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Microbiology MBBS > Bloodstream: Enteric fever, AIDS > Flashcards

Bloodstream: Enteric fever, AIDS Flashcards

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1
Q

Clinical classification of salmonella

A
  1. Typhoidal salmonella
  2. Non-typhoidal salmonella:
    They primarily infect other animals though they can cause food borne gastroenteritis and septicaemia
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2
Q

Kauffman White scene or antigenic classification of salmonella

A

Based on O antigen, salmonella are classified into serogroups: 1,2,3,…,67
Each serogroup is further differentiated into serotypes

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3
Q

Non motile species of salmonella

A

S. gallinarum pullorum

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4
Q

Capsulated species of salmonella

A

S. typhi
S. paratyphi C
S. dublin

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5
Q

Species of salmonella

A
  1. S. enterica
    6 subspecies (enterica, indica, arizonae)
    >3000 serotypes (according to Kaufmann and White scheme using the O,H and Vi antigens)
  2. S. bongori
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6
Q

Serotype of Salmonella typhi

A

S. enterica enterica Typhi
9,12 (Vi) : d
9,12 are O antigens
Flagellar antigen is of d type

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7
Q

Serotype of salmonella paratyphi A

A

S. enterica enterica Para A

1, 2, 12 : a

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8
Q

Serotype of salmonella paratyphi B

A

Salmonella enterica enterica Para B
1, 4, 5, 12 : b; 1, 2
Is flagellar antigen shows phase variations or antigenic variations

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9
Q

Biochemical features of salmonella

A 
All are aerogenic except S. typhi
All are non lactose fermenting
All are H2S positive except:
 • Para A
 • Typhisuis
 • Cholesuis 
IMViC -+-+ (except S typhi -+- -)
Urease -ve
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10
Q

Conventional biochemical tests for salmonella

A
  1. Catalase positive and oxidase negative
  2. Indole, citrate and urease test negative
  3. TSI shows:
    • gas present except for S. typhi
    • abundant H2S present except for:
    S. paratyphi A - not produced
    S. typhi - speck of H2S present
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11
Q

Cultivation of salmonella

A 
On MacConkey medium: NLF colonies
Transport medium: Cary Blair 
Enrichment  media:
1. Selenite F broth
2. Gram negative broth
3. Tatrathionate broth
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12
Q

Salmonella on blood culture

Colony appearance

A

Blood agar: non haemolytic moist colonies

MacConkey agar: round, translucent pale colonies and non-lactose fermenting

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13
Q

Selective media for salmonella

A 
Low selective media: MacConkey agar
Highly selective media:
1. DCA:
 Non lactose fermenting pale colonies with black centre
2. XLD agar:
 Red colonies with black centre 
3. Wilson Blair’s medium:
 Isolation of S. typhi from highly contaminated specimens
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14
Q

Features of H antigen of salmonella

A 
Flagella antigen
Protein, so highly antigenic
Heat and alcohol labile
Shows variations
H antibodies:
 Appear earliest after infection and persist for several months
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15
Q

Features of O antigen of salmonella

A 
Somatic antigen
Polysaccharide, so lower antigenicity
Heat and alcohol stable
O antibodies:
 Follow appearance of H antibodies and disappears in a few weeks
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16
Q

Antibodies in case of remote, recent and active infection of salmonella

A

In cases of recent or remote infections:
H antibodies- significant titre, but not
O antibodies
In cases of recent infection or active disease:
Both H and O antibodies are significant

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17
Q

Features of Vi antigen of salmonella

A

Capsular antigen
Polysaccharide so least antigenic
Heat labile but alcohol stable
Present only in casulated species and some E. coli and some citrobacter
Covers O antigen and prevents agglutination with O antibody (so boil the suspension to selectively destroy the Vi antigen)

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18
Q

Features of Vi Antibody against salmonella

A

Spare for a short time during convalescence
Absence indicates poor prognosis
Persistence indicates carrier state

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19
Q

Infections caused by salmonella

A 
1. Enteric fever/ typhoid:
 •Typhi - M/C in India
 •Para A - 2nd M/C in India
 •   “    B
 •   “    C
2. Invasive enteritis out for poisoning:
 •Zoonosis 
 •All other serotypes - non typhoidal salmonella (GI commensal/ pathogen of reptile, birds, mammals other than man)
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20
Q

Typhoid or enteric fever

A 
Strictly human disease
•Incubation P: 1-2 weeks 
•Infective dose ID50: 10^3 - 10^6 bacilli
•Progresses over 3-4 weeks
•Resolves for many, if untreated
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21
Q

Risk factors for typhoidal salmonella transmission

A 
1. Stomach acidity:
• <1 year of age
• antacid consumption
• previous Helicobactor pylori infection
2. Intestinal integrity affected:
• inflammatory bowel disease
• prior GIT surgery
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22
Q

