BIOL 2010 Lecture 10 - Enterobacteriaceae Lecture Notes PDF

BIOL 2010 Lecture 10 - Enterobacteriaceae BAILEY AND SCOT T’S – CHAPTER 19 DIAGNOSTIC MICROBIOLOGY – CHAPTER 19 In this lecture Explain the characteristics and pathogenesis of commonly encountered clinically significant microorganisms, including the most frequently isolated species by body syst...

BIOL 2010 Lecture 10 - Enterobacteriaceae BAILEY AND SCOT T’S – CHAPTER 19 DIAGNOSTIC MICROBIOLOGY – CHAPTER 19 In this lecture Explain the characteristics and pathogenesis of commonly encountered clinically significant microorganisms, including the most frequently isolated species by body system Gram negative Rod Enterobacteriaceae – Pathogens Salmonella spp. Shigella spp. Yersinia spp. Discuss bacterial virulence, as related to these organisms Media Review How would you describe A? How would you describe B? Media Review What media is this? How would you describe colonies? Media Review What media is this? How would you describe colony A, A B B and C? Which one is a non-pathogen? Which one is a pathogen? C Media Review What media is this? How would you describe colony A, B and C? A B Which one is a non-pathogen? Which one is a pathogen? C Overview Primary human intestinal pathogens that are not normal biota of the intestinal tract Salmonella Inhabit the gastrointestinal (GI) tracts of animals Human infection occurs via contaminated or undercooked animal food products. Shigella Human carriers coupled with improper sanitary conditions and poor personal hygiene Yersinia Transmitted by wide variety of animals Salmonella Species Gram-negative rods, facultatively anaerobic Clear, colorless, nonlactose- fermenting on MAC and colonies with black centers on HE or XLD Key ID tests Serological tests are key – tests for antigens Negative for indole, VP, urease, PAD Most produce H2S Exception: Salmonella paratyphi A Salmonella - ID S. enterica S. enterica is the main human pathogen (and only 1 of 2 Salmonella species) Six subspecies in S. enterica All others are serotypes of S. enterica Nomenclature: serotype name is not italicized Salmonella enterica serotype Typhi or Salmonella Typhi Salmonella Virulence Factors Fimbriae used in initiating intestinal infection Ability to traverse intestinal mucosa Enterotoxin involved in gastroenteritis Antigenic Structures O antigen Heat stable, Lipopolysaccharide, Cell Wall antigen H antigen Heat-labile, flagellar antigen Antigens occur in phases (Phase I and Phase II). Phase I antigens are not always present, but if they are they can identify a particular serotype. Phase II are nonspecific. Vi antigen Heat labile, capsular antigen Vi similar to K capsule antigen Important identifier of Salmonella serotype Typhi Antigenic Structures of Salmonellae Used in Serologic Typing Salmonella - Clinical Infections Acute gastroenteritis/food poisoning Associated with Salmonella enterica serotype enterica Enteric fever Associated with Salmonella Paratyphi, Choleraesuis Typhoid fever Type of Enteric fever associated with Salmonella enterica serotype typhi (Also called Salmonella Typhi – note that typhi is NOT a species) Nontyphoid bacteremia Carrier state following Salmonella infection Salmonella - Gastroenteritis Food poisoning Sources of infection Primarily poultry, eggs, milk, egg products, handling pets Ingestion of foodstuffs Peanut butter, cantaloupe, puffed rice and wheat cereals, corn and vegetable coated snack, and others Cooking utensils Direct person to person in institutions Symptoms appear 8 to 36 hours after ingestion of contaminated food. Nausea, vomiting, fever, chills Accompanied by watery diarrhea and abdominal pain Most infections are self-limiting  Salmonella - Enteric Fever VERY serious fever disease. Many strains can cause it, but Enteric fever caused by Salmonella typhi is most serious Enteric fever caused by Salmonella typhi is called typhoid fever. Clinical features Prolonged fever Bacteremia Involvement of the reticuloendothelial system (RES), particularly the liver, spleen, intestines, and mesentery Dissemination to multiple organs Note: NO diarrhea or vomiting Epidemiology highlights Tropical and subtropical areas where international travelers are more likely to acquire the infection Improper disposal of sewage, poor sanitation, and lack of