Pseudomonas aeruginosa

Meticulous drug management programs can have a positive effect on drug-resistant infections, finds a new report published in the Journal of Clinical Microbiology. A team of clinical scientists led by Larissa Matukas studied the effect of antibiotic stewardship surrounding the use of ciprofloxacin to treat bacterial infections caused by Escherichia coli or Pseudomonas aeruginosa. Using a stewardship program that involved reporting ciprofloxacin susceptibility only if no other susceptibilities were found when testing isolates against a multidrug panel, the team observed a strong reduction in the use of this particular antibiotic, which correlated with a trend toward increasing susceptibility in E. coli isolates. The study demonstrates that, while small, antibiotic stewardship programs may help prolong the efficacy of antibiotic arsenals.

“Although several factors could theoretically contribute to a microorganism's ability to colonize the intestinal ecosystem, effective completion for nutrients is paramount to success.” So the editors reference researcher Rolf Freter in their introduction to this new, integrative text. This volume highlights this truth with a biochemical focus on bacterial pathogens and the human host. This includes chapters on enteric, respiratory, urinary tract, and intracellular pathogens. Some chapters also focus attention on the role of commensal communities, such as in dental plaque or in the gut through interaction with host immunity. More species-specific topics include central carbon metabolism by Borrelia burgdorferi, regulation of Escherichia coli fimbriae by host sialic acid, and Pseudomonas aeruginosa metabolism during infection of cystic fibrosis patients. Though it is sparse in its figures, this is a timely and information-rich collection that should be a welcome resource for many microbiologists.

Scientists at the Institut Pasteur in Paris, France, were surprised to discover that an airborne volatile compound released by the bacterium Pseudomonas aeruginosa can promote growth of the fungus Aspergillus fumagatus. First author Benoit Briard, working with senior scientist Jean-Paul Latgé, made the discovery. “That microbes ‘smell’ other microbes is not new,” says Latgé. “But that one species of bacteria is stimulating the growth of a fungus by ‘smell’—this is totally new.” The compound, identified as dimethyl sulfoxide by mass spectroscopy, contains sulfur, which the fungus can use to grow. The findings will be useful when studying coinfections of the lung, where both P. aeruginosa and A. fumagatus can cause disease.

In the summer of 2013, a patient arrived in our emergency department with complaints of high fever and abdominal pain. She came to us straight from the airport following her return from a 3-month visit to India. Identified as septic, she was “pan-cultured,” meaning readily obtained fluids and substances were sent immediately to begin cultures. Due to concerns for bacterial gastroenteritis, she received ceftriaxone in the emergency department and ciprofloxacin after admission. Fevers continued and blood cultures yielded Escherichia coli, which was phenotypically resistant to most antibiotics, including ceftriaxone and ciprofloxacin, but susceptible to “last-resort” carbapenems, which were then used to treat her.

Pseudomonas aeruginosa motility is inversely related to its ability to form biofilms. New research from Boston Children's Hospital shows that this relationship is at least partially reciprocally regulated. Scientists working with Simon Dove identified an operon encoding a σ factor and its anti-σ factor, which they named sbrI and sbrR, respectively. They found that the ΔsbrR mutant strain exhibited extremely reduced swarming motility but formed more robust biofilms than the wild type. This was pinpointed to hyperactivity of the SbrI σ factor in the ΔsbrR strain, which increased muiA transcription 100-fold. Overexpression of muiA in a wild-type strain was sufficient to suppress swarming, demonstrating the mechanistic importance of this transcript. While the exact function of MuiA remains to be uncovered, its regulation by SbrI and SbrR are clear. This may help scientists manipulate biofilm formation, a common state of many P. aeruginosa infections.

When encapsulated in silica nanoparticles, peppermint oil and cinnamaldehyde, which gives cinnamon its characteristic flavor, penetrate biofilms and potently kill drug-resistant pathogens within them, according to Vincent Rotello at the University of Massachusetts, Amherst, and his collaborators. These nanocapsules also promote fibroblast growth, which helps wounds to heal, they say, leading them to call these flavor-loaded nanoparticles a “promising natural disinfectant and wound cleanser.” Details appeared 17 June 2015 in ACS Nano (doi:10.1021/acsnano.5b01696).

