Bacterial Pathogens Lecture Notes

9.1) Family: Staphylococcaceae

• Genus: Staphylococcus

  • Species:

  • S. aureus

  • S. epidermidis

• Virulence Factors:

  • Non-fastidious

• Morphology:

  • G++ cocci (grape shape)

  • Non-motile

  • Non-sporing

  • Clinical strains have G.R. => Facultative

  • Capsule: Anaerobic

  • i) Cell wall associated:

    • a) Peptidoglycans

    • b) Techoic acid

  • ii) Cell surface associated:

    • a) Protein A - binds to the Fc region of human Ig G

  • iii) Extracellular factors:

    • a) Inflammatory cytokines

    • b) Cell-associated polymers increase the release of enzymes:

    • i) Coagulase → plasma clotting (for hiding)

    • ii) Hyaluronidase → damage connective tissue

  • iv) Exotoxins:

    • a) Hemolysins (alpha, beta, gamma) → destroys blood cells, suppresses cell mediated immunity

    • b) Epidermolytic toxin

    • Types: ET-A + ET-B

    • c) Toxic shock syndrome toxin - leads to multi-organ failure

    • d) Enterotoxins: (A, B, C, D, E, H, I) → increase peristalsis

• Diseases:

  • Skin & soft tissue infections

  • Osteomyelitis

  • Folliculitis

  • Food poisoning

  • Impetigo

  • Furuncles

  • Carbuncles

  • Pneumonia

  • Endocarditis

  • Arthritis (suppurative)

• Transmission Modes:

  • Airborne

  • Direct contact

• Pathogenesis:

  • Adhesion to tissue

• Sites of Infection (SOI):

  • Patients, medical devices, contaminated food

• Reservoirs:

  • Humans, Animals, Food products

• Identification:

  • S. epidermidis: White, dull, convex, mucoid colonies

  • Breakdown of tissue, production of toxins & biofilms

  • Culture Media:

  • BA (Blood Agar) → Yellow, circular, smooth, shiny, convex colonies with B-hemolysis

  • OG (Oxacillin Glucose) - high concentration sticky colonies

  • Preferred culture media: SYA

  • Uniform growth on liquid media

  • Gelatin test: proteolytic properties observed

  • Catalase test: H₂O₂ + colonies → bubbles (indicates positive)

  • Coagulase test: plasma + colonies → clot formation indicates S. epidermidis

• Importance:

  • MRSA: Causes pneumonia, surgical site infections, sepsis (hard to treat)

  • Nosocomial infections: Folliculitis, impetigo, furuncles

• Immunological Preparations:

  • Anti-staphylococcal human serum

• Treatment (Tx):

  • Penicillin

  • Resistance to Methicillin

  • MRSA = Methicillin-Resistant Staphylococcus aureus

  • Vancomycin

• Antistaph Monoclonal Antibodies:

  • Staphylococcal bacteriophage

• S. epidermidis: Nosocomial infections of medical devices

  • Produces biofilms & adhesive molecules

9.2) Family: Streptococcaceae

• Genus: Streptococcus

  • Species:

  • S. pyogenes

  • S. pneumoniae

• Morphology:

  • G+ cocci in chains

  • Non-motile

  • Non-sporing

  • Capsulated

  • Growth classification: Non-fastidious, facultative anaerobic

• Classification:

  • i) α hemolytic (green color, size 1-2 mm, indefinite margins): S. viridians

  • ii) β hemolytic (transparent, 2-4 mm size, defined margins)

  • iii) γ hemolytic (no hemolysis)

  • Group A: β hemolytic Streptococcus (important, e.g., S. pyogenes, S. pneumoniae)

• Virulence Factors:

  • Lipoteichoic acid

  • Fimbronectin binding proteins (Adhesion)

  • Hyaluronic acid capsule (invasive soft tissue infections)

  • M-proteins (molecular mimicry, useful for diagnosis)

