# Antioxidant and Antibacterial Properties of Extracts and Bioactive Compounds in Bryophytes
## 3 Antioxidant Activity
Both dilution consists of two-fold serial dilution of the tested compound in a liquid culture medium (e.g., 4, 8, 16 \(\upmu\)g/mL). Standardized bacterial suspensions (1-5 \(\times\) 10\({}^{5}\) CFU/mL) are inoculated in antimicrobial containing tubes. After the incubation (16-24 h at 35 \({}^{\circ}\)C), tubes are examined to spot evidence of bacterial growth (i.e., medium turbidity). The lowest concentration at which bacterial growth is not evidenced represents the minimal inhibitory concentration (MIC) [55]. A wide number of studies have explored the in vitro antibacterial activity of various solvent extracts such as water, ethanol, methanol, chloroform, butanol [31; 56; 57; 58; 59; 60; 61; 62; 63; 64]. Differences in the activity depend on the type of extract used, the tested species, the extraction procedure, and the bacteria strain. Other researchers, who have examined the chemical composition of the extracts and have found that, depending on the solvent used, bryophytic extracts are rich in flavonoids; terpen; terpenoids; phenols; biphenyls; and steroids [33; 65; 66; 67]. These compounds are known to exert an antibacterial activity [68; 69]. Some researchers achieved the isolation of compounds responsible for antibacterial activity in bryophytes: (a) the macrocyclic (bis)bibenzyls marchantin A [70] and perrottein A, B, C, D, F [71; 72]; (b) the biphenyl lunularin [73]; (c) the glycoslate flavonoids luteolin-7-O-neohesperoside, apigenin-7-O-triglycoside, saponarin, (d) the flavonoids apigenin, lucenin-2, butramiaflavone [74], (e) the sesquiterpenoids \(\alpha\)-herbertenol; \(\beta\)-herbertenol; herbertene-1,2-diol; mastigophorene C, \(\alpha\)-formyl herbertenol, and lepidozenolide [75; 76]. These compounds have shown a weak to strong activity against several human pathogenic bacteria [70; 71; 73; 74; 75; 76; 77; 78]. Gram-negative bacteria are particularly worrisome since they are becoming resistant to nearly all the antibiotic drug options available [79]. Among pathogenic bacteria, resistant strains of _Staphylococcus aureus_, _Streptococcus pneumoniae_, _Enterococcus_ ssp, _Pseudomonas aeruginosa_, _Escherichia coli_, _Klebsiella pneumoniae_ are of serious concern [18; 79]. Methicillin-resistant Staphylococcus aureus (MRSA) is a major threat in health care structures, being the most resistant _S. aureus_ strain [18; 80]. Several researches have focused on the efficacy of bryophyte extracts against _S. aureus_ (Table 3). The vast majority of these studies have evidenced the antibacterial activity of several pure compounds against normal strains of _S. aureus_: biphenyls [71; 72; 81; 82]; sesquiterpenoids [75]; extracts [56; 58; 61; 83; 84]. Agar disk diffusion against _S. aureus_ of several sesquiterpenoids isolated from _Mastigophora diclados_ methanolic extracts results in a zone of inhibition ranging from 13 to 17 mm. The sesquiterpenoid mastigophorene C showed the highest activity (17 mm) yet lower to reference antibiotics chloramphenicol (22 mm) and kanamycin (23 mm). Marchantin A purified from methanolic extracts was found to be effective against _S. aureus_ (MIC 3.13 \(\upmu\)g/mL) [81]. Another study found a slightly lower MIC (0.062 mg/mL) and a disk diffusion inhibition zone of 11 mm [82]. Interestingly, in some studies, bryophyte extracts and pure compounds have shown anti-MRSA activity [76; 83]. Ref. [85] have attempted to synthetize three geometrical isomers of the bis(bibenzyl) isoplagiochin D and tested the derivatives molecules on MRSA. They found that two out of three derivatives had a potent anti-MSRA activity (MIC 0.5 \(\upmu\)g/mL and 2 \(\upmu\)g/mL). MDR (Multi-Drug Resistant) _Pseudomonas aeruginosa_ cause 6000 of 51,000 infections and about 400 deaths every year in the U.S. [79]. Interestingly, the inhibitory activities against _Pseudomonas aeruginosa_ have been proved also by other studies both in organic solvent extracts [86; 87; 84; 88] and biphenyls and flavonoids [73; 74]. Depending on the solvent and the selected species, MIC ranged from 3.91 \(\upmu\)g/mL to 110 \(\upmu\)g/mL.