Streptococcus agalactiae

 Streptococcus agalactiae

GENERAL CHARACTERISTICS

·       Gram’s classification – Gram positive bacteria

·       Shape – Spherical (Cocci)

·       Arrangement – Chain form arrangement.

·       Motility – Non-Motile

·       Capsule – Absent

·       Endospores - Absent

·       Respiration – Aerobic/Facultative anaerobic

·       Optimum Temperature - 37 °C

·       Optimum pH – 7.0

·       Streptococcus type (Lancefield classification) – Group B

·       Habitat – Upper respiratory tract and Genitourinary tract.

·       Discovered by Rebecca Lancefield (American Microbiologist) in 1930 from milk and cows with Bovine mastitis.

PATHOGENICITY OF Streptococcus agalactiae

DISEASE TRANSMISSION

            Streptococcus agalactiae infections are mainly transmitted by

a)     Person-to-person spread by respiratory droplets.

b)     Through breaks in skin after direct contact with infected person, fomite, or arthropod vector.

INCUBATION PERIOD

7 Days

VIRULENCE FACTORS OF Streptococcus agalactiae

(i)    Capsular polysaccharide (rich in Sialic acid)

(ii)  Beta Hemolysin 

PATHOGENESIS OF Streptococcus agalactiae

·       Streptococcus agalactiae , originally discovered as a cause of Bovine mastitis in Cattles

·      It is part of the normal bacterial flora colonizing the Gastrointestinal tract and Genitourinary tract of a significant proportion of the human population. However, it occasionally becomes an infectious pathogen colonizing the Uterus, Blood, Brain, and Meninges.

·     Like Streptococcus pyogenes, Streptococcus agalactiae has multiple mechanisms for avoiding Opsonization (molecules enhancing Phagocytosis) and Phagocytosis.

·    Streptococcus agalactiae pathogen is one of the leading causes of invasive infections in non-pregnant Immunocompromised individuals and also causes Bacteremia, Septicaemia, Meningitis, and Pneumonia. 

CLINICAL DISEASES CAUSED BY Streptococcus agalactiae

(i) Early onset Neonatal disease

·    Within 7 days of birth, infected newborns develop signs and symptoms of Pneumonia, Meningitis and Sepsis.

(ii)  Late onset Neonatal disease

·      More than 1 week after birth, neonates develop signs and symptoms of Bacteremia with Meningitis.

(iii)  Infections in Pregnant women

·       Most often present as Postpartum endometritis (Pregnancy infection), Wound infections, and Urinary tract infections; Bacteremia and disseminated complications may occur.

(iv)   Infections in other Adult patients

·       Localized skin infection with pain, inflammation, lymph node enlargement and systemic symptoms.

LABORATORY DIAGNOSIS OF Streptococcus agalactiae

MICROSCOPIC EXAMINATION

·     Gram stating – Violet coloured Gram positive cocci arranged in form of Chains.

·     Motility test – Non-Motile.

 COLONY MORPHOLOGY ON CULTURE MEDIUM

·     Blood agar – Grayish white, transparent to translucent, matte or glossy; smooth; flat; large zone of Beta hemolysis.

·     MacConkey agar – Variable.

BIOCHEMICAL TESTS

a)     Catalase test - Negative

b)     Oxidase test - Negative

c)     Urease test - Negative

d)     Indole test - Negative

e)     Methyl Red (MR) test - Negative

f)      Voges Proskauer (VP) test - Positive

g)     Citrate utilization test – Negative

h)    Starch Hydrolysis – Negative

i)      Casein Hydrolysis – Negative

j)      Alkaline phosphatase activity – Positive

k)     Arginine Dehydrolase – Positive

l)      Hyaluronidase test – Positive

m)   CAMP Test – Positive

n)    Hippurate Hydrolysis Test - Positive

o)     Bacitracin Test  - Resistant

p)     PYT Test – Negative

ANTIBIOTIC THERAPY AND TREATMENT

·     Penicillin G is the drug of choice.

·     Combination of Penicillin and Aminoglycoside is used in patients with serious infections.

·     Cephalosporin or Vancomycin is used for patients allergic to Penicillin.

·     For high-risk babies, Penicillin is given at least 4 hours before delivery.

·     No vaccine is currently available.