Staphylococcus aureus remains a major public health concern due to its capacity for colonization, transmission, and antimicrobial resistance. Both methicillin-resistant (MRSA) and methicillin-susceptible S. aureus (MSSA) serve as reservoirs for resistance determinants, including those conferring reduced susceptibility to topical decolonization agents. We analyzed 2,330 S. aureus isolates collected between 2022 and 2025 from hospitals and community clinics in New Jersey and New York City, including 962 MRSA infection isolates and 1,368 nasal carriage isolates (310 MRSA and 1,058 MSSA) obtained from patients upon admission to intensive care, neonatal intensive care, and transplant units. Whole-genome sequencing and PCR characterized clonal lineages, plasmid structures, and resistance determinants, with focus on mupA, which mediates high-level mupirocin resistance. MRSA infection isolates were dominated by clonal complexes CC8 (63%), CC5 (21%), and CC30 (10%), whereas MSSA carriage isolates were more diverse, with CC398 most prevalent (15%). The mupA gene was detected in 26% of MRSA infection isolates, 50% of MRSA carriage isolates, and 36% of MSSA carriage isolates. Pairwise single-nucleotide polymorphism (SNP) analysis revealed most mupA variants differed by 0-2 SNPs across diverse lineages, consistent with recent horizontal dissemination. Long-read sequencing identified three major mupA-carrying plasmid groups-conjugative, mobilizable, and non-mobilizable-frequently co-harboring qacC, aadD1, msr(A), and mph(C). Non-mobilizable plasmids were confined to CC8, while mobilizable and conjugative variants circulated across multiple lineages. The high prevalence of mupA-bearing plasmids co-associated with quaternary ammonium resistance genes raises concerns regarding empiric mupirocin- and chlorhexidine-based decolonization strategies. Genomic surveillance and rapid resistance screening may be critical to preserving topical agent efficacy.

Staphylococcus haemolyticus is an important zoonotic pathogen. The objective of this study was to investigate the pathogenicity of a Staphylococcus haemolyticus isolated from the blood of Elaphurus davidianus and evaluate its potential risks to public health. A combination of methods including 16S rRNA sequencing, PCR, antimicrobial susceptibility testing and mouse challenge assay was employed to systematically investigate its phylogenetic relationships, growth characteristics, virulence and antimicrobial resistance genes, LD₅₀, and antimicrobial resistance profile. The results indicated that the strain was identified as Staphylococcus haemolyticus. The LD50 of the strain in mice was determined to be 6.4 × 108 CFU/ml, and the strain caused significant pathological lesions in the heart, lung, spleen, kidney and liver of the mice. In addition, the strain harbored 8 virulence genes, including Lipase, Polyglutamic acid capsule, Uge, WbtP, Thermonuclease, Type VII secretion system, Autolysin, and Cytolysin. Meanwhile, it exhibited resistance to 18 antibiotics, such as oxacillin, ampicillin, benzylpenicillin, levofloxacin, ceftazidime, streptomycin, imipenem, minocycline, tetracycline, doxycycline, azithromycin, erythromycin, clindamycin, lincomycin, vancomycin, chloramphenicol, florfenicol, and cotrimoxazole, and harbored 12 antimicrobial resistance genes, including msrA, mphC, PC1, AAC(6')-Ie-APH(2″)-Ia, vanY gene in vanB cluster, vanY gene in vanM cluster, APH(3')-IIIa, vanT gene in vanG cluster, sepA, norC, sdrM, and dfrG. Collectively, these findings indicated that the strain possessed strong virulence and exhibited resistance to multiple antibiotics. This suggested that it posed considerable potential risks to public health. This study provides a scientific basis for further investigation into the pathogenic mechanisms, antimicrobial resistance mechanisms, and prevention and control strategies of this strain.

Staphylococcus aureus (S. aureus) is a causative agent of a wide range of infections such as staphylococcal scalded skin syndrome, toxic shock syndrome, necrotizing pneumonia, endocarditis, and osteomyelitis, posing a significant challenge in clinical management. This study explores the antibacterial potential of lawsone on S. aureus using experimental and computational methods. The minimum inhibitory concentration (MIC) of lawsone (alone and in combination with erythromycin, tetracycline, norfloxacin and ciprofloxacin) on 8 clinical multi-drug resistant S. aureus was evaluated in vitro. The ability of lawsone to modulate antibiotic susceptibility was also determined. Molecular docking was carried out to investigate the binding affinities between lawsone and five efflux pumps (EPP) (NorA, NorB, MsrA, SepA, and MefA) and a ribosomal protection protein (TetM) implicated in S. aureus drug resistance. Furthermore, molecular dynamics simulations (MDS) were performed to assess the stability of the protein-ligand complexes throughout the 100 ns simulation period. In addition, the physicochemical properties, drug-likeness, and toxicity of the lawsone were predicted. Lawsone showed synergistic effects with erythromycin, tetracycline, norfloxacin, and ciprofloxacin, as indicated by the modulation factors (MF) ranging from 2 to > 16. Notably, the strain SA383 showed MF values of > 8 for two antibiotics (ciprofloxacin and erythromycin), and > 16 for norfloxacin. Molecular docking revealed strong binding affinities between lawsone and the evaluated S. aureus drug resistant proteins. The MDS confirmed the stability of the lawsone-protein complexes over 100 ns simulation period, supporting its potential as an efflux pump inhibitor (EPI). ADMET profiling of lawsone demonstrated favorable drug-likeness, pharmacokinetics, and low toxicity. Lawsone does not inhibit major cytochrome P450 enzymes. Toxicity predictions also showed no significant risks of carcinogenicity or immunotoxicity, but potential mutagenicity and nephrotoxicity which require further study. Lawsone also exhibits no predicted activity on androgen receptors, aromatase, or GABA receptors, indicating minimal hormonal disruption. These findings highlight lawsone as a promising candidate for the development of a new EPI candidate, particularly against antibiotic-resistant S. aureus.

