Chapter No.1 1.1: Microorganisms

          1.1: Microorganisms

            Microorganisms are mostly non-pathogenic, harmless and beneficial. They are present around us. Butsome of them are pathogenic which causes the infections. Human body carries the 10¹⁴cells approximately, 10% of it ishuman in origin and rest of it is microbial flora. The organisms which are not seen by naked eye are called as microorganisms such as bacteria.(Larry and Dianna, 2011)

When life arose on earth about 4 billion years ago the first types of cells which evolve were microorganisms (prokaryotic cells). For approximately 2 billion years ago microorganisms were the only form of life on Earth.(Todar,2007)

Microbes produce a variety of toxins which help them to compete in their local environments. The killing rang of these toxins range from quit narrow to quit broad. Bacteriocins are  the member of quite narrow spectrum have been described as the microbial weapon of choice based upon their abundance and diversity among producing bacteria. Very few of microbial lineages produced the broad range of toxins such as classical antibiotics.(Margaret & Milind, 2006)

Microorganisms are classified in to two groups prokaryotes and eukaryotes.The eukaryotic domain is consist of single group which evolved from single celled amoebae through worms, fungi and plants  to complex animals such as humans.Prokaryotes are the most diverse and abundant group of organisms and survive particularly all environments on earth (William, et.al,1998). Microorganisms are vital to humans and the environment.The prokaryotes are divided up into two fundamentally separate domains: the Archaeaand Bacteria(Tom, et. al, 2013).

Archaea. The Archaea are a group of prokaryotes that live in extremeconditions such as thermal pools. While they may bevery important to the health of natural environments, they are not known to cause human infection.

1.2 Bacteria:-        

These are very significant when it comes to human health because some of them must live in or on us  and some of them are capable of causing disease  grow at human body temperature 37°. The majority of bacteria are grow in air called as aerobe but can  also growwithout it known as facultative anaerobes a few of bacteria  can only grow in theabsence of oxygen which are  anaerobes.(Giovannoni & Stingl, 2005). 

Bacteria contain a circular chromosome and extra chromosomal DNA on plasmids. They multiply by binary fission each cell dividing into two daughter cells and within 20 min their number can be increase from one bacterium to one million with in 6h.

Most of the bacteria look the same under themicroscope; it does not meanthat they will behave similarly instead of itthere is a great differencebetween the genes of the bacteria such as in Escherichiacoli andStaphylococcus aureus. (Larry and Dianna, 2011)

1.3 Gram positive and Gram negative:-

Bacteria are divided into two main groups on the basis of chemical staining with the Gram stain.

The differential stainingis based on a major difference in the cell wall. Both have a lipid bilayer cytoplasmic membranewith various proteins inserted in it.  A network of peptidoglycanoutside the cytoplasmic membrane provides the mechanical strength. It is particularlyabundant in Gram-positive organisms and containsthe strands of teichoic acid(lipoteichoic acid and wall teichoic acid).(Hugenholtz, 2002)

Gram-negativeorganisms have an additional outer membranewith a thin layer of peptidoglycan and periplasmic space in which enzymes are present. For the movement of substrates throughmembrane porinsarealso present.(Heijenoort, 2001)

Bacteriocins are produced by both Gram- negative and positive bacteria. There are following bacteria’s which produce bacteriocins.

1.3.1Bacillus:-

Many strains of the Bacillus spp. produced antibiotic substances.Many are poorly characterized but some are bacteriocin-like in nature.Several species have been reported to produce"antibiotics."B.cereushas categorized the inhibitory substancesas bacteriocins.

Other Bacillus spp. that has been reported tohave bacteriocin-like inhibitors areB.stearothermophilus, B.licheniformi, B. thuringiensis and B. subtilis. The studies of B. subtilis and B. Iicheniformishave indicated that the bacteriocinsare of the defective phage type.The most extensively studied and the bestcharacterized   bacteriocins of the Bacillusspp. are produced by B. megaterium. (Luca, et.al, 2002)

1.3.2Clostridium:-

The inhibitory substances with bacteriocin-like properties by clostridia occurred in a study of phage production by C. perfringens. The bacteriocins also produced by strains of C. botulinumand related non toxigenic strains andalsoby C. sporogenes, C. butyricu, and various nonpathogenic clostridia. The best characterized and most extensively studied bacteriocins of C. botulinum and C. perfringens (Robert, et.al, 2012)

1.3.3Corynebacterium:-

The bacteriocins like inhibitory substance also produced by the strains ofCorynebacterium spp.

