Enterobacter, an emerging Nosocomial Infection


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Enterobacter an Emerging Nosocomial infection

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  • E. sakazakii is reclassified into the genus Cronobacter and NOT Achromobacter. Can you correct this?
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Enterobacter, an emerging Nosocomial Infection

  2. 2. ENTEROBACTER LEADING CAUSE OF OPPORTUNISTIC INFECTIONS• Enterobacter is a genus of common Gram-negative, facultatively- anaerobic, rod-shaped bacteria of the family Enterobacteriaceae. Several strains of the these bacteria are pathogenic and cause opportunistic infections in immunocompromised (usually hospitalized) hosts and in those who are on mechanical ventilation. The urinary and respiratory tract are the most common sites of infection. It is also a fecal coliform, along with Escherichia.DR.T.V.RAO MD 2
  3. 3. ENTEROBACTER IS A ENTEROBACTERIACEAE • Enterobacter is a gram- negative bacillus that belongs to the Enterobacteriaceae family. Other members of this family include Klebsiella, Escherichia, Citrobacter, Serratia, Salmonella, and Shigella species, among many others.DR.T.V.RAO MD 3
  4. 4. BACKGROUND OF ENTEROBACTER SPECIES• Enterobacter species, particularly Enterobacter cloacae and Enterobacter aerogenes, are important nosocomial pathogens responsible for various infections, including bacteremia, lower respiratory tract infections, skin and soft-tissue infections, urinary tract infections (UTIs), endocarditis, intra-abdominal infections, septic arthritis, osteomyelitis, and ophthalmic infections. Enterobacter species can also cause various community-acquired infections, including UTIs, skin and soft-tissue infections, and wound infections, among othersDR.T.V.RAO MD 4
  5. 5. OTHER SPECIES OF ENTEROBACTER• The most commonly isolated species include E cloacae and E aerogenes, followed by E sakazakii (recently reclassified into the Achromobacter genus, which produces a characteristic yellow pigment. Other species rarely encountered in the laboratory include Enterobacter asburiae, Enterobacter gergoviae, Enterobacter taylorae, Enterobacter hormaechei, and Enterobacter cancerogenus. Enterobacter agglomerans has been removed from the genus Enterobacter and renamed Pantoea agglomerans.DR.T.V.RAO MD 5
  6. 6. ENTEROBACTER AEROGENES - CHARACTERISTICS • Enterobacter aerogenes is a Gram-negative, oxidase negative, catalase positive, citrate positive, indole negative, rod- shaped bacterium.DR.T.V.RAO MD 6
  7. 7. ENTEROBACTER AEROGENES IS PART OF NORMAL FLORA CAN BE INFECTIVE …• E. aerogenes is part of the flora found in the human intestines. As an opportunistic pathogen it may infect immuno- compromised patients in the urinary and respiratory tracts. It rarely infects healthy peopleDR.T.V.RAO MD 7
  8. 8. DR.T.V.RAO MD 8
  9. 9. ENTEROBACTER AEROGENES IMPORTANT NOSOCOMIAL PATHOGEN• E. aerogenes is a nosocomial and pathogenic bacterium that causes opportunistic infections including most types of infections. Enterobacter species can also cause various community-acquired infections. Some strains can become very treatment resistant, a result of their colonization within hospital environments. However, the majority are sensitive to most antibiotics designed for this bacteria class.DR.T.V.RAO MD 9
  10. 10. SOURCE OF ENTEROBACTER INFECTIONS • Some of the infections caused by E. aerogenes result from specific antibiotic treatments, venous catheter insertions, and/or surgical procedures. E. aerogenes is generally found in the human gastrointestinal tract and does not generally cause disease in healthy individuals. It has been found to live in various wastes, hygienic chemicals, and soil.DR.T.V.RAO MD 10
  11. 11. PROLONGED STAY IN HOSPITAL PREDISPOSES TO ENTEROBACTER INFECTIONS• Although community-acquired Enterobacter infections are occasionally reported, nosocomial Enterobacter infections are, by far, most common. Patients most susceptible to Enterobacter infections are those who stay in the hospital, especially the ICU, for prolonged periodsDR.T.V.RAO MD 11
  12. 12. OTHER PREDISPOSING FACTORS • Other major risk factors of Enterobacter infection include prior use of antimicrobial agents, concomitant malignancy (especially hemopoietic and solid-organ malignancies), hepatobiliary disease, ulcers of the upper gastrointestinal tract, use of foreign devices such as intravenous catheters, and serious underlying conditions such as burns, mechanical ventilation, and immunosuppression.DR.T.V.RAO MD 12
