The research team, led by Francesca Paola Nocera and Luisa De Martino, enrolled 100 dogs admitted to the Veterinary Teaching Hospital in Naples for surgical procedures, most of them orthopaedic operations. Because the animals were already scheduled for surgery under general anaesthesia, the researchers could collect nasal swabs without causing additional stress or discomfort. A single swab was inserted two to three centimetres into each nostril, rotated, and placed into transport medium before being rushed to the microbiology laboratory within two hours. The study was approved by the university’s Institutional Animal Welfare Committee, and written informed consent was obtained from every owner, underscoring the ethical care taken in a study that involved nothing more invasive than routine clinical sampling.

Back in the laboratory, the samples were streaked onto selective culture media, mannitol salt agar and Columbia CNA blood agar, and incubated overnight. Suspect colonies were then identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry, or MALDI-TOF MS, a proteomic technique that fingerprints bacterial proteins to deliver species-level identification. Every staphylococcal strain recovered in the study achieved a reliable species-level score, giving the team a confident catalogue of exactly which organisms were living in these canine noses. Of the 100 dogs sampled, 36 per cent showed no bacterial growth at all, while the remaining 64 per cent yielded bacterial colonies, from which 65 staphylococcal strains were ultimately isolated and characterised.

The species picture was dominated by one familiar name. Staphylococcus pseudintermedius, the staphylococcal species most closely associated with dogs and a notorious opportunist behind skin infections, ear inflammation and postoperative wound infections, accounted for 40 per cent of all isolates, a proportion the researchers confirmed as statistically predominant using a multinomial chi-square test. Staphylococcus aureus, the species of greatest concern in human medicine, came second at 15.4 per cent, followed by Staphylococcus epidermidis, Staphylococcus simulans and Staphylococcus warneri. In one patient, the team even recovered a co-isolation of Staphylococcus haemolyticus and Staphylococcus equorum, a reminder of the ecological diversity packed into this small anatomical niche.

What the antimicrobial susceptibility testing revealed was more troubling still. Using disk diffusion on Mueller-Hinton agar and interpreting results against European Committee on Antimicrobial Susceptibility Testing breakpoints, the researchers tested 14 antimicrobials from 12 different classes, all chosen for their relevance to small-animal clinical practice. Resistance to penicillin topped the list at 83.1 per cent of strains, followed by oxacillin at 63.1 per cent and cefoxitin at 55.4 per cent, the latter two serving as phenotypic markers for methicillin resistance. Erythromycin resistance was detected in 56.9 per cent of isolates, clindamycin in 46.2 per cent and tetracycline in 44.6 per cent. Only fusidic acid, rifampicin and linezolid retained activity against the large majority of strains, with resistance rates below 20 per cent.

Classified according to the internationally standardised definitions of Magiorakos and colleagues, 40 of the 65 strains, or 61.5 per cent, qualified as multidrug-resistant, meaning they were resistant to at least one agent in three or more antimicrobial categories. Three strains, 4.6 per cent, met the stricter criteria for extensive drug resistance, resistant to all but two or fewer categories. Together, the combined multidrug-resistant and extensively drug-resistant prevalence reached 66.2 per cent. Among Staphylococcus pseudintermedius specifically, the picture was even starker: 69.2 per cent of its isolates were multidrug-resistant, and one was extensively drug-resistant, although the difference between this species and the other staphylococci combined did not reach statistical significance. The authors caution that the wide confidence intervals around some of these estimates, particularly for the rarer resistance categories, reflect the limited sample size and warrant careful interpretation.

The second pillar of the study concerned biofilms, the structured microbial communities that bacteria build by embedding themselves in a self-produced extracellular matrix. Within a biofilm, bacterial cells shift their metabolism, shield themselves from antibiotics and evade host immune defences, which is why biofilm-associated infections are so persistent and so difficult to treat. The team quantified biofilm formation using the classic crystal violet assay, growing each strain in 96-well polystyrene plates, staining the adherent biomass and measuring absorbance at 570 nanometres, with all assays performed in triplicate and repeated three independent times. The results were unambiguous: not a single strain failed to produce biofilm. Nearly a quarter were classified as weak producers, but 56.9 per cent were moderate producers and 18.5 per cent were strong producers.

