Shigella species for food testing, and instrument consumables for culture

Shigella Castellani and Chalmers are Gram-negative bacilli, and their morphology is similar to that of other Enterobacteriaceae. No exercise. Facultative anaerobic, with both respiratory and fermentative types of metabolism. The catalase test was positive (with the exception of one species). Oxidase is negative. Organic can be nutritious. Fermented sugars do not produce gas (except for a few species of gas produced). Citrate or malonate is not used as the sole source of carbon. No growth in KCN, no production of H ₂ S. It is an intestinal pathogen of humans and primates, causing bacterial dysentery.

The G+C mol% of DNA is 49 to 53 (Tm).

Morphology and staining

The size is (0.5 ~ 0.7) × (2 ~ 3) μm, no spores, no capsule, no flagella. Most have pili, Gram-negative bacilli.

Culture characteristics

It is a facultative anaerobic bacterium that grows on ordinary medium to form a medium-sized, translucent smooth colony. A colorless colony was formed on the enterobacterial selective medium.

Biochemical reaction

Decomposes glucose, produces acid and does not produce gas. The VP test is negative, does not decompose urea, does not produce hydrogen sulfide, and cannot use citrate as a carbon source. Shigella sonnei can slowly ferment lactose (37 ° C for 3 to 4 days).

Antigen construction and classification

There are K and O antigens without H antigen. The K antigen is a bacterial surface antigen of some strains newly isolated from patients, which is not heat-resistant and is destroyed by heating at 100 ° C for 1 hour. The K antigen is meaningless in serological typing, but prevents the agglutination of the O antigen with the corresponding antiserum. The O antigen is divided into a group-specific antigen and a type-specific antigen, and the former often appears between several similar strains; the specificity of the type-specific antigen is high, and the bacteria are distinguished by the use. According to the different antigenic structure of Shigella, it can be divided into four groups of 48 serotypes (including subtypes).

(1) Group A: Also known as Shigella dysenteriae (Sh. dysenteriae), commonly known as Shigella dysenteriae. Does not ferment mannitol. There are 12 serotypes, 8 of which are subdivided into three subtypes.

(2) Group B: Also known as Sh. flexneri, commonly known as Shigella dysenteriae. Fermenting mannitol. There are 15 serotypes (including subtypes and variants), complex antigen structures, group antigens and antigens. According to the type of antigen, it is divided into 6 types, and the type is divided into subtypes according to different group antigens; X, Y variants have no specific antigen, only different group antigens.

(3) Group C: Also known as Shih's Shigella (Sh. boydii), commonly known as Shigella dysenteriae. Fermented mannitol has 18 serotypes with no cross-reactivity between the various types.

(4) Group D: Also known as Shigella sonnei (Sh.sonnei), commonly known as S. sinensis. Fermenting mannitol and slowly fermenting lactose usually takes 3 to 4 days. There is only one serotype. There are two variant phases, phase I and phase II; phase I is S-type and phase II is R-type.