PROBLEM SOLVING IN MEDICAL MICROBIOLOGY Problem 1 A 75-year old man with muscle weakness ,camps , diffuculty in swallowing , abd. rigidity , increased muscle tone , clenching of fists , extension of lower limbs , lockjaw , & respiratory arrest. Final diagnosis was tetanus . Q. What organism is involved ?
C.tetani • Q. What other neurological conditions caused by Clostridia spp.?
Botulism caused by C.botulinum . • Q. How is tetanus prevented?
Triple vaccine (TDB) at 2-3-4 months. Booster at 4-5 & 15 years . • Wound cleaning • Penicillin • Passive immunization by immuoglobulins .
Problem 2 • A 20-years old student with fever, malaize , headache , diffuculty in sleeping , & healed scar on his arm due to dog bite. Final diagnosis was rabies . • Q. What is the aetiology?
A. Rabies virus . Q. How do you confirm diagnosis ?
@ Virus detection by • immunoflurescence in corneal • scraping & skin biopsy. • @ Viral culture from saliva • @ Antibody serology . • @ detection of Negri bodies in • brain biopsy after death . • @ Animal inoculation. • Q. What is the reservoir of • rabies ?
A. Bats, birds, dogs, foxes , other warm-blooded animals. Q. How is rabies prevented ?
@ Rabies vacciue • from tissue culture. • @Passive immunization.
Problem 3 • A 26-years old woman with lower abdominal pain , fever , vomiting , & vaginal discharge . Final diagnosis was PID (salpingitis+cervicitis ) • Q. Which organisms are involved?
N.gonorrhoeae – E.coli – Enterococci – B.fragilis – Peptostreptococci – C.trchomatis • Q. What specimens you may collect ?
A. Cervical swabs – fluid aspiration from the cul-de-sac behind the cervix
(2) Aspirated fluid was bloody , foul smelling ,& purulent.Gram stain showed gram-negative diplococci & gram-negative rods . Culture revealed oxidase positive colonies on TM agar , that were gram-negative diplococci . Anaerobic culture showed colonies consisting of gram-negative rods • Q.What bacteria isolated aerobically
N.gonorrhoeae • Q.What is the organism isolated anaerobically ?
A. B.fragilis – Fusobacterium Q. Do you do sensitivity testing for the isolated organism ?
A. Yes, because resistance is expected َََ Q. How would you test for syphilis?
Problem 4 • (1) A 52-year old man c/o cough,fever,anorexia,headache Cough is productive,& nonbloody. Lab.test showed:WBC 18000 – Polymorphs 77%-Lymphocytes 12% • Q. What 2 specimens to collect ?
A. Sputum – blood Q. What quick test you do to help diagnosis ?
A. Gram stain of sputum • (2) Sputum was collected for Gram stain & culture . Gram stain showed many pus cells, no organism , few gram-negative & gram-positive cocci . Blood culture was taken . Final • diagnosis was atypical pneumonia • Q. What organisms causing atypical pneumonia ?
A. Mycopl. pneumoniae – Leg.pneumophilia – Chlam. pneumoniae – C.psittici – Influenza virus Q.What organisms causing pneumonia in immuno- compromized patient ?
A. Klebsiella – Pseudomonas – Legionella – S.aureus – CMV H.simplex type 1 Varicella-zoster – Candida Aspergillus – Pneumocystis Strongyloides
(3) Fluorescence examination of sputum showed L.pneumophilia . • Q. What is the natural habitat of this organism ?
Air conditioning units – water taps – lakes • Q. Can the organism be cultured ?
A. Yes, not commonly done – Medium used must be rich in iron & cysteine Q. What other test for diagnosing Legionella ?
Serology : indirect immunofluorescence test. • Q. Why was not seen in Gram stain ?
A. Legionella stains poorly with gram stain – best detected by fluorescence microscopy
Problem 5 • A 30-years old woman c/o nausea , vomiting , swelling of fingers, malaise, fatigue ,anorexia, upper abdominal pain , & dark urine. She was found to have hepatomegaly & tender liver .Lab. tests showed positive urine bilirubin , high serum bilirubin ,& raised ALT test. Final diagnosis was viral hepatitis . • Q. Which viruses are to blame ?
A. Hepatitis A, B , C, D viruses – E-B virus – CMV – yellow fever virus Q. Which tests you perform to establish the aetiology ?
A. *HAIgM antibody *HBcIgM *HBsAg *HBsAb *HCV IgG antibody *Serology for other viruses .
Results of serology are : • *HAIgM-negative *HBsAg-positive , *HBcIgM-poasitive , *HBsAb-negative *HCV IgG – negative *Other tests negative. • Q.What is the diagnosis ?
Acute hepatitis B • Q. What is the diagnosis if : *HAIgM –negative *HBsAg-negative *HBcIgM-positive *HBsAb-negative *Other tests negative ?
A. Acute hepatitis B (Recent infection ). Q. What is the diagnosis if: *HAIgM-negative *HBsAg-negative *HBcIgM-negative *HbsAb-positve *Other tests negative ?
A. Past infecion & immunity to hepatitis B Q. How did the patient acquire infection?
(3) Patient improved , & tests one year later showed posotive HBsAg & HbsAb was negative . • Q. Explain Why ?
Chronic carrier of HBV • Q. What test you do to show if she is infectious to others ?
Problem 6 • A 20-year old man c/o cough, loss of appetite , fever, bloody sputum , & loss of weight. Lab. tests showed 3% neutrophils , & X-ray showed cavitation & infiltration in lungs . • Q. what immediate 2 sputum tests that you may perform to identify the organism?
Gram + ZN stains • (2) Gram stain revealed mixed flora .ZN stain revealed long ,slender ,pink rods. Sputum was sent for culture . • Q. What is your diagnosis ?
Tuberculosis • Q. How is the organism transmitted ?
*Inhalation • *Ingestion of TB. • Q. What is the natural habitat of organism ?
Human lungs • Q. Why is the organism acid-fast?
A. Because it contains high content of lipids Q. Can the organism be cultured in lab. ?
A. Yes, on LJ medium within 6-8 weeks. Q. What is the role of serology in diagnosis ?
Serology is useless • Q. What should be done for his contacts?
A. * Asymptomatic contacts : screened by Mantoux test , if positive , give INAH drug *Symptomatic contacts : do sputum microscopy & culture , if positive , give treatment . Q. What is the immunological basis for Mantoux test ?
A. Cell-mediated immunity to M.tuberculosis Q. Can atypical mycobacteria cause such an infection ?
Problem 7 • (1) A 10-years old immunocompromized girl has fever for 2 days . Blood test showed 10% neutrophils . • Q. What common bacteria ,viruses, fungi to cause this condition ?