Spread of Staphylococcus aureus resistant to penicillin and tetracycline within and between dairy herds.

One hundred and seven bovine isolates of penicillin and tetracycline resistant Staphylococcus aureus, recovered from 25 different dairy herds in various parts of Norway, were characterized using antimicrobial susceptibility testing, multilocus enzyme electrophoresis, ribotyping, plasmid analysis and serotyping of capsular polysaccharide. Forty-one isolates from one particular herd, 37 isolates from 5 herds that used a common pasture and milking parlour in summer and 21 isolates from 12 herds in 8 different counties belonged to the same strain. The remaining 8 isolates, which originated from herds in 5 different counties, were assigned to 6 different strains. Seven out of these 8 isolates had the same plasmid restriction profile. In conclusion, penicillin and tetracycline resistant S. aureus occurring in dairy herds in Norway mainly seems to represent one particular strain that has achieved widespread distribution or belong to one of several different strains carrying identical plasmids.

Horizontal transfer of a multi-drug resistance plasmid between coliform bacteria of human and bovine origin in a farm environment.

Multi-drug-resistant coliform bacteria were isolated from feces of cattle exposed to antimicrobial agents and humans associated with the animals. Isolates from both cattle and humans harbored an R plasmid of 65 kb (pTMS1) that may have been transferred between them due to selective antibiotic pressure in the farm environment.

Comparison of genes involved in penicillin resistance in staphylococci of bovine origin.

Ten penicillin-resistant and -susceptible staphylococci, isolated from bovine mastitis milk, were studied for the presence of genes that are, or may be, involved in resistance against penicillin. The repressor (blaI), antirepressor (blaR1), and structural (blaZ) genes of the beta-lactamase-operon were found to be closely linked in all penicillin-resistant strains. The beta-lactamase gene cluster was more commonly located on chromosomal rather than plasmid DNA in the strains studied. The transposase (p480) gene, which has been identified in the Staphylococcus aureus beta-lactamase transposon Tn552, was found in only one single penicillin-resistant S. aureus strain. The other penicillin-resistant S. aureus isolates contained IS1181 in close location with the beta-lactamase gene cluster. In only one S. haemolyticus isolate was the beta-lactamase gene cluster found in close association with IS257. Penicillin-resistant S. aureus strains, which were additionally resistant to tetracycline, contained IS257 in close association with the tetracycline resistance gene (tetK). Sequence analysis of blaI, blaR1, and blaZ in two penicillin-resistant S. aureus strains revealed 94-96% sequence homology with bla in staphylococci of human origin. The results indicate a predominance of class I bla transposons rather than Tn3 family class II transposons in the isolates used in this study.

Cloning and nucleotide sequence of the DNA gyrase gyrA gene from the fish pathogen Aeromonas salmonicida.

The DNA gyrase gyrA gene from the fish pathogen Aeromonas salmonicida 2148/89 was cloned, and the nucleotide sequence was determined. An open reading frame of 2,766 nucleotides was identified and was found to encode a protein of 922 amino acids with a calculated molecular mass of 101.1 kDa. The derived amino acid sequence shared a high degree of identity with other DNA gyrase A proteins, in particular, with other gram-negative GyrA sequences. When the amino acid sequence of A. salmonicida GyrA was compared with that of Escherichia coli GyrA, a number of conserved residues were present at identical coordinates, including the catalytic Tyr residue at position 122 (Tyr-122) and residues whose substitution confers quinolone resistance, notably, Ser-83, Ala-67, Gly-81, Asp-87, Ala-84, and Gln-106. An intragenic region corresponding to 48 amino acids, which is not present in E. coli or other bacteria, was identified in the C-terminal part of A. salmonicida GyrA. This intragenic region shared sequence identity with various DNA-binding proteins of both prokaryotic and eukaryotic origins.

gyrA mutations in quinolone-resistant isolates of the fish pathogen Aeromonas salmonicida.

gyrA mutations in quinolone-resistant isolates of Aeromonas salmonicida have been detected by using PCR to amplify the quinolone resistance-determining region of gyrA and subsequent cloning and sequencing of PCR products. Comparison of nucleotide and derived amino acid sequences of PCR products from quinolone-susceptible and -resistant bacteria revealed a serine 83-to-isoleucine substitution in the gyrase A protein of resistant isolates. One of the resistant isolates differed from the other by a two- to fourfold-higher MIC of the fluoroquinolone enrofloxacin and carried an additional alanine 67-to-glycine substitution, which may contribute to the higher level of resistance.

Temperature-dependent in vitro antimicrobial activity of four 4-quinolones and oxytetracycline against bacteria pathogenic to fish.

The in vitro antimicrobial activities of oxolinic acid, flumequine, sarafloxacin, enrofloxacin, and oxytetracycline against strains of bacteria pathogenic to fish (Aeromonas salmonicida subsp. salmonicida, atypical A. salmonicida, Vibrio salmonicida, Vibrio anguillarum, and Yersinia ruckeri) were determined at two different incubation temperatures, 4 and 15 degrees C, by a drug microdilution method. The main objective of the study was to examine the effect of incubation temperature on the in vitro activities of 4-quinolones and oxytetracycline against these bacteria. When tested against A. salmonicida subsp. salmonicida, all of the quinolones examined had MICs two- to threefold higher at 4 degrees C than at 15 degrees C. Similarly, 1.5- to 2-fold higher MICs were recorded for all of the quinolones except sarafloxacin at 4 degrees C than at 15 degrees C when the drugs were tested against V. salmonicida. In contrast to those of the quinolones, the MICs of oxytetracycline were two- to eightfold lower at 4 degrees C than at 15 degrees C against all of the bacterial species tested. Of the antimicrobial agents tested against the bacterial species included in the study, enrofloxacin was the most active and oxytetracycline was the least active. Sarafloxacin was slightly more active than flumequine and oxolinic acid, especially against oxolinic acid-resistant A. salmonicida subsp. salmonicida strains.

Physical map of the Bacillus cereus chromosome.

A physical map of the Bacillus cereus chromosome has been constructed by aligning 11 NotI fragments, ranging in size from 200 to 1,300 kilobases. The size of the chromosome is about 5.7 megabases. This is the first Bacillus genome of which a complete physical map has been described.