OK, this may really be the stuff of nightmares
Researchers create hyper-virulent CRE in the lab
By Gary Evans, Executive Editor
I have been reluctant to embrace the somewhat melodramatic moniker of "nightmare bacteria" for emerging carbapenem-resistant Enterobacteriaceae (CRE), which includes Klebsiella pneumoniae carbapenemase (KPC) and New Delhi metallo-β-lactamase (NDM).
Then I found out what was frozen in a lab in New Jersey.
Tom Chiang, MD
Medical researchers have combined a KPC strain now common in much of the U.S. with a highly virulent isolate from Asia, conferring the multidrug resistance of the former and the killing power of the latter into a new microorganism worthy of nightmare: Hyper-virulent KPC.
"Most of the KPC strains, especially in the United States, are not virulent," says researcher Tom Chiang, MD, an assistant professor at Rutgers and infectious disease physician at the VA New Jersey Health Care System in East Orange. "In Asia there are Klebsiella pneumoniae that are not carbapenem resistant but they are hyper-virulent. They cause invasive disease like endocarditis, liver abscesses and so forth. A lot of people don't realize this, but once KPC comes into these hyper-virulent strains we are in for a treat. We will have a pan-resistant Kleb pneumo that is also hyper-virulent. So far it has not been hyper-virulent in the United States, and the mortality for bacteremia is about 40%. So if the hyper-virulent strains obtain this KPC we are in a big trouble."
Though not hyper-virulent, the high morbidity and mortality seen with the predominant strains of KPC-CRE in the U.S. likely reflects their resistance to multiple antibiotics. In any case, such lines of research are controversial, with past efforts including recreating the 1918 pandemic influenza virus and conjugating VRE and MRSA to confer vancomycin resistance in the latter.1,2 In this case, however, the pathogen already exists in the wild based on recent reports from China, Chiang says.
"It has happened already, we need to prepare for it," Chiang says. "There are reports in Asia of this KPC disseminating into their hyper-virulent strains of Kleb pneumo."
Indeed, a recently published paper by researchers in China reports the phenomenon, warning that "K. pneumoniae carbapenemases being found in virulent K. pneumoniae should be emphasized, as this will eventually become a global health threat."3 As KPCs continue to disseminate in China and mingle with the hyper-virulent K. pneumoniae strains more of these superbugs may begin occurring in nature.
Hybrid bug lethal to mice
The research by Chiang and colleagues has been submitted for publication and was presented recently in San Francisco at IDWeek.4
"Our study was important to show that it is possible for the virulent strains to obtain KPCs and we're just beginning to see the tip of the iceberg on carbapenem resistant — possibly pan resistant -- strains of Klebsiella pneumoniae emerge," Chiang says. "It will probably first disseminate in Asia as the virulent strains are endemic there. If it disseminates here, the consequences will be catastrophic for the healthcare system. Klebsiella pneumoniae is the second most prevalent gram negative bacteria in our hospital and our affiliated hospitals, surpassing Pseudomonas aeruginosa several years ago and second only to E. coli now. "
Once primarily seen in outbreaks in the Northeast, KPC has spread throughout the US and most of the world. KPCs are the primary mechanism of resistance for an increasingly wide range of gram-negative bacteria and are no longer limited to expression in K. pneumoniae.
"NDM has not really spread worldwide," he says. "KPC on the other hand is endemic in the Northeastern United States and is all over Israel and found in Greece. A national survey in Taiwan has KPC-2 as the predominate carbapenmase. It's worldwide right now."
For that matter, Chiang didn't have to go to China to find a hyper-virulent strain of K. pneumoniae either. An isolate was gleaned from a patient who returned from travel to the Philippines and developed a liver abscess caused by a hyper-virulent strain of K. pneumoniae. "It was a K-2 strain that was hyper-virulent and caused endocarditis in that patient," he says.
The two most commonly found KPC strains (KPC 2 and 3) at the East Orange VA were used as the non-virulent, drug-resistant components of the experiment. Conjugation of KPC 2 and 3 into the K2 serotype KP isolate was performed.
"We took that bacterial bug and conjugated it — basically 'mated' it — with the KPC strains we have here," he says. "The hyper-virulent strains took up the KPC [drug resistance] plasmid without problem."
Antimicrobial susceptibility testing for the three isolates was done initially and of the tranconjugants afterwards. KPC production by polymerase chain reaction (PCR) and amplicon sequencing confirmed KPC types. PCR was also used to detect virulence associated genes. KPC 2 and 3 were successfully conjugated and retained by the invasive K2 KP recipient isolate, the researchers found.
Though the original isolate from the Philippine patient was only resistant to ampicillin, after conjugation the new hybrid bug was resistant to all beta lactams. Additionally, it retained its lethality on lab mice.
"The hyper-virulent strains kill mice really quickly," Chiang says. "[The local] strain does not. So when I conjugated the KPC into the virulent strain we tested the lethality again. This conjugate strain killed mice really quickly, plus being almost pan-resistant to all antibiotics at that point."
References
- Noble WC, Virani Z, Cree RG. Co-transfer of vancomycin and other resistance genes from Enterococcus faecalis NCTC 12201 to Staphylococcus aureus. FEMS Microbiol Lett 1992; 72:195-198.
- Evans G. Risen from the dead: Can 1918 virus help defeat bird flu threat? Hosp Infect Control 2005 32[12]145-153
- Liu Y, Li XY, Wan LG, et al. Virulence and Transferability of Resistance Determinants in a Novel Klebsiella pneumoniae Sequence Type 1137 in China. Clin Microbiol Infect 2013;19(11):E509-15. doi: 10.1111/1469-0691.12275.
- Koper C, Eng R, Chiang T, et al. KPC Conjugation into Virulent Klebsiella pneumoniae. Session: 110. Antimicrobials: Resistance Mechanisms. IDWeek 2013. San Francisco, CA; Oct. 2-6.
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