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Group B Streptococcus &

Enterococcus

Prabin ShahBScMLT, MScMLT

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Group B Streptococcus

Introduction

Pathogenisis

Laboratory diagnosis Enterococcus

Introduction

Clinical mainifestation

Vancomycin resistance Enterococci

Contents

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Introduction

Gram-positive cocci Chains Encapsulated Non-motile Facultative anaerobes Lactic acid production Multiple nutritional

requirements 1-4 mm diameter, grey-

white, flat, mucoid Selective Broth Media

(SBM) or Lim broth

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• Divided into the following serotypes based on

capsular polysacchride. types Ia, Ib,II and III through VII.

• All serotypes can cause infections in newborns but Ia,II,III,V account for 90%.

• Late onset dx and early-onset meningitis is due to type III.

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β-hemolysis RBCs surrounding the colony are completely lysed

“Hemolysin" toxins Narrow hemolysis zones CAMP factor enhances hemolysis

Carbohydrate Antigens (C substance) Lancefield Group B Group specific antigen

Polysaccharide Capsule Serotypes 150 oligosaccharide subunits with mono-, di-, tri-

side chains Ia, Ib, II-VIII III and V completely sequenced

Classification

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Epidemiology

Approx. 10%-35% of pregnant women are asymptomatic carriers of GBS in the genital and Gastro Intestinal tract.

At birth 1 in 2 infants born to colonized mothers are colonized.

98% of colonized infants are without symptoms, but 1%-2% developed GBS.

Nearly 50% of sexual partners of colonized women are colonized themselves.

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• Incidence rate of 0.2 – 3.7/1000 live births.

• Mortality rate of 5-15/1000 live births.

• More recent surveillance shows a decrease in Incident rate to 0.8 per 1000 live births-reflection of use of maternal antibiotic prophylaxis

• Direct cost of treating neonate with proven GBS – 300 million dollars/year.

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Virulence Factor

GBS Surface Polysaccharide Capsule Antiphagocytic properties Sialic acid residues on capsule inhibit the binding

of active C3 component of complement to the cell surface blocking activation of the alternative

pathway Transplacental passage of type-specific anti-

capsular IgG antibody from mother to infant is an important protective factor against invasive disease

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GBS β-hemolysin Cytotoxic to pulmonary epithelial and endothelial

cells Pulmonary injury and alveolar protein exudate in

early-onset pneumonia

Activity is blocked by surfactant phospholipid Increased risk of premature, surfactant-deficient

neonates for severe pneumonia Induces cytokine release and nitric oxide

production in macrophages Stimulate elements of the sepsis cascade

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C5a-peptidase Cleaves and inactivates the complement-derived

neutrophil chemoattractant C5a

C5a-peptidase-deficient mutants are more rapidly cleared from the lungs of infected animals when compared to the isogenic wild-type strain

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Pathogenesis

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What does group B Streptococcus do?

Colonisation Asymptomatic and

intermittent Intestinal (<30% of

adults) Vaginal (<25% of women)

Infection Newborn babies Adults: the elderly,

pregnant/postpartum women, others with underlying disease

IN MOTHER LOWER GENITAL

TRACT ANORECTUM URINARY TRACT

IN NEONATES EXTERNAL EAR (IN

FIRST 24 H ) ANTERIOR NARES,

THROAT ANORECTUM UMBILICUS

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Risk Factors for Colonization

Heavily colonized mothers Mothers younger than 20 African Americans Lower socioeconomic groups PROM Prolonged labor Maternal Chorioamnionitis Previous delivery with GBS disease

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Early onset vs. Late onset

Occurs in 1st week. Usually before 72hrs

Pathophysiology. -Colonization.

-Immature host defense mechanism particularly among low birth weight infants.

1week to 6months. Usually at 3-4 weeks.

Pathophysiology. - Alteration of the mucosa barrier by a viral respiratory tract infection.

- weakened host defense

- decrease amount of maternal antibodies.

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Early onset vs. Late onset

Transmission: - aquired through vertical transmission.

- during passage through a colonized birth canal.

