By Sean Henahan, Access Excellence

NEW ORLEANS, Sept. 16, 1996 An ever increasing rise in the number of cases of bacterial infection resistant to all antibiotics has researchers on the defensive. The resistant organisms, once limited to hospitals, appear to be spreading into the community, reported researchers at the 36th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

Caption: Streptococcus pyogenes (electron micrograph)

Researchers reported increasing resistance among several types of Gram-positive bacteria associated with common and potentially life-threatening infections. Penicillin-resistant Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci (VRE) complicate the treatment of serious infections and have been linked to extended hospitalizations, higher medical costs and high mortality rates.

"Bacteria are remarkably agile in developing or acquiring new ways to outsmart antimicrobial agents," said Robert C. Moellering, M.D., Chairman, Department of Medicine, New England Deaconess Hospital in Boston. "While resistance was once found primarily in the hospital setting, we're beginning to see more and more evidence of resistant pathogens in the community."

Drug-resistant Streptococcus pneumoniae poses a growing threat to people in places where they live and work, noted G. Douglas Campbell, Jr., M.D., Professor of Medicine and Chief of the Division of Pulmonary and Critical Care Medicine at Louisiana State Medical School in Shreveport. Streptococcus pneumoniae infections, including pneumonia, sinusitis, meningitis and otitis media, are among the leading causes of death and illness among the elderly, young children and persons with underlying medical conditions. These infections often strike vulnerable patient populations in daycare settings, nursing homes and prisons.

Resistance to penicillin, the most common agent used to treat S. pneumoniae, now approaches 40 percent. Additional resistance has been reported against other potent anti-biotics known as cephalosporins and non-beta-lactam agents. Scientists now estimate that nearly half of these S. pneumoniae strains can be classified as highly resistant.

Staphylococcus aureus, the most common cause of more than a dozen conditions in both hospitals and communities, can be considered the "ultimate pathogen," according to Gordon L. Archer, M.D., Professor of Medicine and Chairman, Division of Infectious Diseases, Medical College of Virginia, Virginia Commonwealth University. S. aureus often colonizes without any signs of infection, and then from this reservoir gains access to skin and deep tissue, where it subverts the immune system. Staphylococcal infections range from local skin infections to endocarditis (heart valve infection), osteomyelitis (bone infection) and sepsis (blood stream infection).

Methicillin-resistant S. aureus first emerged in the United Kingdom in the early 1960s. Since then, researchers have observed that several strains of S. aureus can outmaneuver a wide variety of currently available antibiotics.

In the same bacteria family, multi-drug resistant Staphylococcus epidermidis also poses a threat. This coagulase-negative bacteria found primarily in skin tissue was once considered a non-threatening contaminant. Now, it has been established as a leading cause of hospital acquired bloodstream infections. More than 80 percent of S. epidermidis isolates in U.S. hospitals are methicillin resistant, and recent studies have found resistance to quinolones, cephalosporins and vancomycin.

"The emergence of Staphylococcus epidermidis as a pathogen has been fueled by the widespread use of catheters, prosthetic joints, valves and other invasive medical devices, and is a growing concern, particularly for immunocompromised cancer patients," said Issam Raad, M.D., Associate Professor of Medicine and Chief, Section of Infection Control at the University of Texas M.D. Anderson Cancer Center.

"These patients desperately need new effective agents with high activity against this pathogen," he stressed.

One of the most challenging situation of all comes from the development of vancomycin-resistant enterococci (VRE), an increasingly frequent cause of hospital-acquired infections in the United States. These organisms are resistant to virtually all currently available antibiotics including vancomycin, considered the agent of last resort for Gram-positive infections. Vancomycin is used in many hospital settings. While guidelines are in place to help control the administration of this last-resort agent, there are increasing signs that the drug is being used inappropriately, ie for the wrong indication or in the wrong doses.

"It is imperative that clinicians adhere to the federal recommendations for vancomycin use. The first step is to generate pharmacy data for specific service areas, such as surgery, neonatal or transplant units. Data on antimicrobial use patterns can be enormously helpful in targeting clinician education programs to improve use patterns," emphasized William R. Jarvis, M.D., head of the Investigation and Prevention Branch of the Hospital Infection Program at the Centers for Disease Control and Prevention (CDC) in Atlanta.

Meanwhile, new types of antibiotics are still being developed in an attempt to outsmart the bacteria. One new class of drugs called streptogramins work by inhibiting bacterial protein synthesis and appear effective against some otherwise resistant organisms. New versions of existing classes of drugs and new combinations of different drugs are also being studied.

Some of the new agents show promise in treating several important antibiotic resistant strains, according to Dr. Moellering. "New agents, combined with infection control measures and judicious antibiotic use, will help us win the war against treatment-resistant microorganisms," he said.