Investigation on the Epidemiology and Pathogenesis Characteristics of Staphylococcus pseudintermedius-Associated Veterinary Hospital Infections ()
1. Introduction
Staphylococcus pseudintermedius is a coagulase-positive cocci belonging to the Staphylococcus intermedius group. S. pseudintermedius is a commensal bacterium encountered on the skin and mucous membranes of small animal patients, frequently seen on dogs and occasionally on cats [1] [2] . The bacterium is a component of the normal microbiota of dogs, being isolated colonizing the nose of 30%, the mouth of approximately 55% and the perineum-rectum in 52% of samples cultured from dogs [1] [3] [4] . Some additional epidemiologic works place the prevalence of colonization in dogs to 46.2% [5] . In fact, the number of infections caused by S. pseudintermedius in dogs and in cats has been increasing since the year 2000, likely connected to the ability of the organism to develop biofilms. Associated with the increase in number of infections is the observation that many of those S. pseudintermedius isolates are methicillin resistant [6] [7] [8] . In a large study in Europe by Menandro and colleagues, S. pseudintermedius was linked to 76% of the Staphylococcus infections diagnosed in dogs and cats, and 36% of those isolates were methicillin resistant [6] [8] .
Recently, the Veterinary Teaching Hospital at Oregon State University has seen an increase in the number of infections involving S. pseudintermedius, including methicillin-resistant S. pseudintermedius (MRSP) strains [9] . This observation agrees with other epidemiologic studies in the northern hemisphere [6] [8] . For example, a study by Nienhoff and colleagues in Germany found that 7.1% of the dogs admitted in the hospital were colonized with methicillin-resistant S. pseudintermedius [7] .
Antibiotic resistance is a major obstacle to the treatment of bacterial infections in veterinary medicine. It has been previously demonstrated that hospital environment often acts as a reservoir for bacteria, especially those that are adept at forming biofilms, like S. pseudintermedius [10] [11] .
The patients most at risk for developing an infection are those that have compromised immune systems, such as those that have recently undergone surgery, or are experiencing increased stress due to prolonged periods in the hospital. Prolonged stays in the hospital also enhance the chances that a staff member could transfer bacteria from a patient, or from a reservoir within the hospital.
This study was conducted in order to better understand the epidemiology of S. pseudintermedius in the hospital environment. The pathogen is known to form biofilm in the environment, as well as to have the tendency to establish biofilms in host tissues, as an common example, in bones [8] , which creates a very difficult challenge for the treatment with antibiotics [12] [13] [14] . For instance, work by Pompilio and colleagues demonstrated that S. pseudintermedius can establish biofilms in conditions with different pH, and develop resistance to treatment with several different antibiotics [14] . Although the knowledge about the pathogenesis of S. pseudintermedius is not extensive, some information is available about toxins, such as, beta-hemolysin, coagulase, DNAse, leukotoxin, exfoliative toxin, enterotoxin [1] [15] . In addition, not many studies have addressed the similarities and differences of biofilm formation between S. aureus and S. pseudintermedius.
Some of the questions we had, pertained to the hospital environment and the source of infection for the patients. Recent published study has characterized the different strains of S. pseudintermedius according to the function of a quorum sensing gene regulator, agr, which is also important for regulation of gene expression in S. aureus [16] . The investigators showed that among the 4 agr identified groups of S. pseudintermedius, the examination of biofilm formation, toxin gene carriage and antimicrobial resistance, did not show significant difference among the phenotypes.
Epidemiologic study in our hospital for the past several years has identified a significant increase of S. pseudintermedius infection, many of them associated with surgery. In a previous study conducted between 2012 and 2015 at the same facility, it was noticeable that the number of staphylococcus cases were clearly becoming more common, as well as the percent of methicillin-resistant S. pseudintermedius [9] [16] . Since the pathogen is a common colonizer of dogs, and may, like S. aureus, have the ability to survive in the environment of the hospital, this study was intended to identify the potential sources of infection, and to confirm some of the characteristics of the pathogen, which allow it to survive in different environments and infect hosts. The study showed that between 2016 and 2020 a large number of cases were diagnosed, that the pathogen can be isolated from surfaces in the hospital, and form biofilms.
