Escherichia coli 0157: H7 reservoir, transmission, diagnosis and the African situation: a review.

OBJECTIVES: To provide an overview of the current understanding of verotoxigenic Escherichia coli 0157:H7 (VTEC) and to describe clinical picture, reservoir, transmission and diagnosis and African situations of VTEC. DATA SOURCE: A literature review was performed of major published series between 1980 and 2001 inclusive, using the PUB MED and MEDLINE search. Some earlier published series were also reviewed in instances where they directly led to the understanding of current review. STUDY SELECTION: Data from laboratory studies on cultural and isolation, serological and molecular techniques are summarised in this review. RESULTS: Verotoxigenic Escherichia coli 0157:H7 (VTEC) is an important cause of uncomplicated diarrhoea, bloody diarrhoea (BD) and haemolytic uremic syndrome (HUS) in developed countries. The incidence and importance of 0157: H7 (VTEC) infections in most developing countries are not known; however, 0157: H7 (VTEC) cases have been isolated from many sporadic cases of diarrhoea, BD and HUS, while several cases have also been associated with diarrhoeal disease outbreaks in Africa. CONCLUSION: The morbidity and mortality associated with several recent outbreaks of VTEC disease have highlighted the threat these organisms pose to public health. For this reason, there is an increasing demand for improved diagnostic procedures for detection of VTEC in clinical specimen and in particular, in foods such as meat and dairy products in developing countries.

Isolation of Mycobacterium bovis from human cases of cervical adenitis in Tanzania: a cause for concern?

SETTING: Pastoralist communities in the Northern and Southern zones of Tanzania. DESIGN: Observational study. OBJECTIVES: To determine the involvement of Mycobacterium bovis in tuberculosis cases presenting at tuberculosis (TB) clinics in rural areas in these zones. METHODS: A total of 149 tuberculosis cases identified on the bases of clinical manifestation were sampled. Appropriate specimens were cultured on two Löweinstein Jensen slants with respectively glycerol and pyruvate added. Forty-one isolates were cultured and subjected to biochemical typing. RESULTS: Overall, 31 (70.5%) of the mycobacterial isolates recovered from all forms of tuberculosis were identified as M. tuberculosis, seven (16.0%) were identified as M. bovis, and six (13.6%) were other mycobacterial species. There was a significantly higher isolation rate (P < 0.05) of M. bovis among strains recovered from extra-pulmonary (26.8%) than pulmonary tuberculosis samples (4.3%). CONCLUSION: Based on these findings, it is imperative that M. bovis be considered as a pathogen of concern to people living in rural areas of Tanzania. Further work is required to establish a zoonotic link between cattle and the people in these communities who rear them.

Risk factors associated with the occurrence of bovine tuberculosis in cattle in the Southern Highlands of Tanzania.

A study was conducted in the Southern Highlands of Tanzania to determine the prevalence of bovine tuberculosis and the risk factors associated with the occurrence of the disease in cattle of different categories and in different climatic zones. The overall prevalence of the disease was 13.2%, and 51% of the herds tested contained reactor cattle. Assessment of risk factors was based on comparisons of the reactivity of the cattle in the single comparative intradermal tuberculin test (SCITT). Older cattle were more affected by the disease than yearlings and calves (p<0.0001). There were significant differences between male and female cattle (p<0.05) and between cattle with exotic blood compared to indigenous Short Horn Zebu (SHZ) cattle (p<0.05). The castrated bulls, often used for draught power, were more frequently (p<0.01) affected than the entire bulls, mainly used for breeding. Reactivity to tuberculin did not appear to be influenced by the reproductive status of the animal. The reactivity to tuberculin of pregnant cattle was not significantly different from that of the rest of the cows (p>0.05). However, significantly more (14.6%) lactating cattle reacted in the SCITT than did non-lactating cows (12.0%) (p<0.05). There was a highly significant difference (p<0.001) between reactivity in the SCITT among cattle grazing in the hot and dry lower lands (14.0%) and that in those grazing in the cool and wet highlands (8.7%).

Isolation of Mycobacterium species from raw milk of pastoral cattle of the Southern Highlands of Tanzania.

