Etiology of acute diarrhea among United States Embassy personnel and dependents in Cairo, Egypt.

The purpose of this study was to identify the enteropathogens causing acute diarrheal disease in Americans living in the North Africa/Middle East region during a 34-month period from February 12, 1985 to December 30, 1987 to guide preventive and therapeutic measures. Stool specimens were examined and an epidemiologic questionnaire was administered to patients with acute diarrhea at the Outpatient Health Unit of the United States Embassy in Cairo, Egypt. The subjects consisted of 126 American employees and dependents of the U. S. Embassy in Cairo, Egypt with diarrhea of less than two-weeks duration. Subjects received routine medical care administered by the U.S. Embassy Medical staff. A possible etiologic agent was detected in 41% of the subjects. Enteroadherent Escherichia coli was the most commonly isolated enteropathogen. A high degree of antimicrobial resistance was noted among the bacterial isolates, but all were susceptible to the quinolone antibiotics. Episodes of acute diarrhea occurring among American expatriates in Cairo, Egypt were primarily of bacterial etiology, but only a small portion were caused by the bacterial pathogens routinely identified in a standard clinical bacteriology laboratory. Most of the diarrheal episodes were due to noninvasive enteroadherent E. coli that may cause prolonged disease requiring antimicrobial therapy.

Enterobacter sakazakii bacteremia in an adult.

We have reported a case of E sakazakii primary bacteremia in an elderly patient in whom evaluation failed to reveal a source of infection. This patient had an uneventful recovery after intravenous administration of a third-generation cephalosporin for 7 days followed by 1 week of oral ciprofloxacin. This excellent response supports the previous suggestion that agents more active against gram-negative bacilli should be considered, despite apparent susceptibility to less active agents. Since this case attests to the pathogenicity of this organism in adults, isolation of the organism from clinical specimens should not be dismissed as contamination.

Mouse chromosome 1 Ity locus regulates microbicidal activity of isolated peritoneal macrophages against a diverse group of intracellular and extracellular bacteria.

The genotype of a mouse influences whether or not it will survive infection with the agent of murine typhoid, Salmonella typhimurium. The best-characterized murine salmonella response gene is a Chromosome 1 locus designated Ity. Inbred strains of mice that express the Itys allele are unable to contain the net growth of Salmonella typhimurium within their spleens and livers, and usually die early in the infection. By contrast, mice homozygous or heterozygous for the Ityr allele are able to control the net multiplication of Salmonella typhimurium within these organs. The Ity gene also appears to regulate the extent of replication within murine reticuloendothelial cell tissues of the obligate intracellular parasite Leishmania donovani, as well as the facultative intracellular bacteria Mycobacterium bovis and Mycobacterium lepraemurium. Previous studies from our laboratory strongly suggested that Ityr mice are more resistant to S. typhimurium infection than are Itys mice, because resident Ityr macrophages kill salmonellae more efficiently than do Itys macrophages. In this study, we used an in vitro macrophage assay to assess the specificity of the enhanced killing capacity of Ityr macrophages. We found that Ityr macrophages were better able than Itys macrophages to kill both intracellular bacteria (Salmonella typhi) and extracellular bacteria (Escherichia coli, Staphylococcus aureus, Corynebacterium diphtheriae). Thus, the diversity of organisms affected by Ity expression suggests that the product of this gene may play a key regulatory role in the initial interaction of mice with a variety of microbial agents.

Macrophage defect and inflammatory cell recruitment dysfunction in Salmonella susceptible C3H/HeJ mice.

C3H/HeJ mice are homozygous for the Lpsd allele and, as a consequence, are hyporesponsive to all of the biological effects of bacterial lipopolysaccharide (LPS) that have been studied. These mice die in the early phase of infection when inoculated with virulent Salmonella. This susceptibility is also regulated by the Lpsd allele. The mechanism of Lpsd-conferred Salmonella susceptibility was evaluated in these studies. The response of C3H/HeJ mice to S. typhimurium strains of differing virulence was compared in a series of in vivo experiments to the response of: endotoxin-responsive (Lpsn) mice that carry another Salmonella susceptibility gene (Itys) and endotoxin-responsive mice that carry a Salmonella resistance gene (Ityr). The C3H/HeJ mice (genotype Lpsd/Ityr) were more resistant than Lpsn/Itys mice to strains of S. typhimurium of reduced virulence but less resistant than Lpsn/Ityr mice. In addition, C3H/HeJ macrophages cultured in vitro were less able to contain net salmonellae multiplication than were macrophages from Lpsn/Ityr mice. Moreover, histopathological findings revealed that S. typhimurium-infected Lpsn/Ityr animals recruited an abnormally low number of cells into their livers compared to either Lpsn/Ityr mice or Lpsn/Itys mice. These data suggest that the susceptibility of C3H/HeJ mice may be the result of at least two Lpsd-encoded defects: a decreased capacity of macrophages to restrict Salmonella growth and a reduced recruitment of inflammatory cells into liver.

Flagella help Salmonella typhimurium survive within murine macrophages.

