Enterobacteriaceae.pdf

In the Name of God Reza Beigverdi, PhD Associate Professor in Microbiology Department of Microbiology School of Medicine Tehran University of Medical Sciences [email protected] 1 Enterobacteriaceae...

In the Name of God Reza Beigverdi, PhD Associate Professor in Microbiology Department of Microbiology School of Medicine Tehran University of Medical Sciences [email protected] 1 Enterobacteriaceae 2  Enterobacteriaceae  Largest  Most heterogeneous collection of medically important gram-negative rods  More than 50 genera  Hundreds of species and subspecies  Ubiquitous organisms found worldwide in soil, water, and vegetation  Part of the normal intestinal flora of most animals and humans  Classified based on  Biochemical properties  Antigenic structure  Molecular analysis of their genomes by gene sequencing  Protein composition by mass spectrometry 3 General Characteristics  Gram-negative rods  Facultative anaerobes  Ferment glucose and other sugars  Can grow rapidly (on a variety of nonselective (blood agar) and selective (MacConkey agar) media)  Simple nutritional requirements  reduce nitrate to nitrite  Produce catalase  Oxidase negative: a simple test and is used to distinguish the Enterobacteriaceae from many other fermentative (Vibrio) and nonfermentative (Pseudomonas) gram-negative rods  Unlike other members of the family Enterobacteriaceae, Plesiomonas: oxidase-positive 4 Antigenic structure of Enterobacteriaceae cell wall  The heat-stable lipopolysaccharide (LPS)  Major cell wall antigen  O polysaccharide  A core polysaccharide LPS consists of  Lipid A: endotoxin activity  Release of cytokines, leukocytosis, thrombocytopenia  Fever, shock, and death  H antigen, or flagellar antigen  Responsible for motility  Heat-labile  Some pathogenic species: are associated with specific O and H serotypes  E. coli O157:H7: hemorrhagic colitis  K antigen, or capsular antigen  found only in certain encapsulated species  K1 antigen of E. coli and the Vi antigen of Salmonella enterica subsp. enterica serotype Typhi  Protected from phagocytosis 5 Common Virulence Factors Associated with Enterobacteriaceae  Endotoxin  The activity of this toxin depends on the lipid A component of LPS, which is released at cell lysis  Many of the systemic manifestations of gram-negative bacterial infections are initiated by endotoxin  Capsule  interfere with the binding of antibodies to the bacteria and are poor immunogens or activators of complement  Antigenic Phase Variation  The expression of the somatic O antigens, capsular K antigens, and flagellar H antigens is under the genetic control of the organism  This feature protects the bacteria from antibody-mediated cell death  Type III Secretion Systems  A variety of bacteria (Yersinia, Salmonella, Shigella,enteropathogenic Escherichia, Pseudomonas, Chlamydia)have a common effector system for delivering their virulence factors into targeted eukaryotic cells.  Facilitate transfer of bacterial virulence factors into the targeted host cells  Sequestration of Growth Factors  Iron is an important growth factor required by bacteria, but it is bound in heme proteins (hemoglobin, myoglobin) or in iron-chelating proteins (transferrin, lactoferrin)  The bacteria counteract the binding by producing their own competitive siderophores or iron-chelating compounds (enterobactin, aerobactin)  Resistance to Serum Killing  The bacterial capsule can protect the organism from serum killing  Antimicrobial Resistance 6  Common Medically Important Enterobacteriaceae  Escherichia coli  Klebsiella pneumoniae  Salmonella serotype Typhi Always associated  Shigella species (S. sonnei, S. flexneri, S dysenteriae, S. boydii) with human disease  Serratia marcescens  Proteus mirabilis  Enterobacter cloacae  Morganella morganii  Citrobacter freundii  Yersinia pestis, Y. enterocolitica, Y. Pseudotuberculosis  Members of the normal commensal flora  Can cause opportunistic infections 7 Escherichia coli  associated with a variety of diseases  Gastroenteritis infections  Extraintestinal infections (urinary tract infections: UTIs, meningitis, and sepsis)  Large numbers of E. coli are present in the gastrointestinal tract (Most common aerobic gram- negative rods in the gastrointestinal tract)  opportunistic pathogens  When the intestines are perforated and the bacteria enter the peritoneal cavity 8 Escherichia