Bactericidal vs Bacteriostatic

Antibiotics are generally divided into two groups based on their mode of action. Bacteriostatic antibiotics inhibit reproduction and growth, while bactericidal antibiotics kill the bacteria.

Bactericidal vs bacteriostatic can be different in many aspects. This article will highlight those differences as well as other distinction approaches of antibiotics, such as broad spectrum and narrow spectrum antibiotics. Read on to know how to use the right antibiotics at the right time.

Bactericidal vs Bacteriostatic

1. Definition

Bactericidal Antibiotics:As the spelling shows, the suffix 'cidal' means kill; therefore, bactericidal antibiotics works by killing the bacteria and their actions is irreversible.There are different mechanisms in which bactericidal antibiotics kill bacteria. Here is an example:

Polymyxin B works by damaging the membrane of the bacteria, which results in all the contents pouring out. For bacteria to survive, ions have to be balanced on both sides of the plasma membrane because of osmosis. This antibiotic disrupts the balance leading to the pouring out of the important molecules like RNA and DNA of the bacteria. More bactericidal antibiotics can include vancomycin, metronidazole, aminoglycosides, fluoroquinolones, penicillin, cephalosporins, etc.

Bacteriostatic Antibiotics: As the suffix 'static' meaning stable, bacteriostatic antibiotics inhibit growth or reproduction of bacteria, whose actions is reversible. Bacteria divide at a very fast rate leading to their number escalating in a very short period. However, if they are not dividing andgrowing, the human's immune system is able to fight and get rid of the bacteria.

An example of bacteriostatic antibiotics is tetracycline. It operates by inhibiting bacterial ribosome; as a result, new proteins cannot be formed. The bacteria will not die since it already has enough protein to survive, but it will not divide with not sufficient proteins for division. Sulfa drugs are also bacteriostatic. They work by preventingprocesses that bacteria need to make proteins, RNA and DNA. Without these 3 components, bacteria cannot divide. More bacteriostatic antibiotics can include chloramphenicol, trimethoprim, clindamycin,sulfamethoxazole, erythromycin, etc.

2. Bactericidal vs Bacteriostatic Comparisons

Aside from the definition, bactericidal and bacteriostatic antibiotics have some other differences, including:

  • Bactericidal decrease the number of bacteria, while bacteriostatic antibiotics do not decrease instead they stagnate multiplication.
  • When bacteriostatic antibiotics are used, the bacteria are still viable. However, this is not the case for bactericidal.
  • Bacteriostatic antibiotics let the immune system fight infections while bactericidal do not.
  • High doses of bacteriostatic antibiotics can work as bactericidal, meanwhile, low doses of bactericidal antibiotics can work as bacteriostatic
  • Minimum inhibitory concentration (MIC) is the minimum bacteriostatic drugs concentration required to prevent growth of bacteria, while minimum bactericidal concentration (MBC) is the minimum bactericidal concentration required to kill bacteria.

Bactericidal vs Bacteriostatic—When to Apply

From the above comparison, it seems that bactericidal antibiotics are the better choice, which is believed for a long time being as a misconception. The type of infection you have will determine which type of antibiotic to use.

  • Bactericidal drugs treat diseases like meningitis and endocarditis. Noticeably, bactericidal actions can be antagonized by bacteriostatic antibiotics when treating meningitis.
  • For the function of preventing staphylococcal wound infections and treating UTIs (urinary tract infections), bacteriostatic antibiotics work as well as bactericidal antibiotics.
  • For infections that affect the central nervous system,bactericidal antibiotics can cause inflation as a side effect due to the releasing of bacterial products; therefore, it is advisable that bactericidal should be taken together with corticosteroids.
  • In cases of clostridial gangrene and streptococcal, some bacteriostatic drugs are ideal. This is because they prevent the production of toxins, which cause most of the morbidity.

Other Categories and Types of Antibiotics

1. Broad vs.Narrow Spectrum Antibiotics

Antibiotics can also be distinguished as broad spectrum and narrow spectrum antibiotics. Antibiotics that are limited to treating specific infections are known as narrow spectrum while those that can treat a wide range of infections are called broad spectrum.

2. Other Types of Antibiotics


How It Is Used


They are used for several types of infections like urinary tract infections, chest infections and skin infections.


They treat a wide range of infections as well as serious infections like meningitis and septicaemia (presence of disease-causing bacteria in the blood).


They are mostly and merely used to treat serious conditions like septicaemia, due to their severe side effects like kidney damage and hearing loss. Also, they have to be injected or used as eye or ear drops, because they can easily broke down in the digestion system.


Used to treat a wide range of infections. It is mostly used to treat moderate to serious acne as well as rosacea that causes spots and skin flushing.


As a good substitute for penicillin, it is often used for patients who are allergic to penicillin or bacteria that is resistant to penicillin. Diseases like chest and lung infections can be cured by this medicine.


Broad spectrum antibiotics that treat a broad variety of infections.

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