Susceptibility of extended-spectrum- β-lactamase-producing Escherichia coli to commercially available and laboratory-isolated bacteriophages.

Extended-spectrum b-lactamase (ESBL)-producing Enterobacteriaceae (ESBL-E), particularly Escherichia coli and Klebsiella pneumoniae, are resistant to b-lactam antibiotics, b-lactam combinations and often non-b-lactam antibiotics. ESBL-E infections are associated with longer hospital stays and often poorer outcomes. Alternative or complementary therapies for ESBL-E infections are required. In response to the global emergence of antibiotic resistance, there is renewed interest in bacteriophage treatment of bacterial infections. Bacteriophages have high specificity (owing to narrow host ranges), modes of action unrelated to antibiotic targets and self propagating and self-limiting activities, facilitating low dosing and bacteriophage elimination following infection resolution. We determined the in vitro susceptibility of 100 previously characterized ESBL-producing E. coli (ESBL-EC) to four bacteriophage cocktails, used as part of standard clinical practice in the Republic of Georgia.

ESBL production by ESBL-EC was confirmed according to EUCAST criteria in Beaumont Hospital, Dublin, Ireland and ESBL-EC were mainly isolated from urine, blood and respiratory specimens. As found for other ESBL-EC collections, the majority belonged to phylogenetic groups B2 and D (80/100, 80%), but groups A and B1 were also represented. The activities of four bacteriophage cocktails (Pyo, Intesti, Enko and Ses) were determined against each isolate using in vitro spot tests. Isolates were susceptible if confluent, semi-confluent or opaque lysis or individual plaques (n≥1) were observed (single plaques may be propagated to generate bacteriophages with improved lytic spectra) and resistant if lysis was not visible. The bacteriophage cocktails originated in Georgia and are sterile filtrates of phage lysates of bacterial species, including E. coli serovar O25b.