The appearance of flagellated cells can be observed at the leading edge of a growing colony using phase contract, fluorescent or electron microscopy [1]. Alternatively, a motor specified for generating extra moving force can be synthesized in P. The size of wild-type P. Swarmer cells are elongated compared to the vegetative cells cells that are capable of actively growing [12]. Cells at the tip region of the dendrite are approximately two times the length of the center cells [8].
This morphological differentiation may be due to the gene suppression of cell division in tendril-tip swarmer cells. However, no regulatory mechanism of cell division during swarming has been proposed at the molecular level [1]. The genome size of P. The majority of the genes are involved in cell movement, nutrients uptake, antibiotic resistance and environmental stimuli responding systems [11]. Further Microarrays study demonstrates that comparing the swarmer cells at the marginal region of a swarming colony to the bacteria grown under swimming condition, 7.
Genes related to virulence factors synthesis and substance export exhibit a great up-regulating tendency. For example, genes for the extracellular alkaline protease, type III secretion system TTSS , and genes encoding redox-active phenazine compounds show 2 to 13 folds increase [7]. Interestingly, a different Microarray study focused on the distinct bacterial subpopulations within a P.
The swarming motility in P. Several relevant studies demonstrate that the swarming motility is closely related to surfactant production [8] and quorum sensing [3]. The production of rhamnolipid is fundamental for the swarming motility as rhamnolipid is a surfactant facilitating the uptake and biodegradation of insoluble hydrocarbons which help to reduce surface tension and permit spreading motility [1] [10].
When a few amino acids eg. On the contrary, amino acids eg. When the amount of autoinducer AHL production in P. A24, a significant down-regulation in several types of virulence factors and cytotoxic compounds together with a strongly reduced swarming are observed [3].
We investigate here if the swarming behaviour could also be associated with a widespread antimicrobial resistant phenotype. Challenged with 13 antibiotics from various classes, swarm cells of Pseudomonas aeruginosa, Escherichia coli, Serratia marcescens, Burkholderia thailandensis and Bacillus subtilis showed higher resistance than their planktonic counterparts to all the antibiotics tested, except for the antimicrobial peptides. Using P. Resistance of swarm cells towards other antimicrobial agents, such as triclosan and a heavy metal arsenite , was also observed.
Together with the high resistance of biofilms, these results support the hypothesis that antimicrobial resistance is a general feature of bacterial multicellularity.
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