Seagulls and Beaches as Reservoirs for Multidrug-Resistant Escherichia coli

A variety of extended-spectrum β-lactamase–producing Escherichia coli isolates, with a high rate of cefotaximase-15 resistance, were identified in seagull feces from Porto, Portugal, beaches. Beaches may therefore present a risk to public health because of the potential pathogen-spreading capacity of migratory birds.


The Study
During December 2007 through April 2008, wild seagull (L. fuscus, L. cachinnans) feces were collected from the Matosinhos and Leça da Palmeira beaches (Porto, Portugal) (20 samples every 2 weeks) using a sterile spatula. Care was taken during sampling to avoid collection of beach sediment. Samples were placed in sterile tubes and processed. Samples were precultured in buffered peptone water (Oxoid, Basingstoke, UK) at a dilution of 1/10 wt/vol and incubated at 37°C. Cultures were injected by streaking 10 μL of the suspensions onto Tergitol BCIG agar (Biokar Diagnostics, Beauvais, France). Another suspension was made in buffered peptone water supplemented with cefotaxime (CTX) at 2 μg/mL and then streaked in a Tergitol BCIG plate supplemented with CTX at 2 μg/mL. The plates were incubated at 37°C overnight. We identifi ed E. coli isolates by using the API20E system (bioMérieux, Balmes-les-Grottes, France).
Identifi cation of the phylogroups of the different CTX-M producers showed that most belonged to phylogroup B1, and a notable number of isolates belonged to phylogroup D (Figure). In contrast, few isolates belonged to the highly virulent phylogroup B2. Whereas CTX-M-1 producers mostly belonged to phylogroup B1, the CTX-M-15 producers were well distributed among the 4 phylogroups (Figure). Notably, plasmid analysis identifi ed a sizable diversity of plasmid sizes, including E. coli isolates producing the same CTX-M type (data not shown).

Conclusions
CTX-M type β-lactamases are ESBLs of increasing prevalence (2). Infections with multidrug-resistant bacilli occur not only in hospitals but also in the community (11). Previous studies have reported multidrug-resistance in wild birds (12,13). Our study provides additional clues that wild seagulls are carriers of ESBL-producing E. coli, although at a lower rate than previously reported (1). In that study, ESBL determinants were TEM-52, CTX-M-1, CTX-M-14a, and CTX-M-32 (1). Another study (focused on poultry) (3) reported that the main identifi ed CTX-M determinants were of the CTX-M-1 group (CTX-M-1, CTX-M-15, CTX-M-32), as we also found.
We report that CTX-M-15 was the main CTX-M type identifi ed among birds residing mostly on beaches of downtown Porto, which agrees with CTX-M-15 being the most prevalent ESBL in E. coli in Porto-hospitalized pa-tients (14). This observation differs from those of a study reporting mostly TEM-52 producers in wild animals in a reserve near Porto, where indirect contacts with humans are less likely (5).
Previous studies have reported the association of E. coli isolates of groups B2 and D with extraintestinal infections (15). Our report shows that 37% of all ESBL isolates belong to B2 or D phylogroup, a higher rate than previously reported (27% of all ESBL) (1). This fi nding could be a matter of concern for human health. However, we showed that the ST131 type known to be frequently isolated in humans and frequently associated with CTX-M-15 production was quite rare (9%). In addition, those ST131 strains were found to harbor diverse CTX-M determinants. In fact, the frequent identifi cation of CTX-M producers here was related neither to the dissemination of a single clone nor to that of a single plasmid.
Our report suggests that beaches may play a major role in dissemination of resistance determinants and may be a source of the CTX-M-15-related community-acquired infections. Migratory birds, such as seagulls crossing an extensive portion of the European coastline between Portugal and Scandinavia, may be reservoirs for these emerging resistance determinants.
This work was fi nanced by a grant from the Ministère de la Recherche, Université Paris XI, Paris, France; by grants from the European Community (DRESP2, LSHM-CT-2005-01705 and TROCAR HEALTH-F3-2008-223031); and by the Institut national de la santé de la recherche médical, France.
Dr Simões is a veterinary student at Instituto de Ciências Biomédicas Abel Salazar, Porto, and completed this study as the fi nal professional training period of his studies curriculum. His research interests include zoonotic diseases.