2. Materials and Methods
Retrospective Study
All records involving bacterial culture submissions from the years 2016 to 2020 (5 years) were obtained, and the cases specific to S. pseudintermedius were examined. The categories analyzed included, bacterial species, antibiotic resistance/susceptibility, the site of the infection, locations visited in the hospital, sex, age, and treatment and outcome of the patient.
Bacteria
Three different isolates of S. psedintermedius (D1, DS1, DW), obtained from infections in dogs submitted to surgery or isolated from urine (they were part of the isolates tested for antibiotic susceptibility during the period reported in the study) were culture in Mueller-Hinton agar plates (VWR). Also, a strain of Staphylococcus aureus isolated from a dog,, was also cultured on Muller-Hinton agar plates. Prior to the assays, 48 hrs old colonies were suspended in Hanks Balanced Salt Solution (HBSS) and the solution was adjusted to approximately 3 x 108 CFU/mL using a McFarland standard as reported before [9] [17] . The final concentration of bacteria depended on the assay performed.
Environmental Bacteria Isolates
Bacterial swabs were obtained from the Oregon State University Veterinary Hospital (VTH). The samples were collected from ICU, from a computer keyboards, faucet handles, kennel handles, whiteboard markers, door handles and clipboards. The swabs from the anesthesia prep room were from faucet handles, disinfectant bottles, anesthesia machines, clippers, cabinet handles, microwave, anesthesia monitors, clipboards, calculator, light handles, kennel handles, Suntech vet 25 machine, and door handles. Sterile swabs were used to swab the desired surface, then the swab was placed in a sterile tube containing Luria-Bertani (LB) nutrient broth. A 0.1 mL direct sample from the broth was then plated onto LB agar and incubated for up to 72 hours at 37˚C. Cultures that showed growth were then streaked to isolate bacterial colonies. Isolated colonies were collected and added to microcentrifuge tubes filled with 200 µL of disruption beads and 1 mL sterile DI water. The tubes were then vortex agitated and placed in a homogenizer for 35 seconds. Then, the suspension were added to a microcentrifuge tubes on ice and spun down for 60 seconds at 18˚C on maximum speed. Without disturbing the beads or bacterial pellet, 450 µL of supernatant were transferred to a graduated microcentrifuge tube and refrigerated at 4˚C.
Sequencing
The DNA obtained from individual colonies were cleaned and concentrated using a DNA Clean and Concentrator −5 kit (Qiagen) prior to be submitted for sequencing. One hundred fifty µL of bacterial isolate of DNA were combined with 300 µL of DNA binding buffer in a column, then centrifuged at 11,000× g for 30 seconds. The filtrate was then discarded and 200 µL of DNA Wash Buffer was added to the column and then the tube was submitted to centrifugation. This last step was then repeated. The DNA was then eluted by adding 30 µL of sterile molecular water to the column. The column was allowed to stand for 1 minute, and then centrifuged. A Tecan instrument (280/260 wavelengths) was then used to calculate the concentration of the DNA that was been eluted. The purified DNA (concentration was then amplified using a Master Mix for 16 s PCR as reported [9] . This was carried out by combining 5 µL of Mastermix (Bio-Rad), 0.1 µL each of Forward and Reverse Primers (16S V4 region forward primer: GTG YCA GCM GCC GCG GTA A; Reverse: GGA CTA CNV GGG TWT CTA AT obtained from Invitrogen) and 3.8 µL of sterile molecular water in each tube, along with 1 µL of the selected isolated DNA for each sample. The tubes were briefly vortex-agitated before being placed in the BioRad T100 thermocycler for amplification following the reactions conditions: 59˚C annealing temperature, 60 s extension time, and 39 total cycles. Amplified DNA was run on agarose gel (1% in EDTA) for electrophoresis to ensure the correct size of DNA was obtained. The 16s DNA was cut from the gel and put through a gel extraction kit to concentrate and clean the amplified DNA, then submitted to be sequenced at the Center for Quantitative Life Sciences [9] .
