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A colored electron microscopy image of methicillin-resistant staphylococcus aureus (), a bacterium commonly targeted by broad-spectrum antibioticsA broad-spectrum antibiotic is an antibiotic that acts on the two major bacterial groups, Gram-positive and Gram-negative, [1] or any antibiotic that acts against a wide range of disease-causing bacteria. [2]
β-Lactam antibiotics are indicated for the prevention and treatment of bacterial infections caused by susceptible organisms. At first, β-lactam antibiotics were mainly active only against gram-positive bacteria, yet the recent development of broad-spectrum β-lactam antibiotics active against various gram-negative organisms has increased their usefulness.
Infections caused by Gram-negative bacteria, such as Escherichia coli and Klebsiella particularly Pseudomonas aeruginosa. Effective against aerobic bacteria (not obligate/facultative anaerobes) and tularemia. All aminoglycosides are ineffective when taken orally as the stomach will digest the drug before it goes into the bloodstream.
Narrow-spectrum antibiotics have low propensity to induce bacterial resistance and are less likely to disrupt the microbiome (normal microflora). [3] On the other hand, indiscriminate use of broad-spectrum antibiotics may not only induce the development of bacterial resistance and promote the emergency of multidrug-resistant organisms, but also cause off-target effects due to dysbiosis.
Monobactams exert their antibacterial effects by binding to penicillin-binding proteins (PBPs), thereby inhibiting bacterial wall synthesis. [5] Monobactams exhibit poor affinity for PBPs of Gram-positive bacteria as well as of strictly anaerobic bacteria, resulting in a lack of significant antimicrobial activity against these kinds of organisms. [3]
The spectrum of activity of the carbapenems against gram-positive bacteria is fairly broad, but not as exceptionally so as in the case of gram-negative bacteria. Good activity is seen against methicillin-sensitive strains of Staphylococcus species, but many other antibiotics provide coverage for such infections.
[3] [4] Antibiotics are not effective against viruses such as the ones which cause the common cold or influenza. [5] Drugs which inhibit growth of viruses are termed antiviral drugs or antivirals. Antibiotics are also not effective against fungi. Drugs which inhibit growth of fungi are called antifungal drugs.
At one time, methicillin was used to treat infections caused by certain gram-positive bacteria including Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, and Streptococcus pneumoniae. Methicillin is only effective against Staphylococcus aureus 50% of the time.