  • Hemolysins → SL-O (CO₂ labile, antigenic), SL-S (CO₂ stable, non-antigenic)

  • Streptococcal pyrogenic/erythrogenic toxin → Superantigen (non-specific activation of T-cells)

  • Hyaluronidase → breaks down connective tissue

  • Streptokinase → hydrolyzes fibrin clot

  • Peptidoglycan → has pyrogenic & thrombolytic properties

• Diseases:

  • Pharyngitis (greyish-white exudate on tonsils)

  • Complications: glomerulonephritis, rheumatic fever

  • Scarlet fever (strawberry tongue, rashes concentrated on nasolabial folds)

  • Erysipelas (acute infection with systemic symptoms; bacteria enter through damaged skin)

  • Necrotizing fasciitis

  • STSLS: hypotension, high fever, chills, renal failure

• Transmission Modes:

  • Human skin, mucous membranes

• Pathogenesis:

  • Adhesion to human tissue

  • Breakdown of tissue leading to invasion

• Identification:

  • Culture media: BA → transparent colonies, product of toxins, resistant to 10% bile

  • Bile test: differentiate from S. pneumoniae

  • Hiss media: sugar fermentation with acid production without gas

  • Dick test → detect S. pyogenes in gas intradermal

• Rheumatic fever: Complication of pharyngitis; Autoimmune, non-suppurative, multisystem inflammatory disease

  • Manifestations:

  • Carditis, polyarthritis, chorea, subcutaneous nodules

  • Diagnostics: Non-specific tests only provide some markers (Sediment rate)

  • Treatment (Tx):

  • NSAIDs and prevention of heart failure

9.3) Taxonomy: Same Morphology: G++ Classification: Same

• Genus: Streptococcus pneumoniae

  • Morphology: G+ cocci in pairs, elongated, lancet-shaped, non-sporing, non-motile

• Virulence Factors:

  • Polysaccharide capsule (antiphagocytic, resistance to opsonization)

  • Hyaluronidase

  • 90 serotypes

  • Autolysin (important during cell division and at the end of exponential growth)

  • Pneumolysin (lysis of human cells, arrests motility of ciliary epithelium of the respiratory tract)

  • C-polysaccharide & F Ag

  • NanA & Nan B → colonization & virulence, can provoke encephalitis in HIV patients

  • IgA1 proteases → inactivate secretory IgA

• Diseases:

  • Pneumonia (causes community-acquired pneumonia)

  • In children: complications → meningitis

• Reservoirs: Humans

• Sites of Infection (SOI): Humans, water

• Mode of Transmission (WOT): Via air droplets

• Pathogenesis:

  • Adhesion to host tissue in the nasopharynx

  • Breakdown of tissue and invasion

  • Autolysis

• Identification:

  • Culture media: BA → small, flat colonies with raised edges; mucoid colonies in capsulated strains

  • Bile test: 10% bile will cause lysis of bacteria

  • Hiss media: sugar fermentation with acid production without gas

  • Immunochromatography

  • Latex agglutination testing using strep-kits or ELISA

• Immunological Preparations:

  • Pneumococcal polysaccharide vaccine (23 capsular Ag)

  • Pneumococcal conjugate vaccine (PCV-7 for children <2 years old and adults >65 years)

9.4) Family: Neisseriaceae

• Morphology: G- diplococci (coffee bean shape)

• Genus: Neisseria

  • Species: N. meningitidis

• Growth Requirement (G.R.): Fastidious, non-sporing, obligate aerobic

• Virulence Factors:

  • Type IV pili

  • Endotoxin

  • Capsular polysaccharide,

  • Animal proteins, capsulated

  • Heated blood, requires 5% CO₂ environment

• Diseases:

  • Meningitis (photophobia, stiff neck) in children

  • Purpuric rash

  • Part of microflora in the nasopharynx

• Reservoirs: Humans

• SOI: Human carriers and ill individuals

• WOT: Through air droplets

• Pathogenesis:

