Streptococcus agalactiae group B - Effect on newborns and carrier status in pregnant - Culture; Molecular diagnosis (PCR).

 

Information 09-09-2016.

 

Streptococcus agalactiae group B is a Gram positive facultative anaerobic bacteria aerobically-similar in structure to other gram - positive cocci of the genus Streptococcus. His clinical interest mainly lies in being a major cause of sepsis, meningitis and death in newborns. Infections in newborns can be divided from the point of view of time of onset, in early infections (appear before 7 days after birth) and late - onset infections (7 days to three months after delivery). The most serious processes in the context are neonatal sepsis, meningitis and pneumonia. Those affected by this infection require prolonged hospitalization, and those who survive can suffer brain damage with mental retardation and / or visual disturbances.

 

This bacterium can cause unusual infections that can have a (protein complex C) protein complex, comprising four antigenic components (?, ?, ? and ?) involved in the interaction with the defense mechanisms. The strains of this bacterium having the ? and ? components are more virulent because they are more resistant intracellular killing and opsonophagocytosis mediated by the interaction of specific antibodies, serum complement and polymorphonuclear leukocytes. About 60% of the isolates of Streptococcus agalactiae group B, may have the protein complex C.

 

Infections of newborns is usually acquired during childbirth contact with the genital tract of the mother, colonized by this bacteria to vaginal or rectal level. The prevalence of colonization in pregnant usually between 15 and 40%. The same female carriers also are at risk for serious infections after childbirth. For this reason, screening (screening) is recommended to detect colonization in pregnant women, pregnant women to identify candidates for intrapartum prophylaxis receive. Intrapartum antibiotic prophylaxis interrupts transmission from mother to child and reduces the incidence of disease occurring early (before 7 days after birth).

 

Since 2002, the US FDA recommended that all women between 35 and 37 weeks gestation were carried out a detection (screening) to see if they were colonized by this bacteria and were offered prophylactic antibiotics to which they were carriers. For this detection carrier status to vaginal and rectal level it must be performed by culturing at 35 to 37 weeks gestation. If this detection not been made, the risk to the onset of labor can be evaluated, taking into account the existence of maternal fever, prolonged interval between membrane rupture and delivery, or the existence of preterm labor (premature ), in which case it is recommended that antibiotic prophylaxis. The administration of intrapartum antibiotic prophylaxis based solely on risk assessment, has the disadvantage that the administration of antibiotics is often unnecessary, not really exist colonization by this bacterium. Therefore, it is recommended to know before delivery the risk of colonization.

 

Recommended tests:

 

To know the status of colonization in pregnant women is recommended:

 

• Detection of female carriers

• • • Culturing a combined vaginal and rectal sample taken with the same swab previously introduced into vagina (see recommendations after sampling), and subsequently at right (see recommendations after sampling). This sample should be cultured in a liquid medium enrichment antimicrobial inhibitors normal flora in these locations. Once incubated sample in the enrichment medium for 18 to 24 hours, subculturing must be performed on solid medium and then perform the identification of Streptococcus agalactiae group B, so that the diagnosis is not available before 36 to 48 hours. A drawback of the culture is that the presence of Enterococcus spp. in samples can inhibit the growth of Streptococcus agalactiae group B, obtaining negative results although crops were present. Overall the culture is estimated that has a sensitivity of 42% and a specificity of 100%.

• • • Molecular diagnosis to detect genes of group B Streptococcus agalactiae This test has the advantage of not requiring for its accomplishment the time required for cultivation and identification of Streptococcus agalactiae group B, or is inhibited by the presence of Enterococcus spp. in the sample. The sensitivity of this test depends on the target gene used to detect, being between 75 and 99%, with a specificity of 100%.

• Diagnosis of sepsis, neonatal sepsis, neonatal meningitis

The definitive diagnosis of sepsis or neonatal meningitis is often difficult because the signs and symptoms of newborns with these infections can be similar to those of other non - infectious, so is required to perform bacterial cultures and empirical antibiotic combination therapy for presumed sepsis. Even blood cultures may have low sensitivity due to the intermittency of the presence of bacteria in the blood and the low blood volume cultivated. It also requires time on the automatic detection of 24 to 48 hours. Therefore, the molecular detection after previous enrichment in culture for about 5 to 10 hours, is a preferred method.

 

• • • Blood culture or cerebrospinal fluid, blood or CSF respectively.

• • • Molecular diagnosis in blood samples or cerebrospinal fluid, respectively, com prenriquecimiento to increase the sensitivity of the test.

Tests in IVAMI:

 

• Selective culture media and identification.

• Molecular detection (PCR).

Recommended sample:  

• Crops  

• • Vaginal sample: after removal of secretions or vaginal exudates, obtained with a swab mucus secretion inner third of the vagina. Place the swab in transport medium such as Stuart 's medium (0.5 ml). Conducting the culture within 24 hours after sampling.

• • Rectal shows: introducing a swab to a depth of 2.5 cm after having passed through the anal sphincter, carefully rotate the swab to contact mucosal crypts. Place the swab in transport medium such as Stuart 's medium (0.5 ml). Conducting the culture within 24 hours after sampling.

• • Vaginorectal combined sample: take the vaginal sample under the conditions described previously , and then introduce the same swab into the rectum and taking the sample under the conditions described. Place the swab in transport medium such as Stuart 's medium (0.5 ml). Conducting the culture within 24 hours after sampling.

• • Blood samples or liquid cefalorraquíneo in cases of sepsis or meningitis.

• Molecular detection (PCR)  

• • Vaginal swab sample taken identically to that shown in the sample for crops without introducing in transport medium.  

• • Rectal shows sample taken identically to that shown in the sample for crops without introducing in transport medium.  

• • Vaginorectal combined sample: sample taken identically to that shown in the sample for crops without introducing in transport medium.  

• • Blood samples or liquid cefalorraquíneo in cases of sepsis or meningitis.

Preservation and shipment of sample:

 

• Refrigerated (preferred) for less than 2 days.

• Frozen: over 2 days.

 

Cost of the test:

 

• Consult ivami@ivami.com