Resistance to Disinfectant
We chose six bacteria (representing each one of the morphologically different colonies) from those isolated from the environmental swabs (R. mucosa, B. megaterium, A. gandavensis, N. terrae, S. pseudintermedius and S. aureus) along with a strain of S. pseudintermedius 21.153.8 cultured from a bone screw from the VTH (isolated in 2018) and used them to create inoculant solutions. Approximately 3 × 108 bacteria in HBSS were added to 48-well plates, then allowed to be in a lab drawer for five days. After the period, the supernatant was removed and 1.0 mL Accel Ready to Use disinfectant solution or Accel Diluted disinfectant solution was added to two wells of each bacteria. For the Ready to Use disinfectant, at time points of 1, 2, and 5 minutes the disinfectant was removed and replaced with 1.0 mL HBSS. For the Dilute disinfectant, at time points of 5, 7, and 10 minutes the disinfectant was removed and replaced with 1.0mL HBSS. The wells were then agitated to dislodge the bacteria and 0.1 mL was plated directly on LB agar, then left to incubate overnight.
Minimal Inhibitory Concentration
Specimens for culture were collected from canine patients at the Lois Bates Acheson Veterinary Teaching Hospital (Oregon State University, Corvallis, Oregon) and submitted to the associated Oregon Veterinary Diagnostic Laboratory (OVDL).
The protocol used followed the CLSI guidelines. Routine culture set up included inoculation onto Tryptic soy agar (TSA) plates containing 5% sheep blood (Remel), MacConkey agar plates (Hardy Diagnostics), and Thioglycolate broth (Remel). Inoculated media was incubated for a minimum of 18 hours at 35˚C and 6% CO2.
Agar plates were observed for growth over a total of 48 hours of incubation. The Thioglycolate broth was sub-cultured onto TSA w/5% sheep blood and incubated if no growth was observed in the primary agar plates. Colonies were isolated and identified using established phenotypic methods and criteria using traditional biochemical tests as described previously [18] . Beginning in December of 2019, a Vitek MS MALDI-TOF (Biomerieux) was used for identification in conjunction with phenotypic methods.
When requested, antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method. Individual isolates standardized to 0.5 McFarland by the PromptTM inoculation system (BD BBL-Thermo Fisher) were plated onto Mueller Hinton agar (Remel) to achieve a bacterial lawn, and antimicrobial disks (BD-Remel or Hardy Diagnostics) were placed by hand or using a stamper (BD-Remel). The plates were then incubated for 16 to 24 hours, depending on the disks, at 35C ambient air. Disk diffusion zones were measured by the BIOMIC V3 Reader (Giles Scientific). Susceptibility categories were determined using the most current Clinical and Laboratory Standards Institute (CLSI) guidelines, and minimum inhibitory concentration (ug/mL) were reported when available.
Bacterial isolates identified as Staphylococcus pseudintermedius or Staphyloccocus aureus were screened for methicillin resistance via either a latex agglutination assay for penicillin-binding protein PBP2' encoded by the mecA gene (Oxoid-Thermo Fisher), or via Kirby-Bauer disk diffusion of oxacillin for S. pseudintermedius isolates and cefoxitin for S. aureus isolates. Per CLSI Vet08 4th edition: S. pseuintermedius isolates yielding ≤ 17 mm against oxacillin, and S. aureus isolates yielding ≤ 21 mm against cefoxitin disks were considered to be methicillin resistant.
