First report from Saudi Arabia using Diversilab analysis Genetic relatedness of clinical and environmental Acinetobacter baumanii isolates from an outbreak in an intensive care unit: First report from Saudi Arabia using Diversilab analysis Abiola Senok1, Ghada Garaween1, Harish Khubnani2, Adeola Raji1, Atef Shibl1,3 1Department of Microbiology & Immunology, College of Medicine, Alfaisal University, Riyadh, Saudi Arabia 2Prince Salman Bin Abdul Aziz Hospital, Riyadh, Saudi Arabia & 3College of Pharmacy, King Saud University, Riyadh, Kingdom of Saudi Arabia Results Background Acinetobacter baumannii is associated with an increasing incidence of nosocomial infections and outbreaks particularly among critically ill patients in intensive care units (ICU) Environmental contamination in the ICU contributes to the spread of these multidrug resistant pathogens and the occurrence of outbreaks Rapid determination of genetic relatedness of isolates is important for improving efficiency of infection control measures during hospital outbreak. Sources of isolates: 12 Clinical isolates: Endotracheal tube aspirate (n=9) ; urine (n=2); sputum (n=2); wound swab (n=1) ; 14 Environmental isolates : Bed railings (n=10), curtains (n=3) ; one each from stethoscope, computer mouse & telephone Clonal distribution of isolates Most of the isolates within two clusters: Group 2 (n=11) & Group 3 (n=9) Groups 1 and 6 each had one clinical and one environmental isolate obtained from the bed railing of the patient from whom the clinical isolate originated. Groups 4 and 5: Single environmental isolate each 3 clinical isolates were from a single patient: Clustered in Group 2 (P3A and P3D) & Group 3 (P3C) (Figure). All isolates were multidrug resistant Resistance to three or more classes of antibiotics Two clinical strains from Clusters 2 and 3 were resistant to colistin (MIC >4ug/ml).   Objectives To analyze the clonal relationships of clinical and environmental A. baumanii strains isolated during an outbreak in the ICU of a tertiary care hospital in Saudi Arabia. Methods Study site: Prince Salman Bin Abdul Aziz Hospital, Riyadh, Saudi Arabia 12 clinical and 14 environmental A. baumanii isolates were identified during an outbreak in the 14-bed adult ICU 1st -28th February 2013 Bacterial identification and antibiotic susceptibility testing: carried out using Microscan Walkaway automated system Determination of strain clonality: repetitive-sequence-based polymerase chain reaction (rep-PCR) with the semi-automated DiversiLab system (Biomerieux) Conclusions This outbreak was caused by two clonal groups of MDR A. baumanii The presence of multiple environmental clones was suggestive of an environmental source within the ICU Assessment of microbial clonal relationship was useful for formulating effective infection prevention measures in the ICU.