Antimicrobial resistance (AMR) in Staphylococcus aureus is a growing concern in poultry production, driven by the extensive use of antimicrobials for metaphylaxis, prophylaxis, and growth promotion. This study investigated genes linked to β-lactam resistance and multidrug efflux in S. aureus isolated from commercial laying hens and broilers in Pernambuco, Brazil. A total of 200 samples obtained from 100 birds (100 tracheal swabs and 100 cloacal swabs) were collected from 20 flocks. Bacterial DNA was extracted and subjected to PCR to confirm S. aureus and to detect blaZ, mecA, mecC, norA, norC, msrA, and tet38. S. aureus was identified in 5% (5/100) of the commercial birds tested, all from laying hens. Among these isolates, 20% (1/5) carried mecC and blaZ, 100% were positive for norA and norC, and 60% (3/5) for msrA. mecA and tet38 were not detected. These findings underscore the potential dissemination of S. aureus harboring resistance genes in poultry environments and highlight S. aureus as a reservoir of antimicrobial resistance in poultry production, with implications for animal and public health. Therefore, continuous surveillance and the prudent use of antimicrobials in animal production systems are necessary. Although efflux pump and mecC genes have been documented in Brazilian livestock, reports in poultry are scarce. These findings support the inclusion of these genetic determinants of resistance in national surveillance of antimicrobial resistance in poultry.

In this study, the antibacterial properties and efflux pump-inhibitory activities of linalool (Li) and cuminaldehyde (CA) were assessed against oral staphylococci. The minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) of erythromycin (Ery), tetracycline (TET), and benzalkonium chloride (BC) were determined alone and in combination with of a sub-MIC (½ MIC) of CA and Li. The potential inhibition of the efflux pump was assessed using a 4',6-diamidino-2-phenylindole (DAPI) accumulation assay and real-time quantitative PCR (RT-qPCR) to evaluate NorB gene expression in the presence of TET, Li and CA. In addition, molecular docking were conducted using Maestro (Schrödinger Release 2020-3) to predict the interactions of Li and CA with Staphylococcus aureus efflux pumps (NorA, NorB, MefA, TetM, SepA, and MsrA). Our results showed that the MIC values of Li and CA ranged from 4 to 64 mg/ml. A synergistic effect of Li and CA with tetracycline was observed, with a reduction rate of MIC ranging from 2 to 32-fold and 2 to 64-fold respectively. Moreover, the combination of Ery and ½ MIC of Li and CA showed a 2- to 64-fold reduction in MIC values against the most tested strains. We also noted a 2- to 8-fold decrease in the MIC of BC with the combinaition of Li and CA. RT-qPCR showed a down-regulation of the NorB efflux pump gene after the addition of 1/2 MIC of Li and CA respectively. Molecular Docking results showed a binding affinities of CA (-5.8 to -7.3 kcal/mol) and Li (-3.4 to -4.3 kcal/mol) toward efflux pump targets, particularly NorA and SepA. In conclusion, Li and CA may be considered as a potential natural origin for resistance-modifying activities in multidrug resistance strains.