The following antimicrobials were routinely tested: amikacin, amoxicillin-clavulanic acid, clindamycin, chloramphenicol, cefovecin, enrofloxacin, gentamicin, marbofloxacin, penicillin G, trimethoprim-sulfamethoxazole, tetracycline, and erythromycin. amoxicillin-clavulanic acid, cefovecin, and penicillin were reported as resistant for isolates determined to be methicillin resistant regardless of actual MIC. Methicillin resistant isolates were also susceptibility tested for: azithromycin, ceftaroline, nitrofurantoin, rifampin, streptomycin, vancomycin, and doxycycline. Vancomycin was not included on client reports. Chloramphenicol, clindamycin, and erythromycin was not reported for isolates recovered from urine specimens.
Biofilm
In order to test how resilient the bacteria were in different hospital environments, they were stimulated to grow biofilms by simulating five different conditions encountered in hospitals: LB broth, HBSS, sterile water, serum, and dry surface. Each bacteria, three strains of S. pseudintermedius and one strain of S. aureus for comparison, were submitted to all five conditions. This was accomplished by using two 48-well plates with two strains per plate. Three wells were filled with a 1.0 mL aliquot of each condition for every strain, with 0.1 mL of 3 × 105 CFU/mL or 1 × 108 CFU/mL suspension of bacteria in HBSS added to each well, dependent on the assay performed. In the case of the dry condition, 0.1 mL of 3 × 105 bacteria in HBSS was added to an empty well. The well plates were incubated in a drawer in the lab at room temperature, with CFU collected on days 1, 2, 7 and 9. To measure CFU, 0.1 mL of supernatant from each well except the dry surface was diluted 1:10 with HBSS and then plated onto an LB agar and incubated overnight. The dry surface wells were only measured on day 9, which was accomplished by adding 1.0 mL HBSS to the well, drawing up 0.1 mL of supernatant and diluting 1:10 with HBSS and then plating on LB agar. On day 9 the mass of biofilm formed in each well was then measured. The supernatant was removed from each well and the biofilm was washed with 0.2 mL sterile DI water. We then added 0.2 mL of 0.1% crystal violet to every well. After waiting 10 minutes the wells were washed twice with 0.2 mL sterile distilled water. Finally, 0.2 mL of 30% acetic acid was added to each well and left for 10 minutes at 24˚C. The supernatant was then transferred to a new 48-well plate and the absorbance was read at 550 nm with an Epoch spectrophotometer.
In order to establish a biofilm on a dry surface, as many times seen in hospital environments, we established a 1 × 108 suspension of S. aureus and similar suspensions of 2 different strains of S. pseudintermedius. We evaluated several variations of the inoculum and the most consistent was used. Then, 0.1 ml of each suspension was pipetted and inoculated into different wells of a 48-well tissue culture plates. Plates were then incubated in the dark for two weeks at room temperature. Then, biofilm mass and CFU were determined as described [9] [19] .
Scanning Electron Microscopy (SEM) preparations
Samples were prepared for scanning electron microscopy observation. Sterile coverslips were placed on 6-well tissue culture plates. We added 1 ml of a suspension of 3 × 105 bacteria (S. pseudintermedius or S. aureus) and 1 ml of LB broth, then incubated the plates in the dark at room temperature for 2 and 7 days. For the biofilms grown on a dry surface, 1 ml of the same suspension was added to each well and allowed to dry out for 7 days. By the timepoints, the supernatant was removed and the coverslips were fixed with 4% paraformaldehyde and 1% formaldehyde solution as described [20] .
Statistical Analysis
The experiments were performed independently 3 times and the GraphPadPRISM version 8.0 was used for analysis. The results are presented as mean +/− standard deviation from three biological experiments, unless otherwise indicated. The significance level was determined by using Student’s t-test or ANOVA. A p-value of <0.05 was considered statistically significant.
3. Results
Antibiotic Susceptibility
A total of 213 isolates of S. pseudintermedius were submitted from 2016-2020 from 159 animals. Two species were represented, with 153 dogs sampled and 6 cats sampled. An almost equal distribution between males and females (48% and
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CSF: Cerebrospinal fluid; BALT: Bronchoalveolar lavage.
Figure 1. Number of cases per infection site, from January 2016 to December 2020.
