G+ bacilli & Anaerobes & Branching filaments

G+ bacilli

Corynebacteria characteristics

Appearance: Club-shaped G+ bacilli with irregularly stained segments
Appear in V/Y/Chinese letters configurations

Staining: Cells contain metachromatic granules that can be visualized with methylene blue stain (Albert Stain)

Corynebacteria genus

We got:
→ Corynebacterium diphtheriae (pathogen)
→ Diphteroids: commensals of throat/ nasopharynx/ skin/ UT/ Conjunctiva

What’s another name for C. diphtheriae. What does Diphtheros mean?

Klebs-Loeffler bacillus
Leather (for tough leathery pseudomembrane)

How is C. diphtheriae spread?

Respiratory droplets of asymptomatic/ convalescent carriers

What infecctions other than RTIs can C. diphtheriae cause

It can cause cutaneous infections - more common in tropics

Diphtheria toxin mechanism

Classic AB toxin.
It causes inhibition of protein synthesis by ADP-ribosyoation of the Elongation Factor EF2 in the presence of NAD → No chain elongation

→ Necrosis in pharyngeal, cardiac, and CNS tissues

Explain general diphtheria pathogenesis

1. C. diphtheriae gets into RT

2. C. diphtheriae multiplies in superficial layers and causes necrosis

3. Inflammatory response → Pseudomembrane formation on tonsils/Posterior pharynx (Made of dead cells, immune cells, RBCs, and bacteria)

4. Pseudomembrane spreads either up towards the nasopharynx, and down towards the larynx → Mechanical suffocation

Note: Inflammation and antigen drainage cause polylymphadenopathy. And at any point, toxin can become systemic by entering through bloodstream/lymphatics → Major complications

Lab diagnosis C. diphtheriae (Non-culture)

Take swab from lesions and look for G+ bacilli in chinese letter/V/Y arrangements, and use Albert stain that can tell us if there are metachromatic granules

C. diphtheriae culturing

Loeffler serum slope
Tellurite blood agar: Tellurite reduced to tellurium → Gray/black color

C. diphtheriae virulence test

Elek’s gel precipitation test → Leads to toxin precipitation if present

C. diphtheriae treatment

Must suppress toxin production and kill bacteria:
→ Penicillin + Erythromycin
→ Early administration of antitoxin

C. diphtheriae Prophylaxis

Toxoid vaccine , given IM

• DTaP

• TD (10 Times smaller dose of toxoid)

Antitoxins vs B fragment

Listeria monocytogenes general characteristics

Note, motility is just like Yersinia (but yersinia not tumbling)

Where can Listeria monocytogenes be found in nature

Unpasteurized dairy products (soft cheese), unwashed vegetables, raw or undercooked fish and meat products (hot dogs and luncheon meats)

What property of Listeria monocytogenes, makes it something you gotta always be careful about

It’s a psychrophile, and can grow on refrigerated foods.
Also, it can spread from person to person (hands/food prep)

Transplacental transmission OR vaginal transmission during birth

Listeria monocytogenes clinical manifestations in different demographics

Healthy: Asymptomatic carriage or gastroenteritis

Pregneant: Amnionitis & Spontaneous abortion

Neonates and IC individuals: Meningitis and septicemia

*LISTERIOSIS, is the form of the disease in pregnant/neonates/IC, gastroenteritis isn’t “Listeroisis”

Listeria monocytogenes pathogenesis

In the mucosa, Listeria monocytogenes can enter enterocytes (Directly unlike shigella), and once inside, it can manipulate actin filaments to propel it laterally from cell to cell (like shigella - no exposure to complements and antibodies)

Immune evasion: Listeriolysin → Generates pores in phagosome that allow its escape into the cytoplasm

Listeria monocytogenes specimens

Listeria monocytogenes culture

• Blood agar → Small zones of hemolysis

• Enrichment with: NA/ Cold (4 C)/ Bile salts

NOTE: Negative culture should not rule out infection if there is strong clinical evidene

Listeria monocytogenes serology

Unreliable

Uses anti-LLO antibodies, however, common Ags with Strep species and E. feacalis

Listeria monocytogenes treatment

Ampicillin/Erythromycin IV
If pregnant → Give antibiotics immediatly

Anthrax spread in nature

Bacillus anthracis forms spores in soil → Grazers get infected → Shed large amounts in feces (and mouth and nose) → Back to soil

Classify anthrax manifestations according to fatality

Cutaneous: ~10-20% - Most common (95%)
Gastroenteritis: ~25-60% (Even with treatment) - Rare
Pulmonary: ~80-90% (Untreated) / 40-50% if treated

Anthrax pathogenesis

PA gets cleaved by the receptor Furin and bound by ATR in lipid rafts → PA can now bind LF/EF and get them RMEed along with it

• EF → Increase in cAMP → Edema

• LF → Inhibits MAPK pathway → Necrosis and hypoxia (Macrophage apoptosis)

Describe cutaneous anthrax symptoms

Papule → Vesicle → Malignant pustule around a painless necrotic lesion covered by a black Eschar - Hide Porter’s disease

Involved: Face, neck, hands, arms, back

Pulmonary anthra symptoms - Woolsorter’s disease

Life-threatening hemorrhagic pneumonia caused by spore inhalation.

Flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage and mediastinitis (Enlarged mediastinum on X Ray) and Shock

Anthrax serology

Ascoli’s thermoprecipitation → Demonstrates presence of anthrax in tissues

Bacillus anthracis morphological characteristics

Solo, duo, or chains → The entire chain is surrounded by one capsule (Bamboo stick appearance) and spores that are centrally-located within the bacteria

Note: PROTEIN CAPSULE (Poly D-Glu)

How should we culture Bacillus anthracis

Grow on BA or NA at 37 C

Medusa head appearance, Non or weakly hemolytic

Anthrax vaccine

Sterne vaccine: Live-attenuated strains, rendered avirulent by the loss of the plasmid which encodes anthrax toxins.

Mazucchi vaccine: Contains spores of an attenuated strain

*Note: Bacillus anthracis, cereus, talasomething are all genetically identical, they differ in the presence or absence of plasmids

Where is Bacillus cereus commonly found

In soil: Vegetables and also milk/ cereals/ spies/ poultry/ meat

What phenomenon in Bacillus cereus associated with

Reheated rice syndrome (if there were spores on the rice to begin with

What clinical manifestations are associated with Bacillus cereus

2 forms of food poisoning:

• Diarrheal form: Incubation more than 6 hours, longer convalescence (20-36 hours) * Caused by spore ingestion and germination in gut
  → Secretion of LT-like toxin
  → Watery diarrhea & GI pain
  → Associated with meats

• Emetic form: Incubation less than 6 hours, shorter convalescence (8-10 hours) * Caused by ingetion of preformed cereulide toxin
  → Ingestion of preformed toxin: cereulide
  → Severe vomiting
  → Associated with reheated rice (rice is commonly contaminated with emetic strains)

Rarely, we can also have a systemic infection with bacteremia

*Note: The rice vs meat thing isn’t always guaranteed, and the vice-versa can occur in both cases

Bacillus cereus diagnosis

Depends Primarily on clinical picture and patient history (foods eaten)

But we can do labs on stools/ vomit/ food.
Culture stools and test for toxins to differentiate from staphylococcal food poisoning

Bacillus cereus treatment

Food poisoning: Supportive - Rehydration

Systemic infection: Cipro/ Aminoglycosides/ Vanco/ Clindamycin

What are the main features of anaerobes and their infections

They lack either superoxide dismutase or catalse, or both

Anaerobe infections are often polymicrobial

% of C. diff carriers

Normally present in the gut of 3% of healthy adults, and 66% of infants (<1 yo)

Where can C. diff be found in the environment

Soil

Water

What clinical manifestations are associated with C. diff

• Pseudomembranous colitis - PMC

• Antibiotic-associated diarrhea - AAD

• Antibiotic-associated colitis - AAC

Why does PMC occur

Complication of oral antbiotic therapy with PPI, especially:
Fluoroquinolones, Ampicillin, clindamycin, cephalosporins - FACC

→ C diff overgrowth 4-9 days after starting antibiotics and up to 6 weeks after discontinuation

PMC symptoms and complications

Symptoms: Watery diarrhea, Abdominal cramps, Fever, Nausea ± vomiting, Mucus in stool

Complications: Ileus, and toxic megacolon → Perforation and death

C. diff virulence factors

Toxin A - Enterotoxin (Gastroenteritis symptoms)

Toxin B - Cytotoxin (PMC)

C. diff risk factors

C. diff diagnosis

• PCR or ELISA using antitoxin A monoclonal antibodies or Antitoxin A/B polyclonal antibodies

• Colonoscopy

C. diff treatment

Oral vancomycin or fidaxomycin (severe cases)

Probiotics, FMT

Relapse is common cause spore kinda unkillable

Describe the appearance of C. perfringes and C. tetani

C perfringes: Srtandard rod (Subterminal spores)

C. tetanii: Drumstick (Terminal spores with larger diameter)

What are the tetanus toxins

Tetanospamin (toxoidable) and Tetanolysin

Tetanus pathogenesis

Deep anaerobic wound → Germination of spores → Tetanospamin produced → Toxin absorption by peripheral nerve endings → Retrograde transport to CNS → Fixation to gangliosides of inhibitory neurons → Block inhibitory NT release (Glycine and GABA) → Muscle regidity and spasm → Respiratory failure

What are the clinical manifestations of tetanus

Ophisthotonus (Spasms of spinal cord)

Trismus

Risus sardonicus

C. tetanii culture

Gram-postive bacilli with drumstick appearance, capsulated, motile, peritrichous flagella

Rarely isolated in the lab cuz their culture requires trict anaerobiosis

What should be noted about old C. tetanii cultures

They may appear Gram-negative

What antibiotics are used vs C. tetanii

• Beta-lactams

• Chloramphenicol

• Clindamycin

• Vancomycin

• Nitroimidazoles

BCC VN

Tetanus prophylaxis and treatment

Passive: TIG (tetagam shot)

Active: Tetanus toxoid (TT), DPT

Compined

Diazepam for muscle spasms and wound debridement

Clostridium botulinum habitat

Environment and intestines of humans & animals

Different types of botulism?

