Background: Diagnoses of respiratory tract infections usually happen in the late phase of the disease and usually result in reduction of the pathogen load after broad-spectrum antibiotic therapy, but not in eradication of the pathogen. The development of a non-invasive, fast, and accurate method to detect pathogens has always been of interest to researchers and clinicians alike. Previous studies have shown that bacteria produce organic gases. The current study aimed to identify the volatile organic compounds (VOCs) produced by three respiratory tract pathogens, including Staphylococcus aureus, Escherichia coli and Candida albicans. Methods: The VOCs produced were identified by gas chromatography–mass spectrometry (GC-MS), with prior collection of microbial volatile compounds using solid phase microextraction (SPME) fiber. The volatile compounds were collected by obtaining bacterial headspace samples. Results: Results showed that these three organisms have various VOCs, which were analyzed under different conditions. By ignoring common VOCs, some species-specific VOCs could be detected. The most important VOC of E. coli was Indole, also some important VOCs produced by S. aureus were 2,3-Pentandione, cis-Dihydro-α-terpinyl acetate, 1-Decyne, 1,3-Heptadiene-3-yne, 2,5-dimethyl Pyrazine, Ethyl butanoate and Cyclohexene,4-ethenyl furthermore, most of identified compounds by C. albicans are alcohols. Conclusions: The detection of VOCs produced by infectious agents maybe the key to make a rapid and precise diagnosis of infection, but more comprehensive studies must be conducted in this regard.

Natural products are among the safe sources to produce and survey new bioactive compounds. Leutea elbursensis Mozaff. (Apiaceae) is an endemic and wild plant in Iran which grows on the foothills of Alborz Mountains. In this study, the essential oils (EOs) of dried samples of aerial parts and rhizome of L. elbursensis were extracted using Clevenger apparatus. Furthermore, the antibacterial activity of EOs was evaluated against Escherichia coli and Staphylococcus aureus standard strains as the models of Gram-negative and Gram-positive bacteria, respectively. The results of GC/MS spectrums indicated that β-pinene (24.7%), α-pinene (23.1%), and myrtenol (11.9%) were the most dominant products of aerial parts of the plant. Moreover, EO from the rhizome of L. elbursensis contained β-pinene (26.7%), α-pinene (19.3%), myrtenol (13.1%), and n-octanal (10.5%) as significant compounds. The findings showed that essential oils from aerial portions had more antibacterial action than rhizomes did against a number of different microbes. The MIC value of the EO from aerial parts was 8 mg/mL against E. coli, whereas this value was 16 mg/mL for the EO of the rhizome.

Resistance to antibiotics is an emerging and growing threat. To address this threat, attempts are being made by researchers to identify the Volatile Organic Compounds (VOCs) of bacteria. It is believed that unique combinations could be found among the VOCs produced by each microorganism. The current study aimed to identify and compare the VOCs of antibiotic-resistant and standard strains of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae. A polymer of divinylbenzene /carboxen /polydimethylsiloxane was applied for absorption of volatile compounds in headspace bacterial samples in form of a solid phase micro-extraction fiber holder. Gas chromatography-mass spectrometry technique was used for identification of volatile compounds. The analysis of the VOCs indicated that some VOCs appeared only in standard strains while others were common only among resistant strains. Exclusive VOCs to a specific strain were also detected. This study demonstrated that resistant strains of bacteria produced VOCs that were different from those of the standard strains. In addition, VOCs released by bacteria after passing the logarithmic growth phase showed no significant differences. The identification of VOCs can be a precise way to differentiate bacterial species, also it can be said that the VOCs produced by different pathogenic microorganisms can be the suitable biomarkers for their detection.