1.3.4Citrobacter:-

Many strains of Citrobacter spp produced bacteriocins.Other Citrobacter spp. that has been reported to have bacteriocin-like inhibitors areC. braakii,C. koseriand C.freundii. One compound isolated from Citrobacter freundii exhibited antimicrobial activity against a wide range of Gram-negative bacteria and was effective against biofilms.

1.3.5 Enterobacter:-

The bacteriocins like inhibitory substance also producedby the strains ofE. gergoviae, E. aerogenes, E. cloacae (Degraaf, et.al, 1968).

1.3.6Enterococcus:-

Enterococci, includingEnterococcus faecium and Ent. faecalis,have also the ability to produce bacteriocins.Bacteriocins produced by enterococci are known as enterocins.Now the following enterocins have beencharacterized as to their homogeneity: enterocin A , enterocins B, enterocin P , enterocin I, enterocin M, a new variant of enterocin P and enterocins CCM 4231(Viola, et.al,2003).

1.3.7Lactobacillus:-

Various lactobacilli have beenproduced the antibacterial substances that are quiteunrelated to bacteriocins. These include hydrogenperoxide, lactic acidand the broadspectrum antibiotic lactocidin. Well-characterized bacteriocin-like substancesproduced by strains of both homo- and hetero-fermentative species. They have been found to be bacteriocinogenic. Whereas a number of different bacteriocinshaving distinct activity spectra were producedby homofermentative lactobacilli. Bacteriocinsproduced by L. fermenti strain and byL. helveticus strain(Palanisamy, et.al, 2009).

1.3.8 Lactococcus:-

Nisin belongs to the class I bacteriocins and is produced by Lactococcus lactis; it is the most extensively studied LAB bacteriocin. It comprises 34 amino acids, including the post-translationally modified amino acids thioether-bridged lanthionine and 3-methyllanthionine and unsaturated 2, 3-didehydroalanine and 2, 3-didehydrobutyrine. Nisin exhibits antibacterial activity against a wide range of gram-positive bacteria, including LAB and bacteria of the genera Listeria, Staphylococcus spp., Bacillus spp., and Clostridium spp. In addition, nisin is highly stable under conditions of acidic pH and high temperature. Thus far, three nisin variants, namely, nisin A, nisin Z, and nisin Q, have been recognized. Lacticin bacteriocin also produced by some strains of Lactococcus spp. (Olivera, et.al 2003)

1.3.9Listeria:-

Certain strains of Listeria sppproduced the bacteriophages. L. monocytogenesproduced the bacteriophages it wasreported that certain strains produced the substances after irradiation that were similar to thecolicins.

The characteristics of these bacteriocinsincluded high antigenicity, insensitivity totrypsin, and inducibility by ultraviolet light, andrelative heat labiality(Alleson, et.al, 2012).

1.3.10Mycobacterium:-

The strains of mycobacterium spp. produced the phage like particleshaving the characteristicsof bacteriocins such as M.tuberculosis.  The bacteriocin like activity of mycobacteria studied only superficially

1.3.11 Sarcinaspp:-

The strains of Sarcina spp. produced a diffusible inhibitor when they are grown on solid media. The inhibitor was thermo stable, resistant to proteolytic enzymes.

1.3.12Streptomyces:-

Representatives of this genus produce a widevariety of classical antibiotic substances. And the bacteriocin-like substance produced by S. virginiae andS. scopuliridiswhich appeared todifferent from theclassical antibiotics. Bacteriocin-like properties included inducibility by ultraviolet irradiation,'non-lytic action that was restricted to the streptomycetesandspecific adsorption to sensitive cells (Farris, et.al, 2011)

1.3.13Streptococcus:-

Streptococcus gallolyticus subsp. macedonicus ST91KM produces a bacteriocin (macedocin ST91KM) active against Streptococcus agalactiae, Streptococcus dysgalactiae subsp. dysgalactiae, Streptococcus uberis, Staphylococcus aureus, and Staphylococcus epidermidis, including strains resistant to methicillin and oxacillin (Pieterse,et.al, 2008).

1.3.14Pseudomonas:-

The bacteriocin is produced by the pathogenic strains of the Pseudomonas solanacearum. (Cuppls, et.al,1978)