Pathogenic leptospires are fragile little bacteria, and die when exposed to chemicals and conditions that many other bacteria and viruses will happily live with. In terms of chemicals there are two main reasons for lethality – compounds that attack the bacterial envelope, and compounds that damage the internal chemical processes that the bacterium needs to survive. Detergents, alkalis and soaps damage the envelope’s outer layer (which is made of a compound called lipopolysaccharide or LPS), while acids and heavy metals generally attack the inner elements and cell metabolism.
The following conditions showed lethal results in lab tests. Most are reliable in that the same will be true for all pathogenic strains of the bacteria, but in most cases this has not been proven:-
Environmental conditions shown to be lethal
- Heat >55°C
- UV light from sterilisation equipment
- Drying without freeze-drying
- High-speed centrifuging
Chemicals shown to be lethal
| Acid solutions | pH <6.5 |
| Acetic acid | 0.01% in water |
| Citric acid | 0.01% in water |
| Alkaline solutions | pH >8.4 |
| Cationic detergents | >100ppm |
| Anionic detergents | >1000ppm |
| Chlorine | approx 0.5ppm to 3ppm |
| Iodine | 1ppm lethal after 10 mins |
| Lysol | 0.1% |
| Seawater | 3.5% NaCl |
Apart from iron, almost all heavy metals are lethal at low concentrations. Pathogenic leptospires do not tolerate the salt levels in seawater but can slowly adapt to survive in solutions up to 1%.
Human saliva tends to be about pH6.5 to pH7 but drops after eating and during the night, limiting the survival of leptospires in the mouth cavity.
Some of the above data is taken from Handbuch der pathogenen Mikroorganismen, 3e Auflage ed (7i) edited by W. Kolle, R. Kraus, P. Uhlenhuth