Bacteriology related to mbbs microbiology

About topics related to microbiology

1. Microbiology Bacteriology

2. Infective Endocarditis 1) Subacute Bacterial Endocarditis. 2) Blood culture 3) Two blood culture sets should be collected at an interval of >12hrs between first and second set. (A blood culture set refers to blood collected from a single venipuncture site and divided into two bottles) (Blood should be collected before antibiotic therapy). 4) Coagulase Negative Staphylococcus ( CoNS ) ( Eg – Staphylococcus epidermidis ) – Tube Coagulase test negative, White colonies on milk agar 5) Staphylococcus aureus , Viridans streptococci, Enterococci, Pneumococci, HACEK group.

3. Rheumatic Fever 1) Acute Rheumatic Fever (ARF). 2) Group A Streptococcus I.e., Streptococcus pyogenes . 3) Other Complications - Post Streptococcal Glomerulonephritis (PSGN), Guttate psoriasis, Reactive Arthritis, Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcus pyogenes (PANDAS). 4) ASO (Anti- Streptolysin O) Antibody titer by latex agglutination test – Elevated titer indicates Streptococcal infection.

4. Septicemia /Septic Shock 1) Septicemia 2) Typhoidal Salmonellae, Brucella , Spirochetes, Rickettsiae , viridans streptococcus – Primary Sepsis. Staphylococcus, beta – hemolytic streptococcus, enterococcus, pneumococcus, meningococcus , Bacillus anthracis , Listeria, E. coli, Klebsiella , Enterobacter , Pseudomonas, Acinetobacter , Burkholderia , Stenotrophhomonas , Haemophilus, Aeromonas , Bacteroides – Secondary sepsis . 3) Blood Culture by conventional or automated Culture media. 4) Klebsiella pneumoniae - large, dome shaped, mucoid, pink color , LF colonies on MacConkey agar; catalase+ oxidase- indole- citrate+ urease+ TSI A/A, gas present, H2S absent .

5. Septicemia cont’d... 5) Sample Collection - Blood samples for culture should be collected in pairs, from two separate sites, before starting antimicrobial therapy. Skin decontamination - first, treated with 70% isopropyl alcohol and then antiseptic solution such as Povidone Iodine or Chlorhexidine should be applied – applied in a circular motion starting from the centre to the periphery and allowed to air dry. Using a sterile syringe and needle, blood specimen is drawn – 8-10ml of blood per bottle for an adult and 1-3ml per pediatric bottle. The collected blood is then dispensed directly into a blood culture bottle at the bedside (conventional or automated). They should be transported immediately to the laboratory. In case of a delay, culture bottle should never be refrigerated, instead can be kept at 35°C in an incubator or left at room temperature.

6. Enteric Fever - I 1) Enteric Fever. 2) Blood culture (5 days I.e., first week of infection) 3) Volume – 8-10ml of blood to be collected in blood culture bottle, either conventional (Brain Heart Infusion Medium – Monophasic or Biphasic) or automated bottle ( BacT /ALERT). Method of collection is same as that for septicemia (Skin decontamination - drawing of blood – dispensing into culture bottles) 4) Salmonella Typhi – NLF pale colonies with black centre on DCA; Citrate negative, urease negative, TSI – K/A, gas absent, speck of H2S present at the junction of slant and butt .

7. Enteric Fever - II 1) Enteric Fever. 2) Widal test for Detection of Serum Antibodies (12 days I.e., 2 nd week of infection). 3) Both the H and O Antibody titers are significant (>1:200 and >1:100 respectively) – confirms the diagnosis.

8. Bacillary Dysentery - Shigella 1) Bacillary Dysentery. 2) Fresh stool. 3) Wet Mount preparation - large number of pus cells, erythrocytes and macrophages. 4) Shigella dysenteriae – Pale NLF colonies on MacConkey agar; Indole negative, Citrate negative, Urease negative, TSI – K/A, gas absent, H2S absent.

9. Cholera 1) Cholera 2) Motility Testing by Hanging Drop method. 3) Vibrio cholerae - large Yellow colonies on TCBS agar; Indole positive, Citrate positive (variable), Urease negative, TSI – A/A, gas absent, H2S absent. 4) A Notifiable Disease is a disease that, when diagnosed, requires health providers to report to public health officials, by law. 5) AIDS, Dengue, Malaria, Enteric fever, Cholera, Hepatitis A, B, Chickenpox, Measles, Plague, Diphtheria, Pertussis, Tuberculosis, Leprosy, Influenza, Rabies, Tetanus, Polio, Viral encephalitis,

10. Surgical Site Infection 1) Surgical Site Infection (SSI). 2) Wound aspirate. 3) Staphylococcus aureus – Golden yellow colonies surrounded by a narrow zone of Beta hemolysis on blood agar; Tube coagulase test positive, Mannitol fermentation positive. 4) Resistance to Beta lactams ( Eg – MRSA) (Also Resistance to Vancomycin – VRSA, VISA) 5) CoNS , E. coli, Klebsiella , Enterococcus, Bacteroides .