In this study, we evaluated how flagella enhance the pathogenicity of Salmonella typhimurium in strain C57BL/6J mice. When mice were infected orally with flagellated or nonflagellated S. typhimurium, equivalent numbers of bacteria colonized the gastrointestinal tracts of the animals, but the number of flagellated organisms increased faster once colonization began in the spleens and livers. To evaluate this differential rate of Salmonella growth, the rate of blood clearance, and the kinetics of net multiplication of salmonellae in splenic tissue after intravenous challenge, the two groups of mice were compared. We found that clearance of bacteria from the blood was the same for flagellated or nonflagellated strains. However, the number of flagellated bacteria in the spleen increased logarithmically until the death of the animals, whereas the number of nonflagellated salmonellae increased only slightly. In contrast, both flagellated and nonflagellated strains grew exponentially in the spleens of mice pretreated with silica, a macrophage toxic agent. In an in vitro macrophage assay, flagellated salmonellae survived longer than nonflagellated organisms. These results indicate that flagella either protect S. typhimurium from the intracellular killing mechanisms of murine macrophages or that flagella enhance the ability of S. typhimurium to multiply within murine macrophages.

Genetic control of the innate resistance of mice to Salmonella typhimurium: expression of the Ity gene in peritoneal and splenic macrophages isolated in vitro.

The mouse Chromosome 1 locus Ity regulates the extent to which Salmonella typhimurium replicates within the reticuloendothelial cell system (RES) during the first days of infection. If animals are homozygous for the Itys susceptibility allele, the Gram-negative bacterium undergoes rapid net multiplication, and mice die of a typhoid fever-like disease by day 10 of infection. Animals that are homozygous or heterozygous for the resistance allele, Ityr, control net bacterial replication and survive the first phase of salmonellosis. Indirect studies have implicated the resident macrophage as the effector cell for regulation of early in vivo salmonellae growth. To verify this supposition and to evaluate the phenotypic expression of Ity, we developed an in vitro assay to compare kinetics of S. typhimurium growth within Ityr and Itys macrophages. Resident peritoneal and splenic macrophages were used from inbred Ityr and Itys mice and from Ity congeneic mice. With these mice and through the use of radiolabeled S. typhimurium and an avirulent temperature-sensitive mutant of the bacterium, we found that: phagocytosis of S. typhimurium by Ityr and by Itys macrophages was the same; S. typhimurium grew to a greater extent in Itys peritoneal and splenic macrophages than in Ityr cells; Ityr macrophages killed intracellular salmonellae more efficiently than did Itys macrophages. Thus, we have demonstrated directly that Ity is expressed by the macrophage and have shown for the first time with Ity congeneic mice that the basis for differential net growth of virulent S. typhimurium in Ityr and Itys macrophages is a variation in the degree of bacterial kill.

Cat-scratch disease. Isolation and culture of the bacterial agent.

A gram-negative bacterium or its cell wall-defective variants were isolated from lymph nodes of ten patients with cat-scratch disease. Cultured bacteria were morphologically identical to vegetative and wall-defective forms seen in human tissues. Three of seven patients with recent cat-scratch disease had fourfold or greater rises in antibody titer against the cultured bacteria; the remaining four patients had maximum titers of 1:32 to 1:128. Rabbit antiserum to cultured bacilli reacted in immunoperoxidase stains with vegetative and wall-defective cat-scratch disease bacilli in lymph node, skin, or conjunctiva and with vegetative or wall-defective bacteria isolated from ten patients. Vegetative bacteria produced lesions in the skin of an armadillo identical to early lesions in human skin. Vegetative bacteria were recovered from the lesions in the armadillo.

In vitro activity of ciprofloxacin compared to trimethoprim-sulfamethoxazole against Campylobacter spp., Shigella spp. and Enterotoxigenic Escherichia coli causing travellers' diarrhea in Egypt.

The in vitro activity of ciprofloxacin against bacterial enteropathogens isolated from cases of travellers' diarrhea in Egypt was compared to trimethoprim (TMP) and trimethoprim-sulfamethoxazole (SXT). No resistance to ciprofloxacin was noted for any of the Campylobacter jejuni/coli, Shigella spp., and enterotoxigenic Escherichia coli strains examined. However, resistance to TMP and SXT was noted among these same strains. Because of its broad spectrum and lack of resistance, ciprofloxacin is potentially a useful drug for the treatment of diarrhea caused by bacterial enteropathogens encountered in this region of the world.

Association of Aeromonas sobria with human infection.

Fifteen Aeromonas isolates from various human infections and nine isolates from polluted water were identified as either Aeromonas hydrophila or Aeromonas sobria and examined for cytotoxigenicity, enterotoxigenicity, adherence to epithelial cells, and other virulence-associated factors, including proteases, lipases, elastases, and hemolysins. Two groups of organisms (I and II) were distinguishable based on differences in median lethal doses in mice and cytotoxicity for Y-1 adrenal cells. Group I clinical and environmental strains had median lethal doses of less than 10(7) colony-forming units, were cytotoxic, frequently possessed several virulence-associated factors, and had lysine decarboxylase-positive or Voges-Proskauer-positive phenotypes or both. Piliation of Aeromonas was associated strongly with ability to adhere to human buccal cells, and these characteristics were associated with group I strains. Group II clinical and environmental strains had median lethal doses of greater than or equal to 10(7) colony-forming units, were not cytotoxic, and usually were lysine decarboxylase negative or Voges-Proskauer negative or both. Clinical strains in group II exhibited enterotoxigenicity, which was not detected in group II environmental strains. A sobria was more frequently associated with human infections; 13 of the 15 clinical strains were A. sobria, and 2 were A. hydrophila. On the other hand, the majority of the environmental strains (seven of nine) were A. hydrophila.