Picture 35

This picture shows Pseudomonas aeruginosa (on the right) and Shigella dysenteriae (on the left) in nutrient agar.

Pseudomonas aeruginosa

Morphology: Gram negative rods, do not ferment glucose and lactose, are oxidase positive, produce pyocyanin and pyoverdin

Route of transmission: Fomites and food

Investigations: Gram stain, culture in MacConkey's agar or Triple Sugar Iron medium

Diseases:

Pneumonia

Urinary tract infection

Wound infection

Septicemia

Meningitis

Otitis externa

Endophthalmitis

Osteomyelitis

Treatment:

Due to varied antibiotic resistance, choices for empirical treatment include the aminoglycosides (eg. gentamicin and tobramycin), some third generation cephalosporins (eg. ceftazidime and cefoperazone), extended spectrum penicillins (eg. piperacillin, azlocillin and carbenicillin), carbapenems (eg. imipenem and meropenem), and fluoroquinolones (eg. ciprofloxacin and ofloxacin) until results of sensitivity tests are known.

  

Shigella dysenteriae

Morphology: Gram negative cocci that do not ferment lactose, do not produce spores and is motile

Route of transmission: Food, fingers, flies, faeces

Investigations: Gram stain, organism cultured on MacConkey's agar and Triple Sugar Iron (TSI) medium

Diseases:

Usually mild watery diarrhea in developed countries and severe "bacillary dysentery" in developing countries

Treatment:

No antibiotics are given in mild cases

In severe cases, ciprofloxacin or trimethoprim-sulfamethoxazole is prescribed

 

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