Abstract
ObjectivesWe aimed to characterise the staphylococcal cassette chromosome mec (SCCmec) type, genetic relatedness, biofilm formation and composition, icaADBC genes detection, icaD expression, and antibiotic susceptibility of planktonic and biofilm cells of Staphylococcus hominis isolates from blood.MethodsThe study included 67 S. hominis blood isolates. Methicillin resistance was evaluated with the cefoxitin disk test. mecA gene and SCCmec were detected by multiplex PCR. Genetic relatedness was determined by pulsed-field gel electrophoresis. Biofilm formation and composition were evaluated by staining with crystal violet and by detachment assay, respectively; and the biofilm index (BI) was determined. Detection and expression of icaADBC genes were performed by multiplex PCR and real-time PCR, respectively. Antibiotic susceptibilities of planktonic cells (minimum inhibitory concentration, MIC) and biofilm cells (minimum biofilm eradication concentration, MBEC) were determined by the broth dilution method.ResultsEighty-five percent (57/67) of isolates were methicillin resistant and mecA positive. Of the mecA-positive isolates, 66.7% (38/57) carried a new putative SCCmec type. Four clones were detected, with two to five isolates each. Among all isolates, 91% (61/67) were categorised as strong biofilm producers. Biofilm biomass composition was heterogeneous (polysaccharides, proteins and DNA). All isolates presented the icaD gene, and 6.66% (1/15) isolates expressed icaD. This isolate presented the five genes of ica operon. Higher BI and MBEC values than the MIC values were observed for amikacin, vancomycin, linezolid, oxacillin, ciprofloxacin, and chloramphenicol.Conclusions S. hominis isolates were highly resistant to methicillin and other antimicrobials. Most of the detected SCCmec types were different than those described for S. aureus. Isolates indicated low clonality. The results indicate that S. hominis is a strong biofilm producer with an extracellular matrix with similar composition of proteins, DNA and N-acetylglucosamine; and presents high frequency and low expression of icaD gene. Biofilm production is associated with increased antibiotic resistance.
Highlights
Staphylococcus hominis, a coagulase-negative staphylococcus (CoNS) species, is an opportunistic pathogen that is one of the three most common isolates found in the blood of neonates and immunosuppressed patients.[1,2,3] In recent years, reports of S. hominis infection-induced bacteraemia, septicaemia, endophthalmitis, and endocarditis have increased in frequency.[2,3,4,5,6,7] S. hominis infections are often highly resistant to antibiotics and are difficult to treat
Higher biofilm index (BI) and Minimum biofilm eradication concentration (MBEC) values than the Minimal inhibitory concentration (MIC) values were observed for amikacin, vancomycin, linezolid, oxacillin, ciprofloxacin, and chloramphenicol
S. hominis isolates were highly resistant to methicillin and other antimicrobials
Summary
Staphylococcus hominis, a coagulase-negative staphylococcus (CoNS) species, is an opportunistic pathogen that is one of the three most common isolates found in the blood of neonates and immunosuppressed patients.[1,2,3] In recent years, reports of S. hominis infection-induced bacteraemia, septicaemia, endophthalmitis, and endocarditis have increased in frequency.[2,3,4,5,6,7] S. hominis infections are often highly resistant to antibiotics and are difficult to treat. The mecA gene resides within a mobile genetic element called the staphylococcal cassette chromosome mec (SCCmec)[14] that was first described in Staphylococcus aureus. This element is related to mec gene complex classes A–E and ccr gene complex classes 1–8. Eleven types of SCCmec have been described (http://www.sccmec.org/Pages/SCC_ TypesEN.html); S. hominis is prone to carry novel SCCmec types because of the presence of high-frequency non-typeable and new combinations of mec and ccr gene complexes. Eleven types of SCCmec have been described (http://www.sccmec.org/Pages/SCC_ TypesEN.html); S. hominis is prone to carry novel SCCmec types because of the presence of high-frequency non-typeable and new combinations of mec and ccr gene complexes. [11, 13, 15]
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