2. Antimicrobial Activity
There have been hundreds of research studies conducted on the antimicrobial activity of AR (
Table 1). This section will mention the most recent studies conducted, specifically, RA is used as a natural phytogenic additive in animal and poultry nutrition to improve their overall health, performance measures, the digestive system’s structure and function and its potential to modify the intestinal microbiota and decrease the number of disease-causing bacteria such as
Salmonella spp,
E. coli, and several other species of harmful bacteria
[7][8]. Rosemary extracts may contain RA as the primary bioactive antimicrobial agent. However, using the methanol extract containing about 30% carnosic acid, with 16% carnosol and 5% RA, Gram-positive and Gram-negative bacteria were shown to be sensitive to rosemary, making it an excellent antibacterial, in contrast to an aqueous extract containing 15% RA which had more limited effects
[9].
Due to their intense antimicrobial properties, medicinal plants, herbs and their oils are attracting great interest as innovative and alternative drugs, such as RA
[10].
According to Benedec et al.
[11], RA showed better antioxidant activity in vitro (DPPH technique) as well as significant action towards the Gram-positive bacteria. In addition,
Rosmarinus officinalis extract showed even greater inhibition of the growth of Gram-positive bacteria than the Gentamicin control (
Candida albicans). On the other hand, these researchers noted that this extract was without effect toward Gram-negative bacteria such as
S. typhimurium,
L. monocytogenes, E. coli,
S. aureus, and
C. albicans were found to be resistant to RAs derived from:
Hyssopus officinalis L.,
M. officinalis L.,
O. vulgare L.
[11]. RA addition decreases the rate of mortality in Japanese encephalitis virus-infected mice. Compared to animals infected with no RA treatment, the viral load was greatly reduced (
p < 0.001) in RA-treated infected rats 8–9 days after infection
[12].
The antibacterial properties of tannic acid have long been recognized as effective against both methicillin-resistant
Staphylococcus aureus and other microorganisms
[13]. Currently, one of the molecules used as a target for antibacterial polymer applications is the tannic acid–polymer metal complex
[14]. Hospitalized patients are severely harmed by
S. aureus, and tannic acid is known to be an inhibitor of various resistance phenotypes of
S. aureus [15]. Furthermore, by reducing cell counts and numbers, RA inhibits the development of
S. carnosus LTH1502 and
E. coli K-12
[16].
Moreno et al.
[9] examined extracts of
Rosmarinus officinalis through a combination of biological tests. Antimicrobial activities were analyzed by both disk diffusion and dilution broth techniques. Gram-positive bacteria, including
S. aureus,
B. megaterium,
B. subtilis, and
E. faecalis, were more sensitive to the methanolic extract, which contains 30% carnosic acid, 16% carnosol, and 5% rosmarinic acid (minimum inhibition concentration (MIC), 2 to 15 mg/mL). Gram-negative bacteria such as
K. pneumoniae, E. coli,
X. campestris pv. campestris, and
P. mirabilis were also treated with MIC 2 to 60 mg/mL, as well as yeasts such as
S. cerevisiae,
C. albicans, and
P. pastoris (MIC of 4 mg/mL). However, the aqueous extract with a 15% rosmarinic acid content only exhibited a narrow spectrum of activity. The MICs for methanolic and water extracts correlated significantly with the values for pure carnosic acid and rosmarinic acid. So, these results indicated a good performance in relation to the antimicrobial efficacy with rosemary extracts combined with the relevant phenolic extracts. The principal antimicrobial bioactive agents in rosemary extracts were suggested to be carnosic acid or rosmarinic acid. From the point of view of practicality, it could be considered as a good nutritional supplement and herbal pharmaceutical product.
Rosmarinic acid has antibacterial properties against
Staphylococcus aureus,
E. coli,
B. subtilis, and
Salmonella. Hayriye
[17] tested the effect of natural phenolic compounds extracted from vegetables, fruits, herbs and spices against these pathogens and
E. coli had minimum bactericidal concentrations (MBC) of 0.9 mg/mL and minimum inhibitory concentrations (MIC) of 0.8 mg/mL.
Salmonella had MIC and MBC of 0.9 and 1.0 mg/mL, respectively.
Staphylococcus aureus and
B. subtilis had MIC and MBC values of 1.0 and 1.1 mg/mL
[17], respectively.
The strains LM1, LM2, and LM3 of
L. monocytogenes were analyzed, and the presence of rosmarinic acid was shown to have no antibacterial effect over the incubation period of 60 h
[18]. Previously, rosmarinic acid has been shown to exhibit high susceptibility to Gram-negative bacteria when exposed to rosmarinic acid, after 60 h of incubation, Salmonella species showed substantial levels of antimicrobial resistance, and the MICs of rosmarinic acid for
S. enteridis,
S. choleraesuis subsp., and
S. paratyphi were less than 20 ppm
[18].
