ENTEROBACTERIACIAE 2

Question 1

SHIGELLA

Answer 1

Closely related to E.coli both belonging to the family Escherichiae
However not a normal flora of the GIT but only found in stool of infected people, contaminated food or water or surfaces
Infection is called shigellosis

There are 4 known species and they all cause Bacillary Dysentery (S.flexneri, S.dysenteriae, S.boydii and S.sonnei

E.coli invades the GIT epithelial lining in a mechanism similar to EIEC

CULTURAL PROPERTIES OF SHIGELLA

It is a non motile , non flagellate, non capsulated Gram negative bacilli.
•It is both an aerobic and facultative anaerobe.
•The temperature range for its growth is 10-40⁰C but its optimal growth occurs at 37⁰C.
•Its growth is supported on blood, MacConkey, DCA, XLD and SS agar.
•MacConkey: it appear colorless because it is a non lactose fermenter. S.sonnei however is a late fermenter and will appear pink over a prolonged period

Question 2

SHIGELLA BIOCHEMICAL REACTIONS

Answer 2

Methyl red positive
Negative for Voges-proskauer, H2s production, citrate, urease and lysine decarboxylase
All catalase positive except S.dysenteriae
S.sonnei is a late lactose fermenter so appears pink on MacConkay and DCA on prolonged incubation

They possesses O antigen and certain strains have K antigen.
•They release endotoxin after autolysis which causes an irritating effect on the wall of the intestine.
•S dysenteriae 1 produces a potent (endotoxin) verocytotoxin (shiga like toxin). This is similar to EHEC.
•In addition, S dysenteriae 1 produces an exotoxin which is neurotoxic.

Question 3

SHIGELLOSIS PATHOGENESIS

Answer 3

Infective dose is 10-100 organisms, humans are the only natural host and become infected on the consumption of contaminated food or water
Surfaces could also get contaminated by carriers and also lead to infection
Flies too carry it on their feet and contaminate food or water

Hallmark of Shigella infection is Invasion, Intracellular Replication and Toxin Production. They invade the large bowel with various levels of inflammation and capillary thrombosis

The organism continues to multiply within the epithelial cell and cause cell death due to the toxicity of the endotoxin and ulcers are also formed

When Enterotoxin is produced it leads to diarrhea like E.coli and Neurotoxin would cause severe neuro symptoms such as coma and meningismus

Symptoms commence as early as 12 hours after ingestion

Question 4

SHIGELLOSIS SYMPTOMS AND DIAGNOSIS

Answer 4

Typically; Abd pain, Vomitting, fever, tenesmus, mucus in stool, bloody diarrhea

Severe symptoms; Prostration, Convulsions and HUS

DIAGNOSIS

History
Physical examination
Sample: Fresh Stool
Microscopy, Culture, EIA and PCR

Question 5

SHIGELLOSIS TREATMENT

Answer 5

Oral rehydration to replace fluid loss

Antibiotics

• Beta lactams- ampicillin amoxicillin and 3rd gen cephalosporins
• Quinolones- ciprofloxacin, ofloxacin
• Macrolides- Azithromycin

APPROPRIATE INFECTION CONTROL METHODS SHOULD BE PUT IN PLACE TO PREVENT THE SPREAD OF THE ORGANISM

Question 6

SALMONELLA

Answer 6

Ubiquitous, 2 species (S.enterica and S.bongori)

STRUCTURAL PROPERTIES
O antigens (heat stable)
H antigen (heat labile)
Vi antigen is a superficial antigen overlying the O antigen
K capsule conceals the bacteria and helps it from escaping the host self defense mechanism

Motile, flagellated, non lactose fermenting, facultative anaerobe gram neg bacilli
They’re not normal GIT flora but Commensals in Domesticated animals
Growth supported on blood
Growth on MacConkay DCA SS and XLD
Produces black precipitate hence H2S producing

Question 7

SALMONELLA BIOCHEMICAL PROPERTIES

Answer 7

Produce acid/gas from glucose, lactose and sucrose agar.
•Indole Negative
•Methyl red positive
•Voges –proskauer Negative
•Urease negative
•Citrate positive
•H₂S production positive
•Paratyphi A do not produce H₂S

Question 8

SALMONELLA CLINICAL SYNDROMES

Answer 8

Gastroenteritis (tyhimurium and enteritidis)
Enteric fever (S.typhi and S.paratyphy)
Septicemia (typhi, paratyphi, dublin)
Asymptomatic carrier
Focal infection e.g osteomyelitis, arthritis, endocarditis

