a domestic shorthair cat was evaluated for chronic , bilateral , ulcerative dermatitis affecting the inguinal region and lateral aspects of both pelvic limbs . histopathologic examination of skin biopsies collected throughout the course of disease revealed chronic pyogranulomatous ulcerative dermatitis . aerobic bacterial skin cultures yielded growth of a methicillin - resistant staphylococcus aureus and corynebacterium amycolatum . upon referral a deep skin biopsy was collected and submitted for mycobacterial culture . at 5 weeks of incubation mycobacterium thermoresistibile , m thermoresistibile has been isolated after 24 days of incubation , suggesting that this strain may have been a slower growing variant , or other factors ( such as prior antimicrobial therapy ) inhibited rapid growth of this isolate . the cat was hospitalized for intravenous antibiotic therapy , surgical debridement of wounds , vacuum - assisted wound closure therapy and reconstruction procedures . the wounds were ultimately primarily closed and the cat was discharged to the owner after 50 days of hospitalization . to our knowledge , only two cases of m thermoresistibile panniculitis have been reported in cats . in the only detailed report of feline m thermoresistibile panniculitis , treatment was not attempted . the second case only reported detection of m thermoresistibile by pcr without a clinical description of the case . in our case report , severe chronic skin infection with m thermoresistibile was addressed using prolonged specific antibiotic therapy , surgical debridement and reconstructions , and treatment of secondary bacterial infections . mycobacteria that infect and cause disease in cats include tuberculous mycobacteria ( mycobacterium bovis , mycobacterium microti and mycobacterium tuberculosis ) ; opportunistic , non - tuberculous mycobacteria ( ntm ) , which include slow - growing species such as mycobacterium avium and rapidly growing species such as mycobacterium fortuitum and mycobacterium smegmatis ; and lepromatous mycobacteria , which are fastidious or unculturable species that cause nodular pyogranulomatous inflammatory lesions ( feline leprosy syndrome ) . appear to be relatively common in australia and parts of the usa , while tuberculosis ( tb ; due to m bovis ) , feline leprosy syndrome and ntm are regularly diagnosed in new zealand and the uk ( m bovis and m microti ) . mycobacterial panniculitis refers to the clinical syndrome characterized by chronic infection of the subcutis and skin of cats by ntm . in cats rapidly growing mycobacteria are a heterogeneous group of organisms that produce visible colonies on synthetic media within 5 days when cultured at room temperature . they are distributed ubiquitously in nature , and can be isolated commonly from soil and bodies of water . commonly isolated bacteria in this group include m fortuitum , m smegmatis , mycobacterium chelonae and mycobacterium abscessus . mycobacterium thermoresistibile is an ntm that is rarely reported in human and animal infections . to our knowledge , only eight cases of human infection and three cases of feline infection have been reported in the literature . the three previously reported cases of m thermoresistibile infections in cats included two cats with skin infections , and one with pneumonia . that cat was euthanized immediately after diagnosis . the other case of m thermoresistibile feline panniculitis was reported as part of a case series , where identification of infecting mycobacteria was performed using pcr on archived cytology slides . the cat with m thermoresistibile pneumonia was treated empirically with multiagent antibiotic therapy that consisted of doxycycline , rifampicin and clarithromycin . that cat made a clinical recovery , despite the persistence of abnormal findings on thoracic radiographs , and antibiotics were discontinued after 1 year of treatment . in humans with ntm , currently , no published recommendations exist for the treatment of m thermoresistibile infections for feline patients . here we report a cat with severe mycobacterial panniculitis caused by m thermoresistibile and the approach to treatment of the infection . to our knowledge , this is the first report of this infection in companion animals in north america . a 6-year - old , male , neutered , domestic shorthair cat was first evaluated by a referring veterinarian in january 2015 for an ulcerated skin wound in the inguinal area that was suspected to be a fight wound . the ulcers waxed and waned in size and