1. SHIGELLA

Shigella spp.

First isolated by a Japanese microbiologist, Kiyoshi Shiga. One of the species was named after Shiga and is called the Shiga bacillus. Closely related through DNA homology to E. coli. Diarrheal and GIT infections caused by Shigella resemble those caused by E. coli. Prominent characteristic

Kiyoshi Shiga

Japanese microbiologist who first isolated Shigella spp.

Shiga bacillus (S. dysenteriae)

One of the species of Shigella named after Kiyoshi Shiga.

E. coli (Escherichia coli)

Closely related through DNA homology to Shigella spp. Diarrheal and GIT infections caused by Shigella resemble those caused by E. coli. Both belong to the Enterobacteriaceae.

Biochemically and biologically inert

Prominent characteristic of Shigella spp. In most biochemical tests and biological characteristics, they are usually inactive; most biochemical reactions are negative.

Non-motile

Characteristic of Shigella spp.; unlike other members of Enterobacteriaceae that are motile.

Shigellosis (Bacillary Dysentery)

Disease produced by Shigella in the intestinal tracts of humans and other primates. Bacillary Dysentery refers to dysentery caused by bacteria, specifically bacilli. Other bacilli such as Campylobacter, Salmonella, and E. coli can also cause dysentery.

Campylobacter, Salmonella, E. coli (Escherichia coli)

What are other bacilli that can cause dysentery?

S. dysenteriae (Shiga bacillus)

Causes the most severe type of bacillary dysentery because it produces both an enterotoxin (attacks the GIT) and a neurotoxin (targets the CNS).

Common symptoms of Shigella infection

Diarrhea, fever, nausea, vomiting, stomach cramps, and flatulence.

Highly communicable

Shigella has an infective dose on the order of 10^3 CFU organisms, allowing spread from one person to another.

Shigella-associated dysentery

Results in destruction of the epithelial cells of the intestinal mucosa in the cecum and rectum. Stool may contain blood, mucus, or pus.

S. dysenteriae (Shiga bacillus)

Group A; Catalase (-); Ornithine Decarboxylase (-); ONPG (-); Mannitol (-).

S. flexneri (Strong's bacillus, Flexner's bacillus)

Group B; Catalase (+); Ornithine Decarboxylase (-); ONPG (-); Mannitol (+).

S. boydii (Ambigua's bacillus, Boyd's bacillus, Newcastle-Manchester bacillus)

Group C; Catalase (+); Ornithine Decarboxylase (-); ONPG (-); Mannitol (+).

S. sonnei (Sonne-Duval bacillus, Duval's bacillus)

Group D; Catalase (+); Ornithine Decarboxylase (+); ONPG (+); Mannitol (+).

Determinants of Pathogenicity of Shigella spp.

Endotoxin, invasiveness, exotoxin, enterotoxin (Shiga's toxin), and neurotoxin.

Endotoxin

Toxic polysaccharide (LPS) - causes irritation of the bowel wall; may be responsible for the organisms' resistance to gastric acidity.

Invasiveness

Determinant of pathogenicity of Shigella spp.

Exotoxin

Determinant of pathogenicity of Shigella spp.

Enterotoxin (Shiga's toxin)

Aka Shiga's toxin. Causes diarrhea similar to that of EHEC. Inhibits sugar and amino acid absorption; interferes with protein synthesis and is neurotoxic, cytotoxic, and enterotoxic.

Neurotoxin

Causes the extreme severity and fatal nature of S. dysenteriae infections and the CNS reactions observed in them (ie, meningismus, coma).

Meningismus

In meningitis, the patient may experience headache, stiff neck, photophobia.

Ingestion of contaminated food/water; fecal-oral route.

Mode of transmission Shigella

Clinical manifestations

Acute toxigenic gastroenteritis and acute tissue-invasive gastroenteritis.

Acute toxigenic gastroenteritis

Profuse, watery diarrhea and a fever of self-limited course (ibig sabihin, kahit walang treatment, gumagaling ang pasyente).

Acute tissue-invasive gastroenteritis

Diarrhea with tenesmus (feeling na natatae kahit empty ang bowel; siguro katatae lang, then may urge na parang natatae ulit), blood or bloody-streaked mucoid stools, vomiting, fever, abdominal cramps, and abdominal tenderness.

a rectal swab of ulcer taken by sigmoidoscopy (a little invasive to collect); but the usual specimen submitted is stool

Best - Sample for suspec shigellosis

S. flexneri, S. ambigua

What are the Shigella species that are indole positive?

S. dysenteriae (Shiga bacillus)

Lactose (-); Mannitol (-); ODC (-); ONPG (-).

S. flexneri (Strong's bacillus, Flexner's bacillus)

Lactose (-); Mannitol (+); ODC (-); ONPG (-)

S. boydii (Ambigua's bacillus, Boyd's bacillus, Newcastle-Manchester bacillus)

Lactose (-); Mannitol (+); ODC (-); ONPG (-).

S. sonnei (Sonne-Duval bacillus, Duval's bacillus)

Lactose (-); Mannitol (+); ODC (+); ONPG (+).