Mannheimia haemolytica growth and leukotoxin production for vaccine manufacturing: a bioprocess review

Mannheimia haemolytica leukotoxin (LKT) is a known cause of bovine respiratory disease (BRD) which results in severe economic losses in the cattle industry (up to USD 1 billion per year in the USA). Vaccines based on LKT offer the most promising measure to contain BRD outbreaks and are already commercially available. However, insufficient LKT yields, predominantly reflecting a lack of knowledge about the LKT expression process, remain a significant engineering problem and further bioprocess optimization is required to increase process efficiency. Most previous investigations have focused on LKT activity and cell growth, but neither of these parameters defines reliable criteria for the improvement of LKT yields. In this article, we review the most important process conditions and operational parameters (temperature, pH, substrate concentration, dissolved oxygen level, medium composition and the presence of metabolites) from a bioprocess engineering perspective, in order to maximize LKT yields.

Infección grave por Staphylococcus aureus meticilino sensible productor de leucocidina de Panton-Valentine: reportes de dos casos / Severe infection by methicillin sensitive Staphylococcus aureus producing Panton-Valentine leukocidin: reports of two cases

Staphylococcus aureus es uno de los principales agentes etiológicos de infecciones en niños provenientes de la comunidad y del ámbito hospitalario. La gravedad de estos cuadros se asocia a factores de virulencia, entre los que se encuentra la leucocidina de Panton-Valentine. Tanto Staphylococcus aureus resistente como sensible a la meticilina producen esta leucocidina, aunque con frecuencia variable. Presentamos a dos niños con infección grave por Staphylococcus aureus sensible a la meticilina productor de leucocidina de Panton-Valentine con complicaciones osteoarticulares y endovasculares. Es fundamental la sospecha diagnóstica, el tratamiento antibiótico adecuado y el manejo quirúrgico precoz para mejorar el abordaje de estas infecciones. Se debe mantener la vigilancia epidemiológica para detectar la frecuencia de las infecciones causadas por estas bacterias.

Staphylococcus aureus is a major etiologic agent of infections in children from the community and the hospital setting. The severity of these conditions is associated with virulence factors, including the Panton-Valentine leukocidin. Both methicillin resistant and sensitive Staphylococcus aureus produce this leukocidin although with varying frequency. We present two children with severe infection by sensitive Staphylococcus aureus producer of Panton-Valentine leukocidin with musculoskeletal and endovascular complications. It is essential the suspected diagnosis, appropriate antibiotic treatment and early surgical management to improve the approach of these infections. Epidemiological surveillance should be mantained to detect the frequency of infections caused by these bacteria.

Success stories about severe pneumonia caused by Panton-Valentine leucocidin-producing Staphylococcus aureus

We describe three cases of community-acquired necrotizing pneumonia which were caused by Panton-Valentine leucocidin-producing strains of Staphylococcus aureus (one of them methicillin sensitive). All cases were successfully treated without any sequelae for the patients due to the prompt initiation of adequate antimicrobial therapy. High suspicion toward this fatal pathogen was the key to the successful outcome of the patients.

Selection of phytotoxin producing rhizobacteria

In order to select phytotoxin producing rhizobacteria to control weed plants, twenty five bacterial strains previously isolated from the rhizospheres of various plants were grown in a liquid medium and, after cell removal by centrifugation, the liquid phases were freeze-dried and the products were extracted with ethyl acetate/methanol. The extracts were concentrated to dryness under vacuum and dissolved in water and sucrose solution to be submitted to in vitro assays of lettuce (Lactuca sativa L.) seed germination and wheat (Triticum aestivum L.) coleoptile growth. Although most samples affected coleoptile growth, only those from four strains reduced lettuce seed germination. Two strains of Bacillus cereus, one strain of B. pumilus and one of Stenotrophoonas altophilia were the most promising microorganisms for producing phytotoxin and, consequently, for the development of new weed control products.

Com o objetivo de selecionar rizobactérias produtoras de fitotoxinas para uso no controle de plantas daninhas, vinte e cinco isolados bacterianos previamente obtidos das rizosferas de diferentes plantas foram cultivados em meio líquido e, após remoção das células por centrifugação, as fases líquidas foram liofilizadas e os resíduos obtidos foram submetidos à extração com acetato de etila/metanol. Os extratos foram concentrados sob vácuo até secura e dissolvidos em água e solução de sacarose para serem submetidos a testes in vitro de germinação de sementes de alface (Lactuca sativa L.) e de crescimento de coleóptilos de trigo (Triticum aestivum L.). Embora a maior parte das amostras tenha desfavorecido o crescimento dos coleóptilos de trigo, somente as provenientes de quatro isolados reduziram a germinação das sementes de alface. Dois isolados de Bacillus cereus, um isolado de B. pumilus e um de Stenotrophomonas maltophilia foram os microrganismos mais promissores para a produção de fitotoxinas, com possibilidade de uso no desenvolvimento de novos produtos para o controle de plantas daninhas.