Pathogenesis of enteric fever

A
  1. Entry through epithelial cells, M cells:
    Trigger formation of membrane ruffles.
    BME- bacteria mediated endocytosis (via specialised type III secretion system and ruffles) into vacuoles
  2. Entry into macrophages
  3. Survival inside macrophages
  4. Primary bacteremia:
    Macrophages reach lymphatics
  5. Spread to RES, gall bladder, kidneys,…
  6. Secondary bacteremia
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23
Q

Clinical manifestations of enteric fever

A
  1. Step ladder pyrexia
  2. Malaise and anorexia
  3. Vomiting 🤮
  4. Faget sign: fever with bradycardia
  5. Rose spots
  6. Hepatosplenomegaly
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24
Q

Complications of enteric fever

A
  1. Intestinal haemorrhage- M/C
  2. Intestinal perforation- 2nd M/C
    The above 2 occurs mostly in 3rd week
  3. Meningitis, deafness, psychosis
  4. Arthritis, periostitis
  5. Nephritis, cholecystitis
  6. Visceral abscesses
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25
Q

Diagnosis of enteric fever

A 
First week of illness:
• blood culture
• bone marrow
• duodenal aspirate culture
Second/third week of illness:
 Serum specimen for serology like Widal test
Third/fourth week of illness:
 Urine and stool culture
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26
Q

Blood specimen for salmonella diagnosis

A
  1. 5-10 ml sterile blood in 50-100 ml of bile broth
  2. Subculture on MacConkey and blood agar for 10 days
    Preferred is 5-10 ml sterile blood
    Biphasic/Castaneda medium (BHI infusion with broth)
    Rate of positivity for each week:
  3. > 90%
  4. 75%
  5. 60%
  6. 25%
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27
Q

Stool and urine samples for salmonella infection

Positivity rates

A

Stool:
• selective medium used
• becomes positive at end of 2nd week in 40-50% of cases
Urine:
• becomes positive at end of 3rd week in 30-50% of cases
• salmonella are shed in urine infrequently

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28
Q

Bone marrow aspirate as sample for salmonella

A

Similar to blood culture, recommended for first week
Advantages:
1. Most sensitive at all stages
2. Remains positive for around 5 days after the start of treatment

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29
Q

Tests for Salmonella

A
  1. Widal test
  2. Typhidot
  3. Diazo test
  4. Antigen detection:
    (ELISA/ Latex agglutination/ co-agglutination)
  5. Probes/ nucleic acid amplification tests NAATs:
    (most specific but limited availability)
    NOTE: serology is considered neither sensitive nor specific
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30
Q

Widal test

A 
Tube agglutination test measuring titre of H and O antibodies of salmonella
H ab-ag reaction:
 Fluffy or woolly agglutination
 Done in Dreyer’s tube
O ab-ag reaction:
 Granular/chalky agglutination
 Felix tubes
31
Q

Inference of Widal test

A

Significant titre of:
O antibodies: >100
H antibodies: >200
Significant titre of O antibodies indicate recent infection
Significant titre of H antibodies indicates the serotype

32
Q

False positive for Widal test

A
  1. Anamnestic response: due to unrelated infections in persons who had prior enteric fever
  2. If bacterial antigen suspensions are not free from fimbriae
  3. Persons with inapparent infection
  4. Persons with prior vaccinations (TAB vaccine)
33
Q

False negative for Widal test

A
  1. Early stage - first week
  2. Later stage - after fourth week
  3. Carriers
  4. Patients on antibiotics
  5. Prozone phenomenon: antibody excess
    Avoided by serial dilution
34
Q

Diazo test

A

Biochemical test for salmonella
Defects a phenolic compound in urine
Good sensitivity and specificity only in 1st week

35
Q

Typhidot test

A

ELISA based method
Immuno-Chromatographic test for salmonella
IgM and IgG antibodies detected separately
But no quantification

36
Q

Treatment of salmonella

A 
Empirical:
• Ceftriaxone
• Azithromycin
Fully sensitive strains:
1. Ciprofloxacin
2. Amoxicillin 
3. Azithromycin
4. Cotrimoxazole 
5. Chloramphenicol
37
Q

Treatment of MDR strains of salmonella

A 
MDR strains:
 resistant to Amoxicillin, Cotrimoxazole and Chloramphenicol
Using:
1. Ciprofloxacin
2. Azithromycin 
3. Ceftriaxone (severe cases)
38
Q

Treatment of NARST

A 
Nalidixic acid resistant S. typhi
Also called fluoroquinolone resistant strains
Treatment:
1. Azithromycin
2. Ceftriaxone
39
Q

Types of carriers of salmonella based on duration

A
  1. Convalescent: upto 3 months
  2. Temporary: 3 months -1 year
  3. Chronic: >1 year
40
Q

