Diversity of Staphylococcus pseudintermedius in carriage sites and skin lesions of dogs with superficial bacterial folliculitis: potential implications for diagnostic testing and therapy

Occurrence and characterization of methicillin-resistant Staphylococcus spp. in diseased dogs in Brazil

Staphylococcus pseudintermedius is a major commensal bacterium of the skin and mucosae of dogs and an opportunistic agent responsible for several clinical infections, such as pyoderma, otitis, and surgical wound infections. The emergence of methicillin-resistant S. pseudintermedius (MRSP) has become a problem of great concern in veterinary and human medicine because it is multidrug resistant (MDR) and can also infect humans. This study aimed to identify the occurrence of Staphylococcus spp. in infected patients and investigate the antimicrobial resistance profiles and molecular structure of MRSP isolates. Samples were obtained from two different veterinary clinics; suggestive colonies were submitted to matrix-assisted laser desorption ionization-time of flight (MALDI-ToF) mass spectrometry and confirmed at the species level by polymerase chain reaction (PCR). Sequencing of the 16S rRNA and rpoB genes were used in selected samples that were not identified by MALDI-ToF and by the species-specific PCR. Antimicrobial susceptibility and PCR detection of mecA were performed. MRSP isolates were subjected to multilocus sequence typing. Of all the clinical staphylococci (n = 131), 98 (74.8%) were identified as S. pseudintermedius. Multidrug resistance (resistance to ≥3 classes of antimicrobials) was observed in 63.2% of S. pseudintermedius isolates, and 24.5% of S. pseudintermedius isolates were methicillin-resistant. Half of the MRSP isolates were isolated from surgical site infections. Among the ten sequence types (ST) identified, nine were novel. ST71 was the most prevalent and associated with resistance to fluoroquinolones. Prior antimicrobial therapy, hospitalization, and surgical site infections seemed to be risk factors for MRSP acquisition. The present study showed a high rate of MDR staphylococci in infected dogs. MRSP was isolated from different clinical conditions, mainly surgical site infections. Additionally, this is the first study to extensively investigate the population structure of MRSP in Brazil, which revealed the dispersion of CC71 and nine novel ST. These findings raise concerns for both animal and human health due to the zoonotic potential of this species and limited therapeutic options available for MRSP infections.

On Gram-Positive- and Gram-Negative-Bacteria-Associated Canine and Feline Skin Infections: A 4-Year Retrospective Study of the University Veterinary Microbiology Diagnostic Laboratory of Naples, Italy

Simple Summary

Pet animals’ bacterial skin infections represent the main reason for presentation in small animal practice and are generally secondary complications of other pathological conditions. Pyoderma and otitis externa are generally caused by Staphylococcus spp., and particularly Staphylococcus pseudintermedius is often isolated from dogs and cats suffering from skin disorders. However, also Gram-negative bacteria, such as Pseudomonas aeruginosa and Escherichia coli, can be responsible for both otitis externa and pyoderma. Since multi-drug-resistant bacterial strains have become a relevant threat in veterinary medicine, this study aimed to identify the bacteria most frequently associated with the most common clinical cases of skin infections in dogs and cats attending the University Veterinary Teaching Hospital of Naples in the period from January 2016 to December 2019. Moreover, their antibiotic resistance profiles were evaluated, highlighting an increasing spread of multi-drug-resistant strains. It is worth noting that this spread may also concern humans because of their close contact with pets. Thus, it not only is of veterinary significance but also has zoonotic importance, with pets acting as reservoirs for humans, especially pet owners and veterinarians.

