How microbiological tests reflect bacterial pathogenesis and host adaptation

Historically, clinical microbiological laboratories have often relied on isolation of pure cultures and phenotypic testing to identify microorganisms. These clinical tests are often based on specific biochemical reactions, growth characteristics, colony morphology, and other physiological aspects. The features used for identification in clinical laboratories are highly conserved and specific for a given group of microbes. We speculate that these features might be the result of evolutionary selection and thus may reflect aspects of the life cycle of the organism and pathogenesis. Indeed, several of the metabolic pathways targeted by diagnostic tests in some cases may represent mechanisms for host colonization or pathogenesis. Examples include, but are not restricted to, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella enterica, Shigella spp., and enteroinvasive Escherichia coli (EIEC). Here, we provide an overview of how some common tests reflect molecular mechanisms of bacterial pathogenesis.

Differential expression of cytokine genes in THP-1-derived macrophages infected with mild and virulence strains of Shigella flexneri 2a

Shigella is an intracellular bacterial pathogen that causes bacterial dysentery called shigellosis. The assessment of pro- and anti-inflammatory mediators produced by immune cells against this bacteria are vital in identifying the effectiveness of the immune reaction in protecting the host. In Malaysia, Shigella is ranked as the third most common bacteria causing diarrheal disease among children below 5 years old. In the present study, we aim to examine the differential cytokine gene expressions of macrophages in response to two types of clinical strains of Shigella flexneri 2a (S. flexneri 2a) isolated from patients admitted in Hospital Universiti Sains Malaysia, Kelantan, Malaysia. THP-1-derived macrophages, as the model of human macrophages, were infected separately with S. flexneri 2a mild (SH062) and virulence (SH057) strains for 6, 12, and 24 h, respectively. The gene expression level of inflammatory mediators was identified using real-time quantitative polymerase chain reaction (RT-qPCR). The production of nitric oxide (NO) by the macrophages was measured by using a commercialized NO assay kit. The ability of macrophages to kill the intracellular bacteria was assessed by intracellular killing assay. Induction of tumor necrosis factor-alpha (TNFα), interleukin (IL)-1β, IL-6, IL-12, inducible NO synthase (iNOS), and NO, confirmed the pro-inflammatory reaction of the THP-1-derived macrophages in response to S. flexneri 2a, especially against the SH507 strain. The SH057 also induced a marked increase in the expression levels of the anti-inflammatory cytokine mRNAs at 12 h and 24 h post-infection. In the intracellular killing assay, both strains showed less viable, indicating the generation of pro-inflammatory cytokines in the presence of iNOS and NO was crucial in the stimulation of macrophages for the host defense against shigellosis. Transcription analysis of THP-1-derived macrophages in this study identifies differentially expressed cytokine genes that correlated with the virulence factor of S. flexneri 2a.

Clinical and microbiological profiles of shigellosis in children

Shigellosis presents with varied clinical features are dictated by the species involved, virulence factors of the strain, and the host immune status. We studied the species, virulence genes, and antibiotic susceptibility pattern of the Shigella strains isolated from 33 children aged less than 12 years, with clinical features of shigellosis. Identification and antibiotic sensitivity of Shigella species were done using disc diffusion and E-test. Multiplex PCR was done for the detection of virulence genes (ipaH, ial, set1A, set1B, sen, and stx) and ESBL genes. Parents of the children were interviewed using structured questionnaire to assess the severity of the disease; 26 (79%) of the isolates were Shigella flexneri. Ciprofloxacin and ceftriaxone resistance was seen in 23 (69%) and 3 (9%) Shigella isolates respectively. Two ceftriaxone-resistant strains were found to harbour blaCTX gene and the third blaTEM gene. Virulence gene ipaH was detected in 100% of strains while ial, sen, setlA, and setlB were detected in 85%, 61%, 48%, and 48% respectively.

The Shigella flexneri type 3 secretion system is required for tyrosine kinase-dependent protrusion resolution, and vacuole escape during bacterial dissemination

Shigella flexneri is a human pathogen that triggers its own entry into intestinal cells and escapes primary vacuoles to gain access to the cytosolic compartment. As cytosolic and motile bacteria encounter the cell cortex, they spread from cell to cell through formation of membrane protrusions that resolve into secondary vacuoles in adjacent cells. Here, we examined the roles of the Type 3 Secretion System (T3SS) in S. flexneri dissemination in HT-29 intestinal cells infected with the serotype 2a strain 2457T. We generated a 2457T strain defective in the expression of MxiG, a central component of the T3SS needle apparatus. As expected, the ΔmxiG strain was severely affected in its ability to invade HT-29 cells, and expression of mxiG under the control of an arabinose inducible expression system (ΔmxiG/pmxiG) restored full infectivity. In this experimental system, removal of the inducer after the invasion steps (ΔmxiG/pmxiG (Ara withdrawal)) led to normal actin-based motility in the cytosol of HT-29 cells. However, the time spent in protrusions until vacuole formation was significantly increased. Moreover, the number of formed protrusions that failed to resolve into vacuoles was also increased. Accordingly, the ΔmxiG/pmxiG (Ara withdrawal) strain failed to trigger tyrosine phosphorylation in membrane protrusions, a signaling event that is required for the resolution of protrusions into vacuoles. Finally, the ΔmxiG/pmxiG (Ara withdrawal) strain failed to escape from the formed secondary vacuoles, as previously reported in non-intestinal cells. Thus, the T3SS system displays multiple roles in S. flexneri dissemination in intestinal cells, including the tyrosine kinase signaling-dependent resolution of membrane protrusions into secondary vacuoles, and the escape from the formed secondary vacuoles.

A piglet model of acute gastroenteritis induced by Shigella dysenteriae Type 1

BACKGROUND

The lack of a standardized laboratory animal model that mimics key aspects of human shigellosis remains a major obstacle to addressing questions about pathogenesis, screening therapeutics, and evaluation of vaccines.

METHODS

We characterized a piglet model for Shigella dysenteriae type 1.

RESULTS

Piglets developed acute diarrhea, anorexia, and dehydration, which could often be fatal, with symptom severity depending on age and dose. Bacteria were apparent in the lumen and on the surface epithelium throughout the gut initially, but severe mucosal damage and bacterial cellular invasion were most profound in the colon. Detached necrotic colonocytes were present in the lumen, with inflammatory cells outpouring from damaged mucosa. High levels of interleukin (IL)-8 and IL-12 were followed by high levels of other proinflammatory cytokines. Elevated levels of tumor necrosis factor-alpha, IL-1beta, IL-6, and IL-10 were detected in feces and in gut segments from infected animals. Bacteria were present inside epithelial cells and within colonic lamina propria. In contrast, an isogenic strain lacking Shiga toxin induced similar but milder symptoms, with moderate mucosal damage and lower cytokine levels.

