Gram-negative curved bacilli & Coccobacilli

What’s a common feature among curved rods?

They’re all Oxidase +

What are the morphological and motility characteristics of V. cholerae

→ Gram-negative, slender bacilli, comma-shaped

→ Darting motility (Vibrio = Vibrate) - Long polar flagellum

How is V. Cholera transmitted?

*Fecal oral route:

→ Food (Shellfish) - Fecally-contaminated water

Describe cholera symptoms

Acute diarrheal disease:

• Rice water stools

• Dehydration

• Hypovolemic shock

• Metabolic acidosis

What is the ID₅₀ of Cholera

10¹¹ Cell/mL

What can decrease cholera ID₅₀

If someone has lowered stomach acid (antiacid or PPI) - Vibrios are very sensitive to stomach acid

What are cholera’s virulence factors

• Cholera toxin CT

• Toxin-coregulated pilus (Type IV pilus for adhesion)

Describe Cholera toxin’s mechanism

It’s a classic AB toxin: B for tropism/ A for activity

Endocytosis → Adenylyl cyclase → cAMP → Cl^- and Na⁺ efflux

What kind of specimens are taken to screen for cholera

Stool samples or mucus flakes BEFORE GIVING ANTIBIOTICS

Morphology and Characteristics of Vibrio cholerae?

• Gram-negative, curved bacilli

• Non-sporing, non-capsulated

• Facultative anaerobe

How is V. cholera cultured

It requires an aerobic alkaline culture medium (pH<8):

• Bile Salt Agar (BSA)

• Thiosulfate Citrate Bile salts & Sucrose Agar (TCBSA)

• Monsur’s Gelatin

• Taurocholate Trypticase Tellurite Agar (GTTA)

Vibrio cholera biochemistry

• Oxidase + (Rare case of Oxidase-positive sugar fermenters, oxidase negative would otherwise suggest E. Coli/ shigella/ Salmonella)

• Suc +

• Lac + (late fermenter)

• String test +

  • Uses 0.5% Deoxycholate (a bile salt), which can lyse Vibrio cholerae’s cell wall, which will cause DNA to leak out and give a stringy texture

• Cholera Red Reaction +

  • Peptone water (contains Trp + NO2-) + H₂SO₄→ V. cholerae should metabolize Trp to indole: Indole + NO2- + H₂SO₄ → Red coloration

• Side agglutination with cholera O subgroup then test for serotypes, cuz only O cause disease (Check image)

• Immobilization test using antiserum same concept as agglutination

• Phage typing

Vibrio cholera Prophylaxis and treatment

Prophylaxis: Oral vaccines - Immunity for 6-12 months

Treatment: Oral rehydration fluid, antibiotic therapy SECONDARY importance

Vibrio Vulnificus characteristics

G- curved bacillus found in marine environments

Vibrio vulnificus clinical significance

It can cause severe wound infections or septicemia due to exposure to contaminated sea water → Cellulitis that can progress to NF in high-risk patients (Liver disease: Cirrhosis, hemochromatosis)

May require surgical debridement

Campylobacter jejuni characteristics

Curved or spiral-shaped (S-shape) with polar flagella

Campylobacter jejuni biochemistry + Optimal growth conditions

• Oxidase +

---

• Microaerophile

• Grows best at 42C

Campylobacter jejuni incubation period

2-5 days

Campylobacteriosis symptoms

• Bloody diarrhea (Especially in children)

• Abdominal cramps

• Malaise

• Fever

• Nausea and vomiting

Usually self-limiting

Campylobacter sources

Raw or undercooked meat and poultry, water, unpasteurized milk, contact with animals (dogs/cats/pigs)

Campylobacteriosis Complictions

• GBS (Some serotypes more than others)

• Septic arthritis

What is the carriage rate for H. pylori

50% of world population asymptomatically

What exactly does H. pylori colonize

Mainly the antrum of the stomach → Peptic ulcers

What is the probability of carriers developing peptic ulcers

5-10%

Peptic ulcers are risk factors for what conditions?

• Gastric adenocarcinoma (1%)

• MALT lymphoma (0.1%)

→ First infectious agent associated with cancer development

What are some histological diagnostic methods for H. pylori

After gastric biopsy, and transport of media at 4C (very fragile), we can do:

• Giemsa (Sensitive & Inexpensive)

• Steiner or Warthin-Starry stain (More sensitive but expensive)

• Immunohistochemistry

H. pylori culture

Less reliable

H. pylori is quite fastidious, but can be grown on Chocolate Agar (Microaerophilic conditions) and takes about 10 days to grow

Discuss H. pylori serology

• We can get positive IgG at ~3 weeks post-infection

• However, we can’t differentiate between recent, ancient, and even cured infection (ABs persist after triple therapy)

• In pediatrics, we often do stool Ag detection instead of PCR

H. pylori biochemistry

• Ox +

• Cat +

• Urease +++

What non-cultural, non-serological, and non-histological tests can we also use

Molecular → RT-PCR on biopsies and stools

Urease rapid test on biopsies→ 80% Sensitivity, 95% Specificity

13C-Urea breath test → Sensitivity and specificity both >95%

*Note: Must stop TTT treatment before doing urea test (Mainly PPI, it is well-known to reduce sensitivity)

