Pseudomonas putida: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, and Prevention

Introduction

Table of Contents

Pseudomonas putida is a versatile, Gram-negative, rod-shaped bacterium primarily known for its bioremediation capabilities but recognized as a rare opportunistic human pathogen. Found globally in soil, water, and plant roots, it thrives in diverse environments due to its unique metabolic endurance.

Morphology and Characteristics

Cell Shape: Straight, rod-shaped bacilli measuring 0.5 to 1.0 µm in length.
Arrangement: Occurs mostly as single cells or in end-to-end pairs.
Gram Reaction: Gram-negative (stains pink/red).
Motility: Highly motile via multiple polar flagella.
Pigmentation: Produces pyoverdine, a fluorescent yellow-green pigment.
Key Distinction: Does not produce pyocyanin (the blue-green pigment unique to Pseudomonas aeruginosa).

Pseudomonas putida colony morphology on blood agar after 48 hours of incubation — Fig. *Pseudomonas putida* colony morphology on blood agar after 48 hours of incubation

Colony Appearance: Smooth, circular, convex, and creamy-white on standard agar.

Pathogenicity

Target Audience: Affects immunocompromised patients, newborns, and hospitalized individuals.
Risk Factors: Associated with medical devices like indwelling urinary or central venous catheters.
Clinical Manifestations: Causes bloodstream infections (bacteremia), urinary tract infections (UTIs), pneumonia, skin/soft tissue infections, and neonatal sepsis.
Virulence Factors: Relies on pili for tissue adherence, flagella for invasion, and biofilm formation to shield itself from host immune defenses.

Laboratory Diagnosis

Specimen Collection: Blood, urine, sputum, or wound swabs depending on infection site.
Microscopy: Gram staining reveals Gram-negative rods.
Culture Media: Grows easily on Nutrient Agar and MacConkey Agar (appearing as a non-lactose fermenter).

Pseudomonas putida colony morphology on MacConkey agar — Fig. *Pseudomonas putida* colony morphology on MacConkey agar

Incubation: Grows optimally at 30°C to 35°C; cannot grow at 41°C (unlike P. aeruginosa).
Biochemical Tests:
- Oxidase-positive.
- Catalase-positive.
- Citrate-positive.
- Gelatin liquefaction-negative.

Pseudomonas putida in wet mount of culture — Fig. *Pseudomonas putida* in wet mount of culture

Treatment

Susceptibility: Shows high sensitivity to colistin, gentamicin, amikacin, and meropenem.
Resistance: Exhibits intrinsic or acquired resistance to aztreonam, levofloxacin, and ciprofloxacin.
Approach: Requires a mandatory Antimicrobial Susceptibility Test (AST) due to emerging multidrug-resistant strains.
Device Removal: Prompt removal or replacement of contaminated catheters or implants is required for cure.

Prevention

Hygiene: Implementation of rigorous handwashing protocols among healthcare workers.
Sterilization: Strict disinfection of catheters, ventilators, and surgical instruments.
Environmental Control: Minimizing standing water and damp areas in clinical environments to restrict habitat growth.
Aseptic Care: Maintaining sterile techniques during the insertion and maintenance of indwelling lines.