CONCLUSION

We conclude that piglets are highly susceptible to shigellosis, providing a useful tool with which to compare vaccine candidates for immunogenicity, reactogenicity, and response to challenge; investigate the role of virulence factors; and test the efficacy of microbial agents.

Acute non-outbreak shigellosis: ten years experience in southern Taiwan

BACKGROUND

We conducted a retrospective study of both the clinical and laboratory characteristics of shigellosis in southern Taiwan.

METHODS

We collected shigella dysentery cases at Kaohsiung Chang Gung Memorial Hospital and Kaohsiung Veterans General Hospital from 1996 to 2005. Fifteen children and twelve adults were enrolled and their clinical presentations analyzed.

RESULTS

Watery diarrhea (63.0%) was the most prevalent symptom in this study. Although the C-reactive protein (CRP) level was higher in patients with bloody diarrhea than those with watery diarrhea (123.5 +/-73.4 mg/L vs. 40.5 +/-36.7 mg/L, p= 0.005), there was no significant difference in the hospital stay (p= 0.072) and total number of days with fever (p= 0.981) between these 2 groups. The white blood cell (WBC) and neutrophil counts were significantly lower in patients with Shigella flexneri (S. flexneri) than those with Shigella sonnei(S. sonnei) enterocolitis (p= 0.038 and p= 0.001). WBC counts lower than 13,500/ mm(3) (OR = 3.17, 95% CI: 1.63-6.14, p= 0.005) and neutrophil counts lower than 9,400/ mm(3) (OR = 12.00, 95% CI: 1.16-123.68, p= 0.030) were more likely to be encountered in infections caused by S. flexnerithan S. sonnei. Resistance was highest to trimethoprim-sulfamethoxazole (TMP-SMX) (56%), with ampicillin (28%) second. There was no significant difference between children and adults in total number of days with fever (p= 0.532), incidence of bloody diarrhea (p= 1.000), WBC count (p= 0.177), CRP level (p= 0.858), or hospital stay (p= 0.734).

CONCLUSION

Shigellosis should be considered in patients with watery diarrhea even without a contact history. There were lower blood WBC and neutrophil counts in S. flexneithan in S. sonneienterocolitis. TMP-SMX and ampicillin should be used cautiously because of high resistance. There were no specific differences in the clinical and laboratory presentations between children and adults with shigellosis.

Interaction between enteric epithelial cells and Peyer’s patch lymphocytes in response to Shigella lipopolysaccharide: Effect on nitric oxide and IL-6 release

AIM: To investigate the effect of interaction between enteric epithelial cells and lymphocytes of Peyer’s patch on the release of nitric oxide (NO) and IL-6 in response to Shigella lipopolysaccharide (LPS).

METHODS: Human colonic epithelial cells (Caco-2) were mixed cocultured with lymphocytes of Peyer’s patch from wild-type (C57 mice) and inducible NO synthase knockout mice, and challenged with Shigella F2a-12 LPS. Release of NO and mIL-6 was measured by Griess colorimetric assay and enzyme-linked immunosorbent assay (ELISA), respectively.

RESULTS: In the absence of LPS challenge, NO was detected in the culture medium of Caco-2 epithelial cells but not in lymphocytes of Peyer’s patch, and the NO release was further up-regulated in both cocultures with lymphocytes from either the wild-type or iNOS knockout mice, with a significantly higher level observed in the coculture with iNOS knockout lymphocytes. After Shigella F2a-12 LPS challenge for 24-h, NO production was significantly increased in both Caco-2 alone and the coculture with lymphocytes of Peyer’s patch from the wild-type mice but not from iNOS knockout mice. LPS was found to stimulate the release of mIL-6 from lymphocytes, which was suppressed by coculture with Caco-2 epithelial cells. The LPS-induced mIL-6 production in lymphocytes from iNOS knockout mice was significantly greater than that from the wild-type mice.

CONCLUSION: Lymphocytes of Peyer’s patch maintain a constitutive basal level of NO production from the enteric epithelial cell Caco-2. LPS-induced mIL-6 release from lymphocytes of Peyer’s patch is suppressed by the cocultured epithelial cells. While no changes are detectable in NO production in lymphocytes from both wild-type and iNOS knockout mice before and after LPS challenge, NO from lymphocytes appears to play an inhibitory role in epithelial NO release and their own mIL-6 release in response to LPS.

Shigellosis : challenges & management issues

Infectious diseases kill about 11 million children each year while acute diarrhoeal diseases account for 3.1 million deaths in children under 5 yr of age, of which 6,00,000 deaths annually are contributed by shigellosis alone. Shigellosis, also known as acute bacillary dysentery, is characterized by the passage of loose stools mixed with blood and mucus and accompanied by fever, abdominal cramps and tenesmus. It may be associated with a number of complications of which haemolytic uraemic syndrome is the most serious. Shigellosis is caused by Shigella spp. which can be subdivided into four serogroups namely S.sonnei, S.boydii, S.flexneri and S.dysenteriae. Organisms as low as 10-100 in number can cause the disease. Shigellosis can occur in sporadic, epidemic and pandemic forms. Epidemics have been reported from Central American countries, Bangladesh, Sri Lanka, Maldives, Nepal, Bhutan, Myanmar and from the Indian subcontinent, Vellore, eastern India and Andaman and Nicobar islands. Plasmid profile of shigellae in Kolkata has shown a correlation between presence of smaller plasmids and shigellae serotypes- indicating epidemiological changes of the species. Diagnosis of shigellosis is essentially clinical. Laboratory diagnosis includes stool culture and polymerase chain reaction (PCR). Treatment includes use of an effective antibiotic, rehydration therapy (if there is dehydration) and appropriate feeding during and after an episode of shigellosis. Hand-washing is the single most important strategy for prevention of transmission of shigellosis from person to person. A safe and effective vaccine should be developed against the more important circulating strains i.e., S. dysenteriae type 1 and S. flexneri 2a.

Pathogen-induced actin filament rearrangement in infectious diseases

Host defence mechanisms involve the establishment and maintenance of numerous barriers to infectious microbes, including skin and mucosal surfaces, connective tissues, and a sophisticated immune system to detect and destroy invaders. Defeating these defence mechanisms and breaching the cell membrane barrier is the ultimate challenge for most pathogens. By invading the host and, moreover, by penetrating into individual host cells, pathogens gain access to a protective niche, not only to avoid immune clearance, but also to replicate and to disseminate from cell to cell within the infected host. Many pathogens are accomplishing these challenges by exploiting the actin cytoskeleton in a highly sophisticated manner as a result of having evolved common as well as unique strategies.

