Serotypes and putative virulence markers of Streptococcus suis isolates from cats and dogs

Streptococcus suis and an Incidentally Diagnosed Metastatic Colon Cancer

Background: Streptococcus suis is a zoonotic infection known to cause meningitis and sepsis, in addition to several other rare manifestations. Infection with this organism is rare in the absence of pork ingestion or a handling history. Case presentation: The authors report the case of a 62-year-old male with no animal contact history, who presented with symptoms of urinary tract infection. It was his second infection over the course of 2 years. His urine culture was positive for Escherichia coli but his blood culture was positive for S. suis. Ultrasound of the abdomen ruled out underlying predisposing urinary pathology. However, it did show several heterogeneous liver masses with abnormal vascularity. A follow-up abdominal CT revealed a malignant neoplastic process involving the sigmoid colon with metastatic liver lesions. Colonoscopy demonstrated a fungating mass at the sigmoid colon and biopsies revealed a moderately differentiated adenocarcinoma. Conclusion: This case suggests the possibility of associated colon cancer in patients presenting with S. suis with no explicit history of animal or pork contact. It also proposes the existence of an association between colon cancer with Streptococcus species other than bovis.

Assessment of MALDI-TOF MS as Alternative Tool for Streptococcus suis Identification

The accuracy of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) for identifying Streptococcus suis isolates obtained from pigs, wild animals, and humans was evaluated using a PCR-based identification assay as the gold standard. In addition, MALDI-TOF MS was compared with the commercial multi-tests Rapid ID 32 STREP system. From the 129 S. suis isolates included in the study and identified by the molecular method, only 31 isolates (24.03%) had score values ≥2.300 and 79 isolates (61.24%) gave score values between 2.299 and 2.000. After updating the currently available S. suis MALDI Biotyper database with the spectra of three additional clinical isolates of serotypes 2, 7, and 9, most isolates had statistically significant higher score values (mean score: 2.65) than those obtained using the original database (mean score: 2.182). Considering the results of the present study, we suggest using a less restrictive threshold score of ≥2.000 for reliable species identification of S. suis. According to this cut-off value, a total of 125 S. suis isolates (96.9%) were correctly identified using the updated database. These data indicate an excellent performance of MALDI-TOF MS for the identification of S. suis.

Characterisation of Streptococcus suis isolates from wild boars (Sus scrofa)

Wild boar are widely distributed throughout the Iberian Peninsula and can carry potentially virulent strains of Streptococcus suis. The objective of this study was to determine the prevalence of S. suis in wild boars from two large geographical regions of Spain. Serotypes 1, 2, 7 and 9 identified were further genetically characterised by virulence-associated genotyping, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) to determine the population structure of S. suis carried by these animals. Streptococcus suis was isolated from 39.1% of the wild boars examined: serotype 9 was the most frequently isolated (12.5%), followed by serotype 1 (2.5%). Serotype 2 was rarely isolated (0.3%). Eighteen additional serotypes were identified indicating wide diversity of this pathogen within the wild boar population. This heterogeneity was confirmed by PFGE and MLST analyses and the majority of isolates exhibited the virulence-associated genotype mrp-/epf-/sly-. The results of this study highlight that the carriage of S. suis by wild boars is commonplace. However, MLST data indicate that these isolates are not related to prevalent clonal complexes ST1, ST16, ST61 and ST87 typically associated with infection of pigs or humans in Europe.

Identification of virulence associated markers in the cell wall of pigeon Streptococcus gallolyticus strains

The cell wall protein profiles of 56 isolates of Streptococcus gallolyticus of differing virulence for pigeons were compared by SDS-PAGE. Additionally, Western blot analysis was performed on the cell wall proteins of 14 strains using sera of pigeons, experimentally infected with A(+)T1 or A(-)T2 strains of S. gallolyticus. The profile of silver stained gels exhibited a complex array of 20-50 bands ranging from less than 6.5-210kDa. A band with molecular mass of 114kDa was only observed in isolates that belonged to the highly virulent A(+)T1, A(+)T2, A(+)T3 and A(-)T1 culture supernatant groups. A band with a slightly higher molecular mass (115kDa) as well as a 207kDa band were only detected in isolates that belonged to the moderately A(-)T3 or low A(-)T2 virulent culture supernatant groups. The 114 and 115kDa band were recognised by all homologous and heterologous pigeon sera used whereas the 207kDa band was only recognised by sera of pigeons infected with a A(-)T2 strain. These findings may indicate that the 114, 115 and 207kDa bands are useful as additional virulence associated markers for pigeon S. gallolyticus strains.

