Mikio Shimizu

Appearance of enterotoxigenic Escherichia coli in piglets with diarrhea in connection with feed changes.

Twelve weaned piglets (3‐week‐old) were divided into three groups according to the time of feed change and observed for diarrhea during the time they were 3 to 8 weeks of age. A total of 553 strains of Escherichia coli were isolated from rectal fecal samples and examined for heat‐labile (LT) and heat‐stable (ST) enterotoxins, pilus antigens (K88, K99, and 987P), hemolysin (Hly), raffinose utilization (Raf) and drug resistance. Enterotoxigenic and/or hemolytic E. coli strains appeared in the rectal feces of 5‐ to 6‐week‐old piglets with diarrhea in connection with feed change and changing temperatures. Most of the isolates showed multiple drug resistance to sulfonamides (Sa), streptomycin (Sm), chloramphenicol (Cp), tetracycline (Tc), kanamycin (Km), spectinomycin (Sp), ampicillin, and/or mercury. Enterotoxigenic E. coli isolates represented four phenotypes: K88+.LT+.Hly+.Raf+.(SaSmCpTcKmSp) (12 strains), K99+.ST+.Raf+.(TcKm) (7 strains), ST+.Raf+.(TcKm) (7 strains), and ST.+(SaSmKm) (25 strains). The drug resistance determinants were transferable concurrently and some of them mobilized the determinants for K88, LT, Hly, and Raf to an E. coli C strain.

Drug Resistance and R Plasmids in Bordetella bronchiseptica Isolates from Pigs

A total of 207 strains of Bordetella bronchiseptica isolated from pigs in 1978 and 1979 were tested for drug resistance and for the properties of their R plasmids. Apart from intrinsic resistance to spectinomycin, single (sulfadimethoxine), double (sulfadimethoxine and streptomycin), andt riple (sulfadimethoxine, streptomycin, and ampicillin) resistance were found in 54.1%, 1.0%, and 15.9% of the strains, respectively. All of the triple‐resistance determinants were associated with mercury resistance and were conjugative. pBB1, one of these R plasmids, was identified as Fi− (F) and Spp− (no suppression of phage multiplication) type, and as a member of incompatability group IncP. The single‐ and double‐resistance determinants were nonconjugative. pBB2, one of the double‐resistance determinants, was mobilized by an R plasmid, RP4, with the high efficiency of 80% and at a frequency of 3.3% without cotransfer of RP4. The molecular weight of pBB1 and pBB2 was estimated at 36 × 106 and 13 × 106 daltons, respectively, by electron microscopy and agarose gel electrophoresis. pBB1 had five cleavage sites for EcoRI endonuclease, and four sites for HindIII. pBB2 had two EcoRI sites, one HindIII, and one BamHI site. Cells carrying pBB1 or pBB2 produced enzymic activity that inactivated streptomycin in the presence of ATP.

MACROLIDE RESISTANCE IN STAPHYLOCOCCI

It is known that there are two types of resistance to macrolide (Mac) antibiotics and to lincomycin (LCM) in staphylococci, i.e., inducible and constitutive resistance. Among strains with inducible resistance, those in which erythromycin (EM) is only an active inducer are isolated most frequently from clinical specimens.4 These strains were first reported by Garrod2 and have been studied by many workers.3.4J5Je When these strains were treated with subinhibitory concentrations of EM, high resistance to both Mac and LCM appeared. The optimal concentration of E M as an inducer is about lo- M. Induced resistance was lost when the cells were cultured in inducer-free medium. Previously, we reported that constitutive resistant type mutants could be isolated from inducible strains on the plates containing leucomycin (LM) .3 From transductional analysis, it was found that the loci governing both inducibility and resistance to Mac antibiotics were cotransducible, and that the loci governing the resistance to both Mac and LCM in constitutive resistance could not be separated as far as we could determine.s The present paper describes the mechanism of inducible resistance to Mac antibiotics. MATERIALS AND METHODS