Antimicrobial susceptibility of sixty human fecal isolates of Aeromonas species

Composition of the cutaneous bacterial community of a cave amphibian, Proteus anguinus

The European cave salamander Proteus anguinus is a charismatic amphibian endemic to the concealed and inaccessible subterranean waters of the Dinaric Karst. Despite its exceptional conservation importance not much is known about its ecology and interactions with the groundwater microbiome. The cutaneous microbiota of amphibians is an important driver of metabolic capabilities and immunity, and thus a key factor in their wellbeing and survival. We used high-throughput 16S rRNA gene sequencing based on seven variable regions to examine the bacteriome of the skin of five distinct evolutionary lineages of P. anguinus and in their groundwater environment. The skin bacteriomes turned out to be strongly filtered subsamples of the environmental microbial community. The resident microbiota of the analyzed individuals was dominated by five bacterial taxa. Despite an indicated functional redundancy, the cutaneous bacteriome of P. anguinus presumably provides protection against invading microbes by occupying the niche, and thus could serve as an indicator of health status. Besides conservation implications for P. anguinus, our results provide a baseline for future studies on other endangered neotenic salamanders.

[Extraintestinal infection due to Aeromonas spp.: review of 38 cases]

INTRODUCTION

Aeromonas spp. typically cause gastroenteritis, but can occasionally produce extraintestinal infections. The aim of this study was to determine the clinical and microbiological characteristics of extraintestinal infections caused by Aeromonas spp. in our area.

PATIENTS AND METHODS

The clinical histories of patients with extraintestinal infections by Aeromonas spp. diagnosed in Hospital Universitario de Guadalajara (Guadalajara, Spain) from January 1990 to December 2005 were reviewed. Identification and susceptibility testing of the strains were performed by the MicroScan WalkAway-40 automated method (DadeBerhing).

RESULTS

Thirty-eight cases of extraintestinal infections were diagnosed: 18 abdominal infections, 11 skin and soft tissue infections, 3 urinary tract infections, and 3 episodes of bacteremia with no primary focus. The species most frequently found was A. hydrophila (16 cases). Infection occurred most often in patients with underlying diseases (76.3%), including malignancy (34.2%) and diabetes mellitus (21%). Polymicrobial infections were detected in 50% and the etiology was nosocomial in 21%. The mortality rate was 16.2%. Gentamicin, amikacin, cefotaxime and ciprofloxacin had the highest activity against the Aeromonas species isolated.

CONCLUSIONS

Aeromonas spp. as the causative infectious agent should be kept in mind in patients with infections of the biliary system, surgical wounds in the abdomen and posttraumatic cellulitis. Extraintestinal infection is usually polymicrobial, appears most commonly in patients with underlying diseases, and generally has a good prognosis. The most active antibiotics in vitro were gentamicin, amikacin, cefotaxime and ciprofloxacin.

Antimicrobial susceptibility patterns of Aeromonas jandaei, A. schubertii, A. trota, and A. veronii biotype veronii

Fifty-six isolates of four Aeromonas species, which have been documented as causative agents of human infections or isolated from human clinical specimens, were subjected to antimicrobial susceptibility testing using a MicroScan WalkAway conventional (overnight incubation) gram-negative panel. The four species tested and the number of isolates of each were as follows: Aeromonas jandaei, 17; A. schubertii, 12; A. trota, 15; and A. veronii biotype veronii, 12. All isolates of A. trota were susceptible to all antimicrobial agents tested, except cefazolin (20% of isolates were resistant) and cefoxitin (13% of isolates were resistant). All isolates of A. schubertii and A. veronii biotype veronii, as well as 88% of A. jandaei isolates, were resistant to ampicillin. Resistance to ampicillin-sulbactam ranged from 25% of A. schubertii strains to 100% of A. veronii biotype veronii strains. Cefazolin resistance ranged from 17% of A. veronii biotype veronii isolates to 59% of A. jandaei isolates. Imipenem resistance was detected in 65% of A. jandaei strains and 67% of A. veronii biotype veronii strains. A. jandaei displayed resistance to piperacillin and ticarcillin in 53 and 71% of the isolates, respectively. A. veronii biotype veronii strains were 100% susceptible to piperacillin and 100% resistant to ticarcillin. These antibiogram data may be useful in establishing the identification of these four species when members of the genus Aeromonas are isolated from human clinical sources.

Musculoskeletal and soft tissue Aeromonas infection: an environmental disease

During a 4-year period from November 1985 to November 1989, Aeromonas was isolated from wounds and soft tissues with clinical evidence of infection in 28 patients at our institution. Of the 28 patients, 23 (82%) had sustained an acute open or penetrating injury, more than half of which (13 of the 23) were water-related trauma. One patient had Aeromonas osteomyelitis. Five patients had no history of trauma, and three of these five had an underlying chronic disease. Treatment included débridement and antimicrobial agents. Susceptibility testing on 25 isolates from 23 patients showed uniform resistance to ampicillin and considerable resistance to cefazolin sodium (68%), but all isolates were sensitive to gentamicin sulfate, cefuroxime sodium, and the third-generation cephalosporins.

Susceptibilities of motile Aeromonas sp. to antimicrobial agents

Resistance to antimicrobial agents of 106 isolates of motile Aeromonas sp. was characterized. The results indicated that in vitro susceptibilities among the three species of the motile Aeromonas sp. were similar, and only the distribution of susceptibility to cephalothin was different. The percentage of resistance of A. sobria strains was lower than the percentage of the resistant strains of A. hydrophila and A. caviae. All of the isolates were susceptible to kanamycin, nalidixic acid, tobramycin, amikacin, netilmicin, cefuroxime, ceftriaxone, cefoperazone and cefotaxime. Three of the tested strains (two A. hydrophila and one A. caviae) transferred resistance plasmids to the Aeromonas hydrophila recipient.

Treatment of symptomatic enteric aeromonas hydrophila infection with ciprofloxacin

As a part of local sporadic outbreak of Aeromonas hydrophila gastroenteritis, 3 symptomatic patients required hospitalisation. Treatment with ciprofloxacin appeared to accelerate recovery from severe or persistent diarrhoea due to this organism. All the isolates from the outbreak were sensitive to this drug.

In vitro susceptibility of Aeromonas caviae, Aeromonas hydrophila and Aeromonas sobria to fifteen antibacterial agents

In vitro testing of the activity of 15 antibacterial agents against 522 clinical isolates of Aeromonas species demonstrated some species-associated trends. Amoxicillin plus clavulanic acid was effective against approximately 45% of Aeromonas caviae and Aeromonas hydrophila, but all Aeromonas sobria isolates were resistant. Aztreonam, piperacillin and mezlocillin were highly active against all the strains of Aeromonas tested. Ticarcillin was equally effective against Aeromonas caviae and Aeromonas hydrophila, but more than 50% of Aeromonas sobria isolates were resistant. The latter species was more susceptible to cephalosporins than Aeromonas hydrophila and Aeromonas caviae. Chloramphenicol, tetracycline and trimethoprim-sulfamethoxazole were extremely active against all three Aeromonas species, likewise ofloxacin and ciprofloxacin. Aztreonam, third-generation cephalosporins, chloramphenicol and the quinolones can thus be considered for therapy of infections when Aeromonas is implicated.