Abstract
Considering the prevalence of resistance to antibiotics, the discovery of effective agents against resistant pathogens is of extreme urgency. Herein, 26 mecA-positive methicillin-resistant S. aureus (MRSA) isolated from clinical samples were identified, and their resistance to 11 antibiotics was investigated. Next, the antibacterial and anti-biofilm activity of the ethanolic extract of M. communis on these strains was evaluated. Furthermore, the effect of this extract on the expression of biofilm-associated genes, icaA, icaD, bap, sarA, and agr, was studied. According to the results, all isolated strains were multidrug-resistant and showed resistance to oxacillin and tetracycline. Also, 96.15 and 88.46 % of them were resistant to gentamicin and erythromycin. However, the extract could effectively combat the strains. The minimum inhibitory concentration (MIC) against different strains ranged from 1.56 to 25 mg/ml and the minimum bactericidal concentration (MBC) was between 3.125 and 50 mg/ml. Even though most MRSA (67 %) strongly produced biofilm, the sub-MIC concentration of the extract destroyed the pre-formed biofilm and affected the bacterial cells inside the biofilm. It could also inhibit biofilm development by significantly decreasing the expression of icaA, icaD, sarA and bap genes involved in biofilm formation and development. In conclusion, the extract inhibits biofilm formation, ruins pre-formed biofilm, and kills cells living inside the biofilm. Furthermore, it down-regulates the expression of necessary genes and nips the biofilm formation in the bud.
Highlights
As one of the leading causes of nosocomial infections, the treatment of Staphylococcus aureus infections are arduous due to the emergence of antibiotic-resistant strains
Isolation of strains The S. aureus strains used in this study had been initially isolated from the wound, abscess, ear, urine, blood, and bronchoalveolar lavage samples collected during one year by the microbiology laboratory of Afzalipour and Shafa hospitals of Kerman province, Iran
Identification of Methicillin-resistant S. aureus (MRSA) strains and screening their antibiotic resistance Among 40 Staphylococcus aureus strains isolated from clinical specimens, 26 strains (65 %) were able to grow on MHA medium containing 4 % NaCl and 6 μg / mL oxacillin
Summary
As one of the leading causes of nosocomial infections, the treatment of Staphylococcus aureus infections are arduous due to the emergence of antibiotic-resistant strains. Methicillin-resistant S. aureus (MRSA), is resistant to penicillin and other semi-synthetic beta-lactams, such as methicillin and oxacillin (Klein et al 2007). The first outbreak of MRSA in European. What makes the S. aureus a virulent strain are both its adhesion and invasion properties. The adhesion ability is associated with biofilm formation and results in a sheltered life toward antibiotics. A microbial biofilm consists of a community of microbial cells that irreversibly attach to the substrate or each other. This community produces a surrounding matrix of extracellular polymeric
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