Identification of the high-virulence clone of group B streptococci in Mexican isolates by growth characteristics at 40 degrees C.

Group B streptococci (GBS) colonizing the vagina and rectum of pregnant women cause invasive disease of the offspring in a small number of cases. The immune status of the host and differences in virulence among strains appear to be the main determinants for neonatal infection. A high-virulence clone (HVC) was proposed to cause much of the morbidity and mortality when a collection of GBS isolates was examined by multilocus enzyme electrophoresis. HVC isolates could be further distinguished by their inability to grow at 40 degrees C. This characteristic was used in the present study to examine a collection of 57 GBS isolates from Mexico City for the HVC. Three serotype III invasive strains were classified in the HVC. The other eleven invasive strains and all carrier isolates had growth curves unaffected at 40 degrees C. These results demonstrate the presence of the HVC in Mexico. Such a low prevalence could explain in part the low rate of GBS invasive neonatal disease in Mexico.

Decreased capacity for type-specific-antigen synthesis accounts for high prevalence of nontypeable strains of group B streptococci in Mexico.

The low incidence of group B streptococcal (GBS) invasive neonatal disease in Mexico has been attributed to the low prevalence of serotype III strains, a major serotype in developed countries. In addition, nontypeable strains account for 12% of the isolates in Mexico and < 1% of the isolates in the United States. In this study, 57 GBS isolates (28 nontypeable by the Lancefield procedure) from carrier and infected neonates and women from Mexico were also examined for the presence of type-specific antigen by an enzymatic procedure using N-acetylmuramidase digestion of the cell wall to release soluble type-specific antigen. Of the 28 nontypeable strains from Mexico, 23 were typeable by the enzyme extraction procedure, with serotype III being the predominant serotype in invasive disease. These results suggest that nontypeable isolates of GBS should be further examined by the enzymatic extraction procedure to determine the presence of type-specific antigen. Furthermore, these limited results suggest that serotype III is likely a major serotype in invasive disease also in Mexico.

Extracellular neuraminidase production by clinical isolates of group B streptococci from infected neonates.

A total of 73 clinical isolates of group B streptococci obtained from diseased infants in 23 states and Puerto Rico were examined for extracellular neuraminidase production. The association of elevated levels of neuraminidase with serotype III isolates was evident in a broad geographical distribution.