A study to determine the secretion of Mycobacterium spp. in milk from indigenous cattle was carried out in pastoral cattle reared in the Southern Highlands to Tanzania. The study was aimed at elucidating the dangers associated with milk-borne zoonoses in a society where milk is normally consumed raw. Out of 805 milk samples, 31 (3.9%) were positive for mycobacteria. There was a preponderance of atypical mycobacteria (87%) whereas only two isolates (6.5%) were confirmed as M. bovis. Atypical mycobacteria included: M. terrae (n = 7), M. fortuitum (n = 2), M. flavescens (n = 13), M. gordonae (n = 1) and M. smegmatis (n = 4). Although the number of M. bovis positive samples was low, the habit of pooling milk may still pose great public health dangers to milk consumers in this part of the world. Moreover, isolation of atypical mycobacteria should also be considered to be a danger to human health in countries such as Tanzania, where the number of people with lowered immunity due to HIV infection is on the increase.

Bovine tuberculosis in the Lake Victoria zone of Tanzania and its possible consequences for human health in the HIV/AIDS era.

A total of 8190 cattle from 42 well-managed herds in the Lake Victoria zone of Tanzania were tested for bovine tuberculosis by a single comparative intradermal test (SCITT) using avian and bovine purified protein derivative (PPD) antigens. The prevalence of bovine tuberculosis in this area was found to be 0.2%. There was significant variation (p < 0.001) among the herds tested in the four regions in this zone (Kagera, Mara, Mwanza and Shinyanga). The highest prevalence (2.12%) was in a herd of 566 cattle which had recently arrived in Kagera region from Dar-es-Salaam. None of the 915 cattle tested in Shinyanga or of the 254 resident cattle in the Kagera region were positive by SCITT. This area, and particularly the Kagera region, has the highest human morbidity and mortality due to the acquired immunodeficiency syndrome in Tanzania. Therefore, the presence of bovine tuberculosis in cattle necessitates further investigations on the role of animal-derived tuberculosis in human health.

The role of management systems in the epidemiology of thermophilic campylobacters among poultry in eastern zone of Tanzania.

A total of 255 samples of droppings collected from a total of 22 different poultry units were examined for the presence of thermophilic campylobacters and the isolates biotyped using Skirrow's protocol. The organisms were isolated from 90 (35.3%) of all samples. Among the 22 units investigated, 13 (59%) were found to have unsatisfactory management systems, while 7 (32%) and 2 (9%) were found to have unsatisfactory and good systems respectively. Significantly large numbers of isolations, 68 of 147 (46.2%), were made from samples collected from poultry units with poor management (P < 0.005), compared with 19 out of 84 (22.6%) samples which were collected from satisfactory units and 3 out of 24 (12.5%) samples collected from units exercising particularly good management. Nineteen of 72 (26.4%) samples collected from broilers, 32 out of 132 (24.2%) samples collected from layers and 39 out of 51 (76.49%) samples collected from indigenous free range poultry were positive for campylobacters. Among the 90 strains isolated from various units, 64 (70.1%) were Campylobacter jejuni, 25 (27.7%) were C. coli, and only 1 (2.2%) was C. laridis.

Bacteriological quality of potable water sources supplying Morogoro municipality and its outskirts: a case study in Tanzania.

Bacteriological quality of potable water supplying Morogoro municipality and its outskirts (population 135,000 people) was assessed by the determination of the most probable number (MPN) of faecal coliforms, Escherichia coli, faecal streptococci and Clostridium perfringens for a period of 6 months. River water and chlorinated pipeborne water were found contaminated with microorganisms in the order of 3.8 x 10(1) to 4.95 x 10(3); 3.2 x 10(1) to 4.5 x 10(3); 10(1) to 6.4 x 10(1) and 1.2 x 10(1) to 2.5 x 10(2)/100 ml of water respectively. Injured coliforms in treated water averaged 87%. Pollution of river water by organic matter was much above acceptable standard. These findings indicate that there is a need for further treatment of water before consumption in order to avoid potential health hazards.

An epidemic of fatal posterior paralysis and sudden death in goats: a case report.

An epidemy of fatal posterior weakness was observed in Norwegian dairy goats with a spontaneous character (high fever, collapse, death). Clinical, postmortem, and histopathological findings indicated gastroenteritis, liver damage (necrotic foci), soft kidneys, pneumonia, and depletion of liver glycogen in goats up to 4 months of age. In older animals there was a prevalence of muscle degeneration. Indigenous goats did not exhibit any mortality, whereas the mortality rate in male crosses Norwegian X Tanzanian was 100%, regardless of their age. In young goats, the existence of a high mortality infectious syndrome with enterotoxaemia and fever is suspected, whereas older goats were probably exposed to a non-infectious myodegeneration.

Siderophore production by enterotoxigenic Salmonella.

