The role of Aeromonas species in gastrointestinal disease is controversial. The aim of this study was to know the epidemiological distribution of Aeromonas spp. isolated from stool in our health area, determine the existence of diarrhea as a significant symptom, identification of existing species in our environment and association as co-pathogen.
MethodsIt was a retrospective descriptive study of isolates of Aeromonas spp. in feces (2016–2020). The protocol for these isolates included coproculture, identification by MALDI-TOF (Vitek-MS®, BioMerieux) and confirmation by multiplex PCR.
ResultsA total of 366 Aeromonas spp. isolates were analyzed being Aeromonas caviae the most prevalent species (289, 78.7%). A total of 58 (15.8%) co-infections were identified, being more frequent in pediatric age (49;84.5%) (p=0.01) and mostly associated with Campylobacter spp.
DiscussionAeromonas spp. prove to be a gastrointestinal pathogen more frequently associated with co-infections in pediatric age, evidencing its appearance especially with Campylobacter spp.
El papel de las especies de Aeromonas en la enfermedad gastrointestinal es muy controvertido. El objetivo de este estudio fue conocer la distribución epidemiológica de Aeromonas spp. aislada de heces en nuestra área de salud, determinar la existencia de diarrea como síntoma significativo, la identificación de especies existentes en nuestro entorno y la asociación como copatógeno.
MétodosSe trata de un estudio descriptivo retrospectivo de aislados de Aeromonas spp. en heces (2016-2020). El protocolo para estos aislamientos incluía coprocultivo, la identificación por MALDI-TOF (VITEK®MS, bioMérieux) y la confirmación por PCR multiplex.
ResultadosSe analizaron un total de 366 aislados de Aeromonas spp., siendo Aeromonas caviae la especie más prevalente (289; 78,7%). Se identificaron un total de 58 (15,8%) coinfecciones, siendo significativamente más frecuentes en edades pediátricas (49; 84,5%) (p=0,01) y asociadas principalmente con Campylobacter spp.
DiscusiónAeromonas spp. resulta ser un patógeno gastrointestinal que se asocia con mayor frecuencia a coinfecciones en la edad pediátrica, evidenciando su aparición especialmente con Campylobacter spp.
The genus Aeromonas belongs to the Aeromonadaceae family and comprises a group of Gram-negative bacteria widely distributed in aquatic environments, but its great capacity for adaptation also makes Aeromonas species able to colonize terrestrial environments, so these microorganisms can be identified from different sources, such as soils, plants, fruits, vegetables, birds, reptiles, amphibians, among others.1 The genus Aeromonas comprises of two different groups of bacteria. One is non-motile psychrophilic Aeromonas salmonicida and the other group comprising of three mesophilic motile spp. Aeromonas hydrophila, Aeromonas caviae, and Aeromonas sobria.2 Some species of Aeromonas are known to be pathogenic in both mammals and reptiles or fish, particularly in humans, Aeromonads, are known to cause gastroenteritis and extraintestinal diseases such as septicemia, skin, eye, wound and respiratory tract infections.3 It has not always been easy to identify Aeromonas spp. by traditional biochemical tests in clinical microbiology laboratories. Today, thanks to the new technologies used such as mass spectrometry, which is increasingly used because it is faster, simpler and with high precision with respect to traditional methods, make it easier identifying them. Some Aeromonas species are found forming part of the human gastrointestinal microbiota, varying the rates of frequency from 0% to 4% in persons with no disease to 0.8–7.4% in persons with diarrheal illness.4 The prevalence in case of diarrhea in pediatric age is around 4.6%5 and also it has been described as a co-pathogen at 1.9–57.7% in pediatric age.6,7
The objective of this study was to know the epidemiological distribution of Aeromonas spp. in our health area, to determine the most significant symptom associated with Aeromonas, frequency of association as co-pathogen, identification of existing species as well as age of distribution or existence of seasonal association in our environment.
Material and methodsRetrospective descriptive study, through the laboratory information system (SIL), of isolates of Aeromonas spp. in stool between 2016 and 2020 in the Microbiology Department of the University Hospital Marqués de Valdecilla, Santander, that serves a total of 313.040 census population. The protocol for these isolates included inoculated on Yersinia Selective Agar (CIN Agar; BD, Heidelberg, Germany) and incubated at 37°C for 24h. Identification was performed by MALDI-TOF system (Vitek-MS®, BioMerieux) and most of them were confirmed by multiplex PCR developed by Perssons S et al.8 The statistical analysis was performed by Fisher statistical test with SPSS program.
