Lethal interaction between heat and methylene blue in Escherichia coli

Hyperthermia Prevents In Vitro and In Vivo Biofilm Formation on Endotracheal Tubes

There is currently an urgent need to find new strategies to tackle antimicrobial resistance and biofilm-related infections. This study has two aims. First, we evaluated the in vitro efficacy of hyperthermia in preventing biofilm formation on the surfaces of polyvinyl chloride discs. Second, we assessed the in vivo efficacy of hyperthermia in preventing biofilm formation in endotracheal tubes (ETTs) of a rabbit model. For the in vitro studies, nine clinical extensively drug-resistant/multidrug-resistant Gram-negative isolates of Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa and three clinical methicillin-resistant Staphylococcus aureus strains were studied. For biofilm formation, an adhesion step of 30 or 90 min followed by a growth step of 24 h were performed with application of one, two, and three pulses at 42°C for 15 min each pulse after the adhesion step. For the in vivo studies, New Zealand rabbits were intubated with ETTs previously colonized with K. pneumoniae or P. aeruginosa strains, and three pulses at 42°C for 15 min were applied after the adhesion step. The application of three pulses at 42°C for 15 min each pulse was needed to achieve the prevention of the in vitro biofilm formation of 100% of the tested strains. The application of heat pulses in a rabbit intubation model led to biofilm prevention of 85% against two K. pneumoniae strains and 80% against two P. aeruginosa strains compared to the control group. Hyperthermia application through pulses at 42°C could be a new nonantibiotic strategy to prevent biofilm formation in ETTs. IMPORTANCE Biofilm-producing microorganisms are considered medically crucial since they cause 80% of the infections that occur in the human body. Medical devices such as endotracheal tubes (ETTs) can act as a reservoir for pathogens providing the surface to which microorganisms can adhere and cause biofilm-associated infections in critically ill patients. This biofilm has been related with the development of ventilator-associated pneumonia (VAP), with an incidence of 8 to 28%, a mortality rate up to 17% and its associated high extra costs. Although some VAP-preventive measures have been reported, they have not demonstrated a significant reduction of VAP incidence. Therefore, we present a new nonantibiotic strategy based on hyperthermia application to prevent biofilm formation inside ETTs. This technology could reduce VAP incidence, intubation duration, hospital and intensive care unit (ICU) length stays, and mortality rates. Consequently, this could decrease the antibiotics administered and influence the impact of antibiotic resistance in the ICU.

Microwaves, a potential treatment for bacteria: A review

Bacteria have brought great harm to the public, especially after the emergence of multidrug-resistant bacteria. This has rendered traditional antibiotic therapy ineffective. In recent years, hyperthermia has offered new treatments to remove bacteria. Microwaves (MW) are a component of the electromagnetic spectrum and can rapidly heat materials. Taking advantage of this characteristic of MW, related studies have shown that both thermal and non-thermal effects of MW can inactivate various bacteria. Even though the understanding of MW in the field of bacteria is not sufficient for widespread use at present, MW has performed well in dealing with microorganisms and controlling infection. This review will focus on the application of MW in bacteria and discuss the advantages, prospects and challenges of using MW in the bacterial field.

Methylene blue mediated photodynamic therapy in experimental colorectal tumors in mice

Methylene blue (MB+) is a well-known dye in medicine and has been discussed as an easily applicable drug for the topical treatment during photodynamic therapy (PDT). The therapeutic response of MB+ was investigated in vivo by local injection of MB+ in a xenotransplanted subcutanous tumor (adeno-carcinoma, G-3) in female nude mice. MB+ in a concentration of 1% was applied both undiluted and diluted to 0.1 and 0.01% with isotonic sodium chloride. Treatment with 1% MB+ and subsequent irradiation at 662 nm with 100 J/cm2 led to complete tumor destruction in 79% of the treated animals. A decrease of the fluence rate from 100 to 50 mW/cm2 increased the phototoxic response as well as fractionated light application. Small sensitizer concentrations reduced the PDT effect significantly. It seems that the light induced reaction of MB+ could be correlated with the rapid production of reactive oxygen species. Below a threshold dose of MB+ oxidative damage of the tissue is prevented. However, above this dose, as a point of no return, MB+ acts as an extremely potent oxidant.

Methylene blue sensitizes E. coli cells to X-rays

Methylene blue (MB) is shown to sensitize E. coli cells to the effects of X-rays. This sensitization is dependent on factors such as dye concentration, incubation temperature, membrane permeability, and repair capacities, suggesting that the binding and/or penetration of the dye into the cells determines the potentiation of the lethal effects of X-rays by MB. It is also demonstrated that the presence of the polymerase 1 enzyme is essential for this sensitization to take place. Since MB is known to penetrate, accumulate, and be retained preferentially in some malignant tissues, the possibility of using this dye as a specific sensitizer to X-rays in the radiotherapy of some cancers is discussed.