Case 506 -- Small colony variant-Staphylococcus aureus

Contributed by Anca Florea, MD, William Pasculle, Sc.D and Mrs. Debbie Simonetti
Published on line in April 2007


This was a 62 years old gentleman with a medical history of single right lung transplant for idiopathic pulmonary fibrosis. Post transplant cultures showed heavy Staphylococcus aureus (S.aureus) and he was treated with IV Vancomycin for 10 days. The first surveillance bronchoscopy with biopsy was negative for organisms or rejection and the patient was discharged.

The next surveillance bronchoscopy with broncho-alveolar lavage was performed 5 weeks later and it showed >100,000 CFU/ml S.aureus, >100,000CFU/ml Streptococcus viridans and >100,000 CFU/ml coagulase negative Staphylococcus.The bronchial wash of the left lung read light S. aureus No. 1 and light S. aureus No. 2 along with light coagulase negative Staphylococcus and moderate viridans Streptococcus.

On routine microbiological work-up, the 1st and 2nd reported S. aureus strains showed similar gram-stain appearance as gram positive cocci in clusters (Figure 1) but on blood plates , two distinct types of colonies were growing (Figures 2 and 3). The Kirby Bauer sensitivity test for the two morphologically different S. aureus strains were similar with the exception that the S. aureus labeled No.2 was resistant to trimethoprim/sulfamethoxazole (SXT) while the one labeled No.1 being sensitive to it.


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