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In four patients with Pseudomonas aeruginosa infections, the infecting strain developed resistance to moxalactam during therapy with this drug. In addition, P. aeruginosa isolates from two of these four patients showed increased resistance to aminoglycosides. Isolates from a third patient acquired cross-resistance to other antipseudomonal ,3-lactams. with a final volume of 3 ml and a final inoculum of 105 colony-forming units (CFU) per ml. The minimal inhibitory concentration (MIC) was defined as the lowest antibiotic concentration preventing macroscopically detectable growth after 18 h of incubation at 35°C in air. Subcultures (0.01 ml) were made of all clear tubes to drug-free agar, and the minimal bactericidal concentration (MBC) was defined as the lowest concentration preventing growth upon subculture. This represented a 99.9o kill of the original inoculum (12). MICs or MBCs for posttherapy isolates were considered increased above results obtained with pretherapy isolates if they differed at least fourfold. Tests on pre-and posttherapy isolates were performed simultaneously. Results of susceptibility tests were interpreted according to criteria pubished by the National Committee for Clinical Laboratory Standards (10). For moxalactam, an organism was considered (i) resistant if the MIC was 264 ,ug/ml and (ii) susceptible if the MIC was c32 pLg/ml. ,B-Lactamase assays were performed by a spectrophotometric test as described previously (16). Enzymes were induced by growing the strains overnight on cefoxitin agar (16). Strains resistant to aminoglycosides were tested for inactivating enzymes by R. Hare (Schering Corp., Bloomfield, N.J.).Agarose gel electrophoress. To compare the plasmid profiles of the isolates, cultures were lysed by the method of Meyers et al.

Mice depleted of T-lymphocytes by thymectomy and irradiation (TXB) and immunologically competent mice were compared for gross and histological pathology as well as immune responses after cutaneous and/or intravenous challenge with Candida albicans. In response to a first cutaneous inoculation with viable Candida, TXB, sham-operated (SXB), and unmanipulated (normal) mice, all developed lesions of comparable size, duration, and histopathology. When challenged a second time cutaneously, normal and SXB mice developed lesions which were greatly increased in size when compared with those produced by a first cutaneous infection, whereas TXB mice developed lesions comparable in size to those initiated by the first infection. Histologically, the first and second lesions in all animals were acute abscesses predominantly comprised of polymorphonuclear leukocytes. The larger second lesions in SXB and normal mice were accompanied by detectable circulating antibody and by delayed hypersensitivity. Neither circulating antibody nor delayed hypersensitivity were stimulated in the TXB mice. When challenged intravenously, all previously uninfected mice, regardless of T-cell status, were equally susceptible to C. albicans. Contrary to SXB or normal mice, however, TXB mice which had been infected cutaneously were not more resistant to a subsequent intravenous challenge as judged by 6-week survival. The results suggest that T-cells do not play a significant role in innate resistance of mice to systemic candidiasis, but that such cells are important in the development of acquired resistance.Candida albicans (Robin) Berkhout is a fungus which does not usually invade the normal host, although it is a member of the normal human microbial flora. The mechanism by which healthy individuals resist invasion is unclear, but it is generally believed that cell-mediated immunity, and thus the T-lymphocyte, is an important factor in acquired resistance. The latter statement is based primarily on clinical evidence, in that individuals with immunodeficiency diseases (3,18,22,32,35) or with diseases for which the treatment itself is immunosuppressive (1, 17, 20, 24, 28, 37) are particularly susceptible. Experimental evidence to corroborate the clinical evidence is somewhat meager.Recently, however, a natural model of immunological modification, viz., the nude or athymic mouse, has been used to investigate innate resistance to C. albicans. Cutler (10) inoculated nude mice with large doses of C. albicans intravenously and observed that such mice were more t Present address: Mt. Sinai Hospital, Department of Microbiology, New York, NY 10029.

Cutaneous infection of mice with Candida albicans elicited a predominantly acute inflammatory response, stimulated the production of precipitating antibodies, and conferred protection against subsequent intravenous challenge with the same organism. The acute inflammatory skin reaction seen after cutaneous infection suggested a predominantly humoral response to Candida. Animals infected cutaneously a second time with viable C. albicans developed larger skin lesions than animals infected only once, and the twice-infected animals were more resistant to an intravenous challenge as well. The cutaneous inoculation of mice with heat-killed C. albicans was less effective in stimulating antibody production, in eliciting the inflammatory response, and in inducing a protective response demonstrable by intravenous challenge with viable Candida. This model of experimental candidiasis represents a reproducible means of studying a protective immune response to the organism. times with nonpyrogenic physiological sodium chloride (NPS) (Cutter Laboratories, Berkeley, Calif.). More than 95% of the cells in such suspensions were blastospores. The cells were then quantitated in a hemacytometer, and the counts were verified by diluting and plating the same suspensions with which animals were inoculated. Killed cells for animal inocula-499 on July 16, 2020 by guest http://iai.asm.org/ Downloaded from on July 16, 2020 by guest http://iai.asm.org/ Downloaded from