Decreased SMP30 Expression Is Related With EMT in the Kidneys of Two Siberian Tigers With CKD.

BACKGROUND/AIM: Chronic kidney disease (CKD) is one of the most common causes of mortality in wild non-domestic felidae. The molecular mechanism regulating renal fibrosis in nephropathy is not fully understood especially in the felidae. This study aimed to elucidate senescence marker protein 30 (SMP30) expression patterns and its relationship with epithelial-mesenchymal transition (EMT) by immunostaining in two necropsied Siberian tigers (Panthera tigris altaica) with CKD. MATERIALS AND METHODS: Two kidney samples from male Siberian tigers were fixed and tissue sections were stained for histopathological assay. RESULTS: In CKD, renal tubular epithelial cells lost their tubular structures surrounded by severe interstitial fibrosis and were detached from the basement membrane. These damaged cells resembled the morphology of mesenchymal cells and showed much lower SMP30 expression compared with intact tubular epithelial cells. These cells also expressed vimentin, which is specifically expressed by mesenchymal cells, and through double staining, it was observed that vimentin was expressed in the tubular epithelial cells where SMP30 was not expressed. In addition, double-positive expression of pan-cytokeratin (pan-CK) and vimentin was found in damaged epithelial cells with mesenchymal features. CONCLUSION: We demonstrated possible evidence to understand the role of SMP30 as a new pivotal factor and the possibility of decreased SMP30 as a potential indicator of EMT at the end stage of CKD.

In vitro effects of omeprazole in combination with antifungal compounds against Malassezia pachydermatis.

BACKGROUND: Fungal and yeast infections, including those caused by Malassezia spp., are becoming increasingly difficult to treat, likely due to the occurrence of drug resistance. OBJECTIVES: This study aimed to evaluate the antifungal effects of omeprazole (OME), a proton pump inhibitor, against antifungal-resistant Malassezia pachydermatis and to investigate the potential synergistic effects between OME and other antifungal compounds. METHODS: In total, 15 samples of M. pachydermatis isolated from the skin of dogs were tested. The susceptibility of M. pachydermatis to itraconazole, ketoconazole, miconazole, terbinafine and OME was assessed using a modified broth microdilution (BM) method. The in vitro efficacy of OME alone and in combination with other antifungal compounds was evaluated for all isolates using the BM chequerboard method. The data obtained were analysed using the fractional inhibitory concentration index (FICI). RESULTS: The minimum inhibitory concentration (MIC) values of antifungal compounds and OME against quality control strain (M. pachydermatis CBS1879) were lower than the MIC90 values of same drugs against clinically collected strains. There was no significant difference in MIC values between drugs alone and combination. According to the analysis by the FICI method, no interaction was observed with OME and antifungal compounds. CONCLUSIONS: Most M. pachydermatis strains were resistant to azole antifungal compounds. OME exerted antifungal effects against Malassezia spp. and even showed good effects on antifungal-resistant strains. No synergistic effects were observed between the antifungal compounds and OME.

Tick Populations and Molecular Analysis of Anaplasma Species in Ticks from the Republic of Korea.

The present study was performed to survey the dominant tick populations and molecularly determine the pathogenic agents of anaplasmosis in ticks from Gyeongsang, Republic of Korea. A total of 3825 questing ticks were collected by the flagging method from 12 sites near animal farms in Gyeongsang from March to October 2021. A molecular genomic study was performed with ticks stored in 70% ethanol to detect Anaplasma genes by the previously described method. The monthly incidence of ticks varied by developmental stages, i.e., nymphs, adults, and larvae, and each of their populations peaked in May, March, and October, respectively. The predominant tick species were Haemaphysalis longicornis, Haemaphysalis sp., Haemaphysalis flava, Ixodes nipponensis, and Amblyomma testudinarium in order. To determine the Anaplasma infection rate, collected ticks were pooled into 395 groups. The minimum infection rate (MIR) of Anaplasma was 0.7% (27 pools). That of A. phagocytophilum was highest (23 pools, MIR 0.6%), followed by A. phagocytophilum-like Anaplasma spp. clade B (2 pools, MIR 0.1%), A. bovis (1 pool, MIR 0.1%), and A. capra (1 pool, MIR 0.1%), respectively. In this study, five species of ticks, including unidentified Haemaphysalis species, were collected in 12 survey sites in Gyeongsang, but their prevalence was somewhat different according to the tick species and survey sites. Further, the incidence rate (6.8%) of 4 Anaplasma spp. was not as high in tick pools. However, the results of this study may offer a basis for future epidemiological research and risk assessment of tick-borne diseases.

