MICR102A - PART 3

Neisseria

Gram-negative diplococci

Pathogenic species

N. meningitidis, N. gonorrhoeae

Gram-negative

Present

Bean-shaped diplococci

Present

Capsule

Present

Pili

Present

Flagella

Absent

Spores

Absent

Strict parasite

Poor survival outside host

Aerobic

Present

Oxidative metabolism

Present

Catalase production

Present

Oxidase production

Present

Requires enriched complex media

Present

Requires CO₂ for optimal growth

Present

Size

0.8 × 0.6 µm

Media

Blood Agar, Chocolate Agar

Growth Enhancement

Blood or Serum

CO₂ Requirement

2–8% CO₂ improves growth

Temperature

36–39 °C

pH

6–8

Colony Appearance

1–2 mm diameter, convex, grey, transparent

Hemolysis on Blood Agar

Absent

Oxidase

Positive

Catalase

Positive

Mannitol Fermentation

Fermented

Maltose Fermentation

Fermented

β-lactamase production

None

Polysaccharide Capsule

Antiphagocytic

Endotoxin (LPS)

Causes septic shock, induces cytokine release

IgA protease

Cleaves IgA antibodies in respiratory mucosa

Natural host

Humans

Transmission

Airborne droplets

Colonization

Nasopharynx

Pathogenesis

Enter bloodstream, spread to meninges, multiply in CSF

Most common disease

Meningitis in persons 2–18 years old

Outbreak seasons

Winter, early spring

High-risk environments

Close contact

Main diseases

Meningitis, Meningococcemia

Specimens for diagnosis

Blood, CSF

Diagnostic methods

Gram Staining, Culture, Oxidase Test, Fermentation Tests, Latex Agglutination Test

Gram staining result

Gram-negative bean-shaped capsulated diplococci

Oxidase test

Detects cytochrome oxidase enzyme, positive = purple within 10 seconds

Latex agglutination test

Detects capsular polysaccharide antigen in CSF

Treatment

Penicillin G, Sulphonamides

Alternative drugs

Chloramphenicol, Cefotaxime, Ceftriaxone

Prevention

Meningococcal Vaccine containing capsular polysaccharide antigens

Escherichia

Gram-negative short rods

Family

Enterobacteriaceae

Spores

Absent

Capsules

Present

Slime Layer

Present

Motility

With peritrichous flagella

Fimbriae (Pili)

Present

Oxygen Requirement

Facultatively anaerobic

Glucose Fermentation

With acid production

Nitrate Reduction

NO₃ → NO₂

Oxidase

Negative

Catalase

Positive

Nutritional Requirements

Simple (except Shigella and Klebsiella are non-motile)

K antigen

Capsular polysaccharide (heavy in Klebsiella)

H antigen

Flagellar protein of motile genera or species

O antigen

Somatic antigen, O-specific polysaccharide of LPS

F antigen

Fimbrial antigen

Vi antigen

Capsule of Salmonella

Lactose Fermenters

Citrobacter, Escherichia, Enterobacter, Klebsiella

Non-Lactose Fermenters

Shigella, Yersinia, Proteus, Salmonella

Other Genera

Morganella morganii, Providencia spp., Serratia spp., Erwinia

Opportunistic Enterobacteriaceae

Citrobacter, Enterobacter, Serratia, Morganella morganii, Edwardsiella

E. coli Host Location

Lower intestines of warm-blooded animals

Intestines of fish and cold-blooded animals

Absent

Carnivores

Present

Omnivores

Present

Stomach

Absent

Anterior bowel

Absent

Normal Flora Role

Produces Vitamin K, prevents colonization of pathogenic bacteria

Pathogenic Importance

Food poisoning, urinary tract infections (UTI)

Transmission

Fecal to oral route

Discoverer

Theodore Escherich, 1885

Model Organism

Most widely studied prokaryotic model organism

Toxin-producing strains

O157:H7

O Antigen

Somatic antigen

K Antigen

Capsule

H Antigen

Flagellar antigen

F Antigen

Adhesive fimbrial antigen (best known: K88/F4)

Heat-Labile Enterotoxin (LT)

Plasmid encoded, 1 A subunit, 5 B subunits, increases intracellular cAMP, causes diarrhea

Heat-Stable Enterotoxin (STa)

Activates guanylate cyclase, inhibits Na⁺ and Cl⁻ absorption, active in suckling mice

Heat-Stable Enterotoxin (STb)

Insoluble, no activity in suckling mice, causes fluid secretion in pig intestine

Edema Disease Toxin

Thermolabile protein, related to Shiga-like toxin 2, causes paralysis and vascular damage

Shiga-Like Toxin (SLT)

Inhibits protein synthesis, lethal to mice, enterotoxic in rabbits, destroys intestinal microvilli

Pathogenesis

Intestinal disease, septicemia of newborns, respiratory disease in poultry, opportunistic infections in udder, uterus, other tissues

ETEC

Enterotoxigenic E. coli, produces LT and ST toxins, non-invasive

EPEC

Enteropathogenic E. coli, uses intimin adhesin, causes attachment and effacement

EIEC

Enteroinvasive E. coli, invades intestinal mucosa, shigellosis-like disease

AEEC

Attaching and Effacing E. coli, produces Shiga-like toxin, destroys microvilli

EHEC

Enterohemorrhagic E. coli, e.g., O157:H7, bloody diarrhea, HUS

EAEC

Enteroaggregative E. coli, aggregates cells, watery diarrhea

AIEC

Adherent Invasive E. coli, invades epithelial cells, replicates intracellularly

Diseases in Swine

Enteric colibacillosis, neonatal enteritis, weanling enteritis, edema disease

Neonatal Enteritis

Adhesion → colonization → toxin production, watery diarrhea, fatal dehydration, up to 90% mortality