1. Introduction
In clinical cases in dogs, diseases related to the skin are very important. In general, the normal skin of dogs has a variety of defense mechanisms against foreign pathogens at the outermost periphery of the entire body. In addition to physical and chemical barriers, the regular microbial flora on the skin surface is also an important protective layer for the maintenance of healthy skin. The microbial flora with a wide diversity can maintain the balance of the entire microenvironment. They can actively secrete certain substances with antibiotic properties to inhibit the proliferation of foreign microorganisms or perform a scavenging effect [
1,
2]. However, even with multiple layers of protection, if the dog has a primary or secondary bacterial infection caused by local wounds, skin parasitic infection, or sebum leakage, it will cause a variety of skin lesions. In bacterial infections of the skin, superficial pyoderma is the most common disease in dogs [
3].
Superficial pyoderma in dogs refers to bacterial infections involving the dog’s epidermis and epithelium at the hair follicles and can be further subdivided according to the site of bacterial infection. For example, bacterial infections that occur in the hair follicles are called superficial bacterial folliculitis (SBF), while bacterial infections that occur around the mouth or on the lips are called mucocutaneous pyoderma [
3]. In dogs, SBF is more common than in other mammalian species and is usually caused by
S. pseudintermedius [
4]. Routine treatment with systemic antimicrobial agents has increased the multi-resistant bacteria, particularly methicillin-resistant
S. pseudintermedius (MRSP). In staphylococci, resistance to beta-lactam antibiotics, such as methicillin, occurs due to the acquisition of a mobile gene segment called the Staphylococcal cassette chromosome mec (SCCmec) [
5]. In SCCmec, the
mecA gene enables bacteria to produce a “penicillin-binding protein 2a” (PBP2a) that is different from the normal penicillin-binding protein, making bacteria resistant to methicillin. The increasing frequency of multidrug resistance of MRSP complicates the selection of antimicrobial therapy in veterinary medicine.
In addition to the skin of dogs,
S. pseudintermedius can also be isolated from other organs or systems. However, it can hardly be isolated from healthy humans.
S. pseudintermedius isolates from humans have been found to be associated with frequent contact between their own dogs, so this species has been regarded as an important zoonotic pathogen in recent years [
6,
7,
8]. In addition to the direct transmission of
S. pseudintermedius to dog owners, the drug-resistant gene fragments carried by the strain also have the opportunity to exchange with other staphylococci in humans [
7,
8]. The risk of horizontal gene transfer from the dog to owner strain may induce more multi-drug-resistant bacteria in the future, eventually making it difficult for humans to treat bacterial infections.
As mentioned above, there were fewer studies focusing on risk factors analysis of Staphylococcus species isolated from dogs with superficial pyoderma and their owners. Therefore, this study collected samples from dogs with superficial pyoderma and their owners at the Veterinary Medical Teaching Hospital, Department of Veterinary Medicine, National Chung-Hsing University from 2017 to 2018. In addition to the isolation of canine pathogens, the drug resistance profiles of S. pseudintermedius isolates, the detection of drug resistance genes mecA and blaZ, and the risk factors for MRSP infection in dogs were also investigated. The detection rate of S. pseudintermedius will be confirmed in the owner’s samples, and the questionnaire results will be combined to explore the possible risk factors for their owners. Finally, dru gene type of the isolated MRSP will also be classified in order to understand the type of strains in Taiwan currently and compare the differences with foreign countries.
4. Discussion
Superficial pyoderma is a superficial infection by bacteria, such as
S. pseudintermedius,
S. schleiferi,
Escherichia coli, and species of the genera
Pseudomonas and
Proteus.
S. pseudintermedius is a species that has only been identified in the past ten years, and it was often identified as another species of
Staphylococcus due to insufficient development of classification technology [
15,
16].