Carriers of salmonella based on persistence

A 
1. Fecal carriers:
• more common
• site: gall bladder
• seen in patients with biliary tract abnormalities
2. Urinary carriers:
• site: kidney
• seen in: 
  Urinary tract abnormalities
  Schistosoma haematobium infections
41
Q

Is MALDI-TOF useful in identifying Salmonella

A

No
It can identify salmonella upto genus level
It poorly differentiates between serotypes as they share the same ribosomal proteins

42
Q

Vaccines for typhoid fever

A 
1. Vi antigen capsular polysaccharide Vi-CPS vaccine:
 Protection for 2 years
 Poorly immunogenic in children- T independent
2. Typhoral- oral liver attenuated
 Lasts for 4 years
3. Parenteral TAB vaccine:
 Heart killed whole cell vaccine
 Not used- significant side effects
43
Q

Drug resistance in Salmonella

A
  1. MDR S. typhi:
    Resistant to Chloramphenicol, ampicillin and cotrimoxazole
  2. Fluoroquinolone FQ resistance
  3. Resistance to ceftriaxone
44
Q

Diagnosis of carriers of salmonella

Treatment

A

Screening:
Vi agglutination test to detect Vi antibody
Confirmation: culture
specimens - stool or duodenal aspirate
Treatment: ampicillin/amoxicillin + probenecid

45
Q

Non-typhoidal salmonella NTS

A

Usually cause gastrointestinal manifestations
In a small proportion, may develop into bacteremia ➡️:
1. Endovascular infection
2. Seedling to various organs leading to metastatic symptoms

46
Q

Risk factors for bacteremia by non typhoidal salmonella are

A 
1. NTS serotype:
 S. choleraesuis of pig
 S. dublin of cattle
2. Age: infants and elderly
3. Immunity: Immunocompromised patients
4. People with pre existing heart conditions
47
Q

Genera in retroviridae that are pathogenic to humans

A
  1. Genus Lentivirus:
    Contains HIV-1 and 2
  2. Genus Deltaretrovirus
    Contains HTLV-1
48
Q

Parts of HIV

A 
1. Envelop
• liquid part- host cell membrane
• protein part:
  gp 120 knob-like spikes 
  gp 41 anchoring transmembrane predicles
2. Nucleocapsid:
 Capsid icosahedral
 Core contains 2 copies of ss RNA
 reverse transcriptase, integrase and protease
49
Q

Structural genes of HIV

A
  1. gag gene: matrix and core antigen
  2. pol gene: reverse transcriptase, protease and integrase
  3. env gene: gp 120 binding to CD4 and fusion protein gp 41
50
Q

Non-structural genes of HIV

A 
Essential regulatory:
 tat: transcriptional transactivator
 nef: negative factor
 rev 
Accessory regulatory:
 vif viral infectivity factor
 vpr 
 vpu
51
Q

HIV serotyping

A

Based on differences in env gene
1. HIV-1:
3 distinct groups: M (dominant worldwide), N, O
M comprises 11 subtypes or clades A to K (geographically different)
2. HIV-2:
8 subtypes A (common) to H mostly in Africa

52
Q

HIV

mode of transmission

A 
1. Sexual mode 75%:
• heterosexual M/C
• anal has higher risk
2. Blood transfusion 5% but highest risk
3. Percutaneous/ mucosal like needles, razors
4. Perinatal 20-40%
 can occur any time during pregnancy and breast feeding
 but maximum during delivery
53
Q

Viral load of HIV in secretions

A

Maximum in blood, genital secretions and CSF
Variable in breast milk and saliva
Zero or minimal in other secretions

54
Q

Host receptors involved in HIV entry

A
  1. Main receptor CD4 with gp 120:
    T cells, monocytes, macrophages, Langerhans cells, astrocytes,…
  2. Co-receptor binding to gp 120:
    Usually chemokine receptors like CXCR4 of T cells, CCR5 of macrophages
  3. DC-SIGN, of dendritic cells of mucosa and skin bind and facilitates transport to lymphoid organs
    But no entry into dendritic cells
55
Q

Stages of HIV replication

A
  1. Fusion to host cells by gp 41
  2. Penetration and uncoating
  3. Reverse transcription
  4. Transcription to form viral proteins
  5. Pre-integration complex
  6. Integration to form provirus
  7. Latency: infectious to other cells
56
Q

Pre-integration complex of HIV

A

Nucleoprotein complex transported into nucleus before integration containing:

  1. Linear ds DNA
  2. gag matrix protein
  3. Accessory vpr protein
  4. Viral integrase
57
Q

Stages of HIV progression

Typical or natural course

A
  1. Acute HIV disease/ acute retroviral syndrome:
    •Primary viremia with flu-like illness
  2. Clinical latency/ asymptomatic stage:
    CMI (CD8 T cells) and humoral immunity
    HIV replication in lymph nodes for years
  3. Persistent Generalised Lymphadenopathy
  4. Symptomatic HIV infection/AIDS related complex
  5. AIDS
58
Q

