Pulsed field gel electrophoresis typing of coagulase-negative staphylococci with decreased susceptibility to teicoplanin isolated from an intensive care unit

Antimicrobial Susceptibility, Biochemical and Genetic Profiles ofStaphylococcus haemolyticusStrains Isolated from the Bloodstream of Patients Hospitalized in Critical Care Units

Staphylococcus haemolyticus strains (n=20), responsible of blood stream infections, were consecutively isolated from patients hospitalized in two different wards at high risk of infection. Strains displayed high rate of resistance to oxacillin (90%). All strains but two with decreased susceptibility (MIC = 4 microg/mL), were sensitive to vancomycin. Ten strains were resistant to teicoplanin. Among the strains susceptible to glycopeptides, three displayed heteroresistance to vancomycin and seven to teicoplanin, when tested by Etest technique with 2 x McFarland inoculum. Biochemical reactions allowed to assign strains to eight biotypes, with 11 strains clustering under two main biotype A and biotype B. Pulsed-field-gel-electrophoresis (PFGE) identified 11 different PFGE-types. Seven strains grouping under the major PFGE-type 1 and three strains clustering in PFGE-type 2, closely correlated to biotype A and biotype B respectively. Seven teicoplanin-resistant isolates clustered in the PFGE-type 1, two in the PFGE-type 2 and one in PFGE-type 5. Therefore, teicoplanin-resistant strains were biochemically and genetically related and clonally distributed, despite different clones of S. haemolyticus circulated in the units during the study period.

Genetic analysis of glycopeptide-resistant Staphylococcus epidermidis strains from bone and joint infections

Glycopeptide-resistant Staphylococcus epidermidis (GRSE) strains are of increasing concern in bone and joint infections (BJIs). Using multilocus sequence typing and multilocus variable-number tandem repeat analysis, we show that BJI-associated GRSE strains are genetically diverse but arise from related, multiresistant hospital sequence types (STs), mostly ST2, ST5, and ST23.

RAPD for the typing of coagulase-negative staphylococci implicated in catheter-related bloodstream infection

OBJECTIVES

A rapid random amplification of polymorphic DNA (RAPD) technique was developed to distinguish between strains of coagulase-negative staphylococci (CoNS) involved in central venous catheter (CVC)-related bloodstream infection. Its performance was compared with that of pulsed-field gel electrophoresis (PFGE).

METHODS

Patients at the University Hospital Birmingham NHS Foundation Trust, U.K. who underwent stem cell transplantation and were diagnosed with CVC-related bloodstream infection due to CoNS whilst on the bone marrow transplant unit were studied. Isolates of CoNS were genotyped by PFGE and RAPD, the latter employing a single primer and a simple DNA extraction method.

RESULTS

Both RAPD and PFGE were highly discriminatory (Simpson's diversity index, 0.96 and 0.99, respectively). Within the 49 isolates obtained from blood cultures of 33 patients, 20 distinct strains were identified by PFGE and 25 by RAPD. Of the 25 strains identified by RAPD, nine clusters of CoNS contained isolates from multiple patients, suggesting limited nosocomial spread. However, there was no significant association between time of inpatient stay and infection due to any particular strain.

CONCLUSION

The RAPD technique presented allows CoNS strains to be genotyped with high discrimination within 4h, facilitating real-time epidemiological investigations. In this study, no single strain of CoNS was associated with a significant number of CVC-related bloodstream infections.

In vitro combined bactericidal activity of cefpirome and glycopeptides against glycopeptides and oxacillin-resistant staphylococci

Infections caused by coagulase-negative staphylococci are becoming increasingly important, particularly those of nosocomial origin, as the organisms are frequently multi-resistant. New antimicrobial strategies are needed. The bactericidal activity of a combination of cefpirome with either vancomycin or teicoplanin against 12 strains of methicillin-resistant staphylococci with a decreased susceptibility to teicoplanin was determined in vitro by a time killing method. Strains Mu3 and Mu50 of Staphylococcus aureus were also studied. Cefpirome (0.125-0.5 x MIC) combined with vancomycin (0.25-1 x MIC) or teicoplanin (0.125-1 x MIC) acted synergically against 12 isolates over 18 h in most cases. A synergistic killing effect was also observed with the Mu3 and Mu50 strains of glycopeptide-intermediate S. aureus but over a longer period.

[Bacteremia caused by coagulase-negative staphylococci: incidence, frequency of teicoplanin resistance and molecular epidemiology]

All the patients hospitalised at Besançon Hospital between October 2000 and December 2000 were included in a prospective study in order to determine the incidence of bloodstream infections caused by coagulase-negative staphylococci (CNS), the prevalence of decreased susceptibility to glycopeptides and the molecular epidemiology of these pathogens. CNS isolates from bloodstream infections were collected and characterised by analysis of antibiotic susceptibility and restriction fragment length polymorphism using pulsed field gel electrophoresis. Forty-five episodes of CNS bacteremia occurred in 43 patients. The crude incidence of infected patients was 0,51 per 1,000 days of hospitalisation. These 45 bacteremia represented 23.3% of the total number of bacteraemia. Forty three of 45 bacteremia were studied, 36 were positive with a single PFGE pattern, 5 bacteraemias with 2 PFGE patterns, and 2 bacteraemias with 3 PFGE patterns. We identified 52 distinct PFGE patterns and 42 major PFGE patterns (35 were isolated in a single patient, 5 in 2 patients and 2 in 3 patients). The dendrogram generated showed deep but limited branching, each large branch corresponding to a species. Of these CNS isolates, 28.8% and 25.0% showed decreased susceptibility to teicoplanin, with the reference method and E-test respectively. The 16 strains belonging to multiple PFGE patterns were not more resistant to teicoplanin. Clonal dissemination did not seem to play a major role in the spread of glycopeptides resistance among CNS.