  • Enters through the nasopharynx

  • Attaches to epithelia of the respiratory tract via type IV pili

  • Leads to upper respiratory tract infection, hypotension, fever, thrombosis, increased ICP, headache, may invade to the brain leading to bacteremia and meningococcemia

  • Symptoms include bluish-grey, round, convex colonies

• Identification:

  • Culture: Chocolate agar - translucent colonies

  • Mueller Hinton agar

  • Biochemical Characteristics (B.C.A.):

  • a) Oxidase +ve

  • b) Catalase +ve

  • c) Susceptible to salts & fatty acids

  • Diagnosis: ELISA using meningococcal monoclonal Ab

• Treatment (Tx):

  • Benzylpenicillin, Rifampicin

• Prophylaxis: Isolation of ill and contact persons, vaccinations

• Immunological Preparations:

  • Meningococcal conjugate vaccine

  • Dose: 11-12 years; booster at 16 years old

  • Serogroup B meningococcal vaccine for ages 16 through 23 years old

9.5) Family: Neisseriaceae

• Genus: Neisseria

  • Species: N. gonorrhoeae

• Morphology: G- diplococci (kidney shape)

  • Non-sporing, obligate aerobic

• Growth Requirement (G.R.): Fastidious

  • Twitching motility, highly pilliated for attachment

  • Requires heated blood and 5% CO₂

• Virulence Factors:

  • Type IV pili

  • Endotoxin

  • Opa protein

  • Lipopolysaccharide (LPS)

  • Hemagglutinin (antiphagocytic)

• Diseases:

  • Gonorrhea (often asymptomatic in women)

  • Clinical picture: Urethritis with yellow purulent discharge

  • Blennorrhea in newborns (conjunctivitis)

• Reservoir: Humans

• Pathogenesis:

  • Invades the mucous membranes of the urogenital tract, throat, rectum, and eyes

  • Leads to acute suppuration and tissue invasion, chronic inflammation, and fibrosis

  • Complications include epididymitis or salpingitis

• Site of Infection (SOI): Carriers and ill pregnant women

• WOT: Direct contact during natural birth

• Treatment (Tx):

  • III generation cephalosporins for treatment of conjunctivitis with yellow purulent discharge

  • Prophylaxis: 1% silver nitrate eye drops for infants

• Identification:

  • Culture: chocolate agar (larger white non-piliated colonies), Mueller Hinton agar (translucent, granular colonies)

  • Biochemical Characteristics (B.C.A.):

  • a) Oxidase +ve

  • b) Catalase +ve

  • c) Susceptible to fatty acids & salt

  • Diagnosis of chronic cases: Gonococcal vaccine for diagnosis

9.6) Family: Pseudomonadaceae

• Genus: Pseudomonas

  • Species: P. aeruginosa

  • Commonly referred to as blue pus bacillus (non-fermenter)

• Morphology: G- rod shaped bacilli (slightly curved)

• Growth Requirement (G.R.): Non-fastidious, motile (polar flagella), obligate aerobic

• Virulence Factors:

  • Pili for attachment

  • Protects against inhalation with slim layer

  • Produces a flower/grape-like odor during growth

  • Lytic enzymes: hemolysin, protease, phospholipase C

  • Exotoxin A: inhibits protein synthesis, tissue destruction, interrupts mitochondrial activity

  • Lipopolysaccharide (LPS): endotoxin causing septic shock

  • Pigments:

  • a) Pyocyanin: kills competing bacteria, affects ciliary motility in the respiratory tract

  • b) Pyorubin: protects against oxidative stress

  • c) Pyomelanin: protects against UV light

  • d) Pyoverdins: fluorescent yellow-green, regulates the activity of exotoxin A and biofilms

• Diseases::

  • Outpatient: Suppurative otitis, lung infections in patients with cystic fibrosis

