Neisseria Gonorrhoeae

Characteristics/Epidemiology

Infects epithelial cells in urethra, rectum, cervix, pharynx, conjunctiva.

Most often colonises genitourinary tract and rectum

Pathogenesis/Transmission

Transmission - sexual, or through vaginal delivery

Does not survive long outside human body due to sensitivity to dehydration.

1. Pili

• Helix made up of repeating peptide (pilin)
• Enhance attachment to epithelial and mucosal cells.
• Gives resistance to phagocytosis and also antigenic
• Most important virulent factor (Only piliated gonococci are virulent)

Also, gene conversion and phase variation help avoid immune response and cause repeated infection

• A single strain of N. gonorrhoeae has genes for different pili but not expressed at the same time. At different times it can synthesize different pilins (gene conversion).
• Sometimes no pilin is made due to reading frame shift, and thus the strain becomes nonpiliated (phase variation)

2. Lipooligosaccharide (LOS)

More branched than other gram-negative bacteria's lipopolysaccharide (LPS).

Targeted by IgM

3. Outer membrane proteins (OMPs)

OMPI and OMPIII complex together to form a porin.

OMPII - mediates attachment (along with pili).

   -> also goes through antigenic variation

   -> contribute to evasion of immune response

   -> aka "opacity protein"

   -> because it makes gonococcal colonies less translucent

4. IgA protease

Clinical significance

A higher proportion of female infections are asymptomatic than male.

Co-infection with other STD is common

   -> 10-20% male and 30-50% females has co-existing chlamydia

1. Genitourinary tract infections

In males: Yellow, purulent, exudate + Painful urination

In females: Initially endocervical infection

   -> Greenish-yellow cervical discharge

   -> Intermenstrual bleeding

   -> Can progress to uterus

In uterus, can cause:

• salpingitis
• pelvic inflammatory disease (N. gonorrhoeae most common cause)
• fibrosis
• Infertility in 20% due to tubal scarring

2. Rectal infection

Prevalent in male homosexual

Constipation, painful defecation, purulent discharge

3. Pharyngitis

Oral-genital contact.

May mimic streptococcal/virla sore throat

4. Ophthalmia neonatorum

Conjunctivitis acquired by a newborn during vaginal delivery

If untreated -> may lead to blindness

Adult gonococcal conjunctivitis can also occur.

5. Disseminated infection

Bacteremia is rare (in contrast to N. meningitidis)

Can cause fever, erythematous, or maculopapular lesion in skin.

Can also cause painful purulent arthritis

   -> most common cause of septic arthritis in sexually active adults

Laboratory identification

Microscopy

• Seen inside PMN leukocytes
• Unencapsulated (unlike N. meningitidis)
• Piliated, nonmotile
• Resemble a pair of kidney beans

Culture

• Culture best under aerobic, enhanced CO2 condition
• Cultured on Thayer-Martin medium (chocolate agar with several antibiotics) - normal flora suppressed
• Culture need to be plated promptly due to sensitivity to drying and heating.

Other

• Oxidase test to identify nesseria species
• Ferments glucose, not maltose (N. meningitidis does both)

 

 

Treatment

Over 20% resistant to penicillin, tetracycline, cefoxitin, and/or spectinomycin (due to penicillinase)

   -> called PPNG (penicillinase-producing N. gonorrhoeae)

First line: 3rd generation cephalosporin (ceftriaxone)

May also include doxycycline to treat co-existing chlamydia infection.

Prevention/immunity

Prevention of ophthalmia neonatorum - routine use of silver nitrate or erythromycin drop in eyes immediately after birth. Erythromycin is also good against chlamydia trachomatis.

Immunity - no lasting immunity

 

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Things to revise/add later:

Bibliography: LWW microbiology

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