Resistance of gram-negative bacteria to gentamicin has become an increasingly common problem among clinical isolates from human beings. Susceptibility of isolates from horses to gentamicin and amikacin was evaluated for the period from July, 1983 to June, 1985. All isolates of Escherichia coli, and species of Enterobacter, Klebsiella, Proteus, and Pseudomonas examined were susceptible to amikacin, except 2 of the 46 Pseudomonas isolates. In contrast, 13 to 50% of isolates were resistant to gentamicin. Escherichia coli, and Klebsiella, Proteus, and Enterobacter species isolates were highly significantly more susceptible to amikacin (P less than 0.01) than to gentamicin. Pseudomonas spp (P = 0.13) were not significantly different in susceptibility to the 2 drugs. There was significant variation among genera in their susceptibility to gentamicin (P = 0.002), primarily because of the frequency of resistance in isolates of Klebsiella spp and Proteus spp, compared with the other 3 organisms (E coli, Enterobacter spp, and Pseudomonas spp). There was no significant difference of susceptibility to amikacin among the genera studied (P = 0.06).

This paper dealt wih the distribution of Shigella spp. on 5 piggeries in Taegu and Kyongbuk during the period from August to October 1987. Isolated Shigella were examined for serogrouping, antimicrobial drug resistance and detection of R plasmid. Genetic properties of R plasmid in Shigella were examined for fertility inhibition (F1) and gel electrophoresis was performed for the isolation of plasmid DNA. Of total 2,978 samples from 5 piggeries, 82 strains (2.8 %) of Shigella spp. were isolated from 82 samples. The isolated strains were identified as S. dysenteriae (60 strains), S. flexneri (20 strains) and S. sonnei (2 strains). Of the 82 strains examined 67 (95.1 %) were resistant to one or more antibiotics, such as ampicillin (Am), chloramphenicol (Cm), kanamycin (Km), nalidixic acid (Na), rifampicin (Rf), streptomycin (Sm), sulfademethoxine (Su), and tetracycline (Tc) and higher resistance to Su (90.2 %), Sm (63.4 %) and Tc (63.4 %). Of the 78 resistant Shigella strains 26 (33.3 %) harbored conjugative R plasmids and the transfer frequency of Sm (50.0 %), Cm (33.3 %) resistance was much higher than that of the other drug resistance. The most common resistant patterns were SmSuTc, Su and AmSmSuTc. Out of the 26 Shigella R plasmids examined for Fi, 14 (53.8 % were Fi + and the remainder were Fi-. The plasmid DNA profiles in Shigella spp. (9 strains) isolated from pigs were confirmed as being 2 to 9 fragments by the gel electrophoresis. Their molecular size ranged 2.17 to 87.62 kilobase (Kb). All strains of Shigella spp. consisted in 15.4 Kb plasmids.