Pseudomonas aeruginosa: resistance and infections

Pseudomonas aeruginosa is an opportunistic pathogen common in the environment and building water systems. It causes infections of the lungs, bloodstream, urinary tract, postoperative wounds, eyes, and ears, especially in hospitalized patients and immunocompromised individuals. Early identification, prompt initiation of active therapy, and source control are essential for the clinician. [1]

Hospital-acquired and healthcare-associated P. aeruginosa infections are a significant component of the overall burden of healthcare-associated infections. According to international surveys, on average, one in ten patients out of every 100 develops such an infection, and the proportion of resistant pathogens in this group is high. This necessitates special attention to prevention and rational antibiotic therapy. [2]

The clinical significance of the pathogen is enhanced by the tendency toward multidrug resistance and the emergence of a "difficult to treat" phenotype, which exhibits resistance to all standard first-line drugs. For such cases, specific recommendations have been developed for the selection of new beta-lactams and optimization of antibiotic exposure. [3]

Reservoirs in healthcare facility water systems, biofilms in sink drains, and wet equipment create conditions for persistence and outbreaks. Water system management and hand hygiene are key to reducing risk. [4]

Table 1. Briefly about the main points

Paragraph	The essence
Where does he live?	Water, soil, bio-films in buildings
Who is at risk?	Patients in intensive care units, with invasive devices, with immunodeficiency
What is dangerous?	Multiple resistance, severe pneumonia and sepsis
What decides the outcome	Early active antibiotic and source control
What warns	Water management programs and infection control measures
[5]

Epidemiology

P. aeruginosa is a leading cause of hospital-acquired infections, particularly in intensive care units. Seasonal fluctuations are limited, but the risk increases with poor water management practices and reconfiguration of water systems. Risk points include cooling and recirculation units, showers, sink traps, humidifiers, and whirlpool equipment. [6]

A separate clinical niche is patients with cystic fibrosis and bronchiectasis, who develop chronic colonization and frequent exacerbations, affecting survival. Inhaled antibacterial regimens and biofilm suppression strategies are used for this group. [7]

Clusters and outbreaks associated with water reservoirs, including siphons and faucets, as well as household water products, have been described. Control is carried out through epidemiological investigation, typing, and sanitary measures at the outbreak site. [8]

Table 2. Risk factors for infection in hospital

Factor	Why does it increase the risk?
Intubation, mechanical ventilation, central and urinary catheters	Breakdown of barriers and formation of bio-films
Long-term hospitalization, antibacterial therapy	Selection of resistant strains
Contaminated water systems	Aerosolization and contact transfer
Cystic fibrosis, bronchiectasis, neutropenia	Lack of local and general protection
[9]

Structure of bacteria

It is a motile, Gram-negative rod with a polar flagellum, outer membrane, and a well-developed set of virulence factors. The most important of these are the type III secretion system, the effector proteins ExoS and ExoU, elastases, phospholipases, the pigments pyoverdin and pyocianin, and the polysaccharide matrix alginate in mucoid strains. This combination of factors ensures adhesion, invasion, tissue damage, and immune evasion. [10]

The type III secretion system transports effector proteins directly into host cells, disrupting the cytoskeleton and signaling pathways. The presence of ExoU is more often associated with rapid tissue damage and severe disease progression, while ExoS promotes invasion and persistence. [11]

Table 3. Virulence determinants and their role

Factor	Biological effect	Clinical significance
ExoU, ExoS and other effector proteins	Blockade of phagocytosis, cytotoxicity	Severe course, rapid complications
Elastases, phospholipases, exotoxin A	Destruction of the extracellular matrix and cells	Invasiveness, necrosis
Alginate and bio-films	Protection from immunity and antibiotics	Chronic infections, relapses
[12]

Life cycle

Outside of humans, P. aeruginosa lives in water and soil, forming persistent biofilms on moist surfaces. In healthcare settings, it colonizes plumbing fixtures, drains, and showers, where biofilms protect it from disinfectants and drying out. [13]

In the body, the bacteria attach to the epithelium of the respiratory tract and catheters, quickly forming biofilms. In the lungs, especially in cystic fibrosis and bronchiectasis, mucoid phenotypes with alginate hyperproduction are realized, making the infection chronic and resistant to therapy. [14]

Table 4. Stages and “vulnerability points” of intervention

Stage	Vulnerability
Formation of bio-films in water	Water systems management and sanitary regulations
Adhesion to catheters	Asepsis, antimicrobial coatings, early device change
Persistence in the lungs	Inertial airway clearance, inhalation schemes
[15]

Pathogenesis

Tissue damage is determined by a combination of factors: direct cytotoxic action of effectors, destruction of the intercellular matrix by proteases and phospholipases, and generation of oxidative stress by the pigment pyocyanin. These mechanisms cause necrosis, disrupt mucociliary clearance, and promote dissemination. [16]