depth . in july 2015 , a swab specimen was obtained from the affected skin . treatment with clavulanic acid - amoxicillin ( 15 mg / kg po q12h for 2 weeks ) did not result in clinical improvement . the cat was referred to the dermatology service at the university of california - davis in august 2015 ( 7 months after original wound appearance ) . histopathologic examination of a punch skin biopsy from the inguinal region at that time revealed severe , chronic , ulcerative , multifocal - to - coalescing , pyogranulomatous , deep dermatitis and panniculitis . no infectious organisms were evident on sections stained by hematoxylin and eosin stain , brown and brenn gram stain , ziehl neelsen acid - fast stain , grocott - gomori s methenamine silver stain , periodic acid  schiff stain and giemsa stain . the cat was treated with marbofloxacin ( 4.6 mg / kg po q24h ) for suspected mycobacterial infection and oral amoxicillin ( 37 mg / kg po q12h ) for suspected secondary bacterial infection , pending the results of aerobic and anaerobic bacterial culture and susceptibility of a macerated skin biopsy specimen , fungal culture of the biopsy specimen and aerobic bacterial culture of a swab from a draining tract . subsequently , culture of the skin biopsy yielded growth of small numbers of a corynebacterium species , and culture of the draining tract yielded growth of corynebacterium amycolatum and a methicillin - resistant staphylococcus aureus ( mrsa ) . time of flight mass spectrometry and confirmed by 16s rrna gene pcr and sequencing of the 574-base pair product . the c amycolatum isolate was susceptible to gentamicin , amikacin , chloramphenicol , clindamycin , doxycycline , erythromycin and trimethoprim sulfamethoxazole ; had intermediate susceptibility to imipenem ; and was resistant to amoxicillin  clavulanic acid and cefazolin . the minimum inhibitory concentration for enrofloxacin and marbofloxacin was 0.25 g / ml ( no breakpoint available ) . the mrsa was susceptible to amikacin , chloramphenicol , clindamycin and trimethoprim sulfamethoxazole , and resistant to beta()-lactams , fluoroquinolones , erythromycin and rifampin . given these results and continued clinical suspicion for mycobacterial panniculitis , fluoroquinolone treatment ( marbofloxacin 4.6 mg / kg po q24h ) was recommended in combination with trimethoprim sulfamethoxazole ( 22 mg / kg po q12h , dose listed for combined components of sulfamethoxazole and trimethoprim at a ratio of 5:1 ) . an elizabethan collar was placed to prevent the cat from licking its wounds . the owner was not able to prevent the cat from removing the elizabethan collar or to administer consistently the antibiotics at home , and so the cat was brought to the internal medicine service for re - evaluation in october 2015 ( 9 months after original wound appearance and 2 months after the first evaluation by the dermatology service ) . at that time , the cat was admitted to the veterinary medical teaching hospital ( vmth ) for wound care due to progression of lesions . on physical examination , the cat was alert and responsive and in good body condition ( score 5/9 ) with normal vital signs . the cat was non - ambulatory and assessed to be painful in the pelvic limbs . within the inguinal region there were deep skin wounds that were 25 cm  15 cm . a large amount of purulent exudate discharged from the wounds . an ulcerated , 10 cm  5 cm lesion with exudate and crusts was present on the lateral aspect of the right thigh . a complete blood count showed mild normocytic normochromic anemia with a hematocrit of 26.3% ( reference interval [ ri ] 3050% ) . a serum chemistry panel showed mild hyperphosphatemia ( 7.1 mg / dl ; ri 3.26.3 mg / dl ) , mild hyperglycemia of 198 mg / dl ( ri 63118 mg / dl ) and a mildly increased creatine kinase concentration of 408 u / l ( ri 73260 u / l ) . the cat was negative for feline immunodeficiency virus antibodies and feline leukemia virus antigen ( snap ; idexx laboratories ) . aerobic bacterial blood cultures ( two samples of 3 ml each , collected from each jugular vein ) yielded no growth . the cat s wounds were cleaned and debrided under general anesthesia ( figures 1 and 2 ) . a vacuum - assisted wound closure device was used to treat the inguinal wounds , as previously described , to assist with healing and skin apposition ( figure 3 ) . the right lateral thigh wounds were debrided and treated with wet - to - dry bandaging . inguinal region at time of hospitalization ( october 2015 ) and prior to wound debridement