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The resistance of Pseudomonas aeruginosa by action of gram-positive antibiotics
Your name and Instructor’s name
Department of Biology, Harold Washington College
One of the major groups of microorganisms responsible for most of the infections is the bacteria. This group are
unicellular microorganisms without nucleus (prokaryotes), their genetic material is contained within a single
circular chain of DNA. The interior of the bacteria (cytoplasm) is enclosed within a cell membrane that also is
surrounded by a rigid cell wall and a capsule layer, made of lipopolysaccharides and lipoproteins (Knight &
Schlager, 2002). The presence of peptidoglycans in the cell wall is a taxonomical criterion for bacteria
classification and could be determined by the Gram stain test, dividing the bacteria in two groups: gram-positive
-like Staphylococcus aureus- and gram-negative bacteria -like Pseudomonas aeruginosa and Escherichia coli(Madigan, Martinko, Stahl, & Clark, 2012).
The growth and multiplication of bacteria can be blocked by the action of chemicals called antibiotics They are
classified by their structure and action mechanism. Neomycin is classified as an aminoglycoside, it's used
against gram-negative and gram-positive bacteria and inhibit the subunit 30S of the ribosome in the protein
synthesis. Erythromycin, a macrolide used against gram-positive bacteria, also inhibit another subunit in the
protein synthesis, the 50s subunit in the ribosome. Instead, bacitracin, used against gram-positive bacteria,
blocks the synthesis of the cellular wall (Madigan et al., 2012).
Bauer, Kirby, Sherris & Turck, (1966) improved the paper disk method, for determining susceptibility of bacteria
to antibiotics and chemotherapeutic agents, by the interpretation of the inhibition zones. The interpretation of the
antibiotics used in this work could be reviewed in the Table 1.
Inhibition zone diameter
Resistant Intermediate Sensitive
12 or less
17 or more
Erythromycin 13 or less
18 or more
8 or less
13 or more
Table 1. Zone sizes and their interpretation for antibiotics used in this work (Bauer et al., 1966).
The increasing occurrence of resistant bacteria is happening worldwide, endangering the efficacy of antibiotics.
This “crisis” has been attributed to abuse of antibiotics, extensive agricultural use, and slow development of new
antibiotics by the drug industry due...