a modern potable water system contribute to typhoid fever cases and outbreaks. Salmonella – Typhoid fever Organisms eventually reach the bloodstream and spread to the liver, spleen, bone marrow where they are immediately engulfed by mononuclear phagocytes. Organisms multiply intracellularly and are later released into the bloodstream for the second time. Febrile episode becomes more evident. Salmonella – Typhoid fever Contact with 1st week of 2nd-3rd week: Prolonged Carriage state organism disease Incubation Flu-like Sustained fever Bacteria seeds Main organ period until symptoms Rose patches blood again, affected: symptoms Bacteremia Bacteria invades other gallbladder appear - varies Lab samples: reached organs Blood Culture intestinal system Intracellular Lab samples: growth in Urine, Stool monocytes Salmonella - Typhoid Fever Timeline Symptoms develop 9 to 14 days after ingestion of organisms. Incubation time varies - The larger the inoculum, the shorter the incubation time First week of disease patients typically develop Fever, malaise, anorexia, lethargy, myalgia, and a dull headache Looks like the flu Salmonella - Typhoid Fever Timeline Weeks 2 and 3 of the disease Patient experiences sustained fever with prolonged bacteremia. Organisms invade the gallbladder and Peyer’s patches of the bowel; they also reach the intestinal tract via the biliary tract. “Rose spots” appear during week 2 of the fever. Infection of the intestinal tract typically transpires resulting in large numbers of organisms. May be isolated from the stool Salmonella - Typhoid Fever Prolonged infections: Seed the bloodstream Spread to spleen, liver, and bone marrow Engulfed by monocytes and grow intracellularly Bacteria is re-released into the blood stream Prolonged bacteremia “Rose spots” in the periumbilical region Invasion of the gallbladder and Peyer’s patches; release of bacteria into the bowel via the biliary duct Gallbladder is the foci in long-term infections. Severe infections can cause necrosis of gallbladder and/or Peyer’s patches. Hemorrhage and perforation of the bowel Other complications that may occur Pneumonia, thrombophlebitis, meningitis, osteomyelitis, endocarditis, abscesses Salmonella - Typhoid Fever What repercussions will this have on laboratory diagnosis? Q to think about Are blood cultures likely to be positive at weeks 3-4? Is urine culture likely to be positive at week 2? What would be an optimal strategy to detect Salmonella typhi in the lab? Salmonella - Carrier State Individuals who recover from infection may harbor the organisms in the gallbladder. Gallbladder becomes the site of chronic carriage. Organisms are excreted in the feces either continuously or intermittently. Carrier state may be terminated by antimicrobial therapy if gallbladder infection is not evident. Cholecystectomy has been the only solution to chronic carrier. Salmonella - Nontyphoidal Bacteremia Characterized by prolonged fever and intermittent bacteremia Two groups at risk for developing infection Young children Fever and gastroenteritis with brief episodes of bacteremia Adults Transient bacteremia during episodes of gastroenteritis or develop symptoms of septicemia without gastroenteritis Salmonella - Treatment Gastrointestinal Salmonellosis Replacement of fluids is most important. Antimicrobial therapy generally is not recommended Susceptibility testing may be done for some instances (Ex. Immunocompromised hosts, adults, children) Typhoid Fever: Treatment is required Common agents: quinolones, chloramphenicol, trimethoprim/sulfamethoxazole, and advanced-generation cephalosporins such as ceftriaxone Non-typhoidal bacteremia:Treatment is required Use 3rd generation cephalosporin (ex. Ceftriaxone) Shigella Species 4 species based on O antigens 1. S. dysenteriae (group A) Most serious infection (developing countries) 2. S. flexneri (group B) Second most common isolate in the United States Associated in men who have sex with men and in young adults ~25 years old 3. S. boydii (group C) More common in developing countries 4. S. sonnei (group D) Most common isolate in the United States Short, self-limiting; patients have fever and watery diarrhea Shigella - Colony Morphology On MAC: Clear, nonlactose-fermenting colonies On XLD: Red colonies On HEK: green/clear