Streptococcus suis: past and present

Steptococcus suis is a Gram-positive, facultatively anaerobic coccus that has been implicated as the cause of a wide range of clinical disease syndromes in swine and other domestic animals. In swine, the disease has spread worldwide but is more prevalent in countries with intensive swine management practices. The disease syndromes caused by S. suis in swine include arthritis, meningitis, pneumonia, septicaemia, endocarditis, polyserositis, abortions and abscesses. S. suis has also been implicated in disease in humans, especially among abattoir workers and swine and pork handlers. In humans, S. suis type 2 can cause meningitis, which may result in permanent hearing loss, septicaemia, endocarditis and death. The pathogenic mechanism of S. suis is not well defined. Several virulence factors have been identified, but their roles in pathogenesis and disease have not been well elucidated. Much work is in progress on characterization of virulence factors and mechanisms, with emphasis on the control of the disease. Because of the non-availability of suitable immunoprophylaxis, control of S. suis infection has depended mainly on the use of antimicrobials.

Binding properties of Streptococcus suis for immunoglobulin G and other plasma proteins

Immunoglobulin G (IgG) binding proteins on the surface of Streptococcus suis could be readily detected by direct cultivation of the bacteria on nitrocellulose membranes and subsequent treatment of the membranes with human IgG. Among the 75 S. suis isolates tested two cultures (S. suis P43, S. suis P143) caused a blue colouration of the membranes indicating IgG binding activities. The IgG binding proteins could be solubilized by heat treatment of the bacteria at an acid pH and also by mutanolysin treatment. Western blot analysis revealed numerous protein bands with IgG binding activities. The IgG binding proteins were also released into the culture supernatant of the bacteria. This could be detected for 51 of the 75 S. suis using a microfiltration assay. In binding studies with 125I-IgG S. suis P43 and S. suis P143 but none of the other S. suis isolates showed a significant binding of the protein. These two cultures additionally bound 125I-albumin, 125I-alpha 2-macroglobulin and 125I-fibrinogen all from humans but not 125I-chicken IgG or 125I-human haptoglobin 2-1. The binding profiles of the two S. suis cultures tested indicate a close relation of these binding proteins with streptococcal protein G.

Properties of a Streptococcus suis isolate of serotype 2 and two capsular mutants

Encapsulation is thought to be a critical virulence factor of Streptococcus suis. In the present study two capsular type 2 mutants of S. suis (M42 and M2) and their S. suis parent strain (89-1591) were further characterized. All three cultures reacted with group D specific antiserum whereas parent strain 89-1591 and mutant M42 but not mutant M2 reacted with specific antiserum against capsular type 2. Both mutants had higher surface hydrophobicity and showed an increased adherence to human epithelial cells and to lung macrophages of rabbits as compared to the parent strain. In phagocytosis experiments with polymorphonuclear leucocytes the encapsulated parent strain was more resistant to phagocytosis than both mutant strains. These findings might help to understand the role of encapsulation of S. suis in the process of infection.

Distribution of serotype, virulence markers and further characteristics of Streptococcus suis isolates from pigs

This study was designed to comparatively investigate 28 S. suis cultures isolated from various pathological processes of pigs. All cultures could be identified biochemically and most of the cultures could be serogrouped with specific antiserum against Lancefield's serogroup D. Serotyping of the S. suis isolates mainly revealed capsular types 2, 1, and 22. In addition, part of the cultures, mostly those of serotype 2, reacted with monoclonal antibodies to the virulence protein muraminidase-released protein, and, in parallel with monoclonal antibodies against the virulence protein extracellular factor. Independently of serotype and the occurrence of both virulence proteins, four cultures haemagglutinated erythrocytes from pigs, humans and rabbits. The haemagglutination reaction appeared to be related to the surface hydrophobicity of the isolates. However, part of the cultures with hydrophobic surfaces did not haemagglutinate the available erythrocyte preparations. The surface characteristics of the S. suis isolates shown in this investigation could be used to characterize individual isolates of S. suis that might be of importance for epidemiological studies.