Current aspects of Shigella pathogenesis

Bacillary dysentery (shigellosis) is a severe human disease caused by Shigellae. In recent years, a large amount of information has been generated regarding the host, pathogen and environmental factors that impact the pathogenesis of shigellosis at the cellular and molecular level. This review summarizes what is currently known about Shigella, detailing those factors that contribute to pathogenesis and examining the current progress in the development of a vaccine.

Shigella dysenteriae serotype 1, Kolkata, India

Since July 2002, bacteriologically confirmed shigellosis cases have increased, and multidrug-resistant Shigella dysenteriae serotype 1 strains have reemerged in patients hospitalized with diarrhea in Kolkata, India. The isolated strains of S. dysenteriae 1 showed resistance to chloramphenicol (80%), ampicillin (100%), tetracycline (100%), co-trimoxazole (100%), nalidixic acid (100%), norfloxacin (100%), and ciprofloxacin (100%). Emergence of fluoroquinolone resistance in S. dysenteriae 1 strains complicated treatment of shigellosis patients. Six strains belonging to provisional serovars of S. dysenteriae were also identified for the first time in patients hospitalized with diarrhea in Kolkata, India.

Shiga toxins and apoptosis

The enteric pathogens Shigella dysenteriae serotype 1 and Shiga toxin-producing Escherichia coli (STEC) cause bloody diarrheal diseases that may progress to life-threatening extraintestinal complications. Although the S. dysenteriae and STEC differ in the expression of a number of virulence determinants, they share the capacity to produce one or more potent cytotoxins, called Shiga toxins (Stxs). Following the ingestion of the organisms, the expression of Stxs is critical for the development of vascular lesions in the colon, kidneys and central nervous system. It has been known for some time that following the intracellular routing of Stxs to the endoplasmic reticulum and nuclear membrane, the toxins translocate into the cytoplasm and target ribosomes for damage. However, numerous recent studies have shown that Stxs trigger programmed cell death signaling cascades in intoxicated cells. The mechanisms of apoptosis induction by these toxins are newly emerging, and the data published to date suggest that the toxins may signal apoptosis in different cells types via different mechanisms. Here we review the Stxs and the known mechanistic aspects of Stx-induced apoptosis, and present a model of apoptosis induction.

Analysis of virulence and inflammatory potential of Shigella flexneri purine biosynthesis mutants

Several Shigella flexneri mutants with defects in aromatic amino acid and/or purine biosynthesis have been evaluated as vaccines in humans or in animal models. To be suitable as a vaccine, a mutant has to show virulence attenuation, minimal reactogenicity, and a good immunogenic potential in animal models. With this aim, we have constructed five S. flexneri 5 (wild-type strain M90T) mutants with inactivation of one or two of the loci purEK, purHD, and guaBA, governing early or late steps of purine biosynthesis. The mutants have been analyzed in vitro in cell cultures and in vivo in the Sereny test and in the murine pulmonary model of shigellosis. M90T guaBA, M90T guaBA purEK, M90T guaBA purHD, and M90T purHD purEK gave a negative result in the Sereny test. In contrast, in the murine pulmonary model all of the strains had the same 50% lethal dose as the wild type, except M90T guaBA purHD, which did not result in death of the animals. Nevertheless, bacterial counts in infected lungs, immunohistochemistry, and reverse transcription-PCR analysis of mRNAs for tumor necrosis factor alpha (TNF-alpha), gamma interferon (IFN-gamma), interleukin-1beta (IL-1beta), IL-6, IL-12, and inducible nitric oxide synthase (iNOS) revealed significant differences among the strains. At 72 h postinfection, M90T guaBA purHD still induced proinflammatory cytokines and factors such as IL-1beta, IL-6, TNF-alpha, and iNOS, along with cytokines such as IL-12 and IFN-gamma. Moreover, in the absence of evident lesions in murine tissues, this mutant highly stimulated major histocompatibility complex class II expression, showing a significant ability to activate the innate immunity of the host.

Acute gastroenteritis in children : what role for antibacterials?

The aim of this article is to define the currently accepted role of antibacterials in the treatment of acute gastroenteritis in children. Most cases of acute gastroenteritis in children are viral, self-limited, and need only supportive treatment. Appropriate fluid and electrolyte therapy, with close attention to nutrition, remain central to therapy.Antibacterial therapy serves as an adjunct, to shorten the clinical course, eradicate causative organisms, reduce transmission, and prevent invasive complications. Selection of antibacterials to use in acute bacterial gastroenteritis is based on clinical diagnosis of the likely pathogen prior to definitive laboratory results. Antibacterial therapy should be restricted to specific bacterial pathogens and disease presentations. In general, infections with Shigella spp. and Vibrio cholera should usually be treated with antibacterials, while antibacterials are only used in severe unresponsive infections with Salmonella, Yersinia, Aeromonas, Campylobacter, Plesiomonas spp., and Clostridium difficile. Antibacterials should be avoided in enterohemorrhagic Escherichia coli infection. However, empiric therapy may be appropriate in the presence of a severe illness with bloody diarrhea and stool leucocytes, particularly in infancy and the immunocompromised. The benefits and risks of adverse drug reactions should be weighed before prescribing antibacterials. Moreover, a major concern is the emergence of antibacterial-resistant strains due to the widespread use of antibacterial agents.

A newborn mouse model for the study of intestinal pathogenesis of shigellosis

Shigella infection is characterized by the induction of acute inflammation, which is responsible for the massive tissue destruction of the intestinal mucosa. A murine model would be a valuable tool for gaining a better understanding of the physiopathology of shigellosis and the host immune response to Shigella infection, but adult mice do not develop disease upon oral inoculation. We therefore attempted to develop a model of infection in newborn mice. Four-day-old mice inoculated with 50 microl of 5 x 10(9) invasive wild-type Shigella flexneri 5a were susceptible to bacterial infection, but mice inoculated with the non-invasive strain BS176 were not. Histologically, 4-day-old mice infected with the invasive strain presented intestinal lesions and inflammation similar to those described in patients with shigellosis. Moreover, cytokine and chemokine responses consistent with inflammation were observed. Lower bacterial inocula induced less severe intestinal damage. In contrast, 5-day-old mice inoculated with either the invasive or the non-invasive strain were not infected. We have thus established a mouse model that is suitable for the study of the pathogenesis of intestinal Shigella infection.

