Encapsulation, slime production and surface hydrophobicity of coagulase‐negative staphylococci

Received 20 January 1983 Accepted 23 January 1983 1. INTRODUCTION 2. MATERIALS AND METHODS Infections associated with prosthetic implants or medical devices are most commonly caused by coagulase-negative staphylococci (CNS) [1]. The ability of CNS to produce slime has been sug- gested to play a critical role in the adhesion onto surfaces of implants and medical devices [2] and in the course of medical device-associated infections [3]. Staphylococcus aureus, the pathogenic counter- part of CNS, can be encapsulated [4]. Such strains possessed increased virulence in comparison with their non-encapsulated variant strains [5,6]. Char- acterization of CNS has been advocated [7,8], but no special attention has been given to the presence of a capsule, although encapsulated CNS have been reported [9]. Bacterial adhesion onto surfaces is also regarded to be an important virulence fac- tor [10]. Bacterial interaction with mammalian cells and artificial surfaces is promoted by the hydro- phobicity of the bacterial cell surface [11-13]. After characterization of twenty one CNS, the presence of a capsule and the ability to produce extracellular slime were studied. In addition, the surface hydrophobicity of the strains was mea- sured using a xylene-water system [14]. * Correspondence should be addressed to J. Dankert. 2.1. Bacterial strains and growth conditions 21 CNS strains isolated from open-heart surgery patients and laboratory staff members were classi- fied according to the scheme of Kloos and Schleifer [8] using the API Staph gallery (API Systems S.A., Montalieu Vercieu, France). 7 strains (NCTC) were a gift of Dr. R.R. Marples, Central Public Health Laboratory, Colindale Avenue, London, England. Strains stored at -20°C in skim milk were grown on sheep blood agar plates (Oxoid, Ltd., U.K.) and maintained on nutrient agar slants (Oxoid) at 4°C for 1 month. The strains were cultured in Trypticase soy broth (TSB, BBL Microbiology Systems, Cockeys- ville, MD) for 20 h at 37°C. Late exponential phase cells were obtained by culturing 2 ml of the overnight broth into 100 ml of fresh TSB for 5 h at 37°C in a rotary shaker incubator (New Bruns- wick Sci. Co., New Brunswick, N J) at 90 rev./min. The bacteria were harvested by centrifuging (20000 ×g, 4°C, 10 min; Beckman Instruments Inc., J2-21, Palo Alto, CA), washed three times with phosphate-buffered saline (PBS; 8.1 mM Na2HPO4, 1.5 mM KHzPO4, 140 mM NaC1, 3 mM KC1, pH 7.2) and resuspended in PBS. To determine the effect of glucose depletion, all strains were grown in glucose-free TSB (GF-TSB, BBL). 0378-1097/83/0000-0000/$03.00 © 1983 Federation of European Microbiological Societies