Prevalence of antibiotic resistance in multi-drug resistant coagulase-negative staphylococci isolated from invasive infection in very low birth weight neonates in two Polish NICUs.

BACKGROUND: Multi-drug resistant coagulaso-negative staphylococci (CNS) have become an increasing problem in nosocomial infections connected with the presence of medical devices. The paper aimed to analyze the prevalence of antibiotic resistance in CNS isolated from invasive infection in very low birth weight (VLBW) neonates. METHODS: Continuous prospective target surveillance of infections was conducted in 2009 at two Polish NICUs that participated in the Polish Neonatology Surveillance Network (PNSN). The study covered 386 neonates with VLBW (≤1500 g), among which 262 cases of invasive infection were detected with predominance of CNS (123; 47%). Altogether, 100 CNS strains were analyzed. The resistance phenotypes were determined according to EUCAST. Resistance genes: mecA, ermA, ermB, ermC, msrA, aac(6')/aph(2''), ant(4')-Ia and aph(3')-IIIa were detected using multiplex PCR. RESULTS: The most common species was S. epidermidis (63%), then S. haemolyticus (28%) and other CNS (9%). Among S. epidermidis, 98% of isolates were resistant to methicillin, 90% to erythromycin, 39% to clindamycin, 95% to gentamicin, 60% to amikacin, 36% to ofloxacin, 2% to tigecycline, 3% to linezolid and 13% to teicoplanin. Among S. haemolyticus isolates, 100% were resistant to methicillin, erythromycin and gentamicin, 18% to clindamycin, 50% to amikacin, 86% to ofloxacin, 14% to tigecycline and 4% to teicoplanin. No resistance to linezolid was detected for S. haemolyticus isolates. Moreover, all isolates of S. epidermidis and S. haemolyticus were susceptible to vancomycin. The mecA gene was detected in 98% of S. epidermidis isolates and all of S. haemolyticus ones. Among macrolide resistance isolates, the ermC was most common in S. epidermidis (60%) while msrA was prevalent in S. haemolyticus (93%). The ermC gene was indicated in all isolates with cMLSB, whereas mrsA was found in isolates with MSB phenotype. Of the aminoglycoside resistance genes, aac(6')/aph(2'') were present alone in 83% of S. epidermidis, whereas aac(6')/aph(2'') with aph(3')-IIIa were predominant in 84% of S. haemolyticus. CONCLUSIONS: Knowing the epidemiology and antibiotic resistance of CNS isolated from invasive infection in VLBW neonates is a key step in developing targeted prevention strategies and reducing antibiotic consumption.

[Phenotypic evaluation of hydrophobicity and the ability to produce biofilm in coagulase-negative staphylococci isolated from infected very-low-birthweight newborns]. / Fenotypowa ocena hydrofobowosci powierzchni oraz zdolnosci do tworzenia biofilmu przez gronkowce koagulazo-ujemne izolowane z zakazen od noworodków z bardzo mala masa urodzeniowa.

INTRODUCTION: Coagulase-negative staphylococci (CNS), particularly Staphylococcus epidermidis and Staphylococcus haemolyticus, are the leading cause of infection among infants with very low birth weight (<1500 g). The most important virulence factor of these pathogens is their ability to form biofilm. The aim of this study was to evaluate the surface properties, the ability to produce slime and biofilm formation of S. epidermidis and S. haemolyticus strains isolated from infections in very low birth weight neonates. METHODS: Isolates ofS. epidermidis (n=60) and S. haemolyticus (n=38) were obtained from neonates, hospitalized in two neonatal intensive care units in Poland. Cell surface hydrophobicity was determined by autoagglutination test (AA) in 0.9% NaCl and salt aggregation test (SAT) in ammonium sulphate solution. In order to determine the ability to produce slime, Christiensen's tube test with safranin staining and Congo Red Agar (CRA) test were carried out. The quantitative assessment of biofilm production was determined by crystal violet (CV) assay. RESULTS: Based on the AA test, it was demonstrated that almost all S. epidermidis and S. haemolyticus isolates showed no agglutination in sodium chloride saline. The SAT test indicated that the greatest number ofS. epidermidis isolates aggregated in concentration of 2 M, whereas, for S. haemolyticus, it was 0.5 M. In the Christiensen's method, the largest amount of the S. epidermidis isolates produced a small amount of slime (40%), whereas 68% of the S. haemolyticus isolates produced a large amount of slime. In CRA test, in both species, the most common result was the bacterial culture colour being almost black, which corresponds to low production of biofilm. Quantitative assessment of biofilm production in CV assay revealed that while 97% of the S. heamolyticus isolates produced high levels of biofilm, similar results were observed in only 43% of the S. epidermidis isolates. CONCLUSIONS: Based on the results obtained by phenotypic methods, it was demonstrated that the S. haemolyticus isolates showed a statistically significant stronger ability to produce mucus and form biofilm than the isolates ofS. epidermidis.