Eleven Salmonella strains of diverse origin studied previously for enterotoxigenicity, cell surface hydrophobicity (HIC) and haemagglutination (HA) were studied for the production of a siderophore precursor 2,3-dihydroxybenzoic acid (DHB) by colorimetry. The Salmonella strains were similarly grown aerobically and anaerobically in a deferrated (DF) medium containing 0.05 micrograms/ml iron at 22 degrees C and 37 degrees C. Salmonella strains positive for both heat-labile (LT) and heat-stable (ST) enterotoxins, i.e. ST+ LT+ strains produced 25-70 mg/l, DHB, bound to hydrophobic phenyl sepharose gel and exhibited mannose-resistant haemagglutination (MRHA) of bovine, chicken and human group A erythrocytes. Conversely, heat-labile enterotoxin-positive, only i.e. ST- LT+ strains produced less than 25 mg/l DHB and were negative for the three aforementioned parameters. This dichotomy was shown by strains grown aerobically at 22 degrees C. Strains grown at 37 degrees C gave disparate results while Salmonella anaerobically grown at both growth temperatures did not produce DHB. These studies demonstrate production of a siderophore during iron stress.

Hemagglutinating and hydrophobic surface properties of salmonellae producing enterotoxin neutralized by cholera anti-toxin.

Eleven Salmonella strains known to produce enterotoxin under aerobic culture conditions in deferrated (DF) medium at 37 degrees C were shown to produce enterotoxin with and without aeration at 22, 28, 37 and 42 degrees C. Heat-labile enterotoxin was generally produced with growth temperatures up to 37 degrees C irrespective of aeration. Heat-stable enterotoxin was produced up to 42 degrees C, mainly aerobically, as indicated by infant mouse assay (IMA), by six of the eleven strains tested. Nine strains produced heat-stable rapid permeability factor (RPF) in rabbit skin. Cholera anti-toxin neutralized reactivities of Salmonella heat-labile enterotoxin in four different biological assays. Mixed gangliosides also neutralized this activity in the cell-test systems. With guinea-pig erythrocytes, all strains underwent mannose-resistant hemagglutination (MRHA) irrespective of growth temperatures, i.e. 22 and 37 degrees C or medium, i.e., DF, tryptose soy broth (TSB) and colonization factor antigen (CFA) agar. At both growth temperatures, CFA agar-grown cells of each strain caused MRHA of bovine erythrocytes. Excepting three Salmonella typhimurium strains, DF broth-grown cells gave MRHA of bovine, chicken and human group A erythrocytes, CFA agar-grown cells caused MRHA of chicken and human blood, whereas TSB-grown cells caused few MRHA reactions. Salmonellae producing both heat-stable, (ST) and heat-labile, (LT) enterotoxins adsorbed to Phenyl Sepharose whereas salmonellae that produced only LT enterotoxin did not. The presence of MRHA adhesions did not correlate with cell-surface hydrophobicity. However, mannose-resistant hemagglutinins may occur more commonly among salmonellae than has been previously recognized.

Enterotoxigenicity, hemagglutination and cell-surface hydrophobicity in Aeromonas hydrophila, A. sobria and A. salmonicida.

Thirty-one Aeromonas hydrophila, 13 A. sobria and two A. salmonicida strains of diverse sources were tested for enterotoxigenicity, hemagglutination and cell surface hydrophobicity. Although 93% of the culture supernatant fluids of the Aeromonas strains exhibited cytotoxic effects on Y1 adrenal and Chinese hamster ovary (CHO) cells, typical rounding of Y1 adrenal cells was reproducibly observed before cytotoxicity for 80% of the isolates within 1 h of exposure. Twenty-eight strains were positive for delayed permeability factor (DPF) activity in rabbit skin. Culture filtrates of 16 of 20 strains that were positive both in the Y1 adrenal cell test and for DPF activity elicited fluid accumulation in rabbit ileal loops. The DPF and ileal loop activities were neutralizable by cholera antitoxin. All, except two strains each of A. sobria and A. hydrophila, produced a heat-stable, rapid permeability factor (RPF) detected in rabbit skin. Heat-treated culture supernatant fluids of two A. hydrophila and one A. sobria isolate gave positive responses in the infant mouse assay. Nine other strains gave borderline reactions. When A. hydrophila and A. sobria isolates were grown in broth, approximately 90% agglutinated bovine, chicken, human group A and guinea-pig erythrocytes in the presence of mannose at 4 degrees C and/or 20 degrees C. The two A. salmonicida isolates produced mannose resistant hemagglutination (MRHA) of these four blood types. Hydrophobic interaction chromatography indicated adhesive potential in 61% A. hydrophila and 100% A. sobria strains expressing weak to strong hydrophobic cell surface properties. The results of these investigations strongly imply that the Aeromonas strains produce a cytotonic enterotoxin immunologically related to cholera toxin. Adhesive characteristics were commonly found in both clinical and routine isolates.

