Doctors warn that a garden-variety type of bacteria, which is normally present in the human intestinal tract, may be morphing into a tough-to-treat superbug.
A new report from physicians in New York, New Mexico and the US Centres for Disease Control and Prevention describes the cases of two patients with group B streptococcus infections that turned out to be resistant to vancomycin, often considered an antibiotic of last resort.
In the past, group B strep infections were relatively easy to subdue because the bacteria were vulnerable to penicillin and other common antibiotics.
"Every time there is information about another genus, species or strain of bacteria showing resistance to yet another class of antibiotic, that's bad news because it means that yet another antibiotic weapon is about to become useless," said Elizabeth Scott, co-director for the Centre for Hygiene and Health in Home and Community at Simmons College in Boston.
Read: Good bacteria vs. bad bacteria
In the new cases, reported in a letter in the New England Journal of Medicine, both patients were infected by strains of strep B that had acquired a gene that gives protection against vancomycin.
Bacterial genetic mutation spreading
Doctors usually reserve vancomycin for use in cases when other antibiotics have failed.
"Although the report is for only two cases, they were unrelated, indicating that the bacterial genetic mutation is popping up in different locations or spreading rapidly," said Scott, who was not involved in the research.
Further testing showed that beyond vancomycin, the bacteria were impervious to other classes of antibiotics as well.
Strep B bacteria are a leading cause of meningitis and bloodstream infections. About one in four pregnant women carries the bacteria, which can cause life-threatening infections in newborns. Strep B is also a common cause of joint and skin infections in the elderly and those with compromised immune systems, according to the CDC.
Antibiotic resistance evolving
Dr Connie Park, an infectious disease fellow at Montefiore Medical Center in New York City, took care of the New York patient. She was an 82-year-old woman with diabetes who developed a step B infection of her ankle joint after surgery to repair a fracture.
The infection eventually spread to her bloodstream. After more surgery to drain and clean the wound and a change of antibiotics – from vancomycin to another strong drug called linezolid – she eventually recovered.
The second patient, a New Mexico man, 48, who was on dialysis because of kidney disease, developed a bloodstream infection from strep B that spread from a skin wound. When doctors cultured the bacteria, they discovered it was resistant to vancomycin. He, too, recovered from his infection.
Read: Can bacteria survive microwaves?
The two patients had no apparent connection, suggesting that resistance arose separately.
"I think we don't know yet how remarkable something like this will be. I think it is another commentary on how our antibiotic resistance is evolving. This could be a problem in the future if we run out of more options than we have now," Park said.
Another expert, who was not involved in the treatment of either patient, agreed that the cases are important warnings to other physicians.
Vancomycin losing its power
"These bacteria were multidrug-resistant, and two separate events occurred," said Dr. Stuart Levy, director of the centre of adaptation genetics and drug resistance at Tufts University School of Medicine in Boston. "It shows this could be occurring elsewhere, and alerts you that the drug of last resort, vancomycin, is clearly losing its power."
Levy stressed the importance of the findings. "Infectious disease specialists need to know this could be cropping up and may be a reason for the failure of treatment," he said.
Desks crawling with bacteria
Bacteria to target cancer
Food passes bacteria to humans