Bactericidal Monoclonal Antibodies Specific to the Lipopolysaccharide O Antigen from Multidrug-Resistant Escherichia coli Clone ST131-O25b:H4 Elicit Protection in Mice

Abstract

The Escherichia coli sequence type 131 (ST131)-O25b:H4 clone has spread worldwide and become responsible for a significant proportion of multidrug-resistant extraintestinal infections. We generated humanized monoclonal antibodies (MAbs) that target the lipopolysaccharide O25b antigen conserved within this lineage. These MAbs bound to the surface of live bacterial cells irrespective of the capsular type expressed. In a serum bactericidal assay in vitro, MAbs induced >95% bacterial killing in the presence of human serum as the complement source. Protective efficacy at low antibody doses was observed in a murine model of bacteremia. The mode of action in vivo was investigated by using aglycosylated derivatives of the protective MAbs. The significant binding to live E. coli cells and the in vitro and in vivo efficacy were corroborated in assays using bacteria grown in human serum to mimic relevant clinical conditions. Given the dry pipeline of novel antibiotics against multidrug-resistant Gram-negative pathogens, passive immunization with bactericidal antibodies offers a therapeutic alternative to control infections caused by E. coli ST131-O25b:H4. Escherichia coli is a member of the intestinal commensal flora. Certain variants (pathotypes) of the species, however, can cause either intestinal or extraintestinal infections, such as urinary tract infection, meningitis, or bacteremia (1). Extraintestinal pathogenic E. coli (ExPEC) strains harbor a large array of virulence traits that enable them to cause disease outside the intestinal tract. ExPEC strains have been evolving antibiotic resistance, often a combined resistance against most of the clinically relevant antibiotics, such as fluoroquinolones, aminoglycosides, and ␤-lactam antibiotics. Typically, multidrug-resistant (MDR) strains are compromised in their fitness and virulence, which restricts their prevalence to a nosocomial setting and conversely limits their spread in the community. Some successful MDR clonal lineages do, however, retain high virulence potential (2, 3). The E. coli clonal lineage sequence type 131 (ST131)-O25b:H4, first described in 2008 (4, 5), has spread globally not only in hospitals (as do most other MDR clones) but also in the community (6-9). This clone is responsible for ϳ15% (up to 25% [10,11]) of all extraintestinal E. coli infections and represents the majority of fluoroquinolone-resistant isolates (12) and about half of the extended-spectrum ␤-lactamase (ESBL)-producing isolates (13). The progressive acquisition of additional resistance phenotypes in ST131-O25b:H4 strains leaves very few effective antibiotics for treatment of patients infected by members of this lineage (14). Even more alarming is the recent appearance of carbapenem-resistant ST131 isolates (15-17). Recently, ST131-O25b:H4 strains were shown to predominate among carbapenem-resistant E. coli isolates (18). A major clinical concern is the lack of development of novel antibiotics against Gram-negative pathogens, again leaving very limited treatment options (19). The p...

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Multiple Modes of Action of a Monoclonal Antibody against Multidrug-Resistant Escherichia coli Sequence Type 131-H30

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