[Alteration of phagocyte functional activity depending on the presence of pR50 plasmid in bacteria]

The relationship between the presence, or the absence, of conjugative plasmid pR50 detected in Klebsiella oxytoca 89, in the isogenic pairs of attenuated strains Shigella flexneri 2a 516 Near and Salmonella typhimurium 129 Rifr and the regeneration of the active forms of oxygen by mouse peritoneal phagocytizing cells was studied. As indicated by the data obtained in the course of the experiment, plasmids pR50 could influence the chemiluminescent response of phagocytes. The inhibition of the synthesis of oxygen metabolites was found to occur at the primary stage of the infectious process, that later this synthesis increased, that facilitated the survival of the animals infected with the cultures carrying plasmid pR50.

[Some aspects of evaluating endogenous intoxication in patients with acute dysentery]

AIM

To evaluate endogenic intoxication in patients with acute dysentery (AD) by examination of substances of low and medium molecular mass (LM and MM) in different body media.

MATERIAL AND METHODS

122 patients with acute dysentery were tested for LM and MM substances by M. Ya. Malakhova in plasm, red cells, urine in the course of the disease.

RESULTS

Concentration of LM and MM substances in patients with AD was much higher compared to healthy subjects in all the examined fluids at the height of the disease. In decline of clinical symptoms the studied concentrations diminished, in early convalescence the substances were at normal levels in red cells and urine being higher in plasm. Maximal changes of the LM and MM substances' concentrations were noted in a severe course of AD.

CONCLUSION

In acute bacterial dysentery concentration of LM and MM substances in blood plasm, red cells and urine depend on the period of the disease course and AD severity. This may indicate the degree of endogenic intoxication in these patients.

[Clinical and morphological aspects of shigellosis flexneri in patients with an aggravated premorbid state]

The analysis of 10 fatal outcomes in patients with acute shigellosis during the period of 1999-2000 made it possible to find out that most of deceased shigellosis patients belonged to the group inclined to alcohol abuse and having initial alimentary disturbances. In 6 cases of acute shigellosis with fatal outcome the causative agent was S. flexneri 2a, in 2 cases--S. flexneri 3a, in 1--S. flexneri 4b. The main cause of fatal outcomes was accompanying double pneumonia. Lesions of the intestinal tract in deceased shigellosis patients were of destructive character, resulting, in a number of cases, in serous and perforative peritonitis.

Sodium and water homeostasis in children with shigellosis

Studies in Bangladesh have shown that the mortality in shigellosis is significantly higher in hyponatraemic (HN) than in normo- (NN) or hypernatraemic children. The aim of this study was to describe the effect of shigellosis on renal haemodynamics and sodium and water homeostasis before treatment was started. Twenty-one moderately ill children infected with Shigella dysenteriae type I were studied. Eight of them had a serum sodium concentration below 130 mmol/L. Renal function was determined by glomerular filtration rate measured by clearances of inulin and iohexol. Effective renal plasma flow was estimated by clearance of para-aminohippuric acid. Plasma renin, aldosterone and anti-diuretic hormone were also studied. The HN children had significantly higher haemoglobin and haematocrit levels than the NN group. There was an inverse correlation between serum sodium and haemoglobin, and a direct correlation between serum sodium and urinary sodium and urinary chloride. Direct correlations were found between serum aldosterone and haemoglobin, plasma renin and systolic blood pressure and an inverse correlation between serum aldosterone and serum sodium. Clearances of inulin and iohexol were normal. Detectable levels of ADH were found in both groups, despite low serum osmolalities.

CONCLUSION

The HN state seems to be triggered by multiple factors. The normal glomerular filtration rate excludes a volume expansion secondary to reduced renal function. Inappropriate or a physiological increase of anti-diuretic hormone secretion may be of importance. The higher sodium losses in stools of the HN children might also be a factor contributing to the HN.

Exploitation of host factors for efficient infection by Shigella

Shigellosis is a worldwide endemic ulcerating disease of the large intestine caused by enteroinvasive bacteria. Shigella takes the route via M-cells and macrophages to access the basolateral pole of enterocytes. After invasion of and cell-to-cell spread within the epithelial cell layer, the bacterium multiplies within the cytoplasm of enterocytes. Induced by a limited number of bacterial effector proteins, Shigella makes use of established signaling pathways of the host cell to achieve internalization, transcytosis, apoptosis or cell-to-cell spread. This review addresses the host factors required for efficient infection focusing on Shigella-induced cytoskeletal rearrangements and associated signaling.

Increased nitrite and nitrate concentrations in sera and urine of patients with cholera or shigellosis

OBJECTIVES

Nitric oxide (NO) is an important regulator of cell function. In the intestine, NO regulates blood flow, peristalsis, secretion, and is associated with inflammation and tissue injury. The objectives of this study were to assess and compare the role of NO in cholera, a noninflammatory enteric infection, and in shigellosis, a bacterial inflammation of the colon.

METHODS

We determined serum and urinary concentrations of nitrite and nitrate during acute illness and early convalescence in 45 hospitalized children: 24 with cholera and 21 with shigellosis; 18 healthy children served as controls. Nitrite and nitrate concentrations were determined spectrophotometrically using Greiss reaction-dependent enzyme assay.

RESULTS

Serum nitrite and nitrate concentrations were significantly (p < 0.05) increased during acute illness compared to the early convalescence in both cholera and shigellosis. Urinary nitrite and nitrate excretions were significantly (p < 0.01) increased during acute disease in shigellosis, but not in cholera. Nitrite concentrations correlated with stool volume (r2 = 0.851) in cholera and with leukocytosis (r2 = 0.923) in shigellosis.

CONCLUSIONS

Both cholera and shigellosis are associated with increased production of NO, suggesting its pathophysiologic roles in these diseases.

[Shigella: from the rupture to the invasion and to the destruction of the colonic epithelium]

CROSSING THE EPITHELIAL BARRIER: Shigella acts on the immune system in order to cross the intestinal epithelial barrier which is normally impermeable to intestinal flora. Among the effectors of the immune system of the colonic mucosa are translocation sites corresponding to lymphatic follicles carrying a follicular epithelium in the presence of M cells. These cells capture molecules, particles and microorganisms from the intestinal barrier that they translocate to immune competent cells present in the follicles (antigen presenting cells including resident macrophages and then B and T lymphocytes). MACROPHAGE APTOTOSIS AND ITS CONSEQUENCES: The first cell infected by Shigella appears to be the macrophage once the translocation has been made via the M cells. This infection rapidly leads to apoptotic death of the macrophage allowing the Shigella to infect the laterobasal epithelial cells and the development of an inflammatory response. This response in turn facilitates the invasion, rupture and permeability of the intestinal epithelium and the initiation, by Shigella, of a cell-to-cell invasion pathway.

