Dissemination of Escherichia coli with CTX-M type ESBL between humans and yellow-legged gulls in the south of France

Abstract

Extended Spectrum beta-Lactamase (ESBL) producing Enterobacteriaceae started to appear in the 1980s, and have since emerged as some of the most significant hospital-acquired infections with Escherichia coli and Klebsiella being main players. More than 100 different ESBL types have been described, the most widespread being the CTX-M beta-lactamase enzymes (bla(CTX-M) genes). This study focuses on the zoonotic dissemination of ESBL bacteria, mainly CTX-M type, in the southern coastal region of France. We found that the level of general antibiotic resistance in single randomly selected E. coli isolates from wild Yellow-legged Gulls in France was high. Nearly half the isolates (47.1%) carried resistance to one or more antibiotics (in a panel of six antibiotics), and resistance to tetracycline, ampicillin and streptomycin was most widespread. In an ESBL selective screen, 9.4% of the gulls carried ESBL producing bacteria and notably, 6% of the gulls carried bacteria harboring CTX-M-1 group of ESBL enzymes, a recently introduced and yet the most common clinical CTX-M group in France. Multi locus sequence type and phylogenetic group designations were established for the ESBL isolates, revealing that birds and humans share E. coli populations. Several ESBL producing E. coli isolated from birds were identical to or clustered with isolates with human origin. Hence, wild birds pick up E. coli of human origin, and with human resistance traits, and may accordingly also act as an environmental reservoir and melting pot of bacterial resistance with a potential to re-infect human populations.

Figure 1. Map shows location of Yellow-legged Gull populations in the study.

Port Saint-Louis Carteau colony feeds mainly at the Marseille city dump, and Aigues-Mortes colony mainly offshore.

Figure 2. Distribution of 16 ESBL producing E. coli isolates within a minimum spanning tree representing 273 previously reported STs (dots) from a collection of 459 diverse E. coli isolates.

The tree is based on the degree of allele sharing by MLST analysis. Clonal complexes composed of at least three ST members are indicated by dots proportional in size to the number of STs within them. STs, isolate designations, phylogenetic group, and distribution of CTX-M genes of ESBL producing E. coli from birds are indicated (black dots). Uniformly colored dots indicate a shared phylogenetic group. Thick lines connecting pairs of STs indicate that they share six (thick lines) or five (thin lines) alleles. Dotted connecting lines represent less allele sharing.