Gram-Negative Cocci and Rods – Unit 14

Vocabulary flashcards summarizing key pathogens, laboratory features, clinical manifestations, and treatments from the Unit 14 lecture on Gram-negative cocci and rods.

Neisseria genus

Group of oxidase-positive, Gram-negative diplococci that includes commensals and the pathogens N. meningitidis and N. gonorrhoeae

Gram-negative diplococci

Microscopic appearance of paired, kidney-bean–shaped cocci typical of Neisseria species

Chocolate agar

Enriched culture medium needed for the growth of fastidious organisms such as Neisseria spp. and Haemophilus spp.

Oxidase positive

Bacteria that possess cytochrome-c oxidase; produces a purple color in the oxidase test (e.g., Neisseria, Pseudomonas)

Neisseria meningitidis

Human nasopharyngeal commensal that can cause meningitis or meningococcemia; encapsulated, droplet-transmitted, notifiable disease agent

Meningococcemia

Hematogenous dissemination of N. meningitidis, often producing petechiae, purpura, shock, and high mortality

Petechiae

Small, non-blanching red spots on skin or mucosa caused by capillary hemorrhage; classic in meningococcemia

Purpura

Larger hemorrhagic skin lesions that may accompany severe meningococcal infection

Capsular polysaccharide serogroups

Immunochemical classification of N. meningitidis (A, B, C, Y, W135, etc.) based on capsule composition

Serogroups B and C

Leading meningococcal serogroups causing disease in Spain (≈85–90 % of cases)

Conjugate vaccine

Polysaccharide capsule linked to a protein carrier to improve immunogenicity; used for N. meningitidis serogroup C and A/C/Y/W135

Recombinant protein MenB vaccine

Vaccine composed of surface proteins of N. meningitidis serogroup B, licensed since 2014

Chemoprophylaxis (meningococcus)

Preventive antimicrobial regimen for close contacts: rifampicin (2 days), single-dose ciprofloxacin, levofloxacin, or ceftriaxone

Neisseria gonorrhoeae

Fastidious, Gram-negative diplococcus causing gonorrhea; exclusive to humans and transmitted sexually or perinatally

Gonorrhea

STD characterized by urethritis in men and endocervicitis in women; may involve rectum, pharynx, conjunctiva

Ophthalmia neonatorum

Purulent conjunctivitis in newborns acquired during birth from maternal N. gonorrhoeae infection

Urethritis

Inflammation of the urethra; in men, intracellular Gram-negative diplococci seen in urethral exudate suggest gonorrhea

First-line therapy for gonorrhea

Ceftriaxone or cefixime plus doxycycline or azithromycin to cover possible Chlamydia co-infection

Pseudomonas aeruginosa

Motile, oxidase-positive, non-fermenting Gram-negative rod producing pigments (pyocyanin, pyoverdine); major opportunistic pathogen

Non-fermenting Gram-negative bacilli (NFGNB)

Group of aerobic rods (e.g., Pseudomonas, Acinetobacter) that oxidize but do not ferment sugars

Pyocyanin

Blue-green, water-soluble pigment produced by P. aeruginosa; contributes to oxidative tissue damage

Pyoverdine

Yellow-green fluorescent siderophore pigment of P. aeruginosa

Ecthyma gangrenosum

Necrotic skin lesion with central black eschar and peripheral erythema, classically linked to P. aeruginosa septicemia

Opportunistic pathogen

Organism that rarely infects healthy hosts but causes disease when barriers are breached or immunity is impaired

Antipseudomonal cephalosporin

Third-generation agent active against P. aeruginosa, e.g., ceftazidime or cefepime

Enterobacteriaceae family

Large family of oxidase-negative, Gram-negative rods that ferment glucose; includes E. coli, Salmonella, Shigella, Klebsiella, etc.

Lactose fermentation

Metabolic property tested on MacConkey agar; lactose fermenters form pink colonies, non-fermenters are colorless

MacConkey agar

Selective and differential medium for Gram-negative rods; differentiates lactose fermenters by colony color

API test

Commercial strip of biochemical reactions used for rapid identification of Enterobacteriaceae and other bacteria

Triple Sugar Iron (TSI) agar

Slant medium detecting glucose/lactose/sucrose fermentation, H₂S and gas production in enteric bacteria

H antigen

Flagellar protein antigen used for serotyping Enterobacteriaceae

K antigen

Capsular polysaccharide antigen of Enterobacteriaceae; involved in virulence

O antigen

Somatic lipopolysaccharide antigen used for epidemiologic serotyping of enteric bacteria

Escherichia coli

Common gut commensal and opportunistic pathogen; certain strains are primary pathogens causing diarrheal disease

Enterotoxigenic E. coli (ETEC)

Toxin-producing strain causing traveller’s and infantile watery diarrhea

Enteropathogenic E. coli (EPEC)

Strain causing infant diarrhea via attaching-and-effacing lesions

Enteroinvasive E. coli (EIEC)

Strain that invades colonic epithelium producing dysentery-like illness

Enterohemorrhagic E. coli (EHEC)

Shiga-toxin–producing strain causing hemorrhagic colitis and hemolytic uremic syndrome

Shigella

Non-motile Enterobacteriaceae genus causing bacillary dysentery through fecal-oral spread

Bacillary dysentery

Severe inflammatory diarrhea with blood, mucus, fever, caused by Shigella spp.

Salmonella Typhi

Human-restricted serovar causing typhoid fever via fecal-oral transmission

Typhoid fever

Systemic febrile illness with intestinal invasion caused by S. Typhi or S. Paratyphi

Salmonella Enteritidis

Zoonotic Salmonella serovar commonly producing self-limited gastroenteritis

Gastroenteritis (Salmonella)

Acute enterocolitis with fever, vomiting, and diarrhea following contaminated food or water ingestion

Carrier state

Condition in which a person harbors and sheds a pathogen without symptoms (e.g., Salmonella Typhi carriers)

Yersinia pestis

Gram-negative coccobacillus, agent of bubonic, septicemic, and pneumonic plague

Bubonic plague

Severe infection with painful, swollen lymph nodes (buboes) caused by Yersinia pestis

Yersinia enterocolitica

Enteric Yersinia species producing enterocolitis, often from contaminated pork or milk

Oxidase negative

Characteristic of Enterobacteriaceae; absence of cytochrome-c oxidase activity

Glucose fermentation

Ability to metabolize glucose anaerobically, a hallmark of Enterobacteriaceae

Peritrichous flagella

Flagellar arrangement around the entire cell surface, providing motility to many enteric rods

Oxidase test

Biochemical assay detecting cytochrome-c oxidase; differentiates oxidase-positive Pseudomonas from oxidase-negative Enterobacteriaceae

Rifampicin chemoprophylaxis

Use of rifampicin twice daily for 2 days to eradicate N. meningitidis carriage in close contacts