Pseudomonas and Related Nonfermenters

1. Pseudomonas and Related Nonfermenters

2. Introduction • Obligate aerobic nonfermenters, representing a mixture of opportunistic pathogens of plants, animals and humans. • Genera of significance are (out of 15): • Pseudomonas (aeruginosa) • Acinetobacter (baumannii) • Moraxella (catarrhalis) • Burkholderia (cepacia) • Alcaligenes (fecalis) • Stenotrophomonas (maltophilia)

3. Pseudomonas • Pseudomonads are ubiquitous organisms found in soil, decaying organic matter, vegetation and water. • The broad environmental distribution of pseudomonas is afforded by their simple growth requirements. • More than 30 organic compounds can be used as a source of carbon and nitrogen, and some strains can even grow in distilled water by using trace nutrients.

4. They are also found throughout the hospital environment; in moist reservoirs such as food, cut flowers, sinks, toilets, floor mops, respiratory therapy equipment, and even disinfectant solutions. • Persistent carriage as part of the normal microbial flora in humans is uncommon unless the individual is hospitalized or immunocompromised.

5. Pseudomonas also possess a number of structures and toxins that enhance the virulence potential of the organism, as well as render them resistant to most commonly used antibiotics. • Indeed, it is surprising that these organisms are just opportunistic pathogens.

6. Physiology and structure • Gram-negative, motile (one polar flagellum), nonfermenters and use relatively few carbohydrates (glucose, ribose, gluconate) by oxidative metabolism. • Oxygen is the terminal electron acceptor, and the presence of cytochrome oxidase is used to differentiate this group from Enterobacteriaceae.

7. Some strains appear mucoid because of the abundance of a polysaccharide capsule. • Some strains produce a sweet grape like odor and diffusible pigments as pyocyanin (bluish), pyoverdin (greenish), pyorubin (dark red) or pyomelanin (black). • Pseudomonas aeruginosa is the most common clinically significant and best characterized species of the genus which includes about 30 species.

9. Pathogenesis • Pseudomonads have a number of virulence factors, including structural components, toxins, and enzymes. • Structures: Pili, polysaccharide capsule, and endotoxin. • Exotoxin A: blocks eukaryotic cell protein synthesis.

10. Exoenzyme S: heat-stable, can inhibit protein synthesis. • Elastase: can catalyze the destruction of the elastic fiber in blood vessel walls resulting in hemorrhagic lesions. • Phospholipase C: breaks down lipids and lecithin. • Proteases: tissue destruction, inactivation of antibodies, and inhibition of neutrophils.

11. Clinical Syndromes of Pseudomonas aeruginosa • Bacteremia and endocarditis: similar to that of gram negative but mortality is higher (due to host factors). Originate from other infections. • Pulmonary Infections: range from colonization or benign tracheobronchitis to severe necrotizing bronchopneumonia common in those with cystic fibrosis and chronic pulmonary disease.

12. Ear Infections - External otitis is most frequent with swimming as a significant risk factor (swimmer's ear). - A more virulent form of disease (malignant external otitis) can invade the underlying tissue and be life threatening. Also associated with chronic otitis media. • Burn Infections • Ecthyma gangrenosum • Others: UTI, eye infections, CNS infections, GI infection.

13. Burkholderia Burkholderia cepacia : common in hospitals causing necrotizing pneumonia and bacteremia. Burkholderia mallei : causes glanders, a disease of animals that may be transmitted to humans. It usually begins as an ulcer of the skin and mucous membranes followed by lymphangitis and sepsis. Burkholderia pseudomallei : causes meliodosis; a localized suppurative infection that may lead to septicemia. The most common form is pulmonary which could be chronic.

14. Stenotrophomons Maltophilia • A free living oxidase negative rod. • Second most commonly isolated nonfermenter as an opportunistic pathogen. • Multiresistant to antimicrobials (except cotrimoxazole).

15. Acinetobacter • Most commonly responsible for nosocomial respiratory infections. • Thrive in moist environments and have been found as common contaminants of respiratory therapy equipment and monitoring devices.

16. Pasteurellaceae • The family consists of three genera; Hemophilus, Actinobacillus and Pasteurella. • Hemophilus is the most common human pathogen of the family. • Small, gram –negative, non motile bacilli that are aerobes or facultative anaerobes. • Most are fastidious requiring enriched media for isolation.

17. Hemophilus • Small, sometimes pleomorphic gram-negative bacilli that are obligate parasites. • They are present on the mucous membranes of humans. • H. influenzae is the species most commonly associated with disease. • Most species require supplementation of media with growth- stimulating factors, specifically x factor (hemin) and/or v factor (NAD).

