Ventilator-associated pneumonia (VAP) is considered a nosocomial infection that significantly increases the risk of mortality, ventilator time, length of stay, and cost of care (Zampieri et al., 2015). The prevalence of pneumonia in patients with an endotracheal tube is 6–21 times higher than in patients without this tube (Othman et al., 2017). The prevalence of this pneumonia in intensive care units (ICU) has been reported differently in various parts of the world. In a Thai study, the prevalence of VAP was 36%. The report also identified VAP as the most common infection in Pakistan (28%), Lebanon (47%), and India (81%) wards (Khalifehzadeh et al., 2012).

The most important risk factors for VAP are the duration of intubation and mechanical ventilation (MV), intestinal feeding, supine position, number of antibiotics used, disease severity, and underlying diseases such as chronic obstructive pulmonary disease, burn, and trauma (E.-V. S. Investigators, 2014, Kunis and Puntillo, 2003, Ranjan et al., 2014, Torres and Carlet, 2001). Patients with severe trauma are at high risk for pneumonia. Although it is well known that MV is the most important risk factor for pneumonia, trauma patients appear to be particularly susceptible. Up to 44% of trauma patients who require MV develop respiratory-related pneumonia (Brown et al., 2001, Rodriguez et al., 1991).

Evidence-based research and guidelines have suggested a number of measures to prevent VAP, including mouth care and hand washing, head-of-bed alarms, subglottic suctioning (Sedwick et al., 2012), reduced duration of MV, and length of stay, which are consistently reported by investigators when interventions facilitating early extubation are bundled together (Hsieh et al., 2019, Pun et al., 2019). Therefore, minimising sedation and early mobilisation are considered to be most beneficial in VAP prevention (Papazian et al., 2020). The use of antimicrobials for the prevention and treatment of VAP, which is often caused by multidrug-resistant Gram-negative pathogens, is recommended as well (Michalopoulos and Falagas, 2013).

Today, due to the spread of multidrug-resistant bacteria and the increase in antibiotic resistance, different types of nosocomial pneumonia do not respond to common antibiotics in treatment, leading to more complications and mortality in these patients (Zaragoza et al., 2020). Thus, various researchers have focused on the antimicrobial effects of plants and their extracts. Trachyspermum ammi is one of the drugs used in complementary medicine.

T ammi is a plant of the genus Umbelliferae, shrubby, herbaceous, annual, hairless to a height of 60–90 cm, and full of foliage. It is called “Trachyspermum ammi” in Persian, and its plant is called the Abyssinian commune in traditional medicine books with the name of Anison Berry (Asif et al., 2014). The T ammi (L.) of the Apiaceae family is an ancient plant with various healing properties. There are medical and traditional reports about the effects of T ammi oil and hydrosol on neurological disorders such as paralysis and tremors, as well as chronic pain, eye and ear infections, digestive diseases, and female genital disorders.

It also has diuretic (Zarshenas et al., 2013), antibacterial, antiviral (Kazemi Oskuee et al., 2011), antifungal (Natanzian Ghahfarkhi et al., 2008), anticough (Ali and Blunden, 2003, Qureshi and Barabde, 2021), anti-inflammatory (Thangam and Dhananjayan, 2003), analgesic (Singh and Mandal, 2021), antitumour (Zahin et al., 2010), antioxidant, and bronchodilator effects (Boskabady et al., 2007, Goyal et al., 2022). Chewing T ammi seeds mixed with cloves and a little salt has been reported to be effective in treating pharyngitis and influenza. In addition, if a tablespoon of T ammi seeds is crushed and then inhaled, it can be effective in treating common colds and nasal congestion. The seeds of T ammi with salt are useful for treating acute pharyngitis, sore throat, throat congestion, and hoarseness due to colds (Arif, 2019).

The main compounds in T ammi are thymol and carvacrol, which are responsible for their antimicrobial properties. Thymol is resistant to common third-generation antibiotics. Multidrug-resistant microbial pathogens, and thus they act as 4th generation herbal antibiotic formulations (Arif, 2019).

A study conducted by Nouri Gharajalar (2021) has shown that T ammi can be used as an important natural alternative to prevent the growth of shared human-animal bacteria. Another study evaluated the inhibitory effect of this oil on Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae, and it was found that T ammi essential oil (EO) has antibacterial effects against human pathogens (Mood et al., 2014).

According to the literature review, no study, to the best of our knowledge, has so far investigated the effect of T ammi on VAP. Therefore, this randomised clinical trial was conducted to examine the effect of the enteral feeding of T ammi syrup on VAP in patients in the trauma ICU.