In a quiet laboratory in Moscow, a discovery about a dangerous pathogen was made not in a sick patient, but in the healthy staff working to understand it.
Imagine a deadly bacterium that can lurk undetected in healthy people, spreading silently before causing severe infections in vulnerable individuals. This isn't science fiction—it's the reality of hypervirulent Klebsiella pneumoniae, a "superbug" that has become a grave concern in hospitals worldwide.
In 2021, Russian microbiologists made a startling discovery while studying these bacteria: they found them in the most unexpected place—the very researchers who worked with them. This finding revealed a hidden reservoir of dangerous pathogens within healthy populations, offering crucial insights into how these microbes spread and evade our defenses. The silent carriage of such pathogens by healthy individuals represents a critical challenge for infection control and public health.
Klebsiella pneumoniae is a Gram-negative, non-motile, capsulated opportunistic bacterium that belongs to the Enterobacteriaceae family 2 . First identified by German pathologist Carl Friedländer in 1882 during his research on pneumonia, the bacterium was later named in honor of Edwin Klebs in 1896, recognizing his significant contributions to medical microbiology 2 .
Klebsiella pneumoniae is ubiquitous in our environment—found in soil, water, and plant surfaces—and commonly resides on human skin, in the respiratory tract, and within intestines without causing harm 2 6 .
A prevalent hospital-acquired infection source, ranking second only to E. coli in infection rates. It poses significant risks to people with compromised immune systems, such as those with diabetes or malignant tumors 2 .
Since the 1990s, this variant has garnered increased attention as a notable cause of community-acquired infections, with a case fatality rate ranging from 3% to 32% 2 . Unlike its classic counterpart, hvKP infections frequently occur in otherwise healthy people.
Klebsiella poses a dual threat: not only is it highly virulent, but it's also developing alarming resistance to antibiotics. The problem has evolved from Multidrug Resistance (MDR) to Extensively Drug Resistance (XDR) and even Pan-Drug Resistance (PDR) 2 .
Antibiotic Resistance Progression
According to 6 , Klebsiella shows resistance against main antibiotic classes including carbapenems, cephalosporins, aminoglycosides, and fosfomycin, leading to therapeutic failure.
The World Health Organization recognizes extended-spectrum β-lactam (ESBL)-producing and carbapenem-resistant K. pneumoniae (CRKP) as a critical public health threat 6 . Even more concerning is the emergence of carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKP) strains that combine resistance to last-resort antibiotics with heightened pathogenicity 2 .
The groundbreaking Russian study, "Carriage of Capsular Serotype K1 Klebsiella pneumoniae Sequence Type 23 Strains in Healthy Microbiology Laboratory Staff in Russia," provided crucial insights into how hypervirulent strains silently circulate among populations 3 .
Researchers designed a comprehensive approach to detect and analyze these bacteria in asymptomatic carriers:
The team collected 100 Gram-negative bacterial isolates from 33 healthy microbiology laboratory staff members in the Moscow Region. These included 87 stool samples and 13 throat samples 3 .
Initial isolation used lactose triphenyl-tetrazolium chloride (TTC) agar with tergitol-7. Scientists then identified bacteria using matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) with the reference strain K. pneumoniae ATCC 700603 3 .
The researchers performed a string test to identify the hypermucoviscous phenotype associated with hypervirulent strains 3 .
The Minimum Inhibitory Concentrations (MICs) of antibacterials were determined using a Vitek 2 compact instrument, interpreted according to Clinical and Laboratory Standards Institute guidelines 3 .
DNA was extracted from overnight cultures, and whole-genome sequencing was performed using Illumina MiSeq platform. Multilocus sequence typing (MLST) and identification of antibiotic resistance genes, virulence genes, and plasmids were conducted using bioinformatics resources 3 .
The results revealed something concerning: among 100 Gram-negative isolates, 20 cultures were identified as K. pneumoniae. Three of these K. pneumoniae isolates collected from three different individuals were characterized as hypermucoviscous bacteria by string test and identified as sequence type 23 (ST23) and capsular type K1 through whole-genome analysis 3 .
| Feature | Strain F18R-1Kp/19 | Strain F19R-1Kp/19 | Strain Z27-Kp/19 |
|---|---|---|---|
| Sequence Type | ST23 | ST23 | ST23 |
| Capsular Type | K1 | K1 | K1 |
| Isolation Source | Stool | Stool | Throat |
| Collection Date | 11 April 2019 | 12 April 2019 | 12 April 2019 |
| Genome Size | 5,560,322 bp | 5,560,734 bp | 5,552,064 bp |
| No. of Contigs | 74 | 72 | 83 |
| Resistance/Virulence Category | Gene(s) Identified | Function |
|---|---|---|
| Beta-lactam resistance | blaSHV-190 | Confers resistance to β-lactam antibiotics |
| Fosfomycin resistance | fosA3 | Provides resistance to fosfomycin |
| Efflux system | oqxА1, oqxB1 | Pump antibiotics out of bacterial cells |
| Mucoid phenotype regulator | rmpA2 | Controls hypermucoviscosity |
| Siderophore systems | iroBCDN, kfuABC | Iron acquisition mechanisms |
| Allantoin metabolism | allABCDRS | Nutrient utilization |
This discovery of hvKP K1 ST23 carriage in healthy people in Russia was significant for several reasons:
This was the first report of such carriage in Russia, indicating the silent spread of these strains into new geographical regions 3 .
Healthy carriers can unknowingly transmit dangerous pathogens to vulnerable individuals in community and healthcare settings.
The strains carried two plasmids attributed to incompatibility groups IncHI1B and IncFIB, which are mobile genetic elements that can facilitate the spread of virulence and resistance genes to other bacteria 3 .
The Russian study highlighted what researchers had observed elsewhere—asymptomatically colonizing strains of capsular serotype K1 K. pneumoniae ST23 had previously been reported as related to liver abscess cases in South Korea and more recently in the United States 3 .
The silent spread of hypervirulent K. pneumoniae comes at a time when antibiotic resistance is rapidly increasing worldwide. CTX-M enzymes have become the predominant extended-spectrum β-lactamases (ESBLs) globally, contributing to increased patient morbidity, mortality, and healthcare costs 9 .
A recent study in Baghdad hospitals found a shocking 100% prevalence of CTX-M genes among K. pneumoniae isolates, with the most frequent alleles being blaCTX-M-15 (65.2%) and blaCTX-M-1 (30%) 9 . Additionally, 95.6% of these isolates could form biofilms—protective structures that make bacteria even more resistant to antibiotics and host defenses 9 .
Based on 6
The discovery of hypervirulent K. pneumoniae in healthy laboratory staff serves as a powerful reminder that in our interconnected world, pathogens know no boundaries. The silent carriage of dangerous bacteria by healthy individuals represents a significant challenge for infection control and public health surveillance.
As research continues, scientists are exploring novel approaches to combat these pathogens, including investigating plant extracts like Platanus orientalis Linn, which has shown promise in reducing biofilm formation 9 . However, the race between bacterial evolution and medical innovation continues.
The Russian study concludes with a crucial recommendation: "Our report shows the need for continued monitoring of hvKP and indicates the importance of clinical awareness of this pathotype" 3 . In the silent spread of these bacteria, vigilance and continued research remain our best defenses.