**2.2 Anti-microbial effect**

The list of antibiotics is supplementing day by day due to antimicrobial resistance issues. These antibiotics are helpful and have extended spectrum but are responsible for various adverse effects. These adverse effects minimize the patient compliance, and, therefore, the search for new, effective and affordable antibiotic is a big challenge to phytochemical researchers. In this respect, natural antibiotics could have multiple uses in addition to the antibiotic effect; therefore, the use of natural antibiotic can minimize the polypharmacy. Within this context, research findings indicated that the crude leaf extract of *P. lenticus* and *P. atalantica* significantly reduce the fungal growth, whereas weak bacterial inhibitory effect was reported [1]. Roozegar investigated the effect of *P. atalantica* leaf extract against mouth and saliva bacterial load, and reported a significant effect against *S. mutans* and *S. mitis* in disk diffusion method with zone of inhibition of 19 and 25 mm, respectively; no significant effect was observed against *S. salivarius* [8]. The mouthwash of *P. atalantica* exhibited excellent antimicrobial effect against gingival microorganism. Therefore, this mouthwash was recommended as effective and safe [9].

Similarly, the hydro extract of *P. atalantica* was tested against different bacteria *in vitro* and was found effective against *E. coli*, *P. aeruginosa* and *S. aureus*, except for *H. pylori* [10]. Additionally, the hydro distilled essential oil from the stem of *P. vera* was tested against some pathogenic bacteria, and exhibited significant effect against *E. coli* and *S. aureus* [11]. Furthermore, the antibacterial potential of *P. lenticus* extract was tested against gram positive and gram-negative bacteria. Results demonstrated that the extract exerts significant effect against gram positive as compared to gram negative bacteria [12]. The leaf extract of *P. khinjuk* when screened for the antibacterial and antifungal potential exhibited significant activity [13]. On the other hand, the essential oil of *P. khinjuk* was found to contain, through GC–MS analyses γ-terpinene (81.14%) (w/w), β-pinene (3.93%) (w/w), and α-terpinolene (2.38%) (w/w). This essential oil was tested for activity against *P. aeruginosa* and *S. subtilis.* Chemical constituents of the essential oil might be responsible for the antibacterial effect against the tested pathogenic bacteria [14]. Similarly, the essential oil from the leaves of *P. lenticus* was also tested against different gram positive and gram negative pathogenic bacteria. The major chemical constitutes in essential oil were α-pinene and β-pinene, and a variable degree of antibacterial effects were observed [15]. Volatile compounds from the essential of leaves and fruits of *P. lenticus* exhibited best antibacterial effect [16]. Likewise, the antimicrobial effect of *P. integerrima* has been reported against various pathogenic microbes. The oil was found rich in 1-terpinen-4-ol (28.82%), p-menth-1-en-8-ol, (43.38%), *n*-octyl acetate (19.91%), and β-farnesene (7.88%). The concentration of α-terpinolene, limonene and α-thujene were less than 1%. The tested oils exhibited promising antibacterial activities. The zone on inhibition against *E. coli, S. aureus, K. pneumonia, Straptodirimu, B. stearothermophilus* and *S. typhimurium* was 16, 18, 26, 22, 18 and 20 mm, respectively [17]. The essential oil of *P. terebinthus* (collected from Tunisia and Italy) was reported along with chemical composition (GC and GC–MS). The oil was isolated through hydrodistillation. The oil consisted of monoterpene hydrocarbons (86.3% and 90.9%, respectively), α-pinene (62.4 vs. 35.0)%, camphene (3.0 vs. 2.4)%, β-pinene (12.1 vs. 4.5)%, terpinolene (1.7 vs. 35.2)% and β-phellandrene (3.8 vs. 4.5)% as the main components. The oil demonstrated significant effect against *T. rubrum*, *M. canis* and *E. floccosum*, with MIC and MLC values in the range (0.16–0.32) μL/mL [18]. In view of the above discussion, these plants might help against different pathogenic infections. Plants accumulate numerous phytochemicals that interact with the micro-organisms. The inhibition or the killing of these micro-organisms might be due to cell wall inhibition or protein synthesis inhibition or might be due to the antimetabolite action of constitutes. These plants' use for the above infections needs to explore the exact mechanism on related microbes and clinical trials.
