First countrywide survey of acquired metallo-beta-lactamases in gram-negative pathogens in Italy

Abstract

Metallo-beta-lactamases (MBLs) can confer resistance to most beta-lactams, including carbapenems. Their emergence in gram-negative pathogens is a matter of major concern. Italy was the first European country to report the presence of acquired MBLs in gram-negative pathogens and is one of the countries where MBL producers have been detected repeatedly. Here, we present the results of the first Italian nationwide survey of acquired MBLs in gram-negative pathogens. Of 14,812 consecutive nonreplicate clinical isolates (12,245 Enterobacteriaceae isolates and 2,567 gram-negative nonfermenters) screened for reduced carbapenem susceptibility during a 4-month period (September to December 2004), 30 isolates (28 Pseudomonas aeruginosa isolates, 1 Pseudomonas putida isolate, and 1 Enterobacter cloacae isolate) carried acquired MBL determinants. MBL producers were detected in 10 of 12 cities, with a predominance of VIM-type enzymes over IMP-type enzymes (4:1). Although having an overall low prevalence (1.3%) and significant geographical differences, MBL-producing P. aeruginosa strains appeared to be widespread in Italy, with a notable diversity of clones, enzymes, and integrons carrying MBL gene cassettes.

FIG. 1.

Locations of the clinical microbiology laboratories participating in the survey (3 laboratories, whose data were pooled, were in Turin, while the remaining 11 were in the other cities) and distribution of the MBL-producing isolates. For each city, the MBL-producing species and enzyme types are indicated. For P. aeruginosa, the percentages of MBL producers among the total number of isolates (tot) and the total number of carbapenem-nonsusceptible isolates (CP-NS) are also shown in parentheses. The locations of Verona, where the VIM-1-producing P. aeruginosa index strain VR-143/97 was first detected (20), and Trieste and San Giovanni Rotondo, where two major outbreaks of infection with MBL-producing P. aeruginosa have been reported previously (18, 25), are also shown.

FIG. 2.

Structures of the variable regions of class 1 integrons carrying MBL gene cassettes in different clones and variants of MBL-producing P. aeruginosa. The gene cassettes are indicated by arrows (those representing cassettes carrying MBL genes are black; those representing cassettes carrying other known resistance genes are gray). 5′ conserved segments (5′CS) and 3′ conserved segments (3′CS) flanking the cassette arrays are also indicated. Underlined integrons are those first detected in this study.