  13. 13. ENDOGENOUS SOURCE – MAJOR SOURCE OF INFECTION• The source of infection may be endogenous (via colonization of the skin, gastrointestinal tract, or urinary tract) or exogenous, resulting from the ubiquitous nature of Enterobacter speciesDR.T.V.RAO MD 13
  14. 14. PATHOPHYSIOLOGY• These bacteria have an outer membrane that contains, among other things, lipopolysaccharides from which lipid-A plays a major role in sepsis. Lipid- A, also known as endotoxin, is the major stimulus for the release of cytokines, which are the mediators of systemic inflammation and its complications.DR.T.V.RAO MD 14
  15. 15. IMPORTANT OTHER SOURCES • Multiple reports have incriminated the hands of personnel, endoscopes, blood products, devices for monitoring intra-arterial pressure, and stethoscopes as sources of infection. Outbreaks have been traced to various common sources: total parenteral nutrition solutions, isotonic saline solutions, albumin, digital thermometers, and dialysis equipment.DR.T.V.RAO MD 15
  16. 16. ENTEROBACTER PRODUCE BETA LACTAMASES• Enterobacter species contain a subpopulation of organisms that produce a beta-lactamase at low-levels. Once exposed to broad-spectrum cephalosporins, the subpopulation of beta- lactamase–producing organisms predominate. Thus, an Enterobacter infection that appears sensitive to cephalosporins at diagnosis may quickly develop into a resistant infection during therapyDR.T.V.RAO MD 16
  17. 17. MICROBIOLOGICAL STUDIES• The most important test to document Enterobacter infections is culture. Direct Gram staining of the specimen is also very useful because it allows rapid diagnosis of an infection caused by gram- negative bacilli and helps in the selection of antibiotics with known activity against most of these bacteriaDR.T.V.RAO MD 17
  18. 18. CAN BE ISOLATED ON COMMONLY USED MEDIA • In the laboratory, growth of Enterobacter isolates is expected to be detectable in 24 hours or less. Enterobacter species grow rapidly on selective (ie, MacConkey) and nonselective (ie, sheep blood) agars.DR.T.V.RAO MD 18
  20. 20. AS GROWN ON EOSIN METHYLENE BLUE MEDIUM • Grown on eosin methylene blue (EMB) agar. EMB agar contains the indicator dyes eosin and methylene blue.DR.T.V.RAO MD 20
  21. 21. FASTER DETECTION WITH OXOID CHROMOGENIC ENTEROBACTER SAKAZAKII AGAR (DRUGGAN-FORSYTHE- IVERSEN (DFI) FORMULATION• Oxoid has introduced Oxoid Chromogenic Enterobacter sakazakii Agar (Druggan- Forsythe-Iversen (DFI) formulation) that allows recovery and detection of E. sakazakii in just 3 days – 2 days faster than by conventional methodsDR.T.V.RAO MD 21
  22. 22. OXOID CHROMOGENIC ENTEROBACTER SAKAZAKII AGAR • This innovative new chromogenic medium contains the substrate 5- bromo-4-chloro-3-indolyl-α, D-glucopyranoside which is cleaved by the enzyme α- glucosidase, expressed by E. sakazakii, to form easily distinguishable blue-green colonies.DR.T.V.RAO MD 22
  23. 23. MERCKS NEW CHROMOGENIC MEDIUM FOR DETECTION OF ENTEROBACTER SAKAZAKII• Mercks new ChromoCult® Enterobacter sakazakii Agar will increase the security in detecting this microorganism in milk powder and infant formula.• Based on the alpha-D-Glucosidase - an enzyme specific for E. sakazakii - only the colonies of E. sakazakii appear turquoise while other bacteria grow colourless. ChromoCult® Enterobacter sakazakii Agar allows a fast and reliable detection within only 24 hours with no further confirmation step.DR.T.V.RAO MD 23
  24. 24. BLOOD CULTURE FOR IDENTIFICATION• Two sets (with one aerobic and one anaerobic bottle in each set) should be obtained 20-30 minutes apart, from 2 different sites (if possible). If the patient has a central venous catheter, one set should be drawn through it. In the adult patient, 8-10 mL of blood should be collected in each bottle. Enterobacteriaceae ferment glucose and should thus grow in both bottles.DR.T.V.RAO MD 24
  25. 25. DRUGS TO INCLUDE FOR ANTIMICROBIAL SUSCEPTIBILITY TESTING• Penicillins should include ampicillin and at least one of the extended-spectrum penicillins (eg, carboxy, ureido, or acylaminopenicillin) such as ticarcillin, mezlocillin, or piperacillin. The addition of ticarcillin-clavulanic acid or piperacillin-tazobactam is optional.DR.T.V.RAO MD 25
