Physicians have an increased understanding of patients entering the hospital for acute stroke, and the association between certain types of stroke and the presence of the oral bacteria centronuclear myopathies gene (cnm)-positive Streptococcus mutans.
Small vessel diseases (SVDs) of the brain such as cerebral microbleeds (CMBs), lacunar infarcts, and white matter lesions are important biomarkers of vascular injury and burden of brain dysfunction. The underlying mechanisms and risk factors of the SVDs of the brain are poorly understood.
A team of scientists led by those at the National Cerebral and Cardiovascular Center (NCVC; Osaka, Japan) enrolled patients admitted to the NCVC because of acute heart disease, between February and August 2014, consisting of 67 subjects with ischemic stroke, 5 with transient ischemic attack, and 27 with intracerebral hemorrhage (ICH). The cnm gene in S. mutans isolated from saliva was screened using polymerase chain reaction (PCR) techniques and its collagen-binding activities examined. Oral saliva and dental plaque specimens were collected from the subjects in the first three days following admission.
Oral samples were inoculated on Mitis-Salivarius medium with bacitracin (MSB, 100 U/mL; Sigma-Aldrich; St. Louis, MO, USA) and 15% sucrose (MSB agar) and anaerobically incubated at 37 °C for 48 hours. S. mutans strains were isolated morphologically and all strains were anaerobically grown in brain heart infusion (BHI) broth (Difco Laboratories; Detroit, MI, USA) at 37 °C for 24 hours. DNA of each strain was extracted. S. mutans and cnm gene encoding CBP was screened using polymerase chain reaction techniques. MKD primer32 was used to detect S. mutans and cnm primer was used to identify cnm gene33. A collagen-binding assay with type I collagen was conducted to examine collagen-binding activities of each isolated S. mutans strain.
Eleven cases showed Streptococcus mutans strains positive for cnm. The presence of cnm-positive Streptococcus mutans was significantly associated with ICH and increased number of deep CMBs. In subjects positive forStreptococcus mutans, collagen binding activity was positively correlated with the number of deep CMBs. The authors hypothesize that the S. mutans bacteria may bind to blood vessels weakened by age and high blood pressure, causing arterial ruptures in the brain, leading to small or large hemorrhages.
Robert P. Friedland, MD, a professor of Neurology and co-author of the study, said. “This study shows that oral health is important for brain health. People need to take care of their teeth because it is good for their brain and their heart as well as their teeth. The study and related work in our laboratories have shown that oral bacteria are involved in several kinds of stroke, including brain hemorrhages and strokes that lead to dementia.” The study was published online on February 5, 2016, in the journal Scientific Reports.