Plesiomonas shigelloides
Authors: David R Murdoch, Selwyn D R Lang, MBChB, FRACP, FRCPA
Microbiology
The genus Plesiomonas includes a single species, Plesiomonas shigelloides. Although originally classified with Aeromonas as belonging to the family Vibrionaceae, recent evidence based on small subunit ribosomal RNA sequencing has shown that P. shigelloides is more closely related to members of the Enterobacteriaceae (37, 51), with which it is now classified. Previous names for P. shigelloides include Aeromonas shigelloides, C27, Pseudomonas shigelloides, Vibrio shigelloides and Fergusonia shigelloides (18).
P. shigelloides is a motile, facultatively anaerobic gram-negative, oxidase-positive, nitrate-reducing bacillus that does not ferment lactose (1). It possesses two to five polar flagella, and grows readily on enteric agars such as MacConkey, deoxycholate and Hektoen. It’s positive oxidase reaction distinguishes it from other Enterobacteriaceae. A positive ornithine decarboxylase differentiates it from most Aeromonas spp. and fermentation of inositol differentiates it from both Aeromonas spp. and Vibrio spp. (1). P. shigelloides is susceptible to the vibriostatic agent O/129. Many different enrichment methods have been used in attempts to increase the recovery of P. shigelloides from stool (47). In one study the best yield was obtained following 24-hour enrichment in bile-peptone broth (47). Using this method 4% of patients with diarrhea in Bangladesh have P. shigelloides recovered as the sole bacterial pathogen (67). Such a high rate is, however, clearly location-dependent.
Epidemiology
Asymptomatic stool carriage in adults is rare and P. shigelloides is not considered to be part of the normal human gastrointestinal flora. It has been recovered from both fresh and salt water, and in aquatic invertebrates from coastal ecosystems (41). Although more commonly reported from tropical and subtropical environments, P. shigelloides may also be isolated from cold fresh water sources (33). Infection has been associated with the ingestion of seafood (24, 28, 29, 36) or untreated water (29), travel, especially to Mexico, Central America and Southeast Asia (24, 29, 52), and trauma involving either water exposure (12, 13) or fish handling (20). Some 9% of adults presenting to an emergency department in Hong Kong with acute bacterial gastroenteritis had P. shigelloides identified from fecal samples (9). Several large common-source outbreaks of diarrheal illness have been associated with food or water contaminated with P. shigelloides (58, 59). Neonatal infection is thought to follow perinatal exposure; some mothers of infected neonates have been shown to have infection or genital colonization with P. shigelloides, while others had recently consumed uncooked seafood (3, 34, 38, 63). P. shigelloides can infect or colonize a wide variety of animals that may serve as vehicles of transmission to humans, including fish, shell fish, newts, snakes, vultures, cattle, pigs, poultry, dogs and cats (6). Dual infection with P. shigelloides and other microorganisms associated with aquatic ecosystems, such as Aeromonas spp., Vibrio vulnificus, Shewanella putrefaciens, and Edwardsiella tarda also indicate that water is the environmental niche for P. shigelloides (7, 13, 35).
Clinical Manifestations
P. shigelloides has been implicated as the causative agent of both gastrointestinal and extra-intestinal infections. Gastroenteritis is the most common clinical manifestation, and is associated with either watery or bloody diarrhea (6, 24, 28, 29, 36, 43, 65). Pathogenic mechanisms are largely unknown (23), although recent in vitro experiments provide the first definitive evidence of the invasive potential of P. shigelloides (57). Disease typically occurs 2-5 days after consuming untreated water or infected seafood (24, 29), and resolves slowly over a mean duration of about 11 days (24). In one series 76% and 36% of patients were symptomatic for more than two and four weeks respectively (29). Symptoms vary, but may include abdominal pain or cramps (72-100%), nausea and/or vomiting (32-40%), headache and dehydration (32%), and fever (18-51%) (24, 29, 65). Vomiting was a predominant feature (71%) among a series of children with P. shigelloides-associated diarrhea in Bangladesh (31). Although bacteremia has been reported in association with intestinal infection, this is uncommon (14, 28, 40, 43, 45, 50, 65). Approximately 80% of patients with P. shigelloides bacteremia have been immunocompromized either by their age (i.e. neonates), hyposplenism, leukemia, or liver disease (12, 14, 16, 18, 22, 27, 34, 40, 50). Meningitis is virtually restricted to infants (3, 15, 17, 44, 55), although, at least one case of meningitis has been reported in an adult (25). Meningoencephalitis is also reported (56). Other types of infection, often accompanied by bacteremia, are not common, and include biliary tract pathology (10, 32, 35), small bowel overgrowth syndrome (46), endophthalmitis (13, 38), septic arthritis (22, 28), cellulitis with or without compartment syndrome (18, 21, 39) infected pleural effusion (27), pyometria (62), osteomyelitis (28) and peritonitis associated with continuous ambulatory peritoneal dialysis (66).
