Integration of molecular characterization of microorganisms in a global antimicrobial resistance surveillance program

The SENTRY Antimicrobial Surveillance Program has incorporated molecular st rain typing and resistance genotyping as a means of providing additional in formation that may be useful for understanding pathogenic microorganisms wo rldwide. Resistance phenotypes of interest include multidrug-resistant path ogens, extended-spectrum beta -lactamase (ESBL)-producing Enterobacteriacea e, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, and fluoroquinolone-resistant (FQR) strains of gram-negative bacilli and Streptococcus pneumoniae. Clusters of greater than or equal to2 isolates within a given resistance profile that are linked temporally and by hospital location are flagged for DNA fingerprinting. Further characteri zation of organisms with respect to resistance genotype is accomplished wit h use of polymerase chain reaction and DNA sequencing. This process has bee n highly successful in identifying clonal spread within clusters of multire sistant pathogens. Between 50% and 90% of MRSA clusters identified by pheno typic screening contained evidence of clonal spread. Among the Enterobacter iaceae, ESBL-producing strains of Escherichia coli and Klebsiella pneumonia e are the most common pathogens causing clusters of infection, and 50% of r ecognized clusters demonstrate clonal spread. Clusters of Pseudomonas aerug inosa, Acinetobacter species, and Stenotrophomonas maltophilia have been no ted with clonal spread among patients with urinary tract, respiratory, and bloodstream infections. Characterization of mutations in the FQR-determinin g region of phenotypically susceptible isolates of E. coli and S. pneumonia e has identified first-stage mutants among as many as 40% of isolates. The ability to characterize organisms phenotypically and genotypically is extre mely powerful and provides unique information that is important in a global antimicrobial surveillance program.