Acute HIV disease/ acute retroviral syndrome

A
  • Multiplication in lymph nodes
  • Primary viremia with flu-like illness
  • Significant fall of CD4 T cells
59
Q

Persistent generalised lymphadenopathy

PGL

A

Enlarged lymph nodes of more than 1cm size in two or more non-contiguous sites that persist for at least 3 months

60
Q

AIDS related complex or

Symptomatic HIV infection

A

After clinical latency, CD4 T cell starts falling

  1. Unexplained diarrhoea for at least 1 month
  2. Severe weight loss, fatigue, malaise and night sweats
  3. Mild opportunistic infections like oral thrush
61
Q

Features of AIDS

A
  1. Rapid fall in CD4 T cells
  2. High viral load
  3. Lymphoid tissue is totally destroyed and replaced by fibrous tissue
  4. Opportunistic infections
  5. Neoplasia development
  6. Direct HIV induced manifestations like HIV encephalopathy
62
Q

Classification systems for HIV

A 
1. CDC classification:
 Nine stages based on associated clinical conditions and CD4 T cells
2. WHO clinical staging for adults:
 Based on clinical conditions only
 Into 4 stages
63
Q

High risk groups for HIV

A
  1. Extremely high risk:
    Female sex workers, men who have sex with men, transgenders and IV drug abusers
  2. Moderately high risk:
    • HCW
    • haemophiliacs and other blood product recipients
    • people with other STIs
64
Q

Opportunistic infections of HIV infected people

A

M/C TB in world and India
Fungal: candidiasis, Pneumocytis jirovecii
Viral: Herpes simplex, CMV
Parasitic: Cryptosporidium, Toxoplasma, Strongloides

65
Q

When is p24 antigen test used for HIV

Is it the best confirmatory test

A

12-26 days of infection
The IgG antibodies remain for long
IgA is used for serum, mucus secretions and newborn
The best confirmatory method is HIV RNA detection

66
Q

Specific tests for HIV infection

A 
1. Screening tests: Ab detection
• ELISA 
• Rapid/simple tests
2. Supplementary tests: Ab detection
• Western blot assay
• Line Immuno-Assay LIA
3. Confirmatory tests:
• p24 Ag detection
• viral culture
• HIV RNA
• HIV DNA
67
Q

NACO strategic algorithms

A
  1. Strategy I: transfusion and transplantation safety
    Just one test
  2. Strategy IIa: Unlinked anonymous testing
    2 tests
  3. Strategy IIa: symptomatic patients
    3 tests, first confirmatory test positive ➡️ positive
  4. Strategy III:
    Asymptomatic HIV patients, antenatal , pre-op screening
    All screening test positive confirmed by 2 tests
68
Q

Difference between strategy IIb and III of NACO

A 
Strategy IIb:
 When first two positive ➡️ ➕ve
 When 2nd negative ➡️ indeterminate or negative
Strategy III:
 When 3 positive ➡️ ➕ve
 When any confirmatory is negative ➡️ indeterminate
 When both confirmatory negative ➡️:
 •  high risk - indeterminate
 • low risk - negative
69
Q

Prognosis of HIV

A
  1. CD4 T cell count- M/C
  2. HIV RNA load: best
  3. p24 Ag detection
  4. Neopterin and β2 macroglobulin level
70
Q

Diagnosis of paediatric HIV infection

A 
• Baby’s IgG cannot be differentiated from maternal IgG which disappears by 18 months. 
Screening tests can be done after that. 
• HIV DNA 🧬 PCR: most recommended
 after 6 weeks
 confirmed by same test again
• HIV RNA detection
• p24 antigen detection
71
Q

Prophylaxis required for opportunistic infections before starting ART

A 
1. For pneumocystis pneumonia: 2 types 1° and 2°
 Cotrimoxazole 
2. For Crytococcal meningitis
 Fluconazole
3. Isoniazid preventive therapy for TB
72
Q

Anti retroviral drugs

A
  1. NRTI
  2. NNRTI
  3. PI
  4. NtRTI
  5. Others like fusion inhibitor
74
Q

First line treatment for HIV-1 infection for adults with normal serum creatinine levels

A

TLE

Tenofovir + Lamivudine + Efavirenz

74
Q

Post exposure prophylaxis for HIV

A

Occupational exposure within 2 hours
TL + LR regimen
Tenofovir-Lamivudine + Lopinavir-Ritonavir
also used for:
•HIV-2 or HIV-1 and 2 co-infection
• women received with single dose nevirapine in past pregnancy

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