Comparison of MALDI-TOF MS and AFLP for strain typing of ESBL-producing Escherichia coli.

Typing of bacterial isolates using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) potentially provides an efficient on-site method to monitor the spread of antibiotic-resistant bacteria and rapidly detect outbreaks. We compared MALDI-MS typing results to those of amplified fragment length polymorphism (AFLP) in a collection of 52 ESBL-producing Escherichia coli, isolated in a Dutch nursing home with an on-going outbreak of ST131 E. coli. Specific MALDI types were defined based on spectral data from four replicate colony samples of isolates grown on Columbia agar using multivariate statistical procedures. Type-specific superspectra were computed for four E .coli MALDI-types and tested for the potential of rapid and automated typing. The effect of different incubation conditions on typing performance was tested by analysing five isolates incubated for 24 h and 48 h on five different media. Types defined based on MALDI spectra were largely in agreement with the AFLP results, although some MALDI types comprised of more than one AFLP type. In particular, isolates belonging to ST131 showed distinct mass patterns. The proportion of isolates correctly assigned was substantially lower for isolates incubated on Sabouraud-dextrose and Drigalski agars for 24 h, and for those incubated for 48 h (all media). Our results show that the identification of type-specific peaks potentially allows direct typing of isolates belonging to specific clonal lineages. Both incubation time and media affected type assignment, suggesting that there is a need for a careful standardization of incubation time and culturing conditions when developing MALDI-typing schemes for E. coli.

Community-acquired methicillin-resistant Staphylococcus aureus: current perspectives.

Methicillin-resistant Staphylococcus aureus (MRSA) has become a worldwide problem, although its prevalence varies considerably among countries. The epidemiology of MRSA is now changing; infections are no longer confined to the hospital setting, but also appear in healthy community-dwelling individuals without established risk factors for the acquisition of MRSA. Reported prevalence rates of community-acquired MRSA (CA-MRSA) vary widely among studies-largely because of the different definitions employed and different settings in which the studies have been performed. At present, molecular epidemiological definitions, based on staphylococcal cassette chromosome mec (SCCmec) typing and phylogenetic analyses of the MRSA isolates, are considered the most reliable means by which to distinguish between hospital-acquired MRSA (HA-MRSA) and CA-MRSA. CA-MRSA has been isolated predominantly from skin and soft tissue infections, such as abscesses, cellulitis, folliculitis and impetigo. Although CA-MRSA infections are usually mild, they may also be severe, and can result in hospitalisation and even death. CA-MRSA strains differ from the major pandemic clones of MRSA that account for the majority of epidemic HA-MRSA strains. Differences are found in SCCmec types, bacterial growth rate, and the distribution of antibiotic resistance genes and toxin genes. Mathematical models have shown that CA-MRSA has a high potential to become endemic in the community, and this will impact significantly on the control of MRSA in the hospital setting. Well-designed, community-based studies with adequate risk factor analysis are required to further elucidate the epidemiology of CA-MRSA and to improve strategies to control MRSA in both the community and hospital settings.

Dutch guideline for preventing nosocomial transmission of highly resistant microorganisms (HRMO).

Hospitals are faced with the increasingly rapid emergence and dissemination of antimicrobial-resistant microorganisms. US and European guidelines on the prevention of antimicrobial resistance in hospitals were, until recently, mainly directed at methicillin-resistant Staphylococcus aureus (MRSA). In 2004, the Dutch Working Party on Infection Prevention issued a guideline on the prevention of nosocomial transmission of highly resistant microorganisms (HRMO), in order to fulfill the growing need for additional guidance on the control of other pathogens with acquired resistance and the potential to spread within hospitals (such as glycopeptide-resistant Enterococcus faecium, penicillin-resistant Streptococcus pneumoniae, extendedspectrum beta-lactamase producing Enterobacteriaceae, and other (multi)drug-resistant gram-negatives). In addition to providing criteria for defining HRMO, the Dutch guideline provides recommendations on isolation of patients, active surveillance, and contact tracing. The guideline will enable the comparison of HRMO rates between hospitals, and may be used to evaluate the efficacy of programs to control antibiotic use and/or nosocomial transmission of resistant pathogens. The eventual success of nationwide implementation of this guideline remains to be established in the coming years.