A total of 110 staphylococcal isolates from human skin were found to express a novel type of erythromycin resistance. The bacteria were resistant to 14-membered ring macrolides (MIC 32-128 mg/l) but were sensitive to 16-membered ring macrolides and lincosamides. Resistance to type B streptogramins was inducible by erythromycin. A similar phenotype, designated MS resistance, was previously described in clinical isolates of coagulase-negative staphylococci from the USA. In the UK, MS resistance is widely distributed in coagulase-negative staphylococci but was not detected in 100 erythromycin resistant clinical isolates of Staphylococcus aureus. Tests for susceptibility to a further 16 antibiotics failed to reveal any other selectable marker associated with the MS phenotype. Plasmid pattern analysis of 48 MS isolates showed considerable variability between strains and no common locus for the resistance determinant. In one strain of S. epidermidis co-resistance to tetracycline, penicillin and erythromycin (MS) was associated with a 31.5 kb plasmid, pUL5050 which replicated and expressed all three resistances when transformed into S. aureus RN4220. The MS resistance determinant was localised to a 1.9 kb fragment which was cloned on to the high-copy-number vector, pSK265. A constitutive mutant of S. aureus RN4220 containing the 1.9 kb fragment remained sensitive to clindamycin. This observation, together with the concentration-dependent induction (optimum 5 mg/l of erythromycin) of virginiamycin S resistance suggests that the MS phenotype is not due to altered expression of MLS resistance determinants (erm genes) but probably occurs via a different mechanism.

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The extracellular lipids of the stratum corneum, which are comprised mainly of cholesterol, fatty acids, and ceramides, are essential for epidermal permeability barrier function. Moreover, disruption of the permeability barrier results in an increased cholesterol, fatty acid, and ceramide synthesis in the underlying epidermis. This increase in lipid synthesis has been shown previously to be due to increased activities of HMG-CoA reductase, acetyl-CoA carboxylase, fatty acid synthase and serine palmitoyl transferase, key enzymes of cholesterol, fatty acid, and ceramide synthesis, respectively. In the present study, we determined whether the mRNA levels for the key enzymes required for synthesis of these three classes of lipids increase coordinately during barrier recovery. By northern blotting, the steady-state mRNA levels for HMG-CoA reductase, HMG-CoA synthase, farnesyl pyrophosphate synthase, and squalene synthase, key enzymes for cholesterol synthesis, all increased significantly after barrier disruption by either acetone or tape stripping. Additionally, the steady-state mRNA levels of acetyl-CoA carboxylase and fatty acid synthase, required for fatty acid synthesis, as well as serine palmitoyl transferase, the rate-limiting enzyme of de novo ceramide synthesis, also increased. Furthermore, artificial restoration of the permeability barrier by occlusion after barrier disruption prevented the increase in mRNA levels for all of these enzymes, except farnesyl pyrophosphate synthase, indicating a specific link of the increase in mRNA levels to barrier requirements. The parallel increase in epidermal mRNA levels for the enzymes required for cholesterol, fatty acid, and ceramide synthesis may be due to one or more transcription factors that regulate lipid requirements for permeability barrier function in keratinocytes.

Cholesterol sulfate is a multifunctional sterol metabolite, produced in large amounts in squamous keratinizing epithelia. Because patients with recessive x-linked ichthyosis display not only a 10-fold increase in cholesterol sulfate, but also a 50% reduction in cholesterol, we assessed here whether cholesterol sulfate accumulation and/or cholesterol deficiency produce abnormal barrier function in recessive x-linked ichthyosis. Patients with recessive x-linked ichthyosis display both an abnormal barrier under basal conditions, and a delay in barrier recovery after acute perturbation, which correlate with minor abnormalities in membrane structure and extensive lamellar-phase separation. Moreover, both the functional and the structural abnormalities were corrected by topical cholesterol. Yet, topical cholesterol sulfate produced both a barrier abnormality in intact skin and extracellular abnormalities in isolated stratum corneum, effects largely reversed by coapplications of cholesterol. Together, these results suggest that cholesterol sulfate accumulation rather than cholesterol deficiency is responsible for the barrier abnormality. Despite the apparent importance of cholesterol sulfate-to-cholesterol processing for normal barrier homeostasis, neither steroid sulfatase activity nor mRNA levels are upregulated following acute perturbations. These results demonstrate both a potential role for cholesterol sulfate-to-cholesterol processing in normal permeability barrier homeostasis, and that basal levels of steroid sulfatase are sufficient to accommodate acute insults to the permeability barrier.

