A cytotoxin-producing strain of Vibrio cholerae non-O1, non-O139 as a cause of cholera and bacteremia after consumption of raw clams

We report a case of a cholera-like gastroenteritis subsequent with bacteremia in a healthy man following consumption of raw clams. Although we failed to recover the organism from the patient's stool culture, his blood culture was positive for a non-cholera toxin-producing yet cytotoxin-producing non-O1 and non-O139 Vibrio cholerae.

Abiotrophia species as a cause of endophthalmitis following cataract extraction

Microorganisms of the genus Abiotrophia, members of the oral flora, are known as important causes of bacterial endocarditis. In this study, we report two individual cases of acute vitreous infection caused by Abiotrophia adiacens and Abiotrophia defectiva approximately a week after cataract extraction. Abiotrophia isolates were recovered by cultivation of vitreous humor on chocolate agar and identified via conventional and API 20 Strep identification systems. An 83-year-old male patient (A) and an 80-year-old female patient (B) demonstrated almost identical symptoms of infectious endophthalmitis manifested as hypopyon and opaque media. The vision of both patients was reduced to detection of hand motion in the left and the right eyes, respectively. An emergency pars plana core vitrectomy was performed, and intraocular antibiotics were administered to each patient, who presented 8 months apart in two different institutions. Patients A and B were treated with an intravitreal injection of vancomycin-amikacin and vancomycin-ceftazidime, respectively, which resulted in complete recovery.

Comparison of culture and acid-fast bacilli stain to PCR for detection of Mycobacterium tuberculosis in clinical samples

The major drawback in effective use of polymerase chain reaction (PCR) for detecting Mycobacterium tuberculosis (MTB) in clinical samples is the presence of PCR inhibitors and unique cell components of the organism that complicate DNA extraction and subsequent PCR amplification. A PCR assay with a unique multistep DNA extraction method that minimizes these problems was compared in a prospective study to acid-fast bacilli stain (AFBS) and culture for detecting MTB in clinical samples. A total of 254 clinical specimens in two separate studies were processed for MTB by these techniques. While PCR and culture were 100% sensitive and specific, culture required up to 8 weeks of incubation and additional time to perform biochemical testing to identify the isolated micro-organism. Acid-fast bacilli stain had a specificity of about 87% and did not differentiate among Mycobacterial species. In contrast, the results from PCR were available within 48 h and did not require additional testing to attain a final result. Polymerase chain reaction was highly reliable for detection and confirmation and interpretation of positive AFBS results. The assay was easy to perform with a turn around time of about 2 days.

A PCR assay for identification of Enterococcus faecium

Enterococcus faecium has recently emerged as a serious nosocomial pathogen. The prevalence and severity of enterococcal infections, the mortality rate from such infections, and the antibiotic resistance of enterococci are often species dependent. Since conventional biochemical methods fail to differentiate E. faecium from certain newly described enterococcal species, a PCR-based assay was developed for the rapid identification of E. faecium.

Listeria monocytogenes infections: laboratory investigation of an unexpected increase in incidence

Listeria monocytogenes is a facultative intracellular pathogen causing mainly meningitis and septicemia in immunocompromised hosts. From July 1988 through December 1989, 16 patients at The Mount Sinai Hospital were diagnosed as having listeriosis shortly after admission, 14 within a one-year period (July 1988-July 1989). Because this incidence was almost double the incidence in previous years (< 8 annually), an epidemiologic and microbiologic investigation was undertaken to determine a potential route of acquisition of L. monocytogenes. On the basis of plasmid profile, bacteriocin (enterocin) susceptibility pattern, and serotype, no single epidemic strain could be identified. Although direct evidence was lacking, we concluded that our patients may have acquired L. monocytogenes through transient contamination of food.

Aeromonas caviae: ecologic adaptation in the intestinal tract of infants coupled to adherence and enterotoxin production as factors in enteropathogenicity

Aeromonas caviae isolated from stools of diarrheic formula-fed infants and environmental sources produce acetic acid when grown in glucose broth, which is bactericidal (suicide phenomenon). A. caviae grows anaerobically in a minimal medium or under permissive conditions such as the intestinal tract of formula-fed infants. These isolates adhered to HEp-2 cells and produced a cytotoxic and a cytotonic enterotoxin which underscore their enteropathogenicity.

