Post-antibiotic era in hemodialysis? Two case reports of simultaneous colonization and bacteremia by multidrug-resistant bacteria

ABSTRACT The emergence of resistance mechanisms not only limits the therapeutic options for common bacterial infections but also worsens the prognosis in patients who have conditions that increase the risk of bacterial infections. Thus, the effectiveness of important medical advances that seek to improve the quality of life of patients with chronic diseases is threatened. We report the simultaneous colonization and bacteremia by multidrug-resistant bacteria in two hemodialysis patients. The first patient was colonized by carbapenem- and colistin-resistant Klebsiella pneumoniae, carbapenem-resistant Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus (MRSA). The patient had a bacteremia by MRSA, and molecular typing methods confirmed the colonizing isolate was the same strain that caused infection. The second case is of a patient colonized by extended-spectrum beta-lactamases (ESBL)-producing Escherichia coli and carbapenem-resistant Pseudomonas aeruginosa. During the follow-up period, the patient presented three episodes of bacteremia, one of these caused by ESBL-producing E. coli. Molecular methods confirmed colonization by the same clone of ESBL-producing E. coli at two time points, but with a different genetic pattern to the strain isolated from the blood culture. Colonization by multidrug-resistant bacteria allows not only the spread of these microorganisms, but also increases the subsequent risk of infections with limited treatments options. In addition to infection control measures, it is important to establish policies for the prudent use of antibiotics in dialysis units.


Resumo
The emergence of resistance mechanisms not only limits the therapeutic options for common bacterial infections but also worsens the prognosis in patients who have conditions that increase the risk of bacterial infections. Thus, the effectiveness of important medical advances that seek to improve the quality of life of patients with chronic diseases is threatened. We report the simultaneous colonization and bacteremia by multidrug-resistant bacteria in two hemodialysis patients. The first patient was colonized by carbapenem-and colistin-resistant Klebsiella pneumoniae, carbapenem-resistant Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus (MRSA). The patient had a bacteremia by MRSA, and molecular typing methods confirmed the colonizing isolate was the same strain that caused infection. The second case is of a patient colonized by extended-spectrum beta-lactamases (ESBL)-producing Escherichia coli and carbapenem-resistant Pseudomonas aeruginosa. During the follow-up period, the patient presented three episodes of bacteremia, one of these caused by ESBL-producing E. coli. Molecular methods confirmed colonization by the same clone of ESBL-producing E. coli at two time points, but with a different genetic pattern to the strain isolated from the blood culture. Colonization by multidrug-resistant bacteria allows not only the spread of these microorganisms, but also increases the subsequent risk of infections with limited treatments options. In addition to infection control measures, it is important to establish policies for the prudent use of antibiotics in dialysis units.

IntRoductIon
Antimicrobial resistance has complicated the treatment of patients with bacterial infections by limiting the available options 1,2 . This situation has led the World Health Organization to warn of the arrival of a post-antibiotic era, in which common or previously easily-treated infections lead to therapeutic failures and deaths as a result of the simultaneous presence of different mechanisms of resistance 2,3 .
Patients with chronic renal failure on hemodialysis are highly susceptible to colonization and development of bacterial infections, with percentages exceeding those reported in individuals with other types of exposure to health care 4 . Bacterial infections are the second most common cause of hospitalization and death after cardiovascular disease and the risk of bacteremia is 26 times higher in comparison with the general population 4 . Likewise, the spread of resistant bacteria has been increasingly reported in this group of patients, who circulate continuously between the hospital environment and the community 5,6 . In this way, it has been described that 28% of these patients may be colonized by at least one resistant microorganism and that colonization generates a higher risk of infection, with a worse prognosis and with mortality rates up to 2.8 times higher compared to the general population 4 .
In this paper, we report the simultaneous colonization and bacteremia by multidrug-resistant bacteria in two hemodialysis patients included in a cohort study in which colonization by these microorganisms in stool, nostrils, and skin was evaluated at three timepoints (at the beginning of the study, at month two and month six), in a renal unit of Medellín, Colombia. To refine the analysis, we used molecular typing methods to confirm if the patients were infected with the same multidrug-resistant strain that had been previously identified colonizing them.
The study protocol was approved by the Bioethics Committee for Human Research at the University of Antioquia (CBEIH-SIU) (approval no.18-35-819) and written informed consent was obtained from each subject.

Case 1
The first case is a 90-year-old man with a history of type II diabetes mellitus, arterial hypertension, and remission of colon adenocarcinoma. At the time of admission to the study, the patient had been on hemodialysis for four years and had a tunneled jugular dialysis catheter due to the dysfunction of different arteriovenous fistulas. As background, he reported hospitalization and antibiotic use (aztreonam) in the last six months. In addition, he complained of itching and frequent scratching around the insertion site of the catheter. The patient was positive in two of the three screenings for intestinal colonization by carbapenem-resistant Klebsiella pneumoniae and Pseudomonas aeruginosa, according to CLSI criteria. The K. pneumoniae isolate was positive for KPC carbapenemase by PCR and presented simultaneous resistance to colistin. Although the mcr plasmid gene that generates the transferable resistance to colistin was not detected, the alteration of the mgrB gene was mediated by the insertion sequence ISKpn25.
In the third screening, the patient was positive for MRSA in the nostrils and on the skin around the catheter insertion site. Two months later, he presented an episode of bacteremia due to this same bacteria. He received treatment with vancomycin and required dialysis catheter replacement. When processing the MRSA isolates from colonization and infection by pulsed-field gel electrophoresis (PFGE), it was confirmed that they corresponded to the same bacterial clone, which led to the conclusion that the colonizing strain was the same that caused the infection ( Figure 1A). Laboratory markers of inflammation, malnutrition and renal function and echocardiogram results are shown in Table 1.

