Staphylococcal slime: a cautionary tale

Abstract

Slime production by Staphylococcus epidermidis may be important in the adherence to and colonization of biomedical devices, and slime has been proposed to have various effects on the immune system. Attempts were made to isolate, purify, and chemically characterize slime from S. epidermidis cultivated under fluid on tryptic soy broth-agar medium. "Crude slime" from slime-producing strain RP-12 was characterized by a high galactose content. Similar materials in similar yields were isolated from slime-producing strain Kaplan, a non-slime-producing mutant, Kaplan-6A, and stérile medium controls, suggesting that crude slime was derived mainly from the medium. The occurrence of D-and L-galactose and pyruvate and sulfate residues and methylation analysis of these crude slime preparations, monitored by gas-liquid chromatography and mass spectrometry, showed that the agar was the main source of crude slime, suggesting that the preparation was largely an artifact of the growth and isolation procedures. Similar high-galactose-content preparations from both S. epidermidis and Staphylococcus aureus, assumed to be bacterial products and with a variety of biological activities, have been described by other investigators. Growth attached to a solid surface appears to be important for slime production. An accumulation of turned-over cell surface molecules and released macromolecules such as DNA may contribute to slime production. Avoidance of agar and development of a chemically defined medium for slime production are recommended for further studies.

Influence of nutrient media on the chemical composition of the exopolysaccharide from mucoid and non-mucoid Pseudomonas aeruginosa

“…In the literature, many authors stress the influence of the in vitro conditions of experiments on the biochemical constitution of the bacteria, especially capsule formation [5,6,27] and the importance of the solid media in duplicating in vivo conditions [28]. Another advantage of a solid medium recovered by a cellophane membrane, as we used, is to avoid contaminants from medium components.…”

“…The importance of a chemically defined medium for slime production has been demonstrated in studies of Staphylococcus epidermidis slime [5,6]. In previous works about alginate from P. aeruginosa, the strains used as the source of alginate have been grown in various liquid or solid media, and the extraction and purification procedures have also differed widely resulting in varying results for the chemical composition [7][8][9][10][11].…”

“…l. GLC analysis of the methylglycosides from the total EPS extracted from the nM-CF strain grown for 72 h on PIA medium (a) after the 1st methanolysis; (b) after reduction and the 2nd methanolysis. (1) Rha, (2) Man A, (3) Man, (4) gal,(5) glc, (6) gaiN, (7) glcN, (8) 1-6 anhydro-gul, (9) gul.…”

The slime of coagulase-negative staphylococci: Biochemistry and relation to adherence

“…In animal and in vitro experiments, crude slime preparations have been reported to interfere with host defence mechanisms [81,82]. However, the results of the studies of Drewry et al [77] and Hussain et al [34] demand the reassessment of the suggested biological properties of slime [44]. Slime prepared by growing bacteria on complex media solidified with agar has been used in many in vitro and animal studies [81][82][83][84][85][86].…”

“…Such results confirm that much of the material which hitherto has been regarded as staphylococcal slime is really agar. Drewry et al [77] have independently reported their suspicion that slime isolated from media solidified with agar is very heavily contaminated with agar. Thus the use of a chemically defined medium (if it is solidified with agar) does not completely overcome the problem of spurious high molecular mass material, because the agar remains a potential source of foreign material.…”