Effect of antipyretic therapy on the duration of illness in experimental influenza A, Shigella sonnei, and Rickettsia rickettsii infections

STUDY OBJECTIVES

To determine whether antipyretic therapy prolongs the course of experimental influenza A, Shigella sonnei, and Rickettsia rickettsii infections.

DESIGN

Retrospective observational study.

SETTING

University Center for Vaccine Development.

SUBJECTS

Fifty-four volunteers with experimentally induced influenza A, 45 with S. sonnei, and 21 with R. rickettsii infections participated.

INTERVENTIONS

Subjects from the six influenza A studies were challenged intranasally. If they met certain criteria, they were offered aspirin or acetaminophen for symptomatic relief. Subjects from the three Shigella studies were challenged with the bacteria and then given trimethoprimsulfamethoxazole. Acetaminophen also could be administered. In the one R. rickettsii trial, subjects were inoculated intradermally and treated with tetracycline. Again, acetaminophen was administered for symptomatic relief.

MEASUREMENTS AND MAIN RESULTS

Data, excerpted from subjects' study records, were evaluated using Wilcoxon tests, Spearman's correlation coefficients, and multiple regression analysis. Two-tailed hypotheses with a p value of 0.05 were used for all of the analyses. There was a striking correlation between antipyretic therapy and duration of illness in subjects infected with influenza A and S. sonnei, but not R. rickettsii.

CONCLUSIONS

Multivariate analysis suggested that antipyretic therapy prolonged illness in subjects infected with influenza A, but its use was the result of prolonged illness in those infected with S. sonnei. The precise nature of these relationships requires a prospective, randomized, placebo-controlled trial.

Shigella actin-based motility in the absence of vinculin

Reports on the role of vasodilator-stimulated phosphoprotein (VASP) and proline-rich sequences in actin-based motility of Listeria and potentially of Shigella flexneri have led to the suggestion that vinculin might be an essential docking protein on the surface O2 motile Shigella. Therefore, whether vinculin had a functional role in Shigella actin-based motility was tested by examining Shigella infection of the vinculin-deficient F9 cell line variant 5.51. Shigella are able to form actin tails and surface protrusions in 5.51 cells that are indistinguishable from those they produce in F9 cells, and Shigella rates of intracellular movement and protrusion formation are similar in the two cell lines. These data disprove the model of Shigella actin-based motility in which vinculin is an essential docking protein for either the formation of actin tails or the acceleration of motile bacteria.

The sigA gene which is borne on the she pathogenicity island of Shigella flexneri 2a encodes an exported cytopathic protease involved in intestinal fluid accumulation

In this study, the sigA gene situated on the she pathogenicity island of Shigella flexneri 2a was cloned and characterized. Sequence analysis showed that sigA encodes a 139.6-kDa protein which belongs to the SPATE (serine protease autotransporters of Enterobacteriaceae) subfamily of autotransporter proteins. The demonstration that SigA is autonomously secreted from the cell to yield a 103-kDa processed form and possesses a conserved C-terminal domain for export from the cell were consistent with the autotransporter pathway of secretion. Functional analysis showed that SigA is a secreted temperature-regulated serine protease capable of degrading casein. SigA was cytopathic for HEp-2 cells, suggesting that it may be a cell-altering toxin with a role in the pathogenesis of Shigella infections. SigA was at least partly responsible for the ability of S. flexneri to stimulate fluid accumulation in ligated rabbit ileal loops.

Short-chain fatty acids improve clinical, pathologic, and microbiologic features of experimental shigellosis

Because of the metabolic and antibacterial actions of short-chain fatty acids (SCFA), their roles in modifying the clinicopathologic features of shigellosis were evaluated in a rabbit model of shigellosis. Acute colitis was induced in adult rabbits by intracolonic administration of Shigella flexneri 2a. After 24 h, rabbits were given 6-h colonic infusions of SCFA (acetate, propionate, n-butyrate; 60:30:40 mM) or SCFA-free solution (control); groups of rabbits were killed in batches of 2 or 3 animals at 24, 48, 72, and 96 h after treatment, for histologic and bacteriologic assessment. SCFA significantly reduced fecal blood and mucus and improved clinical symptoms. Histologically, SCFA significantly (P<.01) reduced mucosal congestion, cellular infiltration, and necrotic changes. SCFA also significantly (P<.05) reduced the number of shigellae in the colon. No such improvements occurred in the control group. SCFA may be useful agents in improving clinicopathologic features of shigellosis and should be clinically evaluated.

Central nervous system manifestations of childhood shigellosis: prevalence, risk factors, and outcome

BACKGROUND AND OBJECTIVE

Alterations in consciousness, including seizures, delirium, and coma, are known to occur during Shigella infection. Previous reports have suggested that febrile convulsions and altered consciousness are more common during shigellosis than with other childhood infections. Those reports, however, have been from locations where S dysenteriae type 1 was not common, thus making it difficult to assess the specific contribution that S dysenteriae type 1 infection, and Shiga toxin, might make to the pathogenesis of altered consciousness in children with shigellosis. In this study we seek to determine the prevalence, risk factors, and outcome of altered consciousness in children with shigellosis in Bangladesh, a country where infection with all four species of Shigella is common. We particularly focus on the importance of metabolic abnormalities, which we have previously shown to be a common feature of shigellosis in this population.

METHODS

This study was conducted at the Diarrhea Treatment Centre of the International Centre for Diarrhoeal Disease Research, Bangladesh in Dhaka, Bangladesh, which provides care free of charge to persons with diarrhea. During 1 year, a study physician identified all inpatients infected with Shigella by checking the logs of the Clinical Microbiology Laboratory daily. Study physicians obtained demographic and historical information by reviewing the patient charts and by interviewing patients, or their parents or guardians, to confirm or complete the history of illness obtained on admission. Patients were categorized as being conscious or unconscious based on a clinical scale; having a seizure documented in the hospital; or having a seizure by history during the current illness that was not witnessed by medical personnel. Patient outcome was classified as discharged improved, discharged against medical advice, transferred to another health facility, or died in the Treatment Centre. Laboratory examinations were ordered at the discretion of the attending physician; all such information was recorded on the study form. Clinical management was by the attending physician. Factors independently predictive of a documented seizure, or of unconsciousness, were determined using a multiple logistic regression analysis. For this analysis variables associated with unconsciousness or a documented seizure in the analysis of variance or chi2 analyses were entered into the regression equation and eliminated in a backward stepwise fashion if the probability associated with the likelihood ratio statistic exceeded .10.

