Staphylococcus epidermidis: commensal or pathogen?
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Biomedical subjects
Publications and source records attributed to W C Noble.
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Acquisition of resistance to neomycin, gentamicin, fusidic acid, or clindamycin has been observed in three strains of Staphylococcus aureus and data from three patients infected with these strains are presented in detail. Clindamycin resistance followed the expected pattern by appearing in a strain of Staph. aureus with dissociated resistance to erythromycin after treatment with erythromycin and clindamycin. Low-level resistance to fusidic acid appeared in two strains in the apparent absence of exposure to that antibiotic. Labile neomycin resistance was encountered in a previously sensitive strain after topical neomycin therapy. Gentamicin resistance appeared in all three strains after topical therapy. In all three strains, a labile resistance (presumably plasmid-mediated) occurred with minimum inhibitory concentrations (MICs) of 64-128 microgram/ml but in one strain a stable resistance with MIC over 3000 microgram/ml appeared.
Patients whose skins are colonized with Staphylococcus aureus resistant to penicillin and/or tetracycline may carry variants that are sensitive to these antibiotics. The skin of most individuals yields the fully resistant type as the predominant flora and the nose harbours the sensitive version. This probably represents plasmid loss in vivo. The plasmid-positive cells were not more resistant to desiccation or more deeply pigmented than plasmid-negative cells. The explanation for such distributions is unknown.
Thirty-nine clinically uninflamed cysts of the three most common varieties, epidermoid cysts, trichilemmal cysts and steatocystoma multiplex were removed under sterile conditions and the contents cultured under aerobic and anaerobic conditions. Seventy-three percent of epidermoid cysts grew significant numbers of organisms whereas none of the trichilemmal cysts did so. The organisms found were the common skin commensals, Staphylococcus epidermidis biotype I, anaerobic Gram positive cocci of the Gaffya type and Corynebacterium acnes Type I. This indicates that cysts which clinically have a punctum, namely epidermoid cysts, may become colonized with surface bacteria under normal circumstances. If they become colonized with pathogenic bacteria they become inflamed, a not uncommon clinical picture. The results from patients with steatocystoma multiplex were difficult to interpret because of the small numbers of patients involved and the unusual clinical appearance they presented.
Dispersal of skin micro-organisms into the air during undressing was studied in 72 members of surgical and nursing staff. Few pathogens were found to be dispersed. Males dispersed more normal skin organisms than did females. Males were also more heavily colonised than females, and sex differences in dispersal diminished when allowance was made for the denser colonisation of males. Dispersal was correlated most strongly with the counts on the thighs and abdomen in males but on the shins in females.
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Endemic infection in male surgical wards has been studied during three periods. There was some infection due to gram-negative bacilli, though Staphylococcus aureus remained as the single most important pathogen even in the absence of epidemic spread. Beta haemolytic streptococci were isolated in large numbers from the lesions of four patients with deep wound infection. Changes introduced in the pattern of post-operative care reduced sepsis due to Staph. aureus, reduced the severity of wound infection and apparently decreased the need for antibiotic therapy. Patients who became infected were retained in hospital longer than those who escaped clinically apparent infection.
A microbiologic technique for the assay of methotrexate (MTX) in urine, serum, erythrocytes, feces, and skin is described. The accuracy of the method equals that of routine microbiologic assays of folic acid. Important differences in serum MTX levels in psoriatic patients during the 24 hours after standardized intravenous and intramuscular administration were demonstrated. Repeated intravenous doses tended to be cleared from the blood univormly. After oral doses many patients achieved peak serum levels within 2 hr. with fall of level by 4 hr. Others achieved lower levels and responded less well clinically. Persistence of high serum levels at 24 and 48 hr did not confer obvious clinical benefit or necessarily give rise to by renal function when the creatinine clearance was greater than 50 ml/min. However, impaired renal function was clearly correlated with slow clearance. Routine measurement of MTX blood levels is of value in patients with suspected malabsorption or partial renal failure.
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During investigations of the microbial flora of the skin over haemodialysis shunt sites it has not proved possible to predict clinical infection by a preceding colonization of the shunt site with a pathogenic organism. The normal non-pathogenic flora of the sites is not specifically related to the flora of other sites on the body though Staphylococcus aureus on a shunt site appeared to be acquired principally from the nose when the shunt was in the arm or from the perineum when the shunt was in the leg. Cimino shunt sites had a greater density of organisms than did Scribner shunt sites; this may be related to the disinfection procedures.
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