MIIM30011 Salmonella/Shigella Lecture Notes PDF 2024

GI infections Salmonella/Shigella Nancy Wang, PhD [email protected] MIIM30011 Medical Microbiology: Bacteriology 8th May 2024  Learning objectives At the end of this lecture, students should be able to: - have a general understanding of the infectious diseases caused by different...

GI infections Salmonella/Shigella Nancy Wang, PhD [email protected] MIIM30011 Medical Microbiology: Bacteriology 8th May 2024  Learning objectives At the end of this lecture, students should be able to: - have a general understanding of the infectious diseases caused by different serotypes of Shigella and Salmonella; - compare and contrast Shigella and Salmonella with respect to their: - key mechanisms of gut invasion; - functions of type 3 secretion system (T3SS); - intracellular lifestyle; - the role of gain and loss of gene function in pathogen evolution and host adaptation. - give examples of immune evasion mechanisms in Salmonella 3  Gastrointestinal (GI) infections - The causative microbial agent can be bacterial, viral or parasitic - Common symptoms: - diarrhoea (≥ 3 loose stools over a 24hr period) - abdominal pain - vomiting - fever - nausea - dehydration - Diarrhoeal diseases remain a leading cause of morbidity and mortality - most common aetiologies: Rotavirus, Shigella and Salmonella - 1.31 million deaths (38.1% in children S. flexineri > S. sonnei - Conventional bacterial culture still the gold standard for diagnosing Shigella infection - most commonly faecal samples or rectal swabs - not easy to distinguish from other enteric bacteria (e.g. MALDI-TOF can’t distinguish Shigella and pathogenic E. coli) 6  Is Shigella a pathogenic biotype of E. coli? “Using a genetic definition for species, the four species of Shigella would be regarded as serologically defined anaerogenic biotypes of E. coli.” - Manual of Clinical Microbiology (2015). Ø If discovered today, Shigella would probably Genotypic diversification based on be called xxECs! housekeeping gene rpoB Ø Shigella clusters (except of S. boydii 13) most likely Ragupathi et al, 2018. emerged from non-invasive E. coli by convergent EPEC=enteropathogenic E. coli evolution some 35,000-270,000 years ago EIEC=enteroinvasive E. coli Ø Original taxonomy is still kept today so it remains STEC=Shiga toxin-producing E. coli in-line with clinical diseases EHEC=enterohaemorrhagic E. coli 7  Shigellosis: disease and transmission - Very low infectious dose (~10-100 bacteria), acid-stable - Primary symptom is diarrhoea: watery to bloody (dysentery) - infection in the colon and rectum - clinical presentations range from asymptomatic, intestinal (most common and usually self- limiting) to invasive - Mode of transmission: - person-to-person, e.g. households, childcare centres, very close living environment - contaminated food or water, e.g. food hygiene, water safety incl. bathing/swimming - sexually transmitted, e.g. MSM - Estimated 188 million cases in 2017, approx. 1/3 in