Virulence and antimicrobial resistance features among clades of Escherichia coli ST131 strains causing community-acquired urinary tract infection in Rio de Janeiro, Brazil

This study characterizes a collection of 133 Escherichia coli ST131 strains from Rio de Janeiro, revealing that subclade C2 exhibits high multidrug resistance and ESBL production while clades B and C2 possess distinct virulence profiles, collectively suggesting that Clade C strains are the primary drivers of ST131 dissemination and persistence in the region.

The Gist

Imagine a bustling city (your body) where a specific type of troublemaker bacteria, E. coli, is causing chaos in the plumbing system (the urinary tract). While there are many different "gangs" of this bacteria, one particular gang is the most notorious: ST131.

This study is like a police report from Rio de Janeiro, Brazil, investigating exactly how this specific gang operates, how they hide, and why they are so hard to catch.

Here is the breakdown of the investigation in simple terms:

1. The Suspects: The "ST131" Gang

Think of the ST131 bacteria not as a single group, but as a family with different branches (clades). The researchers looked at 133 of these bacteria caught from patients in Rio.

• The Victims: Most of the infections happened to women (92%) and older adults (65%). It's like a gang that prefers to target specific demographics.
• The Hierarchy: The family has different branches: Clade A, Clade B, and the "C" family (which is split into C1, C1-M27, and C2).

2. The Weapons: Antibiotic Resistance

The biggest problem with this gang is that they are wearing bulletproof vests.

• The "Super-Resistant" Branch (Subclade C2): This is the most dangerous branch. They are resistant to almost every standard medicine doctors try to use. If you think of antibiotics as keys to lock the bacteria out, Subclade C2 has stolen all the keys and melted the locks.
  • They are resistant to Ciprofloxacin (a common drug) 100% of the time.
  • They carry a special gene (aac(6')-Ib-cr) that acts like a shield against these drugs.
• The "Bulletproof" Branch (Subclade C1): While not as resistant to drugs as C2, this branch has a different superpower: Biofilms.

3. The Hiding Spots: Biofilms

Imagine the bacteria building a fortress made of slime (a biofilm) on the walls of the urinary tract.

• Why it matters: This slime fortress protects them from antibiotics and the body's immune system. It's like a tank that won't stop moving.
• The Surprise: The branch that builds the best fortresses is Subclade C1. Even though they aren't the most drug-resistant, they are the best at sticking around and hiding, making infections hard to cure and likely to come back.

4. The Specialized Tools: Virulence Factors

Virulence factors are like the gang's specialized tools or weapons used to invade and hurt the host.

• Clade B: They have a unique tool called ibeA. Think of this as a specialized key that allows them to break into the brain's blood vessels. It's a very specific and dangerous trait found mostly in this branch.
• Subclade C2: They are the "all-rounders." They carry a heavy load of weapons (like papGII, hlyA, and cnf1) that help them stick to the bladder, destroy cells, and cause severe infections. They are the most aggressive invaders.

5. The Verdict: Who is Running the Show?

The study concludes that the C Family (specifically C2 and C1) is the main reason this bacteria is spreading so fast in Rio.

• Subclade C2 is the heavy hitter: They bring the resistance (the bulletproof vests) and the heavy weapons. They are the ones making the infections hard to treat with drugs.
• Subclade C1 is the sneaky survivor: They might not have the strongest guns, but they build the best fortresses (biofilms), allowing them to hide and persist in the community.

The Big Picture

This research tells us that in Rio de Janeiro, the battle against urinary tract infections is getting harder because the bacteria are evolving. They aren't just one type of enemy; they are a coordinated team where some members are experts at resisting medicine, while others are experts at hiding and surviving.

To win the war, doctors and scientists need to understand these different "branches" of the gang. You can't use the same strategy to fight a bulletproof tank (C2) as you would to fight a ninja hiding in a slime fortress (C1). The study suggests that if we want to stop the spread, we need to target these specific traits, especially the biofilms and the specific resistance genes found in these high-risk clones.

Technical Summary

1. Problem Statement

Urinary tract infections (UTIs) are a leading cause of community-acquired bacterial infections globally, primarily caused by extraintestinal pathogenic Escherichia coli (ExPEC). The high-risk sequence type ST131 has emerged as a dominant global clone, associated with multidrug resistance (MDR), extended-spectrum beta-lactamase (ESBL) production, and the spread of virulence factors. While ST131 is well-characterized in North America and Europe, there is a significant lack of data regarding its epidemiological profile, virulence potential, and resistance mechanisms in Latin America. Specifically, the drivers of ST131 dissemination and persistence in Brazil remain poorly understood. This study aims to fill that gap by characterizing the molecular and phenotypic virulence and resistance profiles of ST131 clades causing community-acquired UTIs in Rio de Janeiro.

