Biomedical subjects
Publications and source records attributed to A M Carnahan.
Campylobacter upsaliensis was isolated from the blood of a 60-year-old female with hairy cell leukemia. This spiral-shaped organism was detected in the aerobic BacT/Alert bottle (Organon Teknika, Durham, N.C.) by acridine orange staining and was recovered only on chocolate agar in a microaerophilic atmosphere at 35 degrees C.
Vibrio hollisae was recovered from the stool culture of a 40-year-old female hospitalized for severe abdominal cramping, vomiting, fever, and watery diarrhea. She had consumed two dozen raw oysters 5 days prior. There was only a single colony on thiosulfate-citrate-bile salts-sucrose-agar, and definitive identification required conventional test media with 1% NaCl.
There are currently eight proposed or validated Aeromonas spp. of which five have been implicated in human disease: A. hydrophila, A. sobria, A. caviae, A. veronii, and A. schubertii. Recent studies have extended the geographic distribution and source of isolation of the newer species and resulted in the possibility of two new species, A. jandaei and A. trota, from diarrheal, wound, blood and environmental sources.
A small subset (n = 18) of highly discriminatory tests was derived from the feature frequency of 50 tests used in the study of 167 predominantly clinical Aeromonas strains. Seven of these eighteen tests were used to construct a flexible, dichotomous key, Aerokey II, for identifying clinical aerontonads: esculin hydrolysis, gas from glucose, acid from arabinose, indole production, acid from sucrose, Voges-Proskauer reaction, and resistance to cephalothin (30 micrograms). This schema was initially evaluated in a single-blind trial of 60 well-characterized clinical Aeromonas hydrophila (n = 21), A. caviae (n = 19), and A. veronii bv. sobria (n = 20) strains from an independent laboratory. Of the 60 strains tested, 58 (97%) were accurately identified to the species level. Aerokey II was further evaluated with 18 additional American Type Culture Collection and reference strains representing the more recently proposed taxa A. veronii bv. veronii, A. schubertii, A. jandaei, and A. trota and accurately identified all of these strains.
Exudate removed from an infection that developed below the left eye of a 10-year-old male following a previously inflicted wound after aquatic exposure was cultured and revealed two different Aeromonas spp. Further characterization showed that one strain was phenotypically identical to Aeromonas veronii, while the other strain was confirmed by DNA hybridization analysis to be Aeromonas jandaei sp. nov. This is the first report of these more recently described aeromonads, thus far rarely reported from clinical disease, occurring simultaneously in a human infection.
Previous DNA hybridization studies established 12 Aeromonas genospecies, from which nine phenotypic species have been proposed: Aeromonas hydrophila, A. sobria, A. caviae, A. media, A. veronii, A. schubertii, A. salmonicida, A. eucrenophila, and A. jandaei. We have delineated a new Aeromonas genospecies, A. trota, on the basis of 13 strains isolated primarily from fecal specimens from southern and southeastern Asia. All strains were highly related to the proposed type strain, AH2 (ATCC 49657T): 51 to 100% (60 degrees C) and 49 to 99% (75 degrees C), with 0.2 to 2.2 divergence. AH2 was only 16 to 41% (60 degrees C) related to all other Aeromonas type strains and DNA group definition strains. The unique profile of A. trota includes negative reactions for esculin hydrolysis, arabinose fermentation, and the Voges-Proskauer test, positive reactions for cellobiose fermentation, lysine decarboxylation, and citrate utilization, and susceptibility to ampicillin, as determined by the broth microdilution MIC method and the Bauer-Kirby disk diffusion method (10 micrograms). Nine of the A. trota strains were from a single study of 165 geographically diverse aeromonads. This finding questions the efficacy of screening fecal specimens for Aeromonas spp. with ampicillin-containing media and suggests a previously unrecognized prevalence of this new species.
