Plasmid R1drd-19 is present in a small number of copies per cell of Escherichia coli. The plasmid was reduced in size by in vivo as well as in vitro (cloning) techniques, resulting in a series of plasmid derivatives of different molecular weight. All plasmids isolated contain a small region (about 2 x 10(6) daltons of deoxyribonucleic acid) of the resistance transfer factor part of the plasmid located close to one of the IS1 sequences that separates the resistance transfer factor part from the resistance determinant. All these derivatives were present at the same copy number, retained the incompatibility properties of plasmid R1drd-19, and were stably maintained during cell division. Genes mutated to yield copy mutations also were found to be located in the same region.

Plasmid incompatibility was studied in Escherichia coli K-12. By doubleantibiotic selection, clones were constructed that carried the two R-factors Rl and R100, both belonging to the compatibility group F,1. After release of the selection pressure, each of the two plasmids was lost at the same rate (8% per generation). Mutants of R-factor Rl showing an increased number of copies per chromosome (copy mutants) were tested for their incompatibility towards Rfactor R100. The results indicate that plasmid incompatibility is quantitative and not just a qualitative property. All copy mutants studied affected incompatibility, and there were two classes of mutants: one increasing and one decreasing the incompatibility exerted towards the test plasmid R100. Evidence is presented that incompatibility is related to the mechanisms that control replication. The implications of such a relation on proposed models for control of replication are discussed. The data do not support the hypothesis that plasmid incompatibility is due to competition for a replicational or segregational site.

Background: Acinetobacter baumannii is a Gram-negative opportunistic pathogen with a notorious reputation of being resistant to antimicrobial agents. The capability of A. baumannii to persist and disseminate between healthcare settings has raised a major concern worldwide. Methods: Our study investigated the antibiotic resistance features and molecular epidemiology of 52 clinical isolates of A. baumannii collected in Pakistan between 2013 and 2015. Antimicrobial susceptibility patterns were determined by the agar disc diffusion method. Comparative sequence analyses of the ampC and bla OXA-51-like alleles were used to assign the isolates into clusters. The whole genomes of 25 representative isolates were sequenced using the MiSeq Desktop Sequencer. Free online applications were used to determine the phylogeny of genomic sequences, retrieve the multilocus sequence types (ST), and detect acquired antimicrobial resistance genes.Results: Overall, the isolates were grouped into 7 clusters and 3 sporadic isolates. The largest cluster, Ab-Pak-cluster-1 (bla OXA-66 and ISAba1-ampC-19) included 24 isolates, belonged to ST2 and International clone (IC) II, and was distributed between two geographical far-off cities, Lahore and Peshawar. Ab-Pak-clusters-2 (bla OXA-66 , ISAba1-ampC-2), and -3 (bla OXA-66 , ISAba1-ampC-20) and the individual isolate Ab-Pak-Lah-01 (ISAba1-bla OXA-66 , ISAba1-ampC-2) were also assigned to ST2 and IC II. On the other hand, Ab-Pak-clusters-4 (bla OXA-69 , ampC-1), -5 (bla OXA-69 , ISAba1-ampC-78), and -6A (bla OXA-371 , ISAba1-ampC-3) belonged to ST1, while Ab-Pak-cluster-6B (bla OXA-371 , ISAba1-ampC-8) belonged to ST1106, with both ST1 and ST1106 being members of IC I. Five isolates belonged to Ab-Pak-cluster-7 (bla . This cluster corresponded to ST158, showed a well-delineated position on the genomic phylogenetic tree, and was equipped with several antimicrobial resistance genes including bla OXA-23 and bla . Conclusions:Our study detected the occurrence of 7 clusters of A. baumannii in Pakistan. Altogether, 6/7 of the clusters and 45/52 (86.5%) of the isolates belonged to IC I (n = 9) or II (n = 36), making Pakistan no exception to the global domination of these two clones. The onset of ST158 in Pakistan marked a geographical dispersal of this clone beyond the Middle East and brought up the need for a detailed characterization.

This article by Müller et al. was published in Mol Microbiol

A force-measuring optical tweezers instrumentation and long time measurements of the elongation and retraction of bacterial fimbriae from Uropathogenic E. coli (UPEC) under strain are presented. The instrumentation is presented in some detail. Special emphasis is given to measures taken to reduce the influence of noise and drifts in the system and from the surrounding, which makes long term force measurements possible. Individual P pili from UPEC bacteria were used as a biological model system for repetitive unfolding and refolding cycles of bacterial fimbriae under equilibrium conditions. P pili have evolved into a three-dimensional helix-like structure, the PapA rod, that can be successively and significantly elongated and/or unfolded when exposed to external forces. The instrumentation is used for characterization of the force-vs.-elongation response of the PapA rod of individual P pili, with emphasis on the long time stability of the forced unfolding and refolding of the helical structure of the PapA rod. The results show that the PapA rod is capable of withstanding extensive strain, leading to a complete unfolding of the helical structure, repetitive times during the life cycle of a bacterium without any noticeable alteration of the mechanical properties of the P pili. This function is believed to be importance for UPEC bacteria in vivo since it provides a close contact to a host cell (which is an initial step of invasion) despite urine cleaning attempts.