Potential International Spread of Multidrug-Resistant Invasive Salmonella enterica Serovar Enteritidis

Irene Rodríguez

, M. Rosario Rodicio, Beatriz Guerra, and Katie L. Hopkins

Author affiliations: Federal Institute for Risk Assessment, Berlin, Germany (I. Rodríguez, B. Guerra); Universidad de Oviedo, Oviedo, Spain (M.R. Rodicio); and Health Protection Agency, London, UK (K.L. Hopkins)

Abstract

In developing countries, Salmonella enterica serovar Enteritidis causes substantial illness and death, and drug resistance is increasing. Isolates from the United Kingdom containing virulence-resistance plasmids were characterized. They mainly caused invasive infections in adults linked to Africa. The common features in isolates from these continents indicate the role of human travel in their spread.

Worldwide, nontyphoidal Salmonella enterica is a major cause of foodborne illness, and Enteritidis is one of the most commonly reported serovars (www.who.int/salmsurv/links/GSSProgressReport2005.pdf

). In industrialized countries, S. enterica serovar Enteritidis commonly causes self-limiting gastroenteritis, for which treatment with antimicrobial drugs is usually not needed. However, in developing countries, this serovar, together with serovar Typhimurium, frequently causes invasive infections and substantial illness and death among young children with underlying diseases and among adults with HIV infection (1). Although antimicrobial drug resistance is not as high in S. enterica serovar Enteritidis as in other zoonotic disease serovars, multidrug-resistance (resistance to >4 antimicrobial drugs) has been increasingly reported (2), threatening treatment success for patients with severe infections. In recent years, in association with multidrug resistance, another trend has arisen: the emergence of virulence-resistance (VR) plasmids; these are hybrid plasmids that harbor resistance (R) and virulence (V) determinants. The appearance of these plasmids is of concern because they could lead to the co-selection of virulence (in addition to resistance) through the use of antimicrobial drugs (3,4). One such plasmid, pUO-SeVR1, has been recently reported in a multidrug-resistant (MDR) clinical isolate of S. enterica serovar Enteritidis (CNM4839/03) from Spain (5). This mobilizable plasmid of ≈100 kb derives from pSEV, the serovar-specific V plasmid of S. enterica serovar Enteritidis, and carries most of its V determinants, including the spvRABCD locus (Salmonella plasmid virulence). This plasmid greatly increases the ability of salmonellae to proliferate intracellularly and has been associated with severe infections in humans (6). The plasmid also harbors several R genes—bla_TEM-1, catA2, strA-strB, sul1, sul2, tet(A)—and a class-1 integron with the 700-bp/dfrA7 variable region, which confer resistance to ampicillin, chloramphenicol, streptomycin, sulfonamides, tetracycline, and trimethoprim (R-type ACSSuTTm). To investigate their international spread, we studied the presence of S. enterica serovar Enteritidis isolates carrying pUO-SeVR1–like plasmids in the United Kingdom.