  • Nosocomial infections: Suppurative diseases of soft tissue, wound & burn infections, urinary tract infections, pneumonia

• Reservoir: Soil, water, humans

• Sites of Infection (SOI): Carriers

• WOT: Inhalation, ingestion, direct contact

• Pathogenesis:

  • Adhesion → invasion & biofilm production → enters bloodstream leading to bacteremia, systemic symptoms

• Identification:

  • Culture media: MacConkey agar (non-lactose fermenters) → dense turbidity, surface film

  • Preferred culture media: Tryptic soy agar → circular elevated colonies, pigmentation in center

  • BA, CA → large grey colonies with β-hemolysis, metallic sheen, alligator skin structure

  • Biochemical Tests:

  • a) G-stain

  • b) Oxidase and fermentation tests to differentiate from Enterobacteriaceae

• Treatment (Tx):

  • Extremely resistant to antibiotics, nosocomial strains can be pandrug-resistant

  • Options include:

  • a) Piperacillin + tazobactam (antipseudomonal penicillin)

  • b) Ceftazidime combined with avibactam

  • Carbapenems & polymyxin B & E are potent drugs

• Immunological Preparations:

  • Antipseudomonal gamma globulin for animals

9.7) Family: Enterobacteriaceae

• Genus: Escherichia

  • Morphology: G- rod shape (monobacilli/diplobacilli)

• Species: E. coli

• Growth Requirement (G.R.): Non-fastidious, facultative anaerobic

• Virulence Factors:

  • Adhesion, colonization, hemagglutination

  • Antiphagocytic properties

  • i) LPS (O-antigen)

  • ii) Fimbriae

  • iii) Capsule (K-antigen)

  • iv) Toxins:

  • a) Heat-labile toxin (cholera-like) → increase cAMP → diarrhea

  • b) Heat-stable toxin → increase cGMP

  • c) Enteroaggregative toxins

  • d) Vero or shiga-like toxin (cytotoxin) → similar effects as heat-stable toxin

  • e) EAST toxin → similar to ST, but less active

• Classification:

  • i) UPEC: causes UTIs

  • ii) IPEC: diarrheal disorders

  • ETEC: produces LT and ST → Traveler's diarrhea

  • EPEC: localized lesions → watery diarrhea with mucus

  • EIEC: properties like dysentery and Shigella → diarrhea with blood, mucus

  • EHEC: produces Shiga toxin, localized lesions, can cause HUS (hemolytic uremic syndrome)

  • EAEC: produces EAST and LT toxins, have AAF (adherence factors) → watery diarrhea with no blood or mucus

  • DAEC: causes watery diarrhea without blood or mucus

• Diseases:

  • UTIs, diarrhea, nosocomial infections

  • HUS: Triad → hemolytic anemia, thrombocytopenia, acute renal failure; complicated by ischemia, stenosis, perforation of bowel.

• Reservoirs: Humans, part of normal microflora of the bowel; contaminated food and water

• SOI: Fecal-oral route, direct contact

• Identification:

  • Culture media: BA → white large colonies with rare hemolysis, serotyping with immune agglutinating sera for O-antigen, H-antigen, K-antigen

  • MacConkey agar → bright pink colonies for differentiation

  • Kligler iron agar → fermentation with acid production without H₂S

• Treatment (Tx):

  • Rehydration and compensation of lost electrolytes, ampicillin

  • Immunobiological preparations: Colibacter in treatment of intestinal diseases

• Prevention:

  • Hygiene measures are critical, immunization is possible

9.8) Family: Enterobacteriaceae

• Genus: Salmonella

  • Species: S. typhi, S. paratyphi A, B, C

• Morphology: G- bacilli, peritrichous, non-sporing

• Growth Requirement (G.R.): Non-fastidious, facultative anaerobic

• Virulence Factors:

  • i) LPS (O-antigen)