H. pylori Treatment

• Triple therapy: PPI + Amoxicillin or Metronidazole (If allergy) + Clarithromycin

• Bismuth-based quadruple therapy (When concerned about macrolide resistance)

• Fluoroquinolones, Tetracycline, Rifampicin

What are Parvobacteria

Gram-negative, pleomorphic bacteria

These bacteria are usually fastidious and require enriched media for isolation: Blood or chocolate agar

THEY ALL STAIN POORLY IN GRAM STAIN

Discuss H. influenzae’s Habitat/ Transmission/ Virulence factors

Habitat: Normal flora of URT and Vagina

Transmission: Respiratory droplets

Virulence factors: Capsule, IgA protease

How do we classify H. influenzae

They are classified according to whether or not they are encapsulated, and if they are encapsulated, then there are 6 capsule types to differentiate between: a to f

What clinical pictures are capsulated strains of H. influenzae’s mostly associated with?

Capsulated strains mainly infect children from 2 months to 3 years of age

Hib specifically can cause meningitis, pneumonia, sepsis, and epiglottitis

Note: Epiglottitis can have a “Cherry red” appearance in children, and a “Thumb sign”

What clinical pictures are unencapsulated strains of H. influenzae’s mostly associated with?

• Unencapsulated-Nontypeable H. influenzae are the most common cause of mucosal infections → Otitis Media, Conjunctivitis, Bronchitis

• They are also associated with invasive infections

What can other Hemophilus serotypes cause?

• H. aegyptius can cause conjunctivitis “pink eye”

• H. ducreyi can cause Chancroid

1) What are the treatment guidelines for H. influenzae:

• Mucosal infections

• Meningitis

2) H. influenzae Prophylaxis

1) * For mucosal infections, treat with Amoxicillin +/− Clavulanic acid.
* For meningitis, Ceftriaxone

2) Give Rifampin for post-exposure prophylaxis

Describe the available vaccines for H. influenzae

We only got the Hib vaccine; it contains Hib’s capsular polysaccharide conjugated to diphtheria toxoid

→ Given between 2 and 18 months of age

How do we culture H. influenzae?

We can either use CSF or blood samples and directly culture them on Blood or Chocolate Agars
* CSF if meningitis suspected (Hib)
* Blood if patient is positive for laryngoepiglottitis, or pneumonia

How do we make the culture medium for H. influenzae more selective?

We add bacitracin to CA, it inhibits many G+ URT bacteria

What are some unique tests that we can use to identify H. influenzae

• Satellitism: If you streak S. aureus across a BA or CA, it will provide Factor V, which will help enlarge H. influenzae colonies

• X&V: Add factors X and V, they favor H. influenza growth

Describe the basic characteristics of Bordetella, brucella, and francisella

They’re extremely small, Gram-negative, aerobic, non-fermenter (OxidizersName ) coccobacilli, true pathogens (isolation always associated with disease)

Name all the bordetellas, fracisellas, and brucellas and the diseases they are associated with

Bordetella pertussis: habitat & reservoir, transmission, virulence factors

Habitat & Reservoir: Commensal of the human respiratory tract, healthy carriers are reservoirs - Childhood disease.

Transmission: Direct contact - Respiratory droplets and aerosols

Virulence factors: Pertussis toxin (toxoidable)

What does the pertussis toxin do?

• It destroys and dislodges ciliated epithelial cells → Whooping cough

• It activates adenylate cyclase by inactivating Gi, the inhibitory subunit

Describe the pertussis cough

Hacking coughs followed by abrupt deep inhalation (Whoop)

Describe the progression of pertussis

• Catarrhal stage: Low grade fever, coryza - MAX infectivity

• Paroxysmal stage: Whooping cough stage *Note: In adults, causes “100-day cough”

• Convalescence stage: Gradual recovery

Lymphocytosis in Catarrhal and paroxysmal stages

Bordetella pertussis specimen and culture

Specimen: Postnasal or Prenasal swab

Culture: Cough plate method/ Charcoal BA (Cephalexin)/ Regan-Lowe agar/ Bordet-Gengou medium → “Split pearls” or “mercury drops” colonies

B. Pertussis treatment and prevention

Treatment

Macrolides, but use TMP-SMX if allergic

Prevention

Tdap - Full strength (teens and adults)

DTaP - Reduced dose (Infants & children)

Legionella pneumophila morphology

Thin, non-capsulated, Gram-negative coccobacilli

Stains poorly (Like most parvobacteria → Use silver stain)

Legionella pneumophila: Habitat, transmission, outbreaks, and diseases

Habitat: Water (air conditioners, cooling systems, and hot water tanks)

Transmission: Contaminated aerosols - NO PERSON-PERSON transmission

Outbreaks: Cruise ships and nursing homes

Diseases:

• Legionnaires’ disease: Severe atypical pneumonia (Unilateral lobar pneumonia), fever, GI, and CNS symptoms

• Pontiac fever - Mild- flu-like

What are the risk factors for developing legionnaires’ disease over Pontiac fever

Older age, tobacco smoking, chronic lung disease

What kind of immune-evasion mechanisms does legionella have

It can form biofilms (Inside and outside the body), and it can also prevent the fusion of phagosomes with lysosomes in macrophages

Describe Legionella pneumophila diagnostics

• Culture: Charcoal yeast extract buffered with iron and cysteine medium

• PCR

• Detection of ANTIGEN IN URINE

*Note: Labs may show hyponatremia

Treatment for legionella

Macrolides or quinolones

Francisella tularensis appearance

Gram-negative coccobacilli with bipolar staining - Safety pin appearance

What does Francisella tularensis cause?

