Gastrointestinal Bacterial Infections

1. Gastrointestinal Bacterial Infections • Salmonella • Shigella • Yersinia enterocolitica Liliana Rodríguez, MPH, RM (AAM), M(ASCP) UT Health Science Center at Houston Liliana.F.Rodriguez@uth.tmc.edu

2. Salmonella • Motile Gram-negative rods, members of the Family Enterobacteriaceae • Common species • S. cholerasuis (pigs) • S. typhimurium (cattle, pigs, poultry) • S. typhi, S. paratyphi A and B (humans) • S. enteritidis (1500 serotypes) many hosts • Non-lactose fermentors; production of H2S

3. Laboratory Identification Biochemical reactions on TSI Non-lactose fermenting colonies on MacConkey agar

4. Serotyping

5. Salmonella: Epidemiology • Ubiquitous pathogens • All are associated with animals, except S. typhi, S. paratyphi A, B, and C • Transmitted to humans via contaminated food, water (less frequent), or person-to-person • Killed by gastric acid • High infectious dose

6. Virulence factors • Virulence polysaccharide (Vi antigen) • Adhesion to M-cells • Motility • Tolerance to acid in phagocytic cells • Survival in macrophages (S. typhi) • Endotoxin

8. Salmonella: Clinical Syndromes • Gastroenteritis • Extra-intestinal • Septicemia • Typhoid fever (enteric fever) • Chronic carriage

9. Gastroenteritis • Most common manifestation • Highest rates of infection in children • S. enteritidis (many serotypes) • Contaminated food - eggs, poultry, dairy • Exotic pets • Incubation period 12-48 hrs

10. Gastroenteritis PathogenesisAttachment to the brush border Ruffles

11. Invasion and penetration of enterocytes ← bacterial death

12. Inflammatory Response • PMN confine infection to GI tract • Mediates release of prostaglandins • Stimulates cAMP, activates fluid secretion resulting in diarrhea • S. enteritidis can become invasive in immunocompromised patients

13. Summary Salmonella enteritis ingestion absorbed to epithelial cells in terminal portion of small intestine bacteria penetrate cells and migrate to lamina propria layer of ileoceal region multiply in lymphoid follicles causing reticuloendothelial hyperplasia and hypertrophy polymorphonuclear leucocytes confine infection to GI tract stimulates cAMP and active fluid secretion inflammatory response also mediates release of prostaglandins diarrhea

14. Gastroenteritis: Clinical Presentation • Nausea, vomiting (rare) • Fever (50%) • Abdominal cramps • Acute but self-limiting watery or bloody diarrhea with fecal leukocytes • Symptoms subside in 7 days, but stool cultures remain (+) several weeks

15. Bacteremia • Caused by salmonellas highly adapted to animals: • S. cholerasuis • S. typhimurium • S. enteritidis heidelberg • Severe disease in humans • Portal of entry: GI tract • Phagocytes in lamina propria cannot stop infection

16. Pathogenesis

17. Bacteremia: Pathogenesis • Penetrates mucosa - invades bloodstream • Localizes in abnormal cardiovascular surfaces of some patients (It has a predilection for the artherosclerotic plaque) • It can cause metastasic infection in bones (osteomyelitis) • Sepsis can be seen in those with cell-mediated immune system deficiencies

18. Clinical Presentation • High fever without localizing findings • Minimal or absent GI symptoms • Meningitis • Arthritis • Endocarditis

19. Typhoid Fever • Systemic infection of mononuclear phagocytes • Etiologic agent: S. typhi • Parathypoid fever caused by S. paratyphi A, S. scottmulerii (paratyphiB) and S. hirschfeldii (paratyphi C) • Humans-humans (no animal reservoir) • S. typhi virulence • binds to intestinal M-cells (adhesin) • motility • intracellularity

20. Typhoid Fever: Pathogenesis • Infective dose: 105 • Penetration of gut mucosa (jejunum, ileum) • Reaches intestinal lymph nodes, survives and multiply within macrophages

21. Typhoid Fever: Pathogenesis • After 5-7 days reaches blood, taken up by liver, bone marrow, and spleen, where intracellular replication continues (asymptomatic incubation period) • Multiplication within macrophages continues → release into the bloodstream • Resolves, gets complicated, or patient becomes a chronic carrier (1-3 %)

22. Typhoid Fever: Pathogenesis

23. Typhoid Fever: Clinical Manifestations • Incubation period: 1-2 weeks after ingestion • A sustained period of high fever (4-8 weeks if untreated) • Malaise, aches • Respiratory symptoms (flu-like) • Occasional diarrhea or constipation • Rose spots (50%)

25. Diagnosis • Gastroenteritis • Stool culture • Biochemical id • Bacteremia • Blood cultures • Stool cultures usually negative • Leukocytosis (many WBC)

26. Diagnosis of Typhoid Fever • Clinical history • Blood cultures during the first 2 weeks • Stool and urine culture during weeks 3-4 • Bone marrow aspiration if needed

27. Serology: Widal test 1:20 1:40 1:80 The Widal test measures the patient’s antibodies against Salmonella typhi “O” and “H” antigen preparations. Dilutions 1:20-1:1280 and negative control. In this case “O” antigen titer = 1:80.

