Vibrio Infections: Risk Factors, Diagnosis, and Treatment

Introduction of Genus Vibrio

The genus Vibrio consists of Gram-negative straight or curved rods, motile by means of a single polar flagellum.  They are distinguished from enterics by being oxidase-positive and motile by means of polar flagella. Vibrios are distinguished from pseudomonads by being fermentative as well as oxidative in their metabolism. Of the vibrios that are clinically significant to humans, Vibrio cholerae, the agent of cholera, is the most important. Found in fresh water, shellfish and other sea food. Man is the major reservoir of V. cholerae-01, which causes epidemic cholera.  Readily killed by heat and drying; dies in polluted water but may survive in clean stagnant water, esp. if alkaline, or sea water for 1-2 weeks.

What is a genus vibrio?

Vibrio is a genus of Gram-negative bacteria that naturally live in aquatic environments, especially in coastal waters, estuaries, and river mouths.  They are typically curved-rod (or comma-shaped) and are highly motile due to a single flagellum. Many species of Vibrio are "halophilic," meaning they require salt to grow. While many are harmless, about a dozen species can cause an infection in humans called vibriosis.

Species of medical importance

1. Vibiro cholerae:

This is arguably the most historically and globally significant species. It is the causative agent of cholera, a severe and often fatal diarrheal disease. V. cholerae has been responsible for seven pandemics, and it continues to be a major public health concern in regions with poor sanitation and limited access to clean water. Its ability to cause widespread epidemics makes it a top-tier pathogen. Gastrointestinal illness caused an infection with the gram-negative bacterium vibrio cholerae. Toxin-producing variants (01 and 0139). It cause of traveler’s diarrhea. Endemic to many countries in Africa and Asia.  The disease is characterized by profuse watery diarrhea, vomiting and leg cramps. These symptoms result from rapid loss of body fluids leading to dehydration and shock. Death can occur within hours when person with rapid fluid loss are left untreated.

Transmission of vibrio cholera

V.cholerae  is transmitted by fecal contamination of water and food, primarily from human sources. Human carriers are frequently asymptomatic and include individuals who are either in the incubation period or convalescing. The main animal reservoirs are marine shellfish, such as shrimp and oysters. Ingestion of these without adequate cooking can transmit these disease.

 

Risk factors

• Decreased sanitation

• Ingestion of certain foods

• Blood group o patients

• Decreased gastric acidity

• Malnutrition

• Overcrowding

• Inadequate medical services

2. Non-01 V.cholerae:

Cause mild, sometimes bloody, diarrhoea often accompanied by abdominal cramp.  Also cause wound infection in patients exposed to aquatic environments, and bacteraemia and meningitis.  May elaborate a wide range of virulence factors including enterotoxin, cytotoxin, haemolysins and colonizing factors.  A few strains produce cholera toxin.

Pathogenesis and clinical manifestations

Route of infection is fecal-oral route.  After ingestion of the V.cholerae 01, the bacteria adheres to the intestinal wall without invasion then produces an exotoxin causing excessive fluid secretion and diminished fluid absorption resulting in diarrhea (rice water stool) containing vibrios, epithelial cells and mucus  and result in severe dehydration.

Laboratory diagnosis

Specimen: Stool flecks.  Smear: Gram-negative motile curved rods. Motility of vibrio is best seen using dark-field microscopy.

Culture: Thiosulphate citrate bile salt sucrose agar (TCBS) - selective media for primary isolation of V.cholerae. Observe for large yellow sucrose fermenting colonies after 18-24 hrs of incubation. Alkaline peptone water: Enrichment media for V.cholerae 01 growth on and just below the surface of peptone water within 4-6 hours at room temperature as well as 37 oc. Biochemical Reaction: Oxidase-positive. Ferment sucrose and maltose (acid; no gas). Do not ferment L-arabinose. On TSI agar, an acid slant and an acid butt without gas or h2s are seen because the organism ferments sucrose. A presumptive diagnosis of v. cholera can be confirmed by agglutination of the organism by polyvalent 01 or non-01 antiserum. A retrospective diagnosis can be made serologically by detecting a rise in antibody titer in acute and convalescence-phase sera.

Haw to treatment vibrio cholera   

Fluid and electrolyte replacement occasionally short-course antibiotic therapy, e.g. with tetracycline (but resistance is common) or deoxycycline, tetracycline (500mg four times daily for 3 days)

Ciprofloxacin (not recommended as first-line due to resistance concerns). Azithromycin (1g single dose for adults or 20 mg/kg for children).

Prevention and control

Prevention mainly achieved by clean water and food supply. Use of tetracycline for prevention is effective during close contact with infected patients but cannot prevent the spread of a major epidemic. Prompt detection of carriers is important in limiting outbreaks. The vaccine, composed of killed organisms, has limited usefulness: it is only 50% effective in preventing disease for 3 to 6 months and does not interrupt transmission. A live vaccine is available in certain countries but not in the United States. Neither the killed nor the live vaccine is recommended for routine use in travelers.

Conclusion

The genus Vibrio is a significant and diverse group of Gram-negative bacteria that are naturally found in aquatic environments, particularly in marine, estuarine, and brackish waters. While many species are harmless, the genus is well-known for containing several clinically important pathogens that can cause a range of illnesses in humans and aquatic animals.