A plague-like disease of rodents and other small mammals (Rabits, - Reservoirs |||| Ticks and deerflies→ Vectors)

Francisella tularensis treatment

Charcoal yeast extract buffered with iron and cysteine medium

Francisella tularensis treatment

Streptomycin and gentamicin

Francisella tularensis prevention

Avoid insects

Live-attenuated vaccines administered by multiple skin punctures (Like if grass was many needles)

Pasteurella multocida appearance

Gram-negative, nonmotile, coccobacillus

How is Pasteurella multocida transmitted

Through bites and scratched, especially the ones caused by dogs and especially cats.

What clinical manifestations can Pasteurella multicoda cause?

Clinical manifestation depends on the infection site:

1. Animal bite or scratch: Soft tissue infection (Majority and potentially dangerous)

   • Can cause rapidly developing cellulitis at the infection site

   • Chronic local infection

   • Osteomyelitis

2. Nasopharyngeal colonization → Infection (Less common)

Laboratory identification of Pasteurella multicoda

Culture

• Charcoal yeast agar with buffered cysteine and iron

• Small, translucent, non-hemolytic colonies on blood agar

Blood smear

• Bipolar staining on blood smear

Pasteurella treatment

Penicillin (P for Pasteurella)

Responds well to many drugs tho

What’s another name for brucellosis

Malta fever

Name the Brucellas and their source

• B. abortus - mainly cattle

• B. melitensis - sheep & goats

• B. suis - pigs

• B. canis - dogs

B. melitensis is the most common one worldwide

Brucella is Zoonotically-transmitted, but how exactly?

Brucella is concentrated in animal milk, urine and genital organs.

Transmission:

1. Orally through unpasteurized milk and raw milk or meat products

2. Skin → Through abrasions (Farmers and Vets)

3. Respiratory in lab workers

4. Conjunctival/ Blood transfusion/ person to person

Note: Possible transplacental transmission

Describe Brucella’s infection process

Very similar to viruses

Entry through mucosas → Macrophage activation and phagocytosis → Intracellular multiplication → Spread to Reticuloendothelial organs through lymphatics → Spread to blood → Spread to any organ

*Note: Forms noncaseating granulomas (Non-necrotic - No white necrotic center)

Compare the clinical manifestations of acute, undulant, and chronic brucellosis

Main takeaways from the table

• More acute if younger the patient, more chronic the older the patient

• Arthralgia in all but more in chronic

• Fever associated with acute, and undulant fever is undulant -No chronic

• No Hepatomegaly in chronic

• Rare splenomegaly in chronic

• Psychiatric symptoms more common with chronic

• More common ocular symptoms the more chronic

What can you find on a blood test of a patient with brucellosis

We will notice monocytosis, which is characteristic of chronic infections unlike leukocytosis for most acute infections

What are the culture techniques used for brucella?

It usually takes a lot of time (4 weeks), however, BACTALERT, an automated medium, can culture in 2-8 days

Mostly Blood culture, however, we can also do CSF, LN, BMI, pus, synovial fluid

Can we use serology to diagnose Brucella?

Yes, it’s the main diagnosis method (Can also do PCR)
→ Serum agglutination tests for IgG, IgM, and IgA

What is the standard for brucellosis treatment

Doxycycline + Rifampin or Streptomycin

Doxycycline is important cuz brucella can be IC

What are the risk factors for brucellosis relapse

• Male se

• Inadequate antibiotic treatment

• Thrombocytopenia

Describe Gardnerella Vaginalis’s general characteristics

Gram-variable, facultative-anaerobic, non-motile, rod

Describe how Gardnerella vaginalis causes bacterial vaginosis

BV is not an STD but it is common in women who have a lot of sex:

Frequent exposure of the vagina to alkaline pH results in loss of Lactobacillus → further ↑ vaginal pH (>4.5) → Gardnerella-centered anaerobic, polymicrobial biofilm (Allows for Moblincus and Prevotella overgrowth) → amine production causing odor and discharge (fishy odor)

What are the diagnostic methods for BV

• Amine-whiff test - Mixing discharge with 10%KOH enhances the fishy odor

• Papanicalou test:

  • Normal: reveals Doederlein bacilli (Lactobacilli)

  • BV: Reveals cells with stippled appearance along outer margin, Doerderlein bacilli will not be found in BV

What’s the standard treatment for BV?

Metronidazole or clindamycin