8 types depending on the toxin produced
→ A, B, C1, C2, D, 3, F, G
→ All identical in their activity except C2, which is a CYTOTOXIN

Describe the botulinum toxin

• Mechanism: It blocks acetlycholine release → Inhibits muscle cell contraction

• Extremely potent

• Heat-labile

• The bacterium needs to autolyse to release the cells

• Slow acting

Botulism clinical pictures

Infant botulism: Floppy baby syndrome (Honey)
Wound botulism

Foodborne botulism: AB/EF (E → Fish products)
*Cans are inflated and show bubbles
→ 5Ds: Diplopia/ Dysarthia/ Dysphagia/ Dyspnea/ Descending flaccid paralysis
→ Death due to respiratory paralysis

Botulism treatment

• Alll Beta-lactams

• Stomach wash

• Botulinum Ig IM

• Botulinum toxoid

C. perfringes toxins

• Alpha (Lecithinase)

• Beta

• Epslion

• Iota

What strains of C. perfringes cause most diseases

Type A

C. perfringes food poisoning

Spores in spore-contaminated food germinates if left for too long <60 C → Production of heat-labile enterotoxin → Produces late-onset → Resolution in 24 hours

Necrotizing enteritis *Type C”

List some things that can cause gangrene

Follows Trauma: burns, crush injuries, battle wounds, open fractures, surgeries, clinical abortion & Caesarian section, IM injections

Gangrene

Edema

Necrosis

Crepticus (Gas production - H2/ CO2/ N2/ O2)

→ Can rapidly progress to septicemia/shock/death

C. perfringes llab and culture

Very very important to note the Double Zone of Hemolysis on BA

Nagler reaction → Look for alpha-toxin

C. perfringes wound treatment

Supportive/ debridement/ Antibiotics (They don’t work alone cuz can’t penetrate the necrotic tissue)

Number of anaerobes in different anatomical sites compared to aerobes

List the anaerobes

BLAME MPPP CLAMP VF

What are the risk-factors for anerobe-infections

• Trauma/Tissue necrosis

• Impaired circulaton - Seen in: Diabetes, malnutrition, malignancy, hematoma

• Presence of foreign bodies in the body

• Prolonged treatment with aminoglycosides

What does bacteroides fragilis cause

Brain abcess/ intra-abbdominal abcess/ Genital tract infections in females

Prevotella melaninogenica

Lung or liver abcess

Pelvic inflammation and breast abcess in females

Wound infection

Porphyromonas infections

Dental root canal infections - Periodontal diseases

Fusobacterium necrophorum & nucleatum

Aspiration pneumonia → Lung/liver abcess (Especially in unconscious patients)

Oral infection/ chronic sinusitis/ abdominal infetions

Decribe bifidobacteria morphology

Pleomorphic bacilli with true and false branching

What is the clinical significance of peptococcus and peptostreptococcus

Involved in mixxed anaerobic infections:
→ Puerperal sepsis & genital infections
→ Wound infection
→ Gangrenous appendicitis
→ Osteomyelitis
→ UTI
→ Brain and lung abcesses

General treatment for anaerobic infections

Pus drainage from abcesses

Wound debridement and removal of necrotic tissue

Antibiotics:
→ Metronidazole
→ Penicillin (Cocci)
→ Clindamycin
→ Cephamycins

What is Atinomyces israelii, and what is it associated with

Anaerobic, endogenous microbiota of the oral and reproductive cavities and GIT

It causes Actinomycosis → Multiple abscesses and granuloma formation

Describe actinomycosis

Mostly

• Cervico-facial lesions

• Endogenous infections,

But can also cause:

• Thoracic actinomycosis (aspiration)

• Pelvic Actinomycosis → PID with intrauterine devices

Actinomycosis treatment

Surgery and Long-term penicillin

Actinomycosis diagnosis

Take specimen from open aspiration material and look for yellow-ish sulfur granules

Culture: Molar tooth appearance on agar (Teeth are Oral → Actinomyces)

Describe Nocardia asteroides

Saprophytic, aerobic, rare opportunistic pulmonary pathogen

Nocardia asteroides clinical manifestation

• TB-like pneumonitis (- PPD)

• Can cause ectopic foci that can help spread the infection to any other organ (Brain/spleen/kidney/liver/heart)

What is Nocardia Brasiliensis associated with

• Madura foot

• Lympho-cutaneous disease

How can we diagnose nocardia in the lab

• Exudates from samples contain sulfur granules

• Acid-fast branching filament into rods and cocci

• Culture will reveal bread crumb appearance

Nocardia treatment

TMP-SMX

Compare Nocardia and actinomyes