Spices such as ginger and cinnamon as well as other natural products have potent antimicrobial activities against methicillin-resistant Staphylococcus aureus (MRSA), various strains of Pseudomonas aeruginosa, and other pathogens, including those that form biofilms, according to several researchers who presented findings during the 2015 ASM General Meeting, held in New Orleans, La., last May. If they prove safe and effective, these natural products or derivatives based on them could lead to new treatment strategies for infections caused by these clinically challenging bacterial strains, the researchers say.

Microbes live as densely populated multicellular surface-attached biofilm communities embedded in self-generated, extracellular polymeric substances (EPSs). EPSs serve as a scaffold for cross-linking biofilm cells and support development of biofilm architecture and functions. Biofilms can have a clear negative impact on humans, where biofilms are a common denominator in many chronic diseases in which they prime development of destructive inflammatory conditions and the failure of our immune system to efficiently cope with them. Our current assortment of antimicrobial agents cannot efficiently eradicate biofilms. For industrial applications, the removal of biofilms within production machinery in the paper and hygienic food packaging industry, cooling water circuits, and drinking water manufacturing systems can be critical for the safety and efficacy of those processes. Biofilm formation is a dynamic process that involves microbial cell migration, cell-to-cell signaling and interactions, EPS synthesis, and cell-EPS interactions. Recent progress of fundamental biofilm research has shed light on novel chemical biology strategies for biofilm control. In this article, chemical biology strategies targeting the bacterial intercellular and intracellular signaling pathways will be discussed.

The stable maintenance of low-copy-number plasmids in bacteria is actively driven by partition mechanisms that are responsible for the positioning of plasmids inside the cell. Partition systems are ubiquitous in the microbial world and are encoded by many bacterial chromosomes as well as plasmids. These systems, although different in sequence and mechanism, typically consist of two proteins and a DNA partition site, or prokaryotic centromere, on the plasmid or chromosome. One protein binds site-specifically to the centromere to form a partition complex, and the other protein uses the energy of nucleotide binding and hydrolysis to transport the plasmid, via interactions with this partition complex inside the cell. For plasmids, this minimal cassette is sufficient to direct proper segregation in bacterial cells. There has been significant progress in the last several years in our understanding of partition mechanisms. Two general areas that have developed are (i) the structural biology of partition proteins and their interactions with DNA and (ii) the action and dynamics of the partition ATPases that drive the process. In addition, systems that use tubulin-like GTPases to partition plasmids have recently been identified. In this chapter, we concentrate on these recent developments and the molecular details of plasmid partition mechanisms.

Antibiotic sensitivity and the effect of temperature on microbial growth are two standard laboratory activities found in most microbial laboratory manuals. We have found a novel way to combine the two activities to demonstrate how temperature can influence antibiotic sensitivity using a standard incubator in instructional laboratory settings. This activity reinforces the important concepts of microbial growth and temperature along with Kirby-Bauer antibiotic susceptibility testing. We found that Pseudomonas fluorescens can be manipulated to become more sensitive to several antibiotics by simply increasing growth temperature and exposing the organism to various antibiotics. No additional equipment is required beyond a standard incubator. Pseudomonas fluorescens is an excellent choice for this activity since it is a safe alternative to Pseudomonas aeruginosa, a biosafety level 2 agent. Pseudomonads are important to explore in the microbiology laboratory since Pseudomonas aeruginosa poses a serious issue in health care settings, as this organism is known to be a multi-drug-resistant pathogen (6). More importantly, P. fluorescens is a good alternative in the laboratory to P. aeruginosa since it is also pigmented (5) and a possible reservoir of antibiotic resistance genes (4). In addition, it grows best at room temperatures and can easily be thermally stressed by placing in a standard 35ºC to 37ºC incubator