Quantitative Evaluation of Five Liquid Media for Growth Promotion Legionella Pneumophila

Abstract

Legionella pneumophila, the etiological agent responsible for Legionnaires’ disease is typically grown using elaborate broth. The feasibility of utilizing five different liquid media to cultivate L. pneumophila, famed for its fastidious growth requirements, was examined. Five non-supplemented (-) liquid media, namely sterile distilled water (SDW), skimmed milk glucose glycerol (SGG), skimmed milk tryptone soy glucose glycerol (STGG), thioglycolate (TGL) Oxoid, and tryptone soy (TSB), were tested, along with their five counterparts (+) supplemented with L-cysteine (LC), ferric pyrophosphate (FPP) and glycerol over 11 days at 37°C. The culture method recommended by ISO 11731 was employed to enumerate these ATTC 33152 L. pneumophila strains on Modified Wadowsky Yee agar. All broths significantly boosted their growth (P=0.07), with optimal growth observed after 5 days of incubation. However, loads in TSB (-) declined to -0.15 log units within the period. In the remaining broth, loads were 1-3 times higher in the supplemented media compared to their non-supplemented ones. The highest loads of L. pneumophila occurred in SGG (+), where loads increased by 2.66 log units from initial loads of 1.91, achieving the best growth rate (μ≈4.48 log units hr-1), lowest doubling time (14.9 hrs.), and highest yield (4.58log units). This was followed by loads in STGG (-), TSB (+), and SDW (-) with log unit increases of 2.32, 2.36, and 2.36, respectively. Furthermore, no significant loss in viability was observed even after 11 days of incubation in STGG (+) (-), SGG (+), and SDW (-). Linear growth of L. pneumophila in SDW (-) highlights its innate ability to thrive in nutrient-deprived water environments. Overall, the growth of L. pneumophila was facilitated by majority of the liquid media tested. These findings highlight their potential use for the cultivation of L. pneumophila, which may have implications for the detection and prevention of Legionnaires' disease.

Keywords: Legionella pneumophila, L cysteine, Ferric pyrophosphate, Culture method, liquid media