In the oncology unit of a tertiary care hospital, an outbreak of nosocomial infections was observed. Blood stream and urinary tract infections were predominant. The causative agent of the outbreak was a multiple drug resistant (MDR), catalase-negative, Gram- positive coccus that is known to be a major etiological agent of nosocomial infections. As part of infection control measures, surveillance cultures were carried out to detect patients colonized by this nosocomial pathogen. What specimen is ideal for this purpose?