Gram-Negative Cocci and Rods – Unit 14

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

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53 Terms

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Neisseria genus

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

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Gram-negative diplococci

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

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Chocolate agar

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

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Oxidase positive

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

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Neisseria meningitidis

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

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Meningococcemia

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

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Petechiae

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

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Purpura

Larger hemorrhagic skin lesions that may accompany severe meningococcal infection

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Capsular polysaccharide serogroups

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

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Serogroups B and C

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

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Conjugate vaccine

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

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Recombinant protein MenB vaccine

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

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Chemoprophylaxis (meningococcus)

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

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Neisseria gonorrhoeae

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

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Gonorrhea

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

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Ophthalmia neonatorum

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

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Urethritis

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

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First-line therapy for gonorrhea

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

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Pseudomonas aeruginosa

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

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Non-fermenting Gram-negative bacilli (NFGNB)

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

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Pyocyanin

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

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Pyoverdine

Yellow-green fluorescent siderophore pigment of P. aeruginosa

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Ecthyma gangrenosum

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

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Opportunistic pathogen

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

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Antipseudomonal cephalosporin

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

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Enterobacteriaceae family

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

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Lactose fermentation

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

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MacConkey agar

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

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API test

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

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Triple Sugar Iron (TSI) agar

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

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H antigen

Flagellar protein antigen used for serotyping Enterobacteriaceae

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K antigen

Capsular polysaccharide antigen of Enterobacteriaceae; involved in virulence

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O antigen

Somatic lipopolysaccharide antigen used for epidemiologic serotyping of enteric bacteria

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Escherichia coli

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

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Enterotoxigenic E. coli (ETEC)

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

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Enteropathogenic E. coli (EPEC)

Strain causing infant diarrhea via attaching-and-effacing lesions

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Enteroinvasive E. coli (EIEC)

Strain that invades colonic epithelium producing dysentery-like illness

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Enterohemorrhagic E. coli (EHEC)

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

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Shigella

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

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Bacillary dysentery

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

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Salmonella Typhi

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

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Typhoid fever

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

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Salmonella Enteritidis

Zoonotic Salmonella serovar commonly producing self-limited gastroenteritis

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Gastroenteritis (Salmonella)

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

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Carrier state

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

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Yersinia pestis

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

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Bubonic plague

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

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Yersinia enterocolitica

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

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Oxidase negative

Characteristic of Enterobacteriaceae; absence of cytochrome-c oxidase activity

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Glucose fermentation

Ability to metabolize glucose anaerobically, a hallmark of Enterobacteriaceae

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Peritrichous flagella

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

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Oxidase test

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

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Rifampicin chemoprophylaxis

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