It's important to note that using "natural" bacteria killers can be risky, as they may not be as effective as conventional antibiotics and can have unintended side effects. It's always best to consult with a healthcare professional for any bacterial infections.

However, here are 4 substances with natural antibacterial properties that have been studied:

1. Honey: Honey contains hydrogen peroxide and other enzymes that can kill bacteria. It's been used for centuries to treat wounds and infections.

2. Garlic: Garlic contains allicin, a compound with strong antibacterial properties. It has been shown to be effective against certain types of bacteria, including E. coli and Salmonella.

3. Tea tree oil: This essential oil is known for its antiseptic and antibacterial properties. It can be diluted and used topically to treat skin infections.

4. Oregano oil: Oregano oil contains carvacrol and thymol, powerful antimicrobials. It can be taken orally or used topically to treat infections.

Remember, it's crucial to use these substances responsibly and under the guidance of a medical professional. They may not always be effective against all types of bacteria, and some individuals may have allergies or sensitivities to them.