Critical Review for the Article

Executive Summary

The focus of this review is on a patient suffering from leukemia but that has shown persistent Staphylococuss epirdemidis infection after aplasia that has been prolonged. Isolation of the patient was done for a period of six weeks and was introduced to a genetically and phenotypically unstable Staphylococcus epidermidis strain related to an epidemic clone that has been shown in many hospitals all over the world. (Mark et al 2006). The results of this experiment showed a strain that had a high degree of variability and impeccable evidence of selection and predominance of the biofilm producing and oxacillin resistant variants over the six months period.

In the early stages of infection, there are several findings. One, the strain is found to generate into subpopulations which had been lost the biofilm mediating ica locus along with oxacillin resistance conferring mecA gene. The mutants were out competed by the ica- and mecA-positive wild type genotype, with the selection and predominance of biofilm forming and oxacillin resistance variants in the later stages of the infection. It was also detected that this infection was noticed in a switch from protein to polysaccharide intercellular adhesion/poly-N-acetylglucosamine-mediated biofilm production. This was formed among ica-positive variants in the course of infection (Miragaia et al, 2007). The review also highlights the impacts of distinct Staphylococcus epidermidis clonal lineages as serious nosocomial pathogens that through the generation and highly pathogenic variants, may critically determine the disease progression and outcome.

There is further demonstration on how colonial lineages for coagulase negative staphylococci may be seen to easily spread and persist in health care units. Multilocus sequence typing studies have shown that an epidemic staphylococcus epidermis clone, also known as sequence type ST27, is the cause of nosocomial Staphylococcus epidermidis infections in many health care units. Staphylococcus epidermidis has been known as a major factor in biofilm formation for the colonization of the medical devices. Biofilm can be shown by using a number of mechanisms and the most common one is the formation of polysaccharide intercellular adhesion mediated biofilm. The facilitation of polysaccharide intercellular adhesion (PIA) is by an enzyme encoded by the four gene operon icaADBC. It is very evident in many diseases associated with S. epidermidis strains. There is therefore a focus of the review on the leukemic patient who received allogenic hematopoietic stem cell transplantation (HSCT) and experienced a generalized S. epidermidis infection. An elaboration on the description of the association of the strain to epidemic ST27/ST2 clone and an investigation on the genomic instability and variations in biofilm expression and oxacillin resistance that occurred in the course of the infection (Foka, 2006).

The age of the patient isolated was 23 years and with this, they present a situation where the patient is treated with allogenic cord blood HSCT. This is done for reoccurrence of high risk common B-cell acute lymphoblastic leukemia for the second time. It was found out that the patient febrile after five days. The patient is then treated by piperacillin-tazobactam that is then supplemented with caspofungin treatment on the 13th day. After this the patient is treated with vancomyacin for ten days. The blood culture of the patient is then seen to be negative. Stopping of the treatment shows that bactemeria forms again.(Rodgers et al, 2008). On treating the patient with vancomyacin in combination with catheter lock therapy, the blood culture remain positive.redness and tenderness on the tibial musles and pain thereof was reported with the increase of dosage to 2×1.5g. Further revelations were that there was fluid collected in the musles when the doctors used Magnetic resonance imaging (MRI) there were no abnormalities of the fascias which helped detect the presence of myositis.

Further, on the 42nd day the patient shows necrosis and clusters of coccoid bacteria at different sites on the tibial muscles. There was also the yielding of S.epidermidis with the addition of Amikacine to Vancomyacin treatment. The daily blood cultures were a sterile until the 52nd day with the yielding of another S. epidermidis. The patient consistently complained of headache and rigidity on day 55 with the MRI showing the enhancing lesions in the prefrontal cortex which is also consistent with the presence of septic emboli. To react to these changes noticed, the doctors added rifampin to vancomyacin for the treatment and stopped the use of amikacine. 70 days later there was a report of non engraftment, haplo-identical rescue transplantation from the patients’ mother was performed (Widerstorm et al, 2006). The patient was later seen to have developed acute respiratory failure with rapidly progressive acute respiratory distress syndrome. Despite mechanical ventilation and extracorporal oxygenation, the patient died two days later of the multiorgan failure. However, the autopsy did not reveal any sign of leaukemia or any sign of endocarditis.

From the summary it is possible to note that Staphylococcus epidermidis is a commensal bacterium with a low level of pathogenic potential. This makes it difficult to understand whether isolation is the reason for an infection or if it represents a contamination that has not been specified. The authors will mostly come up with an argument that the appearance of the various colony morphotypes cultures that are detected from the patients in a mix culture which indicates that there is an indication of contamination. The strain identified as ST27/ST2 which is an S. epidermidis sequence type has emerged as an epidemic nosocomial pathogen in medical facilities worldwide. The authors, having seen these results speculate that the successful and the continous distribution of ST27/ST2 strains are highly related to the specific genetic makeup of these strains (Weisser, 2010). This is explained by the fact that majority of the strains carries the ica operon and have the potential of producing biofilms. These strains have tendencies of acquiring and exchanging mobile genetic element such as various SCCmec cassettes and ARE elements. Therefore one can see that these experiments demonstrate the genomic instability if the ica and mecA genes as a molecular background for the observed heterogeneity rather than a mixed infection by different strains.