LUCRĂRI ŞTIINłIFICE MEDICINĂ VETERINARĂ VOL. XL, 2007, TIMIŞOARA 105 THE ANTIBIOTIC RESISTANCE PHENOMENON IN SALMONELLA STRAINS ISOLATED FROM PIG ANCA MĂRCULESCU, GH. RĂPUNTEAN, N.A. OROS, M. CERNEA University of Agricultural Sciences and Veterinary Medicine, Cluj-Napoca Summary Antibiotics from the groups of aminopenicillins, cephalosporins, aminogycosides, polymyxins, fluoroquinolones, tetracyclines and potentate sulfonamides were tested on 16 bacterial strains from the genus Salmonella, isolated from pig that were diagnosed with enteritis. Antibiotic resistance had been observed for streptomycin, in all bacterial strains. A high percentage of resistance was noticed for tetracycline (87.50%) and for potentate sulfonamide (68.75%), the last one having also intermediate values (6.25%) – only 25% of the strains being susceptible. The bacterial strains showed resistance also in some aminoglycosides and aminopenicillins, but in a lower percentage: spectinomycin – 31.25%, neomycin – 25%, gentamicin, ampicillin – 18.75%, amoxycillin – 12.5%. Intermediate values, in a pretty high percentage (31.25%), were registered for neomycin and spectinomycin. From the group of cephalosporins, ceftiofur had had maximum efficiency, meanwhile the use of cephalotin determined 87.5% susceptibility and 6.25% intermediate values in the Salmonella strains. No resistance was noticed for colistin and enrofloxacin. Antibiotic therapy has made many advances that have given veterinary medicine a large number of effective drugs. This use led to the selection of resistant forms of microorganisms to antibiotics, which is a natural and unavoidable phenomenon (FVE, 2005). Antibiotic resistance is a world-wide problem and is worse in some parts of the world than others. In pig medicine, antibiotics are used to restore the health and welfare of pigs in the face of disease challenge (Burch, 2005). The range of antibiotics currently available for use is relatively limited. Veterinarians regularly monitor the sensitivity to antibiotics of organisms isolated from sick pigs to ensure that the antibiotics used will be efficient (Potter et al., 2002). Antimicrobial resistance is a source of major concern in the case of zoonotic pathogens such as Salmonella. However, widespread and extensive use of a particular antibiotic does not always lead to resistance. Therefore, it is very important to determine the antibiotic sensitivity for the Salmonella strains. Materials and methods A variety of laboratory techniques can be used to measure the in vitro susceptibility of bacteria to antimicrobial agents. In this study we used agar disk diffusion method for testing the bacterial pathogens. The materials used for the antibacterial diffusion studies were: 24 h broth bacterial culture (37°C) (Răpuntean Gh., 1999), agar medium and antibiotic discs.