Transmission: - aquired through horizontal transmission: -nurseries -hospital personnel

-community

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Early onset vs. Late onset

Clinical Manifestation - Pneumonia

- respiratory distress

- cyanosis,

- hypoxaemia

- apnea - Shock

- Poor feeding -Less often meningitis

- Abnormal temprature

Clinical manifestation: Occult bacteremia Meningitis Ventriculitis other focal

infections, e.g. septic arthritis, osteomyelitis.

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Laboratory Diagnosis

Colony morphology Grayish-white,

mucoid, creamy, narrow zone of b-hemolysis

Presumptive Identification tests Catalase-negative Bacitracin-

resistant

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Presumptive

identification tests Bile-esculin-

hydrolysis–negative

Does not grow in 6.5% NaCl

CAMP-test–positive

Hippurate test- positive

Latex agglutination test

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“Gold Standard” test for GBS carriage

When? 35-37 weeks of pregnancy

Where & who? Low vagina & anorectal swab/s (no speculum) Health care professional or pregnant woman

What culture method? Enriched Culture Medium (ECM) - 24-48 hours to

grow HPA BSOP58 Processing Swabs for GBS carriage

Pigmented Broth — Positive Result

Positive color change

Photo courtesy of Dr. Lesley McGee, CDC

Inoculate into enrichment broth Non-pigmented broth

Lim broth, TransVag brothTransVag broth should be supplemented with 5% defibrinated sheep blood

ORPigmented broth

StrepB carrot broth, Granada biphasic broth

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Antibiotic Recommendations —Intrapartum Prophylaxis

Standard: Penicillin (PCN) or ampicillin

Alternatives: • PCN-allergic and low risk for anaphylaxis:

cefazolin• PCN-allergic but high risk for anaphylaxis

depends on susceptibility to clindamycin & erythromycin

– If susceptible to clindamycin (including lack of inducible resistance) clindamycin

– If unknown or not susceptiblevancomycin

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Introduction to Enterococci

Enterococci are gram-positive cocci which often occur in pairs (diplococci)

Two species are common commensal organisms in the intestines of humans: E. faecalis and E. faecium

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Characters of Enterococci

Gram(+) , Catalase(－ ) Cocci

Can grow in media : 6.5% sodium chloride

E. faecalis and E. faecium (90%)

Part of the normal bowel flora. the prominent cause of nosocomial infections.

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Habitat of Enterococci

Enterococci normally inhabit the bowel.

They are found in the intestine of nearly all animals, from cockroaches to humans.

Enterococci are readily recovered outdoors from vegetation and surface water

In humans, typical concentrations of enterococci in stool are up to 108 CFU per gram .

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normal flora of the intestinal tract. Enterococcus faecalis frequently causes infections

within the peritoneal cavity especially following penetrating trauma such as gunshot wounds and surgical wounds urinary tract infections prostate infections infections of damaged or compromised skin, such

as diabetic or decubitus ulcers, burns, and surgical wounds.

Other opportunistic fecal streptococci include E. faecium and E. durans.

Growing Importance of Enterococci

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Prominent Cause of Nosocomial Infections

The enterococci have become the second most common bacterium isolated from nosocomial urinary and wound infections, and the third most common cause of nosocomial bacteremia.

Furthermore, the enterococci are among the most antibiotic resistant of all bacteria, with some isolates resistant to all known antibiotics

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Clinical Manifestation

Infections with VRE do not differ from other enterococcal infections other than in their therapy.

The most common sites of infection : The urinary tract and bloodstream.

In addition, enterococci may cause endocarditis due to their ability to adhere to heart valves.

They rarely cause respiratory tract infections.

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Identification

PYR-positive which differentiates them from S.bovis

Bile esculin agar test positive

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Vancomycin Resistant

ENTEROCOCCI

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Glycopeptides Mechanism of Action

Vancomycin and teicoplanin inhibit cell wall synthesis by forming complexes with peptidyl-D-alanyl-D-alanine termininal

vanA and vanB resistance phenotypes are associated with the acquisition of gene clusters that lead to the production of peptidoglycan ending in D-alanyl-D-lactate

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Vancomycin-resistant enterococci (VRE), first

reported in Europe in 1988, are emerging as a global threat to public health .

The incidence of VRE infection and colonization among hospitalized patients has increased rapidly in the last few years.