ResultsA total of 366 isolates of Aeromonas spp. were analyzed. It was 1.1% of the total of coprocultures analyzed and 15.8% of all enteropathogens identified in the years under study, behind Campylobacter spp. (57.8%) and Salmonella enterica (25.2%), but at the same time far ahead of other genera such as Yersinia enterocolitica (1.3%) or Shigella spp. (0.5%). A. caviae was the most prevalent species (78.5%), at a large distance from other species such as A. sobria/veronii (9.0%) or A. hydrophila (2.4%). Without taking into account the enteropathogenic Escherichia coli serotypes that are identified at the express request of the clinician.
No significant differences were found in sex distribution (190; 52.0% women) nor in the frequency of infection in adults (>16 years) with respect to pediatric age (185; 50.5%), with a mean age of infection of 34 years (range 0–98 years). Diarrhea was found as the most common referred symptom (162;44.0%), followed by acute gastroenteritis (78; 21.3%). A total of 58 co-infections were identified (15.93%), being significantly more frequent in pediatric ages (49;84.5%) (p=0.05) and mostly associated with Campylobacter spp. (75.9% of the total co-infections and 75.5% in pediatric age). A. caviae (51, 87.9%) was the most frequently isolated species as a copathogen regardless of age.
Antimicrobial sensitivity to the most commonly used antibiotics showed good activity to cotrimoxazole (92.9%), ciprofloxacin (86.1%) and cefepime (98.9%).
The 52.0% of the studied samples were requested from health centers, followed by emergency service for both pediatric 12.6% and adult age 10.9%. The most frequently observed symptom was diarrhea 44.2%, being bloody in 4.6% of cases, followed by acute gastroenteritis in 21.3%.
In the cases accumulated by months, there is a clear increase in the incidence in summer, especially in the month of August (15.8%), being significant this increase for adults (p=0.02) and children (p=0.04) (see Fig. 1).
Discussion
Aeromonas spp. ranks third in terms of incidence of enteropathogenic bacteria in our area of influence, as opposed to other series in the 1990s, possibly due to the fact that in those years it was not yet considered a primary pathogen. But in more recent series this enteropathogen does not appear possibly because it is not included in the molecular syndromic panels of recent massive introduction in clinical diagnostic laboratories.9 It is true that its finding in association with another enteropathogen,7 as well as its known role as part of the usual intestinal microbiota10 or doubts about its possible pathogenicity mechanism,11 relegate it to the identification of classical enteropathogens. Even more in case of isolation of A. caviae in pediatric age where it is not given much attention, although published series show that A. caviae is the most frequently isolated species12 a fact that coincides with our population.
In the present study, Campylobacter spp. showed a significant association with Aeromonas spp. particularly in the younger age group, as other studies in our country.13 Is reported Aeromonas spp. as a part of a polymicrobial infection, which raises the question of whether it is behaving as a nonpathogenic “co-traveler”, perhaps acquired from the same source as the true pathogen, or is interacting with other agents to cause disease. The almost exclusive appearance of the species A. caviae and its lower virulence can indicate its appearance in feces as a colonizer. Pathogens commonly reported in literature to coexist with Aeromonas are rotavirus, Shigella, Campylobacter, and Escherichia coli O157:H7.12,14 This feature in identifying Aeromonas can help the microbiologist and pediatrician be alert to a possible primary enteropathogen.
But the pathogenicity is clear both by its association with diarrhea, as in this and other works and by the identification of virulence genes especially in species such as Aeromonas hydrophila or Aeromonas sobria.15
We can conclude that Aeromonas spp. is an enteropathogen that appears very frequently in the feces of patients with digestive symptoms both in our health area and in other published case series. Circumstance that should be taken into account when deciding to diagnose patients with gastrointestinal pathology with syndromic panels in which Aeromonas spp is not included.
The appearance of Aeromonas spp. in feces of patients at an early age, in many cases, is associated with the appearance of a classic primary copathogen, in our case Campylobacter spp. This finding could alert in the active search by molecular techniques for primary pathogens if they are not isolated by stool culture, especially in those cases that are associated with diarrhea, bloody diarrhea or acute gastroenteritis.
Transparency declarationsAll authors have nothing to declare. This study has not been financially supported by any Diagnostic/Pharmaceutical company.
Ethical approvalNot applicable.
FundingThis study was supported by Plan Nacional de I+D+i 2013–2016, Instituto de Salud Carlos III, Subdirección General de Redes y Centros de Investigación Cooperativa, Ministerio de Economía y Competitividad, Spanish Network for Research in Infectious Diseases (REIPI RD16/0016/0007).
Conflict of interestThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
