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We monitored the presence of Listeria monocytogenes in environmental sources and evaluated phenotypic and molecular characteristics of the isolates recovered. L. monocytogenes was isolated in 12 of the 107 samples from wild and farm environments, and from vegetation. Most isolates (83.3%) were of serotype 1/2a and the remainder (2) were of serotype 4b. All 12 isolates were susceptible to the whole range of antimicrobials tested. These 12 strains were carriers of the virulence genes prfA, hlyA, actA, plcA, plcB, inlA, inlB, inlC, and inlJ. The detection of the inlA gene in 4 strains using the PCR-RFLP suggests the potential of some of these strains to penetrate into epithelial cells of the intestinal barrier. Macrorestriction analysis also confirmed clonal identity of some environmental isolates with food and human isolates. These results indicate that the external environment is a source of potentially pathogenic strains of L. monocytogenes.

Marker exchange mutagenesis is a fundamental approach to understanding gene function at a molecular level in bacteria. New plasmids carrying a kanamycin resistance gene or a trimethoprim resistance gene were constructed to provide antibiotic resistance cassettes for marker exchange mutagenesis in Ralstonia solanacearum and many antibiotic-resistant Burkholderia spp. Insertion sequences present in the flanking sequences of the antibiotic resistance cassette were removed to prevent aberrant gene replacement and polar mutation during mutagenesis in wild-type bacteria. Plasmids provided in this study would be convenient for use in gene cassettes for gene replacement in other Gram-negative bacteria.

Abstarct Trimethoprim-potentiated sulphonamides (TPS) are among the most frequently administered antimicrobials in equine medicine. Anecdotally, TPS has been implicated as a cause of mild to moderate diarrhea in horses. The purpose of this study was to document the prevalence of diarrhea in horses receiving TPS, to characterize the severity of the diarrhea, and to identify any other factors associated with the development of diarrhea. A 2–part study was designed to identify the prevalence of diarrhea associated with TPS in our clinic population. Part I was a case-control retrospective study of 135 records over a 10.5–year period from January 1, 1980 through June 30, 1990. Part II was a historical cohort study of 784 records over a 37–month period from July 1, 1990 through July 31, 1993. There was no significant difference in the occurrence of diarrhea associated with TPS therapy in either study. The occurrence of diarrhea was 21% and 3% in parts I and II, respectively. Significant factors identified in association with diarrhea in part I were duration of hospital stay, and antibiotic therapy other than TPS or penicillin. Significant factors identified in part II included other antibiotic therapy, penicillin therapy, and combined penicillin and TPS therapy. Diarrhea does occur after the administration of antibiotics, most likely because of the alteration of the patient's normal intestinal flora. Diarrhea was noted in association with administration of TPS in this study; however, its prevalence was not significantly different than that in horses receiving other antibiotics, such as penicillin and its derivatives. J Vet Intern Med 1996;10:258–264. Copyright © 1996 by the American College of Veterinary Internal Medicine.

Hepatic necrosis in association with trimethoprim‐sulfonamide (TMS) combination therapy was diagnosed in 4 dogs based on history, clinical presentation, and examination of histopathologic specimens collected postmortem. Duration of TMS therapy prior to onset of clinical signs ranged from 4 to 30 days. The dose of TMS ranged from 18 mg/kg to 53 mg/kg bid. Despite supportive medical therapy, all dogs died or were euthanized due to hepatic failure. This report highlights the potential for hepatotoxicity during TMS therapy. Duration of therapy, type of TMS combination, and dose did not appear related to the development of toxicity. The low number of dogs affected suggests an idiosyncratic drug reaction.

The work was aimed at estimating the detection limits of 21 antibiotics (beta-lactam antibiotics, cephalosporins, aminoglycosides, macrolides and others) by means of three types of detection systems (disk diffusion method with Bacillus stearothermophilus var. calidolactis C 953, Delvotest SP and Penzym S 100) and to verify their sensitivity in the evaluation of the admissible maximum residual limits (MRL). The high sensitivity and the good correlation of results have been achieved mainly by applying the rapid methods, i.e. Delvotest SP and Penzym S 100, versus the less sensitive disk diffusion method. In the next stage of the work, detection limits of the mutual combinations of antibiotics in milk were estimated. In a model experiment, synergic effects between ampicillin and oxacillin, cefuroxime and trimethoprim and between cephalosporins (combination of cefazolin with cefoperhazon) were observed.