SUSCEPTIBILITY IN VITRO AND IN VIVO
The results of seven in vitro studies are summarized in Table 1. P. shigelloides is usually susceptible to chloramphenicol, trimethoprim-sulphamethoxazole, the quinolones, cephalosporins, aztreonam and imipenem (4, 6, 11, 24, 26, 30, 48, 53, 60, 61, 65, 67). Tetracycline and aminoglycoside susceptibility is variable. In seven studies the proportion of strains susceptible to tetracycline has ranged from 39% to 100%, median 89% (24, 26, 30, 48, 53, 60, 66). For gentamicin, between 50% and 100% of strains are susceptible (11, 24,26, 30, 48, 53, 60, 66), for tobramycin 36% to 97% (11, 30, 53), for amikacin between 54% and 100% (11, 30, 53, 60) and for netilmicin 94% to 100% (30, 53, 60). Activity of the combination agent trimethoprim-sulphamethoxazole is essentially due to the trimethoprim component alone (24, 30, 49). Production of a β-lactamase which confers resistance to penicillin, ampicillin, amoxicillin, carbenicillin, ticarcillin and piperacillin is essentially invariable (5, 6, 11, 24, 30, 49). The addition of a β-lactamase inhibitor, e.g. clavulanate, sulbactam or tazobactam, restores susceptibility to agents such as amoxicillin, ampicillin and piperacillin respectively (11).
P. shigelloides has been observed to have pronounced inoculum effects in susceptibility testing with cephalosporins using microdilution methods (54, 64). This phenomenon appears to be due to formation of extensive filaments rather than the cumulative activity of β-lactamases at higher inocula (64).
ANTIMICROBIAL THERAPY
Patients with P. shigelloides diarrhea have improvement or resolution of their symptoms after taking an antimicrobial agent to which the strain is susceptible (6, 24, 29, 40,49). Norfloxacin or trimethoprim is recommended for gastrointestinal infection, however, it appears that a large proportion of infections are self-limiting (65). Some 87% of children with P. shigelloides-associated diarrhea in one series were successfully treated with oral rehydration solution alone (31). Ampicillin should not be used to treat P. shigelloides infection because this microorganism produces β-lactamase.
Antimicrobial therapy, with local debridement if necessary, is required for a successful outcome in extraintestinal disease. If treatment with a cephalosporin, with or without an aminoglycoside, is ineffective, ciprofloxacin can be used. Ciprofloxacin brought about prompt lysis of fever in an infected bone marrow transplant patient who had failed to respond to combination therapy with amikacin and ceftazidime (34).
Although neonatal infection with P. shigelloides has a 50% mortality, most infants who survive do so without sequelae. In one review of 10 cases of neonatal septicemia and meningitis only one of 5 survivors suffered sequelae (20). This infant developed extensive multiocular brain cysts, and died when respiratory support was withdrawn (56). Cefotaxime appears to be the treatment of choice for neonatal septicemia and meningitis due to P. shigelloides. Four of ten patients who received cefotaxime alone or as a component of the initial treatment regimen survived, whereas 5 of the remaining 6 who initially received regimens not including cefotaxime (commonly ampicillin plus aminoglycoside) died (20). The addition of an aminoglycoside to which the isolate has been shown to be susceptible, or therapy with ciprofloxacin, could be considered if there is a poor response to cefotaxime alone.
ENDPOINTS FOR MONITORING THERAPY
Gastrointestinal infections respond readily to antibiotic therapy and repeat stool cultures are rarely necessary. For disseminated infections, if fever persists on therapy, repeat cultures from the original site of infection may be indicated.
