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At least 1,621 records · Page 90Linked to original sources
PubMed2007

Tools for the genetic analysis of Mycoplasma.

The mycoplasmas have attracted much scientific attention since they contain the smallest known genomes of any independently viable bacterial species. However, the detailed genetic analysis of these bacteria has lagged behind the well-analyzed bacterial model organisms for a long time. This is due to the use of the UGA codon for tryptophan rather than as stop codon, which had often prevented the expression of full-length Mycoplasma proteins in heterologous hosts. Additionally, insufficient efficiency of homologous recombination prevented the targeted disruption of genes in some species such as M. pneumoniae whereas homologous recombination is operative in other mycoplasmas. Only recently, efficient screening systems for the use of transposon-based mutagenesis have been developed to circumvent this problem and to allow the targeted isolation of desired transposon insertion mutants. With the availability of several Mycoplasma genome sequences, artificial plasmids based on the chromosomal origin of replication were constructed that can now be used for complementation studies and for the stable introduction of foreign genetic material. In this review, we give an overview on recent developments in Mycoplasma genetics that facilitate the genetic manipulation of these interesting organisms.

Codon↗
PubMed1979

Re-examination of transformation within different species of Rhizobium.

Investigations of the phenomenon of transformation in Rhizobium were carried out. Streptomycin resistance (str) was the genetic marker used in all experiments, with the exception of auxotrophic strains. Twenty-one experiments were performed on nine different Rhizobium strains. Some of these strains were previously reported to be transformed, while others had no prior history of transformation. Different conditions which are thought to affect the development of competence were used. In these experiments no positive results were obtained. The possibility that the experiments failed, due to inactivation of donor DNA during its preparation, was ruled out by comparison with results obtained with strains of Bacillus subtilis.

Bacillus subtilis↗
PubMed1973

Trimethoprim-resistance and its transferability in E. coli isolated from calves treated with trimethoprim-sulphadiazine: a two year study.

Regular examination of rectal swabs revealed the presence of very low numbers of trimethoprim resistant Escherichia coli in the faeces of 10 batches of calves successively reared in the same shed and none of these strains transferred trimethoprim resistance to E. coli K12. All the calves had received oral doses of 30 mg/kg day of trimethoprim-sulphadiazine for 5 consecutive days. From two subsequent batches of calves reared in the same shed, however, several isolations were made of E. coli with transmissible R factors determining trimethoprim and streptomycin resistance. Shortly before these strains were detected, isolations of E. coli with similar properties had been made from other calves, in a different shed, which had been fed much higher doses of trimethoprim-sulphadiazine. Serological evidence indicated that all the E. coli isolated carrying this R factor belonged to the same strain, which had apparently spread from the second shed to the first. No evidence of ;in vivo' transfer of the R factor to other enteric bacteria was obtained.

Agglutination Tests↗
PubMed1996

Characteristics of gonococci isolated from men with urethritis in Dubai.

Neisseria gonorrhoeae were collected from men attending out-patient clinics in Dubai. The susceptibility to a range of therapeutic antibiotics and their auxotype and serotype was determined. The plasmid content of all penicillinase-producing strains was also analysed. Thirty-six strains of N. gonorrhoeae were isolated from specimens collected from 79 patients over a 24-day period. Of the 36 isolates, 9(25%) were penicillinase-producing N. gonorrhoeae (PPNG) and 15 (42%) were chromosomally resistant N. gonorrhoeae (CMRNG). CMRNG exhibited higher levels of resistance to cefuroxime, chloramphenicol, tetracycline and erythromycin than PPNG. All isolates were susceptible to ceftriaxone and spectinomycin. Three (8%) isolates showed reduced susceptibility (MIC, > or = 0.25 mg/l) to ciprofloxacin. Six isolates of PPNG carried the 4.4 MD and three the 3.2 MD penicillinase encoding plasmid. The total gonococcal population was phenotypically diverse, with 12 serovars, 6 auxotypes and 21 A/S classes. Gonorrhoea was found to be a major cause of urethritis in Dubai and the strains exhibited high levels of resistance to penicillin.

Adolescent↗