How to Play

The mission is simple – you’re the doctor and you have patients to save! Choose antibiotics from a large selection of real world antibiotics to fend off the onslaught of infections caused by real world bacteria. The interactions between your antibiotics and the bacteria are based on the real world data that we have at this time.

The key parts of the game are the bacteria (creep), patient(s), antibiotics and white blood cells (towers) and the maze board. Learn about each part below. You can also view the Gameplay Demo Video below.

Bacteria Creep

Waves of bacteria come in from the entrances on the left side of the maze board and make their way to the exits to the right. The only way to stop them is to kill them with your towers. You can impede their progress by building a maze with your antibiotic towers. Waves consist of varying numbers of bacteria which can be of mixed species as well characteristics. You get money and points from killing the bacteria.

BacteriaTD Sample Maze
Example Maze

The bacteria have different characteristics such as life, speed, and money. Some crawl on the maze board (ground) and can be blocked by your towers. Others fly over your towers. Some waves have “boss” bacteria which have extra life. Their shape and color is based on their actual appearance under the microscope (gram stain and morphology). Using their appearance, you’ll be better able to narrow down their identity and empirically pick antibiotics to attack them. With some practice, you’ll become an expert in identifying the bacteria! You can also click on individual bacterial to reveal a panel with information about it.

If you let bacteria get through, it will attack the patient and damage an organ(s). Let too many through and your patient will die! In the normal and hard difficulties, bacteria which make it to the patient will spawn copies of themselves which will enter the maze from the left. Be aware that the spawned bacteria have “armor” and are resistant to your towers. If they spawn too many times, you will have super-bacteria that will be very difficult to kill!


You’re job is to cure the patient(s). He/she will help you by announcing a “chief complaint” which is a clue as to what kind of bacteria you should expect. After playing several times, you’ll be able to pick up patterns which can help guide your antibiotic choices. Be sure to keep an eye on the patients’ life bar on the bottom. Once it runs out, the game is over!

Antibiotic/White Blood Cell Towers

BTD has a wide selection of real antibiotic towers for you to choose from. They come from all the major classes and come in oral and IV forms. You can pick cheap, narrow-spectrum ones or opt for the expensive “big-gun” antibiotics. The choice is yours. However, just like in real hospitals, your pharmacy can only carry a limited selection of antibiotics. Keeping in mind their costs and various characteristics, you’ll have to choose the best combination of antibiotics to stock in your pharmacy.

The first tower slot is dedicated to the white blood cell, one of the body’s innate defense mechanisms. It is a cheap tower which fires quickly and in a focused manner.

You can customize the antibiotics for the remaining 11 slots in your pharmacy in the beginning of the game before you send the first wave in. Click on the green “customize” button next to the PHARMACY label to go to the customization screen.

On the customization screen, you will see all of the available antibiotics in the game. Mouse over the towers to see their stats in the panel at the bottom right. To select a tower, drag and drop the desired tower into one of the empty container boxes in the pharmacy box. To remove a tower from your pharmacy, click and drag it out of the pharmacy box and then release the mouse button. It will automatically return to its proper location in the list of antibiotic towers. You must fill all of the pharmacy slots to continue.

You can save your customized pharmacy selections with the “save” button. You can load those selections at a later time with the “load” button. Clear all of your selections with the “clear” button. No idea what to pick? No problem – start with the default pharmacy by clicking on the “default” button. When you are satisfied with your antibiotic selections, click on “done” to return to the game.

Hint: When you choose antibiotic towers, pay attention to their stats, especially their coverage. You’ll be encountering bacteria of varying types. The pink, blue, and green power bars on the antibiotic stats panel gives you a general idea of how effective it is against bacteria that fall in that classification (e.g. gram +, gram -, anaerobe) Also, some antibiotics are bactericidal while others are bacteriostatic. Bactericidal towers are generally more powerful. Bacteriostatic towers deal less damage but have the ability to slow down the bacteria it is effective against.

