Detection and Characterization of Extended-spectrum Beta-lactamase-producing Enterobacteriaceae in High-risk Patients in an Irish Tertiary Care Hospital

Background: Extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-E) are Gram-negative, multi-drug-resistant organisms that are of major clinical significance among immunocompromised patients in high-risk areas in hospital settings. In Ireland, the number of ESBL-E bloodstream infections is increasing.

Aims: To conduct a prevalence study of ESBL-E among immunocompromised patients in high-risk areas [intensive care unit (ICU), liver transplantation and haematology/oncology wards], characterize any ESBL genes detected by polymerase chain reaction (PCR), and perform epidemiological typing using pulsed-field gel electrophoresis (PFGE).

Methods: In total, 317 non-duplicate rectal swabs from patients in high-risk wards were screened anonymously for ESBL-E carriage. Positive isolates were characterized using PCR to detect blaCTX-M, blaTEM, blaOXA-1 and blaSHV ESBL-E genes. Clonal relationships of these isolates were investigated using PFGE.

Findings: Fifty (15.8%) high-risk patients were found to harbour ESBL-E. Prevalence rates of 21.9% (N = 28), 14.3% (N = 15) and 8.3% (N = 7) of ESBL-E were isolated from patients on the liver transplantation, ICU and haematology/oncology wards, respectively. Seventy percent of ESBL-E isolates carried more than one resistance gene. Of the 25 ESBL-producing Escherichia coli isolates typed by PFGE, two pairs of two isolates demonstrated >80% homology, and four of the five ESBL-producing Enterobacter cloacae isolates typed by PFGE demonstrated >80% homology, suggesting clonal relatedness and potential cross-transmission from individual patients.

Conclusion: A significant proportion of the patients screened were found to be colonized with ESBL-E. Typing revealed three incidents of potential cross-infection. Therefore, timely detection of ESBL-E among patients in high-risk wards is critical for treatment and infection control.