Phenotypic characteristics of coagulase-negative staphylococci: typing and antibiotic susceptibility.

Abstract

The present thesis deals with various aspects of handling coagulase-negative staphylococci (CoNS) in the local clinical microbiology laboratory. CoNS are normal inhabitants of the skin and mucus membranes and are increasingly being recognised as opportunistic pathogens causing infection in the immunocompromised host, in particular patients with indwelling plastic devices. In particular the finding of CoNS in specimens which should normally be sterile, such as blood cultures, is of interest. The isolation of the same strain of an opportunistic pathogen, such as CoNS, enhance the likelihood of the bacteria causing infection. Multiple antibiotic resistance, in particular methicillin resistance, is frequent among CoNS hospital-strains on a global scale. beta-lactam antibiotics are the most valuable antibiotics for the treatment of infection with susceptible CoNS. A reliable method for the detection of methicillin resistance, and hereby resistance to all beta-lactam antibiotics, is therefore important. A simple identification method, Minibact-S, has been developed. Minibact-S can identify the CoNS species, which are the most frequently occurring in human specimens. Furthermore, Minibact-S can subtype Staphylococcus epidermidis. Another phenotypic typing method, lectin typing, has been developed for typing S. epidermidis. Lectin typing involves the binding of various biotinylated lectins to the surface of whole immobilised cells of CoNS. Lectins are proteins or glycoproteins which bind specifically to various glycans. When the lectins: Wheat Germ Agglutinin (WGA), Soy Bean Agglutinin (SBA), Concanavalin A (ConA), and Lens Culinaris Agglutinin (LCA) were included, typing of S. epidermidis gave a discriminatory power of the same magnitude as found for DNA-plasmid profile analysis. Lectin typing could be used as a supplementary typing method for S. epidermidis in the local clinical microbiology laboratory, since the method is simple, reproducible and does not require expensive and sophisticated equipment. Various typing schemes for S. epidermidis, i.e. typing which involves several typing methods, have been tested: lectin typing, DNA-plasmid profile analysis, antibiotic susceptibility testing, phage typing, and slime production lectin typing, antibiotic susceptibility testing, biotyping (Minibact-S), phage typing antibiotic susceptibility testing and biotyping (Minibact-S) For use as a "first line" typing scheme in the local clinical microbiology laboratory, the typing of S. epidermidis by combined antibiotic susceptibility testing and biotyping is easy to handle. Antibiotic susceptibility testing should include antibiotics from several groups of antibiotics having different resistance mechanisms. Antibiotic susceptibility among Danish CoNS-strains from blood cultures was studied. A major diversity in species distribution and antibiotic susceptibility was found between different Danish regions, for example methicillin resistant CoNS accounted for 40% in Copenhagen County and only for 21% in Northern Jutland County. Diversity in species distribution was also marked; an example of this is that 73% of the strains from Copenhagen Municipality were identified as S. epidermidis compared to only 46% in Northern Jutland County. In a study from Rigshospitalet, Copenhagen, great diversity in antibiotic susceptibility was detected between the different wards. In four wards investigated, high consumption of carbapenems, Third-generation cephalosporins, and quinolones was associated with high prevalence of methicillin resistance. Furthermore, for ciprofloxacin, ciprofloxacin-resistant CoNS-strains were practically not detected in the Neonatal Ward where ciprofloxacin is not used. In contrast to the nationwide study, glycopeptide resistance was found at Rigshospitalet: 5% of the CoNS strains were teicoplanin-resistant but all strains were vancomycin-susceptible. In both the above mentioned studies, antibiotic resistance was strongly associated with