S. pseudintermedius is a member of the
S. intermedius group, which also includes
S. intermedius and
S. delphini. The species in this group have similar biochemical properties and high 16s rDNA sequence similarity [
17]. According to the evolution of molecular biology, there are various tools that can assist in the identification of
S. pseudintermedius species and even further classify them according to their genotypes [
18,
19]. The results of genotyping can be used in epidemiological surveillance and improve the medical care of dogs and their owners.
Previous studies showed that Staphylococcus was the main species isolated from dog skins and most of them can be identified as
S. pseudintermedius [
20,
21]. A one-year study in Australia found that 70.8% of the bacteria isolated from companion animals were
S. pseudintermedius [
21]. Another study in South America from 2007 to 2012 found that staphylococci were isolated in 26.5% of samples from various body parts of dogs, and 71.7% were identified as
S. pseudintermedius [
20]. According to the results of this study,
S. pseudintermedius had the highest rate (72.3%) in dogs with superficial pyoderma, indicating that
S. pseudintermedius plays an important role in the skin infection of dogs.
Among staphylococci, the most frequently isolated species from human nasal mucosa have been reported to be
S. epidermidis and
S. aureus, but the composition ratio varies from person to person [
22]. In this study, only 4.4% of the isolates in the owner’s survey were identified as
S. pseudintermedius. Compared with previous reports, the rate of
S. pseudintermedius isolated from the nasal cavity of ordinary humans is much higher, probably because the humans in this survey are all dog owners. Many studies have also shown that dog owners have a higher chance of severing SIG or
S. pseudintermedius, indicating the risk factors of pathogens transfer from pets to owners [
23,
24].
In this study,
S. pseudintermedius was significantly more resistant to doxycycline and gentamicin than the rest of the isolated staphylococci among the tested antibiotics. These two antibiotics, doxycycline and gentamicin, are not the first-line treatment for dogs with superficial pyoderma in most veterinary hospitals in Taiwan. Our results may reflect two facts: First, relative to other staphylococci, in facing the treatment of
S. pseudintermedius, there is a more frequent treatment with non-first-line drugs. Second,
S. pseudintermedius is a pathogen that is often isolated from canine infections (whether skin or other organs and systems) [
25]. Therefore,
S. pseudintermedius exposure to more diverse antibiotics is predictable. The bacteria have more opportunities to screen out individuals with resistance to multiple antibiotics and cause clinical treatment challenges finally.
According to the results, a total of 47 strains of
S. pseudintermedius were isolated from the skin lesions of dogs, among which 16 strains carried the
mecA gene. The proportion of
mecA-positive
S. pseudintermedius resistant to the 10 antibiotics tested in this survey was significantly higher than that of
mecA-negative strains. Interestingly, the 16
mecA-positive strains were all multi-drug resistant strains, indicating the presence of
mecA was significantly correlated with multi-resistant characteristics of
S. pseudintermedius.
S. pseudintermedius with the mecA gene can be identified as MRSP because of its resistance to β-lactam antibiotics, such as methicillin. Although different SCCmec species have been reported to have different degrees of multi-drug resistance, most research studies agree that MRSP is related to strains with multi-drug resistance, which is consistent with the findings of this study [
26,
27,
28].
In the results of the blaZ gene analysis, most strains of S. pseudintermedius were blaZ positive and resistant to gentamicin, clindamycin, ampicillin, doxycycline, penicillin G and enrofloxacin. Interestingly, the blaZ-negative strains were all susceptible to the antibiotics tested in this study. The possible reason for this phenomenon is blaZ-negative S. pseudintermedius is more sensitive to commonly used first-line penicillin antibiotics than blaZ-positive strains, so it has less chance to encounter other antibiotics and the chance of developing resistance to multiple antibiotics is also reduced.
