Colonisation of gastrointestinal tract by extended spectrum beta lactamase (ESBL)-producing Gram-negative bacteria is a source for infections. The present work is a prospective study in Latvia aimed to determine the role of two surgical profile wards in transmission of ESBL-producing bacteria. Differences between hospital wards were not analysed due to low number of patients. We have also determined a correlation between the duration of hospitalisation and risk of ESBL colonisation. Tests for ESBL-producing bacteria were made twice for 136 patients — upon admission and upon discharge from the hospital. Of them, 21 (15.4%) patients already were ESBL-positive at the time of admission and 115 (84.6%) patients were ESBL-negative. Upon discharge from hospital, 45 (33.1%) patients were ESBL-positive, one patient was ESBL-negative, and 25 (18.4%) of ESBL-positive cases had emerged during hospitalisation. In total, 46 (33.8%) from 136 patients were ESBL-positive and ESBL was positive in 51 bacterial isolates. On discharge from hospital, the newly acquired ESBL-positive bacterial isolates were K. pneumoniae (n = 18), E. coli (n = 7) and P. mirabilis (n = 3). The prevalence of ESBL-positive E. coli from all detected E. coli was 7.0% and from all Klebsiella spp. — 88.9% in gut flora. Analysis of patientassociated wound infections did not show correlation between the ESBL-producing gut microbiota and the bacterial species involved in wound infection.