92

Practical Urology: EssEntial PrinciPlEs and PracticE

bladder catheterization), the fewer the virulence

Susceptibility and Resistance

requirements of any bacterial strain to induce

infection. This is supported by the well-docu-

In the microbiological laboratory, cultured bac-

mented in vitro observation that bacteria iso-

teria are usually tested for phenotypic expres-

lated from patients with a complicated UTI

sion of resistance mechanisms to direct the best

frequently fail to express typical virulence fac-

antimicrobial treatment and to avoid ineffective

tors. The virulence concept also suggests that

treatment. The results of these tests are rendered

certain bacterial strains within a species are

to the practicing physician by categorized terms

uniquely equipped with specialized virulence

called susceptible, intermediate, and resistant.

factors, for example, different types of pili,

This information over the time merges in a local

which facilitate the ascent of bacteria from the

and regional surveillance of resistance and is

fecal flora, introitus vaginae or periurethral area

therefore the guide for empiric antimicrobial

up the urethra into the bladder, or less fre-

treatment.

quently, allow the organisms to reach the kid-

The cut-off concentrations used for the break-

neys to induce systemic inflammation. In

points can follow two different principals.

complicated UTI other factors may become

The epidemiological breakpoint and the clinical

more important, such as the ability of the bacte-

breakpoint7:

ria to form biofilms. Biofilm has been defined as

• The epidemiological breakpoint is the cut-

an accumulation of microorganisms and their

off concentration that delimits the wild-

extracellular

products, forming

a structured

type population of a bacterial species of the

community on a surface. A biofilm infection

non-wild-type population. For example,

develops not only around foreign body surfaces,

the antibacterial concentrations needed to

such as urinary catheters or stents, but also in

inhibit bacterial growth (minimal inhibi-

urinary stones,scars or necrotic tissues,obstruc-

tory concentrations-MIC) differ in the bac-

tive uropathies, or even chronic bacterial pros-

terial populations. The

epidemiological

tatitis.

In

biofilm infection

antimicrobial

breakpoints can be used as the most sensi-

susceptibility of the pathogens is several-fold

tive measure of resistance development for

reduced

when compared with

planctonic or

measuring resistance development in hos-

pure culture cells.6

pitals and the community, for measuring

This differentiation into uncomplicated and

the effect of interventions, and for develop-

complicated UTIs is important for therapy. In

ing strategies to counteract further resis-

uncomplicated UTI almost exclusively antibi-

tance development.

otic treatment is required, whereas in compli-

• The clinical breakpoint is the cut-off con-

cated UTI, in addition to high-dosed antibiotic

centration

predicting if

an antimicrobial

treatment, the removal of the

complicating

treatment

in a certain

dosage will have

factor is essential.

clinical success. For example, based on

pharmacological data, the predicted likeli-

Testing of Antimicrobials

hood of antimicrobials at certain dosages

to achieve clinical success in an individual

in the Laboratory

patient is considered. The clinical break-

points should be used in everyday clinical

An antimicrobial agent is a drug that acts pri-

laboratory work to advice on therapy in the

patient.

marily against infectious organisms. The testing

The clinical breakpoints have been interna-

of an antimicrobial in the laboratory evaluates

the in vitro interactions between an isolated

tionally accepted and adapted. Until recently,

microbe and antimicrobial agents that would be

however, significantly different standards were

appropriate for treatment of an infection in vivo.

used all over the world. Harmonization in

This testing in the laboratory provides data to

Europe was recently achieved by offering uni-

help the clinician decide whether an antimicro-

form standards in the EUCAST (European

bial would be clinically efficient and the selected

Committee on

Antimicrobial Susceptibility

doses are adequate.

Testing) definitions7: