NAME: Streptococcus agalactiae
SYNONYM OR CROSS REFERENCE: Group B streptococci, GBS
CHARACTERISTICS: Streptococcus agalactiae is a gram-positive bacterium that is a facultative anaerobe Footnote 1, Footnote 2. Usually found in pairs or chains of up to 50 cells or more, this ovoid bacterium is usually 0.5-1.0 x 1.0-2.0 µm in size Footnote 1, Footnote 3. It is β-hemolytic on blood agar and has 9 different serotypes (Ia, Ib, II, III, IV, V, VI, VII, VIII) Footnote 1, Footnote 2, Footnote 4.
PATHOGENICITY/TOXICITY: Streptococcus agalactiae is most commonly associated with neonatal infections such as sepsis, pneumonia and meningitis Footnote 1. In early onset disease, usually occurring within the first 24-48 hours 1-7 days of life, the newborn may be colonized by the bacterium through the amniotic fluid or during birthing, and 50% of early onset cases show signs of disease at birth Footnote 1, Footnote 5. Symptoms include respiratory distress, fever, lethargy, irritability, apnea and hypotension Footnote 1. Late onset disease which occurs at the age of 1-3 months 7 days to 3 months is more likely to cause bacteremia or meningitis (25% of cases). Focal infections, such as of the bones and joints, can also occur Footnote 1, Footnote 5. The risk of death is twice as high in older infants as it is in neonates and, even with appropriate treatment, neonatal infections with Streptococcus agalactiae have a 20% mortality rate Footnote 1, Footnote 5. 65% of deaths in neonates are seen in infants weighing less than 2500 grams Footnote 5. In adults, this bacterium can cause peripartum choriomamniotitis and bacteremia in new mothers (0.03% of cases) as well as pneumonia, skin and soft tissue infections, endocarditis, osteomyelitis and UTIs in other adults Footnote 1, Footnote 2. It is only fatal in adults in the immunocompromised or elderly (mortality rate of 15% in patients aged 65 or older) Footnote 1, Footnote 5. Neonates who are premature, have a low birthweight or a ruptured amniotic membrane, as well as adults who are elderly, immunocompromised, alcoholic or who have diabetes mellitus, cancer, HIV-AIDS, cirrhosis or stroke are at higher risk for developing a Group B streptococcal infection Footnote 1, Footnote 2, Footnote 6.
EPIDEMIOLOGY: Worldwide distribution. One third of all clinical cases caused by Streptococcus agalactiae occur in neonates who are 24-48 hours old, and only 8% of cases happen in infants older than 2 days Footnote 5. The incidence of infection was lowest in the 3 month to 14 year old age group Footnote 5. About 2% of all infants are infected by this bacterium although 75% of infants exposed are colonized without any clinical signs of infection Footnote 1, Footnote 5. 10-30% of women are colonized and are asymptomatic although 0.03% of pregnant women do get a Streptococcus agalactiae infection Footnote 1, Footnote 5. Serotypes Ia, III and V are the most common cause of disease by this bacterium in neonates, pregnant women and nonpregnant adults Footnote 4.
HOST RANGE: Humans (neonates, elderly, immunocompromised, diabetic, alcoholic, and stroke and cancer patients have a higher risk of infection), cattle (mastitis), dogs, cats, rabbits, horses, guinea pigs, and goats have been shown to contain the infectious agent Footnote 1, Footnote 2, Footnote 7, Footnote 8.
INFECTIOUS DOSE: Not known.
MODE OF TRANSMISSION: 10-30% of women have Group B streptococci in their genital tracts although the bacterium is normally a resident of the gastrointestinal tract Footnote 1. During birth, the bacterium can colonize the baby via the amniotic fluid or the mucous membranes (oral, nasopharyngeal, vaginal, and anal mucosa, as well as skin) and produce an early onset infection 24-48 hours after birth Footnote 1, Footnote 9. Late onset cases (1-3 months after birth) may be contracted by contact with the mother or the environment Footnote 1. Fecal-oral transmission may occur and sexual contact plays a role in colonization Footnote 7. Hand-to-mouth and aerosol transmission is common for streptococci Footnote 10.
