Abstract
ESKAPE pathogens, namely, Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species, are responsible for a majority of all healthcare-acquired infections (HAI). The bacteria cause nosocomial infections in immunocompromised patients. Extracts from Callistemon viminalis have been shown to have antibacterial, antifungal, and anti-inflammatory activities. Tormentic acid congener, a pentacyclic triterpene saponin, was isolated from C. viminalis leaves. This study aimed to investigate the antibacterial effects of tormentic acid congener and leaf extracts on biofilm formation by A. baumannii, S. aureus, S. pyogenes, and P. aeruginosa. The antibacterial effects were determined by the microbroth dilution method, and ciprofloxacin was used as the standard antibacterial drug. Biofilm formation and detachment assays were performed using crystal violet staining. Production of extracellular polymeric DNA and polysaccharides from biofilms was also determined. Tormentic acid congener showed time-dependent antibacterial activity against P. aeruginosa with a MIC of 100 µg/ml and caused significant protein leakage. Antibacterial activity was found when tormentic acid congener was tested against both S. aureus and P. aeruginosa. The MICs were found to be 25 µg/ml and 12.5 µg/ml for P. aeruginosa and S. aureus cells, respectively. S. pyogenes was found to be susceptible to tormentic acid congener and the hydroethanolic extract with an MIC of 100 µg/ml and 25 µg/ml, respectively. A. baumannii was found not to be susceptible to the compound or the extracts. The compound and the extracts caused a significant decrease in the biofilm extracellular polysaccharide content of S. pyogenes. The extracts and tormentic acid congener caused detachment of biofilms and decreased the release of extracellular DNA and capsular polysaccharides from biofilms of P. aeruginosa and S. aureus. Tormentic acid congener and extracts, thus, have significant antibacterial and antibiofilm activities on these selected ESKAPE bacteria and can act as source lead compounds for the development of antibacterial triterpenoids.
Highlights
ESKAPE pathogens are responsible for two-thirds of all healthcare-associated infections [1]. e Infectious Diseases Society of America (ISDA) formulated an acronym ESKAPE to emphasize the group of pathogens that cause hospital infections and effectively “escape” the effects of antibacterial drugs [2]
E principle active showed the molecular ion (M+) at m/z 488, which agrees with the molecular formula C30H48O5. e 1H-NMR spectrum showed the presence of six singlet methyls and two doublet methyls, which were characteristic of the ursene skeleton, and exhibited signals of an olefinic proton (δ 5.14). e spectrum showed a singlet at δ 3.49 (m) and two oxygen-bearing methine protons suggestive of the 2α, 3β, 19αtrihydroxy structure. ese results indicated that the compound was an ursane-type triterpene
After incubation with MTT, the number of viable cells was determined spectrophotometrically. e antibacterial susceptibility tests showed S. aureus and K. pneumoniae (Figure 1) to be more susceptible to both extracts of C. viminalis than P. aeruginosa. ese results are consistent with those of other studies which suggest that Gram-negative bacteria are less susceptible to xenobiotics than Gram-positive bacteria [35]
Summary
ESKAPE pathogens are responsible for two-thirds of all healthcare-associated infections [1]. e Infectious Diseases Society of America (ISDA) formulated an acronym ESKAPE to emphasize the group of pathogens that cause hospital infections and effectively “escape” the effects of antibacterial drugs [2]. ESKAPE pathogens are responsible for two-thirds of all healthcare-associated infections [1]. E Infectious Diseases Society of America (ISDA) formulated an acronym ESKAPE to emphasize the group of pathogens that cause hospital infections and effectively “escape” the effects of antibacterial drugs [2]. Nosocomial infections are responsible for hospital-acquired infections largely in immunocompromised patients [4]. K. pneumoniae and P. aeruginosa have been found to cause life-threatening hospital infections in critically ill individuals [5]. Ese two pathogens have acquired resistance against some of the common antibacterial drugs [6]. K. pneumoniae belongs to the family Enterobacteriaceae [7], and it is one of the most common pathogens associated with hospital-acquired infections [8]. A. baumannii has the ability of surviving for long periods on hospital surfaces and equipment. is is aided by its ability to develop resistance to multiple antibiotics [14] leading to outbreaks in clinical settings [15]
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