The potential of therapeutic hyperthermia to eradicate Staphylococcus aureus bacteria; an in vitro study.

Staphylococcus aureus is one of the most common infectious agents, causing morbidity and mortality worldwide. Most pathogenic bacteria are classified in the group of mesophilic bacteria and the optimal growth temperature of these bacteria changes between 33 and 41 °C. Increased temperature can inhibit bacterial growth and mobility, which in turn, can trigger autolysis and cause cell wall damage. Hyperthermia treatment is defined as a heat-mediated treatment method applied using temperatures higher than body temperature. Nowadays, this treatment method is used especially in the treatment of tumours. Hyperthermia treatment is divided into two groups: mild hyperthermia and ablative or high-temperature hyperthermia. Mild hyperthermia is a therapeutic technique in which tumour tissue is heated above body temperature to produce a physiological or biological effect but is often not aimed at directly causing significant cell death. The goal of this method is to achieve temperatures of 40-45 °C in human tissues for up to 2 h. Hyperthermia can be used in the treatment of infections caused by such bacterial pathogens. In addition, using hyperthermia in combination with antimicrobial drugs may result in synergistic effects and reduce resistance issues. In our study, we used two different temperature levels (37 °C and 45 °C). We assessed growth inhibition, some virulence factors, alteration colony morphologies, and antimicrobial susceptibility for several antibiotics with three methods (Kirby-Bauer, E-test and broth microdilution) under hyperthermia. In the study, we observed that hyperthermia affected the urease enzyme, antibiotic sensitivity levels showed synergy with hyperthermia, and changes occurred in colony diameters and affected bacterial growth. We hypothesise that hyperthermia might be a new therapeutic option for infectious diseases as a sole agent or in combination with different antimicrobials.

In vitro activity of hyperthermia on swarming motility and antimicrobial susceptibility profiles of Proteus mirabilis isolates.

AIM: Swarming motility is a virulence factor for Proteus mirabilis and is a coordinated multicellular movement of bacteria. In this study, we investigated the inhibitory effect of hyperthermia on bacterial swarming motility and antimicrobial resistance. METHODS: Thirty-one P. mirabilis isolates were included in the study. Seven inoculated agar plates were incubated inside incubators with increasing temperature levels: at 36 °C (control) and 40-45 °C. On the next day, inhibition of swarming was evaluated and minimum paralyzing temperature (MPT) values were determined. An antimicrobial susceptibility test (antibiogram) is performed by exposing bacteria to increasing concentrations of antibiotics, in vitro. Thus, we used the Kirby-Bauer disk diffusion test as a screening method to analyze the antibiogram profiles of the isolates at 36 °C and 42 °C. Finally, a time-kill assay was performed to analyze the killing effect of hyperthermia (42 °C) on planktonic bacteria, in combination with the antibiotic meropenem at the first and third hours. A Wilcoxon signed-rank test was used to compare the killing effects of meropenem, hyperthermia and their combinations. RESULTS: The median MPT value was determined as 44 °C. In the disk diffusion assay, susceptibility development was observed in 94% of isolates for at least one antibiotic. In the time-kill assay, we observed a significant killing effect of hyperthermia in combination with meropenem. Under the microscope, we observed the formation of spherical cells by the effect of heat. CONCLUSION: We conclude that these findings might be useful when employing the hyperthermia method to treat infectious diseases caused by P. mirabilis in the future.

Are infectious diseases and microbiology new fields for thermal therapy research?

Antimicrobial chemotherapy and surgery are classical methods for treating infectious diseases. However, there is a need for alternative methods to cure infections caused by antibiotic-resistant pathogens, recurrent or chronic infections, and unreachable local infections in which the use of drugs or surgery is anatomically and physically restricted. Several micro-organisms are known to be sensitive to mild hyperthermia, and this sensitivity is one of the potential benefits proposed for the host during an episode of fever. Additionally, some immunological or biophysical changes occur during hyperthermia. These changes may be useful for eliminating thermo-susceptible microbial pathogens using local heat therapy. There are several experimental studies proposing the use of hyperthermia to treat local infections. The infected organs or tissues may be heated up to a temperature that can inhibit invading microorganisms. Here, it is hypothesised that local heat therapy may become an alternative or adjuvant method for curing local infections. Here, we highlight the potential for local hyperthermia in the treatment of bacterial infections caused by thermo-susceptible pathogens in a systematic plan. If the proposed thermal-microbiology concepts and local thermal therapies can be adapted to clinical microbiology and infectiology, new medical fields, such as thermo-microbiology and thermo-infectiology, may be created in the future.

[Epidemiological evaluation of a rapidly-prevented tularemia outbreak in Canakkale province, Turkey]. / Çanakkale'de Hizla Önlenen Bir Tularemi Salgininin Epidemiyolojik Olarak Degerlendirilmesi.

Tularemia is a disease caused by Francisella tularensis and widely seen at northern hemisphere of the world. In Turkey, oropharyngeal infections caused by a less virulent serotype F.tularensis subsp. Holarctica are more prevalent. The aim of this study was to present the results of an epidemiological research performed after the detection of tularemia cases from Biga county of Canakkale province, Turkey, in December 2009. Following the report of two tularemia suspected cases from two villages (Baliklicesme and Sinekci) of Biga, an epidemiological investigation was undertaken to inspect the situation in this area. Water samples, clinical samples as throat swabs, wound swabs and serum samples were collected. Samples were cultured on heart agar supplemented with sheep blood, cysteine and antibiotics. Cultures were incubated at 37°C in 5% CO(2) and followed for 10 days. Suspected colonies were identified by slide agglutination test using F.tularensis antisera. F.tularensis antibodies were investigated by standard tube agglutination method. Positive results obtained with agglutination test were also checked for a probable crossreaction with Brucella antibodies by Rose-Bengal test. Water and wound samples were investigated using real-time polymerase chain reaction (RT Taqman PCR; Quantica, Techne Inc, UK) with probe and primers specific for ISFtu2 gene. All of the cultures yielded negative results, however eight of 16 water samples, one lymph node aspirate and one throat sample were found positive in F.tularensis TaqMan RT-PCR test. In tube agglutination test positive antibody titers between 1:20-1:1280 were detected in 36 of 115 serum samples. Two cases with antibody titers of 1:1280 and accompanying acute clinical findings, were diagnosed as tularemia and treated accordingly. Lymphatic drainage fluid samples obtained from one of these patients yielded positive result in PCR, however clinical sample could not be obtained from the other patient. The only epidemiological linkage between these acute cases (n= 2) and the other seropositive subjects (n= 34) was the use of local water supply system. It was learned that water obtained through reverse osmosis system had been used as drinking water at Baliklicesme village. Pre- and post-reverse osmosis system water samples from Baliklicesme village and samples from water supply of Sinekci village revealed positive results for F.tularensis by PCR. Since the only epidemiological relation between these two villages was using local water supply, tularemia cases encountered in this area were attributed to a waterborne epidemic and an automatic chlorination system was set up at each water reservoir in these villages. The establishment of these preventive measures curbed the growth of the epidemic. The cases presenting with throat sore, fever, lymphadenopathy (more than 2 cm), non-responsive to beta-lactam antibiotics, should be further investigated for tularemia. This work emphasizes that systematic setup and control of water disinfection systems are crucial to prevent tularemia outbreaks. Community and related authorities should be educated about the importance of water sanitation and chlorination.