Estimation of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of Cell-Free Extracts of &amp;lt;i&amp;gt;Bifidobacterium&amp;lt;/i&amp;gt; Species Against Methicillin-Resistant &amp;lt;i&amp;gt;Staphylococcus aureus in vitro&amp;lt;/i&amp;gt;

Zainab Nashaat Al-Saadi`

doi:10.11648/j.ajbls.20160405.12

Abstract

The aim of this study was to examine if extract of bifidobacteria, a major species of the human colonic microflora participates in the barrier effect against enteropathogens by developing antimicrobial activity against virulent bacteria. Six human bifidobacteria strains were isolated from infant stools. They were characterized and identified through physiological, biochemical tests and API 20 A test system. The isolates belonged to the three species: B. breve, B.longum and B.infantis. The cell extracts of the isolates were examined for antimicrobial activity by determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). For this purpose, the methicillin-resistant S. aureus (MRSA) was chosen as an indicator. MRSA treated with cell-free supernatants (CFS) from bifidobacteria were examined. All the Bifidobacterium isolates used have been identified as novel probiotics with a greater ability to survive at low pH and high concentrations of bile salt in vitro . 0.5 McFarland standard (10 8 CFU/ml) of a confirmed MRSA strain was challenged with the CFS strains by employing the tube dilution method and subculture on MRS agar assays. The cell-free supernatants of the 6 LAB strains exhibited MIC values between 50 µl/ml and 200 µl/ml. Only two CFS of bifidobacteria (b3 and b 4) had no MIC and MBC values with the concentrations under the current study. The b1, BL and BI strains showed highest antibacterial activity by MIC value with 100 conc. and by MBC value with 150 conc. Increased concentration levels of the cell-free extract (CFE) correlated with a decrease in MRSA viability. MRS broth medium (control) showed a high growth rate of MRSA without CFE.These results may provide a basis for alternative therapies for the treatment of MRSA superbug.

Highlights

The probiotic micro-organisms are single-celled, nonpathogenic organisms which do not promote or cause disease
The results summarized in table (5) show that after 24 h at 37 °C incubation of methicillin-resistant S. aureus (MRSA) with b1, B. longum (BL) and B. infantis (BI) extracts, more than 99% of the MRSA bacteria were eliminated at concentration (1.5 %) of bifidobacterial cell-free extract (CFE)
These bacteria are "antibiotic resistant" and have proven problematic in healthcare settings where they increase the risk of worse clinical outcomes and death, a high percentage of hospital-acquired infections are caused by highly resistant bacteria, such as methicillin-resistant staphylococcus aureus (MRSA)

Summary

Introduction

The probiotic micro-organisms are single-celled, nonpathogenic organisms which do not promote or cause disease. Most commonly used probiotic supplements contain the species of Lactobacillus and Bifidobacterium and they are part of normal human intestinal microbiota [1]. The World Health Organization deemed probiotics to be the next-most important immune defense system when commonly prescribed antibiotics are rendered useless by antibiotic resistance [2]. Bifidobacterium breve is primarily located in human breast milk and the gastrointestinal tract of infant and adult humans, where they are among the first microbial colonizers, passed from the mother to her offspring. B. breve has not been recorded as the cause of human disease and has been in commercial use as a probiotic since 1976 [4]

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