Abstract

A 4-year retrospective study (2016–2019) of selected routine bacteriological examinations of the veterinary microbiology laboratory of the University Veterinary Teaching Hospital of Naples (Italy) was carried out. A total of 189 bacteriological samples were collected from 171 dogs and 18 cats suffering from skin infections. In dogs, the most common cutaneous infection was otitis externa, while pyoderma was found to be prevalent in cats. The number of recorded Gram-positive strains over the study period did not vary considerably from year to year and was always significantly higher (p-value = 0.0007) in comparison with Gram-negative bacterial isolations. In dogs, Staphylococcus pseudintermedius was the most common identified Gram-positive bacterium (65%), while Pseudomonas aeruginosa (36%) was the one among the isolated Gram-negative bacteria. In cats, coagulase-negative staphylococci were the most predominant isolated bacteria (47%). The phenotypic profiles of antibiotic resistance showed that most of the strains were resistant to amoxicillin–clavulanate, penicillin, clindamycin, and trimethoprim–sulfamethoxazole. Several multi-drug-resistant strains (35%) were detected in canine isolates. An updating of antibiotic resistance profiles of the main Gram-positive and Gram-negative bacteria principally associated with skin infections of pet animals is necessary to improve stewardship programs of veterinary hospitals and clinics.

Antibacterial and Antivirulence Activity of Manuka Honey against Genetically Diverse Staphylococcus pseudintermedius Strains

Staphylococcus pseudintermedius is an important member of the skin microbial community in animals and can cause opportunistic infections in both pets and their owners. The high incidence of antimicrobial resistance in S. pseudintermedius highlights that this opportunistic zoonotic pathogen can cause infections which require prolonged and intensive treatment to resolve. Manuka honey has proven efficacy against many bacterial pathogens and is an accepted topical treatment for infections in both veterinary and clinical practice, and so it is a particularly appropriate antimicrobial for use with zoonotic pathogens such as S. pseudintermedius. Here, we demonstrate that not only is manuka honey highly potent against novel multidrug-resistant S. pseudintermedius isolates, it also acts synergistically with clinically relevant antibiotics. In addition, manuka honey modulates S. pseudintermedius virulence activity, even at subinhibitory concentrations. In a clinical setting, these attributes may assist in controlling infection, allowing a more rapid resolution and reducing antibiotic use.

Staphylococcus pseudintermedius causes opportunistic infections in dogs. It also has significant zoonotic potential, with the emergence of multidrug resistance leading to difficulty treating both animal and human infections. Manuka honey has previously been reported to inhibit many bacterial pathogens, including methicillin-resistant Staphylococcus aureus, and is successfully utilized in both clinical and veterinary practice. Here, we evaluated the ability of manuka honey to inhibit strains of S. pseudintermedius grown alone and in combination with antibiotics, as well as its capacity to modulate virulence within multiple S. pseudintermedius isolates. All 18 of the genetically diverse S. pseudintermedius strains sequenced and tested were inhibited by ≤12% (wt/vol) medical-grade manuka honey, although tolerance to five clinically relevant antibiotics was observed. The susceptibility of the isolates to four of these antibiotics was significantly increased (P ≤ 0.05) when combined with sublethal concentrations of honey, although sensitivity to oxacillin was decreased. Virulence factor (DNase, protease, and hemolysin) activity was also significantly reduced (P ≤ 0.05) in over half of isolates when cultured with sublethal concentrations of honey (13, 9, and 10 isolates, respectively). These findings highlight the potential for manuka honey to be utilized against S. pseudintermedius infections.

IMPORTANCEStaphylococcus pseudintermedius is an important member of the skin microbial community in animals and can cause opportunistic infections in both pets and their owners. The high incidence of antimicrobial resistance in S. pseudintermedius highlights that this opportunistic zoonotic pathogen can cause infections which require prolonged and intensive treatment to resolve. Manuka honey has proven efficacy against many bacterial pathogens and is an accepted topical treatment for infections in both veterinary and clinical practice, and so it is a particularly appropriate antimicrobial for use with zoonotic pathogens such as S. pseudintermedius. Here, we demonstrate that not only is manuka honey highly potent against novel multidrug-resistant S. pseudintermedius isolates, it also acts synergistically with clinically relevant antibiotics. In addition, manuka honey modulates S. pseudintermedius virulence activity, even at subinhibitory concentrations. In a clinical setting, these attributes may assist in controlling infection, allowing a more rapid resolution and reducing antibiotic use.

