How long has this been going on?
Bacteria got a 3.5 billion year jump on us
The antibiotic era modern medicine’s greatest triumph over infection appears strikingly short-lived when compared to the vast history of disease-causing bacteria, a clinician recently reminded attendees in St. Louis at the annual conference of the Society for Healthcare Epidemiology of America (SHEA).
Bacteria species appeared on the plant some 3.5 billion years ago; mammals 65 million years year ago; humans some 250,000 years ago but the antibiotic era is only a scant half-century old, noted Michael B. Edmond, MD, MPH, director of the internal medicine residency program at the Medical College of Virginia in Richmond.
Put another way, by compressing biological history into the span of a single year, bacteria appeared on Jan. 1; mammals on Christmas Eve; and humans on New Year’s Eve. The antibiotic era began less than a second before midnight on the final day of the year.
The antibiotic era began with the development of penicillin during World War II, but by 1948 the first cases of penicillin-resistant Staphylococcus aureus had already been reported. Likewise, methicillin was introduced in 1960 and the first cases of methicillin-resistant S. aureus were seen one year later in 1961, he reported. A host of new drugs and resistant organisms followed, resulting in the current era of vancomycin-resistant enterococcus, multidrug-resistant tuberculosis, and multi-resistant gram negative rods.
"Although there are some exceptions, we moved from eras of nosocomial pathogens which were quite virulent but antibiotic-susceptible, to now seeing lots of nosocomial infections that are due to organisms which are not very virulent, but can be highly antibiotic-resistant," he said at SHEA.
At the microbiological level, bacteria represent a "moving target" capable of rapidly regenerating themselves in a stronger form, said another SHEA speaker, Louis Rice, MD, associate professor of medicine at Case Western Reserve School of Medicine in Cleveland.
"When you grow up every 20 minutes, you get smart pretty quick," he said.
Thus, repeated exposures particularly to broad-spectrum antibiotics create selective pressure for organisms with resistance capabilities to multiply. Somewhat surprisingly, more antibiotics are being used in agriculture and farming then on hospital patients, Edmond noted. About 80% or more of the antibiotics used in farm animals occur in subtherapeutic doses for growth promotion, he said.
"Every year in the United States, about 40,000 to 50,000 pounds of antibiotics are sprayed on fruit trees, which actually calculates out to be enough to treat about 20 million people for a day," Edmond added.
Problems controlling antibiotic resistance in medical settings are complicated by the frequent movement of patients throughout the health care continuum, from community hospitals to tertiary care centers to day care and nursing homes. Use of broad-spectrum antibiotics creates selective pressure in hospitals, where very ill patients may be more prone to colonization and infection. Sites of infection such as the respiratory tract and wounds lend themselves to bacterial growth and poor penetration for antibiotics a setup for antibiotic resistance to occur, Edmond said.
"When we see patients who are clinically infected with these antibiotic-resistant organisms, we are only looking at the tip of the iceberg," he told SHEA attendees. "For every patient we know is clinically infected, there are probably several more who are colonized that we haven’t picked up on yet. So the problem can be deceptive."
With the frequent presence of indwelling devices in critical care settings and the ongoing problem of ensuring compliance with hand washing and other infection control measures resistant pathogens move to other clinical areas via transient colonization on the hands of health care workers, he said. The result is a downward spiral of increased morbidity and mortality in patients, increased and prolonged hospitalizations, and more pressure to use the few remaining effective antibiotics as more resistance appears. Among the immediate strategies needed are ongoing surveillance for resistant pathogens, careful use of antibiotics, maximizing the use of vaccines to prevent the need for antibiotic therapy, practicing good infection control, eliminating prophylactic use of antibiotics in agriculture, and reviewing prophylactic use in humans as well, Edmond told SHEA attendees.
"It really is going to require a worldwide approach because this is a global problem," he says. "Once introduced into a hospital, many of these organisms will become endemic and they are rarely eradicated."
Such measures may prove effective in controlling the spread of drug resistance, but outright eradication of resistant pathogens is likely out of the question, Rice noted.
"Let’s face it: The bugs are here," Rice told SHEA attendees. "We’re not going to get rid of them, but hopefully we can control them at a low level."
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