52%) was observed, with 71% of males castrated and 66% of females spayed. Among all of the cases examined, 40.9% were associated with a surgical site incision or hardware (screws, TPLO plates, stents), 25% were associated with a urine culture, 17.9% were associated with a non-surgical wound site, and 9% of isolates had an unidentified etiology. Of all the patients examined in this study, 75.2% had previously undergone a surgical procedure within the year. Out of 213 isolates, 45% were methicillin-resistant strains of S. pseudintermedius.
The susceptibility to a number of antibiotics was determined. As seen in Table 1, the percentage of resistance to commonly used antibiotics is shown, a total of 213 isolates from 159 animals. Among, 159 were dogs, 6 were cats. The distribution
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Table 1. Percentage of Antimicrobial resistance of S. pseudintermedius isolates from animal sources.
Abbreviations: Amp: ampicillin; Pen: Penicillin; Amox/cla: amoxicillin/clavulanic acid; TPM/sulfa: trimethoprim/sulfamethoxazole, Cefov: cefovecin; Cefpo: cefpodoxime; Ceph: cephalotin; Chlora: chloramphenicol; Clinda: clindamycin; Enro: enrofloxacin; Marbo: marbofloxacin; Oxa: oxacillin; Genta: gentamycin; Amik: amikacin, Trobra: tobramycin; Tetra: tetracycline; Azith: azithromycin; Ceftar: ceftaroline; Erytho: erythromycin; Rif: Rifampin. ND: Not Done; BALT: Bronchial alveolar lavage.
by sex was 48% males and 52% females. Out of the patients, 75.2% has undergone anesthesia within a year. Remarkably, 45% of the isolates were methicillin resistant (MRSP).
Environmental Samples
Of the six locations swabbed in the ICU, 5 bacterial isolates were sequenced (4 S. aureus and 1 Curtobacterium). Of the fifteen locations swabbed in the anesthesia prep room, 20 bacterial isolates were sequenced (5 S. aureus, 3 Micrococcus luteus, 2 each of A. gandavensis, Bacillus spp., Bacillus megaterium, and Bacillus pumilus and 1 each of Bacillus subtilis, Nocardiopsis terrae, Roseomonas mucosa, and a S. pseudintermedius). The isolated S. pseudintermedius was then submitted to the Microbiology diagnostic laboratory for antibiotic resistance and susceptibility testing.
Resistance to Disinfectant
According to the product description, Accel Ready to Use (RTU) solution (1:40 dilution) should be killing off all of the bacteria within 1 minute, and the Dilute solution within 5 minutes. Of the seven bacteria tested, both the Dilute and RTU disinfectants killed at least 99% of both S. pseudintermedius strains and one strain of S. aureus. The other strain of S. aureus proved resilient with only 45.7% killed at the 5 minute time point for RTU, and 24% killed at the 10
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Figure 2. Number and species of bacteria isolated by two hospital locations (critical care and pre-anesthesia areas).
minute time point for Diluted disinfectant. Similarly, N. terrae showed no appreciable decrease in numbers until the 5 minute RTU (79.8% killed) and 10 minute Dilute (33.6% killed) time points. Only 25.9% of A. gandavensis was killed off in RTU 1 minute wells, and 53.4% in the RTU 5 minute wells. In the Dilute wells, 41.9% and 67.5% were killed off in the 5 minute and 10 minute wells respectively.
The determination if a strain of S. pseudintermidius, obtained from the hospital environment, was resistant to antibiotics, we evaluated the antibiotic susceptibility. Table 2 shows that the strain was methicillin-resistant, but was susceptible to many other compounds.
Biofilm:
S. pseudintermedius is known to form biofilm in the environment, much like S. aureus. To determine whether S. pseudintermedius can establish biofilm, and if those biofilms in the condition used were more or less robust than biofilms established by S. aureus, we compared the bacteria abilities. As shown in Table 3, S. pseudintermidius strains were more efficient in biofilm formation then S. aureus, under the conditions used. Electron micrographs of the biofilms, appear
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Table 2. Susceptibility of Environmental obtained S. pseudintermedius to antibiotics.
