NURUL SAFFA BINTI ZAINAL ABIDIN 

LAB 5: DETERMINATION OF ANTIMICROBIAL EFFECTS OF MICROBIAL EXTRACT :

INTRODUCTION :

An antimicrobial is a substance that kills or inhibit the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes (microbiocidal) or prevent the growth of microbes (microbiostatic). Disinfectants are antimicrobial substances used on non living objects or outside the body. Organic acids, hydrogen peroxide, diacetyl and bacteriocins are included among these antimicrobial compounds. Interest in naturally produced antimicrobial agents such as bacteriocins, is on the rise, since nowadays consumer demand “natural” and “minimally processed” food.

Bacteriocins are proteinaceous toxins produced by bacteria to inhibit the grpwth of similar or closely related bacterial strains. They are typically considered to be narrow specturum antibiotics, though this has been debated. They are phenomenologically analogous to yeast and paramecium killing factors and are structurally functionally, and ecologically diverse.

Bacteriocinc can be found in numerous Gram-positive and Gram-positive bacteria, those produced by lactic acid bacteria (LAB) have received attention due to potential application in food industry as natural biopreservatives. Different class LAB have different biochemical and genetic characterization. These bacteriocins inhibit the growth of Listeria monocytogenes, Staphyloccocus aureus, enterococcus faecalis and Clos tridium tyrobutyricum.

OBJECTIVES : 

To determine the antimicrobial effects of extracellular extracts of selected LAB strains

PART 1 : determination of bacteriocin activity via agar diffusion via agar diffusion

PART 2 : Determination of bacteriocin activity via optical density :

DISCUSSION :

PART 1 :

The lactic acid bacteria (LAB) comprise a clade of Gram-positive,acid tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological charactheristic. This trait has throughout history, linked LAB with food fermentations, as acidification inhibits the growth of spoilage agents. Proteinaceous bacteriocins are produced by several LAB strains and provide an additional hurdle for spoilage and pathogenic microorganism.

Lactic acid bacteria produce variety of antagonistic factors that include metabolic end products, antibiotic-like substances and bactericidal proteins, termed bacteriocins. The range of inhibitory activity by bacteriocins of lactic acid can be either narrow inhibiting only those strains that are closely related to the producer organism, or wide, inhibiting a diverge group of Gram-positive.

The extract of lactic acid bacteria gave zones of inhibition onto the indicator pathogen strains tested. In the agar diffusion means measuring the effect of antimicrobial agent against bacteria grown in culture. Nutrient that mixed with pathogenic bacteria and Lab extract (sterile paper disk) is place on it which is then incubate it for 24 to 48 hours at 37 degree celcius. Then measured the diameter of inhibition zone (in cm) as shown in result. The size of inhibition indicate the difference og bacteriocin activity between LAB

PART 2 :

Optical density that measured in a spectrophotometer can be used as a measure of concentration of bacteria in a suspension. It also commonly used for the measurement of transmittance or reflectance of solution depending on the wavelength of the photometric determination. As visible light pass through the cell suspension the light is scattered. The greater scattered the greater bacteria present.

Optical density of extracellular extract of LAB contained MRS medium and pathogenic microorganism was determined with spectrophotometer at 600nm. One type of Lab used in this experiment is Lactobacillus plantirum. Three types of pathogenic microorganisms have been used are S. Aureus, P. Aeruginosa and K. Pneumonia.

Negative-control is prepared for auto-zero via spectrophotometer (MRS with 2ml distilled water). While positive-control which show higher optical density than the other sample show antimicrobial effect.

CONCLUSIONS :

Bacteriocins that produced by lactobacillus is useful in kill or inhibit the growth of other bacteria, fungal or protozoa. some of the, inhibit the growth of variety species of pathogenic microorganism.

REFRENCES :

http://en.wikipedia.org/wiki/Spectrophotometry

http://en.wikipedia.org/wiki/Lactic_acid_bacteria

http://en.wikipedia.org/wiki/Bacteriocin