Perhaps the most scientifically interesting finding emerged when the researchers asked whether drug resistance and biofilm capacity travel together. Within the Staphylococcus pseudintermedius subset, they compared the biofilm phenotypes of multidrug-resistant strains against those of fully susceptible ones using Pearson’s chi-square test. The answer was no: biofilm-forming ability occurred independently of resistance status, with a p-value of 0.236. In fact, one strong biofilm-producing strain was susceptible to every antimicrobial tested. This statistical independence matters, because it suggests these two threatening traits are being acquired and maintained through separate evolutionary routes, meaning a strain can be dangerous in one dimension while benign in the other, and that controlling resistance alone would not necessarily eliminate the persistence advantages conferred by biofilm production.

The clinical implications reach beyond the individual dog. The nasal cavity is a well-established ecological niche where staphylococci persist and spread, and animals carrying resistant, biofilm-competent strains into a hospital setting may seed the environment, contaminate surgical sites or transfer organisms to veterinary staff and owners. Previous work has already linked methicillin-resistant Staphylococcus pseudintermedius carriage to surgical site infections following orthopaedic procedures in dogs, and biofilms are known to promote environmental persistence on hospital surfaces. The authors suggest that preoperative nasal screening for multidrug-resistant and biofilm-forming staphylococci might be worth considering in high-risk surgical patients, potentially guiding infection control measures and refining prophylactic antibiotic protocols before the first incision is made.

The study is not without limitations, and the researchers are candid about them. The numbers of certain staphylococcal species were small, the cross-sectional design cannot establish whether nasal colonisation precedes infection, and no information on prior antimicrobial treatment was available to identify risk factors. Crucially, methicillin resistance was assessed phenotypically only, without molecular confirmation through detection of the mecA or mecC genes, leaving open the possibility that some borderline isolates were misclassified, since mechanisms such as beta-lactamase hyperproduction can mimic methicillin resistance in disk diffusion tests. Even so, the overall message stands firm: the noses of dogs entering veterinary operating theatres harbour a complex staphylococcal population in which drug resistance is the norm rather than the exception, and biofilm formation is universal. As antimicrobial resistance continues its global rise, this study adds companion animals to the growing list of reservoirs that surveillance programmes cannot afford to ignore, and it makes a data-driven case for looking up dogs’ noses before, not after, the scalpel comes out.

Subject of Research: Nasal colonization by antimicrobial-resistant and biofilm-producing Staphylococcus species in dogs undergoing surgery in Italy

Article Title: Nasal Colonization of Antimicrobial‐Resistant and Biofilm‐Producing Staphylococcus spp. in Surgical Canine Patients From Italy

Article References: Nocera, F. P., Schena, R., Romano, A., Cavalli, S., Cortese, L., Fatone, G., & Martino, L. D. (2026). Nasal Colonization of Antimicrobial‐Resistant and Biofilm‐Producing Staphylococcus spp. in Surgical Canine Patients From Italy. Veterinary Medicine and Science, 12(5), Article e71235. https://doi.org/10.1002/vms3.71235

Image Credits: AI Generated

DOI: 10.1002/vms3.71235

Keywords: Staphylococcus pseudintermedius, antimicrobial resistance, biofilm, dogs, nasal colonization, methicillin resistance, veterinary medicine, multidrug resistance, MALDI-TOF, surgical patients, One Health, Italy

