In the Journal of Clinical Microbiology, we describe an unusual Candida pseudo-outbreak that based on patterning on culture plates mimicked true infection.  Specifically, colonies were not randomly distributed on plates, but demonstrated in a graded pattern typical of true infections with decreasing number of colonies on subsequent quandrants of streak plates.  The culprit was eventually identified, as a contaminated Anoxomat chamber that was used to hold anaerobic plates prior to use in cultures.   The Anoxomat rapidly purges and instills a hydrogen/nitrogen gas mixture into a closed jar in order to rapidly establish anaerobiosis. We believe that the Anoxomat overcame the natural swan neck barrier of Petri dishes allowing Candida guilliermondii containing aerosols to randomly contaminate anaerobic plates. C. guilliermondii does not grow anaerobically obscuring this contamination. However, randomly contaminated anaerobic plates were subsequently the source of contamination for the primary quandrants of aerobic media during specimen planting leading to simulation of true infection by microbiological criteria. Pseudo-outbreak strains were proven clonal by a combination of pulsed-field gel electropheresis and optical restriction mapping. The study represented a combined effort of the clinical microbiology laboratory and the infection control/hospital epidemiology divisions at BIDMC; Dan Diekema at the University of Iowa (PFGE analysis and expertise); and OpGen (optical mapping).     

See:   www.pnas.org/content/early/2017/01/10/1616248114.abstract