The stability and in vitro antibacterial efficacy of enrofloxacin and gentamicin solutions against Staphylococcus pseudintermedius over 28 days.

BACKGROUND: Many clinicians prepare compounded otic solutions to treat otitis externa (OE). Research evaluating the stability and antimicrobial efficacy of these solutions is limited. HYPOTHESIS/OBJECTIVES: This study determined the chemical stability and in vitro bactericidal efficacy of compounded solutions of enrofloxacin and gentamicin during storage for 28 days. MATERIALS AND METHODS: Solutions of enrofloxacin (10 mg/mL, 1%) and gentamicin (3 mg/mL, 0.3%) were prepared with normal saline and 1 mg/mL dexamethasone. Solutions were stored at room temperature (25°C) for 0, 14 and 28 days. The chemical stability of the antibiotics and dexamethasone were determined using liquid chromatography tandem mass spectrometry in triplicate. Efficacy assessment was made with 10 isolates of Staphylococcus pseudintermedius obtained from dogs with OE. Serial 10-fold dilutions of the bacteria with the compounded solutions were prepared and the colony count results were converted into colony-forming units (cfus). The mean cfu/mL and cfu/mL reduction rates were compared between Day (D)0, D14 and D28. All of the antimicrobial testing solutions were performed in triplicate. RESULTS: Chromatography showed that both antibiotics and dexamethasone were stable for 28 days. No significant differences were observed in the antibiotic bactericidal efficacy of stored solutions at D0, D14 or D28. CONCLUSIONS AND CLINICAL RELEVANCE: Solutions of 1% enrofloxacin and 0.3% gentamicin in normal saline with 0.1% dexamethasone maintained chemical stability and bactericidal efficacy over 28 days. These solutions can be considered as alternatives to commercial preparations for treatment of canine OE when indicated.

Effect of Photodynamic Therapy with Chlorin e6 on Canine Tumors.

This work aims to prepare pure Chlorin e6 (Ce6) and establish Ce6-mediated photodynamic therapy (Ce6-PDT) as a better therapy option for canine tumors as well as mouse tumor models. Five dogs suffering from various cancers were treated with Ce6-PDT from one to several times. After receiving the Ce6 (2.5 mg/kg) for 3 h, tumors were illuminated superficially or interstitially with 660 nm light. Two dogs underwent Ce6-guided fluorescence imaging by photodynamic diagnosis (PDD). Cell proliferation and apoptosis were detected by the 4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and western blot assay, respectively. Ce6-PDT efficacy was also determined using melanoma and pancreatic cancer mouse models. Two veterinary patients with mammary carcinoma and histiocytic sarcoma had their tumors significantly diminished and showed improved health after receiving Ce6-PDT. Moreover, in the cases of canine tumors, the adjunctive use of Ce6-PDD revealed cancers that were not visible with white light viewing and provided a visual contrast from surrounding tissues. Also, in vivo, Ce6-PDT remarkably reduced melanoma and pancreatic tumors in the mouse model. These findings could pave the way for a better understanding of the underlying processes of Ce6-PDT, making it an effective and safe candidate for use in human and veterinary applications to abolish various cancers.

Heat Stress during Summer Attenuates Expression of the Hypothalamic Kisspeptin, an Upstream Regulator of the Hypothalamic-Pituitary-Gonadal Axis, in Domestic Sows.

The release of reproductive hormones in the hypothalamic-pituitary-gonadal (HPG) axis is regulated by its upstream regulator, kisspeptin, and influenced by external stresses, including heat stress. Since the effect of heat stress (summer infertility) on hypothalamic kisspeptin expression in domestic sows is not yet understood, the present study attempted to identify changes in kisspeptin expression in different seasons (summer and spring). The high atmospheric temperature in summer decreased the pregnancy rate and litter size and increased stress-related hormones as a chronic stressor to domestic sows. The hypothalamic kisspeptin expression in summer was decreased regardless of the estrus phase and negatively correlated with atmospheric temperature, indicating that high temperature decreased kisspeptin. When the activity of hypothalamic kisspeptin neurons in the follicular phase was assessed using c-Fos staining, a decreased number of kisspeptin neurons coexpressing c-Fos was observed in domestic sows in summer. Accordingly, lower expression of kisspeptin induced decreased levels of HPG axis-related reproductive hormones, such as gonadotropins and estrogen, and fewer large ovarian follicles. In conclusion, the present study demonstrated that reduced kisspeptin expression and its neuronal activity in the hypothalamus under heat stress in summer induced downregulation of the HPG axis and caused summer infertility in domestic sows.

