Epidemiology of enterotoxigenic Escherichia coli diarrhea in a pediatric cohort in a periurban area of lower Egypt.

Enterotoxigenic Escherichia coli (ETEC) are diverse pathogens that express heat-labile (LT) and/or heat-stable (ST) enterotoxins, yet little is known about whether epidemiologic patterns of pediatric ETEC diarrhea vary by the expressed ETEC toxin phenotype. In total, 242 Egyptian children aged <3 years were prospectively followed in 1993-1995. ETEC episodes were detected during twice-weekly home visits, and asymptomatic ETEC excretion was identified from monthly cross-sectional surveys. ETEC episodes were 0.6 per child-year. ST-only ETEC was 2.6 times (P<.001) more common in warmer than cooler months, while LT-only ETEC showed no seasonal variation. Ownership of a household sanitary latrine, but not breast-feeding, was associated with a lower risk of both enterotoxin phenotypes. Coexpression of a colonization factor by LT- or ST-only ETEC strengthened the association with diarrhea. These findings indicate that the epidemiologic patterns of LT-only and ST-only ETEC are not identical and that disease interventions should include improved household sanitation.

Evaluation of antibodies reactive with Campylobacter jejuni in Egyptian diarrhea patients.

Serum and stool samples were collected from 128 individuals: 96 diarrhea patients and 32 apparently healthy controls. Stool specimens were cultured for enteric bacterial pathogens, while sera were screened by enzyme-linked immunosorbent assay for Campylobacter jejuni-reactive antibodies. Of 28 diarrhea patients who demonstrated C. jejuni-reactive antibodies (titers, > 100), 14 were culture positive for this organism. The 32 healthy controls showed significantly lower antibody titers (P < 0.05) with the exception of 10 subjects who were culture positive for C. jejuni and had reactive immunoglobulin M (IgM) (6 subjects) and IgG (7 subjects). IgA was not detected in those 10 individuals (asymptomatic). Avidity was expressed as the thiocyanate ion concentration required to inhibit 50% of the bound antibodies. The avidity was higher in symptomatic patients than asymptomatic healthy controls. IgG was less avid (0.92 M) compared to IgM (0.1 M) and IgA (1.1 M), with no correlation between antibody titer and avidity. However, the thiocyanate ion concentration required for the complete inhibition of IgG (5 M)-bound antibodies was higher than that of IgA (2 M) and IgM (3 M). This study also shows that C. jejuni antibodies were variably cross-reactive with Escherichia coli, Shigella flexneri, Shigella sonnei, and Neisseria meningitidis in addition to Campylobacter coli and Campylobacter rectus.

Enteropathogens associated with diarrhea among military personnel during Operation Bright Star 96, in Alexandria, Egypt.

This study investigated the microbial causes of diarrheal disease among U.S. troops deployed near Alexandria, Egypt, during October 1995. Bacterial causes associated with 19 cases of diarrhea included: enterotoxigenic Escherichia coli (ETEC), 42% (21% heat-stable, 11% heat-labile, and 11% heat-stable/ heat-labile producers); enteropathogenic E. coli (5.3%); and enteroadherent E. coli (42%). Four cases of diarrhea were associated with enteroaggregative E. coli based on probe analysis for enteroaggregative heat-stable enterotoxin 1. Protozoan causes included; Entamoeba histolytica (11%), E. hartmanni (5%), E. nana (5%), Blastocystis hominis (5%), Chilomastix mesnili (11%), Dientamoeba fragilis (5%), Entamoeba coli (5%), and Cryptosporidium (5%). Shigella, Aeromonas, Plesiomonas, Vibrio, Campylobacter, and Salmonella were not detected. Of the eight ETEC cases, one was colonization factor antigen (CFA)/I only, one was both CFA/I and CFA/III, three were CFA/II, two were CFA/IV, and two were CFA-negative. Antibiograms of the ETEC and enteroadherent E. coli strains showed that all isolates were susceptible to norfloxacin, ciprofloxacin, and nalidixic acid but resistant to ampicillin, tetracycline, chloramphenicol, and sulfamethoxazole.

Rapid and sensitive detection of Campylobacter spp. from chicken using the polymerase chain reaction.

The polymerase chain reaction (PCR) using a target region in the flaA gene of C. coli VC167 flagellin was used to detect Campylobacter spp. in chicken without an enrichment culture. DNA extracted from 79 cloacal swabs from broiler chickens gave an amplification signal in the 450-bp region upon PCR. DNA extracted from 9 enteric and 6 non-enteric organisms included in the assay as negative controls failed to hybridize with the probe. Direct plating of all cloacal specimens on Campylobacter blood agar plates did not yield any growth. The PCR assay was sensitive enough to detect between 35-120 bacteria per PCR and thus provide a basis for detecting Campylobacter spp. in poultry.

