Food Microbiology (FM) | Bioactive Compounds or Metabolites: Function and Application
Microbiol. Biotechnol. Lett. 2022; 50(2): 193-201
https://doi.org/10.48022/mbl.2201.01007
Sompong Tabunhan* and Parunkul Tungsukruthai
Chulabhorn International College of Medicine, Thammasat University, Pathum-Thani 12120, Thailand
Correspondence to :
Sompong Tabunhan, tabunhan@tu.ac.th
Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) are major causes of hospital- and community-acquired infections. The treatment of biofilm-related infections caused by these bacteria is a global healthcare challenge. Therefore, the development of alternative therapeutics is required. An essential oil extracted from Curcuma zedoaria (CZ) Rosc, also known as white turmeric, has been reported to possess various antimicrobial activities. In the present study, we evaluated the antibiofilm activities of an ethanolic extract of the CZ rhizome against MRSA and MSSA. The results showed that the CZ extract with the highest sub-minimum inhibitory concentration (sub-MIC), 1/2 MIC (0.312 mg/ml), significantly inhibited biofilm production by up to 80-90% in both tested strains. Subsequently, we evaluated the ability of the CZ extract to prevent cell-surface attachment to a 96-well plate and extracellular DNA (eDNA) release from the biofilm. The CZ extract demonstrated an inhibitory effect on bacterial attachment and eDNA release from the biofilm biomass. The CZ extract may inhibit biofilm formation by preventing eDNA release and cell-surface attachment. Therefore, this CZ extract is a potential candidate for the development of alternative treatments for biofilm-associated MRSA and MSSA infections.
Keywords: Curcuma zedoaria, antibiofilm, methicillin-resistant Staphylococcus aureus, methicillin-susceptible S. aureus, extracellular DNA, attachment
Antibiotics resistance in bacteria has increased dramatically worldwide and is a major cause of death and healthcare-associated infections (HAIs) [1]. One of the major pivotal characteristics that enhance bacterial resistance to antimicrobial agents is biofilm formation. Biofilm is a microbial community structure enclosed by a self-produced extracellular polysaccharide matrix that attaches to biotic or abiotic surfaces [2]. Biofilm-associated infections can complicate treatments involving catheter-related infections and lead to treatment failure [3]. Several studies have reported that biofilm-forming bacteria are more resistant to antibiotics than the plank-tonic form and also have an increased ability to persist within infected hosts, resulting in chronic infection [4, 5].
Currently, infectious diseases caused by methicillinresistant
The biofilm-forming ability of MRSA and MSSA strains is considered a key characteristic influencing its persistent infection in the host and results in complications of treatment, especially those associated with medical device-related infections such as catheters and medical implants [11]. The treatment of biofilm-associated infections of MRSA and MSSA is more difficult, leading eventually to chronic device-related infections [12]. The single use of standard antibiotics is ineffective, especially for infections in biofilm form. Several studies have demonstrated the use of alternative treatment strategies for combating biofilm-associated infections, especially plant extract or a combination of plant extract and antibiotics.
The ethanol extract of the rhizome of CZ was prepared as follows. Briefly, 20 g of mashed CZ rhizome was extracted with 150 ml of 70% ethanol (HPLC grade) in 250 ml Erlenmeyer flask and sonicated for 30 min; sonication was repeated 4 times until extraction was exhaustive. After sonication, the combined extract of each time was filtrated through Whatman filter paper no. 1. The filtrate was evaporated using a rotary evaporator for ethanol removal and drying in a water bath at 40℃ until the excess solvent was completely removed, and the percent yield of dry weight was recorded. The extract was stored at 20℃ until use.
Curcuminoids (curcumin, bisdemethoxycurcumin, and demethoxycurcumin), a major phenolic compound found in rhizome of
Methicillin-resistant
The broth microdilution method using a 96-well microplate (Nunclon, Thermo Scientific, China) was used to determine the inhibitory efficacy of CZ ethanolic extract against MRSA and MSSA. Two to three single colonies of the bacteria were inoculated into 3 ml MHB and incubated overnight at 37℃ with shaking at 250 ×g for 18 h. Two hundred microliters of the bacterial suspension were then transferred into fresh 10 ml MHB and continued incubation until attaining the exponential phase. The bacterial cells were adjusted to 0.5 at OD600 by a spectrophotometer (bacteria no.1-1.5 × 108 CFU). Bacterial broth cultures were diluted to correspond to the final inoculums of 5 × 105 CFU/ml upon inoculation into each well containing two-fold serial dilution of test samples. The extract was then tested with concentrations varying from 0.019 mg/ml to 5 mg/ml parallel with control antibiotics, vancomycin, and ampicillin.
