Chapter 11: Neisseriae: Meningococci & Gonococci

The two primary species discussed are Neisseria gonorrhoeae (the gonococcus) and Neisseria meningitidis (the meningococcus), both of which are obligate human pathogens and recognized as pyogenic cocci due to the purulent discharge they elicit during infection. While structurally similar, they are differentiated in clinical settings by their sugar utilization—gonococci oxidize only glucose, whereas meningococci oxidize both glucose and maltose—and the presence of a polysaccharide capsule in meningococci, which serves as a critical antiphagocytic virulence factor. Neisseria gonorrhoeae is a major cause of sexually transmitted infections, utilizing surface structures like pili and Opacity (Opa) proteins to facilitate adherence to mucosal surfaces. A hallmark of this pathogen is its ability to evade the host immune system through antigenic variation by gene conversion and phase variation, constantly altering its surface molecules. Clinical manifestations include urethritis in men, while women may suffer from cervicitis, which can progress to pelvic inflammatory disease (PID), salpingitis, and infertility. It also causes ophthalmia neonatorum in newborns and can lead to disseminated gonococcal infection, frequently presenting as septic arthritis. Diagnosis has shifted toward highly sensitive Nucleic Acid Amplification Tests (NAATs) and culture on selective Thayer-Martin medium. Treatment is complicated by widespread antibiotic resistance to penicillin and fluoroquinolones, necessitating dual therapy with ceftriaxone and azithromycin. Neisseria meningitidis is a leading cause of bacterial meningitis and life-threatening meningococcemia. Transmission occurs via respiratory droplets, with the bacteria colonizing the nasopharynx before potentially invading the bloodstream. The disease can progress rapidly to Waterhouse-Friderichsen syndrome, characterized by adrenal failure, shock, and a distinctive petechial rash. Public health efforts focus on conjugate vaccines targeting major serogroups (A, C, W, and Y) and newer protein-based vaccines for serogroup B. Emergency treatment often involves high-dose penicillin or third-generation cephalosporins, with rifampin used for post-exposure prophylaxis in close contacts. The chapter concludes by briefly distinguishing Neisseriae from related organisms like Moraxella catarrhalis, a cause of respiratory infections, and Acinetobacter baumannii, a significant multidrug-resistant nosocomial pathogen.