Abstract
The lytic phage ST79 of Burkholderia pseudomallei can lyse a broad range of its host including antibiotic resistant isolates from within using a set of proteins, holin, lysB, lysC and endolysin, a peptidoglycan (PG) hydrolase enzyme. The phage ST79 endolysin gene identified as peptidase M15A was cloned, expressed and purified to evaluate its potential to lyse pathogenic bacteria. The molecular size of the purified enzyme is approximately 18 kDa and the in silico study cited here indicated the presence of a zinc-binding domain predicted to be a member of the subfamily A of a metallopeptidase. Its activity, however, was reduced by the presence of Zn2+. When Escherichia coli PG was used as a substrate and subjected to digestion for 5 min with 3 μg/ml of enzyme, the peptidase M15A showed 2 times higher in lysis efficiency when compared to the commercial lysozyme. The enzyme works in a broad alkaligenic pH range of 7.5–9.0 and temperatures from 25 to 42 °C. The enzyme was able to lyse 18 Gram-negative bacteria in which the outer membrane was permeabilized by chloroform treatment. Interestingly, it also lysed Enterococcus sp., but not other Gram-positive bacteria. In general, endolysin cannot lyse Gram-negative bacteria from outside, however, the cationic amphipathic C-terminal in some endolysins showed permeability to Gram-negative outer membranes. Genetically engineered ST79 peptidase M15A that showed a broad spectrum against Gram-negative bacterial PG or, in combination with an antibiotic the same way as combined drug methodology, could facilitate an effective treatment of severe or antibiotic resistant cases.
Highlights
A bacteriophage or phage is the virus of bacteria that is very specific to its host
When the MEROPS batch Blast tool was used to detect peptidases and their non-peptidase homologues sequences in ST79 genome, it showed common amino acids among peptidases found in other bacterial genome, such as: B. glumae, B. thailandensis, B. cenocepacia, Burkholderia sp
The increase in antibiotic-resistant bacteria makes the use of possible phage therapy as an alternative treatment for bacterial infections as one of multiple options for treatment
Summary
A bacteriophage or phage is the virus of bacteria that is very specific to its host. It can replicate, multiply after transfection and either lyse the host or become integrated into its genome (Golkar et al 2014). Phage therapy has been evaluated in Khakhum et al AMB Expr (2016) 6:77 overcome antibiotic resistant bacteria and are available in large quantities in nature. The enzymes related to the lysis mechanism of the phages that are used to lyse the bacterial host during the release of their progeny have been studied and revealed the classical holin-endolysin lysis system found in phages of both Gram-positive and Gram-negative bacteria (Young et al 2000). The enzymes or the phages themselves are extensively applied in several fields, for example, the food industry and biological control of unwanted bacteria (Ruyter et al 1997) including pathogenic bacteria in medicine as it shows neither toxicity nor stimulates hyperimmune sera in the mouse model (Jado et al 2003)
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