  • ii) Slim layer (Vi-antigen)

  • iii) Flagella (H-antigen)

  • iv) Fimbriae

  • v) Superoxide dismutase

• Diseases:

  • i) Enteric fever (typhoid + paratyphoid fever)

  • Symptoms include headache, malaise, pale skin, bradycardia, coated tongue

• Reservoirs: Animals and humans (common in birds, reptiles)

• SOI: Animals leading to human infections

• WOT: Fecal-oral route, transmitted through contaminated food, water, and soil

• Pathogenesis:

  • Attaches to M cells, leading to damage and invasion; results in increased lymphocytes & monocytes

  • Ulceration occurs

  • Phagocytosed bacteria can re-enter bloodstream leading to bacteremia

• Identification**:

  • Culture media: MacConkey agar → colorless colonies; XLD agar → brighter colonies than Shigella

  • Selective media: XLD agar, HE agar

  • Differential media: KIA → glucose fermentation with acid and gas, H₂S-variable

• Treatment (Tx):

  • Ampicillin, cephalosporins

  • Prophylaxis: Isolation of affected, eradication of carriers

• Immunobiological preparations:

  • Salmonella bacteriophage, inactivated typhoid vaccine

  • Live typhoid vaccine (Ty21a), conjugate vaccine (Vi+TT)

9.9) Family: Enterobacteriaceae

• Genus: Shigella

• Morphology: G- rod shape, non-motile

• Growth Requirement (G.R.): Non-fastidious, non-sporing

• Species: S. dysenteriae group, S. flexneri, S. boydii, S. sonnei

• Virulence Factors:

  • i) LPS (O-antigen)

  • ii) Slim layer (K-antigen)

  • iii) Fimbriae and mucinase

  • iv) Plasmid-encoded proteins (contribute to invasion)

  • v) Enterotoxin similar to heat-labile toxin of E. coli

  • vi) Shiga toxin

• Diseases:

  • i) Shigellosis → destruction of enterocytes leading to ulcerative colitis

• Reservoirs: Ill individuals

• SOI: Large primates, humans (both sick and carriers)

• WOT: Fecal-oral transmission

• Symptoms: Malaise, watery diarrhea, abdominal pain, myalgia

• Pathogenesis:

  • Adhesion & invasion of colonic epithelium via M-cells causes destabilization of epithelial junctions

  • Recruitment of PMN cells by pro-inflammatory cytokines

  • Shiga toxin produced by S. dysenteriae serotype 1 can evade detection by the immune system

• Treatment (Tx):

  • Ampicillin, cephalosporin

  • Prophylaxis: Isolation of patients, eradication of carriers, proper sanitation

  • Remains lactose-negative

9.10) Family: Vibrionaceae

• Genus: Vibrio

  • Species: V. cholerae, V. parahaemolyticus, V. vulnificus

• Morphology: G- bacilli (comma-shaped)

  • G.R.: Facultative anaerobic

• Virulence Factors:

  • i) LPS (O-antigen)

  • ii) Flagella (H-antigen)

  • iii) Neuraminidase, proteases, adherence factors which include hemagglutinating pili

  • iv) Cholera toxin (CT-14, CT-2)

• Diseases:

  • Cholera

• Reservoirs: Environmental (natural aquatic organisms)

• Transmission Modes: Human carriers (possible), fecal-oral route

• Symptoms: Nausea, vomiting, watery diarrhea resembling “rice water”

• Pathogenesis:

  • Ingestion leads to adhesion to the mucosal epithelium of the intestine

  • Toxin production increases cAMP leading to secretion of salts; passive transport of water occurs as a result of diarrhea

• Treatment (Tx):

  • Fluid and electrolyte replacement

  • Prophylaxis: Disinfection of water, proper cooking, and sanitation measures

• Immunobiological Preparations:

  • Cholera dipstick test, live vaccine (Vaxchora), and inactivated vaccines

9.11) Family: Enterobacteriaceae

• Genus: Yersinia

  • Species: Y. pestis, Y. pseudotuberculosis, Y. enterocolitica

• Morphology: G- coccobacilli (safety-pin appearance in Giemsa stain)

  • Non-sporing, non-capsulated

  • G.R.: Non-fastidious, facultative anaerobic

• Virulence Factors:

  • i) F1 antigen

  • ii) V and W antigens

  • iii) Pesticin

  • iv) Coagulase from fleas (produced at 25°C)

• Diseases:

  • i) Plague: a) Bubonic plague (presence of bubo) - transmission does not occur human-to-human
    b) Septicemic plague (develops from bubonic)
    c) Pneumonic plague (last stage, almost always fatal)

• Reservoirs: Rodents and fleas

• SOI: Infected rodents and ill humans

• WOT: Vectors, air droplets

• Pathogenesis:

  • Entry through the bite of an infected flea, leading to development of buboes and systemic symptoms (vomiting, diarrhea, sepsis)

• Identification:

  • Bioaspirate specimens from lymph node, blood, sputum, or CSF

  • Culture Media: a) MacConkey agar (lactose-negative)

  • b) Blood agar → gram +ve, acid-producing colonies with dark brown zones

  • KIA: lactose-negative, hydrogen sulfide-negative, no gas produced

  • Diagnosis: Dipstick test with monoclonal Ab for F1 antigen

• Immunobiological Preparations:

  • Immunoglobulin against F1 antigen, vaccines are in research and development stages

9.12) Family: Bacillaceae

• Genus: Bacillus

  • Species: B. anthracis, B. cereus

• Growth Requirement (G.R.): Facultative anaerobic, non-fastidious

• Morphology:

  • G++ large rods, motile, central oval spores

• Virulence Factors:

  • i) Capsular polypeptide

  • ii) Anthrax toxin:

  • a) Edema factor (EF) + protective antigen (PA) → forms edematous toxin

  • b) Lethal factor (LF) → causes cell death; LF + PA → lethal toxin

• Diseases:

  • i) Cutaneous anthrax → formation of vesicle leading to hemorrhagic bullae

  • WOT: soil, animals

  • SOI: Herbivorous animals

  • ii) Pulmonary anthrax (spores inhaled) → forms severe necrotizing lesions in lungs

• Pathogenesis:

  • Spores germinate in macrophages leading to production of toxins

  • Affects immune system and causes widespread damage leading to fever, septic shock, and death

• Tx:

  • High dose of penicillin G or doxycycline

  • Prophylaxis:

  • Specific: Vaccination of animals and high-risk individuals

  • Non-specific: Disposal of dead animals

• Identification:

  • Culture on Blood Agar → medusa head colonies, ground-glass texture

• Immunobiological Preparations:

  • Live spore suspension vaccine for animals, combined vaccines for humans

• Biothreat: Possible biological warfare or terrorism issues

9.13) Family: Francisellaceae

• Genus: Francisella

  • Species: F. tularensis

• Morphology: G- small pleomorphic rods

• Growth Requirement (G.R.): Obligate aerobic, fastidious

  • Non-sporing, non-motile, requires sulf-hydryl containing compounds

• Virulence Factors:

  • i) Capsule

  • ii) LPS: endotoxin

  • iii) Hemolysin,

  • iv) Vi antigen

  • v) Ability to invade and multiply in macrophages and hepatocytes

• Subspecies:

  • a) F. tularensis subsp. tularensis (highly virulent)

  • b) F. tularensis subsp. holarctica (less virulent)

• Diseases:

  • Tularemia (variety of clinical manifestations)

  • a) Ulceroglandular (WOT: vectors such as ticks and flies)

  • b) Glandular lymphadenopathy → fever, malaise

  • c) Oculoglandular → conjunctivitis; WOT: direct contact

  • d) Oropharyngeal → after ingestion of contaminated food/water

  • e) Pneumonic → airborne transmission through fur and hairs

• Tx:

