A Study on Acinetobacter baumannii and Staphylococcus aureus Strains Recovered from the Same Infection Site of a Diabetic Patient

Abstract

Diabetic foot ulcer infections are frequently polymicrobial in nature and exhibit increased morbidity and mortality, as well as, treatment failures. Interactions between Acinetobacter baumannii and Staphylococcus aureus were studied, which showed strain-dependent changes in growth and antibiotic susceptibility. This study examined the interactions between two clinical strains of A. baumannii (1929) and S. aureus (1928) that were recovered from skin and soft tissues of a diabetic patient. When S. aureus 1928 and A. baumannii 1929 were co-cultured together, there was no significant decrease in growth in either clinical strains, indicating that both strains can co-exist in the same site of infection. Additionally, neither strains experienced statistically significant changes in susceptibility. These findings highlight that these two pathogens can be found in the same niche of infection, which may lead to more aggressive outcome of the infection.

Figure 1.. S. aureus 1928 and A. baumannii 1929 growth patterns.

(A) CFU/ml of S. aureus 1928 mono and co-culture with A. baumannii 1929. (B) CFU/ml of A. baumannii 1929 mono and co-culture with S. aureus 1928. (C) CFU/ml of S. aureus 1928 with or without A. baumannii 1929 CFCM. (D) CFU/ml of A. baumannii 1929 with or without S. aureus 1928 CFCM. Bars and whiskers represent means ± SD of three independent experiments in duplicate. The differences between all groups of isolates were analyzed by unpaired t test.

Figure 2.. Antibiotic susceptibility profiles of S. aureus 1928 and A. baumannii 1929 in mono and co-culture condition.

Zone of inhibition represents the average ± Standard deviation in the halo sizes. (A) S. aureus 1928 mono and co-culture with A. baumannii 1929. (B) A. baumannii 1929 mono and co-culture with S. aureus 1928. Bars and whiskers represent means ± SD of three independent experiments in duplicate. The differences between mono and co-culture were analyzed by two-way ANOVA by Sidak’s comparison test.

Figure 3.. Hemolytic activity of A. baumannii 1929 trigger by S. aureus LS1.

(A)Proximity assay of A. baumannii 1929 and S. aureus LS1 at 24 hr. A. baumannii 1929 plated on the left and S. aureus LS1 on the right at 24hrs. Starting distance is 1cm and increases distance in increments of 0.5cm. (B) Modified proximity assay of A. baumannii 1929 and S. aureus LS1 CFCM at 48 hr. A. baumannii 1929 (top, right, bottom) and LS1 CFCM (top, left, bottom). These photos are representative of three independent experiments.