In Microbiology,it is very important to understand the actions of various antibacterial agents in order to easily guide the physician when giving Chemotherapeutic treatment especially when carrying on susceptibility testing.
Combination of antibiotics are often given
- In case of undiagnosed infections, when a broad cover seems desirable
- In case of mixed infections when multiple antibiotics are required to effectively, deal with the microorganism based on their different sites of actions.
- In order to obtain a synergistic effect between these antibiotics
- Sometimes to prevent or delay the development of resistance by these microorganism.
Hence, attention should be taking into consideration when selecting these antibacterial or chemotherapeutic agents especially when it concerns their Bacteriostatic or Bactericidal effects on Microorganism.
In 1952, Jawetz and Gunnison stated that when:
- Two Bacteriostatic antibiotics were given together, the resulting action was Meaning these two bacteriostatic antibiotics had the same effect even when the quantity was double.
- Two Bacteriocidal antibiotics were given together, the resulting action was Synergistic
- However, when a Bacteriostatic and Bacteriocidal antibiotic were given together, the result was
Antibiotic synergy occurs when two or more antibiotics are used simultaneously to treat and undesirable infection or during susceptibility testing in-vivo or in-vitro. These antibiotics work together in order to produce an effect more potent than if each antibiotics were applied singly.
Method of synergism
A way of demonstating synergism in-vitro (In a petri dish) is to place disc of one antibiotic onto an inoculated culture plate like Blood agar, CLED agar plate, then placing another disc about 2-3 cm from the first disc to observe their combing action when their zone of inhibition join together.
The following are combination of antibiotics which generally results in synergism
- Penicillin and Aminoglycosides
- Cephalosporin and Aminoglycosides
- Fusidic and Lincomycin
- Sulphonamides and Trimethroprim