Maze Board

Once you have picked your antibiotic towers, it’s time for action! If you want, you can start placing your antibiotic towers on the board before the first wave of bacteria arrive. At this time, upgrading and selling towers does not take any time. Also, you can sell your towers for full value at this time. When you are satisfied with your set up, click on the “Start” button to start the action!

Note 1: Once you click on “Start”, upgrading towers takes time. During the upgrade, the tower will not fire. Be sure to upgrade when it’s safe!

Note 2 (Sell Timer): You can rearrange the layout of your towers (maze) by selling towers. However, keep in mind that each time you sell a tower, it takes longer. Make sure to plan ahead for the increased delay.

Money & Interest

You get money by killing bacteria and also from interest. Boss bacteria give more money. At the end of each wave, you get to collect interest on the amount of money you have remaining. You’ll have to decide whether to spend any extra money you have to bolster your defenses or to save it to grow your account. Spend wisely and you’ll have plenty of reserves to wipe out the invading bacteria.

ID & Sensitivities

If you’re having trouble with the bacteria on the board, you can get help by purchasing ID & Sensitivities tests. If you have enough money, click on the yellow button labeled “ID & Sensitivities” and a window will pop up. This window contains a table which lists the efficacy of your chosen antibiotics to all of the different species of bacteria on the board at that time.

+ = 100% effective
~ = 50% effective
- or blank = 0% effective

Use this tool to help you get out of a bind quickly! However, keep in mind that it becomes more expensive each time you use it.

"WBC Stim" Button

When you are having trouble with the bacteria on the screen and are about to be overrun, consider using the WBC Stim button. Pressing the button supercharges your WBC towers, increasing their damage by 10X. It's a great way to wipe out hoards of the hard to kill bacteria! However, the effect only lasts 5 be sure to time it right. (Note: WBC Stim does not work when your WBC towers are in the Neutropenic condition).

Fog of War

In Regular mode, the Fog of War feature is in effect. This effect causes the bacteria to be invisible and unattackable unless they are within range of a sensor tower. Reveal their presence by building sensor towers in strategic locations. Only then will your towers be able to attack them. Be sure to plan the development of your maze carefully!


When this feature is turned on, your patient goes through cycles of neutropenia and antibiotic allergies, just as patients in the real world have different situations. When your patient is neutropenic, your White Blood Cell towers arenon-functional, leaving antibiotic towers as your only defense. When your patient has an allergy to an antibiotic class, antibiotic towers in that class will be non-functional. Diversify your defense so you don't leave your patients unprotected...and be sure to keep an eye on the situation indicator!

Creep Damage

When this feature is activated, your towers aren't the only things dealing out damage...the bacteria also fight back! Your towers have life bars which are reduced when bacteria near it attack it. Bacteria generally attack every 3 seconds or so, and is indicated by a green glowing ring emanating from it. Damage is proportional to the resistance the bacteria has against a particular tower. For example, an antibiotic tower which the bacteria is highly resistant to will take a lot of damage while a highly effective antibiotic tower, which can kill the bacteria easily, will take less damage, if any. Sensor towers are vulnerable to damage as well but WBC towers are not. Build your defense to protect vulnerable towers and be sure to keep a close eye on your towers' life bars!

You can repair individual towers by clicking on the "Repair" button or pressing "R". However, keep in mind that it takes money to repair the towers. If you want to repair all of the towers at once, press "T" or click on the "Repair All Towers" button.

High Scores

At the end of a game, you can submit your score and see where you rank.

Difficulty Modes

Easy – Bacteria have 75% life and do not spawn new bacteria if they survive, 50 waves

Normal – Bacteria have 100% life and spawn 2 bacteria if they survive, 60 waves

Hard – Bacteria have 150% life and spawn 4 bacteria if they survive, 70 waves

Random – 100 waves of random bacteria with increasing life. Every 6th wave is flying and every 8th wave has boss bacteria. Great for testing your skills and knowledge!


Gameplay Demo Video

Want a higher score? Bacteria Tower Defense is actually based on real-life information!

Try getting one of the recommended antimicrobial guides available through

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