MRSA is not an ordinary microbe. It is a Gram-positive bacterium that has evolved a molecular shield against the beta-lactam family of antibiotics, which includes methicillin, penicillin, and their chemical relatives. The shield comes from a gene called mecA, which encodes an altered penicillin-binding protein known as PBP2a. This modified protein has such a low affinity for beta-lactam drugs that the antibiotics simply cannot bind to it and disrupt cell-wall construction, rendering the entire drug class useless against the invader. The consequence is that infections which once yielded to cheap, widely available medicines now demand second-line or more powerful agents, driving up treatment costs, prolonging hospital stays, and increasing mortality. According to the 2019 Global Burden of Disease study, MRSA alone accounted for approximately 3.5 million disability-adjusted life years and more than 100,000 deaths worldwide, placing it among the leading causes of antimicrobial-resistance-related mortality.

The nasopharynx, the moist passage connecting the back of the nose to the throat, serves as the primary reservoir for this bacterium. People who carry MRSA there typically feel perfectly healthy, yet they shed the organism through direct contact, contaminated surfaces, and crowded living or working environments. In healthcare facilities, colonized patients and staff can seed outbreaks that are difficult to contain. In the wider community, persistent colonization raises the risk that the bacterium will eventually breach the skin or mucosal barriers and cause invasive disease, including pneumonia, sepsis, endocarditis, and severe skin and soft tissue infections. The elderly, young children, and immunocompromised individuals face the greatest danger of this progression from harmless carriage to life-threatening infection.

Despite this well-documented threat, the Ethiopian evidence base has long been fragmented. Individual studies reported carriage rates that varied wildly, from under 2 percent to more than 37 percent, and earlier regional syntheses failed to capture all available Ethiopian data. Previous meta-analyses also focused on antibiotics such as linezolid, ceftaroline, and vancomycin that are rarely available or routinely used in Ethiopian hospitals and pharmacies, making their resistance profiles of limited practical value for local clinicians. The new analysis set out to close these gaps by pooling every eligible Ethiopian study published between 2015 and 2025, focusing specifically on antibiotics that Ethiopian prescribers actually reach for, and identifying the factors that put certain people at higher risk of carrying the resistant strain.

The research team followed rigorous systematic review methodology, searching five major bibliographic databases and reporting according to PRISMA guidelines, with the protocol prospectively registered in PROSPERO. From an initial pool of 1,040 records, the investigators whittled the field down through duplicate removal, title and abstract screening, and full-text assessment to twenty qualifying studies. Each study was appraised with the Joanna Briggs Institute critical appraisal tool for prevalence research, and all included studies demonstrated moderate to good methodological quality. Every study identified MRSA using the cefoxitin disc diffusion test, a standardized laboratory technique in which a 30-microgram antibiotic disc is placed on agar inoculated with the bacterium; isolates showing an inhibition zone of 21 millimeters or less were classified as methicillin-resistant.

The headline finding was a pooled nasopharyngeal carriage rate of 7.3 percent, with a 95 percent confidence interval of 5.0 to 10.8 percent. Behind that average, however, lay enormous variability. The heterogeneity statistic, which measures how much of the observed variation among studies is due to real differences rather than chance, reached 95.5 percent, indicating that the studies differed profoundly in their populations, settings, and methods. Subgroup analysis revealed striking contrasts: carriage was highest among people living with HIV at 13.8 percent, followed by inpatients at 12.7 percent, while school children showed the lowest rate at 3.1 percent. Meta-regression confirmed that study population was the single most influential moderator, explaining 58 percent of the between-study variability, with HIV-positive individuals showing significantly elevated carriage compared with college students after adjustment.

The resistance profile of the 3,760 MRSA isolates tested across the included studies tells an equally sobering story. Tetracycline resistance topped the list at roughly 56 percent, followed by trimethoprim-sulfamethoxazole at nearly 50 percent and erythromycin at 44 percent. These are precisely the inexpensive, broad-spectrum antibiotics that dominate prescribing in Ethiopia and are freely available in informal drug outlets, a pattern that creates relentless selective pressure favoring resistant strains. Tetracycline is also used extensively in livestock production, adding an agricultural dimension to the resistance problem. By contrast, clindamycin showed the lowest pooled resistance at about 13 percent, likely reflecting its limited availability and correspondingly lower selection pressure. The authors note that these findings align with reports from other East African settings, including Kenya, where reduced susceptibility of MRSA to commonly used antibiotics has also been documented.

