Chloramphenicol resistance plasmids in Escherichia coli isolated from diseased piglets

Quantifying Attachment and Antibiotic Resistance of from Conventional and Organic Swine Manure

Broad-spectrum antibiotics are often administered to swine, contributing to the occurrence of antibiotic-resistant bacteria in their manure. During land application, the bacteria in swine manure preferentially attach to particles in the soil, affecting their transport in overland flow. However, a quantitative understanding of these attachment mechanisms is lacking, and their relationship to antibiotic resistance is unknown. The objective of this study is to examine the relationships between antibiotic resistance and attachment to very fine silica sand in collected from swine manure. A total of 556 isolates were collected from six farms, two organic and four conventional (antibiotics fed prophylactically). Antibiotic resistance was quantified using 13 antibiotics at three minimum inhibitory concentrations: resistant, intermediate, and susceptible. Of the 556 isolates used in the antibiotic resistance assays, 491 were subjected to an attachment assay. Results show that isolates from conventional systems were significantly more resistant to amoxicillin, ampicillin, chlortetracycline, erythromycin, kanamycin, neomycin, streptomycin, tetracycline, and tylosin ( < 0.001). Results also indicate that isolated from conventional systems attached to very fine silica sand at significantly higher levels than those from organic systems ( < 0.001). Statistical analysis showed that a significant relationship did not exist between antibiotic resistance levels and attachment in from conventional systems but did for organic systems ( < 0.001). Better quantification of these relationships is critical to understanding the behavior of in the environment and preventing exposure of human populations to antibiotic-resistant bacteria.

Antimicrobial drug resistance in porcine enterotoxigenic Escherichia coli of 0-group 149 and non-enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) strains (104) and 96 non-ETEC, all isolated from herds with piglet diarrhea in 1981 and 1982, were investigated with regard to antimicrobial drug resistance and colicinogeny. Eighty strains (77%) of the ETEC were drug resistant as compared to 66 strains (69%) of the non-ETEC. There were no significant differences between ETEC and non-ETEC in the frequencies of the drug resistance determinants investigated, except for tetracycline, to which 51 (49%) of the former and 30 (31%) of the latter strains were resistant (0.05 greater than P greater than 0.01). Of all strains 116 (58%) were resistant to streptomycin, 93 (47%) to sulphadimidin, 81 (41%) to tetracycline, 20 (10%) to trimethoprim, 14 (7%) to ampicillin, 11 (6%) to neomycin, 6 (3%) to chloramphenicol and none to nitrofurantoin. The frequencies of the different drug resistance determinants correlated well with the total amount of active substance of each drug used in farm animals in Sweden in 1981. Of the ETEC, 97 (93%) were colicinogenic whereas only 13 (14%) of the non-ETEC were colicinogenic.

Prevalence and molecular epidemiology of antibiotic-resistant Salmonella typhimurium and Salmonella dublin in Danish cattle

Among 130 strains of S. typhimurium and 191 strains of S. dublin, all from cattle, 80% and 63%, respectively, were resistant to one, two or three antibiotics. Mono-resistance to sulphonamides was most common. Plasmid load was analysed by conjugation, transformation, extraction of plasmid DNA and subsequent electrophoresis in agarose gels. Plasmid DNA from 38 strains was further analysed by restriction with endonuclease EcoR1. On the basis of this, the strains were classified into four groups. Two groups held S. typhimurium, one held S. dublin and one group held both serotypes. This suggests that dissemination of strains and plasmids mainly occurs through clonal spread of strains. However, plasmid transfer per se also takes place, as exemplified by the fact that indistinguishable plasmids were found in two different serotypes. Strains of one group had contaminated a water-course. Strains of this group were furthermore isolated from humans in the same area as the infected cattle. Strains of this group had an R pattern and a phage-type similar to the R pattern and phage-type of the early isolates of a strain that became epidemic in British cattle. It is discussed whether Denmark, which was previously almost free of cattle salmonellosis, is experiencing the first warnings of an epidemic similar to the one in the UK.

Persistence and spread of a chloramphenicol resistance-mediating plasmid in antigenic types of Escherichia coli, pathogenic for piglets

All chloramphenicol-resistant Escherichia coli strains isolated from piglets in the State veterinary Serum Laboratory, Copenhagen, in 1974-1975 harbored plasmids of IncFII group with largely the same resistance markers. Two strains from 1978 carried plasmids with similar characters. Restriction enzyme analysis of DNA from these plasmids with restriction endonucleases EcoRI, BglII, and PstI shows that the Cm plasmids are extremely closely related; but the patterns obtained (particularly from PstI digests) enable the classification of the plasmids into groups. These bear a strong relation to time and place of isolation so that plasmids isolated on the same farm belong to the same group even when their host strains are of different antigenic types. It is concluded that these plasmids have evolved from a single plasmid.

New translocation sequence mediating tetracycline resistance found in Escherichia coli pathogenic for piglets

A discrete piece of deoxyribonucleic acid coding for tetracycline (Tc) resistance was found to move from one R plasmid to another in an Escherichia coli strain which is pathogenic for piglets. Since this phenomenon took place also in rec strains, the Tc segment was classified as a transposon and called Tn804. Restriction enzyme analysis with EcoRI, BglII, and HindIII indicated that Tn804 is related to Tn10, a well-known transposon that codes for resistance to tetracycline. Hybridization between plasmids carrying the two transposons provided proof of homology between Tn10 and prt of Tn804. Electron microscopic studies showed a transposon-like structure composed of one loop-stem structure with inverted repetitions of approximately 0.9 megadaltons inserted into the loop of a second loop-stem structure. It is suggested that Tn804 is composed of Tn10 plus another transposable sequence.

Incidence of antibiotic-resistant Escherichia coli associated with frozen chicken carcasses and characterization of conjugative R plasmids derived from such strains

Escherichia coli were isolated at concentrations of about 10(2)/ml from the fluid obtained after thawing each of five frozen chicken carcasses. Between 13 and 89% of the E. coli were resistant to mercury(II) or to at least one of eight antibiotics tested. Multiple resistance was more common than single resistance, and resistances to tetracycline, streptomycin, sulfathiazole, or chloramphenicol were more frequently encountered than was resistance to ampicillin or mercury(II). Resistance to kanamycin, gentamicin, or trimethoprim occurred rarely. Upwards of 30% of the E. coli apparently carried conjugative plasmids and could transfer at least one of their resistance determinants to E. coli K-12. Twenty-five conjugative R plasmids obtained in this way were characterized within strain K-12 by a variety of phenotypic criteria. Twenty could be assigned to the incompatibility groups Inc X, Inc N, Inc FI, or Inc I alpha.