Antibiotic Resistance in Escherichia Coli Strains

Author(s): Mohamed A Jamal*

Antibiotic resistance is a problem of global concern and is frequently associated with human activity. Studying antibiotic resistance in bacteria isolated from pristine environments, such as Antarctica, extends our understanding of these fragile ecosystems. Escherichia coli strains, important faecal indicator bacteria, were isolated on the Files Peninsula (which has the strongest human influence in Antarctica), from seawater, bird droppings, and water samples from inside a local wastewater treatment plant. The strains were subjected to molecular typing with pulsed-field gel electrophoresis to determine their genetic relationships, and tested for antibiotic susceptibility with disk diffusion tests for several antibiotic families: β-lactams, quinolones, aminoglycosides, tetracycline, phenols, and trimethoprimsulfonamide. The highest E. coli count in seawater samples was 2400 cfu/100 mL. Only strains isolated from seawater and the wastewater treatment plant showed any genetic relatedness between groups. Strains of both these groups were resistant to β-lactams, aminoglycosides and tetracycline, and trimethoprim–sulphonamide. In contrast, strains from bird faces were susceptible to all the antibiotics tested. We conclude that naturally occurring antibiotic resistance in E. coli strains isolated from Antarctic bird faeces is rare and the bacterial antibiotic resistance found in seawater is probably associated with discharged treated wastewater originating from Files Peninsula treatment plants. Patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) are at risk for graft-versus-host disease (GVHD). The gastrointestinal tract has been identified to be a primary target of allogeneic donor T cells in allo-HSCT. The intestinal microbiota is known to interact with the host immune system and has been found to be an important modulator of GVHD. Broad-spectrum antibiotics such as carbapenems are often used in allo-HSCT patients to treat infections but have been found to increase the risk for intestinal GVHD, possibly via bystander depletion of beneficial commensal bacteria. However, whether loss of beneficial commensal bacteria is mechanistically sufficient to aggravate intestinal GVHD is not known. To examine this further, we utilized a mouse model of GVHD to study the effects of meropenem, a commonly used carbapenem in allo-HSCT patients.