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SUMMARYAfter many years in the family Vibrionaceae, the genus Plesiomonas, represented by a single species, P. shigelloides, currently resides in the family Enterobacteriaceae, although its most appropriate phylogenetic position may yet to be determined. Common environmental reservoirs for plesiomonads include freshwater ecosystems and estuaries and inhabitants of these aquatic environs. Long suspected as being an etiologic agent of bacterial gastroenteritis, convincing evidence supporting this conclusion has accumulated over the past 2 decades in the form of a series of foodborne outbreaks solely or partially attributable to P. shigelloides. The prevalence of P. shigelloidesenteritis varies considerably, with higher rates reported from Southeast Asia and Africa and lower numbers from North America and Europe. Reasons for these differences may include hygiene conditions, dietary habits, regional occupations, or other unknown factors. Other human illnesses caused by P. shigelloidesinclude septicemia and central nervous system disease, eye infections, and a variety of miscellaneous ailments. For years, recognizable virulence factors potentially associated with P. shigelloidespathogenicity were lacking; however, several good candidates now have been reported, including a cytotoxic hemolysin, iron acquisition systems, and lipopolysaccharide. While P. shigelloidesis easy to identify biochemically, it is often overlooked in stool samples due to its smaller colony size or relatively low prevalence in gastrointestinal samples. However, one FDA-approved PCR-based culture-independent diagnostic test system to detect multiple enteropathogens (FilmArray) includes P. shigelloideson its panel. Plesiomonads produce ß-lactamases but are typically susceptible to many first-line antimicrobial agents, including quinolones and carbapenems.

In California, both the number of Salmonella enteritidis (SE) cases and the proportion of Salmonella cases due to the SE organism have increased markedly. SE cases increased from 594 in [...]

ABSTRACTA collection of 68 Hafniastrains previously identified to the species level by 16S rRNA gene sequencing were investigated for simple phenotypic properties that could aid in their recognition in the clinical laboratory. Four tests, including malonate utilization, fermentation of salicin and d-arabinose, and expression of ß-glucosidase activity, correctly assigned each strain to either Hafnia alveior H. paralvei. Antibiotic susceptibility profiles were generated for 35 H. alveiand H. paralveiisolates using Etest strips for 24 antibiotics. All strains were susceptible to aminoglycosides, quinolones, carbapenems, and monobactams. Most of the Hafniaisolates had a colistin MIC of =2 µg/ml. Sequencing of an internal ampCgene fragment allowed genotypic differentiation of the two Hafniaspecies. Approximately 70% of the hafniae tested additionally produced a cytolytic toxin active on Vero cells which may play a role in gastroenteritis.

SUMMARYOver the past decade, the genus Aeromonashas undergone a number of significant changes of practical importance to clinical microbiologists and scientists alike. In parallel with the molecular revolution in microbiology, several new species have been identified on a phylogenetic basis, and the genome of the type species, A. hydrophilaATCC 7966, has been sequenced. In addition to established disease associations, Aeromonashas been shown to be a significant cause of infections associated with natural disasters (hurricanes, tsunamis, and earthquakes) and has been linked to emerging or new illnesses, including near-drowning events, prostatitis, and hemolytic-uremic syndrome. Despite these achievements, issues still remain regarding the role that Aeromonasplays in bacterial gastroenteritis, the extent to which species identification should be attempted in the clinical laboratory, and laboratory reporting of test results from contaminated body sites containing aeromonads. This article provides an extensive review of these topics, in addition to others, such as taxonomic issues, microbial pathogenicity, and antimicrobial resistance markers.

ABSTRACTA collection of 52 strains belonging to the Hafnia alveicomplex were subjected to molecular (16S rRNA gene sequencing) and biochemical analysis. Based upon 16S rRNA gene sequencing results, two genetic groups were identified which correspond with previously recognized DNA hybridization group 1 (ATCC 13337Tand ATCC 29926; n= 23) and DNA hybridization group 2 (ATCC 29927; n= 29). Of 46 biochemical tests used to characterize hafniae, 19 reactions (41%) yielded variable results. Of these 19 tests, 6 were determined to have discriminatory value in the separation of DNA groups 1 and 2, with malonate utilization found to be the most differential test. Test results of malonate utilization alone correctly assigned 90% of Hafniaisolates to their correct DNA group.

ABSTRACTCampylobacter curvusis a rarely encountered Campylobacterspecies in human, animal, and environmental samples. During the course of two investigations, one involving a search for possible bacterial agents causing bloody gastroenteritis and a second concerning a small outbreak of Brainerd's diarrhea in northern California, 20 strains of C. curvusor C. curvus-like organisms were isolated by a microfiltration technique and prolonged incubation. The results suggest that C. curvusmay be an underappreciated Campylobacterthat may be involved in sporadic and outbreak cases of bloody or chronic diarrhea in humans.