Investigação da biossíntese de toxinas produzidas por cepas de cianobactérias / Investigation on the cyanobacterial strains toxins biossinthesys

A demanda crescente de água doce de boa qualidade são problemas atuais e mundiais, além do descaso com os dejetos lançados nos ambientes aquáticos que comprometem a qualidade dos recursos hídricos. Um dos parâmetros que atesta a potabilidade da água é a presença de cianobactérias e cianotoxinas. Cianobactérias são microrganismos procariontes aeróbicos fotoautróficos que sintetizam as cianotoxinas. Estes compostos podem ser classificados de acordo com seus mecanismos de ação em hepatotóxicos, neurotóxicos e dermatotóxicos. Por sua diversidade, representam diferentes riscos não só ao ecossistema e a outros organismos dos ambientes aquáticos, como também aos seres humanos. Esse projeto visou o isolamento e cultivo de cepas de cianobactérias produtoras de toxinas para a investigação da biossíntese desses compostos. Com este intuito, foram realizadas coletas de água em três reservatórios no estado de São Paulo e um no Paraná. Cepas de cianobactérais foram isoladas, identificadas e analisadas quanto à produção de toxinas. Uma cepa de Microcystis aeruginosa (LTPNA 02) produtora de microcistinas (MC-LR, MC-RR, MC-YR, MC-LF, MC-LW e desm-MC-LR e desm- MC-RR) foi escolhida para ser estudada frente diferentes condições de cultivo e ter o seu crescimento, produção de toxinas e expressão gênica estudados. Foram utilizados os meios de cultura já referidos na literatura: ASM-1 (N:P=1, 10 e 20), MLA (N:P=10), Bold 3N (N:P=16) e BG-11 (N:P=10 e 100). Para acompanhar o crescimento, dois métodos foram utilizados: contagem de células e espectrofotometria. As toxinas foram quantificadas por LC-MS - QTrap. A análise da expressão gênica foi realizada por reação de PCR em tempo real pelo método de quantificação relativa ΔΔCt. Foi observada diferença no crescimento da cepa estudada nos diferentes meios de cultivo empregados. A contagem das células permitiu a identificação das fases logarítmica e total de crescimento. Durante a fase logarítmica, três experimentos demonstraram...

There is a great concern these days about potable and good quality water due to the increase of the population needs and also to the arising problems with contamination caused by anthropogenic sources. The presence of cyanobacteria and cyanotoxins are some parameters that attest water potability. Cyanobacteria are prokaryotic aerobic photoautotrophic microorganisms that may synthesize cyanotoxins. These compounds can be classified as hepatotoxic, neurotoxic and dermatotoxic according to their action mechanisms. Because of their diversity, they may represent different risks, not only to their ecosystem and other aquatic living organisms, but also to human beings. The aim of this project was the isolation and cultivation of cyanotoxin-producing cyanobacteria for further investigation on the biosynthesis of these compounds. Water samples from three different reservoirs in São Paulo state and one in Paraná state were collected in order to isolate cyanobacteria strains and accomplish their identification and to evaluate the toxin production. The Microcystis aeruginosa (LTPNA 02) microcystin producer strain (MCLR, MC-RR, MC-YR, MC-LF, MC-LW, desm-MC-LR and desm-MC-RR) was chosen to be grown in different cultivation conditions and later analyzed for its growth rate, toxin production and gene expression. All culture media used in this research were chosen according to the literature: ASM-1 (N:P=1, 10 and 20), MLA (N:P=10), Bold 3N (N:P=16) and BG-11 (N:P=10 and 100). To evaluate growth rate, two techniques were used: cell counting and absorbance determination in two different wavelengths (680 nm and 750 nm). Toxins were quantified by LC-MS in a hybrid triple-quadrupole instrument (Qtrap). Gene expression was assessed by real time PCR, using the ΔΔCt relative quantification method. Cell counting allowed total growth and logarithmic phase identification. During the last, three experiments showed statistical difference from control group (p<0,05). Four experiments...

