Bacterial Growth in Venous Ulcers of the Lower Extremity and Its Sensitivity to Antibiotics

Abstract

From 154 consecutive patients, 154 different cultures were obtained from the exudate of lower extremity ulcers due to venous insufficiency.

Subjects were outpatients with venous ulcers from whom cultures were rou tinely obtained at the first visit in the clinic. This prospective study lasted three years. Forty-two cultures failed to grow bacterial contaminants. Among the remaining 112 samples in which bacterial colonization was demonstrated, 78 grew a single microorganism and 34 grew more than one. A total of 124 bacteria species was recorded. Of the 76 Gram-positive cultures, 50 contained Staphylo coccus aureus ; the second most common organism was Staphylococcus epidermi dis, and this was followed by Candida, Streptococcus hemolyticus, and bacilli. Within the 48 Gram-negative bacteria the most common was Pseudomonas aeruginosa followed by Escherichia coli, Enterobacter, Proteus, Acinetobacter, Klebsiella, and Serratia.

Sixteen chemotherapeutic drugs were evaluated by scoring the effect on the bacterial growth and the specificity of activity. The most effective drugs against Gram-positive bacteria were clindamycin (91%), cefotaxime (79%), erythromy cin (76%), and netilmicin (69%), and against Gram-negative bacteria were aztreonan (87%), norphloxacin (85%), netilmicin (79%), and cefotaxime (72%).

The combined antibacterial effectiveness for each ulcer, whether growing single or more microorganisms, was 71 % for cefotaxime, 69% for netilmicin, 66% for norphloxacin, 57% for gentamicin, 50% for cotrimoxazole, 38% for tetracyclines, and 21% for amoxicillin. These data have some practical interest: even though antimicrobial treatment is not usually necessary in the authors' experience if the ulcer does not show clinical evidence of infection, in some instances ulcers do present evidence of active infection. In their opinion the best option in these cases is to collect the exudate, culture it, and while waiting for the result, start with an empiric treatment based on the results as presented in this paper. A prospective clinical study evaluating the effect of these antibiotics on ulcers affected by clinical signs of infection is presently ongoing in their institution with the purpose of giving clinical support to these laboratory find ings.