  • Streptomycin, gentamicin

• Immunological Preparations:

  • Live attenuated vaccines are in research

• Biothreat: Potential biological warfare agent (biosafety level 3)

9.14) Family: Mycobacteriaceae

• Genus: Mycobacterium

  • Species: M. tuberculosis complex (M. tuberculosis, M. bovis, M. africanum, M. microti)

• Morphology: G+ (weak), acid-fast curved rods

  • Non-sporing, non-motile

• Growth Requirement (G.R.): Obligate aerobic

• Virulence Factors:

  • i) Phosphatides

  • ii) Waxes causing tuberculin sensitivity leading to granuloma formation

  • iii) Mycolic acid

  • iv) Cord factor → causes chronic granulomas

  • v) Polysaccharides → induce hypersensitivity reaction

• Diseases:

  • Tuberculosis

• Reservoirs: Ill individuals or carriers

• WOT: Air droplets, can be transmitted via contact or through alimentary routes

• Pathogenesis:

  • Inhalation → alveoli, leading to two types of lesions:

  • 1. Productive (causing granulomas) and

  • 2. Exudative (acute inflammation, edema)

  • Spreads through lymphatics and blood system

• Complications: Lung bleeding, liver disorders, extrapulmonary infections (e.g., GIT TB)

• Identification:

  • Culture: Lowenstein-Jensen medium for growth; bacillary colonies appear brown; Middlebrook agar for further isolation

• Diagnosis:

  • Tuberculin skin tests (Mantoux test)

  • IGRA blood tests for TB

9.15) Family: Mycobacteriaceae

• Genus: Mycobacterium

• Species: M. leprae, M. lepromatosis

• Diseases:

  • Leprosy:

  • a) Tuberculoid leprosy → reduced skin sensitivity, localized skin lesions

  • b) Lepromatous leprosy → extensive body lesions, mutilation possible, severe disability

• SOI: Ill individuals in active state

• WOT: Air droplets during close contact with untreated individuals

• Pathogenesis:

  • Entry through the skin leading to the appearance of skin lesions

• Tx:

  • Patients often isolated, regular check-ups required for relatives

• Diagnosis:

  • Lepromin skin test; Mitsuda's reaction to indicate immunity

• Immunobiological Preparations:

  • BCG vaccine recommended to prevent tuberculosis

9.16) Family: Corynebacteriaceae

• Genus: Corynebacterium

  • Species: C. diphtheriae

  • Biotypes: C.d. mitis, C.d. intermedius, C.d. gravis, C.d. belfanti

• Morphology: G+ club-shaped bacilli

• Growth Requirement (G.R.): Facultative anaerobic, non-motile, non-sporing, clinical strains have microcapsule

• Virulence Factors:

  • Diphtheria toxin (heat-labile)

  • Structural tox gene encoded by B-corynephage

• Diseases:

  • Diphtheria:

  • a) Respiratory type (common)

  • b) Skin type (modern presentations are rare)

• Pathogenesis:

  • Causes tissue destruction by toxin absorption leading to necrosis of infected organs (especially in kidneys and liver)

• Tx:

  • Antitoxic antibodies, Rifampin, erythromycin

• Prophylaxis:

  • Isolation of ill patients

  • Vaccination, eradication of carriers

• Identification:

  • Culture media: CNA agar (white to grey non-hemolytic colonies), cystine tellurite agar, and Loeffler slant

• Immunobiological Preparations:

  • Diphtheria toxoid vaccine (part of DTP vaccine series) and diphtheria antitoxic serum for treatment.

