clinical microbiology

Clinical Microbiology(MLCM- 201)

Prof. Dr. Ebtisam. F. El Ghazzawi.

Medical Research Institute (MRI)

Alexandria University

Intended Learning OutcomesIntended Learning OutcomesBy the end of this lecture the student should be able to

Understand all about Pathogens outside the enteric tract, Types, pathogens, and there Laboratory Diagnostic tests.

These organisms are usually opportunistic

pathogens that cause nosocomial infections,

especially pneumonia and urinary that

infections. Klebsiella pneumonia is an

important respiratory tract pathogen outside

hospital as well. Klebsiella species exhibit

mucoid growth, large polysaccharide

capsules and lack of motility.

Although Klebsiella is a primary pathogen,

patients with Klebseilla pneumonia infections

frequently have predisposing conditions

such as advanced age, chronic respiratory

disease, diabetes or alcoholism. The

organism is carried in the respiratory tract of

about 10% of healthy people, who are prone

to pneumonia if host defences are lowered.

Enterobacter and serratia infections are clearly

related to hospitalization, especially to invasive

procedures such as intravenous

catheterization, respiratory intubation and

urinary that manipulations.

Culture on Mac-Conkey’s agar red colonies

lactose-fermenting.

These organisms primarily cause urinary tract

infections both community and hospital acquired.

Proteus species move very actively by means of

peritrichous flagella resulting in swarming on solid

media unless the swarming is inhibited by

chemicals.

Proteus species Swarming motility on blood agar

Culture on blood agar will produce swarming.

Culture on Mac Conkey’s agar colourless

non-lactose fermenting colonies.

It is motile, rod shaped, gram-negative bacteria.

It is widely distributed in nature and is

commonly present in moist environment in

hospitals. It can colonize normal humans, in

whom it is a saprophyte. It causes disease in

humans with abnormal host defenses; patients

with extensive burns and in those with chronic

respiratory disease.

Ps. aeruginosa causes infections e.g. sepsis,

pneumonia, and urinary tract infections.

Severe external otitis and other skin lesions

occur in users of swimming pools and hot tubs

in which the chlorination is inadequate.

The organisms are strict aerobic and are oxidase

positive. They have a remarkable ability to

withstand disinfectants; this accounts in part for

their role in hospital-acquired infections.

Ps. aesuginasa produces two pigmens useful in

clinical and laboratory diagnosis:

1. Pyocyanin which can colour the pus in a

wound blue.

2. Pyoverdin (fluorescein), a yellow green pigment

that fluoresces under ultraviolet light, a

property that can be used in the early detection

of skin infection in burn patients. In the

laboratory, these pigments, diffuse into the

agar giving a blue green colour that is useful in

identification.

Pseudomonas aeruginosaBlue green pigment (pyocyanin) produced and diffuses into the agar

Specimen from skin lesions, pus, urine, blood,

spinal fluid, sputum and other material should

be obtained as indicated by the type of

infection.

Gram stain shows Gram-negative nods, that are

oxidase positive.

Culture on Mac-conkey’s or EMB agar show

colourless non-lactose-fermenting colonies. On

nutrient media or blood agar a blue green

colour pigment with fruity aroma is produced.

Bacteroides are the most common cause of

serious anaerobic infections, e.g. sepsis

peritonitis and abscesses. Bacteroides are

Gram-negative bacilli and may appear as

slender rods or coccobacilli. They are normal

inhabitants of the bowel. Normal stools

contain 1011 Bacteroides per gram.

By culturing anaerobically on blood agar

plates containing kanamycin or vancomycin

to inhibit unwanted organisms, where

characteristic coloured colonies are grown.

Assignment

Klebsiella.

Study QuestionsState the Laboratory Diagnosis for all kinds of pathogens outside the enteric tract.

Recommended TextbooksManual of Clinical Microbiology, Vols. 1 and 2: Eighth Edition Patrick R. Murray