Biofilm Feast: Stringent Response-Induced Changes in MRSA and MSSA Isolates, Examining icaA/ icaD Gene Expression

Abstract

Introduction: The stringent response is a bacterial adaptation mechanism
triggered by stress conditions, including nutrient limitation. This
response helps bacteria survive under harsh conditions, such as those
encountered during infection. A key feature of the stringent response
is the synthesis of the alarmone (p)ppGpp, which influences various
bacterial phenotypes. In several bacterial species, stringent response
activation significantly affects biofilm formation and maintenance.
Methods: Clinical specimens were collected from multiple hospitals in
Baghdad, Iraq. Staphylococcus aureus was identified using conventional
biochemical tests. The PCR technique was applied to detect mecA,
icaA, and icaD genes, while the Vitek 2 compact system confirmed
Methicillin sensitivity in mecA-negative isolates. Biofilm intensity of all
S. aureus isolates was assessed under normal and starved conditions.
Additionally, the gene expression levels of icaA and icaD were measured
in five MRSA and five MSSA strains under both conditions.
Results: The mecA, icaA, and icaD genes were detected in 94%, 96.3%,
and 100% of S. aureus isolates, respectively. Biofilm production
analysis showed that 24% of isolates were strong producers, 49%
were moderate producers, and 9% were weak producers. Statistical
analysis indicated that biofilm intensity significantly decreased under
nutrient limitation (p < 0.0001) compared to normal conditions across
all isolates. Furthermore, icaA and icaD genes were upregulated under
stringent response conditions, regardless of Methicillin resistance status.
Conclusion: The stringent response influences S. aureus biofilm
formation, with biofilm intensity decreasing under nutrient-limited
conditions. However, the upregulation of icaA and icaD genes suggests
a regulatory role of the stringent response in biofilm-related gene
expression. These findings highlight the potential impact of stress
adaptation mechanisms on bacterial persistence and pathogenicity.

How to cite this article:
Mussa A A, Mathkhury H J F A. Biofilm Feast:
Stringent Response-Induced Changes in MRSA
and MSSA Isolates, Examining icaA/ icaD Gene
Expression. J Commun Dis. 2025;57(1):44-54.

DOI: https://doi.org/10.24321/0019.5138.202505