Question 9

SALMONELLA GASTROENTERITIS

Answer 9

Most common form of salmonellosis
Ingestion of contaminated food or water
Symptoms begin 6-48 hrs after ingestion

Symptoms include; Nausea, Vomitting, Diarrhea, Fever, abdominal pain, myalgia and headache

Majority have spontaneous resolution of symptoms within 2-7 days
Treatment indicated in immunosuppressed

Antibiotics Trimethoprim, ampicillin, ciprofloxacin or chloramphenicol

Prevention includes proper handling of poultry and eggs

Question 10

SALMONELLA ENTERIC FEVER

Answer 10

PATHOPHYSIOLOGY

Typhoid and Paratyphoid fevers are caused by S typhi and paratyphi.

• The organism is acquired after ingesting contaminated food or water.
• The Infective dose is 10⁵CFU.

•The ingested Salmonellae reach the Small intestine, from which they enter the lymphatics(1st week) and then the Blood Stream(2ND Week).

They’re carried by the blood to many organs including the intestine. The organism multiplies in the intestinal lymphoid tissue and are excreted in stool in the 3RD WEEK.

CLINICAL FEATURES
Stepladder fever
Malaise
Headache
Myalgia
Abd pain
Diarrhea
Organomegaly 

TREATMENT
First line of drugs are Ciprofloxacin, Ampicillin, Chloramphenicol and Cotrimoxazole

IV Ceftriaxone and Cefixime in severe cases and resistance

Question 11

ASYMPTOMATIC CARRIER

Answer 11

These categories of people fail to fully clear the organism within one year of recovery and instead progress to a state of a chronic carrier.
•They usually don’t have symptoms but they are of public health importance because of the risk of transmitting disease to others.(especially if they are food handlers)
•Four weeks of eradication therapy with fluoroquinolone is indicated in them

Cholecystectomy may be required too

Question 12

SALMONELLA DIAGNOSIS

Answer 12

Clinical and Laboratory

Clinical: Rose spots, Hepatosplenomegaly and Faget’s sign(fever and bradycardia)

Laboratory:
Culture; Ss agar, DCA, XLA, MacConkey agar
1st week Blood culture positive
>/= 3rd week Stool culture positive 
Serology(widal)
ELISA and Dipstick test

Question 13

SALMONELLA PREVENTION

Answer 13

2 vaccines available

Live Vaccine— Oral Ty2I

Attenuated Vaccine— Vi polysaccharide parenteral

Question 14

PROTEUS STRUCTURAL PROPERTIES

Answer 14

A member of the Enterobacteriaceae family.
•A peritrichious flagellated motile, non lactose fermenting Gram negative bacilli

• They grow on ordinary media eg CLED, MacConkey, chocolate and blood agar.
• They appear in successive waves of concentric circles on blood and chocolate ( swarming) because it lacks bile salt. (P mirabilis andP vulgaris possess the ability to swarm).

They emit Fishy odor

Common species : P.mirabilis, P.vulgaris, P.penneri, P.myxofaciens

Question 15

PROTEUS BIOCHEMICAL PROPERTIES & VIRULENCE PROPERTIES

Answer 15

Most strains are indole negative.
•They produce acid from glucose
•Urease positive
•Oxidase negative
•Methyl red positive.
•Voges –proskauer negative except P mirabilis
•Produces a diennes phenomenon ( a line of inhibited growth where two strains meet)

VIRULENCE PROPERTIES

Urease production that splits urea to ammonium.

• Fimbriae for attachment to uro-epithelium
• Flagella
• Hemolysin.

Question 16

PROTEUS CLINICAL SYNDROME & TREATMENT

Answer 16

P.mirabilis causes UTIs

P.vulgaris important nosocomial pathogen commonly isolated in patients on prolonged antibiotics regimen

Bacteremia

Pneumonia

Wound infections

Bed sores

Osteomyelitis

TREATMENT
Proteus is inherently resistant to Nitrofurantoin and Tetracyclines
P.vulgaris the more resitant one

AMIKACIN, QUINOLONES AND CARBAPENEMS ONLY OPTIONS

Question 17

SERRATIA CULTURAL AND BIOCHEMICAL PROPERTIES

Answer 17

Serratia belong to the family Klebsielleae.
•They are non lactose fermenting, facultative anaerobic gram Negative bacilli.
•The organism itself grows best at 30-37⁰
•Pigment production is best at room temperature(15-20⁰C) and only about 10% produces red pigment called prodigiosin
•The known species are S liquefaciens, S rubidaea S odorifera and S marcescens

S.marcescens is the main specie causing human disease

BIOCHEMICAL PROPERTIES

H₂S production negative
•Voges –proskauer Positive
•Citrate positive

•Production of DNSase which differentiate it from other Enterobacteriaceae.