coli  Most E. coli that cause GI and extraintestinal disease  acquired specific virulence factors encoded: on plasmids or in bacteriophage DNA  The most common gram-negative rods isolated from patients with sepsis  Responsible for causing more than 80% of all community-acquired UTIs and many hospital acquired infections  Most infections (with the exception of gastroenteritis and neonatal meningitis): endogenous  E. coli: part of the patient’s normal microbial flora are able to establish infection when the patient’s defenses are compromised (through trauma or immune suppression) 9 Clinical Diseases of E. coli  Gastroenteritis  Enterotoxigenic E. coli (ETEC)  Enteropathogenic E. coli (EPEC) Small intestine  Enteroaggregative E. coli (EAEC)  Shiga toxin–producing E. coli (STEC) Large intestine  Enteroinvasive E.coli (EIEC) Infections of small intestine (ETEC, EPEC, EAEC): characterized by watery diarrhea, vomiting, and low-grade fever Infections of large intestine (STEC, EIEC): characterized by bloody diarrhea (hemorrhageic colitis) and abdominal cramps 10 Enterotoxigenic E. coli (ETEC)  One of the most common causes of bacterial diarrheal disease in developing countries  Infections: acquired through consumption of contaminated food or water  Person-to-person spread does not occur  Secretory diarrhea: develops after a 1- to 2-day incubation period and persists for an average of 3 to 5 days  The symptoms:  Watery, nonbloody diarrhea  Abdominal cramps  Less commonly nausea and vomiting 11 Enterotoxigenic E. coli (ETEC) Disease requires bacterial attachment to the small bowel epithelium:bacterial surface proteins (colonization factors [CFs]) and produce heat-stable and heat-labile enterotoxins. The genes for the CFs and enterotoxins: encoded on a transmissible plasmid CFs are subdivided into families (CFA/I, CFA/II, and CFA/IV are the most common) Produce two classes of enterotoxins: heat-stable toxins (STa and STb) and heat-labile toxins (LT-I, LT-II) STa but not STb is associated with human disease STa found in 75% to 80% of ETEC 12 Enterotoxigenic E. coli (ETEC)  STa increase in cyclic guanosine monophosphate (cGMP)  subsequent hypersecretion of fluids well as inhibition of fluid absorption  LT-I: more commonly associated with human disease  LT-I increase in cyclic adenosine monophosphate (cAMP) levels  resulting in enhanced secretion of chloride and decreased absorption of sodium and chloride  These changes are manifested in a watery diarrhea  Exposure to the toxin:  stimulates prostaglandin secretion  production of inflammatory cytokines  Resulting in further fluid loss. 13 Enteropathogenic E. coli (EPEC)  Two groups of E. coli (enteric disease)  1- EPEC  2- Shiga toxin–producing E. coli [STEC]  EPEC and STEC possess a of virulence genes located on a chromosomal pathogenicity island called the locus of enterocyte effacement (LEE)  EPEC are further subdivided into:  Typical (EAF+) and Atypical (EAF-) strains  Based on the presence or absence of the E. coli adherence factor (EAF) plasmid  Disease: transmitted by fecal- oral exposure to contaminated surfaces or food products. 14 Enteropathogenic E. coli (EPEC)  Humans: only source of typical strains  whereas both humans and a variety of animal hosts: reservoirs of atypical strains.  EPEC attach to the small intestine by adhesins (bundle-forming pili, intimin) and disrupt the surface  Disease occurs primarily in children younger than 2 years  characterized by watery diarrhea that may be severe and protracted and is often accompanied by fever and vomiting. 15 Enteroaggregative E. coli (EAEC)  Characterized by their autoagglutination in a “stacked-brick” arrangement over the epithelium of the small intestine  an important cause of childhood diarrhea in developed countries  associated with chronic diarrhea and growth retardation in children.  Disease is characterized by  a watery secretory diarrhea  inflammatory cells  Fever  Nausea  Vomiting  abdominal pain  EAEC attach to the small intestine by aggregative adherence fimbriae (AAF) and also disrupt the surface 16 Shiga toxin–producing E. coli (STEC)  All members of this group are defined by the presence of Shiga  toxin 1 (Stx1) or 2 (Stx2)  The most common serotype associated with human disease: O157:H7  Ingestion of fewer than 100 bacteria: produce disease  person-to-person spread occurs  Disease caused by STEC : mild uncomplicated diarrhea to hemorrhagic colitis with severe abdominal pain and bloody diarrhea  STEC initially attach to intestines by bundle-forming pili and intimin, and then produce shiga toxins Stx1 and Stx2 that affect the colonic epithelium  Hemolytic uremic syndrome (HUS)  is the most serious, life-threatening complication following STEC infection  A disorder characterized by : acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia  a complication in 5% to 10% of infected children younger than 10 years. 