Normatividad exigida para la importación de alimentos

The microbiological aspects of biofilms associated with symptomatic CAUTIs in terms of the species identified and their susceptibility can be misleading as they may reflect the organisms that were free floating when the urine specimen was collected as opposed to being isolated from a biofilm on a section of catheter [26]. Antibiotic treatment of planktonic bacteria may suppress symptoms of infection but concentrations fail to act on bacteria embedded in the biofilm [62]. That being said, their ability to at least slow biofilm formation and clear planktonic bacteria is of critical importance and their use continues until better therapeutic options become available [14]. In addition, the use of antibiotics prior to device placement or

29 between device changes is crucial in helping control infection. It is normal for symptomatic patients to have their catheter replaced and by doing this removes the biofilm but detached bacteria may re - seed the urine so it is usual to prescribe a course of antibiotics that are based on the microbiology results of the urine culture [14]. However, when antibiotic treatment is stopped, recurrent infection is common. Of major concern in the formation of biofilms is that the cells embedded in the depths of the biofilm are insusceptible to antibiotics and are inherently protected from host defences. Studies have shown that some organisms within biofilms require >1000 fold higher concentration of antibiotics compared to their planktonic forms in order to kill them [62].

As the understanding of biofilm resistance developed, three main mechanisms were hypothesised:

 Hypothesis 1: the slow penetration of antimicrobial agents into the depths of a biofilm is probably a major factor in conferring resistance [62]. The EPS may retard the antibiotic from reaching buried cells within the biofilm and the matrix may also inhibit the transfer of the antibiotic by destruction, chelation or direct blockage [27]. This may result in sub - lethal concentrations of antibiotic and allow for the build - up of resistance mechanisms [27].

 Hypothesis 2: the development of altered microenvironments within a biofilm may lead to resistance. The decrease in oxygen within the deeper layers of the biofilm can lead to anaerobic niches and some antibiotics lose activity under these conditions [62]. An accumulation of waste products can lead to an alteration in pH which can antagonise the action of antibiotics and

30 waste product levels or depletion of substrates can also cause the bacteria to enter a non - growing state [62]. Several groups of antibiotics are effective only on rapidly growing bacteria. A change in the osmotic environment within a biofilm may also lead to resistance by changing the proportion of porins in a way that reduces cell envelope permeability to antibiotics [62].  Hypothesis 3: the production of a sub - population of microorganisms forms

a highly protected dormant state of cells that are similar to bacterial spores. This is supported by studies that found resistance in newly formed biofilms where the bacteria possess no particular resistance mechanisms to survive. These bacteria remain resistant upon repeat antimicrobial treatment and resume growth once the concentration of antibiotic drops to a sub - inhibitory concentration. This may be a further mechanism that may explain why these persister type cells have reduced susceptibility to antibiotics [27].

Proctor et al (1995) [63] report on small-colony variants (SCVs) of Staphylococcus aureus being cultured from patients with persistent and relapsing infections. SCVs have been associated with some foreign body - associated infections, in particular with chronic catheter - related infections. SCVs are a slow growing sub - population of bacteria which are better able to persist in mammalian cells and are less susceptible to antibiotics than their wild type counterparts [64]. They reflect impaired respiratory metabolism due to disruptions in the synthesis of constituents associated with the electron transport system and have unusual biochemical profiles [63, 64]. Clinically SCVs can be difficult to detect due to their atypical morphology and slow growing nature, but if detected, this may also be a reason for resistance to antibiotic treatment in clinical practice.