Occurrence of toxin-producing cyanobacteria blooms in a Brazilian semiarid reservoir

Nós relatamos a ocorrência de florescimentos de cianobactérias e a presença de cianotoxinas em amostras de água do reservatório Armando Ribeiro Gonçalves (06º 08Æ S; 37º 07Æ W) situado no Estado do Rio Grande do Norte, na região semi-árida do Brasil. Cianobactérias foram identificadas e quantificadas nos períodos seco e chuvoso do ano 2000. Cianotoxinas tais como, microcistinas, saxitoxinas e cilindrospermopsinas foram quantificadas por HPLC e ELISA. Florescimentos tóxicos mistos de Cylindrospermopsis raciborskii, Microcystis spp (M. panniformis, M. protocystis, M. novacekii) e Aphanizomenon ssp (Aphanizomenon gracile, A. cf. manguinii, A. cf. issastschenkoi) foram persistentes e representaram 90-100% da comunidade fitoplanctônica ao longo do período estudado. No período de chuvas, florescimentos tóxicos de Cylindrospermopsis raciborskii coincidiram com maiores valores de saxitoxinas (3,14 µg.L-1). Entre o período de chuva e estiagem, ocorreram florescimentos tóxicos de Microcytis spp, excedendo o valor mínimo aceitável para consumo humano (8,8 µg.L-1). Na estiagem, baixas concentrações de saxitoxinas foram detectadas em florescimentos menos intensos com co-dominância de Cylindrospermopsis raciborskii, Microcystis spp e Aphanizomenon spp. Nossos resultados revelaram a presença de microcistinas (8,8 µg.L-1) e saxitoxinas (3,14 µg.L-1) na água bruta, a partir da segunda quinzena de abril até o final de maio de 2000. A ocorrência de blooms tóxicos de cianobactérias no reservatório em estudo aponta um risco permanente de cianotoxinas em águas de abastecimento e indica a necessidade da implementação de medidas de controle das florações, visando à melhoria da qualidade da água. A exposição das populações locais às cianotoxinas, pela sua potencial acumulação em musculatura de peixes, também deve ser considerada.

Production of cytolethal distending toxin and other virulence characteristics of Escherichia coli strains of serogroup O86

Genetic and phenotypic virulence markers of different categories of diarrhoeagenic Escherichia coli were investigated in 106 strains of enteropathogenic E. coli (EPEC) serogroup O86. The most frequent serotype found was O86:H34 (86 percent). Strains of this serotype and the non motile ones behaved as EPEC i.e., carried eae, bfpA and EAF DNA sequences and presented localised adherence to HeLa cells. Serotypes O86:H2, O86:H6, O86:H10, O86:H18, O86:H27 and O86:H non determined, belonged to other categories. The majority of the strains of serotype O86:H34 and non motile strains produced cytolethal-distending toxin (CDT). The ribotyping analysis showed a correlation among ribotypes, virulence markers and serotypes, thus suggesting that CDT production might be a property associated with a universal clone represented by the O86:H34 serotype

Expression of mosquito active toxin genes by a Colombian native strain of the gram-negative bacterium Asticcacaulis excentricus

Mosquito control with biological insecticides, such as Bacillus sp. toxins, has been used widely in many countries. However, rapid sedimentation away from the mosquito larvae feeding zone causes a low residual effect. In order to overcome this problem, it has been proposed to clone the Bacillus toxin genes in aquatic bacteria which are able to live in the upper part of the water column. Two strains of Asticcacaulis excentricus were chosen to introduce the B. sphaericus binary toxin gene and B. thuringiensis subsp. medellin cry11Bb gene cloned in suitable vectors. In feeding experiments with these aquatic bacteria, it was shown that Culex quinquefasciatus, Aedes aegypti, and Anopheles albimanus larvae were able to survive on a diet based on this wild bacterium. A. excentricus recombinant strains were able to express both genes, but the recombinant strain expressing the B. sphaericus binary toxin was toxic to mosquito larvae. Crude protease A. excentricus extracts did not degrade the Cry11Bb toxin. The flotability studies indicated that the recombinant A. excentricus strains remained in the upper part of the water column longer than the wild type Bacillus strains

Intestinal bleeding and occlusion associated with shiga toxin-producing Escherichia coli 0127: H21

