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Infectious Disease and Microbiology – Pseudomonas Infections, Melioidosis, and Glanders
Members of the genus Pseudomonas are motile, gram-negative, aerobic bacteria associated with a broad range of infections. Burkholderia pseudomallei (formerly Pseudomonas pseudomallei) causes melioidosis, also known as Whitmore’s disease or Nightcliff gardener’s disease. Burkholderia mallei (formerly Pseudomonas mallei) causes glanders, a zoonotic disease primarily affecting horses, mules, and donkeys but also capable of infecting humans. Both B. pseudomallei and B. mallei are considered potential bioterrorism agents.
Pseudomonas aeruginosa is one of the leading causes of hospital-acquired urinary tract infections, pneumonia, and bacteremia. It accounts for approximately 10% of all nosocomial infections and is especially common among patients hospitalized for more than one week. Melioidosis is endemic in tropical regions, particularly Southeast Asia, while glanders remains endemic in parts of Africa, Asia, the Middle East, Central America, and South America. Person-to-person transmission of melioidosis is rare.
Risk factors for P. aeruginosa infection include disruption of normal host barriers through endotracheal intubation or urinary catheterization, immunosuppression, and prior broad-spectrum antibiotic therapy. Patients with cystic fibrosis are especially susceptible to chronic lower respiratory tract colonization and infection. P. aeruginosa is also a major cause of ventilator-associated pneumonia. Central nervous system infections are associated with neurosurgical procedures, indwelling devices, cerebrospinal fluid leaks, penetrating trauma, and bacteremia. Bone and joint infections may occur after surgery, intravenous drug use, or penetrating trauma. Malignant external otitis is a severe invasive infection seen primarily in diabetic or immunocompromised patients and may extend into the central nervous system. Ocular infections, gastrointestinal infections in neutropenic patients, and burn wound infections are also common manifestations.
Risk factors for melioidosis include diabetes mellitus, thalassemia, chronic kidney disease, and occupational or environmental exposure to contaminated soil or water. There is no available vaccine against Pseudomonas infections, and prevention mainly relies on minimizing risk factors and limiting healthcare-associated exposures.
The pathogenesis of Pseudomonas infections begins with bacterial attachment and colonization of surfaces such as catheters, respirators, and damaged tissue. This may lead to localized infection followed by hematogenous dissemination and systemic disease.
P. aeruginosa is the most important human pathogen within this group. Other clinically relevant species include Burkholderia cepacia, associated with respiratory infections in cystic fibrosis patients and various nosocomial infections; Burkholderia pickettii, implicated in hospital outbreaks; Comamonas acidovorans, a rare cause of endocarditis; Pseudomonas fluorescens, linked to contaminated blood products; Pseudomonas putida, which may cause sepsis in immunocompromised hosts; and Stenotrophomonas maltophilia, associated with pneumonia, bacteremia, endocarditis, meningitis, urinary tract infections, and wound infections.
Clinical manifestations depend on the organ system involved. In early cystic fibrosis, P. aeruginosa causes recurrent upper respiratory symptoms, while advanced disease leads to chronic productive cough, recurrent pneumonia, respiratory compromise, weakness, and weight loss. Corneal ulcers due to P. aeruginosa may progress rapidly and threaten vision. Malignant external otitis presents with severe otalgia and otorrhea, and physical examination typically reveals erythema, swelling, purulent discharge, granulation tissue, and debris in the external auditory canal.
Characteristic skin lesions known as ecthyma gangrenosum may occur in P. aeruginosa bacteremia. These lesions begin as hemorrhagic vesicles with surrounding erythema and progress to central necrosis and ulceration. Exposure to contaminated hot tubs or pools may result in diffuse pruritic maculopapular or vesiculopustular eruptions. Osteomyelitis of the foot often follows penetrating injury, while sternoclavicular septic arthritis is associated with intravenous drug use.
Melioidosis most commonly involves the lungs and presents with fever, productive cough, and tachypnea. It may also produce acute or chronic suppurative infections of the skin and internal organs. Glanders may manifest as chronic suppurative abscesses, mucopurulent infection of mucous membranes with granulomatous ulcers, or systemic disease with fever, pleuritic chest pain, diarrhea, headache, and myalgia. Lymphadenopathy and splenomegaly may also occur.
Diagnosis requires appropriate cultures from blood, urine, sputum, bronchoalveolar lavage fluid, wounds, or other affected sites, followed by antimicrobial susceptibility testing. Imaging studies depend on the site of infection. In malignant external otitis, CT and MRI often demonstrate bony erosion and new bone formation. Melioidosis may produce upper lobe infiltrates or thin-walled cavities resembling tuberculosis on chest imaging. MRI is useful in suspected osteomyelitis, while echocardiography is indicated when endocarditis is suspected in bacteremic patients. Bronchoalveolar lavage or endotracheal aspirates are useful for confirming respiratory infections in intubated patients.
Differential diagnosis varies according to the clinical presentation. In cases of pneumonia, alternatives include bacterial pneumonias, viral infections, and Pneumocystis jiroveci pneumonia.
Most P. aeruginosa infections are treated with one or two antibiotics to which the organism is susceptible. Common antipseudomonal agents include aminoglycosides, carbapenems, extended-spectrum penicillins such as piperacillin, third-generation cephalosporins such as ceftazidime, fluoroquinolones such as ciprofloxacin, and monobactams. Increasing resistance to ciprofloxacin necessitates caution when selecting empiric therapy.
Bacteremia is commonly treated with agents such as ceftazidime, cefepime, meropenem, imipenem-cilastatin, piperacillin-tazobactam, or aztreonam in beta-lactam-allergic patients. Addition of an aminoglycoside may be appropriate in settings with high resistance rates. Pneumonia is managed similarly, though inhaled tobramycin may also be used. Osteomyelitis requires prolonged high-dose antipseudomonal beta-lactam or fluoroquinolone therapy, often combined with surgical intervention. Central nervous system infections are treated primarily with ceftazidime, cefepime, or meropenem, while imipenem is generally avoided because of neurotoxicity and rapid resistance development.
Ocular infections require topical, subconjunctival, intravitreal, and sometimes systemic antibiotics depending on severity. Malignant external otitis is treated with beta-lactam antibiotics or ciprofloxacin, although relapse may occur even after prolonged therapy. Urinary tract infections are managed with antipseudomonal beta-lactams, fluoroquinolones, or aminoglycosides. Burn wound infections often require topical therapy and careful antibiotic selection because resistance can develop rapidly.
Treatment of melioidosis depends on disease severity and often requires prolonged therapy. Glanders is initially treated with agents such as imipenem, ceftazidime, or meropenem combined with ciprofloxacin and doxycycline, followed by extended oral therapy to reduce relapse risk.
Surgical intervention is frequently necessary in osteomyelitis and may be required in malignant otitis externa for debridement. Infectious disease consultation is strongly recommended, particularly in cases of melioidosis or glanders.
Close follow-up is essential because of the risk of relapse and emergence of multidrug-resistant organisms. Resistance mechanisms include chromosomal beta-lactamases and extended-spectrum beta-lactamases. Prognosis depends on the site of infection, severity of illness, host immune status, and timeliness of therapy. Complications include septic shock, respiratory failure, metastatic infection, brain abscesses, septic emboli, cranial nerve involvement, meningitis, and death.
Members of the genus Pseudomonas are motile, gram-negative, aerobic bacteria associated with a broad range of infections. Burkholderia pseudomallei (formerly Pseudomonas pseudomallei) causes melioidosis, also known as Whitmore’s disease or Nightcliff gardener’s disease. Burkholderia mallei (formerly Pseudomonas mallei) causes glanders, a zoonotic disease primarily affecting horses, mules, and donkeys but also capable of infecting humans. Both B. pseudomallei and B. mallei are considered potential bioterrorism agents.
Pseudomonas aeruginosa is one of the leading causes of hospital-acquired urinary tract infections, pneumonia, and bacteremia. It accounts for approximately 10% of all nosocomial infections and is especially common among patients hospitalized for more than one week. Melioidosis is endemic in tropical regions, particularly Southeast Asia, while glanders remains endemic in parts of Africa, Asia, the Middle East, Central America, and South America. Person-to-person transmission of melioidosis is rare.
Risk factors for P. aeruginosa infection include disruption of normal host barriers through endotracheal intubation or urinary catheterization, immunosuppression, and prior broad-spectrum antibiotic therapy. Patients with cystic fibrosis are especially susceptible to chronic lower respiratory tract colonization and infection. P. aeruginosa is also a major cause of ventilator-associated pneumonia. Central nervous system infections are associated with neurosurgical procedures, indwelling devices, cerebrospinal fluid leaks, penetrating trauma, and bacteremia. Bone and joint infections may occur after surgery, intravenous drug use, or penetrating trauma. Malignant external otitis is a severe invasive infection seen primarily in diabetic or immunocompromised patients and may extend into the central nervous system. Ocular infections, gastrointestinal infections in neutropenic patients, and burn wound infections are also common manifestations.
Risk factors for melioidosis include diabetes mellitus, thalassemia, chronic kidney disease, and occupational or environmental exposure to contaminated soil or water. There is no available vaccine against Pseudomonas infections, and prevention mainly relies on minimizing risk factors and limiting healthcare-associated exposures.
The pathogenesis of Pseudomonas infections begins with bacterial attachment and colonization of surfaces such as catheters, respirators, and damaged tissue. This may lead to localized infection followed by hematogenous dissemination and systemic disease.