31

1.6.1. Host Immune System Evasion

In addition to cells within a biofilm being resistant to antimicrobial agents they are also inherently protected from host defence systems. To maintain infection in the urinary tract organisms must evade the host immune response [53]. The urinary tract, however, contains receptors that recognize intruding pathogens by their invariant pathogen associated molecular patterns (PAMPs) and of the immune surveillance molecules, toll-like receptors are able to detect PAMPs [65]. These act to mobilize appropriate immune defence systems which help to eliminate bacteria from the urinary system. Uropathogenic bacteria, however, excrete a variety of virulence factors that enable them to inhibit certain host functions and promote colonisation. In Gram negative bacteria, the production of capsules plays a role in immune evasion as they resist phagocytosis. During the course of a UTI, immunoglobulin (Ig) antibodies secreted by the host in response to infection recognise antigenic components of uropathogens. However, some bacteria break down host Ig using Ig proteases and other host defence systems like complement (Clq and C3) [53]. Other virulence factors associated with Gram negative bacteria include toxins such as haemolysin and lipopolysaccharide (LPS). LPS acts as an endotoxin and elicits a strong immune response and is in part responsible for the clinical manifestations during infection brought about through cytokine release. Figure 1.5 [53] depicts the virulence factors of the Gram negative uropathogens E.coli and P.mirabilis. This evasion of the host immune system in response to infection by the biofilm cells along with their insusceptibility to antimicrobials makes treatment difficult and costly.

32

Figure 1.5: Virulence factors of the Gram negative uropathogens E.coli and P.mirabilis [53]. (IM = inner membrane, OM = outer membrane)

1.6.2. Symptoms

Although long - term urinary catheterisation is synonymous with bacteriuria, bacteriuria is not synonymous with symptomatic UTI [26]. Over 90% of cases are asymptomatic [32]. Current evidence suggests that asymptomatic patients should not be treated unless the patient is immunosuppressed, at risk of bacterial endocarditis, pregnant or due to undergo urinary tract instrumentation, as these infections clear up once the catheter is removed [53, 66]

33 The symptoms a patient with symptomatic CAUTI may experience can vary from mild to severe. They may feel pressure in their lower pelvis, have urine that has an odour to it or is cloudy which sometimes may contain blood (haematuria), and a patient may also experience leakage of urine [67]. Additional symptoms may include:- fatigue, fever, vomiting, mental changes or confusion [67]. Often in the elderly, mental changes or confusion are the only symptoms of a possible CAUTI [26]. Symptoms however may be subtle and may also be due to the presence of the catheter itself as opposed to infection [26]. If suspected, analysis of the urine may show the presence of white blood cells (WBCs). A high WBC count of >10 per µl is indicative of infection. A urine culture with counts of >103 cfu/mL of a predominant pathogen will determine the type of bacteria present and susceptibility tests will determine the appropriate antibiotic for treatment. If left untreated, pylenephritis, calculus formation, bacteraemia, urosepsis and even death can result [53].

1.6.3. Treatment

For all patients on LTC, it is recommended that their catheters be changed according to their clinical needs or as recommended by the manufacturer of the catheter which is usually at 10 - 12 week intervals [21]. If symptomatic CAUTI is confirmed, evidence indicates that it is better to change the catheter before antibiotic treatment is initiated [16]. Infection with one type of organism can be treated with either trimethoprim, which acts upon most uropathogens except for Pseudomonas and Enterococcus species, fluoroquinolones which are effective against many Gram negative organisms including most Pseudomonas and Proteus species or with nitrofurantoin, a UTI - specific antibiotic that is effective against most uropathogens except Pseudomonas and Proteus species [53]. Patients with infections that are

34 polymicrobial may be treated with trimethoprim or a cephalosporin such as cefuroxime [53]. Seriously ill patients may require a two - drug treatment regimen to control infection, especially if they have repeated polymicrobial infections. For certain symptomatic patients, due to the high relapse rate, catheter replacement may have to be performed as often as every 2 - 3 weeks.

Infections associated with biofilms are rarely resolved using antibiotics alone even when the patient‟s immune system is fully functioning [27]. Even if a symptomatic patient‟s catheter is replaced and antibiotics given, there is a high incidence of recurrent infection causing severe distress and long - term morbidity to the patient [38]. It has been known for P.mirabilis infections of a single genotype to persist in the urinary tract despite many catheter changes, antibiotic treatment and periods of non - catheterisation [24]. Universally the only recommended guidelines to reduce the risk of bacterial infection are to maintain a closed drainage system and to minimise the duration of catheter usage as much as possible [53]. Despite the treatment measures, for some patients there is no satisfactory resolution to the problem and there remains a need to develop a strategy/measure to reduce the occurrence of CAUTIs.