encapsulated pathogens

Question 1

Hemophilus influenzae structure

Answer 1

This is a small Gram-negative bacillus, which may appear as a coccus hence, the term coccobacillus is frequently used to describe this organism

Question 2

H. flu growth requirements

Answer 2

NAD = V factor Heme = X factor. Grows on Chocolate Agar which has these factors added to it. Can also grow near Staph on blood agar b/c staph provides NAD

Question 3

compare the growth requirements of H. flu, H. ducreyi and H. parainfluenza

Answer 3

H flu: requires factor X and V. H. ducreyi: requires Factor X only. H. parainfluenza: requires factor V only

Question 4

Strep pneumoniae structure

Answer 4

Gram-positive diplococcus that readily grows on blood agar. Lancet shaped-each side of the diplococcus is pointed. Produces alpha hemolysis. Will see capsule as a ring around the diplococcus

Question 5

How to distinguish Strep viridians vs strep pneumonia

Answer 5

Both are alpha hemolytic. OVRPS: optochin- viridian are resistant, pneumonia are sensitive

Question 6

N meningitidis structure

Answer 6

Gram-negative diplococcus, which is very similar morphologically to Neisseria gonorrhoeae.

Question 7

lab diagnosis of encapsulated bacteria

Answer 7

specific tests frequently involve the detection of capsular polysaccharides with antiserum

Question 8

Problems with lab diagnosis

Answer 8

1. if pt has been treated with Abx, use immunological methods to diagnose. 2. Must determine difference between mere colonization and infection. A sufficient laboratory diagnosis is when these organisms are found in a normally sterile site (e.g. blood or spinal fluid) in a patient. 3. Culture may be difficult to obtain

Question 9

Immunological diagnosis of encapsulated bacterial infection

Answer 9

The organism may shed its capsule in the blood, urine or spinal fluid. , it may be possible to detect the capsular material in these body fluids with antiserum directed at the specific capsular polysaccharide without being able to culture the organism.

Question 10

Most important virulence factor for encapsulated bacteria

Answer 10

The polysaccharide capsule (composed of polymers of different kinds of sugars) is the most critical virulence factor necessary for these organisms to produce invasive disease. If these organisms do not produce a capsule then, they are either avirulent or they tend to produce only focal infections (e.g., otitis media, sinusitis) or infections in debilitated patients where trauma has produced a link between sinuses and brain or, in neonates (sepsis).

Question 11

h flu: total number of serotypes, serotype that causes invasive disease, most predominant serotype

Answer 11

6 serotypes a-f. serotype b is most invasive. Serotype a is most common because of the vaccine against serotype b.

Question 12

What is unique about h flu serotype b’s polysaccharide capsule

Answer 12

The same polysaccharide found in serotype b is found in almost all Gram-positive organisms (in the teichoic acids). these other bacteria probably play a role in the ultimate development a protective immune response against H. influenzae. This can lead to a misdiagnosis of H flu or S pneumonia due to cross reactivity btw their antisera

Question 13

s. pneumoniae: total number of serotypes

Answer 13

90 serotypes. 12 types cause most infections. Some of the capsules or the teichoic acid of S. pneumoniae will cross react with H. influenzae type b capsule

Question 14

N. meningitidis: number of serotypes, unique capsules

Answer 14

9 serotypes A,B,D,C,X,Y,Z,W135 and 29E. A-C are most common. The type B polysaccharide is composed of a polymer of N-acetyl neuraminic acid and is non-immunogenic in humans because N-acetyl neuraminic acid, also called sialic acid, is extensively found in humans (e.g. brains, kidneys). This has prevented development of a vaccine against this group. Also, the group B capsule is identical to the K1, capsule of E. coli an organism, which causes meningitis in neonates (0-6 months).

Question 15

Which bacteria produce IgA protease and what is its function

Answer 15

H. flu, S. pneumoniae, N. meningitidis and N. gonorrhea. This enzyme specifically cleaves human IgA, at the hinge region of the antibody molecule. These pathogens initiate infection at mucosal surfaces where IgA is the only kind of antibody available to block adherence of these organisms to mucosal surfaces. By cleaving IgA, they are able to initiate infection better

Question 16

Which encapsulated organisms produce LPS and what does it do

Answer 16

H. flu, N. meningitidis (gram negatives). LPS is a virulence factor which can cause DIC and septic shock

Question 17

encapsulated pathogens epidemiology

Answer 17

H. flu, N. meningitidis and s. pneumonia can all be found in upper respiratory tract of normal people. With H. influenzae and N. meningitidis most of these strains from normal populations are unencapsulated. spread by droplet contact

Question 18

compare viral vs bacterial meningitis

Answer 18

Viral meningitis is generally less severe and most of the time resolves without specific treatment, while bacterial meningitis is quite severe and may result in brain damage, hearing loss, learning disability or death

Question 19

Who is predisposed to encapsulated infections

Answer 19

an increased incidence of disease is found in persons who do not have anti-capsular antibody or who have some predisposing condition (e.g. asplenic-no spleen, as from trauma).