The extract was prepared by two-fold serial dilution with TSB-glucose in a 96-well microplate at concentrations of 5 to 0.019 mg/ml. MRSA and MSSA without the extract were used as the positive control. A single colony of MRSA and MSSA from the overnight culture grown on TSA was inoculated into 3 ml TSB and incubated at 37℃ for 24 h with shaking at 250 rpm. The bacterial suspension was diluted to 1:50 in fresh TSB-glucose to give a final concentration of inoculation size of approximately 1×105 CFU/ml in a total volume of 200 μl in each well of a 96-well microplate (Nunc). The microplate was incubated at 37℃ for 24 h. After static incubation, the plank-tonic cells in each well were removed and washed twice with 200 μl phosphate buffer saline (PBS) and air-dried. Wells were fixed with 200 μl 99% methanol for 15 min and removed, and then the plates were allowed to dry. The plates were stained with 200 μl/well of 0.1% crystal violet for 5 min. Excess crystal violet stain was gently rinsed off with tap water, after which the plates were allowed to air dry. The stain was solubilized with 200 μl of 33% glacial acetic acid and shaken in a microplate orbital shaker for 30 min, and then measured at OD570 nm. The experiment was done in triplicate on different occasions.
The experiment was carried out based on methods previously described by Carolina Santiago
The quantity of eDNA in biofilm biomass of MRSA and MSSA was determined using QuantiFluor dsDNA System (Promega, USA) in a 96-well black plate (Nunclon, Thermo Scientific, Denmark), as described previously by Pakkulnan
The experiments were performed in triplicate. Significance was assessed by one-way analysis of variance (one-way ANOVA), Scheffe test, and Dunnett’s T3 post hoc analysis using IBM SPSS Statistics version 20.0 software. The significance level was considered as a
The extraction yield of ethanolic extracts of CZ rhizome was 17.40 ± 0.58% w/w. Fig. 1 shows the HPLC chromatogram of curcuminoid content in CZ extract consisting of bisdemethoxycurcumin, demethoxycurcumin, and curcumin. Quantitative analysis of the extract based on a simple linear regression equation obtained from standard curcuminoids was determined in μg/ml. The results showed that curcuminoid contents in the sample extract were bisdemethoxycurcumin (49.8 μg/ ml), demethoxycurcumin (255.96 μg/ml), and curcumin (114.72 μg/ml). The highest curcuminoid content found in the CZ extract was demethoxycurcumin.
From the results of the disc diffusion method, an antibiotic disc containing 2.5 mg of CZ rhizome extract showed antimicrobial activity against both MRSA and MSSA with an inhibition zone of 8 mm. A standard disc containing 30 μg of vancomycin was used as a positive control and showed an inhibition zone of 16 mm. The negative control DMSO did not show an inhibition zone. To evaluate the MIC of CZ extract, a two-fold dilution of the concentration ranging from 5 to 0.019 mg/ml was performed in a 96-well microplate. The results showed that CZ extract exhibited antimicrobial activity against both MRSA and MSSA with the same MIC value of 0.625 mg/ml. The MIC of standard antibiotics control, including ampicillin, vancomycin, and oxacillin are also shown in Table 1.
Table 1 . Minimum inhibitory concentration (MIC) of ethanolic extract of CZ rhizome and antibiotic control against MRSA ATCC 43300 and MSSA ATCC 25923.
