Background: Enterobacteriaceae are the most commonly-found pathogens in humans, and they are an important cause of many infections. In the past few decades, extended-spectrum beta-lactamases (ESBL-) producing Enterobacteriaceae have spread worldwide. Carbapenem is the drug of choice for ESBL organism treatment, but carbapenem-resistant Enterobacteriaceae (CRE) have increasingly been reported worldwide. Unfortunately, treatment of CRE organisms has been
limited by the emergence of multidrug resistance, and this has led to increasing mortality rates.
Objective: To investigate the occurrence of CRE isolated from patients in Rajavithi Hospital between 2009 and 2015.
Material and Method: CRE strains isolated in Rajavithi Hospital between 2009 and 2015 were studied. All specimens were screened for CRE isolates using inhibition of carbapenem disks.
Results: In 2015, the prevalence of CRE at Rajavithi Hospital was 5.8% (411/7,039). Of 411 CRE isolates, Klebsiella pneumoniae was the species with the highest number of isolates (n = 290); however, Providencia rettgeri had the highest proportion of CRE isolates per species at 34.4%. Between 2009 and 2015, the percentage of CRE isolates of each species rose
dramatically especially in K. pneumoniae, which increased from 1.3% in 2009 to 1.6% in 2010, 3.8% in 2011, 5.7% in 2012, 11.1% in 2013, 11.8% in 2014 and 16.4% in 2015. Higher numbers of CRE isolates were found in IPD (88.5%) than in OPD
(11.5%), and they were most commonly identified in the medical wards (55.6%). The specimens with the greatest numbers of CRE isolates were urine at 48.3%, followed by pus, sputum, blood and genital tract, at 23.3%, 15.3%, 11.5% and 1.6% respectively. Most CRE strains were resistant to all antimicrobial agents; however, tigecycline (90%S) was active against CRE in E. coli strains and colistin (75%S) was effective against CRE in K. pneumoniae.
Conclusion: The occurrence of CRE organisms in Rajavithi Hospital increased at a worrying rate, and early CRE reporting
is an important step in halting its further proliferation. Prevention of both CRE transmission and CRE infections has become an important infectious control (IC) objective.

Keywords: Enterobacteriaceae, Carbapenem, Carbapenem-Resistant Enterobacteriaceae, CRE, Antimicrobial susceptibility
test, AST