Plesiomonas shigelloides – Culture; Identification; Molecular diagnosis (PCR) 

Información 02-08-2018.

Plesiomonas shigelloides is a Gram-negative, mobile, non-spore-forming, facultatively anaerobic, and oxidase-positive bacillus. Currently, molecular studies indicate that it is a species close phylogenetically to the genus Proteus, so it has been classified within the family Enterobacteriaceae, although it had previously been included in the family Vibrionaceae for a long time. The genus Plesiomonas includes a single species and multiple serotypes.

P. shigelloides is a mesophilic microorganism whose optimum growth temperature for most strains is between 35ºC and 39ºC. It is associated with water and soil in areas with temperatures above 8ºC, since it cannot grow below it. It is found mainly in freshwater or estuarine environments in temperate and tropical climates, although it can also be found in seawater during the warm months. In addition, it can be isolated in a variety of animals such as fish, waterfowl (swans, storks, gulls, ...), land mammals (dogs, cats, foxes, cows, pigs, goats, ...) and marine mammals (belugas, wolf Californian marine, ...). In humans, it usually causes enteric infections related to the consumption of contaminated water and shellfish, contact with animals or trips to tropical countries, although cases of diarrhea without epidemiological antecedents of interest have also been described. Exceptionally, it can cause extraintestinal infections (septicemia and central nervous system disease, eye infections and a variety of different infections) that have a high mortality and that mostly affect patients with some underlying disease or immunosuppressed.

P. shigelloides is a pathogen of worldwide distribution, with the possible exception of the polar ice caps. The prevalence of enteritis due to P. shigelloides varies considerably depending on the geographical area and the method of isolation used (between 0.5 - 16.9%), with higher rates reported in Southeast Asia and Africa, while in United States and Europe seems to be a rare process. Specifically, in our country its incidence is around 0.5%. The reasons for these differences may include hygiene conditions, eating habits, regional occupations or other unknown factors.

Although acute diarrhea caused by P. shigelloides is usually self-limiting, antimicrobial therapy has been effective in patients with diarrhea more than 4 or 5 days old, in immunocompromised individuals with underlying diseases or extraintestinal infections. The different in vitro sensitivity studies have shown that P. shigelloides is a microorganism resistant to ampicillin but sensitive to most antibiotics commonly used for other enteropathogens. For the treatment of severe cases or chronic forms, cotrimoxazole or fluoroquilones are recommended.

Given the current prevalence of diseases associated with Plesiomonas, it is particularly difficult to determine what social, geographical or medical factors may predispose people to Plesiomonas infection. However, several studies have linked gastroenteritis due to P. shigelloides with several specific risk factors, such as the consumption of raw seafood, especially oysters, and to a lesser extent shrimp, of untreated water, trips abroad (destinations more commonly associated: Thailand, Indonesia and Vietnam), as well as having a weakened immune system.

Several methods have been developed for the detection and identification of P. shigelloides such as culture in specific media and biochemical assays. Despite their effectiveness and accuracy, these tests are time consuming, usually requiring up to 5 days to complete. In addition, the isolation of P. shigelloides from clinical samples has often been unsuccessful due to the demanding nature of the organism and the low level of transient bacteremia associated with the disease process. In recent years, molecular techniques (PCR) have been developed by amplifying specific DNA sequences of the bacteria. These tests are rapid, specific and sensitive to detect P. shigelloides by targeting genes that code for 23S rRNA or for major virulence factors.

Tests carried out in IVAMI:

• Culture, isolation and identification of P. shigelloides. 

• Molecular detection (PCR) for 23S rRNA and hugA genes of P. shigelloides. 

Recommended sample:

• In case of enteric processes: feces. 

• When it comes to an extraintestinal infection, the most appropriate sample depends on the affected tissue and the clinical manifestations of the patient. 

Conservation and shipment of the sample:

• Refrigerated (preferred) for less than 2 days. 

• Frozen: more than 2 days. 

Delivery of results:

• Culture, isolation and identification of P. shigelloides: 5 days. 

• Molecular detection (PCR) for 23S rRNA and hugA genes of P. shigelloides: 24-48 hours. 

Cost of the tests:

• Culture, isolation and identification of P. shigelloides: consult ivami@ivami.com. 

• Molecular detection (PCR) for 23S rRNA and hugA genes of P. shigelloides: consult ivami@ivami.com.