Figure 3. Effect of hydroalcoholic extract of P. guajava leaves prepared by Microwave Assisted Extraction method on bacterial growth and QS-regulated pigment production.

( A) P. aeruginosa ( B) S. aureus ( C) S. marcescens ( D) C. violaceum ( E) S. pyogenes. Bacterial cell density and pigment production were quantified as earlier described by us ( Joshi et al., 2016). Bacterial growth was measured as OD ₇₆₄ for the four pigmented bacteria, while for S. pyogenes OD ₆₆₀ was used. OD of pyoverdine was measured at 405 nm, and that of pyocyanin at 520 nm; Pyoverdine Unit was calculated as the ratio OD ₄₀₅/OD ₇₆₄ (an indication of pyoverdine production per unit of growth); Pyocyanin Unit was calculated as the ratio OD ₅₂₀/OD ₇₆₄ (an indication of pyocyanin production per unit of growth. OD of staphyloxanthin was measured at 450 nm, and Staphyloxanthin Unit was calculated as the ratio OD ₄₅₀/OD ₇₆₄ (an indication of staphyloxanthin production per unit of growth). OD of prodigiosin was measured at 535 nm, and Prodigiosin Unit was calculated as the ratio OD ₅₃₅/OD ₇₆₄ (an indication of prodigiosin production per unit of growth). OD of violacein was measured at 585 nm, and Violacein Unit was calculated as the ratio OD ₅₈₅/OD ₇₆₄ (an indication of violacein production per unit of growth). QS: Quorum sensing