Laser Treatment Increases the Antimicrobial Efficacy of Cyanobacterial Extracts against Staphylococcusaureus (SA) and Methicillin-resistantStaphylococcus aureus (MRSA)

Abstract

Staphylococcus aureus (SA) and Methicillin-resistant Staphylococcus aureus (MRSA) are multidrug-resistant bacterial pathogens. A novel approach needs to be followed to combat these pathogens in an ecofriendly manner. Cyanobacterial extracts were previously proven to be affective as antimicrobial agents. To capitalize on this, laser treatments were used to increase their antimicrobial efficacy. Two cyanobacterial strains isolated from Al-Ahsa were identified using molecular methods. Their aqueous extracts were used in the antimicrobial bioassay for these two bacterial pathogens. The first group of aqueous extracts were exposed directly to laser treatment and used in antibacterial bioassay. In parallel, the cyanobacterial biomass of the two isolates was exposed to the laser, then aqueous extracts were prepared. The third group of extracts were not exposed to the laser and were used as a control. Time and distance were the factors tested as they affected the dose of the laser, both individually and in combination. In addition, accessory pigment estimation in extracts before and after laser exposure of extracts was also determined. The two cyanobacterial strains were identified as Thermoleptolyngbya sp. and Leptolyngbya sp. and the molecular analysis also confirmed the identity of pathogenic bacteria. The untreated cyanobacterial aqueous extracts had little effect against the two bacterial strains. In contrast, the extract directly exposed to the laser was significantly more effective, with an inhibition zone of 22.0 mm in the case of a time of 32 min and distance of 10 cm against S. aureus. Accessory pigment composition increased in extracts directly exposed to the laser. This is the first case report on the effect of lasers on enhancing the antimicrobial profile of cyanobacterial extracts against SA and MRSA bacterial pathogens, as well as enhancing accessory pigment content. The laser dose that was most effective was that of 32 min time and 10 cm distance of Thermoleptolyngbya sp. extract directly exposed to the laser, which highlights the importance of time for increasing the laser dose and consequently increasing its antimicrobial impact.

Keywords: Leptolyngbya sp.; Methicillin-resistant Staphylococcus aureus (MRSA); Staphylococcus aureus (SA); Thermoleptolyngbya sp.; antimicrobial bioassay; aqueous extracts; laser; phycocyanin.

Figure 1

PCR products of the partial 23S rDNA amplification.

Figure 2

A neighbor-joining phylogenetic tree of Thermoleptolyngbya sp. The sequence of the organism under study is highlighted in yellow. Green highlights reference database sequences.

Figure 3

A neighbor-joining phylogenetic tree of Leptolyngbya sp. The sequence of the organism under study is highlighted in yellow. Green highlights reference database sequences.

Figure 4

Effect of laser treatment by different exposure times at a distance of 5 cm on Thermoleptolyngbya sp. extracts derived from cyanobacterial biomass pre-exposed to laser and extracts directly exposed to laser against Staphylococcus aureus. (P)—positive control; (N)—negative control; (C)—an extract derived from cyanobacterial biomass pre-exposed to laser; (E)—an extract directly exposed to laser. (a) An agar plate showing the highest inhibition zone of extracts derived from biomass pre-exposed to laser for 16 min. (b) An agar plate showing highest inhibition zone of extracts directly exposed to laser for 4 min.