Aerobic Gram-Negative Bacilli (GNB) 2 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  Salmonella Typhi: Chronic carriage Definition: positive stool cultures 12 months after overcoming the disease Incidence: up to 6% become chronic carriers Potential to transmit S. typhi indefinitely Usually asymptomatic May have increased risk of gallbladder cancer Treatment: ciprofloxacin for at least 1 month Chronic carriers are not allowed to work in the food industry Who was this? Paratyphoid Fever Paratyphoid A – Similar to typhoid except rarely see rose spots and less severe Paratyphoid B – Usually a diarrhoeal illness  Enteric Fever: Diagnosis Culture and PCR of various specimens – Blood: 80% + in 1st week, 20-30% in 3rd week – Faeces: 2nd week onward – Urine: 3rd week – Bone marrow culture May be positive even if treated with antibiotics Widal test – Was the mainstay of diagnosis for decades. – Agglutination test: O or H antigens from Salmonellae added to patient’s serum – Not done now – poor sensitivity and specificity  Enteric Fever: Treatment 1. Fluid & electrolyte replacement and supportive management 2. 10-14 days antibiotics Ceftriaxone 1st line empiric treatment - resistance to other agents (e.g. ciprofloxacin) increasing (Ciprofloxacin, Azithromycin- only if susceptibilities known) - XDR typhoid fever in Pakistan Up to 6% of patients become chronic carriers after symptoms have resolved  Enteric Fever: Prevention Public health measures – Safe drinking water & sanitary disposal of excreta Precautions – Good food hygiene (storage, preparation) – Hand hygiene – When travelling: boil it, cook it, peel it, or forget it! Vaccine – WHO recommended to those travelling to high-risk areas 1. Subunit vaccine (Vi polysaccharide) 2. Live attenuated oral vaccine  Salmonella (2610) Salmonella bongori Salmonella enterica Subsp. v Subsp. I Subsp. II Subsp. IIIa Subsp. IIIb Subsp. IV Subsp. VI (23) enterica salamae arizonae diarizonae houtenae indica (1547) (513) (100) (341) (73) (13) Cause 99% of human & animal infection Typhoidal Salmonella Non-typhoidal Salmonella (Humans only) (Humans & Animals) Typhoid Paratyphoid Gastroenteritis Extra-intestinal fever fever e.g. S. typhimurium S. typhi S. paratyphi S. virchow S. enteritidis S. Dublin  Non-typhoidal Salmonella (Humans & Animals) SALMONELLA Gastroenteritis Extra-intestinal GASTROENTERITIS e.g. S. Typhimurium S. Virchow S. Enteritidis S. Dublin CAUSED BY NON-TYPHOIDAL SALMONELLAE E.G. SALMONELLA ENTERITIDIS SALMONELLA TYPHIMURIUM  Salmonella Gastroenteritis (Non-typhoidal Salmonellae): Epidemiology Over 2,200 different serovars Source: GIT animals & reptiles (pets) & the environment Transmission – Foodborne (next slide) Improperly handled/ inadequately cooked/ stored food contaminated by animal or human faecal material – Faecal-oral From other humans or at farms or from pets Incubation period: 18-72 hours  Salmonella Gastroenteritis Epidemiology: Food Sources 1. Poultrycommonest source, up to 20% contaminated 2. Eggs from infected poultry, oviduct infected & eggs contaminated by transovarian spread 3. Beef & beef products, meat contaminated in the abattoir from animal’s intestines 4. Unpasteurised milk, infected from cow’s faeces  Salmonella Gastroenteritis Pathogenesis (Non-typhoidal Salmonellae) Salmonella Gastroenteritis Pathogenesis (Non-typhoidal Salmonellae) 1. Ingestion 2. Adherence: complex, multiple genes, fimbriae important 3. Invasion – Induce nonphagocytic cells (e.g., enterocytes) to internalize them – Then survive and replicate within modified phagosome Virulent strains of Salmonella induce multiple host inflammatory responses and cytokines (mediated by lipopolysaccharide in the cell wall)  Salmonella Gastroenteritis (Non-Typhoidal Salmonellae) Clinical Features Abrupt onset, short course, self-limiting gastroenteritis (usually lasts 3-7 days) Diarrhoea, nausea, headache, malaise; vomiting rare Severe infection with dehydration a problem in – Extremes of age – Immunocompromised  Non-Typhoidal Salmonellae Chronic Excretion Up to 4 weeks after acute illness Prolonged excretion increased by – Antibiotics (hence only treat if indicated) – HIV – Inflammatory bowel disease – Diverticulosis  Non-Typhoidal Salmonellae Complications (esp. if immunosuppressed) Bloodstream infection (BSI) – 4% of cases of acute gastroenteritis. – more likely with certain strains (e.g., S. Dublin or S. Choleraesuis) Systemic disease – Osteomyelitis (esp. sickle cell disease) – Meningitis – Endovascular + prosthetic material infection (Localised in tissues with pre-existing damage & survive in macrophages) Reactive arthritis  Management of Salmonella gastroenteritis (Non-Typhoidal Salmonellae) 1. Fluid & electrolyte replacement and supportive management = sole treatment required for most cases 2. Antibiotics not routine ONLY if severe illness & high risk of invasive disease –