Vancomycin-intermediate Staphylococcus aureus (VISA) strains represent a serious public health concern. It is crucial to investigate the genetic diversity, biofilm formation, and virulence analysis of VISA isolated from hospitalized patients. During the two-year study period, 42 VISA were obtained from 520 S. aureus isolates collected from various clinical samples, corresponding to a prevalence of 8.1%, as determined by the broth microdilution method. These VISA isolates were further characterized using biofilm formation, antimicrobial susceptibility tests, SCCmec typing, spa typing, multilocus sequence typing (MLST), and PCR analysis for detecting resistance (erm(B), tet(M), mecC, msr(B), mecA, mupA, vanA, aac(6')-Ie/aph(2˝), mupB, msr(A), erm(C), erm(A), vanB, ant(4')-Ia, and aph(3')-IIIa), biofilm (clfA, clfB, fnbA, fnbB, ebp, cna and bap) and virulence (eta, etb, pvl, and tst) genes. Our results indicated that the 42 VISA isolates belonged to three clonal complexes, including CC8 (78.6%), CC22 (11.9%), and CC5 (9.5%). The vast majority of S. aureus isolates belonged to CC8/ST239-SCCmec III/t037 (42.9%). Our result revealed that PVL-positive strains belonged to CC/ST5-SCCmec IV/t002 (9.5%), CC/ST8-SCCmec IV/t008 (19%), and CC/ST22-SCCmec IV/t790 (7.1%) while TST-positive isolates belonged to CC8/ST239-SCCmec III/t030 (9.5%) and CC8/ST239-SCCmec III/t037 (35.7%). The majority of HLMUPR isolates belonged to CC8/ST239-SCCmec III/t037 (14.3%), followed by CC/ST8-SCCmec IV/t008 (7.1%), CC8/ST239-SCCmec III/t030 (4.8%), and CC/ST5-SCCmec IV/t002 (2.4%) lineages carrying mupA. The highest frequency of VISA strain with iMLSB phenotype belonged to the CC8/ST239-SCCmec III/t037 (11.9%) clonal lineage. The study highlights that genetic diversity and characteristics of the VISA strains should be closely and continuously monitored. Besides that, importance of measures to prevent the transmission of VISA to treat such infection were urgently needed.

Antimicrobial resistance in natural environments poses an increasing threat to public health and biodiversity conservation. This study investigated antimicrobial resistance and biofilm formation in bacteria isolated from Inia araguaiaensis, an Amazonian endemic dolphin species. Skin lesion samples were collected from eight individuals in the Mocajuba region, Pará, Brazil. Bacterial isolation was performed on Brain Heart Infusion agar and Mannitol Salt agar. Species identification was carried out using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and antimicrobial susceptibility testing was conducted by disk diffusion following. Resistance genes were detected by polymerase chain reaction, and biofilm formation was assessed using the crystal violet staining method. A total of 19 bacterial isolates were recovered, including Staphylococcus spp. (n = 14) and Mammaliicoccus sciuri (n = 5). The most frequently identified species were Staphylococcus aureus (4/19; 21.1%), S. warneri (4/19; 21.1%), and S. epidermidis (4/19; 21.1%). A high prevalence of penicillin resistance was observed (18/19; 94.7%), followed by resistance to erythromycin, tetracycline, and sulfamethoxazole-trimethoprim (each 4/19; 21.1%), and gentamicin (3/19; 15.8%). Four isolates (4/19; 21.1%) exhibited a multidrug-resistant (MDR) profile. Genotypic screening revealed the presence of the blaZ gene in 8/19 isolates (44.4%), followed by mecA, msrA, and norC (each 2/19; 10.5%). The tetracycline resistance genes tetL and tetM were detected in 3/19 (15.8%) and 1/19 (5.3%) isolates, respectively. Biofilm formation was detected on 15/19 (78.9%) of the isolates, of which 4/15 (26.7%) were classified as strong producers, 1/15 (6.7%) as moderate, and 10/15 (66.7%) as weak producers. These findings support the recognition of river dolphins as potential sentinels for antimicrobial resistance in aquatic ecosystems and reinforce the importance of integrating microbiological monitoring into broader conservation efforts under the One Health perspective.

Background: Antimicrobial resistance (AMR) in Staphylococcus aureus (S. aureus) poses critical public health challenges by limiting treatment efficacy and elevating morbidity, mortality, and healthcare costs. Methods: This study examined the prevalence and characteristics of AMR in S. aureus isolated from humans (veterinarians, veterinary assistants, and pet owners) and animals (dogs and cats) in veterinary clinics across five provinces in Thailand. A total of 882 samples were collected from which 188 S. aureus isolates were recovered and subjected to antimicrobial susceptibility testing and resistance gene detection. Results: Substantial variations in AMR profiles were observed across host categories, with veterinarians and veterinary assistants exhibiting higher resistance rates than pet owners. The β-lactam resistance gene blaZ was prevalent in all groups, whereas mecA was predominantly detected in veterinarians and dogs, emphasizing the occupational risk and zoonotic transmission potential. The aminoglycoside resistance gene aacA-aphD was common in cats, and quinolone resistance genes gyrA and grlA were identified in veterinarians and dogs. Macrolide resistance genes msrA and ermA, lincosamide resistance gene linA, and tetracycline resistance gene tetK were widely distributed across the groups. Agr typing of S. aureus isolates revealed diverse group distributions, with agr group I was predominant in human samples and associated with the highest AMR gene expression, while agr group III was most prevalent in animal samples and also exhibited elevated AMR gene expression within that group. Conclusions: This study underscored the diverse distribution of AMR genes, with veterinarians and veterinary assistants facing higher occupational risks. The findings highlighted the importance of integrated antimicrobial stewardship and surveillance within a One Health framework to mitigate the spread of AMR in veterinary and community settings.