RESULTS

During this 1-year study, 83 402 persons with diarrhea came to the Treatment Centre for care, and 6290 patients were admitted to the inpatient unit. Shigella was isolated from a stool or rectal swab sample of 863 (13.7%) of the inpatients. Seventy-one (8%) of the inpatients with shigellosis were >/=15 years old; 61 (86%) were conscious; 10 (14%) were unconscious; none had either a documented seizure or a seizure by history during this illness. Seven hundred ninety-two patients were <15 years old (92%); 654 (83%) were conscious; 73 (9%) were unconscious; 41 (5%) had a documented seizure (compared with >/=15-year age group); 24 (3%) had a seizure by history during this illness. Of the 41 patients with documented seizures, 19 (46.3%) had a seizure at the time of admission, and 22 (53.7%) had a seizure after admission. Twenty-five (61.0%) of the 41 patients with documented seizures were reported to have a seizure during this illness before coming to the Treatment Centre. Clinical features that are known to cause altered consciousness-fever, severe dehydration, hypoglycemia, hyponatremia, or meningitis-were present in 38 (92.7%) of the 41 patients in whom a seizure was witnessed and in 67 (91.8%) of the 73 patients who were unconscious. Nineteen (46. 3%) of the patients who had a seizure documented had two of these five features, 4 (9.8%) had three, and 1 (2. (ABSTRACT TRUNCATED)

Increased height gain of children fed a high-protein diet during convalescence from shigellosis: a six-month follow-Up study

The impact of dietary supplementation on catch-up growth was evaluated in 69 malnourished children ages 24-60 mo after recovery from shigellosis. They were fed either a high-protein (HP) diet with 15% of energy as protein, or a standard-protein (SP) diet with 7.5% energy as protein, for 3 wk in a metabolic study ward. Children were followed up bi-weekly for 6 mo by trained health assistants when anthropometric measurements and information of any illness were collected. Thirty-one children in the HP group and 28 children in the SP group completed 6-mo follow-up. The increase in height (mean +/- SD) was 5.3 +/- 1.0 cm vs. 4.1 +/- 1.1 cm for HP and SP groups, respectively (P < 0.001), whereas increase in body weight was 1.39 +/- 0.58 and 1.29 +/- 0.72 kg for children fed HP and SP, respectively (P = 0.59). The proportion of children who were severely stunted (< -2 SD height-for-age) decreased from 45 to 29% in the HP group compared to 50 to 46% in the SP group (P < 0.05) at 6-mo follow-up. The number of diarrheal episodes per child tended to be lower in the HP vs. SP than in the SP group (1.9 vs. 2.3, P = 0.41). These results demonstrate that feeding an HP diet to the malnourished children during recovery from shigellosis enhanced linear growth with a modest reduction in diarrheal morbidity during the 6-mo follow-up period.

Severe shigellosis in childhood

A prospective study was performed on 20 bacteriologically proven pediatric cases of severe shigellosis admitted to the Department of Pediatrics, Chulalongkorn Hospital during March 1989 to March 1990. Fourteen patients were male and six were female. Shigella B was found in 85% and Shigella D in 15% of cases. The major indications for admission were convulsions and dehydration. Fifteen per cent of cases had underlying malignancies and 42.1% had malnutrition. Most patients had a peak of fever between 39.5 and 40.5 degrees C, serum sodium between 128-144 mEq/l. Mild acidosis was detected in 45% and moderate acidosis in 30% of cases. There were no statistical differences in peak of fever and serum sodium between patients who had convulsion and who did not. Shigellemia was found in one case who also had underlying neuroblastoma. One patient died due to necrotizing enterocolitis, septic shock and renal failure. Most of the organisms found resisted to ampicillin and trimethoprim-sulfamethoxazole (TMP-SMX). However, TMP-SMX was prescribed in most immunocompetent patients and they recovered well. All of three patients with underlying malignancy responded well to ceftriaxone.

Release of interleukin-2 induced by a major antigenic outer membrane protein of Shigella dysenteriae type 1 in natural infection

An antigen specific modulation of peripheral blood lymphocyte function was examined in a patient-based study of Shigella dysenteriae type 1 infection. Interleukin-2 (IL-2) production by the peripheral blood mononuclear cells (PBMC) from Shigella-infected patients was correlated with the expression of host cellular immune responses. To evaluate the role of a 57 kD major antigenic outer membrane protein of S. dysenteriae 1 in the proliferation of PBMC and the production of IL-2, the in vitro blastogenic transformation assay was employed. The magnitude of the response was monitored morphologically as well as by the proliferation of the IL-2 dependent CTLL-2 cell line. The proliferation of the IL-2 dependent CTLL-2 cell line against PBMC culture fluids after exposure to the major antigen reflected the participation of functionally active T-lymphocytes in shigellosis patients. The precise quantitation of IL-2 concentration in such lymphocyte culture supernatants by immunoassay showed substantial production of IL-2.

Gastric acid secretion and enteric infection in Bangladesh

In developing countries many enteric infections are caused by acid-sensitive pathogens. Failure of the gastric acid barrier to infection has been reported in cholera but gastric acid secretion has been little studied in other enteric infections. We therefore studied basal and stimulated gastric acid in 185 Bangladeshi men admitted to hospital for the treatment of enteric infection. Patients with dysentery (amoebiasis, n = 24 and shigellosis, n = 19) and culture-negative diarrhoea (n = 69) had similar mean gastric acid levels (basal, 3-5 mmol/h; stimulated, 11-17 mmol/h), which remained stable in those patients studied throughout 12 weeks of convalescence. In contrast, patients with secretory diarrhoea caused by cholera or enterotoxigenic Escherichia coli (ETEC) had low gastric acid levels (P < 0.05 compared with other groups) (cholera, n = 34: basal mean 1.8 mmol/h [SD = 2.2], stimulated mean 7.9 mmol/h [SD = 6.4]; ETEC, n = 39: basal mean 2.7 mmol/h [SD = 2.8], stimulated mean 9.4 mmol/h [SD = 7.5]). Cholera patients' gastric acid level rose during convalescence to similar levels to the dysentery patients'. Low gastric acid level was associated with severe disease in patients with cholera (P < 0.02) or ETEC (P < 0.05). Gastric acid level fell with increasing age (P < 0.007) but this did not account for the differences between groups. Gastric acid levels were not associated with Giardia duodenalis or Strongyloides stercoralis co-infection, fever, use of tobacco, or chewing betel nut. Cholera and secretory diarrhoea caused by ETEC may, therefore, partly result from a reduction in gastric acid level which does not occur during dysentery. Factors which impair gastric acid secretion may predispose to diarrhoeal disease in developing countries.

