Info Service on Health Issues (Aug18/12)
Dear friends and colleagues,
Two teams of scientists presented worrisome findings involving multidrug-resistant bacteria in healthcare settings at the annual meeting of the American Society for Microbiology (ASM) in June.
In the first study, researchers from the Emory Antibiotic Resistance Center reported the first strain of hypervirulent, multidrug-resistant Klebsiella pneumoniae in the United States. In the second case, researchers with the Kentucky Department for Public Health and the Centers for Disease Control and Prevention (CDC) found that a small outbreak of carbapenem-resistant infections at a Kentucky hospital in 2017 was caused by different strains and species of bacteria that carried the same drug-resistant plasmids.
Both studies highlight concerns about carbapenem-resistant Enterobacteria (CRE), dubbed the ‘nightmare’ bacteria for their resistance to several classes of antibiotics and their ability to spread quickly in healthcare settings. CRE infections, including bloodstream, wound, and urinary tract infections, are exceedingly difficult to treat and have a mortality rate of nearly 50 percent.
The carbapenem-resistant, hypervirulent K pneumoniae (CR-hvKP) isolated in the first study was not as virulent as a strain identified in China, and the virulence genes were different from those found in similar K pneumoniae isolates in Asia. But analysis showed that the isolate was heteroresistant to the last resort antibiotic colistin. Heteroresistance is a phenomenon where bacteria appear to be susceptible to an antibiotic in standard susceptibility tests, but actually contain a small subpopulation of cells that are resistant.
In the second study, the bacteria involved in the CRE outbreak were K pneumoniae and Escherichia coli, the two most common types of CRE.
The K pneumoniae isolates appear to be unrelated, with researchers finding four different sequence types, while the E coli isolates were more closely related. This is noteworthy as CRE outbreaks in hospitals generally involve closely related bacteria from a single family that have spread from patient to patient.
The identification of different, unrelated types of CRE from a single outbreak with similar resistant plasmids – the highly mobile pieces of DNA that can transfer resistance genes among different families of bacteria – shows that carbapenem resistance can be shared between unrelated bacteria in healthcare settings.