Different characteristics of multidrug-resistant isolates of Pseudomonas aeruginosa in in vitro and in vivo conditions

Bacterial virulence factors play a key role in the outcome of burn wound infections. We aimed to assess the differences in virulence properties of multidrug-resistant (MDR) isolates of Pseudomonas aeruginosa (P. aeruginosa) between in vitro and in vivo environments. Scald burns were induced in 50 adult male rats and the animals were randomly infected with one of the MDR isolates of P. aeruginosa. Isolate-1 expressed the virulence-related genes (exoU, exoS, pilB, nan1, ampC, and rpoD) in vitro, while Isolate-2 only expressed ampC and rpoD genes in vitro. The infected burn wounds in both groups were excised at different time points (2, 4, 6, 8, and 14 days post-burn) for histopathological examinations. The expressions of virulence-related genes within the infected skin tissues were also evaluated using SYBR green real-time polymerase chain reaction (PCR) assays. At the first time point, both MDR isolates caused the same depth of tissue damage. However, during follow-ups, Isolate-2 exhibited a lower degree of inflammation and fibrinous exudate, but faster re-epithelialization, scab formation, and granulation tissue compared to Isolate-1. The results also revealed significant differences between the in vitro and in vivo environments in terms of the expression of virulence-related genes. All virulence-related genes, except pilB, were expressed in burned skin infected by Isolate-2, while they were not detectably expressed in vitro. Based on the findings, the MDR isolates of P. aeruginosa demonstrated distinct virulence properties within in vitro and in vivo environments. This highlights the risks of relying solely on laboratory findings in clinical decision-making for burn wound infections.