Antibiotics and extract | MIC (mg/ml) | |
---|---|---|
MRSA | MSSA | |
Ampicillin | 0.128 | 0.008 |
Vancomycin | 0.001 | 0.002 |
Oxacillin | 0.032 | 0.0005 |
CZ rhizome extract | 0.625 | 0.625 |
The results of crystal violet staining showed the inhibitory activity of CZ rhizome extract on both MRSA and MSSA biofilm formation. The total biofilm production of MRSA and MSSA after being treated with CZ was strongly decreased in a dose-dependent manner when compared with untreated control. To assess the growth of the planktonic cells under biofilm conditions, the turbidity of bacterial growth in a 96-well microplate was measured at OD600. The results showed that planktonic cell growth was comparable to the positive control (data not shown). A sub-minimal inhibitory concentration (sub-MIC) of CZ extract was used to evaluate the biofilm formation of tested strains. At the sub-MIC of CZ ranging from 1/32 MIC to 1 MIC, the percentage of biofilm production of MRSA was significantly reduced (
To evaluate the properties of CZ extract on bacteria adherence ability to an abiotic surface, a bacterial attachment assay was performed in a 96-well microplate. The result of adherence cells was determined by the crystal violet staining method after 1 h of incubation. The results indicated the ability of bacterial adhesion to microplate surfaces was strongly inhibited by CZ extract in a dose-dependent manner when compared with untreated control. At sub-MIC concentrations of 1/32 MIC -1 MIC, CZ extract showed significant (
Based on the hypothesis that eDNA production is associated with bacterial attachment and biofilm formation of
Table 2 . Correlation analysis between eDNA quantity and biofilm biomass of
eDNA quantity | Biofilm biomass of | |
---|---|---|
MRSA | MSSA | |
Pearson correlation’s coefficient | 0.871 | 0.965 |
0.011 | < 0.001 |
In this study, we evaluated the antimicrobial and antibiofilm properties of
Another study also revealed that the water extract of rhizomes of CZ showed an inhibition zone of 9.8 mm at a concentration of 30 mg [23].
In previous studies of the minimum inhibitory concentration (MIC), CZ tubes extract showed inhibitory effects against six bacterial pathogens, both Gram-positive and Gram-negative, with MIC values ranging from 0.01 to 0.15 mg/ml, but did not inhibit the growth of
Biofilm formation plays an important role in the pathogenesis and antimicrobial resistance of several pathogenic bacteria [25]. The biofilm-forming ability of MRSA has been reported to increase pathogenicity and antimicrobial resistance [26, 27]. Therefore, the treatment of highly biofilm-forming strains is more difficult than that for non-biofilm-forming strains [28, 29]. This is the first study to evaluate the effect of CZ extract on the biofilm formation of MRSA and MSSA. The results of our study showed that CZ extract at sub-MIC ranges from 1/16 MIC to 1 MIC significantly reduced the production of MSSA biofilm, while the MRSA biofilm was significantly decreased at lower concentrations of 1/32 MIC to 1 MIC (Figs. 2A and 2B). This result indicated that MRSA biofilm was more easily inhibited by CZ extract than that of MSSA biofilm. The antibiofilm activity of CZ extract has not been reported yet, while other species such as
Factually, the adhesion of the bacterial cell to abiotic or biotic surfaces is the initial step in biofilm formation. Therefore, the reduction of MRSA and MSSA biofilm after being treated with CZ extract was confirmed in this study by cell attachment assay on a 96-well micro-plate. The results indicated that bacterial cell-surface attachment to the microplate was significantly inhibited by CZ extract at sub-MIC concentrations ranging from 1/32 MIC to 1 MIC for MRSA and 1/8 MIC to 1 MIC for MSSA. These results demonstrated the inhibition activity of CZ extract against MRSA and MSSA biofilm formation by preventing bacterial cell-surface attachment. It is worth noting that the percentage of initial attachment is proportional to the percent of biofilm formation in both tested strains. The corresponding initial attachment and biofilm formation has been shown by several studies [41-43]. On the other hand, ampicillin failed to inhibit cell-surface attachment and biofilm production in MRSA. While, ampicillin can inhibit both cell-surface attachment and biofilm formation of MSSA. Previous studies have reported that low doses of β-lectam antibiotics such as ampicillin, penicillin, and amoxicillin enhanced MRSA biofilm formation [44, 45]. The mechanism of ampicillin-induced biofilm production and cell-surface attachment is not well understood. It was proposed that gene-encoding antibiotic resistance such as penicillin-binding protein PBP1, PBP1a/2, and PBP3, and many antimicrobial resistance proteins were up-regulated in an ampicillin-induced biofilm strain of
As a result of CZ extract reducing bacterial attachment and the development of biofilm, we further hypothesized that this extract may interfere with the release of eDNA, a component of extracellular matrix (ECM) released in biofilm biomass by several bacteria, including
This study determined that
This study was supported by Thammasat University Research Fund, Contract No. TUGR 2/59/2562. The authors express their gratitude to Bangkok Drug Co., Ltd. for providing the HPLC standard compounds.
The authors have no financial conflicts of interest to declare.
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