17 Enteroinvasive E.coli (EIEC)  EIEC strains: rare in both developed and developing countries  Pathogenic strains: primarily associated with a few restricted O serotypes: O124, O143, and O164  The bacteria are able to invade and destroy the colonic epithelium  producing a disease characterized initially by watery diarrhea  A series of genes on a plasmid: bacterial invasion (pInv genes) into the colonic epithelium  Hemolytic uremic syndrome: a complication of EIEC infections 18 Clinical Diseases of E. coli  Extraintestinal Infections  Urinary Tract Infection  Most gram-negative rods that produce UTIs: originate in the colon  Adhesins (primarily P pili, AAF/I, AAF/III, and Dr) that bind to cells lining the bladder and upper urinary tract (preventing elimination of the bacteria in voided urine)  hemolysin HlyA: lyses erythrocytes and other cell types (leading to cytokine release and stimulation of an inflammatory response).  Neonatal Meningitis  E. coli and group B streptococci: the majority of CNS infections in infants younger  Approximately 75% of the E. coli strains: the K1 capsular antigen  Septicemia  septicemia caused by gram-negative rods ( E. Coli): originates from infections in the urinary or GI tract (intestinal leakage leading to an intraabdominal infection). 19 Specialized Virulence Factors Associated with E. coli 20 Salmonella More than 2500 unique serotypes tolerant of acids in phagocytic vesicles Can survive in macrophages and spread from the intestine to other body sites Most infection: acquired by eating contaminated food products (poultry, eggs, and dairy products are the most common sources of infection) Transmission : by direct fecal-oral spread in children SalmonellaTyphi and Salmonella Paratyphi: strict human pathogens Other Salmonella serotypes (Salmonella Choleraesuis): adapted to animals and, when they infect humans, can cause severe disease The infectious dose for Salmonella Typhi infections is low, so person-to-person spread is common Asymptomatic long-term colonization occurs commonly 21 Salmonella  Virulence of S. typhi is regulated by genes on two large pathogenicity islands  that facilitate the attachment, engulfment, and replication of bacteria in intestinal cells and macrophages  Pathogenicity island I: salmonella-secreted invasion proteins (Ssps) and a  type III secretion system that injects the proteins into the host cell.  Pathogenicity island II: contains genes that allow the bacteria to evade the host’s immune response and encodes a second type III secretion system for this function  Bacteria are transported: from the intestines to liver, spleen, and bone marrow by macrophages  in contrast with other Salmonella serotypes, Salmonella Typhi, SalmonellaParatyphi: survive in the gallbladder and establish chronic carriage  Infections occur worldwide (the warm months of the year) 22 Clinical Diseases of Salmonella The following four forms of Salmonella infection: 1- Gastroenteritis 2- Septicemia 3- Enteric fever 4- Asymptomatic colonization Gastroenteritis: most common form of salmonellosis Symptoms generally: 6 to 48 hours after the consumption of contaminated food or water nausea, vomiting, and nonbloody diarrhea Fever, abdominal cramps, myalgias, and headache are also common 23 Clinical Diseases of Salmonella  Septicemia  All Salmonella species: bacteremia  although infections with Salmonella Typhi, Salmonella Paratyphi, and Salmonella Choleraesuis more commonly lead to a bacteremic  The risk for Salmonella bacteremia: higher in pediatric and geriatric patients and in immunocompromised patients (those with HIV infections, sickle cell disease, congenital immunodeficiencies). 