Lecture Notes on Sexually Transmitted Infections (STIs)

Global and UK Importance of STIs

Briefly covers gonorrhoea, chlamydia, and syphilis.
Touches on the bacteria that cause these infections and diagnostic tests.
Highlights the need for better diagnostic tests in microbiology research and development.

WHO estimates that over 1 million people acquire an STI daily.
More than 500 million people live with incurable herpes simplex virus infections.
The highest burden falls on low and middle-income countries, requiring global efforts.

Illustrates the large numbers and impact of these infections.
Public health initiatives are in place to prevent and control STIs like HPV.
Burden of infections largely affects lower and middle-income countries.
Research focuses on improving treatments, diagnostics, and public health interventions.

Urine is no longer considered sterile, based on sequencing studies.
Vaginal microbiome has a natural community dominated by Lactobacilli.
Lactobacilli are beneficial bacteria that colonise and form biofilms on epithelial cells.
They inhibit the growth of pathogenic organisms.
When a pathogen attempts to invade, if a dominant commensal species has already created a biofilm, it is harder for the pathogenic organism to take over.
Lactobacilli produce lactic acid, lowering pH.
The acidic environment inhibits the survival of many bacteria.
Lactobacilli prevent long-term colonisation by other species.
They produce hydrogen peroxide, which inhibits the growth of other species and inactivates viruses like HIV and herpes simplex virus.
They produce antimicrobial peptides called bacteriocins to kill other bacteria.

Recent studies show semen has a microbiome related to fertility issues.
Microbiome studies aim to distinguish between healthy and unhealthy states, but it's complex.
Diversity in the microbiome often indicates a healthier environment.
Semen has antibacterial and antimicrobial activity with peptides, enzymes (like lysozyme), phospholipids, and lactoferrin.

Caused by the bacterium Neisseria gonorrhoeae.
Infections can be uncomplicated (localized) or disseminated.
In uncomplicated infections, it generally infects mucous membranes of the urethra or cervix; it can also infect the eye causing conjunctivitis.
Disseminated gonorrhoea can cause arthritis or dermatitis throughout the body.
Most common in young adults.
There are various public health surveillance programs in place.

In males, it tends to manifest in an acute phase.
In women, it can be asymptomatic and undiagnosed, leading to implications during pregnancy like spontaneous abortion.
Disseminated gonorrhoea presents differently.

Fastidious, gram-negative cocci.
Nucleic acid amplification tests are used for initial diagnosis because Neisseria is difficult to culture.
Cultures are still used to monitor antimicrobial resistance.
Has pili for attachment to epithelium, containing constant and hyper-variable regions.
Hyper-variable regions contribute to antigenic diversity and evade body defenses.

Most common curable bacterial STI in the UK, caused by Chlamydia trachomatis.
Obligate intracellular bacterium.
Infection patterns differ between males and females.
Large proportion of infections are asymptomatic.
Classified as uncomplicated or complicated based on whether it has ascended into the upper genital tract.
Highest rates in the young adult population.

Untreated infections can self-resolve or persist, leading to various presentations, including arthritis.
Impacts anxiety and distress, which can affect immune status.
Can cause severe implications in pregnancy.

Nucleic acid amplification tests are used for diagnosis.
Clinical tests balance fast results with sensitivity and specificity.
Cell culture has high specificity but takes weeks.
PCR-based methods offer a rapid result with adequate specificity and sensitivity.

Outer lipopolysaccharide membrane has cysteine-rich proteins that inhibit phagosome fusion.
Adhesion to receptors on mucous membranes.
Antigenic variation evades the host immune response.
A needle-like projection type three secretion apparatus injects bacterial proteins into the cell cytoplasm, which helps divert lipids.

Obligate intracellular organism.
Exists as inert elementary bodies outside the host cell.
Inside the cell, elementary bodies become metabolically active reticulate bodies (RBs).
RBs replicate within the cell.
The conversion from an elementary body into a reticulate body takes 1 to 2 days after infection.
Host cell lysis releases elementary bodies to infect other cells.

Caused by the spirochete Treponema pallidum.
Presents as primary (painless ulcer) or secondary.
Secondary syphilis is a multisystem disease affecting mucous membranes and causing headaches.
Disease development varies; can have latent periods before late syphilis develops.
Syphilis rates are increasing globally and in the UK.

Notable historical and ethical issues, including the Tuskegee Syphilis Study where treatment was withheld from participants.
Reflects the importance of ethical practices in research.
Syphilis can significantly impact mental capacity and decision-making.