Pathogenicity of Bacteria Contaminating Blood Products

Presence of Gram-negative bacteria and Staphylococcus aureus on the skin of blood donors in the Democratic Republic of the Congo

BACKGROUND

Skin bacteria may contaminate blood products but few data are available on sub-Saharan Africa (sSA). We assessed the presence of Gram-negative bacteria and Staphylococcus aureus on blood donor skin and evaluated skin antisepsis in the Democratic Republic of the Congo (DRC).

STUDY DESIGN AND METHODS

Among blood donors at the National Blood Transfusion Center (NBTC) and at a rural hospital, the antecubital fossa skin of the non-disinfected arm (not used for blood collection) was swabbed (25cm² surface) and cultured for total and Gram-negative bacterial counts. Bacteria were identified with MALDI-TOF and tested for antibiotic susceptibility by disk diffusion. For evaluation of the NBTC antisepsis procedure (i.e., ethanol 70%), the culture results of the disinfected arm (used for blood collection) were compared with those of the non-disinfected arm.

RESULTS

Median total bacterial counts on 161 studied non-disinfected arms were 1065 Colony-Forming Units (CFU) per 25 cm² , with 43.8% (70/160) of blood donors growing Gram-negative bacteria and 3.8% (6/159) Staphylococcus aureus (2/6 methicillin-resistant). Non-fermentative Gram-negative rods predominated (74/93 isolates, majority Pseudomonas spp., Acinetobacter spp.). Enterobacterales comprised 19/93 isolates (mostly Pantoea spp. and Enterobacter spp.), 5/19 were multidrug-resistant. In only two cases (1.9%, 2/108) the NBTC antisepsis procedure met the acceptance criterion of ≤2 CFU/25 cm² .

CONCLUSION

Skin bacterial counts and species among blood donors in DRC were similar to previously studied Caucasian populations, including cold-tolerating species and bacteria previously described in transfusion reactions. Prevention of contamination (e.g., antisepsis) needs further evaluation and customization to sSA.

Propagation capacity of bacterial contaminants in platelet concentrates using a luciferase reporter system

INTRODUCTION

Currently the use of molecular tools and techniques of Genetic Engineering in the study of microbial behavior in blood components has replaced the employment of classical methods of microbiology. This work focuses on the use of a novel lux reporter system for monitoring the contaminating propagation capacity of bacteria present in platelet concentrates under standard storage conditions in the blood bank.

METHODS

A miniTn5 promotor probe carrying the lux operon from Photorhabdus luminiscens (pUTminiTn5luxCDABEKm2) was used to construct four bacterial bioluminescent mutants: Escherichia coli, Salmonella typhi, Proteus mirabilis and Pseudomonas aeruginosa. Luminescent mutants were used for contamination tests with 20 CFU in platelet concentrates bags and were stored under standard storage conditions in the blood bank (100 rpm at 22 °C). The measurements of luminous activity and optical density were used to monitor bacterial proliferation during 7 days (168 h).

RESULTS

During the exponential growth phase (log) of bacterial strains, a lineal correlation between luminous activity vs biomass was observed (R(2) = 0.985, 0.976, 0.981) for E. coli::Tn5luxCDABEKm2, P. mirabilis::Tn5luxCDABEKm2 and P. auriginosa::Tn5luxCDABEKm2, respectively. The above indicates that metabolic activity (production of ATP) is directly related to biomass in this phase of microbial growth. While conducting experiments, the inability to propagate S. typhi::Tn5luxCDABEKm2 was detected. We can speculate that platelet concentrates contain specific components that prevent the propagation of S. typhi.

CONCLUSION

The use of luxCDABE system for the quantification of luminous activity is a rapid and sensitive alternative to study the propagation and auto-sterilization of bacterial contaminants in platelet concentrates.

Bacterial screening of platelet concentrates on day 2 and 3 with flow cytometry: the optimal sampling time point?

BACKGROUND

There is growing concern on the residual risk of bacterial contamination of platelet concentrates in Germany, despite the reduction of the shelf-life of these concentrates and the introduction of bacterial screening. In this study, the applicability of the BactiFlow flow cytometric assay for bacterial screening of platelet concentrates on day 2 or 3 of their shelf-life was assessed in two German blood services. The results were used to evaluate currently implemented or newly discussed screening strategies.

MATERIALS AND METHODS

Two thousand and ten apheresis platelet concentrates were tested on day 2 or day 3 after donation using BactiFlow flow cytometry. Reactive samples were confirmed by the BacT/Alert culture system.

RESULTS

Twenty-four of the 2,100 platelet concentrates tested were reactive in the first test by BactiFlow. Of these 24 platelet concentrates, 12 were false-positive and the other 12 were initially reactive. None of the microbiological cultures of the initially reactive samples was positive. Parallel examination of 1,026 platelet concentrates by culture revealed three positive platelet concentrates with bacteria detected only in the anaerobic culture bottle and identified as Staphylococcus species. Two platelet concentrates were confirmed positive for Staphylcoccus epidermidis by culture. Retrospective analysis of the growth kinetics of the bacteria indicated that the bacterial titres were most likely below the diagnostic sensitivity of the BactiFlow assay (<300 CFU/mL) and probably had no transfusion relevance.

CONCLUSIONS

The BactiFlow assay is very convenient for bacterial screening of platelet concentrates independently of the testing day and the screening strategy. Although the optimal screening strategy could not be defined, this study provides further data to help achieve this goal.