18. Although both factors are present in blood enriched media, the blood must be gently heated to release the factors and destroy inhibitors of V factor. • For this reason heated blood agar (chocolate agar) is used for the in vitro isolation of Hemophilus spp. • Many strains are encapsulated with six antigenic types (a-f) and the most important of which is type b.

19. Pathogenesis • Hemophilus species, particularly H. parainfluenzae and non encapsulated H. influenzae colonize the upper respiratory tract in virtually all individuals within the first few months of life. • These organisms can spread locally and cause otitis media, sinusitis, bronchitis and pneumonia.

20. In contrast, encapsulated H. influenzae (esp. type b) is infrequently present in the upper respiratory tract but has been a common cause of epiglottitis and pediatric meningitis. • In the absence of an opsonic antibody, high grade bacteremia can develop with dissemination to the meninges or other distal foci. • The major virulence factor is the capsule (Polyribitol phosphate-PRP) the antibody to which is protective.

21. Clinical Syndromes • Meningitis: Peak incidence is between 3 and 18 months of age. • Epiglottitis: characterized by cellulitis and swelling of the supraglottic tissues. It represents a life –threatening emergency. • Cellulitis: seen in very young children ( fever and cellulitis characterized by a reddish – blue color of the cheek or periorbital area)

22. Arthritis : infection of a single large joint secondary to bacteremic spread. • Conjunctivitis and Brazilian Purpuric Fever. • Otitis, Sinusitis and lower Respiratory tract disease. • Dental abscesses.

23. Actinobacillus • Slow growers (2-3 days) and require carbon dioxide. • A. actinomycetemocomitans is the only significant human pathogen. • The cumbersome name is derived from the fact that this organism is frequently associated with actinomyces. • It is part of the normal oropharyrgeal population detectable in about 20% of healthy individuals. • It is associated with juvenile and adult periodontitis and subacute endocarditis (following dental procedures or from periodontitis)

24. Pasteurella • P. multocida is the most common human pathogen of the genus. • It causes: 1- localized infection (dog / cat scratch or bite). 2- chronic pulmonary disease in those with underlying pulmonary dysfunction. 3- systemic infection in immunocompromised patients.

25. Bordetalla • Very small, strictly aerobic gram-negative coccobacilli. • Three species have been associated with human disease: - Bordetella pertussis: ( Latin for severe cough ) the agent of pertussis or whooping cough. - Bordetella parapertussis (like pertussis). - Bordetella bronchiseptica: primarily an animal pathogen but an occasional human pathogen. • They are fastidious requiring supplementation with many nutritional factors.

26. Pathogenesis • Virulence is mediated by filamentous hemagglutinin, toxins, and LPS. • Filamentous hemagglutinin : agglutinates erythrocytes of a variety of animals and is believed to be important in attachment to ciliated epithelium. Antibodies to it interfere with attachment and are protective. • LPS : consists of two lipids; X and A. Major toxicity is associated with lipid X.

27. Toxins • Pertussis toxin - Histamine sensitizing factor, lymphocytosis promoting factor, islet cell activating protein and pertussigen. - The heat labile toxin is an A-B toxin consisting of six protein subunits. Subunit A is the active portion of the toxin whereas the pentameric B subunit is the binding portion. - It inhibits transfer of signals from cell surface receptor to intracellular mediator system. Antibodies to it confer immunity .

28. Adenylate cyclase toxin - Activates conversion to AMP form ATP. - It inhibits CMI, chemotaxis, phagocytosis and killing. - It protects bacteria in the early stage of disease.

29. Tracheal cytotoxin - A cell wall peptidoglycan monomer that has a specific affinity for ciliated epithelial cells. - It inhibits movement of cilia (ciliostasis ) and it interferes with DNA synthesis leading to impaired regeneration of damaged cells. - This disrupts the normal clearance mechanisms in the respiratory tree and leads to the characteristic cough. • Dermonecrotic toxin: can cause vasoconstriction of peripheral blood vessels in animals.

30. Clinical Picture • Infection is acquired by inhalation of infectious aerosol droplets. • Incubation of 7-10 days and three clinical stages; - Catarrhal stage: The patient is highly infectious (1-2 weeks). - Paroxysmal stage: Corresponds to the extrusion of ciliated epithelial cells from the respiratory tract and impaired clearance of mucus. Whooping cough paroxysm (40-50/day) and marked lymphocytosis. (2-4 weeks). - Convalescent stage: Paroxysms diminish in number and severity

31. Diagnosis - Nasopharyngeal aspirates should be immediately inoculated onto special media. - Direct fluorescent antibody test may be used. • Epidemiology - Worldwide endemicity. - No reservoir except the human host. - Decreased vaccine acceptance led to increased incidence. Whole cell inactivated vaccine has been replaced by the acellular vaccines.