Membrane potential fluctuations of human T-lymphocytes have fractal characteristics of fractional Brownian motion.

The voltage across the cell membrane of human T-lymphocyte cell lines was recorded by the whole cell patch clamp technique. We studied how this voltage fluctuated in time and found that these fluctuations have fractal characteristics. We used the Hurst rescaled range analysis and the power spectrum of the increments of the voltage (sampled at 0.01-sec intervals) to characterize the time correlations in these voltage fluctuations. Although there was great variability in the shape of these fluctuations from different cells, they all could be represented by the same fractal form. This form displayed two different regimes. At short lags, the Hurst exponent H = 0.76 +/- 0.05 (SD) and, at long lags, H = 0.26 +/- 0.04 (SD). This finding indicated that, over short time intervals, the correlations were persistent (H > 0.5), that is, increases in the membrane voltage were more likely to be followed by additional increases. However, over long time intervals, the correlations were antipersistent (H < 0.5), that is, increases in the membrane voltage were more likely to be followed by voltage decreases. Within each time regime, the increments in the fluctuations had characteristics that were consistent with those of fractional Gaussian noise (fGn), and the membrane voltage as a function of time had characteristics that were consistent with those of fractional Brownian motion (fBm).

Colonization factors of enterotoxigenic E. coli (ETEC) from residents of northern Egypt.

Infection caused by enterotoxigenic Escherichia coli (ETEC) poses a serious health problem to children in developing countries. Colonization of the small intestinal mucosa by ETEC strains is mediated by antigenically specific fimbriae, also known as colonization factor antigens (CFA). The importance of this study arises from reports that active and passive immunization with ETEC strains harboring CFAs induced protective immunity against diarrhea in animal models with preformed antibodies. In humans, ETEC containing CFA/I, II, III and IV have been identified. The aim of this study was to define CFAs of ETEC isolated in Alexandria, Egypt. One hundred and seven ETEC isolates from 132 human residents in Alexandria, Egypt were isolated during a birth cohort study. ETEC isolates were screened for heat labile (LT) and heat stable (ST) toxins using a 32P oligonucleotide hybridization probe and a GM1 ELISA. These isolates were examined using monoclonal antibodies against CFA/I, II, III, IV, and against the putative colonization antigens PCF0159 and PCF0166, CS 7 and CS 17. CFAs were found in 48% of ETEC strains. CFA/I was found in 18% of the strains, CFA/II in 10% and CFA/IV in 14%. CFA III was not found. All fifteen strains expressing CFA/IV expressed CS6 and produced ST. CFA/IV was not found in non-ST producing strains, while CFA/I was absent in ST-only producing strains.

Regulation of T lymphocyte proliferation. Interleukin 2-mediated induction of c-myb gene expression is dependent on T lymphocyte activation state.

We previously reported that with time, after antigenic stimulation of antigen-regulated murine T lymphocyte clones, total IL-2-R expression decayed 10-50-fold, commensurate with a decline in the ability of the cells to proliferate to IL-2. However, late after antigenic stimulation, when the cells were refractory to the IL-2-proliferative stimulus, high levels of high affinity IL-2-R remained. In this report we further explore the basis of unresponsiveness to IL-2 in the quiescent clones. We show that the proto-oncogene c-myc is induced in the late cell population by IL-2 to comparable levels observed early after antigen stimulation. IL-2-dependent c-myb induction, however, is seen only early after activation but not in the late-activated population. Analysis of the IL-2-dependent expression of c-myb mRNA with time after antigenic stimulation showed that steadystate c-myb expression declines dramatically with kinetics closely paralleling a decay in IL-2-dependent proliferative ability. In contrast, steadystate c-myc expression remains high throughout this period. Expression of c-myb is critical for proliferation of these cells since antisense oligodeoxy-nucleotide to c-myb can inhibit their IL-2-dependent proliferation. We present evidence for a pathway of c-myb induction via the TCR that is independent of the IL-2/IL-2-R interaction. In addition, the inhibition of IL-2-R-induced c-myb expression by 2-aminopurine and enhanced induction of c-myb via the TCR demonstrate that TCR activation and IL-2-R activation lead to induction of c-myb by different mechanisms.

