2 Main species

GENERAL PROPERTIES

- Gram ____, facultative anaerobic intracellular organism that vary in length

GENERAL PROPERTIES

- Motile with ______ flagella

GENERAL PROPERTIES

- Grow readily on simple media and ________ to ferment

lactose or sucrose on MacConkey Agar

GENERAL PROPERTIES

- Unlike Shigella, it is _______ to form acid and gas from glucose or mannose.

PATHOGENICITY & VIRULENCE FACTORS

After ingestion and passage through the stomach, salmonellae attach to the mucosa of the _____ intestine

PATHOGENICITY & VIRULENCE FACTORS

Encodes Salmonella-secreted invasion proteins

PATHOGENICITY & VIRULENCE FACTORS

Contains genes that allow the bacteria to evade the host’s immune response

VIRULENCE FACTORS

- May be responsible for fever

- More than 2500 O serotypes have been identified

VIRULENCE FACTORS

Mediate adherence to and penetration of intestinal

epithelium and sub-epithelium

VIRULENCE FACTORS

- Small cationic proteins

- Facilitate bacterial penetration

VIRULENCE FACTORS

- Catalase

- Superoxide dismutase

VIRULENCE FACTORS

- Flagellar strain of S.typhi

- With peritrichous flagella

VIRULENCE FACTORS

- Special capsular polysaccharide of S. typhi

- With antiphagocytic properties

MICROBIAL DEFENSES AGAINST IMMUNE CLEARANCE

- Mechanism enabling invading microbe to resist being engulfed, ingested, and/or lysed by phagocytes/ phagolysosomes

- Able to survive in macrophages and spread from intestine to other body sites

- Tolerant to acids in phagocytic vesicles

MICROBIAL DEFENSES AGAINST IMMUNE CLEARANCE

Resistance: to avoid antibodies (humoral)

MICROBIAL DEFENSES AGAINST IMMUNE CLEARANCE

Resistance: evade destruction by phagocytosis (cell-mediated)

CLINICAL MANIFESATIONS

- Incubation period: 7-20 days

- Onset: Insidious

- Fever: Gradual; then high plateau with “typhoidal” state

- Duration: Several weeks

CLINICAL MANIFESTATIONS

- Incubation period: Variable

- Onset: Abrupt

- Fever: Rapid rise; then spiking “septic” temperature

- Duration: Variable

CLINICAL MANIFESTATIONS

- Incubation period: 8-48

- Onset: Abrupt

- Fever: Usually low

- Duration: 2-5 days

CLINICAL MANIFESTATIONS

- GI symptoms: (Early) constipation; (Later) bloody diarrhea

- Blood culture: (+) in 1st-2nd weeks

- Stool culture: (+) from 2nd week onwards; (–) at earlier

stages

CLINICAL MANIFESTATIONS

- GI symptoms: Often none

- Blood culture: (+) during high fever

- Stool culture: Infrequently (+)

CLINICAL MANIFESTATIONS

- GI symptoms: Nausea, vomiting, diarrhea at onset

- Blood culture: (-)

- Stool culture: (+) soon after onset

CLINICAL MANFESTATIONS

- Most common form of salmonellosis with major foodborne outbreaks and sporadic disease

- Most commonly caused by S. typhimurium and S. enteritidis

- Can also be caused by any of >1400 Group I serotypes of salmonellae

- Sources of infection: poultry, eggs, etc.

CLINICAL MANFESTATIONS

- Initially, few leukocytes can be seen in the stool

- Inflammatory lesions of the small and large intestines are present

- Bacteremia is rare except in immunodeficient individuals

- Stool cultures are positive for salmonellae and may remain positive for several weeks after recovery

CLINICAL MANIFESTATIONS

- Caused by a few of the salmonellae and S. typhi is the most important

- S. paratyphi A, B (S. schottmuelleri) & C (S. hirschfeldii) also causes milder form

- Mode of Transmission: fecal-oral

-- Person-to-person spread by chronic carrier

-- Fecally-contaminated food or water

CLINICAL MANIFESTATIONS

- Ingested salmonellae reach the small intestine and pass through the intestinal epithelial cells in ileocecal region