right lateral thigh at time of hospitalization ( october 2015 ) and prior to wound debridement vacuum - assisted wound closure device applied after wound debridement ( october 2015 ) histopathologic examination of a punch biopsy ( 6 mm in diameter ) again revealed severe , chronic , multifocal , pyogranulomatous dermatitis and panniculitis and granulomatous lymphangitis ( figures 4 and 5 ) . neelsen acid - fast stain , giemsa , brown and brenn gram stain and grocott - gomori s methenamine silver stain . tissue pcr for a m tuberculosis  bovis complex ( mtbc ) organism was weakly positive after 40 cycles of pcr ( cycle threshold [ ct ] values 36.57 for mycobacterium species dna and 20.91 for the housekeeping gene , with values < 40 being positive ) . this assay detects the rpob gene of m bovis , mycobacterium caprae , m tuberculosis and m microti . nodular foci of granulomatous inflammation ( black arrows ) are scattered throughout the deep aspect of the dermis and the panniculus adiposus . some foci are more heavily populated by lymphocytes and plasma cells ( open arrows ) . a band of immature connective tissue ( arrowheads ) subtends the deep aspect of the dermis , and is presumably a response to the chronic inflammation . epithelioid macrophages ( arrows ) were the dominant inflammatory cell type in most affected regions . foci of necrotic tissue ( bracket ) with darkly stained eosinophilic cells , and cell debris were scattered throughout many regions of inflammation . scale bar = 40 m the skin biopsy specimens were also submitted to the vmth microbiology laboratory for aerobic and anaerobic bacterial cultures and a fungal culture . a skin biopsy specimen was also submitted for mycobacterial culture and ribosomal rna gene pcr for mtbc at advanced diagnostic laboratory services , national jewish health , denver , co. the mtbc pcr results were reported 3 days later as negative . pending the results of the tests listed above , the cat was treated with doxycycline monohydrate suspension ( 10 mg / kg q12h , followed by 5 ml water through the esophagostomy tube ) and vancomycin ( 15 mg / kg iv q8h ) . the doxycycline was selected based on our previous success with doxycycline at this dose to treat mycobacterial panniculitis . although a controversial choice , vancomycin was selected pending culture and susceptibility test results based on the history of isolation of mrsa and c amycolatum , the need for a parenteral antimicrobial drug , the severity of the lesions and concern for multidrug resistance in the light of the history of treatment with fluoroquinolones , -lactams and trimethoprim sulfamethoxazole . pain was managed with buprenorphine at 0.01 mg / kg intravenously every 46 h for the first 2 weeks of hospitalization and then via the sublingual route . within several days of starting therapy the cat developed anorexia , apparent nausea , lethargy and acute elevations in the activity of serum liver enzymes ( alanine aminotransferase 939 u / l [ ri 27101 1758 u / l ] , alkaline phosphatase 125 u / l [ ri 1471 u / l ] ) and an increase in serum bilirubin concentration ( 1.4 mg / dl [ ri 00.2 mg / dl ] ) . the skin cultures performed at the university of california - davis microbiology laboratory again yielded mrsa and c amycolatum . the mrsa was susceptible to gentamicin , amikacin , chloramphenicol , clindamycin , doxycycline , rifampin , trimethoprim sulfamethoxazole , daptomycin , vancomycin and linezolid but resistant to erythromycin and fluoroquinolones . the c amycolatum isolate was susceptible to chloramphenicol , doxycycline and vancomycin but resistant to aminoglycosides , -lactams , clindamycin , erythromycin , trimethoprim sulfamethoxazole , fluoroquinolones , linezolid and rifampin . treatment was therefore continued with parenteral vancomycin ( for its activity against both the mrsa and corynebacterium species isolates ) and pradofloxacin ( for presumed mycobacterial infection ) . the vacuum - assisted wound closure system remained in place , in the inguinal area , for the first 2 weeks of hospitalization with wound evaluation and bandage changes in both the inguinal area and the right lateral thigh every 23 days . thirty days after admission , the wounds were closed in a staged manner involving two separate surgeries spaced 2 weeks apart . after hospitalization for 50 days , vancomycin was discontinued and the cat was discharged on oral pradofloxacin . four weeks after skin biopsy submission for mycobacterial culture in liquid medium , growth of m thermoresistibile