Lack of IL 2-dependent proliferation despite significant expression of high-affinity IL 2 receptor on murine cytolytic T lymphocyte clones late after antigenic stimulation.

In this study, we examine the expression of IL 2 receptors on class I and class II MHC-restricted, influenza-specific murine T lymphocyte clones at early (day 3) and late (day 8 to day 12) times after antigenic stimulation. IL 2 receptor expression on the three clones examined increases to peak levels early and subsequently decays 10-fold to 50-fold during this time period, as evidenced by monoclonal anti-IL 2 receptor antibody binding. However, in IL 2 binding site studies these clones retain high levels of high-affinity IL 2 receptors (46 to 97% of day 3 levels) at the later time points, despite their inability to proliferate in response to IL 2 in the form of supernatant from Con A-stimulated rat splenocytes. Considerable clone to clone variation is seen in binding site affinity for IL 2, whereas no significant change in binding affinity for IL 2 is exhibited for a particular clone as a function of time after activation, suggesting little structural change in the IL 2 receptor with time. Contrary to this finding, Con A-stimulated murine splenocytes exhibit a sharp decay in IL 2 receptor expression reaching 25% of peak (day 3) levels by day 10 after stimulation by lectin, with a significant decrease in the average binding site affinity for IL 2 in the population. This change in affinity in the Con A-stimulated population may, however, reflect a selection with time for lymphocytes with lower affinity for IL 2. To elucidate where the potential block may be that prevents these CTL clones from proliferating in an IL 2-dependent manner, the ability of the cells to internalize bound IL 2 at late times after activation is examined. All three clones late after activation are able to internalize bound IL 2 with efficiencies equivalent to that seen at day 3. Additionally, two of the three clones late after activation are able to upregulate expression of IL 2 receptors in response to picamolar concentrations of IL 2, indicating that the receptors on these clones are able to transmit a signal, although insufficient to induce proliferation of the cells. These observations strongly suggest that for the CTL clones examined, at late times after antigenic stimulation, engagement of IL 2 by the high-affinity receptor is not a sufficient signal to induce cells to transit through the cell cycle.

C pigment locus mutants of the fowl produce enzymatically inactive tyrosinase-like molecules.

Three albino mutants of the fowl were tested for tyrosinase activity. Two of these mutants (c and ca) are alleles at the autosomal C locus, while the third mutant (sal) is sex-linked. Both the standard type, E, and sal are tyrosinase positive whereas the two C mutants are tyrosinase negative. Anti-chicken tyrosinase mouse serum was produced and all four genotypes were found to have cross-reacting material to this antiserum. Tyrosinase from the standard type was isolated and its location on denaturing two-dimensional gels determined. A co-migrating series of spots was found within the protein pattern of both the standard type and the tyrosinase positive albino, sal. The same pattern of spots was also observed for c and ca with no apparent change in either the pI or the molecular weight. Transmembrane blots also showed spots that reacted with anti-tyrosinase serum in all four genotypes and that migrated to the same location as that of standard tyrosinase. It is proposed that both c and ca are CRM+ mutants which produce tyrosinase-like molecules that are inactive due to a change that is electrophoretically and antigenically "silent".

Activation of virus specific CTL clones: antigen-dependent regulation of interleukin 2 receptor expression.

Interleukin 2 (IL 2) is a lymphocyte-specific growth hormone, whose effect on lymphocyte proliferation is exerted through a cell surface receptor expressed on activated lymphocytes. In this report we have used monoclonal antibodies directed to the murine IL 2 receptor to examine the regulation of the IL 2 receptor expression on cloned populations of influenza virus-specific CTL. The CTL clones, which are dependent on both specific antigenic stimulation and exogenous IL 2 for continuous in vitro propagation, express high levels of the IL 2 receptor shortly after antigenic stimulation (day 2 or 3). Over the next 5 to 8 days of in vitro cultivation in IL 2-containing medium, these cloned CTL cells express decreasing levels of IL 2 receptor. Concomitant with this fall in IL 2 receptor expression, the cells become refractory to the IL 2 proliferative stimulus. The cloned cells remain refractory to IL 2 until specifically stimulated by antigen, which induces high levels of the IL 2 receptor on the cells and renders the cells sensitive to IL 2 once again. These results support the concept that IL 2 receptor expression on activated T lymphocytes is transitory and that receptor expression is endogenously regulated in the activated T lymphocytes. These results also suggest that antigen plays a primary role in regulating T lymphocyte proliferation by maintaining IL 2 receptor levels.