- Enter into the regional lymphatic system, invade the

bloodstream, and infect other organs and parts of the

reticuloendothelial system

- Multiply in intestinal lymphoid tissue and are excreted in stools

CLINICAL MANIFESTATIONS

- After an incubation period of 10-14 days, fever, malaise, headache, constipation, bradycardia, and myalgia

occur

- Fever raises to a high plateau, the spleen and liver

become enlarged

- 2nd week: organisms re-enter bloodstream and cause

prolonged bacteremia; biliary tree and other organs are

infected; gradually increasing sustained fever likely from

endotoxemia

- Rose spots on the skin of the abdomen or chest are

briefly seen in rare cases

CLINICAL MANIFESTATIONS

- 2nd to 3rd week: bacteria colonize gall bladder, re-infect intestinal tract with diarrheal symptoms and possible necrosis of Peyer’s patches

§ In pre-antibiotic era, chief complaint of enteric fever were

intestinal hemorrhage and perforation

- Mortality rate was 10-15%

- Principal lesions are hyperplasia and necrosis of

lymphoid tissue

CLINICAL MANIFESTATIONS

- Can be caused by all species, but more commonly associated with S. cholerasuis, S. paratyphi, S. typhi, & S. dublin

- Old, young and immunocompromised (ex. AIDS patients) at increased risk

- After oral infection, there is early invasion of bloodstream with possible focal lesions in the lungs, bones, meninges

CLINICAL MANIFESTATIONS

- Complications:

-- Meningitis

-- Septic arthritis

-- Osteomyelitis

- Endovascular infections usually involve the aorta (associated with atherosclerotic plaques or aneurysms)

CLINICAL MANIFESTATIONS

Risk of death and complications are higher in adults and

patients with underlying conditions.

CLINICAL MANIFESTATIONS

- Gallbladder is the usual reservoir organ

- Occurs in <1% of cases and does not play a role in human disease transmission

EPIDEMIOLOGY

Mode of transmission

Survivors can become permanent carriers

EPIDEMIOLOGY

Sources of infection

LAB DIAGNOSIS

Culture w/ the highest sensitivity (80-95%)

LAB DIAGNOSIS

- Blood cultures: 80% (+)

- Stool culture: 25% (+)

LAB DIAGNOSIS

Bone marrow aspirate, stool, or urine (+)

LAB DIAGNOSIS

- Stool: 85% (+)

- Blood: 25% (+)

DIFFERENTIAL MEDIUM CULTURE

- Rapid detection of lactose non-fermenters

- Also Shigellae, Proteus, Pseudomonas, etc.

DIFFERENTIAL MEDIUM CULTURE

- Rapid detection of salmonellae

- Forms black colonies because of H2S production

CULTURE

- Salmonella-Shigella (SS) agar, Hektoen enteric (HE) agar, Xylose-Lysine Deoxycholate (XLD) agar, or Deoxycholate-Citrate agar

- All favor growth of salmonellae and shigella over other enterics

CULTURE

- Selenite F or tetrathione broth

- Inhibit replication of normal intestinal bacteria and permit multiplication of salmonellae

SEROLOGY

- No longer available

- 4-fold increase in titer during 2nd-3rd week of S. typhi infection

- Detects antibodies against O and H antigens

- 2 serum specimens obtained at intervals of 7-10 days

SEROLOGY

- Antibodies for S. typhi

- Can cross-react with other organisms = results should correlate with symptoms

- (+) IgM = acute infection

- (+) IgG = recent infection or with vaccination

Serological tests for Salmonella infection can

be relied upon to establish a definitive diagnosis of typhoid fever.

BIOCHEMICAL TEST

(_) H2S, (_) gas

BIOCHEMICAL TEST

IMViC ( _ / _ / _ / _ )

- Indolate (_)

- Methyl Red (_)

- Voges Proskauer (_)

- Citrate (_) (except for S. typhi and S. paratyphi A)

BIOCHEMICAL TEST

Lactate (_), Malonate (_)

BIOCHEMICAL TEST

Glucose (_), Mannose (_)

BIOCHEMICAL TEST

Lactose (_), Sucrose (_)

BIOCHEMICAL TEST

O-Nitrophenyl-β-D-Galactopyranoside (ONPG) (_)

LAB DIAGNOSIS

- Direct detection of salmonellae in fecal samples of patients with acute diarrhea

TREATMENT

Except in young, old, and immunocompromised, antibiotic treatment is not recommended for enteritis because this may prolong the duration of the disease.

TREATMENT

- Drug of choice for typhoid fever

- 14 days of treatment

- Cheapest; very absorbable in oral than IV

- Side effect: reversible aplastic anemia

TREATMENT

Alternatives for typhoid fever

TREATMENT

For chronic carriers