Probing for enterotoxigenicity among the salmonellae: an evaluation of biological assays.

Sixty-eight Salmonella strains representing 39 serotypes were variously screened for enterotoxigenicity by using the Chinese hamster ovary (CHO), Y1 adrenal, and Vero cell tests, rabbit skin tests for delayed permeabiltity factor (DPF) and rapid permeability factor (RPF), the rabbit ileal loop test, and the infant mouse test. An iron-sufficient medium, YT-1, and a deferrated medium, DF, were compared. Of the culture supernatant fluids of strains grown in DF medium, 66% yielded positive reactions in the CHO cell test compared with only 10% with TY-1 medium. The corresponding performances with supernatant fluids of DF medium cultures in Y1 adrenal and Vero cell tests were 85 and 69% positive, respectively. The overall agreement between the Y1 adrenal or CHO cell test and the rabbit skin test for DPF, i.e., positive or negative in both tests, was about 70%. Positivity in DPF tests was a better predictor of positivity in either the Y1 adrenal or rabbit ileal loop test than vice versa. CHO cell, DPF, and rabbit ileal loop reactivities of unheated culture filtrates were each neutralized by anticholera antitoxin. Only four strains gave positive reactions in the infant mouse test, whereas up to 66% were positive for RPF in rabbit skin, based on positivity in Ty-1 or DR medium or both. DPF and RPF were produced by 35% of the strains. Of the 28 isolates from human stools, 82 and 92% and all of 11 strains tested were positive in the DPF, Y1 adrenal cell, and rabbit ileal loop tests, respectively. The corresponding data for 17 sewage isolates, representing 17 different serotypes rarely isolated from human stools in Sweden, were 63 and 69% and 8 of 8 tested. On the basis of this investigation, rabbit skin tests for both DPF and RPF provide the most reliable means of screening for enterotoxigenicity among salmonellae.

Enterotoxigenic bacteria in food and water from an Ethiopian community.

Food and water samples from an Ethiopian community were screened for the presence of enterotoxin-producing bacteria. Using the Chinese hamster ovary cell assay, 40 of 213 isolates (18.8%) produced heat-labile (LT) enterotoxin. These LT-producing isolates comprised 33 of 177 (18.6%) strains from 24 of 68 food samples (35.3%) and 7 of 36 (19.4%) isolates of 4 of 17 water samples (23.5%). One LT-producing strain each of Salmonella emek and of Shigella dysenteriae was found. Three pseudomonads, all LT producers, produced heat-stable enterotoxin as gauged by the suckling mouse test. Two strains of LT-enterotoxigenic Escherichia coli O68 were found in water samples. No enterotoxigenic E. coli were isolated from food samples, but 13 of the LT-producing strains were Enterobacter, Klebsiella, Serratia, and Proteus species, and 7 food samples yielded more than one species of enterotoxigenic bacterium. Of the enterotoxigenic isolates from food, 15 were oxidase-positive strains of the genera Aeromonas, Pseudomonas, Achromobacter, Flavobacterium, and Vibrio. LT-enterotoxigenic Enterobacter, Acinetobacter, Klebsiella, Proteus, Providencia, and Serratia species represented 20 of the food and water isolates. Culture supernatant fluids of representative strains of oxidase-positive and oxidase-negative species giving positive reactions in Chinese hamster ovary cell tests induced fluid accumulation in rabbit ileal loops. Eight of the food samples and two of the water samples contained more than one isolate or species of enterotoxigenic bacterium. The stability of the LT production by oxidase-positive bacteria and non-E. coli strains was assessed by the rabbit skin and adrenal cell tests after 9 months and 1 year of storage, respectively, in Trypticase soy broth with glycerol at -70 degrees C. Only 33% of the oxidase-positive strains were still LT enterotoxigenic. Of the oxidase-negative strains, 50 and 33% were LT producing at 9 months and 1 year, respectively. None of the E. coli isolates, both enterotoxigenic and nonenterotoxigenic, possessed K88, K99, or colonization factor antigen. The survey demonstrates the presence in food and water of enterotoxigenic bacteria of the same species as those isolated from cases of infantile diarrhea in the same community, although a correlation between these sources and infantile diarrhea remains to be established.