Mucosal immune responses to intestinal bacterial pathogens

Current advances in the study of gut mucosal immunology and molecular biology have enhanced our ability to understand the pathogenesis of enteric bacterial infections as well as the role of the immune system in mediating both tissue injury and protection. In this article, we review the immunopathogenesis and the protective immune response to three enteric pathogens, Vibrio cholerae, Shigella, and Salmonella. Each of these pathogens has a distinctive mechanism by which it causes disease, ie, epithelial attachment, epithelial invasion, and epithelial invasion with systemic dissemination. Pathogenicity and immune response can be conceptualized in terms of the interaction of these enteric pathogens with the gut epithelial compartment, immune inductive sites (Peyer's patch of the small intestine and lymphoid follicles of the colon), and a common immune effector compartment in the laimina propria where protective antibody is secreted. V cholerae, the representative noninvasive pathogen, has fimbrial adhesins that mediate attachment and colonization of the luminal surface of epithelial cells where organisms secrete cholera toxin (CT), a potent enterotoxin that induces a voluminous diarrhea via adenylate cyclase-dependent chloride secretion. Protective immunity is based on secretory (s) immunoglobulin A directed against whole-cell components that prevent attachment to gut epithelial cells and is enhanced by CT, an immunogen with potent adjuvant activity. Shigella, an enteric pathogen that locally invades gut epithelium, subverts the usual mechanism of immune sampling by initially invading via M cells overlying inductive sites. Subsequent macrophage invasion induces apoptosis and the release of interleukin-1, a proinflammatory cytokine. This seems to be a critical initiating event in immune-mediated tissue injury. Protective immunity is serotype specific. Infection caused by Salmonella is characterized by mucosal invasion and systemic spread mediated by the organisms ability to survive within macrophages. Both antibody and cell-mediated immunity are important for protection against Salmonella.

Absorption of macronutrients from a calorie-dense diet in malnourished children during acute shigellosis

A metabolic balance study was performed to determine the absorption of macronutrients and energy from different food items in 23 malnourished children aged 12 to 48 months with clinically severe acute dysentery due to shigellosis. In a 72-h balance period, the absorption of carbohydrate, protein, fat, and total energy was determined. All the children received a standard hospital diet; 12 children in the test group were offered an additional calorie-dense milk (5.0 kJ/ml with a protein-energy ratio of 11.0), and 11 children in the control group, on the other hand, received a milk formula with an energy of 2.5 kJ/ml with a protein-energy ratio of 11.0. The intakes (g/kg/day) of protein, fat, carbohydrate, and energy between test and control groups were 4.25 versus 2.32 (p = 0.01), 7.63 versus 3.00 (p = 0.01), 21.09 versus 11.14 (p = 0.01), and 711 kJ/kg/day versus 338 kJ/kg/day (p = 0.01), respectively. The coefficients of absorption of protein, fat, carbohydrate, and energy between test and control groups were 61 versus 67% (p = 0.45), 69 versus 82% (p = 0.11), 77 versus 86% (p = 0.13), and 72 versus 82% (p = 0.13), respectively. The losses (g/kg/day) of protein, fat, carbohydrate, and energy between the two groups were 1.61 versus 0.76 (p = 0.00), 2.44 versus 0.55 (p = 0.00), 5.0 versus 1.6 (p = 0.00), and 204 kJ/kg/day versus 60 kJ/kg/day, respectively. The results of this study indicate that during the acute stage of shigellosis (with a substantially enhanced total intake of protein, fat, carbohydrate, and energy), by adding calorie-dense meals in malnourished children younger than 5 years, the absorption of macronutrients is not significantly different from that with the usual diet but suboptimal dietary energy intake, as is the case under ordinary treatment conditions.

The cell biology of infection by intracellular bacterial pathogens

Listeria monocytogenes and Shigella flexneri are unrelated bacterial pathogens that have independently evolved similar strategies of survival within an infected host animal. Bacteria coming into contact with the surface of an epithelial cell induce cytoskeletal rearrangements resulting in phagocytosis. They then secrete enzymes that degrade the phagosomal membrane, releasing the bacteria into the host cytoplasm. Intracytoplasmic bacteria move rapidly, in association with a "comet tail" made up of host cell actin filaments. When moving bacteria reach the cell margin, they push out long protrusions with the bacteria at the tips that are then taken up by neighboring cells, allowing the infection to spread from cell to cell. This review summarizes what is currently known about the interactions between the bacteria and the host at each stage of the infection and discusses what mammalian cell biologists can learn by studying bacterial pathogens.

A case of childhood shigellosis with mutism

Bacillary dysentery, an acute infection caused by various strains of Shigella, is characterized by abdominal pain, tenesmus, and diarrhea with mucus, pus and blood. Neurologic manifestations including meningismus, delirium and convulsions may accompany the infection. We describe a thirteen-year-old girl who presented with headache, convulsion and loss of consciousness at the onset and developed diarrhea with blood and pus after hospitalization. The diagnosis of shigellosis was based on clinical data and isolation of the microorganism in the stool specimen. After improved physical functions, the patient developed mutism that continued for two days in the course of her illness, despite having no history of neurologic or psychological problems. She was diagnosed by a psychiatrist with organic mental syndrome NOS (Not Otherwise Specified) according to DSM-III-R criteria. None of the conditions that may cause mutism could be confirmed. This is the first reported case of mutism accompanying shigellosis.

[Molecular biology in the pathogenesis of Shigella sp. and enteroinvasive Escherichia coli]

Shigella sp and Escherichia coli (EIEC) are casual agents of bacillary dysentery, mainly in developing countries. Shigella and EIEC share biochemical, antigenic and genetic properties and probably they have the same mechanism of pathogenicity. Both species harbor a 120-140 megadalton plasmid, which is associated to the virulence and whose expression is regulated by chromosomal genes. Shigella sp and EIEC invade colonic epithelium and present virulence auxiliary factors, such as mucinases, superoxide dismutase and aerobactine production. On the other hand, cytotoxin production contributes to the illness' severity. The first step in invasion of the colonic mucosa is epithelium adherence, followed by endocytosis, lysis of the phagocytic vacuole, intracellular multiplication, intra-intercellular spread and killing of the host cell. Identification of these invasive organisms is carried out with the Sereny test, chicken embryo lethality and invasion to culture cells assays, DNA probe hibridization, polimerase chain reaction, ELISA, Congo red binding, and biochemical and serological tests.