was identified by the reference laboratory . antimicrobial susceptibility test results of m thermoresistibile became available 7 weeks from submission and the organism was reported to be susceptible to all antimicrobials tested ( aminoglycosides , third - generation cephalosporins , imipenem , ciprofloxacin , moxifloxacin , doxycycline , clarithromycin , azithromycin , clavulanic acid  amoxicillin , trimethoprim sulfamethoxazole , clofazimine and linezolid ) . treatment with pradofloxacin was continued , but owing to the appearance of new wounds 3 weeks after discharge , clarithromycin ( 7 mg / kg po q12h ) and trimethoprim sulfamethoxazole ( 30 mg / kg po q12h ) were added to the antibiotic regimen . to overcome owner compliance concerns , dehiscence occurred at the surgical closure site in the inguinal region and was allowed to slowly heal by secondary intention ( figure 6 ) . sixteen months after original wound appearance and 7 months after hospitalization , the ulcerative skin lesions had healed completely and the cat had returned to normal activity . several small firm subcutaneous nodules remained palpable on both sides of the abdominal body wall which appeared to be slowly reducing in size and number . mycobacterial panniculitis in cats caused by non - tuberculous mycobacterial species has been well described in the literature . however , to the best of our knowledge , this is only the third report of mycobacterial panniculitis caused by m thermoresistibile in cats and the first report of attempted treatment of m thermoresistibile panniculitis . the extent and severity of disease in this cat likely reflected a combination of delayed diagnosis and problems with owner compliance . in human medicine it has been hypothesized that traumatic inoculation with m thermoresistibile present in soil results in local infection , which may also have been the case in this cat with outdoor exposure . mycobacterial infection was strongly suspected in this cat despite failure to isolate a mycobacterial species owing to clinical presentation and histopathology . the positive result on pcr for an mtbc organism in our laboratory was a concern because of the zoonotic potential of organisms belonging to this complex . however , the clinical presentation combined with the high ct value raised suspicion for a false - positive result , and upon discussion of the result with the laboratory , it was revealed that the primers used had the potential to amplify dna from mycobacterium species that do not belong to the mtbc . in previous reports , m thermoresistibile has been isolated after 24 days of incubation , suggesting that this strain may have been a slower - growing variant , or other factors ( such as prior antimicrobial therapy ) inhibited rapid growth of this isolate . m thermoresistibile was first isolated from soil and house dust in japan in 1966 . for many years m thermoresistibile was considered non - pathogenic , but in the past 20 years cases demonstrating its pathogenicity have been described in people and cats ; cases have been reported from asia , europe and north america . m thermoresistibile is also unusual in that it is thermotolerant , growing optimally at temperatures between 37c and 52c . in people , reports of infection with m thermoresistibile have been associated with postsurgical infection ( in a few of those implants were involved ) in skin and lungs . the majority of infected patients are immunocompromised , as is often true in other ntm infections in humans . this , to our knowledge , is the first report of infection by m thermoresistibile in a cat in north america . it is possible that the paucity of previous reports of infections due to m thermoresistible in cats may result from lack of full identification of the causative organism in some infections . two other bacterial species , c amycolatum and s aureus , were also isolated from the wounds of the cat in this case report . both are components of the normal flora of normal human and animal skin and mucous membranes . , c amycolatum is increasingly being recognized as an important pathogen of humans with multidrug resistance to commonly used antibiotics , although it is typically susceptible to vancomycin . over the course of the disease process , c amycolatum was isolated from the cat in this report four times , despite antimicrobial therapy , and likely contributed to the severity of the wounds in this cat . given that s aureus can normally colonize cat skin , the significance of the s aureus isolate was