MMIC blog 2 - case 4

Probable microorganisms:

Streptococcus pneumoniae
- gram-positive
- alpha-haemolytic diplococcus bacterium
- optochin sensitive

Pathogenesis:
- produce IgA protease that enhances organism’s ability to colonize the mucosa of the upper respiratory tract. It multiply in tissue and causes inflammation.

Lab investigation:
- Gram stain
- Culture on blood agar plates
- catalase negative
- antibiotic susceptibility – susceptible to penicillins and erythromycin.

Moraxella catarrhalis
- gram-negative
- aerobic
- diplococcus
- produce beta-lactamases

Pathogenesis:
- cause respiratory tract-associated infection in humans

Lab investigation:
- Gram stain
- oxidase negative
- antibiotic susceptibility – susceptible to cephalosporins, resistant to penicillin

Haemophilus influenzae
- gram-negative
- coccobacilli
- non-motile
- generally aerobic, but can grow as a facultative anaerobe.

Pathogenesis:
- Their capsule allows them to resist phagocytosis and complement-mediated lysis in the non-immune host. Unencapsulated strains are less invasive, but they are able to induce an inflammatory response that causes disease.

Lab investigations:
- Gram stain
- culture on blood agar
- catalase positive
- oxidase positive

Mycoplasma pneumoniae
- causes infectious bronchitis

Lab investigations:
- lack of bacteria in a gram stained sputum sample
- lack of growth on blood agar
- positive blood test for cold hemagglutinins.
- Antibiotic susceptibility – susceptible to erythromycin

Chlamydia pneumoniae
- causes infectious bronchitis

Lab investigations:
- Giemsa stain
- Serologic test for antibody in patient’s serum.
- Antibiotic susceptibility – susceptible to tetracycline such as doxycycline

Bordetella pertussis
- gram-negative
- coccobacillus
- aerobic
- non-motile

Lab investigation:
- Culture on Bordet-Gengou agar plate with added cephalosporin select for the organism
- Oxidase positive
- urease negative
- nitrate negative
- citrate negative
- Antibiotic susceptibility – susceptible to erythromycin

Klebsiella pneumoniae
- gram-negative
- facultative anaerobic
- non-motile
- lactose fermenting

Lab investigations:
- Culture – MacConkey’s agar with lactose fermenting colonies.
- oxidase negative
- TSI: slant & butt yellow (acidic)
- H2S negative
- indole negative
- methyl-red negative
- Voges-Proskauer positive
- citrate positive
- urease positive
- Antibiotic susceptibility – susceptible to cephalosporin, resistant to penicillin

References:
http://www.merck.com> Lung and Airway Disorders> Bronchitis
http://www.wikipedia.org> Streptoccocus pneumoniae
http://www.wikipedia.org> Moraxella catarrhalis
http://www.wikipedia.org> Haemophilus influenzae

eunice
tg02