Burkholderia SPP. and  Ralstonia pickettii

Because Burkholderia spp. and R. pickettii are uncommon causes of infection in humans, very little is known about what, if any, virulence factors they exhibit. Except for B. pseudomallei, the species listed in Table 1 generally are nonpathogenic for healthy human hosts.

Table1.  Pathogenesis and Spectrum of Disease

The capacity of B. cepacia to survive in the hospital environment, which may be linked to the organism’s intrinsic resistance to many antibiotics, provides the opportunity for this species to occasionally colonize and infect hospitalized patients. In patients with cystic fibrosis or chronic granulomatous disease, the organism can cause fulminant lung infections and bacteremia, resulting in death. In other types of patients, infections of the blood, urinary tract, and respiratory tract usually result from exposure to contaminated medical solutions or devices but are rarely fatal.

Infections caused by B. pseudomallei (capable of survival in human macrophages) can range from asymptomatic to severe. The disease is referred to as melioidosis; it has several forms, including the formation of skin abscesses, sepsis and septic shock, abscess formation in several internal organs, and acute pulmonary disease.

The remaining species listed in Table 1 are rarely encountered in human disease, and their clinical significance should be questioned when they are found in clinical specimens.

Pseudomonas SPP. and  Brevundimonas SPP.

Of the species in the Pseudomonas and Brevundimonas genera, P. aeruginosa is the most thoroughly studied with regard to infections in humans. Brevundimonas spp. are rarely associated with human infection. B. vesicularis has been isolated in clinical cases of bacteremia and from cervical specimens. B. diminuta has been recovered from cancer patients in blood, urine and pleural fluid. Although P. aeruginosa is an environmental inhabitant, it is also a very successful opportunistic pathogen. Factors that contribute to the organism’s pathogenicity include production of exotoxin A, which kills host cells by inhibiting protein synthesis, and production of several proteolytic enzymes and hemolysins capable of destroying cells and tissue. On the bacterial cell surface, pili mediate attachment to host cells. Some strains produce alginate, a polysaccharide polymer that inhibits phagocytosis and contributes to the infection potential in patients with cystic fibrosis. Pyocyanin, the blue phenazine pigment that contributes to the characteristic green color of P. aeruginosa, damages cells by producing reactive oxygen species. The reactive oxygen species are also bacteriocidal to the organism. In order to protect itself from destruction, the organism must produce catalase enzymes.

P. aeruginosa also contains several genes involved in quorum sensing, a mechanism for detecting bacterial products in the immediate environment. When the growth of the organism or neighboring bacteria reaches a critical mass, the concentration of these “inducing” molecules reaches a level that activates transcription of virulence factors, including genes related to metabolic processes, enzyme production, and the formation of biofilm. Although many in vitro studies have examined biofilm formation, no clear evidence exists that demonstrates a clear role for biofilm in the organism’s pathogenesis. Although biofilm studies have been examined in the laboratory, it is evident that P. aeruginosa does not form the same type of biofilm in vivo as is seen on artificial surfaces. Biofilm production related to the overproduction of alginate and the mucoid phenotype isolated from patients with cystic fibrosis is associated with serious infections. P. aeruginosa forms microcolonies in tissue that are associated with quorum-sensing, biofilm-producing strains, which indicates that the quorum sensing is also linked to the formation of microcolonies. These micro colonies contain DNA, mucus, actin, and other products from dying bacterial and host cells. Additionally, P. aeruginosa can survive harsh environmental conditions and displays intrinsic resistance to a wide variety of antimicrobial agents, two factors that facilitate the organism’s ability to survive in the hospital setting (see Table 1).

Even with the variety of potential virulence factors discussed, P. aeruginosa remains an opportunistic pathogen that requires compromised host defenses to establish infection. In normal, healthy hosts, infection is usually associated with events that disrupt or bypass protection provided by the epidermis (e.g., burns, puncture wounds, use of contaminated needles by intravenous drug abusers, eye trauma with contaminated contact lenses). The result is infections of the skin, bone, heart, or eye (see Table 1).

In patients with cystic fibrosis, P. aeruginosa has a predilection for infecting the respiratory tract. Although organisms rarely invade through respiratory tissue and into the bloodstream of these patients, the consequences of respiratory involvement alone are serious and life threatening. In other patients, P. aeruginosa is a notable cause of nosocomial infections of the respiratory and urinary tracts, wounds, bloodstream, and even the central nervous system. For immunocompromised patients, such infections are often severe and frequently life-threatening. In some cases of bacteremia, the organism may invade and destroy the walls of subcutaneous blood vessels, resulting in the formation of cutaneous papules that become black and necrotic. This condition is known as ecthyma gangrenosum. Similarly, patients with diabetes may suffer a severe infection of the external ear canal (malignant otitis externa), which can progress to involve the underlying nerves and bones of the skull.

No known virulence factors have been associated with P. fluorescens, P. putida, or P. stutzeri. When infections caused by these organisms occur, they usually involve a compromised patient exposed to contaminated medical materials. Such exposure has been known to result in infections of the respiratory and urinary tracts, wounds, and bacteremia (see Table 1). However, because of their low virulence, whenever these species are encountered in clinical specimens, their significance should be highly suspect. Similar caution should be applied whenever the other Pseudomonas spp. or Brevundimonas spp. listed in Table 1 are encountered.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الفكرية والثقافية يصدر العدد الرابع من مجلة الاستعمار

لملاكاتها.. جامعة الكفيل تقدم محاضرة تطويرية عن الوظائف اللغوية في الترجمة

ملتقى المبلغات الأول يشهد تقديم محاضرة عن (البركات الإلهية في زيارة الأربعين)

قسم الشؤون الفكرية يباشر أعماله الفنية الخاصة بالموكب الثقافي العام ومسابقة مراقي المجتبى

المزيد

الآخبار الصحية

تعاني من الأرق؟.. إليك تمارين ستساعدك على النوم

تحذير من عادة شائعة بين الركاب تنقل "عدوى مهددة للحياة" ؟

دراسة علمية تكشف مفاجأة حول الأسباب الحقيقية للسمنة

دراسة: الأطباء يتجاهلون "سببا شائعا" لارتفاع ضغط الدم

المزيد

الآخبار التكنلوجية

لأول مرة.. فيديو يرصد ولادة كوكب !

"إكس 59".. ماذا نعرف عن طائرة ناسا "الخارقة"؟

تسريبات جديدة تكشف موعد إصدار آيفون 17 ومواصفاته

كيف تحمي هاتفك الذكي من ارتفاع الحرارة الشديد؟

المزيد

مواضيع ذات صلة

Chlamydia trachomatis

Mycoplasma Pneumonia

Leptospira interrogans

Laboratory Diagnosis of Pseudomonas, Burkholderia, and Similar Organisms

Antimicrobial Susceptibility Testing and Therapy of Acinetobacter, Stenotrophomonas, and Similar Organisms

Laboratory Diagnosis of Acinetobacter, Stenotrophomonas, and Similar Organisms

Clostridium botulinum

Clostridium perfringens

Pasteurella

Yersinia pestis

Brucella

Legionella