Abstract:
Since the discovery of Antibiotics in the 20th century, the idea of searching for
antimicrobial compounds from natural sources came into existence. However natural
products from microbial origin (especially soil microorganisms) have grasped a great
devotion over the course of several decades. Recently, bacterial resistance have been
observed against antibiotics of all classes, however it appears that the emergence of
antimicrobial resistance is inevitable to almost every new drug.This necessitates
carrying out studies that will generate new effective antibiotics. The present study is
an attempt to identify, characterize and improve strains of bacteria for the ability to
produce antibiotics.
About 12 soil samples were screened for antibiotic-producing bacteria against 4
pathogenic microorganisms including Escherichia coli, Klebsiella pneumoniae
Staphylococcus aureus and B. subtilis. After preliminary screening, active isolates with
secondary metabolites showing activity were selected for secondary screening by agar
well diffusion method to identify antibiotic potency. VITEK 2 system was used for rapid
identification of the active isolates. The amplification of the 16s rRNA by PCR followed
by sequencing and sequence analysis was used for the molecular identification of
these strains. Optimization of chemical and physical culture conditions was carried out
by manipulation of fermentation parameter such as pH, Temperature and incubation
period.
The results revealed 7 strains of antibiotic producing organisms. 4 bacterial strains
demonstrated convincing growth inhibitory properties against pathogenic test
organisms. Of these, were identified as Gram-positive cocci and 1 was identified as
Gram-negative of the group of Rods and most of the isolates were active against the
Gram positive than gram negative pathogens. Phylogenetic analysis of amplified 16S
rRNA gene showed the isolates shared sequence identities of 99.65% with known
Staphylococcus and Pseudomonas species. TSH2 and TSP3 clustered together with
a sequence identity of 99.68% with Staphylococcus sciuri. Isolate TSP1 sequence had
a sequence identity of 100% with Pseudomonas formosensis strain CC-CY503. The
production of antimicrobial substances started on the 4th day and went on increasing
till it reached a maximum peak on the 7th day. The optimum growth conditions were
pH 7.5, temperature at 35°C, and incubation period in 7 days.
In conclusion, the results of the present study indicate that soil contain great diversity
of antibiotic producing organisms and the production of antimicrobial substances can
be improved by manipulating the growth conditions.