Strains with ExoU exhibit a more aggressive course with pronounced inflammation and rapid deterioration of organ function. Strains with ExoS are more likely to exhibit invasion and prolonged persistence. The presence of these determinants is considered a prognostic factor for disease severity. [17]

Biofilms create diffusion barriers for antibiotics and form "silent" subpopulations with reduced metabolic activity. This explains clinical failures with proper drug selection and dictates the need to optimize exposure and course duration. [18]

Table 5. "Mechanism - clinical projection"

Mechanism	Result	Clinical conclusion
Effectors of the third type of secretion system	Cytotoxicity, immune evasion	Risk of lightning-fast deterioration
Proteases and phospholipases	Tissue destruction	High prevalence of necrotic foci
Bio-films	Antibiotic tolerance	Increased exposure and focus control are needed.
[19]

Symptoms

The clinical presentation depends on the location. Pneumonia typically presents with fever, cough, increasing shortness of breath, confusion in the elderly, and laboratory signs of systemic inflammation. In patients undergoing surgery or mechanical ventilation, the course is often severe. [20]

Bacteremia rapidly develops signs of sepsis, with the risk of shock and multiple organ failure. Urinary tract infections manifest as dysuria and fever during catheterization. Skin and soft tissue lesions often occur following burns and surgical interventions. [21]

Table 6. Common clinical scenarios

Localization	Typical manifestations
Lungs	Fever, hypoxemia, infiltrates on imaging
Blood flow	Chills, hypotension, signs of shock
Urinary tract	Dysuria, fever, pyelonephritis with catheter
Wounds, burns	Greenish-bluish coating, unpleasant odor
[22]

Stages

Pneumonia is conventionally divided into an early inflammatory stage with fever and respiratory symptoms, an advanced stage with respiratory failure and complications, and a recovery stage with successful therapy. The transition between stages can be rapid, especially in intensive care patients. [23]

The duration of antibacterial therapy for hospital-acquired and ventilator-associated pneumonia in uncomplicated cases is usually about seven days with good dynamics, with an extension in case of complications or immunodeficiency. [24]

Table 7. Stages and tactics

Stage	Leading tasks
Suspicion	Immediate start of active empirical mode
Expanded	Correction based on culture data and sensitivity
Recovery	Early de-escalation and termination based on clinical criteria
[25]

Forms

The most common infections are hospital-acquired and ventilator-associated pneumonia, bloodstream infections, catheter-associated urinary tract infections, wound and burn infections, keratitis, and otitis externa. Chronic lung infection is common in patients with cystic fibrosis. [26]

Table 8. Main forms of the disease

Form	Key Features
Pneumonia in hospitalized patients	High severity, frequent resistance
Blood flow	Rapid progression, high risk of shock
Urinary tract	Catheter-related, recurrent episodes
Keratitis and otitis externa	After contact lenses and water procedures
Chronic lung infection	Cystic fibrosis, bronchiectasis
[27]

Complications and consequences

Common complications include respiratory failure, septic shock, abscesses, empyema, and renal damage secondary to sepsis and drug exposure. Delayed initiation of active therapy directly worsens outcomes. [28]

Difficult-to-treat variants with multiple resistance are characterized by a high risk of treatment failure with standard beta-lactams and fluoroquinolones, which requires a transition to new molecules and optimized administration regimens. [29]

Table 9. Complications and what increases their risk

Complication	Reinforcing factors
Respiratory failure	Late start of therapy, high bacterial load
Shock	Age, comorbidity, stability
Relapses	Bio-films, unsealed source, devices
[30]

Diagnostics

The optimal approach for suspected pneumonia in hospitalized patients is immediate lower respiratory tract swab collection before antibiotic initiation, culture and susceptibility testing, and chest imaging to assess prevalence. Microbiological confirmation is important for surveillance and de-escalation. [31]

Interpretation of results should take into account possible colonization in the presence of devices. For bloodstream infections, paired cultures are mandatory. EUCAST standards with the "susceptible with increased exposure" category are used for resistance assessment, which helps plan extended or continuous infusion regimens. [32]

Table 10. Diagnostic algorithm

Step	What to do	For what
Before the antibiotic	Sowing of material from the lesion and blood	Precise de-escalation
Visualization	X-ray or computed tomography as indicated	Assessment of the extent of damage
Sensitivity	Interpretation according to EUCAST	Selection and exposure
Epidemiological surveillance	Message and source search	Outbreak prevention
[33]

Differential diagnosis

P. aeruginosa must be distinguished from other non-fermenting Gram-negative bacteria, such as Acinetobacter baumannii and Stenotrophomonas maltophilia, as well as from typical pneumonia pathogens. Clues to a Pseudomonas aeruginosa etiology include association with medical devices, contaminated water, and the characteristic green-blue plaque of a wound infection. The final decision is made by culture and susceptibility testing. [34]