Question 18

SERRATIA CLINICAL SYNDROMES & TREATMENT

Answer 18

They are opportunistic pathogens in hospital settings causing diseases in patients on urinary catheters and IV catheters.
•Septic arthritis
•Contaminated IV Therapy.
•Respiratory tract infections
•UTIs
•Skin and wound infections
•Endocarditis
.Osteomyelitis

Amikacin
Piperacillin- Tazobactam
Carbapenems

Question 19

YERSINIA CULTURAL AND BIOCHEMICAL PROPERTIES & VIRULENCE

Answer 19

Yersinia belong to the family Yersinieae.
•It is a Non sporing, non motile and non acid fast, Gram negative coccobacilli or rods that occurs singly or in pairs.

• A methylene blue staining will show the characteristic bipolar appearance called safety pin.
• Its growth is supported on Nutrient, Blood and MacConkey agar.
• Old cultures are pleomorphic and may resemble yeast cells.

There are more than eleven species but only three have been associated with human infections
Y pestis, Y enterolitica and Y pseudotuberculosis.

Y.pestis causes plague and there are 3 types(bubonic, septicaemic, pneumonic)

BIOCHEMICAL PROPERTIES

Catalase positive
•Indole negative
•Methyl red  positive
•Nitrate positive
•Urease negative
•Voges –proskauer negative
•Citrate negative.

VIRULENCE PROPERTIES

V antigen (anti-phagocytic property)
•W antigen(anti-phagocytic property)
•LPS endotoxin
•Yersiniabactin (ability to absorb iron)
•Coagulase
•fibrinolysin

Question 20

YERSINIA PESTIS PATHOGENESIS

Answer 20

The natural reservoirs include rats, squirrels, rabbits, and domestic animals

•A zoonotic infection with humans as the accidental host

• The disease is spread by
• flea bites
• direct contact with infected tissues
• person to person by inhalation of infectious aerosols from a patient with pulmonary disease
• Infection is transmitted from one animal to another by flea.
• Man is infected by bite from an infected flea.
• Lymph node draining site of bite becomes infected after 2-5days

The pathogens reach the lymphatics and an intense hemorrhagic inflammation develops in the enlarged lymph nodes
•The lymphatics may become enlarged , tender (buboes) in the neck, groin, or axillae ( bubonic Plaque) or undergo necrosis.

•Y pestis organisms often reach the bloodstream and become widely disseminated. (septicaemic Plaque)

Hemorrhagic and necrotic lesions may develop in all organs meningitis, pneumonia, and pleuro-pericarditis are prominent features.

• PNEUMONIC PLAGUE results from inhalation of infective droplets and it is characterized by hemorrhagic consolidation, sepsis, and death.
• The ability of this organism to be transmitted by aerosol and the severity and high mortality of pneumonic plague makes Y.pestis a potential biological weapon

Question 21

YERSINIA ENTEROLITICA AND YERSINIA PSEUDOTUBERCULOSIS

Answer 21

Y. enterocolitica has bull’s eye appearance with a red center.

The organism spread through exposure to contaminated food products (Y. enterocolitica)

The usual symptoms are bloody diarhoea, abdominal pain, malaise and prostration

Most Gastroenteritis symptoms resolve without antibiotics
Drug of Choice— combination of Doxycycline and Aminoglycosides

YERSINIA PSEUDOTUBERCULOSIS

Yersinia pseudotuberculosis mimics a TB-like disease in animals.
•Man acquire infection through skin contact with contaminated water or through consumption of vegetables.
•Infected Patients presents with a fatal typhoid-like illness with fever, purpura, mesenteric adenitis +/- erythema nodosum and hepato-splenomegaly.

Yersinia pseudotuberculosis: Treatment

• Ciprofloxacin
• Tetracyclines
• Aminoglycosides
• Sulfonamides
• Penicillin