Lecture 6: Gram negative bacteria -Neisseria

Question 1

What is the most common agar used to isolate Neisseria?

Answer 1

Thayer-Martin VCN agar

Question 2

Neisseria characteristics

• Gram (+) or (-)
• shape
• species

Answer 2

The ONLY Gram (-) cocci

• found in pairs: diplococci
• each coccus shaped like a kidney bean, and a pair of cocci sticks together with their concave sides facing each other
• 2 species causes disease in humans: Neisseria meningitidis, and Neisseria gonorrheae

Question 3

Neisseria meningitidis

• causes what?
• found where?
• high risk groups (2)

Answer 3

Besides causing meningitis, also causes life threatening sepsis (meningococcemia)

• usually found in the normal flora of nasopharynx of some individuals (~5% of population) called carriers, this enables them to develop anti-meningococcal antibodies
• High risk groups:
  (1) infants aged 6mo-2yrs
  (2) army recruits

Question 4

Neisseria meningitidis

-Virulence Factors (4)

Answer 4

(1) Capsule -A polysaccharide capsule surrounds the bacterium; anti-phagocytic as long as there are no specific antibodies to coat (opsonize) it
- N.meningitidis is classified into 13 serogroups based on different capsular polysaccharides that are antigenic
- Serogroups A,B, and C cause meningitis
(2) Endotoxin (LPS) -can release endotoxin which causes blood vessel hemorrhage and sepsis, hemorrhage seen on skin as tiny round red dots calle petichiae
(3) IgA protease -only found in pathogenic sps. of Neisseria. Cleaves IgA in half
(4) Pili -allows attachment to human nasopharyngeal cells and undergoes antigenic variation to avoid attack by immune system

Question 5

Meningococcal disease

-where found/how spread?

Answer 5

• N.meningitidis spreads via respiratory secretions and usually lives asymptomatically in the nasopharynx
• rarely the bacteria will invade the blood stream from the nasopharynx, resulting in meningitis and/or deadly sepsis (meningococcemia)

Question 6

Meningococcal disease

-Meningococcemia

Answer 6

Intravascular multiplication of N.meningitidis results in an abrupt onset of spiking fevers, chills, arthralgia (joint pains),muscle pains,&petichial rash
-once in the blood stream the meningicocci rapidly disseminate throughout the body

Question 7

Meningococcal disease

-Fulminant meningococcemia

Answer 7

Septic shock. Bilateral hemorrhage into the adrenal glands occurs, which causes adrenal insufficiency. Abrupt onset of hypotension and tachycardia occurs, along with rapidly enlarging petichial rash

Question 8

Meningococcal disease

-Meningitis

Answer 8

Usually occurs in infants under 1 yr of age. Infants usually display nonspecific findings of an infection, including fever, vomiting, irritability, and or lethargy. Slightly older infants may display a stiff neck.

Question 9

Meningococcal disease

-Clinical Pearl

Answer 9

• *3 bacteria are responsible for most meningits acquired by the baby coming out of the birth canal:
  
  • Listeria monocytogenes, E.coli, and Group B Strep
• *2 bacteria cause meningitis later in life:
  
  • N.meningitidis and Haemophilus influenzae

Question 10

Meningococcal disease

• Diagnosis
• Treatment

Answer 10

Diagnosis

• Gram stain and culture of meningococcus from blood, CSF, petechial scrapings
• classic medium for culturing Neisseria is Thayer Martin VCN media which is chocolate agar with antibiotics: Vancomycin -kills G(+), Colistin - kills G(-) except Neisseria, Nystatin- kills all fungi

Treatment

• Penicillin G or ceftiaxone is reeq’d at the first indication of disseminated meninococcemia
• close contacts of an infected patient are treated with Rifampin

Question 11

Neisseria gonorrheae

Answer 11

Often called the gonococcus causes the 2nd most commonly transmitted sexual disease, gonorrheae

Question 12

Neisseria gonorrheae

-Virulence factors (x3)

Answer 12

(1) Pili -has complex genes coding for pili. These genes undergo multiple recombinations resulting in the production of pili with hypervariable amino acid sequences. These changing antigens in the pili protect the bacteria from our antibodies as well as vaccines
(2) Outer membrane protein porins -PorA and PorB appear to promote invasion into epithelial cells
(3) Opa proteins -promote adherence and invasion into epithelial cells

Question 13

Gonococcal Disease in Men

Answer 13

• a man having unprotected sex with an infected person can acquire a Neisseria gonorrheae infection
• possible complications of this infection include epididymitis, prostatitis, and urethral strictures
• the disease is easily cured by a small dose of ceftriaxone

Question 14

Gonococcal Disease in Women

Answer 14

• Gonococcal urethreitis in women is characterized by painful burning on urination and purulent discharge from the urethra
• Gonococcal infection of the cervix can progress to pelvic inflammatory disease (PID)
• *PID is an infection of the uterus (endometritis), fallopian tube (salpingitis) and/or ovaries (oophoritis)

Question 15

Complications of PID

Answer 15

• Sterility -the risk of sterility increases with each gonorrheae infection
• Ectopic pregnancy -due to fallopian tube inflammation, fallopian tubes are te most common site for an ectopic pregnancy
• Abscesses -may develop in the fallopian tubes, ovaries, or peritoneum
• Peritonitis -bacteria may spread from ovaries and fallopian tubes to infect the peritoneal fluid
• Peri-hepatitis -the classic presenting symptom of perihepatitis is severe right upper quadrant abdominal pain

Question 16

Gonococcal Disease in Infants

Answer 16

• Neisseria gonorrheae can be transmitted from a pregnant woman to her child during delivery, resulting in ophthalmia neonatorum (gonococcal conjunctivitis)
• this eye infection usually occurs on the 1st or 2nd day of life and can damage the cornea, causing blindness
• neonatal chalmydia eye infections are also a threat, erythromycin eye drops which are effective against both Neisseria gonorrheae and Chlamydia are given to all newborns