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Table 3. Biofilm formation by two different strains of S. pseudintermedius and S. aureus on plastic surface. Biofilm was allowed to form for 4 days in broth, and then the biofilm mass was stained and quantified as described in methods. The results were generated in at least 3 different experiments. In other assays, bacteria were added to the plastic surface and were allowed to dry.
*p < 0.05 compared to the biomass of S. aureus biofilm.
to indicate that biofilm formed by S. pseudintermedius is not exactly similar to biofilm formed by S. aureus. In addition, biofilm were allowed to for in a dry surface, in order to verify the ability to for biofilms in hospital surfaces (Figure 3). As shown in Table 3, biofilm formed in presence of broth has a significant greater biomass than biofilm formed in a dry surface.
4. Discussion
S. pseudintermedius is a commensal bacterium routinely found in dogs, and can
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Figure 3. Scanning electron micrographs of S. pseudintemedius ((a) and (b)) and S. aureus ((c) and (d)) biofilms at 24 hours and 72 hours respectively. In (a), a high magnification of S. speudintermedius (S.p) attached to biofilm. In (b), one can observe many S.p and biofilm on a surface. In (c) and (d) show S. aureus biofilm and bacteria, which are amplified in the image (d). In (e), the image shows a biofilm of S. pseudintermedius in dry surface. The black arrows point to biofilm matrix
become an opportunistic pathogen, causing infections within a hospital setting [1] [4] [21] . In dogs, S. pseudintermedius is a common agent associated with canine pyoderma [1] [7] [21] [22] . In addition, the bacterium can be frequently isolated from wound and ear infections [7] [8] [9] . It is important to consider that S. pseudintermedius very likely evolved with the canine host, and therefore is well adapted to the conditions existing in the host [1] [2] .
Due to increased stress in patients and the high amount of hands-on work performed on the patients in the hospital, besides being exposed to a strange environment, hospitalized animals are increasingly susceptible to pathogens which colonize their own skin or survive in the hospital environment. For example, it has been reported that up to 74% of infections isolated from surgical sites can be attributed to Staphylococcus species [9] [14] [23] , from which the great majority of cases were associated with S. pseudintermidius [7] [11] .
The current study, looking at infections in a veterinarian hospital in the last 5 years, demonstrated that 34% of the reported S. pseudintermedius infections at the OSU VTH were associated with surgery incisions or metals introduced in the animal (TPLO plates, screws, stents etc.). In addition, 75.2% of patients that had cultured positive for S. pseudintermedius had undergone a previous anesthetic procedure (within one year), suggesting a possible correlation between invasive procedure, prior exposure to hospital environment and infection with the bacterium. Also, of interest, was the large number of urinary tract infections identified in this population of patients. S. pseudintermedius is known to colonize the perineum region, and that association might correlate with the infection, once the animal has developed some degree of immunosuppression [24] . One important characteristic of the pathogen is the resistance to many of the available antibiotics, inducing veterinarians to use recent and more potent medication to treat the infections. Past studies have reported an increased resistance of S. pseudintermedius to antibiotics [14] [24] , and as shown in Table 1, in this epidemiological surveillance, only amikacin, rifampin and ceftaroline were effective in vitro against 90% or more of the isolated strains. It is also of note that cephalotin, a first generation cephalosporin, commonly used for surgery prophylaxis, showed to be inactive against approximately 30% of the isolates from surgical infections. Finally, is paramount to realize that an antibiotic used in humans to treat MRSA, such as TMP/SMX, had very low percent of activity against strains of S. pseudintermidius [23] [25] .
