Bacterial Phenotype Variants in Group B Streptococcal Toxic Shock Syndrome1

Variants with markedly different expression of virulence factors can arise in invasive infection in humans

Dynamics of the Immune Response against Extracellular Products of Group A Streptococci during Infection

The immune response against the infecting group A streptococcus (GAS) extracellular products (EP) was determined in acute- and convalescent-phase sera from 75 patients with different clinical manifestations of GAS infection. All EP elicited a high proliferative response in human peripheral blood mononuclear cells. In patients with bacteremia, low neutralization in acute-phase sera was associated with development of streptococcal toxic shock syndrome. Lack of neutralization in acute-phase sera was more common in patients infected with the T1emm1 serotype. The majority of patients did not develop the ability to neutralize the mitogenic activity of their infecting isolate despite a significant increase in enzyme-linked immunosorbent assay titer in early convalescent-phase sera. In patients with the ability to neutralize GAS EP, the immune response remained high over at least 3 years. In contrast, the neutralization capacity conferred by intravenous immunoglobulin and/or plasma treatment disappeared within 3 months

Characterization and Nucleotide Sequence of a Klebsiella oxytoca Cryptic Plasmid Encoding a CMY-Type �-Lactamase: Confirmation that the Plasmid-Mediated Cephamycinase Originated from the

Plasmid pTKH11, originally obtained by electroporation of a Klebsiella oxytoca plasmid preparation into Escherichia coli XAC, expressed a high level of an AmpC-like �-lactamase. The enzyme, designated CMY-5, conferred resistance to extended-spectrum �-lactams in E. coli; nevertheless, the phenotype was cryptic in the K. oxytoca donor. Determination of the complete nucleotide sequence of pTKH11 revealed that the 8,193-bp plasmid encoded seven open reading frames, including that for the CMY-5 �-lactamase (bla CMY-5). The bla CMY-5 product was similar to the plasmidic CMY-2 �-lactamase of K. pneumoniae and the chromosomal AmpC of Citrobacter freundii, with 99.7 and 97.0 % identities, respectively; there was a substitution of phenylalanine in CMY-5 for isoleucine 105 in CMY-2. bla CMY-5 was followed by the Blc and SugE genes of C. freundii, and this cluster exhibited a genetic organization identical to that of the ampC region on the chromosome of C. freundii; these results confirmed that C. freundii AmpC was the evolutionary origin of the plasmidic cephamycinases. In the K. oxytoca host, the copy number of pTKH11 was very low and the plasmid coexisted with plasmid pNBL63. Analysis of the replication regions of the two plasmids revealed 97 % sequence similarity in the RNA I transcripts; this result implied that the two plasmids might be incompatible. Incompatibility of the two plasmids might explain the cryptic phenotype of bla CMY-5 in K. oxytoca through an exclusion effect on pTKH11 by resident plasmid pNBL63