Perhaps most actionable are the risk factors the analysis identified. People with a history of hospitalization had more than fourfold higher odds of carrying MRSA in their nasopharynx, with a pooled odds ratio of 4.48, while those with previous antibiotic exposure had roughly 2.4-fold higher odds. These associations, consistent with meta-analytic evidence from the United States and China, point to a clear target population: anyone with recent healthcare contact or recent antibiotic use. Wounds, respiratory infections, skin lesions, and male sex, by contrast, did not reach statistical significance in the pooled analysis. The implication for public health strategy is straightforward. Screening and decolonization efforts, tightened hygiene practices, and rational antibiotic prescribing should concentrate on patients moving through hospitals and clinics, where the bacterium finds its most fertile transmission ground.

The study is not without caveats, and the authors are candid about them. Publication bias was detected through Egger’s and Begg’s statistical tests, and a trim-and-fill analysis that imputed nine missing studies raised the adjusted prevalence estimate to 14.77 percent, suggesting the true burden may be substantially higher than the headline figure. The geographic coverage of included studies was limited to a few regions, mainly Amhara, Oromia, Tigray, and the Southern Nations, Nationalities, and Peoples’ Region, which may limit national representativeness. Inconsistent definitions of risk factors across studies complicated the pooling of certain determinants, and resistance estimates for some antibiotics rested on few studies, yielding wide confidence intervals. A meta-regression across the 2015 to 2025 period found no significant temporal trend, meaning prevalence has remained stubbornly stable rather than improving.

What emerges from this analysis is a call to action grounded in context-specific evidence. The authors argue for strengthened antimicrobial stewardship programs, national surveillance systems, and targeted infection prevention and control measures aimed at high-risk groups, particularly hospitalized patients, people living with HIV, and those with recent antibiotic exposure. They also recommend that future Ethiopian studies incorporate molecular characterization of MRSA strains, including SCCmec and spa typing and detection of virulence factors such as Panton-Valentine leukocidin, to illuminate how local strains relate to global epidemic clones. For a country where second-line antibiotics remain scarce and expensive, preventing colonization in the first place is far more economical than treating resistant infections after they take hold. The quiet bacteria dwelling in Ethiopian noses may be invisible, but this research makes their scale, and the urgency of confronting them, impossible to ignore.

Subject of Research: Nasopharyngeal carriage, antimicrobial resistance patterns, and risk factors of methicillin-resistant Staphylococcus aureus in Ethiopia

Article Title: Nasopharyngeal Carriage Rate, Risk Factors, and Co‐Resistance Patterns of Methicillin‐Resistant Staphylococcus aureus in Ethiopia: Systematic Review and Meta‐Analysis

Article References: Endalamew, S. G., Kebede, S. A., Assefa, S. K., Zegeye, A. T., Abate, B. J., Asgedom, D. K., Taye, E. A., Andargie, E. M., Alemu, E. A., Kebede, H. A., Wassie, A. T., Assefa, A. Y., Ambaw, Y. G., & Alemaw, H. B. (2026). Nasopharyngeal Carriage Rate, Risk Factors, and Co‐Resistance Patterns of Methicillin‐Resistant Staphylococcus aureus in Ethiopia: Systematic Review and Meta‐Analysis. MicrobiologyOpen, 15(5), Article e70409. https://doi.org/10.1002/mbo3.70409

Image Credits: AI Generated

DOI: 10.1002/mbo3.70409

Keywords: MRSA, Ethiopia, antimicrobial resistance, nasopharyngeal carriage, systematic review, meta-analysis, Staphylococcus aureus, hospitalization, antibiotic use, tetracycline resistance, public health, infection control