Furthermore, rosmarinic acid had previously been recognized as an anti-HIV drug capable of inhibiting HIV replication
[19]. The discovery of nitro and dinitro-rosmarinic acids, which inhibit viral replication by blocking HIV-I integrase, has significantly enhanced the anti-HIV efficacy of rosmarinic acid
[20].
Table 1. Rosmarinic acid and its derivatives are used as antibiotics against several pathogenic microorganisms.
3. Antibiofilm Activity
The production of biofilms is one of the main processes responsible for antibiotic resistance. Recent research has revealed that natural substances based on secondary metabolites from plants can prevent the development of biofilms, which are responsible for about 80% of bacterial diseases
[27][28]. Biofilms, which are bacterial colonies adhering to the surface and enveloped in a protective extracellular matrix, make bacteria up to 1000 times less susceptible to antibiotics and represent a real health problem
[27]. The most common opportunistic fungal diseases in the world are Candida species, which form highly structured biofilms, which are collections of cells of different natures surrounded by an extracellular matrix. Furthermore, the current standard treatment for these infections is to seek innovative treatments for biofilm-related disorders, as these fungal biofilms are typically resistant to conventional antifungal drugs
[28].
The quorum sensing inhibition (QSI) potential of rosmarinic acid (RA) towards
Aeromonas hydrophila strains MTCC 1739, AH 1, and AH 12 was examined. The
A. hydrophila pathogenic strains were isolated from infectious zebrafish species as well as an RA biofilm inhibitory concentration (BIC) versus
A. hydrophila strains that was found as 750 μg mL
−1. RA at this concentration decreased QS-induced production of hemolysin, elastase, and lipase from
A. hydrophila. However, in FT-IR analysis, AR-treated
A. hydrophila cells exhibited a reduction in cellular components, and the analysis of gene expression affirmed the negative regulation of virulence genes such as aerA, ahh1, ahyB, and lip. Zebrafish contaminated with
A. hydrophila and given RA showed increased survival. Therefore, a study demonstrated the use of RA as an herbal compound to control biofilm formation by QS as well as virulence factor generation in
A. hydrophila [29].
Biofilms of
C. krusei H1/16 showed the highest resistance against rosmarinic acid treatment; MBEC > 1.6 mg/mL was the minimum biofilm eradication concentration, and biofilms of both
C. albicans 475/15 and
C. albicans ATCC 10,231 and eradicated with 0.4 mg/mL of rosmarinic acid. In contrast to cell attachment, biofilm formation was more strongly affected for
C. albicans strains than for non-
C. albicans [22].
RA consumption affected the formation of biofilms at a concentration- and the time-dependent manner, further implying for RA as an effective antimicrobial agent as well as for destroying the activity of planktonic cells and reducing the formation of biofilms at the earlier time stage to their development
[30]. RA also inhibits the growth of
E. coli K-12 and
S. carnosus LTH1502, reducing the density and number of cells
[16]. In acidic medium, RA was found to react chemically to nitrite ions to generate 6,6-nitro and 6-dinitrorosmarinic acids, the latter were active at submolecular levels as HIV-1 integrase inhibitors and inhibited viral replication in MT-4 cells, and antiviral effects
[20]. RA nitration significantly increased integrase inhibition and antiviral effects without increasing the levels of cellular toxicity. In addition, RA also possesses antimicrobial effects against lactic acid bacteria, yeasts, molds,
Enterobacteriaceae spp, and
Pseudomonas spp, as well as against psychotropic drugs and
L. monocytogenes from chicken meat
[31]. In addition, RA exhibits inhibitory effects on the
S. aureus cocktail by intimating morphological changes, decreasing and reducing all viable cells, and inducing morphological alterations into cheese and meat samples, from cell shrinkage to the formation of burr-like structures on the cell surface
[32][33][34].
The antibacterial effects of rosmarinic acid (RA) against clinical strains of
S. aureus from catheter infections were tested by Slobodníková et al.
[30]. The regeneration method detected 24 h biofilm eradication activity on microtiter plates. The microtiter plate approach permitted the quantification for biofilm formation activity following application of RA to bacterial samples at 0, 1, 3, and 6 h post biofilm formation, with RA exhibiting antimicrobial activity at concentrations ranging from 625 to 1250 g·mL
−1 (MICs equal to MBCs). In the concentration of the 156 to 5000 g·mL
−1 evaluated range, there were no biofilm eradicating actions on the 24 h biofilm. When processed at the beginning of biofilm formation, RA subinhibitory doses inhibited the synthesis of biofilm; in concentrations less than the subinhibitory level, the formation of biofilm mass was increased in a time- and concentration-dependent manner. This evidence indicates the potential for RA to be an effective topical antimicrobial agent for treating catheter-related infections, with activity against both planktonic forms of bacteria and inhibitory activity during the early stages of biofilm development. However, it is not practical to use RA as the only agent to treat catheter-related infections
[35].