2. Methodology

• Study Population: A collection of 133 E. coli ST131 strains isolated from urine specimens of outpatients with suspected UTIs in Rio de Janeiro in July 2019.
• Strain Classification: Strains were previously classified into clades/subclades: Clade A (n=21), Clade B (n=35), Subclade C1 (n=36), Subclade C1-M27 (n=7), Subclade C2 (n=33), and one non-typable (NT) strain.
• Antimicrobial Susceptibility Testing (AST): Performed via disk diffusion according to CLSI 2025 guidelines against 16 antimicrobials (including ampicillin, ciprofloxacin, cephalosporins, and carbapenems). MDR was defined as non-susceptibility to agents in three or more classes.
• Molecular Detection:
  • Resistance Genes: Multiplex PCR for plasmid-mediated quinolone resistance (PMQR) genes (qnr, qepA, aac(6')-Ib). Sequencing confirmed the aac(6')-Ib-cr variant.
  • Virulence Factors (VFs): Multiplex PCR for 15 key UPEC-associated genes, including adhesins (pap, sfa, afa), toxins (hlyA, cnf1), siderophores (fyuA, iutA), invasins (ibeA, kpsMTII), and pathogenicity island markers (malX).
• Biofilm Production: Assessed using a crystal violet staining method in microtiter plates. Strains were classified as non-producers, weak producers, or strong producers.
• Statistical Analysis: Chi-square or Fisher's exact tests for frequency comparisons; Mann–Whitney U test for virulence scores. Significance was set at p < 0.05.

3. Key Contributions

• Regional Epidemiology: Provides the first comprehensive characterization of ST131 clades in a community-acquired UTI setting in Rio de Janeiro, confirming a high prevalence of ST131 (previously reported as increasing from 3% in 2005 to 14% in 2019).
• Clade-Specific Differentiation: Moves beyond species-level analysis to differentiate resistance and virulence profiles at the clade and subclade level, revealing distinct ecological niches for Clade B, C1, and C2.
• Biofilm-Virulence Link: Investigates the correlation between biofilm formation and specific virulence genes in ST131, a relatively underexplored area for this specific clone.
• Resistance-Virulence Co-occurrence: Analyzes the co-existence of MDR/ESBL phenotypes with specific virulence gene sets, highlighting the "perfect storm" of resistance and pathogenicity in specific subclades.

4. Key Results

Demographics

• 92% of patients were female; 65% were over 59 years old.
• Subclade C2 was slightly more prevalent in the elderly female population.

Antimicrobial Resistance (AMR)

• High Resistance Rates: Overall resistance to first-line agents was high: Ampicillin (77%), Ciprofloxacin (73%), and Sulfamethoxazole-trimethoprim (41%).
• Subclade C2 Dominance: Subclade C2 was the primary driver of resistance, showing:
  • 100% resistance to Ciprofloxacin.
  • 79% MDR rate.
  • 52% ESBL production.
  • Resistance to 11 out of 16 tested antimicrobials.
• Resistance Genes: The aac(6')-Ib-cr gene (conferring ciprofloxacin resistance) was found in 66% of Subclade C2 strains. The qnrB gene was also prevalent (27%) in this subclade.
• Clade A: Surprisingly showed the highest ampicillin resistance (95%).

Virulence Factors (VFs)

• Virulence Scores: Clade B and Subclade C2 exhibited the highest virulence scores.
  • Clade B Signature: Uniquely characterized by the presence of ibeA (brain endothelial cell invasion), papGIII, and sfa/focDE.
  • Subclade C2 Signature: Characterized by afa/DrBC, papGII, hlyA, cnf1, and kpsMTII.
• ESBL/MDR Correlation: ESBL-producing strains harbored higher frequencies of papAH, papGII, hlyA, cnf1, and kpsMTII, resulting in significantly higher virulence scores compared to non-ESBL strains.

Biofilm Production

• Prevalence: 58% of strains were biofilm producers (24% weak, 34% strong).
• Clade C1 Dominance: Despite having the lowest virulence score, Subclade C1 was the most prolific biofilm producer (78%), significantly higher than other clades (p=0.005).
• Gene Association: The sfa/focDE gene was statistically associated with biofilm production (p=0.02). A progressive increase in papA, hlyA, and malX was observed from non-producers to strong producers.

5. Significance and Conclusion

• Dual Threat Mechanism: The study concludes that the dissemination of ST131 in Rio de Janeiro is driven by two distinct mechanisms:
  1. Subclade C2: Acts as a reservoir for multidrug resistance (MDR/ESBL) and high virulence (toxins/adhesins), facilitating treatment failure and severe infection.
  2. Subclade C1: While less virulent and less resistant, it contributes to persistence and recurrence through robust biofilm formation.
• Clinical Implications: The high prevalence of MDR in Subclade C2 suggests that standard empirical therapies (fluoroquinolones, trimethoprim-sulfamethoxazole) are likely to fail in this region. The presence of biofilm producers (C1) indicates a risk for recurrent UTIs even if acute infection is treated.
• Public Health: The findings highlight the need for clade-specific surveillance in Latin America. The co-occurrence of resistance genes (like aac(6')-Ib-cr) and virulence factors in single strains creates a "high-risk" pathogen that is difficult to treat and capable of persistent colonization.
• Future Directions: The authors recommend genomic studies and in vivo models to further understand the expression dynamics of these virulence factors and the specific role of biofilms in ST131 persistence.