11. Burn Wound Infection 1) Burns patients are prone to develop infections because - the loss of cutaneous barrier, avascular eschar formed over the burn surface and impaired immunity – favour the colonization of bacteria. 2) Pseudomonas aeruginosa – large opaque irregular colonies with a metallic sheen on Nutrient agar; Pale NLF colonies on MacConkey agar; Indole negative, Citrate negative, Urease negative, TSI – K/K, gas absent, H2S absent. 3) Staphylococcus aureus , Acinetobacter etc.

12. Diphtheria 1) Samples – a portion of pseudomembrane , throat swab. 2) Simple test – Direct Smear Microscopy by Gram stain (Club shaped Gram positive bacilli arranged in Chinese letter or Cuneiform arrangement) and Albert stain (Green bacilli with bluish black metachromatic granules at the poles). 3) Corynebacterium diphtheriae - black colonies on Potassium Tellurite Agar (PTA)

13. Bacterial Pneumonia A) Acute Bacterial Pneumonia. B) Streptococcus pneumoniae - lanceolate or flame shaped Gram positive cocci in pairs. C) Haemophilus influenzae , Staphylococcus aureus , Gram negative bacilli. (Atypical pneumonia by Mycoplasma, Chlamydia, Legionella) D) Underlying viral URTI like Influenza, Underlying comorbid conditions like Chronic lung, heart, kidney and liver diseases, DM, immunosuppression (HIV). Children <2yrs, post-splenectomy.

14. Ventilator Associated Pneumonia (VAP) 1) Ventilator Associated Pneumonia (VAP). 2) Tracheal aspirate. 3) Acinetobacter baumannii – NLF colonies with faint pink tint on MacConkey agar; Indole negative, Citrate positive, Urease negative, TSI – K/K, gas absent, H2S absent.

15. Acute Bacterial Meningitis A) Acute Bacterial/Pyogenic Meningitis. B) Streptococcus pneumoniae , Neisseria meningitidis , Streptococcus agalactiae , Listeria monocytogenes , Haemophilus influenzae . C) CSF Microscopy and culture. D) CSF is obtained by lumbar puncture under aseptic conditions and is divided into three sterile containers – one each for cell count, biochemical analysis and bacteriological examination. CSF should never be refrigerated as delicate pathogens may die, if a delay is expected, it may be kept in an incubator at 37°C. E) Streptococcus pneumoniae - lanceolate or flame shaped Gram positive cocci in pairs; wide zone of inhibition surrounding the Optochin disk ( Optochin sensitivity).

16. Urinary Tract Infection (UTI) 1) Urinary Tract Infection. 2) Urine culture on CLED agar followed by culture identification and AST; Nitrate Reduction Test / Griess test. 3) Agents – Escherichia coli , Klebsiella pneumoniae , Enterobacter , Proteus, Serratia , Pseudomonas, Acinetobacter . 4) Escherichia coli – Flat pink LF colonies on MacConkey agar; Indole positive, Citrate negative, Urease negative, TSI – A/A, gas present, H2S absent. 5) Therapeutic challenge – diverse variety of pathogens, risk of antibacterial resistance.

17. Syphilis 1) Syphilis (Secondary Syphilis). 2) Rapid Plasma Reagin (RPR) test – slide flocculation test, similar to VDRL test. Positive test is indicated by formation of clumps of antigen antibody complexes, seen by naked eyes (as the clumps are bigger in size). 3) Direct Microscopy – Dark Ground Microscopy, Direct Fluorescent Antibody Staining for T. paliidum (DFA-TP), Silver Impregnation Staining by Levaditi and Fontana stains. Serology (Antibody Detection) – Non- Treponemal or Standard Tests for Syphilis (STS) – VDRL, USR, TRUST; Treponemal or Specific Tests – TPI, FTA-ABS, TPHA, TPPA, Western blot. Molecular methods – Multiplex PCR for simultaneous detection of common agents of genital ulcers (T. pallidum, H. ducreyi , HSV )

18. Gonococcal Urethritis 1) Gonococcal Urethritis (onset of 2 days is associated with GU and >1week in case of NGU). 2) Urethral swab in men, Cervical swab in women. In men, the urethral meatus is cleaned with a gauze soaked in saline. The purulent discharge is expressed out by pressing at the base of the penis and collected directly onto slides or swabs (Dacron or rayon swabs). 3) Gram negative intracellular kidney-shaped diplococci – Neisseria gonorrheae .