Clinical features and management of snake bites in 70 dogs in Korea.

BACKGROUND: Snakebites remain a devastating and life-threatening environmental hazard. While the management of snakebites has been well described in humans, few clinical data and guidelines exist for dogs, especially in Korea. OBJECTIVES: This retrospective study evaluated the clinical features of 70 dogs with snakebite wounds in Korea. METHODS: The medical records of 72 dogs that presented to three animal hospitals from June 2008 to July 2021 were reviewed; among these, 70 dogs that met the inclusion criteria were enrolled. Their signalment, history, clinical signs, physical examination, blood analysis, treatment, and prognosis were also evaluated. RESULTS: Of 70 dog owners, 35 (50%) witnessed the bite, with a mean time between bite and hospital presentation of 9.7 ± 4.1 h in 58 dogs. Blood smears were evaluated in 45 dogs, of which 28 (62%) showed echinocytosis. Anemia and acute kidney injury were found in 21 (29%) and 2 dogs (3%), respectively. A total of 37 dogs (53%) were hospitalized, 5 (7%) of which died. CONCLUSIONS: The most significant finding was the high prevalence of echinocytosis. The data from this retrospective study could inform the management of dogs bitten by snakes in Korea.

PPIA, HPRT1, and YWHAZ are suitable reference genes for quantitative polymerase chain reaction assay of the hypothalamic-pituitary-gonadal axis in sows.

OBJECTIVE: The quantitative reverse transcription polymerase chain reaction (qPCR) is the most accurate and reliable technique for analysis of gene expression. Endogenous reference genes (RGs) have been used to normalize qPCR data, although their expression may vary in different tissues and experimental conditions. Verification of the stability of RGs in selected samples is a prerequisite for reliable results. Therefore, we attempted to identify the most stable RGs in the hypothalamic-pituitary-gonadal (HPG) axis in sows. METHODS: The cycle threshold values of nine commonly used RGs (18S, HPRT1, GAPDH, RPL4, PPIA, B2M, YWHAZ, ACTB, and SDHA) from HPG axis-related tissues in the domestic sows in the different stages of estrus cycle were analyzed using two RG-finding programs, geNorm and Normfinder, to rank the stability of the pool of RGs. In addition, the effect of the most and least stable RGs was examined by normalization of the target gene, gonadotropin-releasing hormone (GnRH), in the hypothalamus. RESULTS: PPIA, HPRT1, and YWHAZ were the most stable RGs in the HPG axis-related tissues in sows regardless of the stages of estrus cycle. In contrast, traditional RGs, including 18S and ACTB, were found to be the least stable under these experimental conditions. In particular, in the normalization of GnRH expression in the hypothalamus against several stable RGs, PPIA, HPRT1, and YWHAZ, could generate significant (p<0.05) elevation of GnRH in the preovulatory phase compared to the luteal phase, but the traditional RGs with the least stability (18S and ACTB) did not show a significant difference between groups. CONCLUSION: These results indicate the importance of verifying RG stability prior to commencing research and may contribute to experimental design in the field of animal reproductive physiology as reference data.

Canine Stem Cell Conditioned Media Accelerates Epithelial Migration in the Canine Tympanic Membrane.

Similar to skin, epithelia in the tympanic membrane (TM) regenerate and move toward the opening of the external ear canal, a process called epithelial migration (EM). EM is important for maintaining healthy ears because this process removes cerumen and debris. Therefore, increasing the rate of EM or TM regeneration could be very important for healthy ear maintenance and function. Stem cells or their conditioned media have been used in medical therapy in humans to increase the rate and efficacy of EM. The purpose of this study was to evaluate the ability of canine stem cell conditioned media to accelerate EM in canine TMs. Canine adipose tissue derived-mesenchymal stem cell conditioned media (cAD-MSCCM), and several cytokines related to keratinocyte growth or migration within the media were quantified using ELISA. Ink drops were placed on the TMs of four normal beagles. Then, cAD-MSCCM was applied weekly, a total of three times to the TMs of one ear, and nothing was applied to the other eye. The results showed a higher TM EM rate in the treatment group than in the control group (p < 0.05). No adverse events were recorded. These results suggest that the weekly application of cAD-MSCCM accelerates the TM EM rate.