32. Treatment - It is primarily supportive. - Antibiotics do not ameliorate the clinical course because convalescence is correlated with regeneration of ciliated epithelial cells. - Erythromycin is effective in eradicating the organisms and can reduce the stage of infectivity but the illness is usually unrecognized during the height of contagiousness.

33. Brucella • Aerobic, nonmotile, nonencapsulated, gram- negative cocobacilli that grow slowly. • Four species can infect humans; B. abortus, B. melitensis, B. suis and B. canis. • They are intracellular parasites of the RES. • Able to evade the host humoral immune response and inhibit leukocyte degranulation. • B. melitensis is the most virulent.

34. Clinical Picture • The disease spectrum is influenced by the infecting organism. • B. abortus and B. canis tend to produce mild disease, in contrast B. melitenis and B. suis cause severe disease with a high incidence of serious complications. • Subclinical, subacute or acute disease .

35. Diagnosisisolation of organism and serology. • Treatment - Tetracycline and streptomycin or gentamicin. - Risk of relapse • Epidemiology - Worldwide distribution. - Direct contact with infected animals. - Consumption of contaminated milk or cheese. - Control of disease in animals leads to its control in humans.

36. Vibrionaceae • Curved or Straight bacilli that are facultative anaerobes, oxidase positive and non spore-forming. • They are primarily found in water and are well known for their ability to produce gastrointestinal disease. • Three Genera: Vibrio, Aeromonas and Plesiomonas.

37. The Vibrios • Gram negative, curved bacilli with a polar flagellum. • They are among the most common bacteria in surface waters worldwide. • They grow on alkaline media (pH 8.5-9.5). • V. cholerae is the most important species.

38. Serogroups OI and O139 cause classic cholera (epidemics) whereas non OI/non O139 cause cholera like disease (sporadic). • Serotypes are Ogawa, Hikojima, and Inaba, and biotypes are classic and El Tor. • Infectious dose is very high if water is the vehicle and low if food is the vehicle in individuals with normal gastric acidity.

39. V. cholerae causes cholera by a heat-labile enterotoxin (A-B toxin). • B subunit binds to the receptor promoting entry of subunit A into the cell which activates adenylate cyclase yielding high levels of intracellular cAMP that results in prolonged hypersecretion of water and electrolytes. • Diarrhea occurs with loss of 20-30 liters fluid per day leading to dehydration, shock, acidosis, and death.

40. 60-75% of infections are asymptomatic. • The incubation period is 1-4 days for persons who develop symptoms followed by sudden onset of nausea, vomiting, and profuse diarrhea with abdominal cramps. • Stools, which resemble “rice water” contain mucus, epithelial cells, and large number of vibrios. • Dehydration, circulatory collapse and anuria develop with death in 25-50% of untreated cases.

41. Diagnosis: - Stool culture: peptone water and TCBS agar. • Epidemiology - V. cholerae is found in fresh water ponds and estuaries in Asia, the Middle East, Africa and along the costal areas of south, Central and North America. - Major reservoir is infected humans (carriers). - Pandemic spread (7 in the last century)

42. V. parahemolyticus causes acute gastroenteritis following ingestion of contaminated sea food, an illness that is of short incubation and self limited. • V.vulnificus can cause severe wound infections after exposure to contaminated sea water and septicemia after consumption of raw oysters.

43. Campylobacter • Campylobacterspecies are curved, comma shaped, oxidase – positive , catalase – positive, microaerophilic gram- negative bacilli that are motile by means of a polar flagellum. • They are commensals of cattle, sheep, dogs, cats, rodents, and fowl. • Humans are infected due to consumption of contaminated food, milk or water. • Contaminated poultry is responsible for >50% infections.

44. Presents as acute enteritis with sudden onset of crampy abdominal pain, profuse diarrhea that may be grossly bloody, headache, malaise and fever. • The illness is self limited within few days. • Systemic disease may be caused by C. fetus in immunocompromised individuals.

45. Helicobacter pylori • Spiral – shaped, motile (one polar flagellum) gram negative rods. • Associated with antral gastritis, duodenal (peptic) ulcer disease, gastric ulcers, and gastric carcinoma. • Most important virulence factor is urease production ( protection from gastric acids ), mucinase and adhernce factors. • It causes gastritis, peptic ulcers, and is associated with gastric cancer.