We report a case of a nine-year old boy with vomiting, abdominal pain and fever, who underwent surgery with a diagnosis of appendicitis in Mendonza and from whom a Shiga toxin-producing Escherichia coli (STEC) 0127:H21 strain was recovered. Forty-eight hours after surgery he presented bilious vomiting and two episodes of intestinal bleeding. Loboratory findings included: hematocrit, 35 per cent; blood urea nitrogen, 0.22 g/L. The urinary output was normal. The following day physical examination showed an alert mildy hydrated child, without fever but with distended and painful abdomen. The patient was again submitted to surgery with a diagnosis of intestinal occlusion. Bleeding and multiple adhesions in jejunum and ileum were found. The patient still had tense and painful abdomen and presented two bowel movements with blood; hematocrit fell to 29 per cent and blood urea nitrogen rose to 0.32 g/L. STEC 0127:H21 eae(-)/Stx2/Stx2vh-b(+)/E-Hly(+) was isolated from a stool sample. He was discharged after 10 days of hospitalization and no long-term complications such as HUS or TTP were observed. This is the first report, to our knoweledge, on the isolation of E.coli 0127:H21, carrying the virulence factors that characterize STEC strains, associated to an enterohemorrhagic colitis case. This serotype was previously characterized as a non-classic enteropathogenic E. coli (EPEC). STEC infections can mimic infectious or noninfectious pathologies. Therefore an important aspect of clinical managements is making the diagnosis using different criteria thereby avoiding misdiagnoses which have occasionally led to invasive diagnostic and therapeutic procedures or the inappropriate use of antibiotics.

Cytotoxicity of non O1, non O139 Vibrios isolated from fresh water bodies in Vellore, south India.

The samples of plankton, soil sediment and water from a pond, a lake and a moat respectively in and around Vellore were studied for environmental vibrios. Vibrios were isolated from all these specimens after enrichment in alkaline peptone water and subculture on selective media. Non O1, non O139 Vibrio cholerae, Aeromonas spp. and Plesiomonas spp. were isolated. There were no isolates of V. cholerae serogroup O1 and O139. Representative strains of non O1 and non O139 V. cholerae from environmental sources were tested for toxin production in Chinese hamster ovary (CHO) and Vero cell monolayer in microtitre plates. Thirty-three (91.7%) of the 36 strains tested demonstrated cytopathic effect (CPE) in both cell lines indicating their toxigenicity. PCR done on representative strains of non O1 and non O139 V. cholerae showed that none of the strains were positive for ctx A, tcp A-E and tcp C genes. These results indicate that these non agglutinating environmental vibrios produced cytotoxins other than the cholera toxin.

Shiga-toxin producing Escherichia coli from healthy cattle in a semi-urban community in Calcutta, India.

From October to December 1998, single faecal samples from 67 healthy cattle in a semi-urban community near Calcutta were examined for Shiga toxin producing Esch. coli (STEC) using a multiplex PCR primary screen followed by plating on sorbitol MacConkey agar. STEC was isolated from the faeces of 7 (10.5%) animals. The eight strains isolated belonged to eight serotypes viz, O146:H1, O149:HNT, ONT:H34, ONT:H19, O88:HN, ONT:H2, O82:H8 and O28ac:H21. Bead enzyme linked immunosorbent assay showed that three strains produced Shiga toxin 1, one produced Shiga toxin 2 and four produced both.

Isolation of verotoxin producing Escherichia coli from diarrhoeal and urinary tract infection patients.

Fourty nine Escherichia coli strains, isolated from diarrhoeal and urinary tract infection (UTI) patients, attending Bareilly district hospital, Uttar Pradesh during October to December, 1998 were screened for verotoxin (VT) production by Vero cell assay. Five strains produced characteristic cytopathic effect on Vero cell line, of which 4 were from diarrhoeal and one was from UTI-patient. The level of VT-production varied widely. Antibiotic sensitivity tests revealed that the VT-producing E. coli (VTEC) were mostly sensitive to kanamycin, norfloxacin and nalidixic acid but resistant to ampicillin and tetracycline.

Occurrence of haemolytic & cytotoxic Aeromonas species in domestic water supplies in Chennai.