A suspected case of a multiple autoimmune syndrome in a poodle dog.

A 9-year-old castrated male poodle dog was presented with icterus, anorexia, and lethargy. The dog was diagnosed with hypothyroidism 1 month before and was treated with levothyroxine. Severe anaemia with spherocytes, positive saline agglutination test, and hyperbilirubinemia indicated immune-mediated haemolytic anaemia (IMHA). Therefore, immunosuppressive therapy with prednisolone, mycophenolate mofetil, and danazol was started. Although the IMHA was well controlled, during tapering of prednisolone, acute multiple joint swelling and oedema suspected immune-mediated polyarthritis occurred twice. First, clinical symptoms improved as the dosage of prednisolone increased. However, the dog showed severe adverse effects to the steroid. Second time, we added leflunomide as another immunosuppressant, and clinical signs of arthritis disappeared. About 3 weeks later, despite the immunosuppressive therapy, skin lesions resembling an autoimmune dermatologic disorder spread throughout the body. Addition of cyclosporine resolved the skin lesions. This is a case report of a dog showing several sporadic clinical signs related to multiple autoimmune syndromes and their management using different immunosuppressant drugs.

Combination of immunosuppressive drugs and allogeneic stem cell treatment in a dog with suspected nephrotic syndrome.

The case study aims to describe the nephrotic syndrome (NS) in a castrated 3-year-old male Cocker Spaniel dog. The patient arrived at the hospital with a loss of appetite and weakness. Skin oedema with ascites was observed along with hypoalbuminaemia, hypoproteinaemia, hyperlipidaemia, hypercholesterolaemia, and proteinuria (urine protein to creatinine ratio = 22.4). Based on these findings, the patient was diagnosed with NS, although a renal biopsy was not conducted. Prednisolone (1 mg/kg, p.o. q12 h) and mycophenolate mofetil (10 mg/kg, p.o. q12 h) were prescribed as the immunosuppressive drugs, and previously cryopreserved allogeneic adipose tissue-derived mesenchymal stem cells (2 × 107 cells/kg) were injected intravenously. After several weeks of treatment, the patient recovered from NS. This is the first case report on immunosuppressive drugs and allogeneic mesenchymal stem cells being used to treat a dog with NS.

IFN-γ Licensing Does Not Enhance the Reduced Immunomodulatory Potential and Migratory Ability of Differentiation-Induced Porcine Bone Marrow-Derived Mesenchymal Stem Cells in an In Vitro Xenogeneic Application.

IFN-γ licensing to mesenchymal stem cells (MSCs) is applied to enhance the therapeutic potential of MSCs. However, although the features of MSCs are affected by several stimuli, little information is available on changes to the therapeutic potential of IFN-γ-licensed differentiated MSCs during xenogeneic applications. Therefore, the present study is aimed at clarifying the effects of adipogenic/osteogenic differentiation and IFN-γ licensing on the in vitro immunomodulatory and migratory properties of porcine bone marrow-derived MSCs in xenogeneic applications using human peripheral blood mononuclear cells (PBMCs). IFN-γ licensing in differentiated MSCs lowered lineage-specific gene expression but did not affect MSC-specific cell surface molecules. Although indoleamine 2,3 deoxygenase (IDO) activity and expression were increased after IFN-γ licensing in undifferentiated MSCs, they were reduced after differentiation. IFN-γ licensing to differentiated MSCs elevated the reduced IDO expression in differentiated MSCs; however, the increase was not sufficient to reach to the level achieved by undifferentiated MSCs. During a mixed lymphocyte reaction with quantification of TNF-α concentration, proliferation and activation of xenogeneic PBMCs were suppressed by undifferentiated MSCs but inhibited to a lesser extent by differentiated MSCs. IFN-γ licensing increasingly suppressed proliferation of PBMCs in undifferentiated MSCs but it was incapable of elevating the reduced immunosuppressive ability of differentiated MSCs. Migratory ability through a scratch assay and gene expression study was reduced in differentiated MSCs than their undifferentiated counterparts; IFN-γ licensing was unable to enhance the reduced migratory ability in differentiated MSCs. Similar results were found in a Transwell system with differentiated MSCs in the upper chamber toward xenogeneic PBMCs in the lower chamber, despite IFN-γ licensing increased the migratory ability of undifferentiated MSCs. Overall, IFN-γ licensing did not enhance the reduced immunomodulatory and migratory properties of differentiated MSCs in a xenogeneic application. This study provides a better understanding of the ways in which MSC therapy can be applied.

