A Coagulase- and α-Glucosidase-Negative Variant of Staphylococcus aureus: a Challenge for Routine Microbiological Diagnostics

Abstract

Staphylococcus aureus can cause serious infections, toxinoses, and life-threatening illnesses. Staphylocoagulase production represents the major criterion for the detection of S. aureus isolates. As coagulase-deficient clinical isolates of S. aureus have been described, additional use of chromogenic media in S. aureus detection was postulated to represent a highly specific (97%) and sensitive (99% after 48 h) tool in the identification of the organism (1,3,4,7,8,10). In this study, we further investigated the genotypic and phenotypic characteristics of a coagulase-and ␣-glucosidase-deficient variant of S. aureus obtained from bovine mastitis milk.Strain MSSA_129 (methicillin-susceptible S. aureus) was identified as S. aureus by species-specific PCR, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) (99.90% identification), and DNA microarray and could be assigned to spa type t543, clonal complex CC479, agr type II, and capsule type 8. It exhibited alpha, beta, and delta hemolysis and was slightly yellow pigmented. Staphaureux (Thermo Fisher Scientific, Wohlen, Switzerland), DNase, and egg yolk test yielded positive results. Still, no opaque zone was visible on rabbit plasma fibrinogen (RPF) agar (Oxoid, Cambridge, United Kingdom) ( Fig. 1). On S. aureus ID agar (SAID; bioMérieux, La Balme les Grottes, France), bright yellow colonies instead of the characteristic green colonies were formed (Fig. 2). DNA microarray detected neither antibiotic resistance determinants nor genes involved in toxic shock and staphylococcal scalded-skin syndrome. While the classical enterotoxin genes (sea, seb, sec, sed, and see) were not detected, the strain exhibited the egc cluster carrying genes encoding newly described staphylococcal enterotoxins and staphylococcal enterotoxin-like superantigens.Determination of the nucleotide sequence of coa revealed a deletion at nucleotide position 653 within the D2 region of the gene, leading to a frameshift. Although coa is known to represent a highly polymorphic region, it can be divided into six common regions: the signal sequence, the D1 and D2 regions enabling contact with prothrombin, the central region, a repeat region, and the C-terminal sequence (5, 9, 11, 12). The frameshift detected results in the reading of a premature stop codon at amino acid position 224, thus rendering the polypeptide abnormally short and most likely not functional.The ␣-glucosidase gene of MSSA_129 and its upstream region were compared to sequences available at GenBank. Although no strain possesses an ␣-glucosidase gene exactly identical over its full length to the one found in MSSA_129, no unique amino acid changes were found. However, variability of amino acid sequences on 12 positions (position 43, 83, 88, 133, 439, 448, 454, 462, 492, 514, 519, and 539) within the available sequences was noticed. Considering the amino acids found at these positions, strain MSSA_129 showed a unique combination. Directly upstream of the ␣-glucosidase gene (malA), we identified a sequence...

Surveillance of antimicrobial resistance of maltose negative Staphylococcus aureus in South African dairy herds

“…A study in the Netherlands has also isolated a maltose negative strain of S. aureus [12]. However the strain found in the Netherlands [12] was different to that investigated in this study in South Africa. In addition to the previous study [17] which attempted to characterise this emerging pathogen, a further evaluation was carried out of the resistance trends evident in historic disk diffusion susceptibility data and more recent MIC data.…”

Surveillance of antimicrobial resistance of maltose negative Staphylococcus aureus in South African dairy herds

“…There is little information known about maltose negative S. aureus from dairy cows. A study in the Netherlands has also isolated a maltose negative strain of S. aureus [12]. However the strain found in the Netherlands [12] was different to that investigated in this study in South Africa.…”

Surveillance of Antibiotic Resistance of Maltose-Negative Staphylococcus aureus in South African Dairy Herds

“…Most of these studies were conducted on traditionally identified coagulase-positive, maltose-positive S. aureus. Although a coagulase-positive, maltose-negative S. aureus strain was subsequently isolated from bovine mastitis [ 12 ], no antibiotic susceptibility profiles of this organism were present. MALDI-TOF MS and 16S r RNA sequence analysis [ 10 ] identified the maltose-negative S. aureus ST 2992 isolated from milk samples in South Africa.…”

“…Inadequate informing concerning maltose-negative S. aureus from dairy cows also exists. A study in the Netherlands also isolated a maltose-negative strain of S. aureus [ 12 ]. The strain established in the Netherlands [ 12 ] differed from that investigated in this study in South Africa.…”

“…A study in the Netherlands also isolated a maltose-negative strain of S. aureus [ 12 ]. The strain established in the Netherlands [ 12 ] differed from that investigated in this study in South Africa. In addition to the previous study [ 10 ], attempting to characterise this emerging pathogen, a further evaluation was conducted from the resistance trends, evident in historic disk diffusion susceptibility data, and more recent MIC data, the results of which are presented in this study.…”