Bacteria encounter a myriad of stresses in their natural environments, including, for pathogens, their hosts. These stresses elicit a variety of specific and highly regulated adaptive responses that not only protect bacteria from the offending stress, but also manifest changes in the cell that impact innate antimicrobial susceptibility. Thus exposure to nutrient starvation/limitation (nutrient stress), reactive oxygen and nitrogen species (oxidative/nitrosative stress), membrane damage (envelope stress), elevated temperature (heat stress) and ribosome disruption (ribosomal stress) all impact bacterial susceptibility to a variety of antimicrobials through their initiation of stress responses that positively impact recruitment of resistance determinants or promote physiological changes that compromise antimicrobial activity. As de facto determinants of antimicrobial, even multidrug, resistance, stress responses may be worthy of consideration as therapeutic targets.

/pdf/bacterial-stress-responses-as-determinants-of-antimicrobial-2nvc1cmi9t.pdf

Bacterial stress responses as determinants of antimicrobial resistance

Escaping the biofilm in more than one way: desorption, detachment or dispersion

Biofilm formation is a complex developmental process regulated by multiple environmental signals. In addition to other nutrients, the transition metal iron can also regulate biofilm formation. Iron-dependent regulation of biofilm formation varies by bacterial species, and the exact regulatory pathways that control iron-dependent biofilm formation are often unknown or only partially characterized. To address this gap in our knowledge, we examined the role of iron availability in regulating biofilm formation in Escherichia coli. The results indicate that biofilm formation is repressed under low-iron conditions in E. coli. Furthermore, a key iron regulator, IscR, controls biofilm formation in response to changes in cellular Fe-S homeostasis. IscR regulates the FimE recombinase to control expression of type I fimbriae in E. coli. We propose that iron-dependent regulation of FimE via IscR leads to decreased surface attachment and biofilm dispersal under iron-limiting conditions.

IscR Controls Iron-Dependent Biofilm Formation in Escherichia coli by Regulating Type I Fimbria Expression

Legionella species are ubiquitous, waterborne bacteria that thrive in numerous ecological niches. Yet, in contrast to many other environmental bacteria, Legionella spp. are also able to grow intracellularly in predatory protozoa. This feature mainly accounts for the pathogenicity of Legionella pneumophila, which causes the majority of clinical cases of a severe pneumonia termed Legionnaires' disease. The pathomechanism underlying L. pneumophila infection is based on macrophage resistance, which in turn is largely defined by the opportunistic pathogen's resistance towards amoebae. L. pneumophila replicates in macrophages or amoebae in a unique membrane-bound compartment, the Legionella-containing vacuole (LCV). LCV formation requires the bacterial intracellular multiplication/defective for organelle trafficking (Icm/Dot) type IV secretion system and involves a plethora of translocated effector proteins, which subvert pivotal processes in the host cell. Of the ca. 300 different experimentally validated Icm/Dot substrates, about 50 have been studied and attributed a cellular function to date. The versatility and ingenuity of these effectors' mode of actions is striking. In this review, we summarize insight into the cellular functions and biochemical activities of well-characterized L. pneumophila effector proteins and the host pathways they target. Recent studies not only substantially increased our knowledge about pathogen-host interactions, but also shed light on novel biological mechanisms.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/cmi.12450

Formation of a pathogen vacuole according to Legionella pneumophila: how to kill one bird with many stones

Staphylococcus aureus is a human pathogen that forms biofilm on catheters and medical implants. The authors' earlier study established that 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) inhibits biofilm formation by S. aureus by preventing the initial attachment of the cells to a solid surface and reducing the production of polysaccharide intercellular adhesin (PIA). Our cDNA microarray and MALDI-TOF mass spectrometric studies demonstrate that PGG treatment causes the expression of genes and proteins that are normally expressed under iron-limiting conditions. A chemical assay using ferrozine verifies that PGG is a strong iron chelator that depletes iron from the culture medium. This study finds that adding FeSO4 to a medium that contains PGG restores the biofilm formation and the production of PIA by S. aureus SA113. The requirement of iron for biofilm formation by S. aureus SA113 can also be verified using a semi-defined medium, BM, that contains an iron chelating agent, 2, 2′-dipyridyl (2-DP). Similar to the effect of PGG, the addition of 2-DP to BM medium inhibits biofilm formation and adding FeSO4 to BM medium that contains 2-DP restores biofilm formation. This study reveals an important mechanism of biofilm formation by S. aureus SA113.

/pdf/involvement-of-iron-in-biofilm-formation-by-staphylococcus-4ysityaaq6.pdf

Involvement of iron in biofilm formation by staphylococcus aureus

In aquatic environments, biofilms constitute an ecological niche where Legionella pneumophila persists as sessile cells. However, very little information on the sessile mode of life of L. pneumophila is currently available. We report here the development of a model biofilm of L. pneumophila strain Lens and the first transcriptome analysis of L. pneumophila biofilm cells. Global gene expression analysis of sessile cells as compared to two distinct populations of planktonic cells revealed that a substantial proportion of L. pneumophila genes is differentially expressed, as 2.3 % of the 2932 predicted genes exhibited at least a twofold change in gene expression. Comparison with previous results defining the gene expression profile of replicative- and transmissive-phase Legionella suggests that sessile cells resemble bacteria in the replicative phase. Further analysis of the most strongly regulated genes in sessile cells identified two induced gene clusters. One contains genes that encode alkyl hydroperoxide reductases known to act against oxidative stress. The second encodes proteins similar to PvcA and PvcB that are involved in siderophore biosynthesis in Pseudomonas aeruginosa. Since iron has been reported to modify biofilm formation in other species, we further focused on iron control of gene expression and biofilm formation. Among the genes showing the greatest differences in expression between planktonic cells and biofilm, only pvcA and pvcB were regulated by iron concentration. A DeltapvcA L. pneumophila mutant showed no changes in biofilm formation compared to the wild-type, suggesting that the pvcA product is not mandatory for biofilm formation. However, biofilm formation by L. pneumophila wild-type and a DeltapvcA strain was clearly inhibited in iron-rich conditions.

/pdf/transcriptional-profiling-of-legionella-pneumophila-biofilm-2yu5jbyibx.pdf

Transcriptional profiling of Legionella pneumophila biofilm cells and the influence of iron on biofilm formation

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Transcriptional profiling of Legionella pneumophila biofilm cells and the influence of iron on biofilm formation