VACCINES
No vaccines are commercially available.
PREVENTION
The main measure to prevent P. shigelloides infection is to avoid consuming raw or inadequately cooked seafood and potentially contaminated water.
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Tables
Table 1. In Vitro Susceptibilities of Plesiomonas shigelloidesa
Antibiotic |
n |
Range |
MIC50 |
MIC90 |
Breakpointb |
% Susceptible |
Reference |
|---|---|---|---|---|---|---|---|
| Amdinocillin | 4 | £0.5-32 | £0.5 | 1 | 8 | ||
| Amoxicillin | 29 | 0.06-³64 | 64 | ³128 | £8 | 7 | 11 |
| Amoxicillin | 14 | 1->32 | >32 | >32 | £8 | 2 | |
| Amoxicillin | 52 | 4-256 | 128 | 256 | £8 | 2 | 53 |
| Amoxicillin-clavulanate | 29 | £0.06/0.03-8/4 | 2/1 | 4/2 | £8/4 | 100 | 11 |
| Ampicillin | 17 | 2-32 | 8 | 16 | £8 | 48 | |
| Ampicillin | 72 | 32-³256 | 128 | 256 | £8 | 0 | 30 |
| Ampicillin | 29 | 0.25-³128 | ³128 | ³128 | £8 | 3 | 11 |
| Ampicillin | 4 | 8-32 | 8 | 8 | £8 | 8 | |
| Ampicillin-sulbactam | 29 | 0.25/0.12-4/2 | 1/0.5 | 2/1 | £8/4 | 100 | 11 |
| Azlocillin | 74 | 4-1024 | 1024 | 1024 | 53 | ||
| Benzylpenicillin | 74 | 0.25-64 | 64 | 64 | 53 | ||
| Oxacillin | 52 | 32-128 | 128 | 128 | 53 | ||
| Piperacillin | 72 | 8-³256 | ³256 | ³256 | £16 | 3 | 30 |
| Piperacillin | 29 | £0.06-³64 | 64 | ³128 | £16 | 7 | 11 |
| Piperacillin | 74 | 4-512 | 512 | 512 | £16 | 1 | 53 |
| Piperacillin-tazobactam | 29 | £0.06/0.0075-1/0.125 | 0.25/0.03 | 1/0.125 | £16/4 | 100 | 11 |
| Ticarcillin | 72 | 64-³128 | ³128 | ³128 | £16 | 0 | 30 |
| Ticarcillin | 29 | 0.5-³128 | ³128 | ³128 | £16 | 4 | 11 |
| Ticarcillin | 74 | 16-512 | 512 | 512 | £16 | 1 | 53 |
| Ticarcillin-clavulanate | 29 | 0.5/2-4/2 | 1/2 | 2/2 | £16/2 | 100 | 11 |
| Mezlocillin | 29 | 0.125-³128 | ³128 | ³128 | £16 | 14 | 11 |
| Mezlocillin | 74 | 0.13-512 | 512 | 512 | £16 | 1 | 53 |
| Carbenicillin | 72 | 128-³512 | 256 | 512 | £16 | 0 | 30 |
| Cefaclor | 14 | 0.5-4 | 1 | 1 | £8 | 100 | 2 |
| Cefaclor | 52 | 0.13-16 | 2 | 8 | £8 | 96 | 53 |
| Cefamandole | 72 | £1-4 | £1 | £1 | £8 | 100 | 30 |
| Cefamandole | 29 | £0.06-0.5 | £0.06 | 0.25 | £8 | 100 | 11 |
| Cefazolin | 72 | £1-8 | £1 | £1 | £8 | 100 | 30 |
| Cefazolin | 74 | 1-4 | 2 | 2 | £8 | 100 | 53 |
| Cefdinir | 52 | 0.03-2 | 1 | 2 | £1 | 81 | 53 |
| Cefepime | 52 | 0.03-32 | 16 | 32 | £8 | 46 | 53 |