Antibiofilm activity of silver nanoparticles against biofilm forming Staphylococcus pseudintermedius isolated from dogs with otitis externa.

BACKGROUND: Silver nanoparticles (AgNPs) are known to possess antimicrobial properties. Although the antibiofilm activity of AgNPs has been demonstrated in humans, this activity has not yet been elucidated in veterinary medicine. OBJECTIVES: The purpose of this study was to evaluate the antibiofilm activity of silver nanoparticles against Staphylococcus pseudintermedius. METHODS: Ten isolates of S. pseudintermedius obtained from dogs with otitis externa were treated with AgNPs, and the antibiofilm activity was measured using a modified microtiter plate and Congo red agar (CRA) method and scanning electron microscopy. RESULTS: AgNPs displayed a significant dose-dependent antibiofilm activity and reduced biofilm formation at concentrations of 20 and 10 µg/ml (p < 0.05). S. pseudintermedius exposed to 20 µg/ml of AgNPs formed less bacterial slime compared to the controls on CRA plates. Scanning electron micrographs showed that the biofilm had few individually scattered cells along its surface when treated with AgNP concentrations of 20 and 10 µg/ml. Untreated surfaces showed an aggregated biofilm. CONCLUSIONS: Our results suggested that AgNP may be a valuable alternative antibiofilm agent for canine otitis externa.

Nuclear VEGFR-2 Expression of Hepatocytes Is Involved in Hepatocyte Proliferation and Liver Regeneration During Chronic Liver Injury.

BACKGROUND/AIM: The pathological role of vascular endothelial growth factor receptor 2 (VEGFR-2) in chronic liver injury and liver regeneration is not fully understood. This study analysed the role of VEGFR-2 in liver fibrosis and its regeneration process. MATERIALS AND METHODS: We administered intraperitoneally 50 mg/kg to 300 mg/kg thioacetamide (TAA) to 9-week-old male mice for 17 weeks. We measured levels of VEGFR-2 protein and identified the location of cells that specifically express VEGFR-2. RESULTS: VEGFR-2 is rarely expressed in normal hepatocytes. However, high VEGFR-2 expression in liver sinusoidal endothelial cells was noted in the TAA group. Conversely, the group that experienced regeneration from liver fibrosis showed significantly higher VEGFR-2 expression in the nucleus of hepatocytes compared to the other groups. CONCLUSION: VEGFR-2 plays a pivotal role in the nucleus of hepatocytes during liver regeneration and VEGFR-2 may be closely related to cell division. Therefore, VEGFR-2 may be a new therapeutic target for liver regeneration.

TATA box binding protein and ribosomal protein 4 are suitable reference genes for normalization during quantitative polymerase chain reaction study in bovine mesenchymal stem cells.

OBJECTIVE: Quantitative polymerase chain reaction (qPCR) has been extensively used in the field of mesenchymal stem cell (MSC) research to elucidate their characteristics and clinical potential by normalization of target genes against reference genes (RGs), which are believed to be stably expressed irrespective of various experimental conditions. However, the expression of RGs is also variable depending on the experimental conditions, which may lead to false or contradictory conclusions upon normalization. Due to the current lack of information for a clear list of stable RGs in bovine MSCs, we conducted this study to identify suitable RGs in bovine MSCs. METHODS: The cycle threshold values of ten traditionally used RGs (18S ribosomal RNA [18S], beta-2-microglobulin [B2M], H2A histone family, member Z [H2A], peptidylprolyl isomerase A [PPIA], ribosomal protein 4 [RPL4], succinate dehydrogenase complex, subunit A [SDHA], beta actin [ACTB], glyceraldehyde-3-phosphate dehydrogenase [GAPDH], TATA box binding protein [TBP], and hypoxanthine phosphoribosyltrasnfrase1 [HPRT1]) in bovine bone marrow-derived MSCs (bBMMSCs) were validated for their stabilities using three types of RG evaluation algorithms (geNorm, Normfinder, and Bestkeeper). The effect of validated RGs was then verified by normalization of lineage-specific genes (fatty acid binding protein 4 [FABP4] and osteonectin [ON]) expressions during differentiations of bBMMSCs or POU class 5 homeobox 1 (OCT4) expression between bBMMSCs and dermal skins. RESULTS: Based on the results obtained for the three most stable RGs from geNorm (TBP, RPL4, and H2A), Normfinder (TBP, RPL4, and SDHA), and Bestkeeper (TBP, RPL4, and SDHA), it was comprehensively determined that TBP and RPL4 were the most stable RGs in bBMMSCs. However, traditional RGs were suggested to be the least stable (18S) or moderately stable (GAPDH and ACTB) in bBMMSCs. Normalization of FABP4 or ON against TBP, RPL4, and 18S presented significant differences during differentiation of bBMMSCs. However, although significantly low expression of OCT4 was detected in dermal skins compared to that in bBMMSCs when TBP and RPL4 were used in normalization, normalization against 18S exhibited no significance. CONCLUSION: This study proposes that TBP and RPL4 were suitable as stable RGs for qPCR study in bovine MSCs.

