Against Planktonic Cells and Inhibits Enterococcus faecalis Biofilm Formation

The aim of this study was to compare the effects of radezolid and linezolid on planktonic and biofilm cells of Enterococcus faecalis. A total of 302 E. faecalis clinical isolates were collected, and the minimum inhibitory concentrations (MICs) of radezolid and linezolid were determined by the agar dilution method. Changes in the transcriptome of a high-level, in vitro-induced linezolid-resistant isolate were assessed by RNA sequencing and RT-qPCR, and the roles of efflux pump-related genes were confirmed by overexpression analysis. Biofilm biomass was evaluated by crystal violet staining and the adherent cells in the biofilms were quantified according to CFU numbers. The MIC₅₀/MIC₉₀ values of radezolid (0.25/0.50 mg/L) against the 302 E. faecalis clinical isolates were eightfold lower than those of linezolid (2/4 mg/L). The radezolid MICs against the high-level linezolid-resistant isolates (linezolid MICs ≥ 64 mg/L) increased to ≥ 4 mg/L with mutations in the four copies of the V domain of the 23S rRNA gene. The mRNA expression level of OG1RF_12220 (mdlB2, multidrug ABC superfamily ATP-binding cassette transporter) increased in the high-level linezolid-resistant isolates, and radezolid and linezolid MICs against the linezolid-sensitive isolate increased with overexpression of OG1RF_12220. Radezolid (at 1/4 or 1/8× the MIC) inhibited E. faecalis biofilm formation to a greater extent than linezolid, which was primarily achieved through the inhibition of ahrC, esp, relA, and relQ transcription in E. faecalis. In conclusion, radezolid is more effective than linezolid against planktonic E. faecalis cells and inhibits biofilm formation by this bacterium.

One Health Approach Reveals the Absence of Methicillin-Resistant Staphylococcus aureus in Autochthonous Cattle and Their Environments

Antimicrobial resistance represents one of the greatest challenges of the twenty-first century, and it is globally recognized that addressing this problem requires a concerted One Health approach involving humans, animals, and the environment. Methicillin-resistant Staphylococcus aureus (MRSA) currently represents a global burden; it is resistant to almost all beta-lactams and some MRSA strains are highly multiresistant. S. aureus infection in cattle results in major economic losses in the food industry. Moreover, cases of livestock-associated MRSA strains responsible for invasive life-threatening infections have been reported among human patients in contact with infected or colonized animals. The autochthonous Maronesa cattle breed is a threatened rustic traditional Portuguese breed of mountain cattle of high importance for the Vila Real region. It has been used for centuries as motive power in all kinds of agricultural work and also for meat production, which is its current dominant use and the main source of economic value, being the Maronesa meat commercialized with PDO - Protected Designation of Origin. This study aimed to determine the prevalence and transmission of MRSA in cattle of the Maronesa breed, through a concerted One Health approach comprising human, water, and soil samples of the animals’ handlers and environments. In a total of 195, 63, 40, and 43 cattle, human, water, and soil samples screened in selective ORSAB media supplemented with 2 mg/L oxacillin; only one human sample harbored a MRSA isolate which was ascribed to spa-type t9413 and to ST30, one of the most common genetic lineages associated with community-acquired MRSA. Considering the increasing reports of MRSA isolation from cattle and handlers in Europe, the absence of this major human and animal pathogen in Maronesa cattle and their production systems represents a serendipitous result, valuing this important autochthonous breed. To our knowledge, this is the first study to determine MRSA prevalence and transmission in Maronesa cattle. Through a concerted One Health approach, this study revealed that the Maronesa cattle and their surrounding environments do not represent reservoirs for Methicillin-resistant Staphylococcus aureus.