Distribution of Genes Encoding Toxin, Adhesion, and Antibacterial Resistance Among Various SCCmec Types of Methicillin-Resistant Staphylococcus aureus Isolated From Intensive Care Unit, Tehran, Iran

Abstract

Background: Most methicillin-resistant Staphylococcus aureus (MRSA) infections occur in health care settings; therefore, it is important to know about antimicrobial susceptibility, and carriage of virulence genes in S. aureus isolates. Objectives: The current study aimed at determining the prevalence of genes coding antimicrobial resistance, toxins, and adhesion factors among various SCCmec types of MRSA isolated from intensive care units (ICUs). Methods: From April 2016 to March 2017, a total of 200 MRSA species were isolated from various clinical samples of patients hospitalized in ICUs. The Kirby-Bauer disk diffusion method was employed to determine resistance pattern. Conventional polymerase chain reaction (PCR) assay was utilized to demonstrate antimicrobial resistance, toxins, and adhesion genes. Different SCCmec types of MRSA strains were determine by the multiplex PCR assay. Results: Antibiotic susceptibility testing revealed that all the isolates were sensitive to linezolid, teicoplanin, and vancomycin. The frequency of high-level mupirocin-resistant MRSA was 5.5%. The presence of resistance genes ant(4')-Ia, aac(6')-Ie/aph(2"), tetM, msrA, ph(3')-IIIa, ermA, msrB, ermB, ermC, and mupA were detected 73.5%, 60.5%, 57.5%, 37%, 36.5%, 34.5%, 24%, 17%, 15% and 5.5%, respectively. The most prevalent adhesion genes were clfA (93.5%) followed by clfB (90%), fnbA (81.5%), fnbB (77%), can (51%), ebp (46.5%), and bbp (2.5%). The frequency of etb, eta, pvl, and tst genes were 4.5%, 9.5%, 21.5%, and 61.5%, respectively. Inducible macrolide-lincosamidestreptogramin B (inducible MLSB resistance; iMLSB), and constitutive MLSB (cMLSB) phenotypes were observed in 88 (44%) and 26 (13%) isolates. Different SCCmec types comprising type III (56.5%), type IV (25%), type II (11%) and type I (7.5%) were identified among the MRSA strains. Conclusions: Results of the current study showed a high prevalence of resistance to commonly used antibiotics that can be a serious threat to patients hospitalized in ICUs. Also, the current study findings showed that different SCCmec types causing nosocomial infections were associated with specific antimicrobial resistance, adhesion, and toxin gene profiles.

Association of tsst-1 and pvl with mecA Genes among Clinical Staphylococcus aureus Isolates from a Tertiary Care Hospital

“…Moreover, we have detected the pvl gene in 23.9% of MRSA and 9.8% of MSSA isolates. This was similar to the findings of Goudarzi and his colleagues, who reported the prevalence of pvl gene of 21.4% within MRSA isolates 37 , and Abiri and his colleagues who detected pvl gene among 21.5% of mecA positive MRSA strains 7 . We found that pvl gene was significantly prevalent in MRSA group (P=0.04).…”

“…They are known producers of different types of toxins and other virulence factors that shape up their clinical significance. Molecular studies have shown that some MRSA strains that carry tsst-1 and pvl genes 7 have the ability to produce toxins encoded by these genes responsible for severe infections such as TSS and necrotic pneumonia with a mortality rate up to 75% 19 . However, treating such infections is considered a challenge to physicians in view of their antimicrobial resistant properties.…”

“…Many virulence factors are responsible for the unique pathogenicity of S. aureus such as toxins, enzymes and adhesion factors. The toxins produced by S. aureus include Panton-Valentine leukocidin (PVL), hemolysin, toxic shock syndrome toxin-1 (TSST-1), exfoliative toxins and staphylococcal enterotoxins 7 . The PVL is a pore forming leukotoxinen coded into by pvl gene and has the ability to target and kill host leukocytes through perforation of plasma membrane together with intracellular organelle membranes.…”

“…In literature, many studies have reported an alarming increase in the MRSA strains positive for tsst-1 and pvl genes 7,13 . Similarly, previous studies conducted in Egypt detected tsst-1 and pvl genes among MRSA strains 14,15 .…”

Molecular Study of Enterotoxins Genes of Staphylococcus aureus Isolated from Patients in Intensive Care Units

“…Different reports defined sea and seg genes as the most frequent enterotoxins genes associated with hospital-acquired sepsis [22]. Other report found tst and txt as the common enterotoxin genes in S. aureus isolates [23]. The distribution of enterotoxin genes differs according to geographic regions and types of studied patients.…”