Novel drugs for emerging diseases

A review of: Darabpour E, Ardakani MR, Motamedi H, Ronagh MT (2011) Isolation of a broad spectrum antibiotic producer bacterium, Pseudoalteromonas piscicida PG-02, from the Persian Gulf. Bangladesh Journal of Pharmacology, 6: 74-83.

The marine environment encompasses 71% of the planet and is an ecosystem with a plethora of biological diversity. The spread of emerging bacterial diseases and multi-drug resistance is a serious global concern hence the development of new synthetic drugs and the ‘hunt’ for novel drugs from natural sources are of paramount importance to pharmaceutical companies.

Marine bacteria thrive in niches that require unique metabolic pathways and secondary metabolites to maintain biological activity, consequently opening up numerous possibilities for novel pharmaceutical agents. Several antibiotics have hitherto been isolated from various marine bacteria such as Streptomyces, Alteromonas, Bacillus, Pseudomonas and Pseudoalteromonas. The objective of the study conducted by Darabpour et al (2011) was to isolate bacteria from sediment and water samples taken from various locations around the Persian Gulf, and to test for antimicrobial properties.

Pure colonies of bacterial isolates were screened for antibiotics and tested using several pathogenic bacteria, including multiple drug resistant strains of Bacillus cereus, Proteus mirabilis, Listeria monocytogenes, Bacillus anthracis and Methicillin Resistant Staphylococcus aureus (MRSA). Out of the 48 bacterial isolates, one strain (PG-02) exhibited antagonistic activity to 81% of the pathogens except L. monocytogenes, P. mirabilis and Kliebsiella pneumoniae. PG-02 was identified as a gram-negative, motile aerobe and a Basic Local Alignment Search Tool (BLAST) search in the GenBank database revealed 98% homology to Psuedoalteromonas piscicida strain B14. The inability to use NH₃ and the ability to reduce NO₃ suggests strain PG-02 is a novel species of Pseudoalteromonas, although the authors indicate that this needs to be confirmed by further phenotypic characterization and DNA hybridization.

Antibiotic production began in the middle stages of stationary phase and extended into the death phase, therefore the authors deduce that the antibiotic is a secondary metabolite associated with biomass production. The antibiotic has a bacteriostatic and bacteriocidal effect to a broad spectrum of bacteria harmful to humans, including a number of multiple drug resistant bacteria such as MRSA - a nosocomial pathogen that has increased in occurrence in recent years, particularly in the developing world.

The marine environment is crucial in various global processes and the study highlights other possible contributions that can be obtained from an environment we know so little about. Paradoxically, using novel synthetic and natural antibiotics to treat the aforementioned pathogens may further complicate curtailment because a strong selection pressure accelerates pathogenic evolution and bacteria are able to acquire and exchange genetic information, subsequently giving rise to increased drug resistance.