Shigella spp.: PCR Detection and Clinical Overview

Shigella spp. are short Gram-negative rods measuring approximately 0.5–0.7 μm × 2–3 μm. They are non-motile, lacking flagella, and do not form spores or capsules. Most strains possess fimbriae that facilitate adhesion to host cells.

They are facultative anaerobes capable of growing on standard laboratory media. Optimal growth occurs at 37°C with a pH range of 7.2–7.4.

On agar plates, colonies typically appear smooth, round, and semi-transparent. Some species, such as Shigella sonnei, may produce flat and rough colonies, aiding differentiation.

Biochemically, Shigella ferments glucose with acid production but no gas formation. It is negative for urease, hydrogen sulfide production, and citrate utilization, and most strains do not ferment lactose.

Shigella spp. possess O antigens and K antigens but lack H antigens. Based on O antigen variations, they are classified into four major groups:

Group A: Shigella dysenteriae
Group B: Shigella flexneri
Group C: Shigella boydii
Group D: Shigella sonnei

These groups differ in pathogenicity, epidemiology, and clinical severity.

Pathogenicity of Shigella is mediated by invasion factors, endotoxins, and in some strains, Shiga toxin.

The bacteria adhere to and invade intestinal epithelial cells, particularly in the distal ileum and colon, leading to mucosal damage and inflammation.

Endotoxins contribute to systemic symptoms such as fever and toxicity, while Shiga toxin (produced by certain strains) can cause severe complications including neurological symptoms and cellular damage.

Clinical manifestations include acute bacillary dysentery characterized by abdominal pain, fever, tenesmus, and bloody or mucoid diarrhea. Chronic and severe forms, including toxic dysentery, may occur, especially in children.

Shigella spp. are primarily transmitted via the fecal–oral route through contaminated food and water.

Mechanical vectors such as flies can also contribute to transmission by contaminating food and surfaces.

Infection occurs through a multi-step process: adhesion to intestinal mucosa, invasion of epithelial cells, intracellular replication, and spread to adjacent cells, leading to inflammatory responses and tissue damage.

Traditional diagnostic methods include stool culture and biochemical identification; however, these methods may be time-consuming and less sensitive.

Real-time PCR (qPCR) provides rapid, sensitive, and specific detection of Shigella spp., making it highly suitable for early diagnosis, outbreak investigation, and food safety monitoring.

Preventive strategies focus on interrupting fecal–oral transmission pathways.

Ensuring safe drinking water and proper food hygiene is critical. Food should be thoroughly cooked, and consumption of contaminated or undercooked items should be avoided.

Maintaining environmental sanitation, including waste management and fly control, reduces transmission risk.

Personal hygiene, especially regular handwashing with soap after using the restroom and before meals, is essential.

In food handling and healthcare industries, routine health monitoring and strict hygiene standards are necessary to prevent outbreaks.