PubMed · 1684607
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N Manek. 1991. Penicillin-resistant pneumococci.. https://doi.org/10.1016/0195-6701(91)90107-j
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We have constructed a series of promoterprobe cassettes that provides powerful tools for insertion mutagenesis, transcription fusions and genetic constructions. These cassettes contain the Tn9 chloramphenicol (CmR) and the Tn903 kanamycin (KmR) resistance genes which are expressed in a large variety of microorganisms; these antibiotic-resistance markers were associated with the uidA promoterless gene. This beta-glucuronidase-encoding gene of Escherichia coli K-12 has been successfully used as reporter gene for various organisms including prokaryotes and eukaryotes. The resulting 'uidA-KmR and 'uidA-CmR cassettes (truncated at the ') can be excized with most of the commonly used restriction enzymes. Furthermore, they are borne by ApR or CmR plasmids which facilitate their utilization. These promoter-probe cassettes allow transcriptional signal localization and regulation studies.
A method for detecting newly cloned DNA fragments in pBR322-based vectors was devised for use in DNA probe production. Escherichia coli strain DH5 containing plasmids with different resistance patterns to tetracycline (Tc) and chloramphenicol (Cm) were grown on nonpigmented media, blotted, transferred, and incubated for 2 h on MacConkey agar containing Tc or Cm. Resistant colonies changed color to pink as they began fermenting the lactose on the agar, while sensitive colonies remained white but were still viable and could be subcultured. This method can be applied to the detection of other plasmids with insertional inactivation of Tc or Cm resistance marker genes following successful cloning experiments, especially if pUC18 or M13 is not a possible vector. It eliminates 1 day of culture and the labor involved in individually transferring hundreds of colonies.
Twenty-two laboratories in England and Scotland sent 2212 clinical isolates of Haemophilus influenzae to The London Hospital Medical College (LHMC) between 1 January and 31 March 1991. After confirmation of identity, the prevalence of resistance was determined and compared with results from previous similar surveys. beta-Lactamase was produced by 8.3% of non-capsulate isolates and 21% of 52 type b isolates; both figures were higher than the 6% and 18% figures recorded, respectively, in 1986. There was an increase in the prevalence of non-beta-lactamase-mediated diminished susceptibility to ampicillin (5.8%) and co-amoxiclav (6.1%) compared with 1986 (4%). Whereas fewer H. influenzae isolates were resistant to tetracycline (1.4%) or chloramphenicol (0.8%), there was an increase in resistance to trimethoprim (6.8%) and to sulphamethoxazole (16.9%) compared with 1986 (4.2% and 3.5% respectively). In addition, 95 isolates (4.3%) were resistant to both of these anti-folate antimicrobials. Six isolates (one type b from CSF) were resistant to all drugs tested, except for co-amoxiclav. Overall, the results demonstrated that changes have occurred in the last decade in England and Scotland, such that H. influenzae isolates are increasingly likely to be resistant to ampicillin, co-amoxiclav and co-trimoxazole.