colonies  Shigella Species - ID Biochemically inert** Nonmotile Generally do not produce gas from glucose Except some types of S. flexneri No urease production No H2 S  What does this mean for TSI, CLD, HEK media?? No decarboxylation of lysine ONPG Negative S. sonnei is exception – it is a LLF ODC negative S. sonnei is positive Serology is important part of ID Shigella Species – serological differentiation Shigella - Antigenic Structures O antigens are separated by serologic grouping. K antigens Must be removed to type O antigen Heat labile Lack H antigens Nonmotile Shigella - Epidemiology Human and large primates are only known reservoirs. Transmission Direct person-to-person Fecal–oral route with carriers as the source Transmitted by flies, fingers, and food or water contaminated by infected persons Personal hygiene plays a major role in transmitting organisms. Groups at risk Children in daycare centers (particularly infants younger than 1 year of age) Individuals living in crowded and inadequate housing Individuals who practice anal–oral sexual activity Known to cause outbreaks on cruise ships Shigella – Infection Main Infection: Shigellosis or Bacillary Dysentery Marked by penetration of intestinal epithelial cells after attachment to mucosal surfaces Local inflammation Shedding of the intestinal lining Formation of ulcers after epithelial penetration Shigella - Infection Severity of disease varies from asymptomatic to severe. Initial symptoms appear 24 to 48 hours after ingestion of the organisms. High fever, chills, abdominal cramps, pain accompanied by tenesmus Organisms multiply in the small intestine and move toward the colon. Isolation in the colon may occur for 1 to 3 days. Organisms invade the colonic tissues. Causes an inflammatory reaction Water diarrhea Bloody mucus and numerous leukocytes follow. Represented in stool samples! Shigella - Treatment Oral rehydration Antimicrobial drug therapy may be used to shorten the period of fecal excretion and perhaps limit the clinical course of the infection. Not common Due to the risk of resistance, using antimicrobial drug therapy for less serious infections may be unwise. Yersinia Two pathogens of note: Yersinia Yersinia pestis enterocolitica Causative Acute agent of the gastroenteritis plague Transmitted Transmitted through contact through infected with swine, fleas cats, dogs Yersinia pestis Y. pestis Causative agent of plague Bubonic, septicemic, and pneumonic forms Transmitted through bite of infected fleas Pneumonic plague through respiratory droplets Class A bioterrorism agent Yersinia pestis - infection Symptoms of bubonic plague High fever with painful regional lymph nodes (known as buboes) Septicemic form occurs when the bacteria spread to the bloodstream. Pneumonic plague Secondary to bubonic plague or the septicemic form when organisms proliferate in the bloodstream and respiratory tract Yersinia enterocolitica - infections Acquired from contact with swine, cats, dogs Ingestion of contaminated food that contacted fecal material Refrigeration is ineffective because it survives in cold temperatures. Most common forms of infection Acute gastroenteritis, simulating appendicitis, arthritis, erythema nodosum * * Tender red nodules with itching and burning on lower legs (shins) Yersinia enterocolitica - infections Acute gastroenteritis is the common form of the infection Often affects infants and young children between the ages of 1 and 5 years Symptoms Acute gastroenteritis with fever accompanied by headaches, abdominal pain, nausea, diarrhea Stools often contain blood. Usually mild and self-limiting Yersinia enterocolitica - infections Appendicitis-Like Syndrome Occurs primarily in older children and adults Possible symptoms Severe abdominal pain concentrated in right lower quadrant Fever Enlarged mesenteric lymph nodes Inflamed ileum and appendix Erythema nodosum Yersinia - cellular morphology Both species are gram-negative coccobacilli with safety pin appearance i.e. bipolar staining Motile at 25C Yersinia – cultural characteristics Grows on BAP and MAC (NLF) Preferential growth at 25 to 30° C Preferential growth at 25 to 30° C Cold enrichment can be used to increase recovery in fecal samples. Motility Y. enterocolitica is motile at 25°C but not at 35°C Y. pestis is motile