28. Salmonella Infections: Therapy Antibiotics Indicated Syndrome Useful Antibiotics Enterocolitis No Immunosuppression Debilitated host Infants, elderly Yes Ampicillin Chloramphenicol Trimethoprim Ciprofloxacin Ceftriaxone Chronic bacteremia Extra-intestinal infection Typhoid fever Yes

29. Prevention • Hand washing • Adequate standards of public health and educational programs • Food workers should be excluded from handling food • Prolonged treatment for chronic carriers

30. Prevention • Typhoid fever immunization • inactivated –parenteral • live – oral • Vi antigen- parenteral • Preventing gastroenteritis presents a challenge because of animal reservoirs

31. Shigella • Closely related to E. coli • Non-lactose fermenter • No gas from glucose • Non-motile • Causes bacillary dysentery Stool Gram stain showing numerous white blood cells and GNR

32. Shigella: Classification Group A B C D Species S. dysenteriae S. flexneri S. boydii S. sonnei

33. Shigella species • S. dysenteriae(Shiga bacillus) first discovered in 1890 Japan; re-emerged in 1969 • causes most serious disease • S.dysenteriaetype 1 produces Shiga toxin (cytotoxin) • associated with 10-20% mortality • S. flexneri is the dominant species internationally. Associated with severe infections in gay man.

34. Shigella species cont.. • S. boydii causes severe infections. Occurs primarily in India • S. soneiiis the most important in the United States (70% of the cases). Shigellosis in the U.S. is primarily a pediatric disease • Species distinguished from one another by serology, not biochemically.

35. Epidemiology • Humans only reservoir • Spread from person-to-person by the fecal-oral route • Extremely low infective dose (10-100 cells) • No seasonal incidence for isolated causes • Epidemics occur in the summer • The most virulent of all enteric pathogens

36. Age distribution of diarrheal disease caused by Campylobacter, Salmonella, and Shigella

37. Shigella: Virulence Factors • Gastric acid resistant • Attachment – invasion plasmid antigens (Ipa) • Intracellular pathogen (local invasion) • Toxins • cytotoxins – “Shiga” toxin (S. dysenteriae) • enterotoxins role unknown

38. Shigella: Local Invasion

39. Shigella: Pathogenesis • Attachment and invasion of mucosal epithelium of distal ileum and colon • Destruction of enterocytes and release of TNF, PG • Vascular abnormalities • Locally invasive • Rarely invade bloodstream (except S. dysenteriae type 1)

40. Shigella

41. Shigella: Clinical Features • Incubation period 1-2 days • Mild diarrhea to dysentery • Diarrhea, abdominal cramps, fever, malaise, anorexia, and sometimes myalgias • Stool contains mucus and blood. Most display many white blood cells • Self-limiting but dehydration can occur, especially in the young and elderly • No chronic carrier state

42. Shigella: Diagnosis • Rectal swabs or stool • Requires transport media • Fecal leukocytes (+) • Culture • Biochemical tests • Agglutination tests • Other: PCR, DNA probes

43. Shigella on MacConkey Agar Non-lactose fermenter Non-motile

45. Shigellosis: Prevention • Education in personal hygiene • Proper disposal of diapers at day-care centers • Hand-washing • Safe sex for gay man

46. Yersinia enterocolitica: “the cold bug” • Gram negative encapsulated cocobacillus with polar staining • Prefers to grow between 22-25 ºC • Requires a special medium to grow

47. Y. enterocolitica: Epidemiology • Food-associated infection in colder parts of the world • More common during colder months • Found in rodents, rabbits, pigs, sheep, cattle, horses, dogs. • Humans are accidental hosts • Survives and multiplies at refrigerator temperatures

48. Y. enterocolitica: Virulence Factors • Invasin - early attachment protein to cells expressing receptor • ST-like enterotoxin (chromosomal) • Complement resistance factor • Yersinia outer proteins or Yops (anti-phagocytic & toxic action)

49. Y. enterocolitica: Pathogenesis • Invasion of M-cells of Peyer’s patches • In contrast to Shigella, Yersinia does not replicate in the M-cells but passes to the underlying tissue • Engulfed by macrophages and carried to MLN where they replicate

50. Y. enterocolitica: Clinical Syndromes • Enterocolitis - young children. • Mesenteric adenitis (mimics appendicitis) - older children. • Focal necrosis of Peyer’s patches. • Bacteremia - high fatality rate. • Arthritis, reactive polyarthritis (post-infection in adults)