Bacteriology - Neisseria and Enterobacterals

Neisseria?

Gram-negative, kidney shaped bacterium

- Arranged in pairs: diplococcus

- Their LPS is short, referred to LOS (lipo-oligosaccharide)

- Is highly adapted to the human host, and quickly dies outside the body.

Only direct transmission is possible, as it does not survive on many surfaces.

- Impossible to have a zoonotic infection (animal)

What are neisseria positive for?

Oxidase positive

What agar is impossible for Neisseria to grow on?

Unable to grow on blood agar

- It is inhibited by some of the lipids on blood agar

If you heat up blood agar (Chocolate Agar), neisseria can grow there

- Also can grow on VPN agar (agar enriched w/ Vancomycin, polymyxin ans nystatin)

Who have high susceptibility for neisseria infection?

Patients with complement system deficiencies

- Unable to form MAC-complex

Virulence factors of neisseria?

Pilus of neisseria

- Allows for attachment to epithelial cells

- Antigenic variation -> difficult for immune system to target it

IgA protease

- Facilitates survival along mucosal surfaces

Neisseria Meningitidis?

Covered by polysaccharide capsule - major virulence factor

- Separates it from N. gonorrhea (non-capsulated)

Can ferment both glucose and maltose

- Only N. meningitidis can ferment maltose

Who are at higher risk for Neisseria Meningitidis infection?

- Sickle cell disease patients

- Splenectomy patients

(Spleen is important for removal of encapsulated organisms)

Transmission of Neisseria Meningitidis?

Spread among people who are tightly gathered

- RESPIRATORY DROPLETS

Pathogenesis of Neisseria Meningitidis?

First colonize in nasopharynx

- With opacity (Opa and Opc proteins) it can eventually reach the circulation

- LOS are released -> inflammatory response

- Cytokine storm occurs

- Can lead to septic shock

Bacteria can cross BBB - cause meningitis

- Based on pro-inflammatory cytokine production of the meningeal cells

BLOOD CULTURE must be performed

Clinical presentation - Neisseria Meningitidis?

- Rash/petechias

- Fulminant fever

- DIC

- Waterhouse-Friderichsen syndrome

- Children < 2 - bulging fontanelles (increased ICP)

Physical examination of meningitis?

Pain is felt in any exercise when the spine is forcefully extended

Diagnosis - Neisseria Meningitidis?

Lumbar puncture

- Draw CSF

- High protein and low glucose level CSF

Blood should ALWAYS be taken

How many are carriers of Neisseria Meningitidis?

10% of population

(nasopharyngeal swab)

Prevention - Neisseria Meningitidis?

Vaccine

- Polysaccharide vaccine

- A, C and D strains

- Does not contain B strain

Treatment - Neisseria Meningitidis?

3rd generation cephalosporin - ceftriaxone

IV/IM

Cefotaxime can be administered - neonates/children

IV/IM

In case of ß-lactamase producing strain, dexamethasone can be considered

Chemoprophylaxis Neisseria Meningitidis?

In case you have been in close contact with someone who just got diagnosed w/ meningitis

= Rifampicin can be given

Neisseria Gonorrhea?

Non-capsulated gram-negative bacterium

- Sexually transmitted disease

- 2nd most common STD

- Oral and anal sex have high transmission rate

Pathogenesis - Neisseria Gonorrhea?

- Attach to cells via Fimbriae/pili and Opa proteins

= Forms biofilm

- The pili is antigenically highly variable - aka NO vaccine

- Membrane vesicles are released containing LOS - strong inflammatory reaction

- Bacteria consumes iron

- Has IgA protease

Clinical manfestation - Neisseria Gonorrhea?

Man:

- Urethritis

- Prostatitis

Female:

- Cervicitis

- Pelvic inflammatory disease

= Infertility can occur - scarring etc.

White, purulent discharge is seen in both men and women

Fitz-Hugh-Curtis syndrome?

Complication of Neisseria Gonorrhea infection

- Spreads to peritoneum

Neisseria Gonorrhea - septic arthritis?

Is (together w/ S.aureus) most common causes of this in adults

Congenital infection - Neisseria Gonorrhea?

Mother who is infected can pass it on during delivery

- Early onset of purulent conjunctivitis

Diagnosis Neisseria Gonorrhea?

- Cotton swabs with plastic sticks

- Special media is required

- Special transport media is used

Treatment Neisseria Gonorrhea?

3rd gen.cephalosporins:

ceftriaxone

Often co-infected w/ chlamydia -> give macrolide such as doxycycline

Escherichia coli?

Gram-negative, rod-shaped bacteria

- Always present in stool and GI

- Standard member of gut flora

- Its pathogenic potential varies of a broad scale

Capsule Escherichia coli?

It is encapsulated

- K-antigen is present on the capsule

Antigen is used to diff bw different serotypes of the bacteria

What media to grow Escherichia coli?

EMB agar

What is E.coli positive for?

Catalase

Characteristic for E.coli?

Long fimbriae (pili)

- Makes it possible to cause UTIs

Common clinical features E.coli?

UTI:

- Accounts for 80%

- ascending infection from gut bacteria

- Damages urothelium

- Urine sample: shed cells, RBCs, WBCs

- Is they have lost their virulence factor -> asymptomatic bacteriuria

Sepsis:

- Responsible for most cases of sepsis that is caused by Gr- bacterias

- LPS endotoxin is main virulence factor for sepsis (not only specific for E.coli)

Neonatal meningitis:

- Initiated by K antigen on the capsule

Different pathotypes of E.coli?

- Eneterohemorrhagic E.coli

- Enterotoxigenic E.voli

Enterohemorrhagic E. coli (EHEC)?