9.17) Family: Spirochaetaceae

• Genus: Treponema

  • Species: T. carateum, T. pallidum

  • Subspecies: T.p. pallidum, T.p. pertenue, T.p. endemicum

• Morphology: G- spirals, motile with axial flagella

• Growth Requirement (G.R.): Microaerophilic, non-capsulated

• Virulence Factors:

  • Cardiolipin

• Diseases:

  • i) Venereal syphilis (primary hard chancre forms)

  • ii) Non-venereal syphilis (secondary roseolar skin rashes)

  • iii) Tertiary syphilis (late manifestations, can cause paralysis, mental disorders)

• SOI: Ill individuals (humans)

• WOT: Sexual contact

• Pathogenesis:

  • Enters through genitals leading to systemic infections

• Diagnostics:

  • Cannot be cultivated in vitro; diagnosed via dark field microscopy or direct fluorescent Ab tests (DFA-TP)

• Immunological Preparations:

  • Cardiolipin tests, Treponemal antibodies (ELISA), Wassermann test (for screening)

9.18) Family: Clostridiaceae

• Genus: Clostridium

  • Species: C. perfringens, C. botulinum, C. septicum, C. difficile, C. tetani

• Morphology: G+ rod-shaped

• Growth Requirement (G.R.): Obligate anaerobic

• Virulence Factors: Various toxins as outlined below:

  • i) CPA (major α-toxin)

  • ii) CPB (major β-toxin)

  • iii) CPE (enterotoxin)

  • iv) ETX (ε-toxin)

  • v) ITX (major L-toxin)

• Diseases:

  • Food poisoning: Caused by improperly cooked or stored food, results in watery diarrhea

  • Gas gangrene: Caused by wound contamination; marked pain and swelling of the area due to gas formation

• SOI: Improperly cooked/stored food (for food poisoning)

  • Contaminated soil (for gas gangrene)

• WOT: Alimentary route (ingestion for food poisoning), wounds (for gas gangrene)

• Tx:

  • Oral rehydration and detection of enterotoxin via ELISA for food poisoning

  • Surgical cleaning of gas gangrene wounds, systemic antitoxic therapy, and amputation for severe cases.

• Identification:

  • Culture media: BA and TSC for lecithinase activity testing

• Immunobiological Preparations:

  • Polyvalent anti-gas gangrene serum

9.19) Family: Clostridiaceae

• Genus: Clostridium

  • Species: C. tetani

• Morphology: G+ with spindle/drumstick shape, spore-forming

• Virulence Factors:

  • i) Tetanolysin

  • ii) Tetanospasmin (neurotoxin)

• Diseases:

  • Leads to generalized wound disease with tonic muscular spasms in the affected area

• SOI: Horses, sheep, and goats

• WOT: Injury from instruments, trauma

• Symptoms: Beginning with localized pain progressing to spasms and seizures

• Tx and Prophylaxis:

  • Surgical cleaning of wounds, use of antitoxin immunoglobulin, central monitoring for respiratory function

  • Active immunization recommended and part of routine vaccinations

• Identification:

  • Diagnosis is clinical, with cultures from media aiding attribution to specific species, being unable to stain in some cases.

9.20) Family: Clostridiaceae

• Genus: Clostridium

  • Species: C. botulinum

• Morphology: G+ rod, spore-forming, non-capsulated, motile (peritrichous)

• Virulence Factors:

  • i) Neurotoxins: A, B, C1, D, E, F, G

  • ii) Enterotoxin → C2 (effects on bowel)

• Diseases:

  • Foodborne botulism, infant botulism, wound botulism

• SOI: Improperly preserved foods, honey as a common carrier for infants

• Symptoms:

  • Neurotoxic manifestations include dysarthria, dysphagia, coma; gastrointestinal issues include nausea, constipation

• Tx and Prophylaxis:

  • Treatment requires antitoxin use and identification of toxin as well as avoidance of contaminated foods.

  • Active immunization is needed for at-risk groups and premature infants.

• Identification:

  • CM: Robertson's cooked meat broth for growth spanning from clinical diagnosis to treatment regimen analysis.