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  1. fleming
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    2025-07-13T18:36:50+00:00
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    Inside a healthy human body the main thing that actually *kills* invading bacteria is your own immune system.

    First line is the nonspecific barriers. Stomach acid drops pH below 2 and that alone can inactivate most ingested microbes. Bile salts in the small gut punch holes in bacterial membranes, same with lysozyme that is dripping from tears and saliva.

    If a bug gets past that the innate immune cells take over. Neutrophils and macrophages literally eat the bacterium then flood the phagosome with reactive oxygen species, nitric oxide and acid hydrolases. That oxidative burst is lethal even for hardy Gram‑positives.

    Complement proteins circulating in blood can assemble a membrane attack complex on Gram‑negative envelopes and they lyse the cell from the outside. Opsonising antibodies make that process faster once you have seen that pathogen before.

    Finally, there are small antimicrobial peptides like defensins and cathelicidins that insert into bacterial membranes and cause leakage. They are produced by epithelial cells and by neutrophils so they are everywhere bacteria try to sneak in.

    So in short it is not one magic bullet but a whole layered system working together that ends up killing bacteria inside you.

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