| Cefetamet | 14 | £0.06-0.12 | £0.06 | 0.12 | 2 | ||
| Cefetamet | 52 | 0.03-4 | 2 | 4 | £4 | 100 | 53 |
| Cefixime | 52 | 0.03-4 | 1 | 2 | £1 | 62 | 53 |
| Cefoperazone | 72 | £1-8 | £1 | £1 | £16 | 100 | 30 |
| Cefoperazone | 29 | £0.06-8 | 1 | 4 | £16 | 100 | 11 |
| Cefoperazone | 52 | 1-128 | 32 | 64 | £16 | 44 | 53 |
| Cefoperazone-sulbactam | 29 | £0.06/0.03-0.5/0.25 | 0.125/0.06 | 0.25/0.125 | £16/8 | 100 | 11 |
| Cefotaxime | 17 | £0.063-0.125 | £0.063 | £0.063 | £8 | 100 | 48 |
| Cefotaxime | 72 | £8 | £8 | £8 | £8 | 100 | 30 |
| Cefotaxime | 29 | £0.06-4 | £0.06 | £0.06 | £8 | 100 | 11 |
| Cefotaxime | 52 | 0.03-8 | 1 | 2 | £8 | 100 | 53 |
| Cefoxitin | 72 | £4 | £4 | £4 | £8 | 100 | 30 |
| Cefoxitin | 29 | 1-4 | 2 | 4 | £8 | 100 | 11 |
| Cefoxitin | 74 | 2-16 | 4 | 8 | £8 | 93 | 53 |
| Cefpodoxime | 52 | 0.03-4 | 2 | 4 | £2 | 88 | 53 |
| Ceftazidime | 72 | £1 | £1 | £1 | £8 | 100 | 30 |
| Ceftazidime | 29 | £0.06-1 | £0.06 | £0.06 | £8 | 100 | 11 |
| Ceftazidime | 52 | 0.03-64 | 16 | 32 | £8 | 19 | 53 |
| Ceftriaxone | 72 | £1 | £1 | £1 | £8 | 100 | 30 |
| Ceftriaxone | 29 | £0.06 | £0.06 | £0.06 | £8 | 100 | 11 |
| Ceftriaxone | 52 | 0.03-1 | 0.25 | 0.5 | £8 | 100 | 53 |
| Cefuroxime | 29 | £0.06-0.125 | £0.06 | £0.06 | £8 | 100 | 11 |
| Cefuroxime | 52 | 0.03-4 | 2 | 4 | £8 | 100 | 53 |
| Cephalexin | 14 | 2-16 | 4 | 8 | 2 | ||
| Cephalothin | 72 | £8 | £8 | £8 | £8 | 100 | 30 |
| Cephalothin | 29 | 0.5-2 | 1 | 2 | £8 | 100 | 11 |
| Loracarbef | 52 | 0.25-16 | 8 | 8 | £8 | 90 | 53 |
| Aztreonam | 29 | £0.06 | £0.06 | £0.06 | £8 | 100 | 11 |
| Aztreonam | 52 | 0.03-32 | 8 | 16 | £8 | 62 | 53 |
| Imipenem | 29 | £0.06-0.25 | £0.06 | 0.125 | £4 | 100 | 11 |
| Imipenem | 74 | 0.03-0.25 | 0.13 | 0.25 | £4 | 100 | 53 |
| Meropenem | 74 | 0.03-0.25 | 0.03 | 0.13 | £4 | 100 | 53 |
| Chloramphenicol | 17 | 0.25-8 | 0.5 | 1 | £8 | 100 | 48 |
| Chloramphenicol | 72 | £4 | £4 | £4 | £8 | 100 | 30 |
| Chloramphenicol | 74 | 0.25-1 | 0.5 | 0.5 | £8 | 100 | 53 |
| Teicoplanin | 74 | 64-256 | 256 | 256 | 53 | ||
| Vancomycin | 74 | 16-128 | 128 | 128 | 53 | ||
| Ciprofloxacin | 17 | £0.063 | £0.063 | £0.063 | £1 | 100 | 48 |
| Ciprofloxacin | 72 | £1 | £1 | £1 | £1 | 100 | 30 |
| Ciprofloxacin | 29 | £0.06 | £0.06 | £0.06 | £1 | 100 | 11 |