Objectives. To identify cases and determine risk factors for an outbreak of Escherichia coli(E. coli) O157:nonmotile (NM) infections in children attending a summer day care program in California.Methods. The authors conducted a retrospective cohort study; the cohort comprised first and second graders who attended the day care program during the last week in August 1999. Shiga toxin testing and molecular subtyping using pulsed-field gel electrophoresis were performed on isolates. Lake water, lake bottom sediment samples, and waterfowl feces from the lake environs were cultured for E. coliO157.Results. Three cases of Shiga toxin-producing E. coliO157:NM infections with matching pulsed-field gel electrophoresis patterns and four probable cases were found. Children who swallowed more than a mouthful of water had a higher attack rate than those who swallowed less than a mouthful or none at all (43% vs. 10%, relative risk = 4.43, 95% confidence interval 1.12, 17.50).Conclusions. E. coliO157:NM infections were associated with swallowing water from a freshwater lake. Potential sources of contamination include feces from humans, cattle, or deer. This outbreak illustrates the value in screening patients with diarrhea for E. coliO157, submitting isolates to public health laboratories, and using molecular techniques to identify related cases. Outbreaks associated with contaminated freshwater could be averted by prevention and early detection of contamination.

ABSTRACTRecent work describing six named species and two unnamed genomospecies within Citrobacterhas enlarged the genus to 11 species. DNA relatedness and phenotypic tests were used to determine how well these species can be identified. One hundred thirty-six strains were identified to species level by DNA relatedness and then identified phenotypically in a blinded fashion. By using conventional tests, 119 of the 136 strains (88%) were correctly identified to species level. Three additional strains (2%) were identified as citrobacteria but were not identified to species level, and 14 strains (10%) were misidentified as other Citrobacterspecies. Carbon source utilization tests were used to identify 86 of the strains. Eighty-four strains (98%) were correctly identified, and two strains (2%) were misidentified as other Citrobacterspecies. Additional strains of Citrobactergenomospecies 10 and Citrobactergenomospecies 11 were identified, allowing these species to be formally named as Citrobacter gilleniisp. nov. and Citrobacter murliniaesp. nov., respectively.

Abstract.: Wild-type strains of Providencia species were evaluated for their ability to invade HEp-2 monolayers based upon microscopic and semi-quantitative assays. Of 14 P. alcalifaciens strains tested, 3 (17%) were found to be highly invasive, 4 (22%) moderately invasive, and the remaining 61% weakly or noninvasive. HEp-2 invasion results were confirmed by thin-section electron microscopy. Invasive capabilities of P. alcalifaciens were greater at higher MOIs (100 to 1000) than at lower inocula (<10 MOI). No strain of P. stuartii or P. rettgeri tested invaded HEp-2 cells. Quantitative assays of Triton X-100-lysed, HEp-2-invaded cells indicated that between 0.001% and 0.013% of the initial bacterial inoculum was gentamicin resistant. Further testing of select strains on various cell lines indicated the efficiency of invasion was Vero > Y1 > INT-407 > HEp-2. Two isolates recovered from a father and son with prolonged diarrhea after returning from Mexico were found to be identical on the basis of biotype, serotype, and genotype. These results provide additional evidence that some P. alcalifaciens strains cause gastroenteritis.

The antimicrobial resistance of 2,246 strains of Salmonellaisolated from humans in California was determined. Resistance to one or more of the 12 antimicrobial agents tested was found in 32% of the isolates. Salmonella typhimuriumstrains represented 31% of the serotypes isolated; 49% of these strains were resistant. Fifty-one percent of S. heidelberg, 42.5% of S. newport, and 40% of S. saint paulstrains were resistant. Seventy-seven percent of all resistant serotypes were resistant to two or more of the antimicrobial agents tested. R factors were demonstrated in 70% of the multiply resistant strains. Resistance of the Salmonellastrains to one or more of the 12 antimicrobials tested and the frequency of resistance to tetracycline and ampicillin were significantly greater than resistance reported in other studies performed in this country. Chloramphenicol resistance was encountered in 33 (1.5%) of the Salmonellaisolates; 19 of these were S. typhidemonstrating a pattern of resistance to streptomycin, sulfisoxazole, tetracycline, and chloramphenicol and carrying an R factor capable of transferring the complete pattern of resistance.

ABSTRACTFive strains of a newly described Escherichiaspecies, Escherichia albertii, were extensively characterized by conventional biochemical methods and by commercial identification panels. E. albertiiis an indole-negative species that ferments d-mannitol but not d-xylose. Because these strains are not included in the databases of commercial systems at present, they were most often identified as Hafnia, Salmonella, Escherichia coli, or, on one system (MicroScan dried overnight panels), Yersinia ruckeri.

The risk of bacteremia in patients with cirrhosis increases with more advanced Child classification. Escherichia coliis the most frequently implicated organism in these bacteremic episodes. Unusually, E. colican produce a bullous cellulitis or myonecrosis. Two previous cases of E. coliassociated myonecrosis in patients with cirrhosis have been reported. We describe a third case in a cirrhotic patient with E. coliassociated bilateral lower extremity gas gangrene and review the existing literature. In the three patients with cirrhosis and E. colimyonecrosis, no obvious gastrointestinal perforation was found as the source of bacteremia. Intestinal edema due to portal hypertension is thought to have facilitated mucosal microperforations and bacteremia. Awareness of this unusual presentation may facilitate earlier diagnosis.