Glucose-mediated catabolite repression of the tricarboxylic acid cycle as an explanation for increased acetic acid production in suicidal Aeromonas strains

Growth in the presence of glucose, even under highly aerobic conditions, significantly reduced the activities of three tricarboxylic acid cycle enzymes, citrate synthetase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase, in suicidal but not nonsuicidal Aeromonas strains. Pyruvate dehydrogenase activity, however, was significantly increased. The activities of all of the enzymes, as well as the glucose-mediated increase in acetic acid production, were shown to be regulated by catabolite repression. The regulator protein is the same one which regulates the utilization of several sugars.

Microbiologic and clinical evidence supporting the role of Aeromonas caviae as a pediatric enteric pathogen

Aeromonas caviae was recovered as the sole potential enteric pathogen from the stools of 14 of 17 symptomatic children (10 younger than 1 year of age) while Aeromonas hydrophila, Aeromonas sobria, and Plesiomonas shigelloides were isolated once each. The infants from whom A. caviae was isolated all presented with a watery diarrhea lasting 1 to 3 weeks. None of these infants was breast-fed, and all had a stool pH of greater than 7.5. All of the A. caviae isolates, including a reference strain (ATCC 15468), adhered to HEp-2 cells, and preliminary data showed that they produced a cytotoxin as well. Because A. caviae can survive at an elevated pH, as found in the gastrointestinal tract of formula-fed infants, and because of the adherence and cytotoxin production capabilities of the species, it should be regarded as an enteric pathogen in pediatric patients and most probably among adults as well.

Suicide phenomenon in mesophilic aeromonads as a basis for species identification

The acetic acid-mediated suicide phenomenon in mesophilic aeromonads in conjunction with tests for aerogenicity and esculin hydrolysis served as the basis for species identification. Of 210 Aeromonas isolates tested at 30 degrees C, 88 were identified as Aeromonas hydrophila (nonsuicidal, aerogenic, esculin positive), 52 were identified as A. sobria (suicide variable, aerogenic, esculin negative), and 70 were identified as A. caviae (suicidal, anaerogenic, esculin positive). These identifications paralleled those achieved by biochemical criteria.

The suicide phenomenon in motile aeromonads

Certain strains of motile Aeromonas species, including all those of Aeromonas caviae examined, were shown to be suicidal. When they were grown in the presence of glucose at both 30 and 37 degrees C, there was rapid die-off of the organisms after 12 h of incubation, and viable cells generally could not be recovered after 24 h. It was shown that this phenomenon was due to the production of relatively high levels of acetic acid by these strains, even during growth under highly aerobic conditions, and to the greater susceptibility of these strains to acetic acid-mediated death. Suicide did not occur when the pH was maintained above 6.5 or in the presence of high concentration of Pi. These observations were consistent with our inability to isolate suicidal Aeromonas spp. from acidic lakes in New England and with their recovery from alkaline waters in Israel and from sewage. Suicidal aeromonads appear to be better adapted than the nonsuicidal biotypes to anaerobic growth in low-nutrient environments.

Correlation of the suicide phenomenon in Aeromonas species with virulence and enteropathogenicity

Certain strains of mesophilic aeromonads (Aeromonas hydrophila, A. sorbria, and A. caviae), when grown in broth containing 0.5% glucose, undergo growth inhibition concomitant with acetate accumulation. Because these strains are nonviable after 24 h, this phenomenon is termed suicide. We investigated suicidal strains of Aeromonas species as a means of understanding animal virulence and enteropathogenicity. To assess virulence, batches of five white mice were inoculated intraperitoneally with 10(7) cells (washed) of suicidal and nonsuicidal strains of A. hydrophila and A. sobria and suicidal strains of A. caviae. The three nonsuicidal strains of A. sobria tested showed lethality as early as 12 h and were uniformly fatal within 36 h postinoculation. After 36 h, the three suicidal strains killed only 1 of 15 mice inoculated. Four A. hydrophila strains tested which showed the suicide phenomenon at 37 degrees C were variably lethal (40 to 100%). None of three suicidal strains of A. caviae were lethal. Enteropathogenicity was studied by orally inoculating three white mice each with the same Aeromonas strains (10(8) cells, in skim milk) and assessing diarrhea and intestinal fluid accumulation. Diarrhea and fluid accumulation were present in all mice inoculated with two nonsuicidal strains of A. sobria and in 4 of 12 mice given four suicidal strains of A. hydrophila. Two suicidal strains each of A. sorbria and A. caviae failed to elicit any gastrointestinal disturbances. These data suggest that the suicide phenomenon may explain strain-specific (A. sobria and A. hydrophila) and species-specific (A. caviae) virulence and enteropathogenicity.