Undercooked meat

- Bloody diarrhea (dysentery)

- Does not ferment sorbitol

- Produces toxin (Shiga) - inhibits ribisome 60s

- Can cause hemolytic uremic syndrome - thrombus in GN -> how urine becomes bloody

Enterotoxigenic E. coli (ETEC)?

Via water sources

- "Traveler's watery diarrhea" - Mexico

- Virulence factors: Heat labile toxin & heat stabile toxins

Treatment E.coli?

Antibiotics are NOT recommended

If the bacteria lyse, more toxins are released

Plasmaphereses is used to get rid of toxin

Shigella?

Gram-negative, rod-shaped bacteria

- Causes gastroenteritis leading to bloody diarrhea

Are genetically very close to E.coli

Culture of Shigella?

On special agar

"Hektoin agar"

- Yields green colonies

(Salmonella would grow black colonies)

Important features of Shigella?

- Immotile

- Acid stable (requires less microorganisms to cause infection)

What type of bacteria is Shigella if it can survive both on its own and inside of another cell?

- Facultative intracellular bacterium

(Salmonella is also this)

How is the bloody diarrhea in Shigella infection?

There is fecal blood and leukocytes in stool

- Only present with occult blood, and not the massive amount found in diarrhea by EHEC

If a child is infected with Shigella dysenteriae?

Chance of infection can precipitate hemolytic uremic syndrome (HUS)

- Shiga toxin inhibits protein synthesis by interfering with 60s subunit of the ribosome

Klebsiella pneumoniae?

Gram-negative, rod-shaped, immotile bacteria

- NOSOCOMIAL INFECTIONS

Ferment lactose: is Lactose positive

- MacConkey agar: colonies turn dark pink

- Urease positive -> increase risk of struvite stones

Virulence factor - Klebsiella pneumoniae?

Polysaccharide capsule

Others:

- Siderophores

What bacterias are the only able to ferment lactose?

- E.coli

- Klebsiella pneumoniae

What is a classical type of Klebsiella pneumoniae?

Infection is often seen in:

- Alcoholics

- Patients w/ underlying diseases (COPD, DM)

What can the hypervirulent form of Klebsiella pneumoniae cause?

- Pyogenic liver abscess

- Aspiration lung abscess

Clinical features Klebsiella pneumoniae?

Hospital acquired pneumonia:

- Currant jelly-like sputum

- Mimics TB on x-ray

UTI

String test?

Klebsiella pneumoniae

- Is very mucoid

- String of mucus adhere to the loop from the agar

Treatment Klebsiella pneumoniae?

Show increasing resistance

- Carbapenems are usually chosen

- Imipenem

- Meropenem

Proteus mirabilis?

Gram-negative, rod-shaped bacteria

- Facultative anaerob (grow in both absence or presence of O2)

- Its high motility is a virulence factor

- Fishy odor

Clinical syndromes - Proteus mirabilis?

UTI

Kidney stones

- Struvite stones (due to urease increasing pH by ammonium)

Prostatitis

- Recurrent infections in older male

Treatment of proteus mirabilis?

Carbapenem like fosfomycin

- Have high AB resistance

Salmonella?

Gram-negative, rod-shaped bacteria

Subtypes of salmonella:

- Salmonella enteritidis

- Salmonella typhi

Characteristics of salmonella?

Encapsulated

- inhibits complement system

Facultative anaerob

Flagellum - induces motility

Fimbriae - adherence

H2S-positive - results in black spots when grown on Hektoen agar

Acid-labile -> are easily degradable in stomach - aka needs HIGH dose to cause infection (high ID)

Siderophores - iron transport

Who is at higher risk of salmonella infection?

- Pernicious anemia

- Diseases that lower stomach acidity

As salmonella is acid-labile, making them more prone to grow an hypochlorhydric conditions

Clinical syndromes - Salmonella?

Enteritis/acute gastroenteritis

- By s.Enteritidis

- Eating undercooked chicken

- Zoonotic disease

- Nausea, vomit and non-bloody diarrhea

Enteric fever: (typhoid fever)

- ONLY by S.typhi

- 10-14 days incubation

- Fever and delirium

Septicemia:

- Due to release of endotoxins

- immunocompromised patients

Asymptomatic carriage - salmonella?

Chronic carriage state is seen in 1-5% of cases following S.typhi infection

- Reservoir: gallbladder

As it is resistant to bile

Treatment: removal of gallbladder

Diagnosis - salmonella?

Blood and urine sample for enteric fever

Stool and food sample in enteritis

Treatment - salmonella?

Enteritis:

- Not recommended w/ AB, only in high-risk patients (Cephalosporins)

Enteric fever:

- AB should be given to prevent carrier state

- Macrolides: children

- Ciproloxacin, ceftriaxone in adults

Vaccine against salmonella?

Live, attenuated vaccine against s.typhi

Yersinia?

Gram negative rod

- 12 different species

- Y.pestis

- Y. enterocolitca

Spread from animals -> zoonotic infection

- Is facultative anaerob

- Encapsulated

Y. enterocolitica?

Spread:

- Dog feces

- Contaminated milk products

- Affect children mostly

- Resistant to cold

- Safety-pin appearance

What does Y. enterocolitica cause?

Enterocolitis w/ bloody diarrhea

- Systemic infection

- Ileus

- Pseudo-appendicitis

Yersinia pestis?

Black death

- Main reservoir is rodent, but it is the FLEAS of the rodent that SPREAD THE DISEASE

- Buboes grow on skin

- Gets into circulation: DIC, cutaneous hemorrhage and necrosis of fingers

Virulence factor Y.pestis?

- Endotoxin

- Exotoxins

- Yersinia associated outer proteins

Prevention - Y. pestis?

- Disinfection

- Inactivated vaccine

Treatment of Yersinia?

Streptomycin

Tetracyclin

Y. pestis:

- Fluorquinolones