Neisseria spp.

Neisseria spp. are gram-negative and coccoidal in morphology, often presented as diploid pairs though other arrangements can be observed. The range of native habitat is limited in the genus and so far, exclusively recovered from warm-blooded mammals. Approximately 30 Neisseria spp. have been identified. Of particular interest are the species N. meningitidis and N. gonorrhoeae for being both exclusively human symbionts and opportunistic pathogens. These two species are of clinical importance, while other members of the genus are exceedingly rare to find described in literature as causing disease in humans and other animals.

Human Microbiome

Carriage rates for Neisseria spp. vary among region and throughout an individual’s life. Because of this, most species are considered common commensals of the human microbiome and can be recovered from various locations, namely the oral cavity. However, N. meningitidis is characterized as having a niche preference for nasopharyngeal tissue whereas the N. gonorrhoeae colonized niche is the urogenital tract. There are documented cases of cross-contamination of these two tracts, possibly due to the genetic relatedness of N. meningitidis and N. gonorrhoeae and how they select their niche, though prolific growth is namely reserved for each species niche of choice.

Clinical Relevance

N. sicca and N. mucosa are commensal bacteria in the human oral flora and normally have low pathogenicity. However, in immunocompromised patients, they can occasionally cause opportunistic infections, such as meningitis, osteomyelitis, endocarditis, otitis media, and acute sinusitis. The two clinically important species are N. meningitidis and N. gonorrhoeae.

1. N. meningitidis affects the central nervous system leading to meningitis and life-threatening sepsis in the meninges (Meningococcemia). N. meningitidis is often referred to as meningococcus due to its ability to cause infections in human meninges coupled with its morphology.

2. N. gonorrhoeae on the other hand causes sexually transmitted diseases (STD). The ability of N. gonorrhoeae to persist and reproduce in the sexual organs and fluids results in gonorrhea in humans, which is often recurring due to the antibiotic resistance mechanism of Neisseria.

Relevance of pathogen in transmission in endoscopy

• Gastroenterology: Low

• Pulmonology: Low

• Ear, nose, and throat: Low

• Urology: High

Relevance for endoscope surveillance

• Low or moderate concern organism

Transmission route

N. gonorrhoeae:

• Sexual transmission route (Direct contact of fluids secreted from sexual organs: Semen, pre-seminal fluid, vaginal secretion, discharge etc.)

• Transmission through oral and anal sex

• Vertical route: From infected pregnant mother to neonate during childbirth (MTCT in NVD)

N. meningitidis:

• The bacterium is transmitted through respiratory droplets and close contact, with transmission increasing in crowded settings such as military camps, universities, and schools.

Resistance to antibiotics

Many strains of Neisseria gonorrhoeae are resistant to quinolones and penicillin-based antibiotics, limiting the available treatment options. To achieve effective results and to minimize the secondary infection a combination of antibiotics (e.g., ceftriaxone+ Azithromycin) are prescribed.

As for Neisseria meningitidis, penicillin was considered as a choice of first-line antibiotic. However, due to the penicillin-resistant strains, ceftriaxone, cefotaxime (Both cephalosporins), or meropenem (Carbapeneme: Considered as last resort in clinical treatment), all of which have good cerebrospinal fluid penetration, are now recommended.

Immune response escape mechanism

The pili (wave-like tails of Neisseria) fulfills the functions of attachment to host cell and escaping from human immune response (antibodies). The pili generates countless surface antigens with different combinations even within a single cell, thus the antibodies produced by the human immune system for a specific antigen turns unspecific for other surface antigens generated by the pili.

This antigenic variation ability of Gonococci also makes them a very difficult target for vaccine development. The Phase IV vaccine against Gonococci is expected to be at only 33% efficacy in humans.