less clear , but it may also have played a role in secondary infection . we ultimately chose pradofloxacin for long - term therapy of the mycobacterial infection , a third - generation fluoroquinolone licensed in the usa at a dose of 7.5 mg / kg for treatment of skin infections in the cat . pradofloxacin possesses an extended spectrum of activity against gram - negative , gram - positive and anaerobic bacteria , as well as mycoplasma species and intracellular organisms ( rickettsia species and mycobacterium species ) . although m thermoresistibile was not tested for susceptibility for pradofloxacin , it was susceptible to moxifloxacin , a human fluoroquinolone that is the chemical equivalent of pradofloxacin . the choice of vancomycin to address the secondary infections in this case was controversial given concerns about use of this antibiotic in animals . however , vancomycin was chosen because vancomycin is the drug of choice for mrsa and resistant corynebacterium species infections in humans , both the mrsa and the multidrug - resistant corynebacterium species isolates in this case had documented susceptibility , and no alternative single bactericidal antimicrobial could be identified that could be given parenterally with a wide therapeutic index . it is possible that a shorter duration of therapy might also have been sufficient , but given the multiple surgeries required and the extent and depth of the infected wounds , the decision was made to continue to treat until surgery had been completed and the cat could be discharged from the hospital . to our knowledge , this is the first case report of the treatment of m thermoresistibile panniculitis in a cat and the first report of infection with this organism in cats in north america . it is also the first report , to our knowledge , of cutaneous infection with c amycolatum in a cat . if clinical presentation is consistent with a mycobacterial infection , appropriate samples should be submitted for mycobacterium growth and identification , even if other bacterial species have been isolated from the patient . successful isolation of some mycobacterial species may require prolonged incubation at institutions with expertise in isolation of mycobacteria . despite intensive wound management and combination therapy with antimicrobial drugs , in addition to efforts to ensure client compliance , resolution of severe mycobacterial panniculitis caused by m thermoresistibile may not be possible , although additional studies are required to support this observation .
case summarya domestic shorthair cat was evaluated for chronic , bilateral , ulcerative dermatitis affecting the inguinal region and lateral aspects of both pelvic limbs . 
 histopathologic examination of skin biopsies collected throughout the course of disease revealed chronic pyogranulomatous ulcerative dermatitis . 
 aerobic bacterial skin cultures yielded growth of a methicillin - resistant staphylococcus aureus and corynebacterium amycolatum . upon referral 
 the clinical findings were suggestive of a non - tuberculous mycobacterium species infection . 
 previously obtained skin cultures failed to yield growth of mycobacterial organisms . 
 a deep skin biopsy was collected and submitted for mycobacterial culture . at 5 weeks of incubation mycobacterium thermoresistibile 
 was isolated . in previous reports , 
 m thermoresistibile has been isolated after 24 days of incubation , suggesting that this strain may have been a slower growing variant , or other factors ( such as prior antimicrobial therapy ) inhibited rapid growth of this isolate . 
 the cat was hospitalized for intravenous antibiotic therapy , surgical debridement of wounds , vacuum - assisted wound closure therapy and reconstruction procedures . 
 the wounds were ultimately primarily closed and the cat was discharged to the owner after 50 days of hospitalization . 
 seven months after hospitalization , the ulcerative skin lesions had healed.relevance and novel informationto our knowledge , only two cases of m thermoresistibile panniculitis have been reported in cats . in the only detailed report of feline m thermoresistibile panniculitis , treatment was not attempted . 
 the second case only reported detection of m thermoresistibile by pcr without a clinical description of the case . in our case report 
 , severe chronic skin infection with m thermoresistibile was addressed using prolonged specific antibiotic therapy , surgical debridement and reconstructions , and treatment of secondary bacterial infections .