How to test for streptococcal infections and how to distinguish streptococci from enterococci

Diagnosis is based on the prevalence of streptococcal infection, the patient's exposure history, and characteristic clinical presentation. Some can confirm the diagnosis based on clinical manifestations alone, such as erysipelas, while others require bacterial culture of secretions and blood from the site of infection to confirm the diagnosis.

Enterococci are Gram-positive cocci round or oval, arranged in single or paired pairs or short chains, without buds, without flagella, and are aerobic or facultative anaerobes. This bacterium has high nutrient requirements, requiring high salt (, high alkali (, 40% bile medium and 10-45 environment growth. Grows well on serum-containing media.

After 37 years of culture on blood plates for 18 hours, gray-white, opaque, smooth surface and diameter round colonies can be formed, and different strains show different hemolytic phenomena. It differs significantly from streptococci of the same family in that it is biochemically tolerant of high salt and bile media, and is inherently resistant to many antimicrobial drugs. In 40% bile medium, esculin can be decomposed, oxidase and touch enzyme test is negative, and most strains can hydrolyze pyrrolidone-naphthalene amide (PYR).

Spherical or oval, diameter, mostly chain-like, the short ones are composed of 4 8 bacteria, and the older ones are composed of 20 30 bacteria. The length of the chain is related to the strain and the growth environment, and the chain length formed in the liquid medium is longer than that formed in the solid medium. Most of the young bacteria can see the capsule formed by hyaluronic acid, and if the culture time is extended, the capsule can be broken down by the hyaluronidase produced by the bacteria themselves and disappear.

Non-sporous, non-flagellant, pimbimal-like structure, containing M protein, positive Gram stain.

After the onset of acute nephritis, the positive rate of bacterial culture from the pharynx or ** foci of infection is generally only 20% to 30%, and it is not easy to detect in those who have used penicillin ** in the early stage. After streptococcal infection, the body can produce corresponding antibodies to the components of the bacteria and their products, so the detection of such antibodies is often used to confirm the prodromal streptococcal infection, and the commonly used antibody tests are as follows:

1) Anti-streptolysin O antibody (ASO): Hemolysin is a protein containing a sulfide and hydrogen group, which has strong antigenicity, and the positive rate of nephritis after acute streptococcal infection is 50% to 80%. It usually appears 2 to 3 weeks after streptococcal infection, with titers peaking at 3 to 5 weeks and gradually decreasing; 50% of the patients returned to normal within half a year, and 75% of the patients turned negative at 1 year, and some patients lasted for a long time.

The following points should be noted when judging the measured results: An increase in ASO titer only indicates that there has been a streptococcal infection in the near future, and is not directly related to the likelihood of acute nephritis and the severity of the disease; Patients who have been given specific antibiotics in the early stages of infection** can affect their positive rate; Acute nephritis titers due to impetigo may not be elevated; Some strains of streptococcus (eg, type 12) do not produce hemolysin, do not cause hemolysis on blood dishes, and do not cause ASO reactions; Hyperlipidemia can also affect ASO test results.

2) Anti-DNASEB and anti-hase: have a high positive rate in acute nephritis caused by impetigo. Its normal value varies according to different seasons, age and other factors, so it is advisable to measure it multiple times, and when the titer is more than 2 times higher, it indicates that there is a streptococcal infection in the near future.