A study on the occurrence of Aeromonas species in the domestic water supplies in Chennai showed that as much as 37.9 per cent of the water samples analyzed from various sources harbored Aeromonas spp. Majority of the isolates belonged to Aeromonas sobria (13.7%), A. caviae (11.6%) and A. hydrophila (9.5%). Among the 37 metropolitan water samples analyzed, 11 samples yielded Aeromonas spp. inclusive of three isolates of A. hydrophila, four of A. sobria and two isolates each of A. caviae and A. jandaei. From a total of 28 bore well water samples analyzed, Aeromonas spp. were recovered from 15 samples, comprising five isolates of A. hydrophila, six of A. sobria and four isolates of A. caviae. Aeromonas spp. inclusive of one isolate of A. hydrophila, five of A. caviae, three of A. sobria and one isolate of A. veronii were isolated from 10 of the 30 water packets of various commercial brands sold in Chennai. Of a total of 36 isolates obtained, 32 (89%) produced beta-haemolysin with the titres ranging from 2-32 and 20 isolates (56%) were cytotoxic to vero cell monolayers. All the Aeromonas isolates were resistant to ampicillin and polymyxin B. All A. hydrophila and A. caviae isolates were also resistant to cephalothin and erythromycin and 83.3 per cent of Aeromonas isolates were resistant to erythromycin. Aeromonads resistant to tetracycline, gentamycin, co-trimoxazole and nalidixic acid appear to be emerging. The study revealed that Aeromonas spp. occur in the potable and domestic water supplies and even in the chlorinated water supplies in Chennai city, which are potentially enteropathogenic and hence may be hazardous to public health. In view of these findings drinking and domestic water quality standards need to be re-evaluated.

Activation and germination of spores of Bacillus thuringiensis var israelensis by alkaline pH and larval (Aedes aegypti) gut fluid.

Alkaline activation of the spores of crystalliferous (Cry+) and acrystalliferous (Cry-) strains of Bacillus thuringiensis var israelensis; wild type B. cereus and its transcipient crystalliferous derivatives and wild type B. subtilis was studied. Also the effect of larval (Aedes aegypti) gut fluid on the activation of spores of these strains was studied. Only the spores of the crystal forming strains were found to be activated by 0.1 M K2CO3 (pH 10) and by the larval gut fluid. The process of alkaline activation was independent of whether crystals were present with the spores in the activation solution. This indicates that protoxin in the spore coat is responsible for the alkaline activation process and may have ecological implications for the organism.

Verocytotoxin-producing Escherichia coli infection in family members of children with hemolytic uremic syndrome

Thirty-four hemolytic uremic syndrome (HUS) patients and ninety-five family members were studied to determine the frequency of infection with verocytotoxin-producing Escherichia coli (VTEC) in household contacts using three diagnostic criteria: VTEC strains isolation and characterization, detection of free fecal VT (FVT) and VT-neutralizing antibodies (VT-NAbs). Gastrointestinal tract symptoms occurend in one to six family members in 8 (23.5 per cent) of the index cases, the week before admission to hospital or simultaneously. The control group consisted of 34 children with acute gastroenteritis who did not develop HUS. Cumulative evidence of VTEC infection was found in 13 (38.2 per cent) of 34 HUS patients, in 30 (31.6 per cent) of 95 family members and in 10 (29.4 per cent) of 34 control children. The serotypes of VTEC isolated were O157:H7 and O25: H2. The prevalent VT type was VT2 in VTEC and FVT; and VT1 in VT-NAbs. Both parents had the same infection rate by fecal toxin or serological data (11.1 per cent FVT, 32 per cent VT-NAbs). These were higher than those detected in siblings (6.2 per cent FVT, 23.5 per cent VT-NAbs) and grandparents (0 per cent FVT, 18 per cent VT-NAbs). Of 16 patients without evidence of infection, 3 had household contacts with FVT and 13 with VT-NAbs. Our results show the wide dissemination of VTEC in the population of Argentina and that family members of HUS patients are usualy infectd. Therefore, person-to-person transmission may play an important role in the high incidence of HUS in our country.

Effect of trace metals on synthesis of exoproteins and exotoxins by Staphylococcus aureus.

Staphylococcus aureus did not grow in chemically defined medium completely free of trace metals. At low concentrations all the trace metals showed stimulating effect on growth and exoprotein production. Increasing concentrations of Ca2+ and Mg2+ were growth stimulatory whereas Co2+, Cu2+, Fe3+, Mn2+, Ni2+ and Zn2+ were inhibitory. The amount of exoprotein and haemolytic exotoxins produced in relation to final viable count increased with increasing concentrations of growth inhibitory trace metals whereas it decreased with increasing concentrations of Ca2+ and Mg2+. Trace metals did not show significant influence on amount of haemolytic exotoxins produced in relation to total exoproteins. The results indicate presence of a common regulatory mechanism for all types of exoproteins produced by S. aureus.

