Microbiology Quiz: Neisseria and Clostridium

Neisseria Meningitidis

• Gram-negative cocci, kidney-shaped (coffee bean shape), arranged in diplococci
• Found intracellularly in cerebrospinal fluid
• Newly isolated strains have a polysaccharide capsule
• Non-motile and non-spore forming

Neisseria Gonorrhoeae

• Gram-negative cocci, kidney-shaped (coffee bean shape), arranged in diplococci
• Predominantly intracellular (phagocytosed by polymorphonuclears)
• Non-spore forming, immobile
• May have a capsule in pathological products and in young cultures

Moraxella Catarrhalis

• Gram-negative diplococcus that resists decolorization
• Non-spore forming, non-capsulated, and non-motile
• Larger than meningococcus or gonococcus

Corynebacterium Diphtheriae

• Gram-positive bacilli with swollen ends, "Chinese lettering" arrangement
• Non-spore forming, non-ciliated, and encapsulated
• Contains metachromatic granules (Babes-Ernst) visible with Del Vecchio stain
• Several growth media can be used
  • Enrichment media: OCST (egg, cysteine, serum, potassium tellurite)
  • Elective Löffler's medium (with ox coagulated serum)
  • Solid selective media (blood and potassium tellurite)
  • Tinsdale and Gundel-Tietz
  • Blood-agar medium
• Colonies vary depending on the media used
  • On Löffler's medium, white and convex
  • On Tinsdale medium, black with a brown halo
  • On solid media containing potassium tellurite and blood, three types exist: gravis – large, black colonies, rough surface, irregular margins (pathogenic) mitis – smaller, black colonies with smooth surface, circular margins intermedius – grey-black colonies with irregular margins
• Ferments glucose and maltose (without gas production)
• Some strains (gravis) can ferment sucrose
• Urease is negative
• Diphtheria toxin (highly immunogenic) is a key antigen
• Possesses corpuscular antigens (carbohydrate and protein nature)
• Toxin remains at entrance gate, diffusing throughout body to cause damage
• Toxin can produce necrotic lesions
• Produces, toxigenic strains are lysogenic

Listeria

• Gram-positive bacilli, non-spore forming, facultative anaerobic
• Size varies (0.4-0.5 µm in diameter, 1-2 µm long) with rounded ends
• Non-encapsulated
• Motile via peritrichous flagella at temperatures ≤30°C
• Several growth media can be used:
  • Various temperatures (0-45°C)
  • pH 6-9, and various salt concentrations (including 10%NaCl)
• On blood agar: beta-hemolytic, small, grey, translucent drop-like colonies.
• On tryptose agar: green-blue colonies
• Catalase positive, and oxidase negative.
• Positive methyl red reaction, positive Voges-Proskauer reaction
• Does not produce indole, utilize citrate or possess urease activity
• Causes meningitis and sepsis, particularly in newborns and adults
• Also diarrheagenic, through ingestion of unpasteurized milk products, leading to bacteremia and septicemia, and meningoencephalitis
• Risk factors include newborns, pregnant women, elderly people with poor immune systems, and people whose immune systems are weak
• Can cause placentitis, neonatal septicemia, and abortion (if transmitted)

Bacillus Anthracis

• Gram-positive, non-motile, rectangular, aerobic, rod-shaped bacterium (with square ends) and capsulated

• Chain formation is common

• Spores are formed easily when discharged from infected animal or isolated bacteria from animal carcass exposed to free oxygen, therefore the carcass should not be necropsied in case of anthrax

• Growth occurs as flocular deposits in broth media

• On blood agar: non-hemolytic colonies with rough, uneven surfaces and multiple curled extensions at the edge (Medusahead)

• Catalase positive, hemolysis negative

• Indole positive, motility negative

• Oxidase negative, urease negative.

• Ferments glucose, maltose, sucrose, and trehalose

• Anthrax toxin is complex with 3 protein components: I (edema factor), II (protective factor), and III (lethal factor).

• Components I and II cause mild edema (low overall mortality), while component III causes high lethality

• Four forms of naturally occurring human anthrax infections exist: -Cutaneous - spores enter through skin breaks and lead to a painless ulcer with black scab formation. -Gastrointestinal - infection upon eating contaminated meat, mouth, and throat are main entry points though it's not expected to result from aerosolized spores -Inhalation - breathing spores into the lungs -Injection- related, injection heroin contaminated with spores

Clostridium

• Species of Clostridium include :
• tetani: Tetanus
• perfringens: Gas gangrene
• botulinum: Botulism
• difficile: Pseudomembranous colitis
• Obligate anaerobes capable of sporulation
• Gram-positive bacilli
• Under microscope, they appear as long, irregular, rod-shaped cells with a bulge at the terminal or subterminal end (forming subterminal spores)
• Various cultural characteristics in regards to oxygen and different growth media
  • c. botulinum: large semitransparent colonies with wavy outlines, beta-hemolytic on most media plates
  • c. tetani: fine film of growth on blood agar media plates, swarming due to motility, hemolytic on blood agar media
  • c. difficile: non hemolytic with large and flat colonies on blood agar media
• C. difficile is catalase- and superoxide dismutase-negative, producing enterotoxin A and cytotoxin B. It causes a spectrum of symptoms, ranging from mild diarrhea to severe colitis, pseudomembranous colitis, or toxic megacolon, especially as a consequence of antibiotic use

Enterobacteriaceae

• Gram-negative bacilli, non-spore forming, typically motile, and do not have a capsule except for Klebsiella

• Some species are always pathogenic but other species act as saprophytes (e.g. part of normal intestinal flora which contribute to food digestion) and only become pathogenic when they leave their normal habitat

• Examples of various pathogenic species in the Enterobacteriaceae family include Escherichia coli, Klebsiella, Proteus, and Pseudomonas

• Species vary in their colonial characteristics -Escherichia coli: colonies are yellow on Istrate-Meitert or Drigalski medium (lactose positive), round, convex, with a medium size -Shigella: transparent, bright colonies, found in the color of the medium (green), also lactose negative; -Salmonella: small, lactose-negative, semi-transparent; some strains have a black center due to hydrogen sulfide -Proteus: produces swarming growth (concentric zones) in simple and blood agar -Klebsiella: large, round, convex colonies with a moist and mucous appearance with large (yellow, round, and convex, moist colonies) on lactose medium -Pseudomonas: small blue colonies, adherent to the medium on Istrate-Meitert medium, gray, shiny colonies surrounded by beta hemolysis on blood agar

• Numerous clinical features are associated with Enterobacteriaceae infections, including digestive, urinary, respiratory, and ENT, genital, and purulent infections.

Haemophilus

• Small, pleomorphic, nonmotile, nonsporing Gram-negative rods, or coccobacilli
• Aerobic or facultative anaerobic, optimal growth with the addition of 5-10% carbon dioxide in the incubation atmosphere.
• Oxidase, catalase reactions vary among species
• require one or both of two accessory growth factors (X and V)