SYNOPSIS Pseudomonas putrefaciens, a strongly H2S-producing pseudomonad, was isolated from 10 human infections over a two-year period. In one patient the organism was repeatedly isolated from a phlegmone developing in the depth of a varicose leg ulcer. This is the first report on the occurrence of Ps. putrefaciens in humans outside the USA and the first to provide the detailed account of a clinical observation where the opportunistic pathogenic role of this unfamiliar organism has been sufficiently documented.Data are presented on the bacteriological properties and on the antibiotic sensitivity of Ps.putrefaciens.Although Pseudomonas aeruginosa is by far the most common pathogenic species of the genus Pseudomonas, several other species have recently attracted the attention of the clinical bacteriologist. Recognition of these species has long been hampered by the lack of a clear classification system for nonfermentative Gram-negative bacteria and by the considerable confusion in their nomenclature. Improvements in bacteriological methods and the increased incidence of opportunistic and nosocomial infections have stimulated interest in Pseudomonas species other than Ps. aeruginosa. Simple criteria for characterization of unusual Pseudomonas species have been presented in a series of well-documented papers (Gilardi, 1971(Gilardi, , 1972Von Graevenitz, 1973).Although easy to recognize because of its abundant hydrogen sulphide production, Ps. putrefaciens is one of the least well-known pseudomonads in medical bacteriology, and we have seen no mention of the isolation of this species in the European literature.The first human isolates of a nonfermenting, H2S-producing Gram-negative rod with polar flagellation were described by King in 1964, who gave them the provisional label 'lb'. In 1970, von Graevenitz and Simon reported 13 isolations of the same microorganism from different clinical speciRequests for reprints should be addressed to Professor J.

54 cases of erythema nodosum, seen in the Department of Dermatology at the St. Raphael University Hospital, Louvain, were reviewed for their possible aetiology. A search for Yersinia enterocolitica (Y.e.) agglutinins was performed in 21 patients of whom 8 had significant serum antibody titres. These cases are presented and discussed. Gastro-intestinal symptoms, preceding by 2 weeks the erythema nodosum, are strongly suggestive for an aetiologic link with Y.e. Our observations confirm and extend to this part of Europe, the experience of other, mainly Scandinavian, authors.

The first well-documented case of an infection of venous phlegmonous ulcers by Pseudomonas putrefaciens is presented. The significance in dermatology is discussed.

Pseudomonas putrefaciens has been presented as an opportunistic pathogen in a few isolations from humans. This is the first documented report of a local infection of P. putrefaciens complicated by invasion of the blood stream. The organism was twice isolated from the blood culture and once from the wound exudate of a 73-year-old woman hospitalized for extensive ulcerations on the legs. Parenteral ampicillin and gentamicin together with local antiseptic treatment led to an uneventful recovery.