Fatal myofascial necrosis due to imipenem-resistant Aeromonas hydrophila

A case report of a fulminant Aeromonas hydrophila soft tissue infection in a patient with acute lymphoblastic leukemia harboring a rare translocation

INTRODUCTION

Aeromonads are gram-negative opportunistic bacteria, mainly found in aquatic environments. Hematologic patients are particularly at risk of Aeromonas soft tissue infections and septicemia, especially during chemotherapy-induced neutropenia.

CASE DESCRIPTION

A 46-year-old man was diagnosed with acute lymphoblastic leukemia characterized by the rare t(12;17)(p13;q21)/TAF15-ZNF384 aberration. On day 22 of chemotherapy, he developed febrile neutropenia followed by necrotizing fasciitis in his upper right extremity. Despite appropriate antibiotic therapy and prompt surgical intervention, he died within 36 h after the appearance of a fever. A multi-sensitive Aeromonas hydrophila was isolated from all cultural sites.

DISCUSSION AND CONCLUSIONS

In a previous paper we characterized the patient's aberration with cytogenetic and FISH analysis. Here, we provide details regarding the patient's rapidly progressing infection and underline the importance of maintaining high clinical suspicion of Aeromonas infections in acute leukemia. Given the unusually rapid progression of an infection caused by a rare non-resistant pathogen, and after considering data on the implication of metalloproteinase function in immune system regulation, a correlation between risk of severe infection and TAF15-ZNF384 aberrated acute lymphoblastic leukemia cannot be ruled out.

Multidrug-resistant (MDR) Aeromonas recovered from the metropolitan area of Valencia (Spain): diseases spectrum and prevalence in the environment

Aeromonas infections are rare in Europe and often related to traveller's diarrhoea. A total of 185 Aeromonas isolates from river water, fish and clinical sources, recovered during a 1-year period, were used to investigate the disease spectrum and impact of multidrug-resistant (MDR) strains. They were all identified by biochemical tests and 25% of them were also identified by sequencing of the 16S rRNA gene. The minimum inhibitory concentrations (MICs) of 21 antimicrobials were determined for all isolates by broth microdilution/E-strips methods, and susceptibility was assessed according to the Clinical and Laboratory Standards Institute (CLSI). Strains pathogenicity was determined by using Swiss Webster mice as the animal model. Aeromonas diseases had an incidence of around 20 cases/million inhabitants in the metropolitan area of Valencia (Spain). Acute gastroenteritis in children with no history of travel abroad was the main pathology. These cases were related to A. caviae, A. veronii biovar sobria, A. hydrophila and A. dhakensis. A significant incidence of A. caviae in humans was found, while the other species were equally present in clinical and environmental origins. A. jandaei, A. bestiarum and A. media had mainly an environmental distribution. The prevalence of MDR Aeromonas was maximal in clinical samples, and resistance phenotypes were significantly related to this source. 7.2% of environmental Aeromonas was resistant to at least five drugs; most of them were moderately virulent for mice and, in addition, belonged to clinically significant species. The present study demonstrates a diseases spectrum similar to that reported in tropical countries, and also that pathogenic and heavily MDR Aeromonas are present in environmental reservoirs. MDR Aeromonas from any source analysed were susceptible to aztreonam, netilmicin, cefotaxime, ceftazidime, cefepime and fluoroquinolones.

Pathogenic Aeromonas hydrophila serogroup O:14 and O:81 strains with an S layer

Five autoagglutinating Aeromonas hydrophila isolates recovered from eels and humans were assigned to serogroups O:14 and O:81 of the Sakazaki and Shimada (National Institutes of Health) scheme. They had the following properties in common: positive precipitation after boiling, moderate surface hydrophobicity (salt-aggregation-test value around 1.2), pathogenicity for fish and mice (50% lethal dose, 10(4.61) to 10(7.11)), lipopolysaccharides that contained O-polysaccharide chains of homogeneous chain length, and an external S layer peripheral to the cell wall observed by electron microscopy. A strong cross-reactivity was detected by immunoblotting between the homogeneous O-polysaccharide fraction of O:14 and O:81 strains but not between them and the lipopolysaccharide of A. hydrophila TF7 (O:11 reference strain). Outer membrane fractions of these strains contained a predominant 53- to 54-kDa protein which was glycine extractable under low-pH (pH 2.8) conditions and was identified as the surface array protein. The S-layer proteins of the O:14 and O:81 A. hydrophila strains seemed to be primarily different from those previously purified from strains A. hydrophila TF7 and Aeromonas salmonicida A450 on the basis of colony hybridizations with both the structural genes vapA and ahsA. This is the first report of the presence of an S layer in mesophilic Aeromonas strains not belonging to serogroup O:11.

