Antibiotic susceptibility of human-associated Staphylococcus aureus and its relation to agr typing, virulence genes, and biofilm formation

Safoura Derakhshan,Masoumeh Navidinia,Fakhri Haghi

doi:10.1186/s12879-021-06307-0

Abstract

Background and objectiveCarriage of virulence factors confers some evolutionary benefit to bacteria, which favors the resistant strains. We aimed to analyze whether antibiotic susceptibility of Staphylococcus aureus strains is affected by agr typing, biofilm formation ability, and virulence profiles.MethodsA total of 123 S. aureus clinical isolates were subjected to antimicrobial susceptibility testing by disk diffusion method, biofilm formation by microtiter plate method, as well as polymerase chain reaction screening to identify virulence genes and the accessory gene regulator (agr) types I-IV. A P value < 0.05 was considered significant.ResultsThe most prevalent virulence gene was staphyloxanthin crtN, followed by hemolysin genes, capsular cap8H, toxic shock toxin tst, and enterotoxin sea, respectively. Resistant isolates were more commonly found in the agr-negative group than in the agr-positive group. Isolates of agr type III were more virulent than agr I isolates. Strong biofilm producers showed more antibiotic susceptibility and carried more virulence genes than non-strong biofilm producers. Associations were found between the presence of virulence genes and susceptibility to antibiotics. Carriage of the virulence genes and agr was higher in the inpatients; while, resistance and strong biofilms were more prevalent in the outpatients.ConclusionThese findings indicated the presence of several virulence factors, biofilm production capacity, agr types and resistance to antibiotics in clinical S. aureus isolates. Considering the importance of S. aureus for human medicine, an understanding of virulence and resistance relationships would help to reduce the impact of S. aureus infections.

Highlights

During the past decade, the rise in the emergence and spread of antimicrobial resistance among the microorganisms has become a major concern worldwide
Staphyloxanthin, a golden pigment produced by more than 90% of S. aureus isolates [6, 7] was suggested to act as an important virulence factor and its inhibition has been shown to reduce the virulence of S. aureus [7, 8]
Carriage of the virulence genes and agr in our study was higher in the inpatients; while, antibiotic resistance and strong biofilms were more prevalent in the outpatients

Summary

Introduction

The rise in the emergence and spread of antimicrobial resistance among the microorganisms has become a major concern worldwide. Antimicrobial resistance is a major threat to public health in Staphylococcus aureus infections. S. aureus is known for its wide range of virulence factors and its ability to infect almost any part of the body. These factors can be divided into different groups, including surface-associated factors, hemolysins and enzymes, and superantigenic toxins [3]. One of the most important surface-associated factors is capsule, which is essential for adherence and initial stages of infection, and can bind to a variety of abiotic surfaces [4]. Carriage of virulence factors confers some evolutionary benefit to bacteria, which favors the resistant strains. We aimed to analyze whether antibiotic susceptibility of Staphylococcus aureus strains is affected by agr typing, biofilm formation ability, and virulence profiles

Objectives

Methods

Results

Discussion

Conclusion