| Ciprofloxacin | <19 | <0.001-0.015 | 0.004 | 0.008 | £1 | 100 | 4 |
| Ciprofloxacin | 13 | £0.06 | £0.06 | £0.06 | £1 | 100 | 26 |
| Ciprofloxacin | 74 | 0.01-0.25 | 0.01 | 0.01 | £1 | 100 | 53 |
| Enoxacin | 17 | £0.063-0.25 | £0.063 | 0.125 | £2 | 100 | 48 |
| Enoxacin | 4 | £0.5 | £0.5 | £0.5 | £2 | 100 | 8 |
| Enoxacin | <19 | 0.03-0.125 | 0.06 | 0.125 | £2 | 100 | 4 |
| Enoxacin | 74 | 0.01-8 | 0.03 | 0.03 | £2 | 99 | 53 |
| Fleroxacin | 74 | 0.01-4 | 0.01 | 0.03 | £2 | 99 | 53 |
| Norfloxacin | 17 | £0.063-0.125 | £0.063 | £0.063 | 48 | ||
| Norfloxacin | 72 | £0.1-1 | £0.1 | £0.1 | 30 | ||
| Norfloxacin | 4 | £0.5 | £0.5 | £0.5 | 8 | ||
| Norfloxacin | <19 | <0.015-0.06 | 0.03 | 0.06 | 4 | ||
| Norfloxacin | 74 | 0.03-2 | 0.03 | 0.03 | £4 | 100 | 53 |
| Ofloxacin | <19 | 0.008-0.03 | 0.015 | 0.015 | £2 | 100 | 4 |
| Ofloxacin | 74 | 0.01-1 | 0.01 | 0.01 | £2 | 100 | 53 |
| Pefloxacin | <19 | <0.015-0.06 | 0.015 | 0.06 | 4 | ||
| Pefloxacin | 74 | 0.01-8 | 0.01 | 0.01 | 53 | ||
| Sparfloxacin | 74 | 0.01-0.25 | 0.01 | 0.01 | 53 | ||
| Pipemidic acid | <19 | 0.125-0.5 | 0.125 | 0.25 | 4 | ||
| Pipemidic acid | 74 | 0.5-64 | 1 | 1 | 53 | ||
| Azithromycin | 74 | 0.06-4 | 0.5 | 1 | 53 | ||
| Clarithromycin | 74 | 2-64 | 16 | 32 | 53 | ||
| Erythromycin | 72 | 4-32 | 16 | 16 | £0.5 | 0 | 30 |
| Erythromycin | 4 | 16-32 | 32 | 32 | £0.5 | 0 | 8 |
| Erythromycin | 13 | 0.5-14 | 1 | 4 | £0.5 | 26 | |
| Erthromycin | 74 | 1-32 | 8 | 32 | £0.5 | 0 | 53 |
| Roxithromycin | 74 | 2-64 | 16 | 64 | 53 | ||
| Clindamycin | 74 | 4-64 | 32 | 64 | 53 | ||
| Lincomycin | 74 | 32-64 | 64 | 64 | 53 | ||
| Furazolidone | 4 | £0.5 | £0.5 | £0.5 | 8 | ||
| Amikacin | 72 | 8-64 | 16 | 32 | £16 | 54 | 30 |
| Amikacin | 29 | £0.06-16 | 0.25 | 8 | £16 | 100 | 11 |
| Amikacin | 74 | 1-64 | 16 | 32 | £16 | 81 | 53 |
| Gentamicin | 17 | 2-8 | 4 | 8 | £4 | 48 | |
| Gentamicin | 72 | 4-16 | 4 | 6 | £8 | 57 | 30 |
| Gentamicin | 29 | 1-8 | 4 | 8 | £4 | 86 | 11 |
| Gentamicin | 13 | 2-12 | 3 | 10 | £4 | 26 | |
| Gentamicin | 74 | 0.5-8 | 2 | 4 | £4 | 95 | 53 |
| Tobramycin | 72 | 4-8 | 4 | 6 | £4 | 36 | 30 |
| Tobramycin | 29 | £0.06-8 | £0.06 | 1 | £4 | 97 | 11 |
| Tobramycin | 74 | 0.5-8 | 2 | 4 | £4 | 93 | 53 |
| Kanamycin | 13 | 0.4-10 | 0.6 | 8 | £16 | 100 | 26 |
| Kanamycin | 74 | 2-32 | 8 | 32 | £16 | 88 | 53 |