Veterinary hospital related infections usually are a combination of host susceptibility and well adapted pathogens. We do not know much about the pathogenic aspects of S. pseudintermedius. Recent reports showed that the bacterium expresses two surface proteins, SpsD and SpsO which have being shown to participate in the adherence to dog’s keratinocytes by binding to host fibronectin [26] [27] . In addition, the ability to form biofilm has been reported to be greater than the ability of S. intermedius to establish biofilm [13] [23] . In fact, in our investigation it was clear that S pseudintermedius was significantly more efficient at forming biofilm the clinical isolate (from a dog) of S. aureus. The results indicated that the biofilms of S. pseudintermedius and S. aureus are also different, as the images of the scanning microscopy suggest. The findings also demonstrate that S. pseudintermedius can be very effective in forming biofilms in dry surfaces, which may explain how some of the infection can be associated with the physical environment. In addition, the observation also supports the isolation of S. pseudintermedius from the hospital sites. In fact, the bacterium was isolated from the pre-anesthesia room, although when tested regarding the susceptibility to the disinfectant used in the hospital, the isolates were shown to be killed. This observation raise a couple possibilities, lie the protocol is not been followed as expected or the disinfectant is not been applied to the surfaces as frequent as needed. Those aspects will require additional study.
Human cases of S. pseudintermedius infection have been reported [7] [28] , although colonization of dogs that share the home with humans, as far is now known, does not commonly leads to owner colonization or infection by S. pseudintermedius [13] [29] . Human cases are usually associated with skin infection or ear infection, and the fact that the organism is capable of colonizing the skin of humans, a potential source of hospital infection can be associated with human transmission. The observation that dogs may be colonized by different strains of S. pseudintermedius in different body sites, and that carriers of the bacterium can be an important source of infection, establishes another layer of complexity to the understanding of the epidemiology of the infection [30] . Certainly, the development of a rapid test, to aid the decision of which animals should receive preventive measures prior to the procedure, may be a necessary development. The observation that prophylactic use of measures in humans have led to a significant decrease in hospital infections by S. aureus [31] , may have similar application in dogs. The percent of S. pseudintermedius causing infections in the veterinary hospital has increased over the years, as the number of isolates that showed resistance to a large number of antibiotics [9] .
A limitation of this study is that only a few veterinary hospital-associated strains were investigated, although the pattern of the results was similar among the strains.
In summary, this study shows that clinical strains of S. pseudintermedius are well-suited to survive in the hospital environment, and be capable of infect hospital veterinary patients. In addition, the pattern of isolates’ susceptibility is clearly becoming a concern, with increased resistant to many antibiotics. Future studies addressing approaches to control the infection are warranted.
5. Conclusion
The epidemiologic study of infections caused by S. pseudintermedius in a veterinary hospital setting confirmed that the pathogen, a common colonizer of dog skin and mucosal areas, is also capable living on surfaces in the hospital. Over the years, this characteristic has been associated with increase of antibiotic resistance, and the ability to cause surgical infections in which host tissue biofilm occurs, that are very difficult to treat.
6. Simple Summary
The incidence of hospital infections caused by Staphylococcus pseuditermedius has increased significantly. The study investigated the infections caused by the bacterium for the last 5 years, and identified surgeries as the most common site of infection. Because S. pseudintermedius is a common bacterium encountered in skin and mucosal surfaces of dogs, we examined if the bacteria would be able to form robust biofilms in the environment of the hospital, as well as the most common hospital locations where it could be found. It was determined that in the last 5 years, there was an increased resistance of S. pseudintermedius isolates to antibiotics and that the bacterium can be cultured from surfaces in the hospital environment. The data suggests that the development of more efficacious approaches to prevent the infections is needed.
Participation
SM: performed assays, analyzed data, wrote the paper: JB: performed assays, analyzed data and wrote the paper, JJ: performed assays, wrote the paper, interpreted the data; SS: performed assays, interpreted the data; ALP: performed assays, wrote the paper, LEB: designed the study, performed assays, analyzed the data, wrote the paper.
Funding
The study was funded by the Summer research program of the Carlson College of Veterinary Medicine.
Institutional Review Board
Not required, since the study only uses clinical laboratory data.
NOTES
*The authors had equal contribution.
#Corresponding Author.