Reliability of the MicroScan WalkAway PC21 panel in identifying and detecting oxacillin resistance in clinical coagulase-negative staphylococci strains

Current status of the distribution and antimicrobial resistance of Staphylococcus felis isolates from feline patients in Japan

We investigated the distribution and antimicrobial resistance of 120 Staphylococcus felis isolates from feline patients in Japan, mainly from the urinary tract (28.3%), abscesses (23.3%), ears (22.5%), and nasal cavity (10.8%). The distribution of S. felis differed from those of previous studies in Japan and other countries. Antimicrobial susceptibility testing revealed a relatively high resistance to penicillin (PEN, 33.3%), followed by erythromycin (ERY, 15.8%), clindamycin (CLI, 13.3%), and levofloxacin (5.0%). However, oxacillin resistance was not detected. Notably, 11/120 (9.2%)S. felis isolates exhibited multidrug resistance, i.e., resistance to more than three classes of drugs, which mainly consisted of PEN-ERY-CLI resistance phenotypes. This is the first investigation on antimicrobial-resistant S. felis isolates from feline patients in Japan.

Identification of coagulase-negative Staphylococcus saprophyticus by polymerase chain reaction based on the heat-shock repressor encoding hrcA gene

Staphylococcus saprophyticus is an uropathogen belonging to the human microbiota and is responsible for community-acquired infections of the urinary tract. Identification of Staphylococcus species by biochemical tests is laborious and costly when compared to routine laboratory tests. Because of their high sensitivity and specificity, molecular methods are better suited for accurate identification of Staphylococcusspp. Therefore, the goal of this work was to standardize a polymerase chain reaction (PCR) protocol using species-specific primers, based on the heat-shock repressor coding hrcA gene, for the identification of S.saprophyticus. A total of 142 S. saprophyticus strains were obtained from different sources, including clinical, environmental, and foodborne strains. We also included 98 strains of Staphylococcus spp. to further validate the proposed method. Reliable results for the detection of S. saprophyticus isolates were obtained for 100% of the strains evaluated. The results were in accordance with matrix-assisted laser desorption ionization-time of flight mass spectrometry identification, thus highlighting the applicability of species-specific PCR for the molecular identification of S. saprophyticus.

Usefulness of Multiplex Real-Time PCR for Simultaneous Pathogen Detection and Resistance Profiling of Staphylococcal Bacteremia

Staphylococci are the leading cause of nosocomial blood stream infections. Fast and accurate identification of staphylococci and confirmation of their methicillin resistance are crucial for immediate treatment with effective antibiotics. A multiplex real-time PCR assay that targets mecA, femA specific for S. aureus, femA specific for S. epidermidis, 16S rRNA for universal bacteria, and 16S rRNA specific for staphylococci was developed and evaluated with 290 clinical blood culture samples containing Gram-positive cocci in clusters (GPCC). For the 262 blood cultures identified to the species level with the MicroScan WalkAway system (Siemens Healthcare Diagnostics, USA), the direct real-time PCR assay of positive blood cultures showed very good agreement for the categorization of staphylococci into methicillin-resistant S. aureus (MRSA), methicillin-susceptible S. aureus (MSSA), methicillin-resistant S. epidermidis (MRSE), methicillin-susceptible S. epidermidis (MSSE), methicillin-resistant non-S. epidermidis CoNS (MRCoNS), and methicillin-susceptible non-S. epidermidis CoNS (MSCoNS) (κ = 0.9313). The direct multiplex real-time PCR assay of positive blood cultures containing GPCC can provide essential information at the critical point of infection with a turnaround time of no more than 4 h. Further studies should evaluate the clinical outcome of using this rapid real-time PCR assay in glycopeptide antibiotic therapy in clinical settings.

Coagulase-negative staphylococci

The definition of the heterogeneous group of coagulase-negative staphylococci (CoNS) is still based on diagnostic procedures that fulfill the clinical need to differentiate between Staphylococcus aureus and those staphylococci classified historically as being less or nonpathogenic. Due to patient- and procedure-related changes, CoNS now represent one of the major nosocomial pathogens, with S. epidermidis and S. haemolyticus being the most significant species. They account substantially for foreign body-related infections and infections in preterm newborns. While S. saprophyticus has been associated with acute urethritis, S. lugdunensis has a unique status, in some aspects resembling S. aureus in causing infectious endocarditis. In addition to CoNS found as food-associated saprophytes, many other CoNS species colonize the skin and mucous membranes of humans and animals and are less frequently involved in clinically manifested infections. This blurred gradation in terms of pathogenicity is reflected by species- and strain-specific virulence factors and the development of different host-defending strategies. Clearly, CoNS possess fewer virulence properties than S. aureus, with a respectively different disease spectrum. In this regard, host susceptibility is much more important. Therapeutically, CoNS are challenging due to the large proportion of methicillin-resistant strains and increasing numbers of isolates with less susceptibility to glycopeptides.

Clinical significance of methicillin-resistant coagulase-negative staphylococci obtained from sterile specimens

Distinguishing true coagulase-negative staphylococci bacteremia from contamination remains a challenge. We conducted a retrospective analysis of 183 patients with methicillin-resistant coagulase-negative staphylococci (MR-CoNS)-positive and methicillin-resistant Staphylococcus aureus-positive cultures obtained from sterile sites such as blood, synovial fluid, ascitic fluid, and cerebrospinal fluid. Of the 209 MR-CoNS isolates, 83 (39.7%) were considered infection associated, and 126 (60.3%) were considered contamination. MR-CoNS isolates cultured from synovial fluid were more likely to be infection associated (P = 0.009). The median interval from insertion of a central venous catheter to onset of infection tended to be longer in MR-CoNS infection cases than in methicillin-resistant S. aureus infection cases (41 days versus 14 days, P = 0.055). In conclusion, our results suggest that the proportion of cases of true MR-CoNS infection may be higher than previously reported.