Tehran University of Medical Sciences Traditional and Integrative Medicine 2476-5104 7 2 2022 06 19 187 194 Zahra Gholami Trauma Nursing Research Center, Faculty of Nursing and Midwifery, Kashan University of Medical Sciences, Kashan, Iran Mansour Dianati Trauma Nursing Research Center, Faculty of Nursing and Midwifery, Kashan University of Medical Sciences, Kashan, Iran Mahboobeh Maghami Biostatics and Epidemiology Department, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran Mohammad Reza Afazel Trauma Nursing Research Center, Faculty of Nursing and Midwifery, Kashan University of Medical Sciences, Kashan, Iran Ismail Azizi-Fini Trauma Nursing Research Center, Faculty of Nursing and Midwifery, Kashan University of Medical Sciences, Kashan, Iran 2021 07 31 2021 10 23 This study aimed to examine the effect of Zataria multiflora Boiss. mouthwash on the microbial load of the oral cavity in patients under mechanical ventilation. This randomized controlled trial was conducted in 2019 on patients under mechanical ventilation. Sampling was performed using the consecutive method. Using a block randomization method, 90 patients were allocated to three equal groups of 30 to receive mouth care using chlorhexidine, Z. multiflora, or normal saline. Mouthwash was used three times a day for a week. Eight hours before and after the intervention, sterile samples of saliva were collected and cultured in the laboratory. Chi-square, Fisher's exact test, paired t and McNemar’s tests, and analysis of variance were used to analyze the data. After the interventions, a significant difference in the microbial load was found between the three groups (P < 0.021). The Tukey post hoc test showed a significant difference between the group treated with Z. multiflora and those who received chlorhexidine (P value = 0.016). The frequency of patients with positive cultures was lower in the group treated with Z. multiflora and the differences were statistically significant in terms of Acinetobacter (P = 0.01) and Klebsiella pneumonia (P = 0.02). Z. multiflora mouthwash was effective in decreasing the microbial load of the oral cavity. This mouthwash can be used to reduce the microbial load of the oral cavity in patients under mechanical ventilation and reduce the risk of ventilator-associated pneumonia. https://jtim.tums.ac.ir/index.php/jtim/article/view/495