Neisseria Gonorrhoeae: Gram-Negative Bacteria

Gram-Negative Cocci Overview

• Includes Neisseria, Moraxella catarrhalis, and Acinetobacter baumanii.

Neisseria

• Gram-negative, aerobic cocci.
• Includes Gonococci and Meningococci.
• Non-motile diplococci.
• Pyogenic.
• Differentiation in the lab achieved by sugar-use patterns and site of primary infections rather than microscopically.

Neisseria Gonorrhea

• Causes gonorrhea, a frequently reported infectious disease in the US.
• Appears as Gram (-) diplococcus.
• Transmitted through sexual contact.
• Can be transmitted, more rarely, during passage of a baby through an infected birth canal.
• Does not survive long outside of the human body and is sensitive to dehydration.

N. Gonorrhea Structure

• Unencapsulated, unlike meningococci.
• Piliated, enhancing attachment to host cell surfaces, and antigenic.
• Nonmotile.
• Appears as paired kidney beans.

N. Gonorrhea Clinical Significance

• Colonizes mucous membranes of the GUT or rectum, producing pus, tissue invasion, chronic inflammation, and fibrosis.
• Females are often asymptomatic, acting as reservoirs for gonococcal infections.
• Genito-urinary tract infections are more acute and easier to diagnose in males.
• Males experience yellow, purulent urethral discharge and painful urination.
• In females, infection starts in the endocervix and spreads to the urethra and vagina.
• Greenish-yellow cervical discharge is common in females, often with intermenstrual bleeding.
• Infections can progress to the uterus, causing salpingitis, pelvic inflammatory disease (PID), and fibrosis.
• 20% infertility rate with gonococcal salpingitis due to tubal scarring.
• Rectal infections primarily affect men who have sex with men, leading to constipation, painful defecation, and purulent discharge.
• Pharyngitis presents as purulent pharyngeal exudate, resembling viral or streptococcal sore throat.
• Ophthalmia neonatorum is a conjunctival sac infection in newborns from passage through infected birth canals, potentially causing blindness.
• Ophthalmia neonatorum is treated with systemic ceftriaxone IM or IV in a single dose, while topical erythromycin ointment is used for prophylaxis.

N. Gonorrhea Lab Identification

• In males, urethral exudate smears show numerous neutrophils with Gram (-) diplococci.
• In females, positive cultures on Thayer-Martin medium (chocolate agar with antibiotics) suppress the growth of non-pathogenic Neisseria.

N. Gonorrhea Treatment

• More than 20% of current isolates are resistant to penicillin, tetracycline, cefoxitin, and/or spectinomycin.
• Ceftriaxone is administered in a single IM dose for uncomplicated infections of the urethra, endocervix, and rectum.
• Treatment includes Azithromycin, Doxycycline (with chlamydia coverage).
• Barrier methods of contraception are essential for prevention.

Neisseria Meningitidis

• A frequent cause of meningitis.
• Causes fulminant meningococcemia with intravascular coagulation, circulatory collapse, and potentially fatal shock, but without meningitis.
• Characterized by extremely rapid onset and great intensity.

N. Meningitidis Structure

• Nonmotile
• Gram (-) diplococcus
• Kidney bean shape, always appears in pairs.
• Piliated
• Encapsulated when isolated from blood or spinal fluid.

N. Meningitidis Epidemiology

• Transmission occurs via inhalation of respiratory droplets from carriers or patients in the disease's early stages.
• Meningococcal disease in the US is most prevalent among infants under 1 year.

N. Meningitidis Clinical Significance

• Initial colonization occurs in the nasopharynx, causing largely asymptomatic meningococcal pharyngitis.
• Can cause disseminated disease by spreading through the blood, leading to meningitis and/or fulminating septicemia.
• Meningitis presents with joint symptoms and petechial and/or purpuric rash.
• Meningitis symptoms: fever and malaise evolving into severe headache, rigid neck, vomiting, and sensitivity to bright lights; coma can occur within hours.
• Septicemia in young children (Waterhouse-Friderichsen syndrome): large, purple, blotchy skin hemorrhages, vomiting, diarrhea, circulatory collapse, adrenal necrosis, and death in 10-12 hours.

N. Meningitidis Lab Identification

• Cultured on chocolate agar with increased CO2.
• Usually cultured from CSF or blood, which are normally sterile, unlike gonococci; therefore, a selective medium is not required.
• Thayer-Martin medium used for skin lesion or nasopharyngeal swab samples to eliminate contaminating organisms.
• Oxidase (+).
• Utilizes both glucose & maltose (glucose only for N. gonorrhea).
• CSF shows increased pressure, elevated protein, decreased glucose, and many neutrophils.

N. Meningitidis Treatment & Prevention

• Bacterial meningitis is a medical emergency, and antibiotic treatment cannot await definitive bacteriologic diagnosis.
• Penicillin G or ampicillin can pass the inflamed blood-brain barrier in large intravenous doses.
• If the etiology of the infection is unclear, cefotaxime or ceftriaxone is recommended.
• A meningococcal vaccine (MCV4) is available for ages 11-55.

Moraxella Catarrhalis

• Nonmotile.
• Gram (-) paired coccobacilli.
• Aerobic.
• Oxidase-positive.
• Fastidious organisms that do not ferment carbohydrates.
• Can cause infections of the respiratory system, middle ear, eye, CNS, and joints.

Acinetobacter Baumanii

• Nonmotile coccobacilli.
• Frequently confused with Neisseriae in Gram-stained samples.
• Generally encapsulated.
• Oxidase (-).
• Obligately aerobic.
• Does not ferment carbohydrates.
• Nosocomial (hospital-acquired) pathogen.