Case 2
The second case is of a 57-year-old man with a history of systemic lupus erythematosus, arterial hypertension and primary hypothyroidism. The patient had lost a transplanted kidney and had been on hemodialysis four years by tunneled jugular catheter, due to a dysfunctional prior arteriovenous fistula caused by an aneurysm. The patient reported hospitalization and previous use of antibiotics (vancomycin and amikacin) in the last six months, as well as a history of multiple infections by multiresistant bacteria. He also reported itching and frequent scratching around the catheter insertion site. In all three screenings, the patient was positive for ESBL-producing E. coli and for carbapenem-resistant Pseudomonas aeruginosa.
During the follow-up period, the patient presented three episodes of bacteremia caused by Enterobacter cloacae, and ESBL-producing K. pneumoniae and E. coli. The use of Enterobacterial Repetitive Intergenic Consensus (ERIC) confirmed colonization by the same clone of ESBL-producing E. coli in two of the three screenings, but with a different genetic pattern to the strain isolated from the blood culture ( Figure 1B). Laboratory markers of inflammation, malnutrition, and renal function are shown in Table 1.   4 . Likewise, a meta-analysis found that the risk of infections in patients colonized by this bacteria was more than 10 times greater compared to non-colonized patients (RR: 11.5; 95% CI, 4.7 to 28.0), with a 19% probability of developing infection in a period between 6 and 20 months in colonized patients compared to only 2% in non-colonized patients 7 . Persistent colonization by this microorganism worsens the prognosis of infections and is associated with a mortality rate increase of more than 85% 8 .
Unlike MRSA, few studies have evaluated colonization by multiresistant Gram-negative bacilli (MDR-GNB) in hemodialysis patients and their role in the development of infections 4-6 ( Table 2). This is worrisome, because the percentage of colonization by these microorganisms may be higher compared to MRSA colonization, as has been suggested by several authors [4][5][6] . The presence of ESBL generates resistance to penicillins, cephalosporins, and aztreonam, leaving carbapenems as the only treatment alternative 9 . Hemodialysis is an independent risk factor for infections by Gram-negative bacilli producing ESBL, so these patients have a higher risk of infection by these bacteria compared to susceptible isolates 9 . Even more worrying is the spread of carbapenemase-producing Gramnegative bacteria, because carbapenems, in addition to cephalosporins and other beta-lactams, are not effective against these microorganisms, leading to polymyxins such as colistin being the last treatment option 10 .
The picture is complicated because many of the resistance mechanisms mentioned are in mobile genetic elements, which favors their rapid spread from one bacterium to another 11 . An example of this is colistin resistance, in which the insertion sequence ISKpn25 that alters the mgrB gene can be present in plasmids that also carry carbapenemases such as KPC, causing strains with simultaneous resistance to carbapenems and colistin, such as was observed in the case presented in this report 11 . Colistin resistance is of importance because it is one of the last treatment options for infections caused by carbapenem-producing bacteria 10 . Therefore, colonization by colistin-resistant microorganisms implies a potential risk of systemic infections with few treatment alternatives. Because infections by multidrug-resistant bacteria are associated with a two to five-fold increase in morbidity and mortality compared to infections caused by susceptible isolates, the prevention of both colonization and infection by these microorganisms in patients in hemodialysis is crucial 10 . The screening of multidrug-resistant bacteria becomes more important in endemic countries, because the spread of these microorganisms exceeds the hospital environment and also occurs in outpatient services and in the community 12 . Therefore, prevention strategies should be focused on preventing the transmission of bacteria between patients, health care personnel and medical devices 4 . Because colonization is more frequent than infection and it can persist for long periods of time, the evaluation of prophylactic treatments in colonized patients is necessary to avoid the development of infections, oriented not only to nasal decolonization in the case MRSA, but other body sites, such as the catheter insertion site, where this and other resistant microorganisms can colonize 12,13 .
The vascular access type is also important to the development of bacteremia in hemodialysis patients. Of all access-related bloodstream infections, 70% occur in patients with catheters, so that the fistula is considered the preferred access due to lower infectious complications and lower cost 14 . However, in Colombia, as in other countries in Latin-America, most of hemodialysis patients have catheter and refuse to use fistula for fear or aesthetic reasons. Therefore, the effect of multidrug-resistant bacteria colonization on the development of infections such as bacteremia may be greater.
Finally, in addition to infection control measures, it is important to establish policies for the prudent use of antibiotics in dialysis units, because the use of these drugs is an important risk factor for the spread of drug-resistant bacteria. Given the few antibiotic treatment options, this is an urgent strategy that must be implemented.