24 Clinical Diseases of Salmonella  Enteric fever  Salmonella Typhi: a febrile illness called typhoid fever  A milder form of this disease ( paratyphoid fever)  produced by Salmonella Paratyphi A, Paratyphi B and Salmonella Paratyphi C  10 to 14 days after ingestion of S. typhi, patients experience gradually increasing fever with nonspecific complaints of headache, myalgias, fever, and anorexia  symptoms persist for 1 week or more followed by gastrointestinal symptoms 25 Clinical Diseases of Salmonella  Asymptomatic colonization The strains of Salmonella responsible for causing typhoid and paratyphoid fevers: maintained by human colonization Chronic colonization for more than 1 year after symptomatic disease: in 1% to 5% of patients Which the gallbladder being the reservoir in most patients 26 Shigella  Four species of Shigella 1- S. Dysenteriae 2- S. flexneri 3- S. Boydii 4- S. sonnei Shigella: attachs, invades, and replicates in cells lining the colon Structural gene proteins: the adherence of the organisms to the cells, as well as their invasion, intracellular replication, and cell-to-cell spread. Shigella: first attach to and invade the M cells located in Peyer patches The type III secretion system: secretion of four proteins (IpaA, IpaB, IpaC, and IpaD) into epithelial cells and macrophages Replicate in the cytoplasm of phagocytic cells and move cell-to-cell without extracellular exposure, thus protected from immune-mediated clearance 27 Shigella Induce programed cell death of macrophages (apoptosis) resulting in the release of interleukin-1βwith resulting stimulation of localized inflammatory response Humans: only reservoir for Shigella Shigellosis: transmitted person to person by fecal-oral route S. sonnei is responsible for almost 85% of U.S. infections, whereas S. flexneri predominates in developing countries. Patients at highest risk for disease: young children in day-care centers, nurseries, and male homosexuals Relatively few organisms (100-200): produce disease (highly infectious) Disease occurs worldwide with no seasonal incidence Shigellosis is characterized by abdominal cramps, diarrhea, fever, and bloody stools 28 Yersinia The best known human pathogens: Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis. Y. pestis: a highly virulent pathogen that causes the potentially fatal systemic disease known as plague Y. enterocolitica and Y. pseudotuberculosis: enteric pathogens Y. enterocolitic : grow at cold temperatures (can grow to high numbers in contaminated refrigerated food or blood products) A common characteristic of the pathogenic Yersinia species: to resist phagocytic killing The type III secretion system mediates this property The type III secretion system also: suppresses cytokine production, in turn diminishing the inflammatory immune response to infection Y. pestis: (1) fraction 1 (f1) gene, which codes for an antiphagocytic protein capsule, and (2) plasminogen activator (pla) protease gene, which degrades complement components C3b and C5a, preventing opsonization and phagocytic migration, respectively. The pla gene also degrades fibrin clots, permitting Y. pestis to spread rapidly. Y. pestis is covered with a protein capsule and inhibits phagocytosis 29 Yersinia There are two forms of Y. pestis infection: 1- Urban plague: rats are the natural reservoirs, 2- Sylvatic plague: squirrels, rabbits, field rats, and domestic cats. Disease is spread by bites from the flea vector (infected reservoir host to humans), direct contact with infected tissues, or person-to-person by inhalation of infectious aerosols from a patient with pulmonary disease (patients with pulmonary disease highly infectious) Approximately two thirds of all Y. enterocolitica infections: enterocolitis, as the name implies Yersinia organisms can grow at 4° C, this organism can multiply to high concentrations in nutritionally rich blood products that are stored in a refrigerator 30 Clinical Diseases of Yersinia The two clinical manifestations of Y. pestis infection: 1- Bubonic plague 2- Pneumonic plague Bubonic plague characterized by an incubation period of no more than 7 days after a person has been bitten by an infected flea. Patients: a high fever and a painful bubo (inflammatory swelling of the lymph nodes) in the groin or axilla. Bacteremia develops rapidly if patients are not treated, and as many as 75% die Pneumonic plague: characterized by development of fever and pulmonary symptoms within 1 to 2 days after inhalation of bacteria; high mortality rate 31 KLEBSIELLA Members of the genus Klebsiella: a prominent capsule capsule