Population patterns and antimicrobial resistance ofAeromonasin urban playa lakes

Bacteria belonging to the genus Aeromonas are indigenous to aquatic environments. Once regarded as unimportant human pathogens, reports of opportunistic infections caused by these organisms have appeared increasingly in the medical literature. To estimate the potential for human infection by Aeromonas where limited water resources are being used intensively, we studied the spatial and temporal variation and incidence of antimicrobial resistance among environmental isolates of Aeromonas from two urban playa lakes in Lubbock, Texas. Aeromonas population densities varied seasonally, with the highest densities occurring from mid-April to late October. The greatest range of densities was 100-fold, from 2.50 to 255.17 colony-forming units per 0.1 mL of water sample. Densities also varied with water depth, although the variation did not display a consistent pattern. One hundred fifty-one Aeromonas isolates were divided into 10 species or subspecies groups by using the BIOLOG identification system. Nine isolates displayed resistance to co-trimoxazole, tetracycline, and cefuroxime, and none was resistant to more than one of these antimicrobial agents. In summary, the results of this study showed that the densities of Aeromonas peak in the late spring and again in late summer, times when human activity around the playa lakes is also high. Thus, we infer that human exposure to these potential pathogens varies seasonally. Compared to other published studies, the incidence of antimicrobial-resistant Aeromonas is relatively low in urban playa lakes in Lubbock, Texas. Nevertheless, resistant organisms were detected.Key words: Aeromonas, water, playa, antibiotic resistance, population dynamics.

Aeromonas hydrophilia infections after penetrating foot trauma

The bacterium Aeromonas hydrophila is an anaerobic gram-negative bacillus commonly found in natural bodies of water and can cause infection in patients who suffer water-associated trauma or in immunocompromised hosts. The authors present 5 cases of penetrating wound trauma that did not involve any aquatic environment and developed rapidly forming infections. All patients presented with severe pain, cellulitis, ascending lymphangitis, fever, and pain on range of motion of the joint near the traumatic site. Presentation of clinical symptoms mimicked that of a septic joint or of severe streptococcal infection. All patients required surgical incision and drainage, intravenous and oral antibiotics using levofloxacin or bactrim, and local wound care. Results from cultures taken intraoperatively showed only A hydrophilia in every case. Resolution of symptoms occurred rapidly after surgery, and clinical resolution was seen within 72 hours. Each patient healed uneventfully and returned to preinjury status.

In vitro and in vivo activities of fluoroquinolones against Aeromonas hydrophila

Aeromonas hydrophila, an uncommon human pathogen, can cause invasive infections in immunocompromised individuals. As the fluoroquinolones have been shown to be active in vitro against mesophilic aeromonads and clinical experience with the use of fluoroquinolones to treat aeromonads infections is limited, the antimicrobial activities of five selected drugs (ciprofloxacin, gatifloxacin, levofloxacin, lomefloxacin, and moxifloxacin) against A. hydrophila were studied in vitro and in mice. The MICs of the fluoroquinolones (except lomefloxacin), cefotaxime, and minocycline for 90% of 64 clinical isolates of A. hydrophila tested by the agar dilution method were <or=1 microg/ml. With a clinical cefotaxime-resistant strain, Ah 2743, in an in vitro time-kill study, at an inoculum of 7 x 10(5) CFU/ml incubated with fluoroquinolones, cefotaxime, or minocycline at concentrations equal to twice the MICs, the inhibitory effect lasted for less than 6 h and regrowth occurred thereafter. In an animal model with female BALB/c mice intraperitoneally infected with an inoculum of 1.1 x 10(7) CFU of Ah 2743, more mice in the ciprofloxacin-treated group survived (72.2%) than in the cefotaxime-, minocycline-, or cefotaxime-minocycline-treated group (P < 0.00001, log rank test). However, there were similar fatality rates, ranging from 71.4 to 87.5%, among mice treated with any of five fluoroquinolones. With a larger inoculum, 4.9 x 10(7) CFU, mice in the ciprofloxacin-treated group survived longer than those in the minocycline-, cefotaxime-, or cefotaxime-minocycline-treated group (30 h versus 18, 12, and 12 h, respectively [P < 0.002, log rank test]). However, in mice infected with cefotaxime-susceptible Ah 2556, ciprofloxacin was as effective as cefotaxime-minocycline. Thus, our results suggest that ciprofloxacin is at least as effective as cefotaxime-minocycline against murine A. hydrophila infections, which warrants clinical studies to delineate its role in human infections.