Jornal de Agentes Antimicrobianos

Antimicrobial photodynamic therapy (aPDT) employs the combination of a photosensitive agent and activating light source to destroy microbes across the prokaryotic spectrum. Disinfection is mediated by high levels of oxidative stress exerted on microbial membranes, resulting in rapid kill without genomic exposure and consequent upregulation of resistance. Specificity results from the electrostatic interaction between cationic photosensitizers and generally anionic microbial membranes, an effect largely absent in zwitterionic human cells. S. pyogenes, a member of Group A streptococci, is a member of skin microbiota strongly associated with invasive skin and soft tissue infections, including necrotizing fasciitis. This study aimed to determine susceptibility of the microorganism in both planktonic and biofilm culture to aPDT, as a preparatory step to deployment in human clinical studies.

Introduction

Coagulase-negative staphylococci (CoNS) such as Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus saprophyticus live as commensals on the human skin and mucous membranes. They can be potentially pathogenic when isolated from immunocompromised patients such as: HIV positive, cancer chemotherapy, hemodialysis, diabetics, etc.

Methodology

This was a prospective study aimed at collecting data on biological sample received at Fann's CHNU bacteriology laboratory in Dakar from April 1, 2018 to March 31, 2019. The classical bacteriology techniques were used and the antibiotic susceptibility performed according to the Recommendations of the Antibiogram Committee of the French Society of Microbiology (CA-SFM 2016).

Results

We isolated 86 strains of CoNS, distributed as follows: 45.3% (n=39) of S. epidermidis and 54.7% (n=47) of S. saprophyticus . Among the 39 strains of S. epidermidis isolated, we obtained 3 strains (3.5%) resistant to all beta-lactams (methicillin-resistant) and of the 47 strains of S. saprophyticus , 4 strains (4.7%) are methicillin-resistant. We isolated 39 strains of S. epidermidis , among which 3 strains (3.5%) are resistant to all aminoglycosides (KTG phenotype) and of the 47 strains of S. saprophyticus , 4 strains (4.7%) are KTG phenotype. All CoNSs strains were susceptibility to vancomycin.

Discussion

Hospitalized patients represented 65.7%, and blood cultures 51.1%, which can be explained by the state of immunosuppression from some patients and the lack of asepsis during care. Strains of CoNS resistant to oxacillin are called méti-R strain, thus resistant to all betalactamines. Aminoglycosides were inactive in the 8.2% (n=7) of CoNS. Vancomycin was active on all CoNS; confirming that diminished susceptibility to glycopeptides is exceptional.
Conclusion CoNS are frequently isolated in the laboratory. The site of infection, immune status, purity of cultures and the antibiotic resistance informs about the clinical pathogenic role of CoNS.

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