ABSTRACT
ABSTRACT Bacteroides fragilis is the strict anaerobic bacteria most commonly found in human infections, and has a high mortality rate. Among other virulence factors, the remarkable ability to acquire resistance to a variety of antimicrobial agents and to tolerate nanomolar concentrations of oxygen explains in part their success in causing infection and colonizing the mucosa. Much attention has been given to genes related to multiple drug resistance derived from plasmids, integrons or transposon, but such genes are also detected in chromosomal systems, like the mar (multiple antibiotic resistance) locus, that confer resistance to a range of drugs. Regulators like MarR, that control expression of the locus mar, also regulate resistance to organic solvents, disinfectants and oxygen reactive species are important players in these events. Strains derived from the parental strain 638R, with mutations in the genes hereby known as marRI (BF638R_3159) and marRII (BF638R_3706) were constructed by gene disruption using a suicide plasmid. Phenotypic response of the mutant strains to hydrogen peroxide, cell survival assay against exposure to oxygen, biofilm formation, resistance to bile salts and resistance to antibiotics was evaluated. The results showed that the mutant strains exhibit statistically significant differences in their response to oxygen stress, but no changes were observed in survival when exposed to bile salts. Biofilm formation was not affected by either gene disruption. Both mutant strains however, became more sensitive to multiple antimicrobial drugs tested. This indicates that as observed in other bacterial species, MarR are an important resistance mechanism in B. fragilis.
Subject(s)
Humans , Anti-Bacterial Agents/pharmacology , Bacterial Proteins/genetics , Bacteroides fragilis/drug effects , Bacteroides fragilis/genetics , Bacteroides Infections/microbiology , Repressor Proteins/genetics , Bacterial Proteins/metabolism , Bacteroides fragilis/isolation & purification , Bacteroides fragilis/metabolism , Gene Expression Regulation, Bacterial/drug effects , Gene Silencing , Microbial Sensitivity Tests , Repressor Proteins/metabolismABSTRACT
OBJECTIVE@#To investigate the effects of Andrographis paniculata (Burm.f.) Wall. Ex Nees (A. paniculata) on expressions and activities of catalase, superoxide dismutase and alkylhydroperoxide reductase C in Staphylococcus aureus (S. aureus) with respect to its survival in vitro.@*METHODS@#Antioxidative property of methanolic leaves extract of A. paniculata (0.06 mg/mL). Minimum inhibitory concentration (MIC) was determined by its ability to reduce hydrogen peroxide (HO) toxicity against S. aureus ATCC 25923 [(3.8 × 10) cfu/mL]. Effects of the extract on expressions of katA (encoding catalase), sodA and sodM [encoding superoxide dismutases (SODs)], and ahpC [encoding alkylhydroperoxide reductase C (AhpC)] in S. aureus were determined by RT-qPCR and corresponding enzyme activity assays were performed. Nitroblue tetrazolium reduction (NBT) assay was performed to determine effects of the extract on intracellular and extracellular levels of O in S. aureus.@*RESULTS@#Cells challenged with 7.5 mmol/L HO showed 0% survival in 30 min whereas 25% survived after treatment with the extract and HO. Cells that were treated with the extract alone had 43% survival in the same exposure period. Expressions of sodA and sodM genes in extract-treated cells were lowered 0.8-fold and 0.7-fold, respectively with decrease in total SOD activity of 26.8 U compared to untreated cells, 32.4 U (P < 0.05). In contrast, extract-treated S. aureus cells showed 3.3-fold increase in katA expression with corresponding increase in catalase activity of 1.828 U compared to untreated cells which was 1.248 U, (P < 0.05). More profoundly, ahpC expression was increased 61-fold in extract-treated cells, (P < 0.05) with corresponding increase in AhpC activity of 0.018 U compared to untreated cells, 0.012 U, (P < 0.05). Extract-treated cells had significantly lower intra- and extracellular O levels with absorbance readings (A) of 0.340 and 0.524 compared to untreated cells which were 0.516 and 0.928 (P < 0.05), respectively.@*CONCLUSIONS@#Taken together these results suggest that the low MIC of A. paniculata methanolic leaves extract (0.06 mg/mL) reduce HO toxicity and more importantly, was in itself effectively inhibitory against S. aureus. Further, our observations suggest that a probable mode of its inhibitory mechanism against S. aureus is by reducing total SOD activity through downregulation of sodA and sodM expressions.
ABSTRACT
Objective To investigate the effects of Andrographis paniculata (Burm.f.) Wall. Ex Nees (A. paniculata) on expressions and activities of catalase, superoxide dismutase and alkylhydroperoxide reductase C in Staphylococcus aureus (S. aureus) with respect to its survival in vitro. Methods Antioxidative property of methanolic leaves extract of A. paniculata (0.06 mg/mL). Minimum inhibitory concentration (MIC) was determined by its ability to reduce hydrogen peroxide (H