Lipase of Staphylococcus epidermidis 9 was purified from culture supernatant fluid. Two polypeptides (51 and 43 kDa) were detected by SDS-PAGE, of which the 43 kDa polypeptide reacted with anti-lipase serum. The S. epidermidis 9 lipase gene (gehC) was cloned in Escherichia coli and localized to a 2.1 kb sequence by subcloning and transposon mutagenesis. The nucleotide sequence of gehC (2064 nucleotides) was determined and the predicted amino acid sequence of the encoded lipase (77 kDa) identified. A 97 kDa lipase was detected in extracts of E. coli harbouring gehC and in post-exponential-phase culture supernatant fluids of S. epidevmidis 9. Data presented indicate that the lipase behaves anomalously during SDS-PAGE and that a pro-lipase is proteolytically processed in cultures of S. epidermidis 9 during growth.

Five independent clones of the Propionibacterium acnes P-37 lipase gene (gehA) were obtained in ischerichia coli, and the gene was localized to a 2.75 kb Xhol fragment by subcloning. The five clones were shown to contain the same gene by Southern blotting with a DIG-labelled probe to gehA. The nucleotide sequence of gehA was determined, and shown to contain a single ORF of 1017 kb, encoding a protein of 339 amino acids. The predicted molecular mass was 36 kDa. A 33 kDa (PAGE) radiolabelled polypeptide was detected from E. coli minicell preparations harbouring gehA, which could correspond to GehA after cleavage of the putative 26 amino acid residue signal peptide. gehA was overexpressed in E. coli under the control of the bacteriophage 17 promoter, and the corresponding polypeptide was found to be present in insoluble aggregates. Active lipase was produced when the overexpressing strain was incubated at a reduced temperature in the presence of sucrose. Purification of lipase from P. acnes culture supernatant fluids confirmed the production of a 33 kDa (PAGE) lipase.

The identification and molecular characterization of a previously unidentified lipase, gehD, from the human cutaneous commensal Staphylococcus epidermidis is reported. A lipase-GehC-deficient but otherwise isogenic mutant of S. epidermidis 9 was constructed by allele replacement. However, the mutant was found to retain 50 % of the wild-type lipase activity in liquid culture. Rescreening of a genomic library revealed the presence of a second lipase gene, gehD, which was subsequently mapped and sequenced. In common with other staphylococcal lipases, GehD appeared to be translated as a 650-700 amino acid precursor which is processed post-translationally to an extracellular mature lipase of 360 amino acids with a size of approximately 45 kDa. Comparison of the amino acid sequence of GehD with those of other staphylococcal lipases revealed a high level of conservation between the mature lipase domains of different species. By hybridization studies, both gehC and gehD genes were found to be present in S. epidermidis isolates from both clinical and non-clinical backgrounds, but neither hybridized to DNA isolated from other staphylococcal strains. Construction of a phylogenetic tree and calculation of amino acid sequence homologies between mature lipases, however, suggested that the lipases of S. epidermidis may be more closely related to those of Staphylococcus aureus than to each other.

Aims: To determine characteristics of the extracellular enzyme activity of Kytococcus sedentarius on human callus. Methods and Results: A concentrate of a continuous culture supernatant fluid of K. sedentarius, which had callus-degrading activity, was subjected to a series of chromatographic purification procedures. The enzyme activity was found to be attributable to two proteases. These were capable of degrading both native callus and extracted keratin polypeptides and were purified to homogeneity, as shown by SDS-PAGE with silver staining. The enzymes P1 and P2 were 30 kDa and 50 kDa in size with isoelectric points of 4AE6 and 2AE7, respectively. The optimum conditions for callus-degrading activity were 40°C, pH 7AE1 for P1 and 50°C, pH 7AE5 for P2. P2 displayed increased activity in the presence of 800 mmol l )1 NaCl and both enzymes were inhibited by PMSF (1 mmol )1 Phenylmethylsulphoryl fluoride) and 1 mmol l )1 EDTA. The main enzyme cleavage sites were Lys-Trp, Val-Lys, Gly-Asp and Asp-Arg, as determined after incubation of P1 and P2 with the b-chain of insulin. Conclusions: K. sedentarius produces two extracellular enzymes that independently degrade natural, insoluble human callus. Both enzymes are serine proteases and have cleavage preference sites that are present in a range of human keratins. Significance and Impact of the Study: The identification, in K. sedentarius cultures, of two enzymes which can degrade human callus strengthens the hypothesis that this organism is responsible for the pitting in human epidermis observed in pitted keratolysis. These enzymes may be of commercial use in the biodegradation of a range of keratin polymers, biological washing powders and in the treatment of unwanted callus on human skin.