Recent studies have resulted in the proposal of a new species, Aeromonas schubertii (mannitol, sucrose, and indole negative), formerly termed Enteric Group 501, on the basis of the study of seven strains isolated from the southeastern and southwestern United States and Puerto Rico. We have isolated two phenotypically similar A. schubertii strains from infected human wounds sustained in the Chesapeake Bay area. Their identification was confirmed by DNA-DNA hybridization to the Centers for Disease Control definition strain 2446-81 (ATCC 43700) for group 12. The strains were further examined for the presence of virulence-associated markers: hemolysin, hemagglutinins, cytotoxin production, agglutination in acriflavine, resistance to normal human serum, and autoagglutination phenotype. Both strains were positive for hemolysin by the plate assay, cytotoxin production at 1:10, and DNase and protease. They were resistant to human serum and negative for acriflavine agglutination, and only one of the strains was autoagglutination positive. Both strains were negative for cell-free hemolysin, hemagglutinins, pectinase, and chitinase. These isolations of A. schubertii further extend its previously described geographic distribution and reinforce its role as a primary causative agent of cellulitis with possible increased antimicrobial resistance.
Twenty clinical strains each of Aeromonas hydrophila, Aeromonas caviae, and Aeromonas sobria were evaluated for their abilities to oxidize one or more of 95 carbon sources on a GN Microplate (BIOLOG, Hayward, Calif.). Nine substrates yielded good, discriminatory values for the three species tested. The panel appears to be useful for the species identification of Aeromonas isolates originating from human material.
An enzymatic characterization of 16 strains of Aeromonas species including A. hydrophila (7), A. sobria (5), and A. caviae (4) was carried out using API Peptidase (strips numbered 1, 2, 3, 4, 5, and 6); API Esterase and API "Osidase" test strips. A total of 89 substrates was used in the assay and included 59 arylamides (aminopeptides), 10 esters, and 20 carbohydrates. All three species were remarkably uniform in their reactivities. Nineteen (32%) of the arylamide substrates used were hydrolyzed by all three species. Very strong arylamidase activity was displayed by all three species for L-lysine, L-hydroxyproline, L-arginine, L-alanine, L-proline, and L-leucyl-L-alanine. Esterase activity was strongest against caproate (C6), caprylate (C8), nonanoate (C9), and caprate (C10) substrates. Only a limited number of carbohydrate substrates were hydrolyzed; strong N-acetyl-beta-D-glucosaminidase activity was given by all strains. Both A. hydrophila and A. caviae gave strong beta-D-glucosidase reactivities, while A. sobria appeared to be negative for this enzyme. The results of our preliminary study show that some of the enzymes examined may be useful in the identification and differentiation of these species. The API enzyme assays yielded rapid (4 hr) results. The assays were easy to perform, relatively inexpensive and reproducible. The importance of replicate testing and the inclusion of uninoculated (buffer only) controls as part of the assay is emphasized.
A total of 166 isolates of Aeromonas, representing diverse geographical regions and originating from various sources, were evaluated for the ability to produce elastase by using a bilayer elastin agar medium (BEAM) plate assay. The degree of elastase activity of individual strains was roughly assessed by measuring the clear area beneath or peripheral to the colony and recorded as 1+, 2+, or 3+. Of the 166 aeromonads tested, 53 (32%) were found to produce elastase, of which 26 (49%) were 3+, 21 (40%) were 2+, and 6 (11%) were 1+. All but one A. hydrophila (n = 45) were observed to produce elastase (98%). One of three A. schubertii strains as well as one isolate of Aeromonas group 501 were elastase positive. All 3+ elastolytic activity was associated with A. hydrophila only. Elastase activity was not detected even after prolonged incubation with A. veronii biogroup sobria (n = 26), A. caviae (n = 57), A. veronii biogroup veronii (n = 4), A. media (n = 1), and A. eucrenophila (n = 1). In addition to its value as a reliable indicator of elastase production for eventual use in virulence assays, we have found that the detection of elastase using the BEAM plate serves as a very useful phenotypic marker for the major, clinically important Aeromonas spp.
From 1996 to 1999, 17 culture-documented systemic infections due to novel, atypical strains of Chryseobacterium meningosepticum occurred in two newborns and 15 immunocompromised patients in a medical center in Taiwan. All clinical isolates, which were initially misidentified as Aeromonas salmonicida by an automated bacterial identification system, were resistant to a number of antimicrobial agents. The isolates were characterized as atypical strains of C. meningosepticum by complete biochemical investigation, 16S rRNA gene sequence analysis, cellular fatty acid analysis, and random amplified polymorphic DNA fingerprinting (RAPD). This is the first report of a cluster of atypically variant strains of C. meningosepticum, which may be an emerging pathogen in newborns and the immunocompromised.