Question 20

H. flu diseases

Answer 20

Meningitis, pneumonia, bacteremia, cellulitis, epiglottitis (usually in kids <7 yrs). Systemic dz in adults can occur from unencapsulated strains. Also otitis media.

Question 21

N. meningitidis diseases

Answer 21

this is the most common cause of bacterial meningitis in the 6 mo - 6 yr. age group and in young adults (i.e. high school and college age)

Question 22

S. pneumoniae diseases

Answer 22

most common cause of bacterial meningitis in all adults. It is the most serious pneumococcal infection with a case fatality rate of ~40%. It is usually preceded by a symptomatic infection of the upper respiratory tract.Can also cause pneumoniaand otitis media. In young children increased incidence is related to lack of specific capsular antibody.

Question 23

most common cause of otitis media

Answer 23

strep pneumo

Question 24

The primary site of colonization for H. flu, S. pneumoniae and N. meningitidis

Answer 24

upper respiratory tract

Question 25

Antibiotics used for H. flu, S. pneumoniae and N. meningitidis

Answer 25

H. flu: third generation cephalosporins. Chloramphenical is alternative (but is toxic). Most are resistant to ampicillin. N. meningitidis: Third and Fourth generation broad, spectrum cephalosporins are now frequently used. S. pneumoniae: Vancomycin only. Resistant to penicillin and multi-drug resistance is emerging.

Question 26

Chemoprophylaxis

Answer 26

Administration of rifampin or ciprofloxacin is given to people who have come in contact with other people diagnosed with meningitis caused by H. flu, S. pneumoniae and N. meningitidis

Question 27

H. flu vaccine

Answer 27

For H flu serotype B: All of them have a polysaccharide linked to a carrier protein (diphtheria toxoid or tetanus toxoid) to make it T-cell dependent. Induces immune response in newborn infants. Is also present in Tetramune vaccine (DPT vaccine). It is recommended that the primary immunizations be administered at 2,4,6 and 15-18 months of age with a booster dose at 4-6 years of age

Question 28

Meningococcal vaccine

Answer 28

MCV4 or MenactraT. Includes serogroups C, Y, W-135 and A. A is most common in Africa.

Question 29

Who should receive MCV4 vaccine

Answer 29

Children aged 2 months through 10 years who are at increased risk for meningococcal disease, Travelers to or residents of countries with high rates of meningococcal dz, kids with asplenia, All children 11-18 yrs, Entry to high school or college, microbiologists, military recruits.

Question 30

What is Bexsero

Answer 30

A group B N. meningitidis vaccine. Contains three serogroup B protein antigens- Neisserial adhesin A single protein, Neisseria Heparin Binding Antigen fusion protein, factor H Binding Protein fusion protein and PorA P1.4 as the main antigen of Outer Membrane Vesicles (OMV). It is FDA approved for use in people 10-25 years of age as a 2-dose series

Question 31

Pneumovax

Answer 31

contains purified capsular materials of the 23 types of S. pneumoniae strains that most frequently caused disease. This vaccine may have little or no value in elderly and chronically ill against pneumococcal pneumonia. It is effective against pneumococcal bacteremia, which is very uncommon.

Question 32

Prevnar

Answer 32

Vaccine against 13 capsular types of S. pneumoniae strains that cause >90% of invasive (e.g. meningitis) diseases in children <6yrs of age in the U.S. The polysaccharides are conjugated to diphtheria toxoid.

Question 33

Who should receive Prevnar

Answer 33

infants and toddlers ages up to 23 months, certain older children 24-59 months – African Americans (especially those with Sickle Cell Disease), Native Americans, Alaskan Americans, children with HIV, immunocompromised children or children with chronic diseases, 24-59 month old children in day care, economically disadvantaged. Also adults over 50 to prevent pneumonia and invasive dz.

Question 34

IgA vs IgG vs IgM in protecting against bacterial meningitis

Answer 34

IgA is cleaved by IgA proteases, so people with IgA immunity against capsules have worse outcomes. IgM and IgG have better protections