INCUBATION PERIOD: For early onset disease, less than 7 days. For late onset disease, the incubation period is unknown Footnote 14.
COMMUNICABILITY: Humans carry the pathogen in their throat, genitourinary tract and their rectum Footnote 11. The organism is spread from the mother to the baby during birth, or, in cases with ruptured amniotic membranes, in the uterus Footnote 1, Footnote 9. Antibiotic treatment of the mother to eradicate genital tract group B streptococci has shown to only be useful temporarily and reinfection may occur Footnote 12.
ZOONOSIS: Cattle to human spread may be possible; however, most strains found in cattle are different from the human strains with regards to serotype, pigmentation, lactose fermentation, β-D-galactosidase activity and drug susceptibility Footnote 7, Footnote 13. They are, therefore, not a significant risk for human infection Footnote 13.
DRUG SUSCEPTIBILITY: Susceptible to penicillin or a combination of ampicillin and an aminoglycoside Footnote 1. Streptococcus agalactiae is also sensitive to vancomycin, ciprofloxacin, clindamycin, erythromycin, cotrimoxazole, and ceftriaxone Footnote 9. It is generally resistant to macrolides and clindamycin resistance has also occurred Footnote 6.
SUSCEPTIBILITY TO DISINFECTANTS: Susceptible to 2-5% phenol, 1% sodium hypochlorite, 4% formaldehyde, 2% glutaraldehyde, 70% ethanol, 70% propanol, 2% peracetic acid, 3-6% hydrogen peroxide, and iodine Footnote 14.
PHYSICAL INACTIVATION: Sensitive to moist heat at 55 ºC for 30 minutes Footnote 3. Bacteria are also susceptible to moist heat (121 ºC for at least 15 minutes) and dry heat (160-170 ºC for at least 1 hour) Footnote 15. Fecal streptococci can be inactivated by ozone Footnote 16.
SURVIVAL OUTSIDE HOST: This bacterium has been found to survive months in dry dust in buildings Footnote 3. It can also survive in milk at -20 ºC for 4 weeks and in fish tissues at -70ºC for at least 9 months Footnote 11, Footnote 17.
SURVEILLANCE: Monitor for symptoms and confirm by culture of blood or CSF Footnote 1. Serology can be used to determine the Lancefield group Footnote 1. Screening of pregnant women with vaginal and rectal swabs and urine cultures.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Antibiotic treatment is used to treat infection by Streptococcus agalactiae Footnote 1.
IMMUNIZATION: No vaccine is available for humans Footnote 18.
PROPHYLAXIS: Intrapartum antimicrobial prophylaxis at the onset of labour or rupture of membranes with IV penicillin or ampicillin has been shown to reduce transmission and morbidity to the neonate, particularly those at risk (premature) Footnote 1, Footnote 2. Prophylaxis should only be given to women who are carriers (can be determined by rectal or vaginal swab as of 35-37 weeks of gestation), GBS bacteriuria, previous infant with invasive GBS disease, less than 37 weeks gestation (unless negative swab in last 5 weeks), intrapartum fever or unknown GBS status and prolonged membrane-rupture Footnote 18, Footnote 19.
LABORATORY-ACQUIRED INFECTIONS: 78 laboratory-acquired infections due to Streptococcus spp. were reported up to 1976 Footnote 14.
SOURCES/SPECIMENS: Streptococcus agalactiae has been isolated from blood, cerebrospinal fluid, joint fluid, peritoneal fluid, pleural fluid, bone, vaginal, throat and rectal cultures, aerosols and feces Footnote 1, Footnote 6, Footnote 7.
PRIMARY HAZARDS: Accidental parenteral inoculation, ingestion, inhalation of infectious aerosols and direct contact are the primary hazards when working with this pathogen (reference needed).
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk group 2 Footnote 20.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures Footnote 10.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 21.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 21.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up Footnote 21.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2011