Aztreonam is commonly used against which two organisms?

Aztreonam is a monobactam antibiotic that is particularly effective against Gram-negative bacteria. Its mechanism of action involves inhibiting bacterial cell wall synthesis, which makes it effective for treating a variety of infections caused by susceptible organisms.

Pseudomonas aeruginosa is a common pathogen in patients with weakened immune systems, and it is known for its resistance to many antibiotics, making aztreonam a valuable option due to its efficacy against this organism. Klebsiella species are also Gram-negative bacteria that can cause serious infections, such as pneumonia and bloodstream infections, and are known to be susceptible to aztreonam as well.

In contrast, the other options listed contain organisms that do not have the same susceptibility profile to aztreonam. Escherichia coli can sometimes be susceptible to aztreonam, but Staphylococcus species are Gram-positive and generally not targeted by this antibiotic. Streptococcus and Clostridium are also primarily Gram-positive, thus not relevant to aztreonam's effectiveness. Salmonella and Proteus might present a mixed susceptibility, but Pseudomonas and Klebsiella remain the more notable targets for aztreonam therapy.