Molecular Detection and Characterization of the mecA and nuc Genes From Staphylococcus Species (S. aureus, S. pseudintermedius, and S. schleiferi) Isolated From Dogs Suffering Superficial Pyoderma and Their Antimicrobial Resistance Profiles

Canine superficial pyoderma (CSP) is a bacterial infection secondary to several skin diseases of the dog. Staphylococcus pseudintermedius, which is a commensal bacterium of the dog's skin, is the leading agent found in dogs affected by CSP, which can progress to deep pyoderma. It is also of clinical significance because S. pseudintermedius strains carry antimicrobial resistance genes, mainly the mecA gene. In this descriptive longitudinal study, molecular characterization of bacterial isolates from dogs affected by CSP was performed in addition to phenotyping, antimicrobial profiling, and assessment of resistance carriage status. Fifty dogs (24 females and 26 males) attending the CES University Veterinary Teaching Hospital were included in the study. CSP was confirmed according to clinical signs and cytological examination. Swabs were taken from active skin lesions for bacterial culture, and phenotyping and antimicrobial resistance profiles were assessed using API-Staph phenotyping and the Kirby–Bauer method, respectively. We also performed molecular detection and characterization of the mecA and nuc encoding gene of coagulase-positive Staphylococci. The mecA gene frequency was established by qPCR amplification of a 131bp gene fragment. Data were evaluated by descriptive statistics. Erythema, peeling, pruritus, and alopecia were the predominant symptoms (72, 56, and 46%, respectively). We isolated bacteria compatible with Staphylococcus species from all samples tested. API phenotyping showed 83.1 to 97.8% compatibility with S. pseudintermedius. PCR-genotyping resulted in 15, 3, and 1 isolates positive for S. pseudintermedius, S. aureus, and S. schleiferi, respectively. Isolated strains showed high susceptibility to Imipenem, Ampicillin/Sulbactam, and Rifampicin (100, 94, and 92%, respectively). The highest resistance was against Vancomycin and Trimethoprim/Sulfamethoxazole (98 and 74%, respectively). S. pseudintermedius, S. aureus, and S. schleiferi isolates were cloned and shared 96% sequence homology. Finally, we found 62% carriage status of the mecA gene in isolates of CSP patients, although only 36% of the isolates were methicillin-resistant. Identification of three Staphylococcus species causing CSP, high-level resistance against conventional antimicrobials, and carriage of the mecA gene highlight the importance of performing molecular characterization of bacteria causing dermatological conditions in dogs.

In Vitro Efficacy of Essential Oils from Melaleuca Alternifolia and Rosmarinus Officinalis, Manuka Honey-based Gel, and Propolis as Antibacterial Agents Against Canine Staphylococcus Pseudintermedius Strains

Essential oils (EOs) and honeybee products (e.g., honey and propolis) are natural mixtures of different volatile compounds that are frequently used in traditional medicine and for pathogen eradication. The aim of this study was to evaluate the antibacterial properties of tea tree (Melaleuca alternifolia) EO (TTEO), Rosmarinus officinalis EO (ROEO), manuka-based gel, and propolis against 23 strains of Staphylococcus pseudintermedius (SP) isolated from canine pyoderma. Antimicrobial resistance screening was assessed using a panel of nine antimicrobial agents coupled with a PCR approach. An aromatogram was done for both EOs, using the disk diffusion method. The minimum inhibitory concentration (MIC) was determined for all the compounds. Among the 23 SP strains, 14 (60.9%) were multidrug-resistant (MDR), 11 strains (47.8%) were methicillin-resistant (MRSP), and 9 (39.1%) were non-MDR. The mean diameter of the inhibition zone for Melaleuca and Rosmarinus were 24.5 ± 8.8 mm and 15.2 ± 8.9 mm, respectively, resulting as statistically different (p = 0.0006). MIC values of TTEO and ROEO were similar (7.6 ± 3.2% and 8.9 ± 2.1%, respectively) and no statistical significances were found. Honeybee products showed lower MIC compared to those of EOs, 0.22 ± 0.1% for Manuka and 0.8 ± 0.5% for propolis. These findings reveal a significant antibacterial effect for all the tested products.