Bacterial isolation and antibiotic susceptibility from diabetic foot ulcers in Kenya using microbiological tests and comparison with RT-PCR in detection of S. aureus and MRSA

Abstract

Objectives: Diabetic foot ulcers (DFUs) often lead to hospital admissions, amputations and deaths; however, there is no up-to-date information on microbial isolates from DFUs and no mention of utilization of molecular techniques in Sub-Saharan Africa. We conducted a cross-sectional study among 83 adult patients at a tertiary hospital in Kenya over 12 months. The study aimed to isolate, identify bacteria, their antibiotic susceptibility patterns in active DFUs, and to compare standard microbiological methods versus a real-time PCR commercial kit in the detection of Staphylococcus aureus DNA and methicillin-resistant S. aureus (MRSA) DNA.

Results: Eighty swabs (94%) were culture-positive; 29% were Gram-positive and 65% were Gram-negative. The main organisms isolated were S. aureus (16%), Escherichia coli (15%), Proteus mirabilis (11%), Klebsiella pneumoniae (7%) and Pseudomonas aeruginosa (7%). The bacterial isolates showed resistance to commonly used antibiotics such as ampicillin, amoxicillin, cefepime, ceftazidime, cefuroxime, clindamycin, erythromycin, piperacillin-tazobactam, tetracycline and trimethoprim-sulphamethoxazole (TMPSMX). Thirty-one percent of the S. aureus isolated and 40% of the Gram-negatives were multi-drug resistant organisms (MDROs). There was a high prevalence of nosocomial bacteria. MRSA were not identified using culture methods but were identified using PCR. PCR was more sensitive but less specific than culture-based methods to identify S. aureus.

Keywords: Diabetic foot ulcers; Kenya; Methicillin-resistant S. aureus; Multi-drug resistant organisms; Polymerase chain reaction.

Fig. 1

Distribution of MDROs among Gram-positive and Gram-negative organisms. The chart in this figure illustrates the distribution of MDROs among Gram-positive and Gram-negative bacteria. S. aureus and other Gram-positive organisms are displayed on different bars. Antibiotic susceptibility was not determined for tests that showed no growth, Kocuria kristinae, and Leuconostoc mesenteroides. AST was also not performed on a sample suspected to have contaminants but was positive for S. aureus on RT-PCR; therefore n = 13

Fig. 2

Quantitation data for Cycling A (PCR Reports). As shown in this figure, the C_t used was ≥ 20 since the exponential of the sigmoid curve of the Internal Control (Orange Channel) begins at this point