The effect of an ex vivo boosted immune cell therapy on canine atopic dermatitis: an open, uncontrolled pilot study.

BACKGROUND: Canine atopic dermatitis (cAD) is associated with an imbalance between multiple T lymphocytes and cytokines. Ex vivo boosted immune cell (EBIC) therapy is the sequential administration of ex vivo cultured and activated lymphocytes to patients to improve immune function. OBJECTIVE: This pilot study aimed to assess the safety of EBIC therapy and demonstrate its efficacy as a novel treatment for cAD. ANIMALS: Ten dogs with AD. METHODS AND MATERIALS: The phenotypes of the immune cells before and after ex vivo culture were analysed by flow cytometry. EBICs (1.0-5.0 × 108 cells/animal) were administered to dogs every two weeks, with a total of six injections. The cAD extent and severity index (CADESI)-03 and pruritus scores were calculated to evaluate the efficacy of EBIC therapy for cAD. For safety assessment, regular blood examination was conducted, and any adverse events recorded. The serum levels of interleukin (IL)-4, IL-10, IL-31 and interferon-gamma (IFN-γ) were evaluated. RESULTS: The cells expanded by an average of 57.52-fold and the proportions of CD8+ cells and IFN-γ-producing cells significantly increased after ex vivo culture. Sequential EBIC therapy improved CADESI-03, and pruritus scores significantly. After stopping treatment the improvement rates increased for the CADESI score and were maintained for the pruritus score. There were no significant changes in cytokine levels. No significant adverse events were observed. CONCLUSIONS AND CLINICAL SIGNIFICANCE: EBIC therapy is a safe and efficient treatment for cAD. This therapy could correct the immunological imbalance in dogs with AD by infusing activated T lymphocytes.

In vitro bactericidal activity of 465-470 nm blue light phototherapy and aminolevulinic acid on Staphylococcus pseudintermedius.

BACKGROUND: Staphylococcus pseudintermedius is the principal pathogen causing bacterial skin infections in dogs. Photodynamic therapy (PDT) involving the combination of light and a topical photosensitizer is used to treat human skin infections. Although the antimicrobial effects of PDT have been demonstrated using in vivo and in vitro studies in humans, its effects on dogs and their pathogens are unclear. OBJECTIVES: The aim of this study was to demonstrate the in vitro efficacy of PDT over a 465-470 nm spectrum to kill S. pseudintermedius using δ-aminolevulinic acid (ALA) as the photosensitizer. METHODS: Six S. pseudintermedius isolates from canine skin were exposed to blue light-emitting diodes (LEDs) at 465-470 nm, with or without ALA. The light doses were 18.4, 36.8 and 55.2 J/cm2 . The number of colony-forming units and optical densities of broth cultures were measured and then compared with Dunnett's test. Bacterial viability was monitored using fluorescence microscopy and the fluorescence intensity values were compared with a paired Student's t-test. RESULTS: Blue light inhibited the growth of S. pseudintermedius; the effect significantly increased with the addition of ALA as a photosensitizer and with increasing light doses. Live/dead staining confirmed that PDT reduced bacterial viability and exerted an antibacterial effect. CONCLUSION AND CLINICAL IMPORTANCE: Blue light has a strong antibacterial effect on S. pseudintermedius in a light dose-dependent manner. ALA alone did not exhibit bactericidal action, but its combination with blue light increased the effect of PDT compared to blue light alone.