Abstract
BackgroundThe hetero-glycopeptide intermediate staphylococci is considered to be the precursor of glycopeptide intermediate staphylococci especially vancomycin intermediate Staphylococcus aureus (VISA). For this purpose, we aimed to investigate the heterogeneous resistance to glycopeptide and their frequencies in 135 Staphylococcus strains.MethodsHeterogeneous resistance of Staphylococcus strains was detected by inoculating the strains onto Brain Heart Infusion agar supplemented with 4 mg/L of vancomycin (BHA-V4). Agar dilution method was used for determining MICs of glycopeptides and population analysis profile was performed for detecting frequency of heterogeneous resistance for the parents of selected strains on BHA-4.ResultsEight (6%) out of 135 Staphylococcus strains were exhibited heterogeneous resistance to at least one glycopeptide. One (1.2%) out of 81 S. aureus was found intermediate resistance to teicoplanin (MIC 16 mg/L). Other seven strains were Staphylococcus haemolyticus (13%) out of 54 coagulase negative staphylococci (CoNS). Six of the seven strains were detected heterogeneously reducing susceptibility to vancomycin (MICs ranged between 5–8 mg/L) and teicoplanin (MICs ranged between 32–64 mg/L), and one S. haemolyticus was found heterogeneous resistance to teicoplanin (MIC 32 mg/L). Frequencies of heterogeneous resistance were measured being one in 106 – 107 cfu/ml. MICs of vancomycin and teicoplanin for hetero-staphylococci were determined as 2–6 folds and 3–16 folds higher than their parents, respectively. These strains were isolated from six patients (7%) and two (4%) of health care wokers hands. Hetero-VISA strain was not detected.ConclusionHeterogeneous resistance to glycopeptide in CoNS strains was observed to be significantly more emergent than those of S. aureus strains (vancomycin P 0.001, teicoplanin, P 0.007). The increase MICs of glycopeptide resistance for subpopulations of staphylococci comparing with their parents could be an important clue for recognizing the early steps in the appearance of VISA strains. We suggested to screen clinical S. aureus and CoNS strains, systematically, for the presence of heterogeneously resistance to glycopeptide.
Highlights
The hetero-glycopeptide intermediate staphylococci is considered to be the precursor of glycopeptide intermediate staphylococci especially vancomycin intermediate Staphylococcus aureus (VISA)
Two of these strains were found as being methicillin susceptible S. aureus (MSSA, 4502 and 4503) and other seven strains were found as being methicillin resistant coagulase negative staphylococci (CoNS) (MRCoNS)
MICs of vancomycin and teicoplanin of strains grew on Brain Heart Infusion agar (BHA)-V4 MICs of vancomycin and teicoplanin for the parents of subclones were as follows: for each of 4502 and 4503 strains were found being susceptible (1 mg/L), for seven MRCoNS strains were found susceptible to vancomycin and ranged between 1–4 mg/L
Summary
The hetero-glycopeptide intermediate staphylococci is considered to be the precursor of glycopeptide intermediate staphylococci especially vancomycin intermediate Staphylococcus aureus (VISA). For this purpose, we aimed to investigate the heterogeneous resistance to glycopeptide and their frequencies in 135 Staphylococcus strains. Since the first report published from Japan in 1997 on vancomycin-intermediate (MIC 8–16 mg/L) Staphylococcus aureus (VISA)[1] and studies from different countries, suggested that the emergence of glycopeptide resistance among staphylococci is a global issue [2]. The second type is heterogeneous resistance, which was described firstly by Hiramatsu et al [1] from Japan in 1997, and it is represented with strain Mu3 (hetero-VISA). Mu3 strain has been isolated from an old man with pneumonia who did not give any response to vancomycin therapy, MIC of Mu3 was 4 mg/L it has been containing a mutant subpopulation of cells having intermediate resistance to vancomycin (MIC 8 mg/L)
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