Questionnaires were also conducted for two items of interest in this survey, namely “Owner works in medical institution” and “Dogs treated with antibiotics within a month”. Originally, speculation had been raised that the owner’s job attributes were prone to encountering severe drug-resistant staphylococci, the interaction between the owner and the dog may lead to the spread of strains, and even further exchange of gene fragments that make bacteria resistant to drugs. However, the results indicated that there was no statistical support for such speculation. A previous study on risk factors for
S. aureus isolates in dogs and owners showed that colonization of dogs was not associated with close human contact but was strongly associated with health-care occupations [
29]. Under the condition that the transmission of strains does exist, the drug resistance gene of Staphylococcus in the owner is likely to be transmitted to the Staphylococcus in dogs. Although this survey has not obtained the predicted results, it may be possible to increase the number of samples and exclude possible interference factors in the future. Moreover, a number of studies indicated that in the dogs who received antibiotic treatment shortly before sampling, the isolation rate of MRSP was significantly increased [
30,
31,
32]. These findings are consistent in this survey and may represent that MRSP has a better survival advantage than MSSP when
S. pseudintermedius in dogs is under pressure caused by antibiotics, so the possibility of being isolated in dogs is also relatively increased.
Although the probability of
S. pseudintermedius in dogs being transmitted to humans and causing a direct infection is not high,
S. pseudintermedius is likely to exchange drug-resistant gene segments with other staphylococci after transmission to humans [
23,
33,
34]. This survey combined questionnaires to clarify whether certain risk factors were associated with the isolation of
S. pseudintermedius in owners. From the statistical results, it can be seen that “Keeping three or more dogs” and “Dogs can lick the owner’s face” have high odds ratios of 3.503 and 5.712, respectively. A similar study on the statistical analysis of “Keeping three or more dogs” found that it was significantly related to the isolation of
S. pseudintermedius from the owner [
24]. In addition, the high odds ratio of the factor “dogs could lick the owner’s face” suggested that the act of licking the owner’s face may increase the chance of severing
S. pseudintermedius in the owner. Several studies have shown that MRSP can also be isolated from other healthy dogs and cats living with MRSP-infected dogs and cats [
35,
36]. Therefore, if the number of dogs raised is greater, the sources of
S. pseudintermedius transmission may increase for owners, and a higher probability of isolation of the strain from owners can be expected.
In this study,
dru typing was used to confirm the genetic diversity of the isolated MRSPs in Taiwan. It was found that three types of MRSPs were included in our isolated MRSPs, namely dt11a (47.06%), dt11y (29.41%) and dt10cp (23.53%). All strains of the three types were all multi-drug resistant, and there was no significant correlation between the type and the tested antibiotic resistance. Compared to other countries, it was found that the MRSP isolated in Canada was dominated by four types of dt11a, dt10h, dt9a and dt11af [
37]. A comprehensive survey of MRSP isolates in Canada and the United States found that dt11a and dt9a were predominant [
38]. Another report also found that dt11a and dt9a were dominant in MRSP collected in Europe and North America [
39]. In Asia, the MRSPs isolated from Korea are dt11a and dt11y, while in Thailand they are dt11a and dt11cj, respectively [
40,
41]. According to the above literature records and our results, dt11a is widely distributed and is the predominant type in the northern hemisphere. Although dt11y also has sporadic been isolated in Europe and the United States, it was identified in South Korea and Thailand in Asia with significantly higher rates of 28.5% and 10.26%. It is considered to be a more prevalent type in Asia. The
dru type dt10cp, which accounted for about a quarter of our results, was relatively undocumented. This type was first recorded in 2016 and only 7.69% of MRSPs were identified as dt10cp from Thailand [
40,
41].
This research involves several aspects, from the isolation and identification of skin pathogens from dogs to the transmission of these zoonotic bacteria to owners, and scientific statistical analysis has also been carried out. Although S. pseudintermedius isolated from the owners might be transferred from their dogs, definite risk factors should be examined in the future study. Therefore, future research on the S. pseudintermedius isolated in Taiwan can use this paper as a stepping stone for more in-depth analysis.