[Study by multiplex PCR of Listeria monocytogenes serotypes isolated in Argentine]. / Estudio mediante PCR múltiple de serotipos de Listeria monocytogenes aislados en Argentina.

A multiplex PCR assay, recently validated to characterize the serotypes of Listeria monocytogenes was evaluated in comparison to conventional serotyping. Three hundred forty two L. monocytogenes strains isolated from human, food, animal and environmental sources during the 1992-2005 period were assayed. The concordance between the two methods for serotypes 1/2a, 1/2b and 1/2c was 100%, whereas for serotype 4b it was 98%. Serotyping is a useful tool for first line strain differentiation during epidemiological surveillance and outbreaks. The multiplex PCR assay offers a fast and low-cost alternative, which is easily adaptable to clinical bacteriology and bromatology laboratories.

Estudio mediante PCR múltiple de serotipos de Listeria monocytogenes aislados en Argentina / Study by multiplex PCR of Listeria monocytogenes serotypes isolated in Argentine

Se comparó una PCR múltiple recientemente validada para la caracterización de serotipos de Listeria monocytogenes con el método tradicional de serotipificación. Se estudiaron 342 aislamientos de origen humano, alimentario, veterinario y ambiental obtenidos durante el período 1992-2005. La concordancia entre ambos métodos para los serotipos 1/2a, 1/2b y 1/2c fue del 100%, y para el serotipo 4b fue del 98%. La serotipificación constituye una herramienta importante como primer nivel de diferenciación de cepas de L. monocytogenes para llevar a cabo la vigilancia epidemiológica y, sobre todo, el estudio de brotes. La PCR múltiple es una técnica alternativa rápida, de bajo costo y fácilmente adaptable en laboratorios de bacteriología clínica y bromatología.

A multiplex PCR assay, recently validated to characterize the serotypes of Listeria monocytogenes was evaluated in comparison to conventional serotyping. Three hundred forty two L. monocytogenes strains isolated from human, food, animal and environmental sources during the 1992-2005 period were assayed. The concordance between the two methods for serotypes 1/2a, 1/2b and 1/2c was 100%, whereas for serotype 4b it was 98%. Serotyping is a useful tool for first line strain differentiation during epidemiological surveillance and outbreaks. The multiplex PCR assay offers a fast and low-cost alternative, which is easily adaptable to clinical bacteriology and bromatology laboratories.

[Diagnosis of caseous lymphadenitis in sheep from Patagonia]. / Diagnóstico de pseudotuberculosis en ovinos patagónicos.

Caseous lymphadenitis (CLA) is a chronic bacterial, infectious and contagious disease caused by Corynebacterium pseudotuberculosis. It affects sheep and results in abscesses of the lymph nodes in subcutaneous tissue, as well as in internal organs such as lungs, liver and kidneys. Differential diagnosis of the disease is based on the isolation and biochemical identification of the etiological agent. The purpose of this study was to characterize the bacteria isolated from typical CLA lesions in sheep from Patagonia, Argentina, at metabolic and genetic levels. Macroscopic observations show a fibrous membrane containing caseous necrotic tissue. Histopathological analysis shows an eosinophilic necrotic area surrounded by epitheloid cells and polymorphonuclear infiltration. Other analyses performed such as microscopic observations, in vitro culture, biochemical tests and 16s rDNA sequencing confirmed diagnosis of caseous lymphadenitis due to C. pseudotuberculosis.

Diagnóstico de pseudotuberculosis en ovinos patagónicos / Diagnosis of caseous lymphadenitis in sheep from Patagonia

La linfadenitis caseosa (LAC) es una enfermedad bacteriana supurativa crónica que afecta a ovinos. El agente etiológico es Corynebacterium pseudotuberculosis. El diagnóstico diferencial con otras afecciones que presentan manifestaciones clínicas similares sólo puede hacerse sobre la base del aislamiento y la identificación del agente etiológico. El objetivo de este trabajo fue caracterizar metabólica y genéticamente al agente causal de abscesos granulomatosos observados en ovinos en la región patagónica. En las muestras, se observó un contenido caseoso rodeado de una membrana fibrosa, y en el examen histopatológico, un centro de necrosis caseosa rodeado por células epitelioides, linfocitos y polinucleares. Mediante estudios microscópicos, bacteriológicos y moleculares fue confirmada la infección causada por C. pseudotuberculosis biovar ovis.

