A case report of Small Colony variant of Staphylococcus aureus isolated from a patient with chronic oesteomyelitis in a tertiary care hospital of eastern India
A 46 years old man had a closed proximal left humeral fracture following a road traffic accident one and half year back. After that he was referred to our hospital where fixation of fractured fragments was done by internal screw fixation followed by pre-emptive treatment with cefoperazone-sulbactum combination and ceftazidime for 10 days. The patients was initially fine for two weeks after that he suffered from persistent pain over affected region and six months later a sinus tract developed along with purulent discharge. [] The patient received various combinations of antimicrobials (mainly second and third generation cephalosporins) to control the disease. Conventional radiographs showed subperiosteal thickening in earlier stage. Bone scintigraphy showed increased uptake in the humeral diaphysis. Laboratory investigations revealed hemoglobin 12 mg/dl, leucocyte count 12 × 103/cmm, erythrocytic sedimentation rate 30 mm/1st hr, random plasma glucose level 130 mg/dl and CRP 180 ug/ml. The expressed pus from the sinus tract was aseptically collected. The direct gram stained smear of collected pus showed gram positive cocci (GPC) arranged in small clusters. The other part of collected sample seeded on blood agar (BA) and McConkey's agar (MA) plate and both the plates were incubated aerobically at 37°C for 48 hours. After 48 hours of incubation non-pigmented small 0.1 mm diameter non haemolytic colonies grew on BA plate. [] MA plate showed no growth. The colonies were further sub cultured on Nutrient Agar (NA) and grew as small non-pigmented colonies. Gram stained smear from colony of BA and NA revealed GPC arranged in small clusters. The colonies were catalase positive and oxidase negative. Slide coagulase test from the isolated colonies was negative and tube coagulase test was positive after 18 hours. Antibiotic susceptibility test result showed the isolated strain was only susceptible to vancomycin and resistant to oxacillin, azithromycin, co-trimoxazole, and cefpodoxime. [] A lawn culture was put on NA plate along with 20 ug and 40 ug menadione impregnated discs over it. The colonies around menadione discs grew as large colonies thereby confirming menadione auxotrophy. Subculture from this large colony revealed yellow pigmented normal Staphylococcal colony. [] These large colonies were catalase, coagulase (slide and tube) tests positive and oxidase negative.