From 1989, the year VRE was first identified in the United States, through 1993. Infection with VRE may be associated with increased mortality , and no effective antimicrobial therapy is available for many VRE .

Vancomycin Resistance Increases Morbidity and Mortality

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VRE Epidemiology

Found world-wide, but rates vary greatly Hospital outbreaks often involve clonal spread Also seen in nursing homes and long term care

facilities First described in Europe Primarily a nosocomial pathogen Alarming increase from 1989 to 1993 intensive care units & teaching hospitals

vanA and vanB Phenotypes

vanA vanB

Vancomycin MIC >64 4-1024

Teicoplanin MIC 16-512 0.5

Usual species faecium, faecalis faecium, faecalis

Acquired Yes Yes

Transferable Yes Yes

vanC, vanD, and vanE Phenotypes

vanC vanD vanE

VancomycinMIC

2-32 128 16

TeicoplaninMIC

0.5 4.0 0.5

Usual species gallinarum,casseliflavis,flavescens

faecium faecalis

Acquired No Yes Yes

Transferable No No No

MOLECULAR BASIS OF VANCOMYCIN RESISTNACE

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ResultSpreading Resistance

Enterococci that acquire the vanA phenotype are highly resistant to vancomycin and to teicoplanin

Enterococci can pass the vanA gene cluster to S. aureus E. faecalis rather

tan E. faecium (so far)

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Urinary tract infection (most common) Intra-abdominal and pelvic infection (also

common) Surgical wound infection Bacteremia—bacteria in the blood Endocarditis —infection of the inner surface of

the heart muscles and valves Neonatal sepsis —bacteria in the blood,

occurring in infants Meningitis —infection of the membranes that

surround the brain and spinal cord

Infections Caused by Vancomycin Resistant Enterococci

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DIAGNOSIS OF DRUG RESISTANCE INENTEROCOCCI

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Detection of Vancomycin Resistance

Susceptibility to vancomycin can be performed by Kirby-Bauer Disc Diffusion Method on Mueller Hinton Agar by using 30µg vancomycin disc

Vancomycin resistance can also be determined by Vancomycin agar screen method using 6µg/ml of vancomycin incorporated in Brain Heart Infusion (BHI) agar.

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Minimum Inhibitory

Concentration (MIC) of all the isolates were done by Macro broth dilution method, using dilutions of vancomycin ranging from 2 µg/ml to 512 µg/ml.

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Drug Resistance can be Established by E-Test

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*Chromogenic Methods in Diagnosis of VRE

Chromogenic medium for the detection of Vancomycin Resistant Enterococcus (VRE) E. faecalis and E. faecium

* Colorex™ Prepared Chromogenic Media by BioMed Diagnostics

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Genotypic Detection of VRE

Rapid detection of vancomycin resistance by polymerase chain reaction (PCR). useful in epidemiologic studies

PCR can`t be performed directly on clinical specimens.

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Control and Prevention

Limiting the use of certain broad spectrum antibiotics may also lead to a decrease in the rates of VRE colonization and infection.

One study suggested that reduction of third-generation cephalosporins with the substitution of piperacillin/tazobactam could reduce the incidence of VRE in an intensive care unit setting Hospital Infection Control Practices Advisory Committee (HICPAC). Recommendations for preventing the spread

of vancomycin resistance. Infect Control Hosp Epidemiol 1995; 16:105

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The CDC has published recommendations

for preventing the spread of vancomycin resistance

Prudent use of vancomycin Education of hospital staff regarding the problem Rapid and accurate identification of VRE in the

microbiology laboratory Aggressive infection control measures utilizing

contact isolation and cohorting where necessary to prevent person-to-person transmission

Hospital Infection Control Practices Advisory Committee (HICPAC). Recommendations for preventing the spread of vancomycin resistance. Infect Control Hosp Epidemiol 1995; 16:105

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Hand Washing can Reduce the Spread of

VRE

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Ananthanarayan & paniker`s , Textbook of

Microbiology Koneman`s Color Atlas and Textbook of

Diagnostic Microbilogy Topley`s and Wilson Textbook of Microbiolgy http://www.gbss.org.uk/filepool/BSOP58.pdf

http://www.cdc.gov/groupbstrep

References