GIHEPL2 GNB SalmShigHP24Stud PDF

Aerobic Gram-Negative Bacilli (GNB) 2 Dr Aoife Kearney Clinical Lecturer Dept of Clinical Microbiology, RCSI  RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn Gram-negative bacilli: Salmonella, Shigella, Helicobacter Class Year 2 Semester 1 C...

Aerobic Gram-Negative Bacilli (GNB) 2 Dr Aoife Kearney Clinical Lecturer Dept of Clinical Microbiology, RCSI  RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn Gram-negative bacilli: Salmonella, Shigella, Helicobacter Class Year 2 Semester 1 Course Undergraduate Medicine Lecturer Dr Aoife Kearney Date 11th September 2023 Prevention of Salmonella gastroenteritis (Non-Typhoidal Salmonellae) Hand hygiene And after handling snakes, lizards, or other reptiles; birds; or baby chicks Good food hygiene (storage, preparation etc) Wash hands, boards, utensils, countertops after contact with raw meat or poultry Wash hands in between handling different kinds of food (meat and vegetables, for example) Wash fresh vegetables and fruit thoroughly before eating Cook food to the recommended safe temperature Keep the refrigerator below 4°C Keep hot foods hot and cold foods cold SALMONELLA LABORATORY DIAGNOSIS APPLIES TO BOTH ENTERIC FEVER AND NON-TYPHOIDAL SALMONELLAE Salmonella spp. Laboratory Diagnosis Direct PCR on faeces increasingly used for non-typhoidal salmonellae Culture of stool (or blood in the case of enteric fever)  Salmonella Serotyping (Testing Antigens) Carried out once the organism has grown, to identify serotype Specialised testing- usually performed at a reference laboratory 3 surface antigens O, cell wall (somatic) antigen H, flagellar antigen K, capsular antigen – Vi (virulence) antigen is a specialized K antigen primarily found in strains causing typhoid fever Salmonella Serotyping  Salmonella Typing: Whole Genome Sequencing (WGS) In Ireland – since 2018 instead of serotyping to type Salmonella isolates at the Irish national reference laboratory in Galway Helpful in investigating outbreaks as can show how closely related isolates are to each other Source: NATIONAL SALMONELLA, SHIGELLA & LISTERIA REFERENCE LABORATORY OF IRELAND 2. Shigella  Shigella Overview Enterobacterales: Gram-negative bacilli Human-only reservoir Fifty Shigella species which fall into one of four serological groups – Group A - S. dysenteriae (12 serotypes) seen particularly in tropical countries - most severe form – Group B - S. flexneri (6 serotypes) – Group C - S. boydii (18 serotypes) – Group D - S. sonnei (1 serotype) most common cause in UK/Ireland Data from HPSC  Shigella Virulence/Pathogenesis Infection usually limited to GIT – Invasion via mucosa of colon (enters colonic M cells via pinocytosis, travels cell-to-cell via actin filaments -helps evade immune system)  Shigella Virulence/Pathogenesis Infective dose Highly contagious; very low infective dose Toxins 1. Enterotoxins (watery diarrhoea) 2. S. dysenteriae serotype 1 expresses Shiga toxin cytotoxin that inhibits protein synthesis causes capillary destruction & focal haemorrhage = bowel ulceration with bloody diarrhoea associated with the haemolytic-uremic syndrome (HUS) Closely related toxins are expressed by enterohaemorrhagic verotoxigenic E.coli (VTEC) including O157-H7 serotype  Shigella Epidemiology Transmission: Faecal-oral – Poor sanitation/ especially if hygiene is poor – Secondary spread within households common – Outbreaks in crowded conditions e.g. prisons – Sexually transmitted (MSM) Foodborne (unpasteurized milk products and raw, unwashed vegetables) Contaminated water Incubation 24-72 hours  Shigella Clinical Features 1. Profuse watery diarrhoea with vomiting & mild to moderate dehydration- e.g. Shigella sonnei, Shigella flexneri – usually self limiting in 5-7 days 2. Dysentery (“bacillary dysentery”) with bloody, mucoid stools, abdominal cramps & tenesmus- Shigella dysenteriae serotype 1 – Early stage Watery diarrhea  Shiga toxin in the small intestine – Second stage Adherence & invasion of large intestine with symptoms of dysentery  Cytotoxic activity responsible for severity  Shigella Complications 1. Intestinal complications (e.g., toxic megacolon, perforation, obstruction) 2. Bloodstream infection S dysenteriae serotype 1 in malnourished infants; uncommon in healthy individuals 3. Convulsions 25% in Gastric ulcer Mucosa Associated Lymphoid Tissue tumour (MALT lymphoma ) ? Other GI cancers  Detection of H. pylori Laboratory a. Faecal antigen testing b. Serology (positive for life even after eradication) c. Culture = difficult (microaerophilic) + rarely done Also 2. Endoscopy biopsy – Rapid urease test (CLO test) – Histology 3. Urea breath test  Treatment Smith et al. The Irish Helicobacter pylori Working Group consensus for the diagnosis and treatment of H. pylori infection in adult patients in Ireland, European Journal of Gastroenterology & Hepatology: May 2017 - Volume 29 - Issue 5 - p 552-559  Treatment decision schematic Smith et al. The Irish Helicobacter pylori Working Group consensus for the diagnosis and treatment of H. pylori infection in adult patients in Ireland, European Journal of Gastroenterology & Hepatology: May 2017 - Volume 29 - Issue 5 - p 552-559  Prevention of acquisition & spread of infections caused by H. pylori Mode of spread unclear – person-to-person & faecal-oral routes both occur Prevention of acquisition – Practice good hygiene and hand washing, especially with food preparation Prevention of spread – All patients with chronic GI symptoms should be tested and treated to prevent exposure to family members – Patients should complete the full course of therapy (antibiotics and acid blockers) to maximize the potential for a cure