Gram Negative Cocci and Obligate Intracellular Flashcards
Gonorrhea manifests as. . .
genital mucosal inflammation without ulceration. It is usually asymptomatic in women and symptomatic in men. Generally limited to the genital, anorectal and/or throat mucosa. May spread to eye via inadvertant innoculation from hands.
Opthalmia neonatorum
The most common manifestation in newborn children with congenital infection. Onset 2-5 days after birth. Conjunctivitis → purulent discharge and ulcerations
Diagnosis of Neisseria meningitidis infection
Cerebrospinal fluid can be tested by Gram stain, culture or PCR. Gram stain is rapid, but only 60-80% sensitive. Culture is sensitive and takes 1 to 2 days. PCR is available in multiplex panels that detect several pathogens. It is rapid, sensitive, specific and expensive.
Blood culture can also be useful. If positive in a patient with symptoms of meningitis, it is diagnostic.
Neisseria meningitidis-mediated damage
Invades into the blood from the pharyngeal mucosa, and then spreads via the blood to the meninges. Survival depends on antiphagocytic capsule, of which there is considerable diversity. Anti-capsule antibody is preventative.
Once in the meninges, the organism elicits a strong inflammatory response. Damage is primarily mediated by host response to PAMPS (LOS in particular).
Vertical transmission of organisms that cause STIs
efficient and usually occurs in the prenatal or perinatal periods
Organisms that are usually transmitted by _____ can also transmitted during sexual contact
Organisms that are usually transmitted by a route other than sexual contact can also transmitted during sexual contact
Just because you think it was contracted via sexual contact does NOT mean it must be an organism which is transmitted this way exclusively. You can absolutely get EHEC from sexual contact as well.
Neisseria meningitidis symptoms
An important cause of meningitis.
Symptoms of meningitis include acute onset of fever, severe headache, photophobia, painful/stiff neck. It can rapidly progress to shock and death. Mortality is high (~10%) if bacterial meningitis is not treated.
Transmission of Neisseria meningitidis
N. meningitidis colonizes the oropharynx in ~10% of the healthy population overall, and up to ~25% of adolescents and young adults. It is transmitted person-to-person in respiratory secretions (droplets) by close contact (cohabitation, kissing, medical exposure to respiratory secretions).
Diagnosis of Serotype D-K Chlamydia trachomatis
The organism cannot be seen in Gram stain
Culture requires use of cell lines to support proliferation of the bacteria. It is slow and insensitive, and has limited utility. Nucleic-acid amplified tests (NAAT), such as PCR are sensitive and specific. They are usually combined with NAAT for N. gonorrhoeae.
Treatment of N. meningitidis infection
Vaccines are the primary means of prevention.
Antibiotic prophylaxis is recommended for people with close contact with people who have N. meningitidis infection.
Treatment should be guided by susceptibility testing results. Third generation cephalosporins or penicillin are usually used
Neisseria gonorrhoeae in a neutrophil.
Gram negative true diplococcus. Have lipooligosaccharide instead of lipopolysaccharide (lacks an O-antigen).
Diagnosis of N. gonorrhoeae infection.
Gram stain of urethral exudate is sensitive and specific for infection in men. Neisseria species are common in the vaginal microbiota, and so Gram-stain is not specific for gonorrhea in women.
Culture of exudate from any body site with subsequent identification of the organism is sensitive and specific. The organism dies in transport to the lab, so the specimens should be plated immediately with appropriate selective and enriched media
Nucleic-acid amplified tests (NAAT), such as PCR are more convenient than culture because the sample can be transported to the lab. They are usually combined with NAAT for C. trachomatis.
Chlamydia trachomatis life cycle
The elementary body (EB) is the infectious form. It is small, dense and does not divide. The reticulate body (RB) is the replicating form. It is larger and non-infectious.
Symptoms of Serotype D-K Chlamydia trachomatis-mediated disease
Most common bacterial STI in the U.S. Chlamydia manifests as genital mucosal inflammation without ulceration. Asymptomatic in women, manifests often as dysuria and penile discharge in men. Ocular infection causes inclusion conjunctivitis.
Inclusion conjunctivitis occurs in 22-44% of newborns of infected mothers. Pneumonia occurs in 11 to 20% of newborns of infected mothers (onset ~1-2 months after delivery). Nasal obstruction, discharge, cough often with history of conjunctivitis. There is peripheral eosinophilia, and elevated immunoglobulin levels.
N. gonorrhoeae-mediated damage
Mediated by the toxic effect of LOS and by the host inflammatory response.
Displays antigenic variation of the surface pili it uses to adhere. This allows the bacterium to escape the host antibody response. Diplococci enter epithelial cells and replicate within a vacuole in the cell. They transit through the cell to the sub-epithelium. The host cell that the bacteria passed through dies due to toxic effect of LOS. Neutrophil response results in sub-epithelial pus buildup.
Deficiency in ______ is extremely predisposing to N. meningitidis infection
Deficiency in complement is extremely predisposing to N. gonorrhoeae infection
Particular the MAC, made up of C5 through C9.
Transmission of Neisseria gonorrhoeae
N. gonorrhoeae is transmitted from the genital, anorectal or throat mucosa during sexual contact. It can also be transmitted by the vertical route, usually during delivery of the child.
Pathogens that cause STI are not ___
Pathogens that cause STI are not hardy
They die quickly outside of their hosts.
Treatment of Serotype D-K Chlamydia trachomatis
It is important to follow current CDC recommendations!!!
Current recommendations are for a single dose of azithromycin (a macrolide). Other protein synthesis inhibitors or fluoroquinolones are alternatives.
Neonatal infection requires two weeks of treatment with erythromycin.
Treatment of N. gonorrhoeae infection
Abstinence or condoms as a preventative measure. Notification of, and follow up with sexual partners of those known to have an STI can be preventative of future cases. Treatment recommendations change frequently as N. gonorrhoeae develops antibiotic resistance, so it is important to follow appropriate recommendations.
Current CDC recommendations:
- Single dose of a third-generation cephalosporin (ceftriaxone) and a single dose of azithromycin
- Opthalmia neonatorum can be prevented w/ erythromycin placed in each eye at birth
pelvic inflammatory disease
An important manifestation that can occur with N. gonorrhoeae or C. trachomatis infection in women.
Caused by spread from vaginal cavity to upper genital tract. May induce endometritis, salpingitis, tubo-ovarian abscess and pelvic peritonitis. Symptoms include pelvic/abdominal pain with tenderness on pelvic exam. If untreated, may result in infertility due to scarring.
Serotype D-K Chlamydia trachomatis-mediated damage
Epithelial cells are killed by replicating organisms. Host response is the primary mechanism of damage (neutrophilic inflammation). Chronic response is characterized by infiltration of plasma cells, CD4/CD8 T cells. These lead to necrosis, epithelial hyperplasia, scar.
The immune response is not very effective against this organism. Little or no immune protection from reinfection. Interferon-γ inhibits RB replication.
STI usually refers to
Infections in which 1. the pathogen is shed from the urogenital mucosa and 2. is transmitted during sexual contact
Surprisingly, there is really no universally used definition of an STI.
Disseminated gonococcal infection (DGI)
occurs in <1% of people with genital gonorrhea. Risk factors for DGI: menstruation, complement deficiency. Strains of N. gonorrhoeae causing DGI are often resistant to killing by complement in human serum.
Genital infection → bacteremia → suppurative (pus-forming) infection of the joints (arthritis) and/or skin lesions.
