Lilly Benthaus Day 5 Meropenem
Microbiological results
Concentration on agar & Microbial load
Next we will consider three parameters:
Today, precise identification of bacterial species is performed using complicated but very quick methods of mass spectrometry. Identification is important as it is used in making a preliminary selection of antibiotics, since not all antibiotics work against all bacteria. The final selection of a medication is based on measured resistances and on patient information (e.g. allergies).
This provides a rough indication of the number of bacterial cells on the agar plate using categories such as ‘dense’, ‘substantial’, ‘thin’ and ‘isolated’.
The microbial load is a more precise indication of the number of bacterial cells per milliliter of material. It can be determined by counting the colonies or by means of quantitative molecular biology methods.
Material: sputum
Query: pathogen identification
Results of culture:
| Day | Pathogens | Concentration on agar | Microbial load (cells/ml) |
| 5 | Pseudomonas aeruginosa | isolated | 3,5 x 10^2 |
Determining resistance with the Kirby-Bauer test
Enter the measured values and mark to indicate which antibiotics Lilly Benthaus’ pathogens are sensitive/resistant to.
Tip: If the diameter of the zone of inhibition is below the breakpoint limit, the patient’s pathogens should be considered resistant to the antibiotic in question. If the diameter of the zone of inhibition is above the limit, the patient’s pathogens should be considered sensitive to the antibiotic in question.
Resistances:
| Antibiotic | Resistance threshold
(mm) |
Zone of inhibition
(mm) |
Day 5
sensitive resistant |
| Ciprofloxacin | 26 | ||
| Gentamicin | 15 | ||
| Meropenem | 24 |
Information on the antibiotics
Bacteria-killing antibiotic from the class of fluoroquinolones. It works by inhibiting a bacterial enzyme which is needed in copying the DNA during cell division. It works well against a broad spectrum of bacteria and is often applied in everyday medical practice for non-life-threatening infections. In the meantime, many resistant strains of different pathogens exist worldwide.
Bacteria-killing antibiotic from the class of aminoglycosides. It works by inhibiting protein synthesis at the bacterial ribosomes. Its effective spectrum is not as wide as that of ciprofloxacin, but it works well against Pseudomonas aeruginosa. Resistances exist worldwide in a few percent of bacteria.
Bacteria-killing antibiotic from the class of β-lactams and therefore a relative of penicillin. It works by disrupting the building of the bacterial cell wall and covers a very wide spectrum of dangerous pathogens. It is often used against Pseudomonas aeruginosa.
Patient consultation
Lilly Benthaus
„I think I’m coughing a little less, but otherwise I haven’t noticed much change from the antibiotic yet. But I was actually feeling pretty well beforehand anyway. In any case I haven’t noticed any side effects.“
New scientific findings
If a bacterium develops a resistance against an antibiotic, this resistance could also make the bacterium sensitive to another antibiotic (Szybalski and Bryson, 1952). A trade-off of this type is called collateral sensitivity (Szybalski and Bryson, 1952). If this is taken advantage of in the strategic planning of treatments, it could limit the adaptability of the bacteria (Imamovic and Sommer, 2013; Lazar et al., 2014; Oz et al., 2014). This includes ideas such as periodically switching antibiotics (AB) over the course of treatment:
- At time t0 treatment of the illness which is caused by
begins with antibiotic AB 1 
. - After some time a few cells of the pathogen develop a resistance to AB 1:
(time t1). At this point AB 1 may even become ineffective. - Then treatment is switched over to AB 2
, which works better against the cells which are resistant to AB 1 () and kills these off. Now once again has an advantage (time t2) and prevails. - But in this case as well, after some time a resistance can develop in against AB 2
(time t3) and so the antibiotic is switched again and AB 1 is given, thereby killing off , which has become collaterally sensitive to AB 1.
Experiments performed to date regarding the effectiveness of this idea have yielded mixed results. Some point to the positive option of slowing down the evolution of resistances (Abel zur Wiesch, Kouyos, Abel, Viechtbauer and Bonhoeffer, 2014). Most of the experiments were also performed only in the laboratory – as yet there are no data from animal experiments or clinical studies to confirm the results (Baym, 2016). It is also not certain whether these exceptional antibiotic interactions still occur under different environmental conditions such as an infected human organ or in the case of different genetic makeups (Baym, 2016).
Daily report – Day 5 Lilly Benthaus
