Positive- and Negative-Control Pathways by Blood Components for Intermedilysin Production in Streptococcus intermedius.

Streptococcus intermedius is an opportunistic bacterial pathogen secreting a human-specific cytolysin called intermedilysin (ILY) as a major pathogenic factor. This bacterium can degrade glycans into monosaccharides using two glycosidases, multisubstrate glycosidase A (MsgA) and neuraminidase (NanA). Here, we detected a stronger hemolytic activity mediated by ILY when S. intermedius PC574 was cultured in fetal bovine serum (FBS) than when it was grown in the standard culture medium. FBS-cultured cells also showed higher MsgA and NanA activity, although overproduction of ILY in FBS was undetectable in mutants nanA-null and msgA-null. Addition of purified MsgA and NanA to the FBS resulted in a release of 2.8 mM galactose and 4.3 mM N-acetylneuraminic acid; these sugar concentrations were sufficient to upregulate the expression of ILY, MsgA, and NanA. Conversely, when strain PC574 was cultured in human plasma, no similar increase in hemolytic activity was observed. Moreover, addition of human plasma to the culture in FBS appeared to inhibit the stimulatory effect of FBS on ILY, MsgA, and NanA, although there were individual differences among the plasma samples. We confirmed that human plasma contains immunoglobulins that can neutralize ILY, MsgA, and NanA activities. In addition, human plasma had a neutralizing effect on cytotoxicity of S. intermedius toward HepG2 cells in FBS, and a higher concentration of human plasma was necessary to reduce the cytotoxicity of an ILY-high-producing strain than an ILY-low-producing strain. Overall, our data show that blood contains factors that stimulate and inhibit ILY expression and activity, which may affect pathogenicity of S. intermedius.

Mistaken identity: severe vomiting, bradycardia and hypotension after eating a wild herb.

A 53-year-old woman presented with severe vomiting 3.5 hours after eating a boiled wild herb thought to be Hosta montana. She was alert, and did not complain of diplopia or numbness of her limbs. Her vital signs were temperature of 35.9°C, blood pressure of 84/33 mmHg, and heart rate of 59 beats/minute. There was no arrhythmia or conduction block on electrocardiogram. Her blood pressure and heart rate were decreased to 75/44 mmHg and 51 beats/minute at the minimum, respectively. Complete blood count and serum chemistry were normal. The herb was correctly identified when the patient's husband brought in the herb for identification.