Table 11. What to look for when differentiating

Suspicion	What strengthens the case for Pseudomonas aeruginosa?
Pneumonia in intensive care	Long-term ventilation, history of antibacterial therapy
Wound foci	Greenish-blue coating, specific odor
Catheter-associated episodes	Long-term catheterization, bio-films
[35]

Treatment

Empirical initiation. For severe pneumonia in hospitalized patients with a high risk of resistance, initiation with two anti-pseudomonal classes is acceptable until microbiology data are available, followed by de-escalation to a single active drug once susceptibility is confirmed. This approach reduces the risk of inappropriate initiation in critically ill patients. [36]

Choice for susceptible strains. First-line drugs include piperacillin-tazobactam, cefepime, ceftazidime, and carbapenems when indicated. Increased exposure to beta-lactams through prolonged infusions is recommended, especially in severe cases and with high minimum inhibitory concentrations in the intermediate susceptibility zone according to EUCA. [37]

A difficult-to-treat variant. If resistance to all standard first-line drugs is detected, new beta-lactams are used: ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-cilastatin-relebactam, and cefiderocol. The choice depends on the resistance mechanism, local epidemiology, and availability. If metallo-beta-lactamases are suspected, a combination of ceftazidime-avibactam with aztreonam or the use of cefiderocol is considered. [38]

Duration and de-escalation. In uncomplicated cases of pneumonia in hospitalized patients, a duration of approximately seven days is recommended, provided clinical progression is good. Prolongation is warranted in the presence of complications, immunosuppression, and non-pulmonary disease. De-escalation and discontinuation of therapy are based on clinical and laboratory criteria. [39]

Special situations. For chronic pulmonary infections in patients with cystic fibrosis, inhalation regimens and suppression courses are used, taking into account microbiology and tolerability. For device infections, removal or replacement of the source is key. [40]

Table 12. Antibacterial options and where they are appropriate

Situation	Preferred options	Comments
Confirmed sensitivity	Piperacillin-tazobactam, cefepime, ceftazidime	Extended infusions to increase time above threshold
Suspected of a difficult to treat variant	Ceftolozane-tazobactam, imipinem-relebactam, ceftazidime-avibactam, cefiderocol	Consider resistance mechanisms
Metallo-beta-lactamases	Ceftazidime-avibactam plus aztreonam or cefiderocol	By local availability and sensitivity
Immunodeficiency, severe course	Start with two classes followed by de-escalation	Only until receiving microbiology
[41]

Prevention

In healthcare facilities, the foundation is a water system management program: risk mapping, temperature control, disinfection, flushing, monitoring, and documentation. Special attention is given to traps and sinks as potential reservoirs. [42]

Hand hygiene, proper use of devices, barriers during catheter care, and adherence to cleaning protocols reduce the risk of nosocomial spread. Preventive measures and water quality monitoring are required when working on water supply systems. [43]

Table 13. Framework for inpatient prevention

Direction	Measures
Water	Control program, temperature monitoring and disinfection
Devices	Asepsis during installation, timely replacement, removal if possible
Staff	Hand hygiene, training, and compliance with standard measures
Supervision	Microbiological monitoring of outbreaks and process audit
[44]

Forecast

Outcome is determined by the location, the speed of initiation of active therapy, resistance mechanisms, and the ability to eliminate the source. With adequate early treatment and control of the outbreak, most episodes of pneumonia in hospitalized patients respond to treatment within one week. Delayed onset and difficult-to-treat variants increase mortality. [45]

Patients with chronic lung diseases may experience frequent relapses, requiring a long-term suppressive strategy and multidisciplinary monitoring. Individualized therapy programs based on microbiology and tolerability enhance effectiveness. [46]

Frequently Asked Questions - FAQ

Is a "double" regimen always necessary for pneumonia in hospitalized patients?
No. Two classes are appropriate when there is a high risk of resistance or local susceptibility data is lacking. After obtaining microbiological data, switch to a single active drug. [47]

When to choose new beta-lactams?
For the "difficult to treat" phenotype and the ineffectiveness of standard options, preference is given to ceftolozane-tazobactam, imipenem-relebactam, ceftazidime-avibactam, and cefiderocol, based on resistance mechanisms. [48]

How long does pneumonia treatment last in hospitalized patients?
In uncomplicated cases with good progress, it's about seven days. Extension is considered in the case of complications or immunodeficiency. [49]

How can the risk of outbreaks in a hospital be reduced?
Water management programs, hygiene measures, and device monitoring are needed. Traps and sinks are considered priority reservoirs for prevention. [50]

Why is the EUCAST interpretation of the "susceptible with increased exposure" category important?
This system helps select regimens with increased exposure to beta-lactams, which is critical for overcoming biofilm effects and borderline susceptibility. [51]