P. aeruginosa is the most important human pathogen within this group. Other clinically relevant species include Burkholderia cepacia, associated with respiratory infections in cystic fibrosis patients and various nosocomial infections; Burkholderia pickettii, implicated in hospital outbreaks; Comamonas acidovorans, a rare cause of endocarditis; Pseudomonas fluorescens, linked to contaminated blood products; Pseudomonas putida, which may cause sepsis in immunocompromised hosts; and Stenotrophomonas maltophilia, associated with pneumonia, bacteremia, endocarditis, meningitis, urinary tract infections, and wound infections.
Clinical manifestations depend on the organ system involved. In early cystic fibrosis, P. aeruginosa causes recurrent upper respiratory symptoms, while advanced disease leads to chronic productive cough, recurrent pneumonia, respiratory compromise, weakness, and weight loss. Corneal ulcers due to P. aeruginosa may progress rapidly and threaten vision. Malignant external otitis presents with severe otalgia and otorrhea, and physical examination typically reveals erythema, swelling, purulent discharge, granulation tissue, and debris in the external auditory canal.
Characteristic skin lesions known as ecthyma gangrenosum may occur in P. aeruginosa bacteremia. These lesions begin as hemorrhagic vesicles with surrounding erythema and progress to central necrosis and ulceration. Exposure to contaminated hot tubs or pools may result in diffuse pruritic maculopapular or vesiculopustular eruptions. Osteomyelitis of the foot often follows penetrating injury, while sternoclavicular septic arthritis is associated with intravenous drug use.
Melioidosis most commonly involves the lungs and presents with fever, productive cough, and tachypnea. It may also produce acute or chronic suppurative infections of the skin and internal organs. Glanders may manifest as chronic suppurative abscesses, mucopurulent infection of mucous membranes with granulomatous ulcers, or systemic disease with fever, pleuritic chest pain, diarrhea, headache, and myalgia. Lymphadenopathy and splenomegaly may also occur.
Diagnosis requires appropriate cultures from blood, urine, sputum, bronchoalveolar lavage fluid, wounds, or other affected sites, followed by antimicrobial susceptibility testing. Imaging studies depend on the site of infection. In malignant external otitis, CT and MRI often demonstrate bony erosion and new bone formation. Melioidosis may produce upper lobe infiltrates or thin-walled cavities resembling tuberculosis on chest imaging. MRI is useful in suspected osteomyelitis, while echocardiography is indicated when endocarditis is suspected in bacteremic patients. Bronchoalveolar lavage or endotracheal aspirates are useful for confirming respiratory infections in intubated patients.
Differential diagnosis varies according to the clinical presentation. In cases of pneumonia, alternatives include bacterial pneumonias, viral infections, and Pneumocystis jiroveci pneumonia.
Most P. aeruginosa infections are treated with one or two antibiotics to which the organism is susceptible. Common antipseudomonal agents include aminoglycosides, carbapenems, extended-spectrum penicillins such as piperacillin, third-generation cephalosporins such as ceftazidime, fluoroquinolones such as ciprofloxacin, and monobactams. Increasing resistance to ciprofloxacin necessitates caution when selecting empiric therapy.
Bacteremia is commonly treated with agents such as ceftazidime, cefepime, meropenem, imipenem-cilastatin, piperacillin-tazobactam, or aztreonam in beta-lactam-allergic patients. Addition of an aminoglycoside may be appropriate in settings with high resistance rates. Pneumonia is managed similarly, though inhaled tobramycin may also be used. Osteomyelitis requires prolonged high-dose antipseudomonal beta-lactam or fluoroquinolone therapy, often combined with surgical intervention. Central nervous system infections are treated primarily with ceftazidime, cefepime, or meropenem, while imipenem is generally avoided because of neurotoxicity and rapid resistance development.
Ocular infections require topical, subconjunctival, intravitreal, and sometimes systemic antibiotics depending on severity. Malignant external otitis is treated with beta-lactam antibiotics or ciprofloxacin, although relapse may occur even after prolonged therapy. Urinary tract infections are managed with antipseudomonal beta-lactams, fluoroquinolones, or aminoglycosides. Burn wound infections often require topical therapy and careful antibiotic selection because resistance can develop rapidly.
Treatment of melioidosis depends on disease severity and often requires prolonged therapy. Glanders is initially treated with agents such as imipenem, ceftazidime, or meropenem combined with ciprofloxacin and doxycycline, followed by extended oral therapy to reduce relapse risk.
Surgical intervention is frequently necessary in osteomyelitis and may be required in malignant otitis externa for debridement. Infectious disease consultation is strongly recommended, particularly in cases of melioidosis or glanders.
Close follow-up is essential because of the risk of relapse and emergence of multidrug-resistant organisms. Resistance mechanisms include chromosomal beta-lactamases and extended-spectrum beta-lactamases. Prognosis depends on the site of infection, severity of illness, host immune status, and timeliness of therapy. Complications include septic shock, respiratory failure, metastatic infection, brain abscesses, septic emboli, cranial nerve involvement, meningitis, and death.
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