[The effect of oral rehydration therapy on pancreatic function in patients with acute intestinal infections]

The results of the study of the level of pancreatic hormones (insulin, glucagon, C-peptide and trypsin), carried out with the aim of finding out the character of relationship between hormonal disturbances and the state of carbohydrate metabolism, as well as the influence of oral rehydration therapy (ORT) with glucose-salt solutions on the function of the pancreas, are summarized. All subjects to be examined were divided into two groups receiving different kinds of ORT. The patients in group 1 (153 subjects) were treated with glucosolan and in group 2 (73 subjects), with sodium citrate in an amount of 2.5-5 lit. over the 6-hour period of treatment. The determination of the content of immunoreactive insulin, glucagon C-peptide and trypsin in the blood as the characteristics of the hormonal activity of the pancreas has made it possible to find out disturbances in the incretory and excretory activity of the pancreas in patients with acute enteric infections of different etiology. ORT with glucosolan and sodium citrate facilitates the restoration of pancreatic function in 65-70% of in patients with acute enteric infections of different etiology.

The effect of shiga toxin and sonicates of Shigella isolates from children with neurologic manifestation on neuroblastoma cell lines

Although neurologic manifestations are frequent during childhood shigellosis, their pathogenesis is unclear and controversial. Shiga toxin and other cytotoxins are often implicated, but their effect on neuronal cells has not been determined. We examined the effect of purified Shiga toxin and sonicates of Shigella isolates from children with neurologic symptoms on well-characterized human neuroblastoma cells in vitro. Quantitative determinations showed high cytotoxicity of Shiga toxin on HeLa cells (1.2 x 10(6) CD50/mg purified toxin), but no effect on LA-N-1, LA-N-5 and IMR neuroblastoma cell lines. Pretreatment with tumor necrosis factor, which increases expression of the Shiga toxin receptor, globotriosyl ceramide, in endothelial cells and enhanced Shiga toxin cytotoxicity, did not affect the susceptibility of neuroblastoma cells to the toxin. Low dilutions (up to 1:16-1:64) of sonicates of Shigella isolates from children with neurologic symptoms caused agglutination of neuroblastoma cells, but no cell killing was observed morphologically. This study shows that Shiga toxin does not exhibit cytotoxic activity on the human neuroblastoma cell lines examined, neither do sonicates of relevant Shigella strains. The mechanism and significance of the agglutination activity on neuroblastoma cells should be further studied.

Asymptomatic Shigella infections in a cohort of Mexican children younger than two years of age

The proportion of Shigella infections that occur asymptomatically in young children has not been established. A community-based cohort study of 367 infants was followed prospectively by weekly home visits from January, 1990, through December, 1991. Stool samples were collected weekly and when diarrhea occurred and were tested for Shigella and other enteropathogens. There were 2925 child months of observation and 65 episodes of Shigella infection. There were 3.1 episodes/100 child months during the warm season (May through September) and 0.97 episode/100 child months during the cold season. Shigella infections were rare during the first 6 months of life but increased with age (P < 0.0001). Overall 55% of detected infections were asymptomatic. The proportion of infections that were asymptomatic increased as age increased (P < 0.01). Symptom status was not significantly associated with Shigella species or season. All isolates from symptomatic and asymptomatic children had the 120- to 140-megadalton virulence plasmid. We conclude that infections with virulent strains of Shigella are commonly asymptomatic in Mexican children during the first 2 years of life.

[The blood circulation of the rectal mucosa and the functional status of the rectal sphincter in acute infectious enterocolitis]

Significant decrease in the tone of the rectal mucosa venules was to be seen at the climax of acute Proteus and Klebsiella enterocolitis, as evidenced by examinations with the aid of rheorectograph and an analyzer of intracavitary motor activity, general blood supply to the intestinal segment under study being not compromised. The tone of the rectal mucous membrane arterioles is raised at the climax of acute dysentery caused by a Flexner type of organism in erosive and haemorrhagic proctosigmoiditis. With the clinical recovery being set in, the blood supply to this area fails to return to normal. The excitability of the inner anal sphincter was noted to be on the increase at the climax of acute S. flexneri dysentery, this showing up predominantly in erosive and haemorrhagic proctosigmoiditis, ceasing to reveal itself in the period of reconvalescentia.

Epidemic Shigella dysenteriae type 1 in Burundi: panresistance and implications for prevention

An epidemic of Shigella dysenteriae type 1 infections has affected Africa since 1979. Reported dysentery cases increase sharply in Burundi during September through December. Of stool samples from 189 patients reporting bloody diarrhea in November 1990, a pathogen was identified in 123 (65%). The pathogen was S. dysenteriae type 1 in 82 (67%). All S. dysenteriae type 1 isolates were resistant to ampicillin, chloramphenicol, nalidixic acid, streptomycin, sulfisoxazole, tetracycline, and trimethoprim-sulfamethoxazole. Thirty-two specimens (26%) yielded other Shigella species. Patients with S. dysenteriae type 1 were more likely than those with other Shigella infections to have abdominal pain, "lots of blood" in the stool, blood in the stool specimen examined by the interviewer, recent contact with a person with dysentery, or recent antimicrobial treatment. Thus, the seasonal increase in dysentery was due largely to multidrug-resistant S. dysenteriae type 1, clinical and epidemiologic features may predict such infection, and efforts to control this epidemic must focus on preventing transmission.

Childhood bacterial diarrhoea in a regional hospital in Saudi Arabia: clinico-aetiological features

Over a one-year period, 210 paediatric patients, who were admitted with acute diarrhoea to a regional hospital in the south-western region of Saudi Arabia, were retrospectively reviewed for bacterial enteropathogens. Bacterial pathogens were isolated from 66 (31.4%) patients, with Shigella being the most common (17.1%), followed by Salmonella (10.5%), and enteropathogenic Escherichia coli (EPEC) (3.8%). Major clinical findings associated with bacterial diarrhoea are similar to those reported before. Our results suggest that bacterial pathogens constitute a major cause of acute childhood diarrhoea in hospitalized children in Al-Baha province. Further prospective community based studies are needed to identify the pattern and risk factors of acute childhood diarrhoea in the region.

Relationship between humoral immune responses and oral temperature during human shigellosis

The relationship between oral temperature and serum IgA and IgG antibody responses to Shigella sonnei infection was examined in 65 experimentally infected adult volunteers. Although the IgA antibody response appeared to correlate directly with the rise in oral temperature following infection, stepwise regression analysis revealed other associated signs and symptoms as the critical elements underlying this apparent correlation. There was no evidence of a positive correlation between the IgG antibody response and the peak increment in oral temperature after infection. Although published data obtained in vitro suggest that fever might have a potentiating effect on antibody production, no such effect was seen in human volunteers with acute shigellosis.