Immunization Issues

Vaccines and Antibiotic-Resistant Bacteria

Updated: Diciembre 22, 2005

Recent reports from public health officials in the United States show that antibiotic resistance is increasing rapidly among the bacteria that cause meningitis and pneumonia. The increase has resulted largely from the frequent use of antibiotics, including unnecessary prescriptions for viral diseases and incomplete treatments that allow resistant bacteria to proliferate.

Antibiotic-resistant bacteria make it difficult—sometimes impossible—to treat serious infections.

Efforts from the government, the medical community, and private industry are under way to slow this trend in drug-resistant bacteria. This article explains what antibiotic resistance is and the role of vaccines in combating them.

Antibiotics vs. Bacteria

Antibiotics are the natural enemies of bacteria; the first antibiotics were produced by other germs that live in your backyard’s soil and at the bottom of the sea, with newer versions created in the laboratories of pharmaceutical companies. In 1928, Alexander Fleming discovered penicillin, the first antibiotic, from mold growing in one of his Petri dishes of bacteria. Penicillin sticks to some bacteria—for example, group A streptococci, the cause of “strep throat”—preventing their walls from being properly formed, eventually destroying the bacteria. However, some bacteria change the shape of their cell walls so the penicillin can’t stick or produce a substance that breaks down penicillin. That means they are resistant to penicillin.

Other types of antibiotics stop the bacteria from growing, giving the body’s immune system time to respond.

When antibiotics are used in an attempt to kill certain bacteria, a few may survive because they happen to have the appropriate genes; thus they will become the predominant strain. For instance, if the antibiotic kills a million bacteria but doesn’t kill five that are resistant, at their incredible multiplication rate—bacteria divide every 20 to 30 minutes—after 15 hours there will be 5 million descendants of those five, all of them resistant to the antibiotic.

Some bacteria carry antibiotic resistance genes that can be passed to other species of bacteria. These transferable genes often carry resistance to many antibiotics.

Staphylococcus aureus is a common germ that normally lives on your skin, but can gain entry to the body and cause abscesses, bone infections, pneumonia or infection of the heart valves. In the 1940s virtually all strains of S. aureus were susceptible to penicillin. Today, more than 90% of S. aureus strains are resistant to penicillin and many other antibiotics that were once effective against these bacteria.

Haemophilus influenzae type b (Hib) bacterium, which used to be a common cause of meningitis in young children, had become resistant to many antibiotics before a conjugate vaccine was developed in 1987. For example, thirty percent of Hib strains both then and now are resistant to the antibiotic amoxicillin, a commonly used antibiotic.

Some decades ago, all strains of Streptococcus pneumoniae (pneumococci) were susceptible to penicillin; by the end of the 1990s, 25% of all pneumococci were resistant to penicillin. Pneumococci are the leading bacterial cause of ear infections, sinus infections, pneumonia requiring hospitalization, and bacterial meningitis. A vaccine against pneumococcal disease has been available for older people for many years; recently, a new vaccine became available for young children.

Vaccines vs. Bacteria

One alternative, at least for some types of bacteria, is vaccination. Since Hib vaccines were introduced, the number of new cases of invasive Hib infections—both drug-sensitive and resistant—in infants and children in the U.S. has decreased by 99%.

Also, vaccination against pneumococci is now routinely recommended for infants and young children so that children will not get serious pneumococcal infections such as meningitis or bloodstream infection.

The children’s vaccine, PCV7, was approved in the United States in February 2000 and contains the 7 most common pneumococcal serotypes causing invasive (serious) infections in children in North America. Thus the PCV7 vaccine only protects against infection with these 7 serotypes. These 7 serotypes are also the most likely to be resistant to the antibiotics used to treat these infections. A recent study1 showed that PCV7 has been successful in preventing invasive pneumococcal disease in children and has resulted in the added benefit of a decrease in penicillin resistance among pneumococcal isolates from children with infection. Another study showed that rates of invasive pneumococcal disease (IPD) due to vaccine serotypes declined after PCV7 introduction in all age groups. However, the rate of IPD due to serotypes not present in the vaccine increased as a cause of IPD in older children and adults.2

These vaccines provide immunity against bacteria that have become resistant to the antibiotics used to treat them. However, there is a viral vaccine that indirectly combats antibiotic-resistant bacteria: varicella vaccine.

Children with varicella (chickenpox) frequently develop skin infections with S. aureus or group A streptococci, both of which may invade the blood stream. By being protected against varicella with the vaccine, children are protected against an infection with these bacteria, including those that are antibiotic-resistant.3

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