Exploring the mysterious world of uncommon pathogens causing severe infections in Italy and their startling antibiotic resistance profiles
When we think of bacterial infections, familiar names like E. coli or Staphylococcus often come to mind. However, lurking in hospital wards and communities across Italy are uncommon bacterial pathogens that pose an exceptional threat—not necessarily because of their inherent virulence, but because of their alarming resistance to antibiotics.
The struggle against antimicrobial resistance (AMR) often focuses on common pathogens, but uncommon bacterial species represent a hidden frontier in this public health battle. Italy, with one of Europe's highest rates of antibiotic-resistant infections, has become a critical surveillance ground where scientists are tracking these elusive microbes 2 6 8 .
This article explores the mysterious world of uncommon pathogens causing severe infections in Italy, their startling antibiotic resistance profiles, and what this means for the future of infectious disease treatment.
Uncommon bacteria represented just 1.2% of all bacterial isolates in the Italian study 1
Despite their rarity, these pathogens caused disproportionately severe diseases
Several uncommon species displayed worrying resistance to multiple antibiotics
To understand the threat posed by uncommon bacteria, researchers in Italy launched the "Severe Infections Project"—a dedicated effort to identify and analyze rare pathogens causing serious illness throughout the country.
In clinical microbiology, "uncommon" human pathogens are those species that represent a small minority of infection cases—often less than 1-2% of all isolates from infected patients. These bacteria are rarely encountered in standard clinical practice, which means their typical behavior and antibiotic susceptibility patterns are not well-established. When they do cause infections, they often present a diagnostic and therapeutic challenge for physicians 1 .
The Italian study isolated approximately 60 uncommon bacterial strains
The research revealed that uncommon bacteria primarily caused:
Among the most frequently identified unusual pathogens were Comamonas testosteroni, Enterococcus hirae, Kluyvera ascorbata, Kluyvera cryocrescens, Leclercia adecarboxylata, and Ochrobactrum anthropi, all recovered from patients with bacteremia (bloodstream infections) 1 .
Researchers gathered bacterial isolates from patients with severe infections across multiple Italian healthcare facilities.
Using advanced laboratory techniques, they identified bacterial species that qualified as "uncommon"—representing only a tiny fraction of all infection cases.
Each bacterial isolate was tested against a panel of clinically relevant antibiotics to determine which drugs could effectively inhibit its growth.
Scientists documented specific resistance profiles, noting which pathogens showed resistance to multiple antibiotic classes 1 .
The findings revealed that several uncommon species displayed worrying resistance to multiple antibiotics:
| Bacterial Species | Primary Infection Site | Resistance Notes |
|---|---|---|
| Comamonas testosteroni | Bloodstream | |
| Enterococcus hirae | Bloodstream | |
| Kluyvera ascorbata | Bloodstream | Multi-drug resistant |
| Leclercia adecarboxylata | Bloodstream | |
| Ochrobactrum anthropi | Bloodstream | Multi-drug resistant |
| Achromobacter xylosoxidans | Various sites | Multi-drug resistant |
| Pseudomonas stutzeri | Various sites | Multi-drug resistant |
The findings on uncommon bacteria occur against a backdrop of concerning AMR trends throughout Italy.
Recent data shows significant increases in resistant infections:
Increased from 2.62% to 4.56% between 2019-2022 6
Rose from 1.84% to 2.81% between 2019-2022 6
Dramatic jump from 0.58% to 2.21% between 2019-2022 6
| Pathogen Type | 2019 Prevalence | 2022 Prevalence | Change |
|---|---|---|---|
| CPO | 2.62% | 4.56% | +74% |
| MRSA | 1.84% | 2.81% | +53% |
| VRE | 0.58% | 2.21% | +281% |
Perhaps most alarmingly, these resistant infections are no longer confined to hospital settings. The 2023 study noted that carbapenem-resistant organisms (CPO) detection rates in community patients surged from 34% in 2019 to 42% in 2022, while hospital rates decreased—indicating these dangerous pathogens are spreading beyond healthcare facilities into the general community 6 .
Studying antibiotic resistance in uncommon bacteria requires specialized laboratory tools and methods.
Function: Determines minimum inhibitory concentration (MIC) of antibiotics
Application: Testing bacterial susceptibility to multiple drug concentrations
Function: Detects resistance genes in bacterial DNA
Application: Identifying genetic basis of resistance mechanisms
Function: Maps complete genetic blueprint of bacteria
Application: Tracing resistance gene origin and spread
Function: Measures antibiotic effectiveness through inhibition zones
Application: Initial screening of antibiotic susceptibility
| Tool/Technique | Function | Application in Research |
|---|---|---|
| Agar Dilution Method | Determines minimum inhibitory concentration (MIC) of antibiotics | Testing bacterial susceptibility to multiple drug concentrations |
| PCR Amplification | Detects resistance genes in bacterial DNA | Identifying genetic basis of resistance mechanisms |
| Whole Genome Sequencing | Maps complete genetic blueprint of bacteria | Tracing resistance gene origin and spread |
| Disc Diffusion Tests | Measures antibiotic effectiveness through inhibition zones | Initial screening of antibiotic susceptibility |
| Cell Culture Systems | Grows bacterial strains for testing | Maintaining bacterial isolates for experimentation |
The study of uncommon bacterial pathogens provides crucial insights beyond simply understanding these rare species themselves.
Uncommon bacteria can harbor resistance genes that may transfer to more common pathogens, accelerating the spread of AMR.
The resistance patterns in uncommon bacteria can signal emerging resistance trends before they become widespread in common pathogens.
Understanding resistance profiles helps clinicians make informed decisions when facing infections that don't respond to standard treatments 1 .
The Italian research offers valuable guidance for empirical therapy—the initial antibiotic treatment chosen before specific pathogen identification is available. When uncommon pathogens are suspected, the resistance patterns documented in this study can help physicians select more appropriate first-line therapies 1 .
The concerning rise of resistant bacteria—both common and uncommon—has accelerated research into novel antibiotics.
Culturing previously unculturable bacteria using specialized diffusion chambers that mimic natural environments, providing access to potentially novel antibiotic compounds from previously inaccessible microbes 3 .
Exploring unconventional microbial habitats such as nematode gut systems, which has led to the discovery of promising compounds like darobactin, effective against resistant Gram-negative pathogens 3 .
Developing antibiotics with multiple mechanisms such as teixobactin, which both inhibits cell wall synthesis and disrupts bacterial membrane integrity, making resistance development more difficult 3 .
The investigation into uncommon bacterial pathogens in Italy reveals a critical dimension of the antimicrobial resistance crisis. These little-known organisms not only cause severe infections but often display resistance patterns that complicate treatment. As the broader surveillance data indicates, antibiotic resistance continues to rise in Italy, affecting both common and uncommon pathogens and spreading from hospitals into communities.
The fight against these resistant uncommon bacteria underscores a fundamental truth in infectious disease medicine: constant vigilance, ongoing surveillance, and innovative therapeutic approaches are essential. As researchers continue to decode the resistance mechanisms of these unusual pathogens, their findings contribute to the larger battle against antimicrobial resistance—a battle with profound implications for global public health.
Acknowledgement: This article is based on analysis of multiple scientific studies, particularly the pioneering Italian "Severe Infections Project" and subsequent surveillance data on antimicrobial resistance trends in Italy.