Nalidixic Acid & Salmonella

Nalidixic acid is a member of a class of antibiotics called fluoroquinolones. Salmonella is often treated with fluoroquinolones like nalidixic acid; in recent years, however, some strains of salmonella have begun to exhibit increasing levels of resistance to these drugs.

Types

• Nalidixic acid is prescribed to treat infections of the urinary tract. Like many other fluoroquinolones, it works by inhibiting an enzyme called DNA gyrase that the bacteria need to help unwind their DNA during replication; consequently, it's active against a wide variety of bacteria, since many bacteria are vulnerable to this kind of attack.

Features

• Infection with salmonella bacteria is the most common cause of food-borne illness in the United States; the Centers for Disease Control estimates that nontyphoid salmonella causes 15,000 hospitalizations and 400 deaths each year. Eggs and poultry are the leading source of infection.

Function

• The second-generation fluoroquinolone ciprofloxacin is one of the main treatments for salmonella infections; nalidixic acid is more often prescribed for urinary tract infections. Strains that are resistant to nalidixic acid, however, have greatly decreased susceptibility to other fluoroquinolones, so resistance to nalidixic acid can help predict whether a given isolate also is resistant to other drugs in the same class.

History

• According to a 2004 article in the journal Antimicrobial Agents and Chemotherapy, as of 2003, some 2.3 percent of salmonella from samples were nalidixic acid-resistant--a significant increase from just 0.4 percent some seven years before.

Significance

• As salmonella bacteria become more resistant to nalidixic acid and other fluoroquinolones, it may become more difficult to treat cases of serious food poisoning.

Theories/Speculation

• As noted in a 2004 article in Antimicrobial Agents and Chemotherapy, fluoroquinolones were first approved for use in food animals in 1995. It's possible although unconfirmed that the use of fluoroquinolones in agriculture may have played a role in the emergence of nalidixic acid-resistant salmonella.