Exotoxin profiles of Campylobacters isolated in Malaysia.

Approximately 57% of clinical and 33% of poultry isolates examined produced a cytotoxin. Cytotoxic activity was detected in 25 (50%) isolates of Campylobacter of which 12 were isolated from bloody diarrhea and 9 from watery stools. The cytotoxin titers were low, ranging from 2 to 16. The crude filtrates from 50 Campylobacter isolates showed no cytotoxic effect in Vero cells, no fluid accumulation in suckling mice and no hemolytic activity.

Coagglutination test for detection of heat labile enterotoxin producing Escherichia coli strains.

A simple particle immunoassay based on the coagglutination (CoA) of Staphylococcus aureus strain Cowan 1 coated with heat labile enterotoxin (LT) specific antibodies was evaluated to detect LT in the cell lysates of blood agar grown Esch. coli. Among strains of Esch. coli isolated from 2661 patients with acute diarrhoea, isolates from 609 patients demonstrated LT production by CoA test. Most prevalent serogroups were 020, 078, 0128, 04, 0117, 068, 0158, 07, 0114, 0148 and 0145. A comparison of CoA with classical rabbit ileal loop and skin permeability factor assay for 100 strains showed 86, 69 and 83 LT positive strains respectively. CoA proved a more specific, simple, rapid and sensitive assay which may be useful for screening of large number of Esch. coli isolates in epidemiological investigations.

Hemolytic uremic syndrome: co-infection with two different serotypes of shiga-like toxin producing Escherichia coli

Se presenta el caso de un niño de 14 meses que desarrolló Sindrome Urémico Hemolítico después de un período prodrómico con vómitos y diarrea mucosanguinolenta del cual se aislaron 2 cepas de E. coli productoras de toxina simil-Shiga (SLT) de diferente serotipo y genotipo. Una de las cepas correspondió al seotipo 0157: H7, biotipo D, productora de SLT II y susceptible a todos los antibióticos probados. Esta cepa hibridizó cona las sondas genéticas para SLT II; la fimbria de adherencia (factor EHEC) y para el factor de fijación y disolución del borde en cepillo ("E. coli attaching and effacing") eae). La otra cepa correspondió al serotipo O25:K2:H2 productora de SLT II en los ensayos de neutralización de efecto citotóxico sobre células VERO utilizando anticuerpos monoclonales, pero negativas para SLT I y SLT II y el factor eae. Sólo fue positiva por hibridización con la sonda para la fimbria de adherencia. Esta cepa presentó además un patron de multiresistencia a los antibióticos probados. Por otra parte, la cepa de E. coli, del serotipo O25: K2: H2 produjo niveles tanto de toxina libre como asociada a células, 20 veces superiores a la cepa del serotipo O157:H7. Esta es la primera publicación de un caso de SUH en el cual se detectó una cepa de E. coli del serotipo O25:H2 produjo niveles tanto de toxina libre como asociada a células, 20 veces superiores a la cepa del serotipo O157:H7. Esta es la primera publicación de un caso de SUH en el cual se detectó una cepa de E. coli del serotipo O25:H2 productora de SLT. Además el hecho de no hibridizar con la sonda genética para SLT II, a pesar de tener una actividad citotóxica neutralizable por el anticuerpo monoclonal (MAb BC5BB12) indicaria que la secuencia que codifica para SLT II no presenta homología con la sonda utilizada. la detección de SLT libre tanto en la materia fecal del niño como en la de su padre (quien padeció diarrea una semana antes), indicaría que el niño adquirió la infección en el entorno familiar

Loss of some virulence factors of enterotoxigenic Escherichia coli on repeated subcultures.

Thirty enterotoxigenic Esch. coli (ETEC) strains of predominant serogroups, isolated from patients with diarrhoea in Ludhiana, Punjab were investigated for expression of heat labile (LT) enterotoxin and colonization factor antigens (CFAs) on repeated subculture. These belonged to serogroup 078 (10), 080 (2), 0114 (6), 020 (3), 0128 (3), 0153 (2) and 08 (4) respectively. The isolates exhibited a differential response for expression of LT and CFAs on repeated subculturing. All the strains were positive for both LT and CFA up to six subcultures. Three strains of serogroup 0114 and one of 080 failed to express CFA while one strain each of serogroups 080, 0114, 020 and 08 failed to elaborate LT in the 8th subculture. Only 25 and 19 isolates were detected as stable producer of LT and CFAs up to 10th subculture.