| Neomycin | 74 | 1-16 | 4 | 8 | 53 | ||
| Netilmicin | 72 | 2-4 | 4 | 4 | £8 | 100 | 30 |
| Netilmicin | 74 | 0.5-16 | 2 | 4 | £8 | 99 | 53 |
| Streptomycin | 74 | 4-64 | 16 | 32 | 53 | ||
| Spectinomycin | 74 | 2-32 | 16 | 32 | 53 | ||
| Apramycin | 52 | 4-128 | 32 | 64 | 53 | ||
| Ribostamycin | 74 | 1-64 | 16 | 32 | 53 | ||
| Lividomycin A | 74 | 4-128 | 32 | 64 | 53 | ||
| Nalidixic acid | 17 | 0.25-2 | 0.5 | 0.5 | 48 | ||
| Nalidixic acid | <19 | 0.5-2 | 1 | 2 | 4 | ||
| Doxycycline | 4 | £0.5 | £0.5 | £0.5 | £4 | 100 | 8 |
| Doxycycline | 74 | 0.06-2 | 0.25 | 0.25 | £4 | 100 | 53 |
| Tetracycline | 17 | 0.25-2 | 0.5 | 0.5 | £4 | 100 | 48 |
| Tetracycline | 72 | £1-64 | ³1 | 32 | £4 | 68 | 30 |
| Tetracycline | 13 | 0.25-2.4 | 0.5 | 1 | £4 | 100 | 26 |
| Tetracycline | 74 | 0.13-8 | 0.25 | 0.5 | £4 | 99 | 53 |
| Minocycline | 74 | 0.03-0.5 | 0.13 | 0.25 | £4 | 100 | 53 |
| Trimethoprim-sulphamethoxazolec | 17 | £0.063-0.125 | 0.125 | 0.125 | £2/38 | 100 | 48 |
| Trimethoprim-sulphamethoxazole | 72 | £0.1-0.5 | £0.1 | 0.5 | £2/38 | 100 | 30 |
| Trimethoprim-sulphamethoxazole | 4 | 0.05 | 0.05 | 0.05 | £2/38 | 100 | 8 |
| Trimethoprim-sulphamethoxazole | 74 | 1-256 | 2 | 16 | £2/38 | 53 | 53 |
| Trimethoprim | 17 | 0.25-4 | 1 | 4 | 48 | ||
| Trimethoprim | 72 | £1 | £1 | £1 | £8 | 100 | 30 |
| Trimethoprim | 4 | £0.5-2 | £0.5 | £0.5 | 8 | ||
| Trimethoprim | 74 | 0.13-64 | 1 | 8 | £8 | 93 | 53 |
| Sulfisoxazole | 72 | £32-³512 | 32 | 256 | 30 | ||
| Sulphamethoxazole | 17 | 4.75-19 | 9.5 | 19 | 48 | ||
| Sulphamethoxazole | 74 | 16-1024 | 1024 | 1024 | 53 | ||
| Nitrofurantoin | 74 | 2-64 | 8 | 8 | £32 | 99 | 53 |
| Rifampicin | 74 | 0.25-64 | 4 | 8 | 53 | ||
| Bicozamycin | 4 | 16 | 16 | 16 | 8 | ||
| Telithromycin | 11 | 4-8 | 4 | 4 | 19 | ||
| Fosfomycin | 74 | 0.5-256 | 32 | 64 | £64 | 92 | 53 |
| Fusidic acid | 74 | 4-64 | 64 | 64 | 53 | ||
| Dalfopristin | 74 | 4-128 | 32 | 64 | 53 | ||
| Quinupristin | 74 | 64-128 | 128 | 128 | 53 | ||
| Dalfopristin/quinupristin | 74 | 4-64 | 32 | 32 | 53 |
a Modified from (2, 4, 8, 11, 26, 30, 48, 53).
b Current CLSI interpretive standards for susceptibility of Enterobacteriaceae (µg/ml) (42)
c Trimethoprim-sulphamethoxazole tested in a ratio of 1:19. The concentration refers to the trimethoprim component.