Shigella flexneri is a Gram-negative bacterium from the Enterobacteriaceae family that causes one of the most common forms of bacterial diarrhea, shigellosis. It was discovered in the early 20th century and has remained a serious threat to healthcare systems ever since, especially in countries with poor hygiene.
This pathogen penetrates the colonic mucosa and causes severe inflammation accompanied by painful symptoms. It is known for its ability to evade the immune response, spread rapidly in closed communities, and cause outbreaks even under relatively normal sanitary conditions.

How infection occurs: simple actions - serious consequences

The primary route of transmission is fecal-oral. A few germs are enough for the immune system to fail to respond. Infection occurs through unwashed hands, contaminated food, water, and contact with an infected person or carrier. Children, the elderly, and those with weakened immune systems are particularly vulnerable.
The pathogenicity of Shigella flexneri is due to its ability to penetrate epithelial cells and destroy intercellular junctions. The bacterium can induce cell death, causing ulcers and erosions in the intestinal wall.

Symptoms and diseases caused by Shigella flexneri

The incubation period ranges from 1 to 3 days. The main symptoms of shigellosis include:

• High temperature (up to 39°C)

• Frequent urge to defecate (up to 20 times a day)

• Blood and mucus in stool

• Severe cramps in the lower abdomen

• General weakness, headache

The illness can last from several days to several weeks. In severe cases, dehydration, electrolyte imbalance, and liver, kidney, and heart damage occur.

Modern treatment: antibiotics are losing their effectiveness

Shigellosis is traditionally treated with antibiotics—ciprofloxacin, azithromycin, and ceftriaxone. However, recent decades have shown a rapid increase in antibiotic resistance among Shigella flexneri strains .
This complicates therapy, leads to frequent relapses and requires new approaches.

How to avoid infection: life-saving rules

Shigella prevention is primarily a matter of hygiene. The most important measures are:

• Wash your hands with soap after using the toilet and before eating.

• Drink purified or boiled water.

• Urgently isolate sick people, especially in kindergartens and schools.

• Keep the kitchen clean and store food properly.

Health education, food quality control and water supply are also important, especially in areas at risk of outbreaks.

Bacteria learn to survive

The main cause of Shigella flexneri resistance is the uncontrolled use of antibiotics. When antimicrobials are used without medical advice or are discontinued, the bacteria gain time to adapt. They alter the structure of proteins targeted by the drugs or produce enzymes that destroy the drug molecule.
In some cases, resistance genes are transferred via plasmids—that is, horizontally between different bacteria. This results in new strains, even previously susceptible ones, quickly acquiring resistance.

Phage therapy against Shigella flexneri: a chance in the fight against an incurable disease

As antibiotics become less effective, phage therapy, a method based on the use of bacteriophages, viruses that infect and destroy bacteria, is attracting increasing attention.
In the case of Shigella flexneri, phages demonstrated high efficacy back in the 20th century in Georgia, Poland, and the former USSR. Today, interest in these "good viruses" is growing again. They act selectively, do not harm normal intestinal flora, and do not contribute to the development of resistance.
Bacteriophages are able to penetrate the biofilms in which bacteria hide, making them extremely valuable in complex, chronic cases. They can be administered orally, rectally, or as enemas.

Examples of successful use

In 2019, the Tbilisi Biotechnology Center conducted a study on children with chronic shigellosis. The use of phages in combination with diet resulted in a complete recovery in 92% of cases. The results were superior to antibiotic therapy.
In India, phage preparations are being developed for the epidemiological control of shigellosis in rural areas. They are used to treat water, surfaces, and even vegetables as an environmentally friendly antiseptic.

The benefits of "good viruses"

• High specificity to the target pathogen

• No side effects on beneficial microflora

• Low risk of resistance development

• Possibility of combination with antibiotics for a synergistic effect

• Adaptation of phages to new strains by selection

Due to these properties, bacteriophages are considered as a tool for personalized medicine, especially in cases where traditional methods have been exhausted.