Caseous lymphadenitis (CLA) is a chronic bacterial, infectious and contagious disease caused by Corynebacterium pseudotuberculosis. It affects sheep and results in abscesses of the lymph nodes in subcutaneous tissue, as well as in internal organs such as lungs, liver and kidneys. Differential diagnosis of the disease is based on the isolation and biochemical identification of the etiological agent. The purpose of this study was to characterize the bacteria isolated from typical CLA lesions in sheep from Patagonia, Argentina, at metabolic and genetic levels. Macroscopic observations show a fibrous membrane containing caseous necrotic tissue. Histopathological analysis shows an eosinophilic necrotic area surrounded by epitheloid cells and polymorphonuclear infiltration. Other analyses performed such as microscopic observations, in vitro culture, biochemical tests and 16s rDNA sequencing confirmed diagnosis of caseous lymphadenitis due to C. pseudotuberculosis.

[Identification, biotypification and characterization of Pasteurella multocida strains isolated in Argentina]. / Identificación, biotipificación y caracterización de cepas de Pasteurella multocida aisladas en la Argentina.

Thirty Pasteurella multocida strains isolated in Argentina from human and animal samples were identified, biotypified and characterized. Twenty-two (73%) strains were identified as P. multocida subsp. multocida, 5 (17%) as P. multocida subsp. gallicida, and 3 (10%) as P. multocida subsp. septica. All strains were grouped in 8 biotypes, and 70% of the strains presented capsular type A. The most frequent somatic serotypes were 1 (n:11) and 3 (n:9). P. multocida strains from swine source were resistant to tiamulin, streptomycin and tetracycline. Characterization of P. multocida strains isolated in Argentina is the first step to conduct future studies intended for the prevention and treatment of pasteurellosis in human and veterinary medicine.

Invasive Streptococcus pneumoniae isolates from Argentinian children: serotypes, families of pneumococcal surface protein A (PspA) and genetic diversity.

PspA is an antigenically variable virulence factor of Streptococcus pneumoniae that inhibits complement deposition and is a potential candidate for human vaccines. Of 64 published strains 96% are in PspA families 1 and 2; optimal protection is family-specific. Effective development of a PspA-containing vaccine requires more information about the PspA family of strains in parts of the world where the vaccine is most needed. In these studies we observed that of 149 isolates (of 19 capsular types) from Argentina, 54.4% were family 1, 41.6% were family 2 and 4.0% expressed both family 1 and family 2 PspAs. Box typing revealed the Argentinian strains to be from at least 10 clonally related groups.

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 occurred in one to six family members in 8 (23.5%) 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%) of 34 HUS patients, in 30 (31.6%) of 95 family members and in 10 (29.4%) 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% FVT, 32% VT-NAbs). These were higher than those detected in siblings (6.2% FVT, 23.5% VT-NAbs) and grandparents (0% FVT, 18% 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 usually infected. Therefore, person-to-person transmission may play an important role in the high incidence of HUS in our country.

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

We report a case of a child who developed Hemolytic Uremic Syndrome in whom two Shiga-like toxin (SLT)-producing Escherichia coli strains of different serotypes and genotypes, were simultaneously isolated from stools. In addition, one of these strains represented a new toxin producing serotype. Strain 1 belonged to serotype O157: H7, biotype D, produced SLT II and was susceptible to all antibiotics tested. This strain hybridized with gene probes for SLT II, fimbrial adhesion (EHEC factor) and attaching and effacing factor (eae). Strain 2 belonged to serotype 025: K2: H2, produced SLT II and had a multiresistant antibiotic susceptibility pattern. This strain hybridized with the EHEC gene probe but not with SLT I, SLT II and eae gene probes. Free fecal SLT II cytotoxin was detected in stools of the child and his father, suggesting that the infection may have been acquired from a household contact.

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

We report a case of a child who developed Hemolytic Uremic Syndrome in whom two Shiga-like toxin (SLT)-producing Escherichia coli strains of different serotypes and genotypes, were simultaneously isolated from stools. In addition, one of these strains represented a new toxin producing serotype. Strain 1 belonged to serotype O157: H7, biotype D, produced SLT II and was susceptible to all antibiotics tested. This strain hybridized with gene probes for SLT II, fimbrial adhesion (EHEC factor) and attaching and effacing factor (eae). Strain 2 belonged to serotype 025: K2: H2, produced SLT II and had a multiresistant antibiotic susceptibility pattern. This strain hybridized with the EHEC gene probe but not with SLT I, SLT II and eae gene probes. Free fecal SLT II cytotoxin was detected in stools of the child and his father, suggesting that the infection may have been acquired from a household contact.