responsible for the mucoid appearance of isolated colonies and the enhanced virulence of the organisms in vivo strains of Klebsiella resistant: to all β-lactam antibiotics including the carbapenems, as well as most other classes of antibiotics are becoming increasingly common globally The management of patients with Klebsiella infections: a major clinical challenge K. pneumoniae and K. oxytoca: cause community-acquired or hospital-acquired primary lobar pneumonia 32 KLEBSIELLA K. Granulomatis: the etiologic agent of granuloma inguinale , which is a granulomatous disease affecting the genitalia and inguinal area Two other Klebsiella species of clinical importance K. rhinoscleromatis: is the cause of a granulomatous disease of the nose K. ozaenae: chronic atrophic rhinitis Penile ulcer caused by Kl. granulomatis 33 PROTEUS MIRABILIS The most commonly isolated member of the genus Proteus: P. mirabilis It is an important cause of urinary tract infections (bladder infection or cystitis; kidney infection or pyelonephritis) P. mirabilis: large quantities of urease, which splits urea into carbon dioxide and ammonia. This process raises the urine pH, precipitating magnesium and calcium in the form of struvite and apatite crystals, respectively , and results in the formation of renal (kidney) stones. 34 LABORATORY DIAGNOSIS Members of the family Enterobacteriaceae grow readily on culture media Specimens of normally sterile material, such as spinal fluid and tissue collected at surgery: nonselective blood agar media. Selective media (MacConkey agar, eosin-methylene blue [EMB] agar):the culture of specimens normally contaminated with other organisms (sputum, feces) Use of these selective differential agars:the separation of lactose-fermenting Enterobacteriaceae genera (Escherichia, Klebsiella, Enterobacter) from nonfermenting genera (Salmonella, Shigella). Another example of a selective differential agar: sorbitol-containing MacConkey agar(S-MAC), which is used to screen stool specimens for sorbitol-negative (colorless), such as E. coli O157. 35 LABORATORY DIAGNOSIS Biochemical Identification the most common members of the family: in less than 24 hours with one of the many commercially available identification systems. Sequencing of species-specific genes (e.g., 16S rRNA gene) or detection of characteristic protein profiles by mass spectrometry: to identify most species of Enterobacteriaceae Nucleic Acid Amplification Tests (NAATs) In the last decade, commercial multiplex nucleic acid amplification tests: for specific diseases, such as respiratory or GI infections The advantage of these tests is that a large selection of enteric pathogens (e.g., Salmonella, Shigella, E. coli, Campylobacter, as well as common enteric viruses and parasites): simultaneously with a single test 36 TREATMENT, PREVENTION, AND CONTROL Antibiotic therapy for infections with Enterobacteriaceae: in vitro susceptibility test results and clinical experience production of enzymes that inactivate all the penicillins and cephalosporins (ESBLs) is now widespread in E. coli, Klebsiella, and Proteus. Carbapenemase producing bacteria: limited the empirical use of carbapenems and all other β- lactam antibiotics for many regions of the world In general, antibiotic resistance: more common in hospital-acquired infections than in community-acquired infections. Antibiotic therapy: not recommended for some infections For example, symptomatic relief but not antibiotic treatment is usually recommended for patients with STEC and Salmonella gastroenteritis because antibiotics can prolong the fecal carriage of these organisms or increase the risk of secondary complications 37 TREATMENT, PREVENTION, AND CONTROL some risk factors for the infections should be avoided. the unrestricted use of antibiotics that can select for resistant bacteria performance of procedures that traumatize mucosal barriers without prophylactic antibiotic coverage use of urinary catheters. Two vaccines for Salmonella Typhi :are available an oral, live, attenuated vaccine and a Vi capsular polysaccharide vaccine. Both vaccines protect 40% - 70% of the recipients Vaccination is recommended for travelers to endemic areas of the world (e.g., Africa, Asia, Latin America). The Vi capsular vaccine: in a single dose but the attenuated live vaccine: in four doses over a 1-week period. 38 Thank you for your attention 39