  26. 26. CHOOSING A RIGHT ANTIBIOTIC• Cephalosporins include a first-generation drug of this class of antibiotics, such as cefazolin, and a third-generation drug with and without Pseudomonas activity, such as ceftriaxone or ceftazidime. Include at least one carbapenem, usually imipenem, or in accordance with available pharmaceutical agents in the institution.Include the aminoglycosides, usually gentamicin and tobramycin. Amikacin may be tested primarily or when bacteria show resistance to these 2 drugs. Include a quinolone, such as ciprofloxacin.Include TMP-SMZ.Some laboratories routinely add aztreonam.DR.T.V.RAO MD 26
  27. 27. EMERGING GENETIC MECHANISMS OF RESISTANCE• Recently, the production of extended-spectrum beta- lactamases (ESBLs) has been documented in Enterobacter. Usually, these ESBLs are TEM1 -derived or SHV1 -derived enzymes, and they have been reported since 1983 in Klebsiella pneumoniae, Klebsiella oxytoca, and E coli. Bush et al classify these ESBLs in group 2be and in molecular class A in their beta-lactamase classification. The location of these enzymes on plasmids favors their transfer between bacteria of the same and of different genera. Many other gram-negative bacilli may also possess such resistant plasmidsDR.T.V.RAO MD 27
  28. 28. DR.T.V.RAO MD 28
  29. 29. CARBAPENEMS TOO ARE BECOMING RESISTANT• Hyper production (stable DE repression) of AmpC beta- lactamases associated with some decrease in permeability to the carbapenems may also cause resistance to these agents. In vitro low-level ertapenem resistance was not associated with resistance to imipenem or meropenem, but high-level ertapenem resistance predicted resistance to the other carbapenemsDR.T.V.RAO MD 29
  30. 30. COLISTIN AND POLYMYXIN B ARE GAINING IMPORTANCE IN TREATMENTS• Colistin and polymyxin B: These drugs are being used more frequently to treat serious infection caused by multidrug- resistant organisms, sometimes as monotherapy or in combination with other antibiotics. Clinical experience, including documentation of success rates and attributable mortality is broadeningDR.T.V.RAO MD 30
  31. 31. 4 TH GENERATION CEPHALOSPORINS ARE A CHOICE• The fourth-generation cephalosporins are relatively stable to the action of AmpC beta- lactamases; consequently, they retain moderate activity against the mutant strains of Enterobacter, hyper producing AmpC beta-lactamaseDR.T.V.RAO MD 31
  32. 32. OTHER NEW GENERATION OF ANTIBIOTICS• Other antibiotics that may be considered for testing include tigecycline, polymyxin B, and colistin, the latter two when particularly resistant organisms are identifiedDR.T.V.RAO MD 32
  33. 33. ENTEROBACTER SAKAZAKII A IMPORTANT SPECIES• Enterobacter sakazakii • Enterobacter sakazakii has been reported as a cause of sepsis and meningitis, complicated by ventriculitis, brain abscess, cerebral infarction, and cyst formation.[ This clinical pattern appears to be specific to E sakazakii in neonates and infants infected with this bacterium. E sakazakii has also been associated with many outbreaks due to contaminated powdered formula for infantsDR.T.V.RAO MD 33
  34. 34. SERMOR-PROVENF• The bacteria designated by the acronym SERMOR-PROVENF (SER = Serratia, MOR = Morganella, PROV = Providencia, EN = Enterobacter, F = freundii for Citrobacter freundii) have similar, although not identical, chromosomal beta-lactamase genes that are inducible. With Enterobacter, the expression of the gene AmpC is repressed, but derepression can be induced by beta- lactams. Of these inducible bacteria, mutants with constitutive hyperproduction of beta-lactamases can emerge at a rate between 105 and 108. These mutants are highly resistant to most beta-lactam antibiotics and are considered stably derepressed.DR.T.V.RAO MD 34
  35. 35. THE NATIONAL HEALTHCARE SAFETY NETWORK (NHSN) REPORTS ON ENTEROBACTER• The National Healthcare Safety Network (NHSN) reported on healthcare- associated infections (HAI) between 2006 and 2007. They found Enterobacter species to be the eighth most common cause of HAI (5% of all infections) and the fourth most common gram-negative cause of HAIs.[DR.T.V.RAO MD 35
  38. 38. • Created by Dr.T.V.Rao MD for ‘e’ learning resources for Microbiologists in Developing World • Email • doctortvrao@gmail.comDR.T.V.RAO MD 38