Discussions
S. pseudintermedius is a novel Staphylococcus specieidentified in the last decade (Devriese et al., 2005) and this organism
has been commonly associated with skin and soft tissue infections
(SSTIs) in pet dogs (Chuang et al., 2010; Savini et al., 2013; Stegmann
et al., 2010), but few raccoon dogs cases have been described. As an
important fur animal, raccoon dog is being widely raised in China and
its SSTIs and zoonotic diseases caused by the pathogens are of
particular concern (Wang et al., 2014; Xu et al., 2016; Wioletta and
Maria, 2018). In this study, about 47% (425/896) of raccoon dogs were
infected by S. pseudintermedius and 17.6% of them had sever
SSTIs and 4.2% of them were dead in 4 weeks. This is a new threaten to
raccoon dogs!
In this study, the clinical symptoms of the raccoon dogs were described
according to the characteristics of the disease at different stages and
the symptom including suppuration of skin or/and joints and severe
respiratory dysfunction was recommended to be used as one of important
basises of clinical diagnosis for S. pseudintermedius infection
in raccoon dogs. In addition, the pathological lesions in many organs of
the diseased raccoon dogs were also examined and described, which
greatly enriches the clinical data of the disease.
It is very difficult to determine the pathogens of the disease in
clinic, because SSTIs and respiratory dysfunction can be caused by many
pathogens, especially staphylococcus (Rashid and Kravitz, 2015). In the
past, this disease in pet dogs had been misdiagnosed as S.
intermedius and other bacteria infection (Sasaki et al., 2007; Bannoehr
et al., 2007; BőRjesson et al., 2015). The mass spectrometer detection
has been recommended as an effective method for diagnosing it (Silva et
al., 2015; Somayaji et al., 2016; Wang et al., 2017). According to the
results in this study, this method can indeed do that from all the
tissues samples, but it is noteworthy that there are 8 species of
bacteria identified from the pus tissue on the skin, and some of them
might severely interfere the correct judgment on the pathogens; whereas,
much less in the visceral organs such as lung and kidney. Therefore, it
is better to aseptically collect samples from deep tissues for detecting
the pathogens using mass spectrometry.
Usually, three species of S. intermedius group (SIG) including S.
pseudintermedius , S. intermedia and S. delphini can
effect the judgment for the pathogens of SSTIs (Fitzgerald, 2009). To
distinguish them, some biochemical reactions to some designated reagents
should be tested. According to the previous reports, S.
pseudintermedius is positive to maltose and trehalose, but negative to
mannitol; S. intermedia is positive to trehalose and mannitol,
but negative to maltose; S. delphini is positive to maltose and
mannitol, but negative to trehalose (Bannoehr and Guardabassi, 2012;
Sasaki et al., 2007; Devriese et al., 2005). The results of biochemical
reactions of the isolated pathogen in this study were exactly the same
as previously reported, so we deduced that the isolated pathogen should
be S. pseudintermedius. This can supply a reference for
distinguishing S. pseudintermedius infection without mass
spectrometer in veterinary clinics.
In some previous reports, S. pseudintermedius has been concerned
as a potential zoonotic pathogen (Stegmann et al., 2010; Somayaji et al.
2016b). To evaluate the pathogenicity of the isolated S.
pseudintermedius from raccoon dogs on other animals, the mice were
inoculated with 1.8×109 CFU of S.
pseudintermedius and most of them developed skin abscess, ulcer,
dyspnea, and sever pathological lesions in some important organs in 14
dpi, which were almost identical with those of the diseased raccoon
dogs. The results suggest that the isolated S. pseudintermediuscan not only cause sever lesions in raccoon dogs, but also in mice.
Although S. pseudintermediu has been previously reported as a
zoonotic pathogen, yet its pathogenicity on cross-species is rarely
evaluated. This study can supply some important data for that.
Some studies suggest that S. pseudintermedius can be divided into
methicillin-sensitive S. pseudintermedius (MSSP) and
methicillin-resistant S. pseudintermedius (MRSP) (Ruscher et al.,
2010; van Duijkeren et al., 2011). Methicillin resistance is mediated by
the mecA gene. The mecA gene is located in the mobile
genetic element SCCmec , which encodes the penicillin binding
protein (PBP) and has a low affinity for β-lactam antibiotics (Chambers
et al., 1997; Bannoehr and Guardabassi, 2012; Ane et al, 2012) When the
bacteria were confirmed to contain mecA gene by PCR method, it
showed that the bacteria were methicillin-resistant (Chambers, 1997). In
recent years, the incidence of MRSP has been increasing, which has
brought more and more challenges to clinical treatment against it
(Moodley et al., 2014; Mccarthy et al., 2015; Richards et al., 2018). In
this study, the resistant gene of mecA was amplified from the
isolated strain, which indicates that it is a MRSP strain, like previous
reported other strains.
Interestingly, how many antibiotics are sensitive or resistant to it?
The results of drug sensitivity test showed that the strain was highly
sensitive to 12 antibiotics and most of them were quinolones and
aminoglycosides, and a few of them were chloramphenicol, macrolides and
polypeptides, these indicate that the isolated strain has not develop
serious multi-drug resistance like the global epidemic MRSP strains,
although it belonged to MRSP. In addition, according to the results of
drug sensitivity test, the diseased raccoon dogs were treated with some
of sensitivity drugs such as quinolones and most of them completely
recovered in two weeks, this greatly helps the treatment of this disease
in clinical practice.