Antimicrobial resistance in clinical patterns of Pseudomonas aeruginosa                

M. M. CASAL, M. CAUSSE, F. RODRÍGUEZ-LÓPEZ, M. CASAL                              

 

Pseudomonas aeruginosa is an opportunistic microorganism that is frequently the cause of nosocomial infections. Multiple mechanisms are involved in its natural and acquired resistance to many of the antimicrobial agents commonly used in clinical practice. We performed an antibiotic resistance study on P. aeruginosa isolated from intrahospitalary and extrahospitalary samples between 2005 and 2010 years. We included in the study a global amount of 3,029 P. aeruginosa isolates from clinical samples received at University Hospital Reina Sofia. Microbiology Service in Córdoba (Spain). Semiautomatic system WIDER I for strains identification and sensibility testing was employed. We considered susceptibility and resistance criteria recommended by MENSURA group. Results of the analysis showed that P. aeruginosa maintanied similar levels of antimicrobial susceptibility during the period 2005-2010, with increased susceptibility to amikacin, gentamicin and cefalosporins. Therewere also important differences in the degree of susceptibility between intrahospital and extrahospital strains during 2010 year, except for tobramicin and fosfomycin. The intrahospital difference in susceptibility was also evaluated, emphasizing the importance of periodically surveillance of susceptibility and resistance patterns of P. aeruginosa, in each setting in order to evaluate different therapeutic guidelines, because it is not always advisable to extrapolate data from different
regions. 

 
Rev Esp Quimioter 2012:25(1):37-41 [pdf]

Changes in the antimicrobial susceptibility of Escherichia coli isolates from community diagnosed urinary tract infections during the period 2003-2007. Multicentre study in Castilla la Mancha (Spain)

D. TENA, A. GONZÁLEZ-PRAETORIUS, J. C. GONZÁLEZ, E. HEREDERO, S. ILLESCAS, C. SAINZ DE BARANDA, G. SESEÑA

 

Objective: To know the evolution of susceptibility patterns of Escherichia coli in patients with communitydiagnosed urinary tract infections (UTIs) during last years in Castilla la Mancha (Spain).
Methods: Descriptive and retrospective study performed between january 2003 and december 2007. We studied data about frequency and susceptibility of 33.651 E. coli isolates from urine cultures that were remited from primary care centres depending of 6 hospitals in Castilla la Mancha (Spain).
Results: Susceptibility rates of E. coli for most antibiotics decreased significantly during the 5-year period, especially for amoxicillin-clavulanic acid, cefuroxime and quinolones. Average rates of susceptibility for amoxicillin- clavulanic acid, ciprofloxacin, cefuroxime, fosfomycin and nitrofurantoin were: 86,7, 75,4, 87,3, 97,6 and 96,2%, respectively. We observed a significantly increase of E. coli isolates producing extended-spectrum betalactamases (ESBLs), from 1,9% in 2003 to 4,9% in 2007 (χ2 TL = 143,6, p<0,001).
Conclusions: We observed a significantly reduction of E. coli susceptibility for most antibiotics and an increase of E. coli isolates producing ESBLs. Fosfomycin and nitrofurantoin are the best choices for empiric treatment. Prospective studies should be performed in the future to confirm the results of our study.

 
Rev Esp Quimioter 2010:23(1):36-42 [pdf]

Activity of vancomycin, ciprofloxacin, daptomycin, and linezolid against coagulase-negative staphylococci bacteremia   

M. FAJARDO, R. HIDALGO, S. RODRÍGUEZ, F. F. RODRÍGUEZ-VIDIGAL, A. VERA, M. ROBLES       

 

Objective. Multiresistant coagulase-negative staphylococci (CNS) infections are mainly increased in hospitalized patients. We have studied the activity of vancomycin, ciprofloxacin, daptomycin and linezolid in methicillin-resistant CNS strains, isolated from true blood cultures.
Methods. We collected 87 strains of different CNS species from positive blood cultures. Staphylococci were identified by MicroScan Walkaway (Dade Behring, Siemens) and with the Api ID 32 Staph (BioMerieux, France). The susceptibility to oxacillin, vancomycin and ciprofloxacin was performed by automatic microdilution plate as cited above. The susceptibility to daptomycin and linezolid was performed by Etest (AB BioMerieux, Solna, Sweden). Interpretative criteria were done following the CLSI guidelines.
Results. Eighty-seven CNS strains were studied: 55 (63%) were S. epidermidis, 15 (17%) S. haemolyticus, 10 (12%) S. hominis, and 7 (8%) other species. Fifty-three (61%) strains showed loss of susceptibility to vancomycin, MIC = 2 mg/L. Ciprofloxacin resistance, MIC > 2 mg/L, was observed in 56 (64%) strains. Daptomycin resistance was not observed, with a susceptibility range between 0.032-1 mg/L and modal value of 0.25 mg/L. Ten strains (11.5%) resistant to linezolid were observed. Nine patients were in ICU, where the average length of stay was 38 days (range 16-58 days) and one belonged to Hepato-Pancreatic Surgery, where he stayed for 64 days.
Conclusions. Low susceptibility to vancomycin is frecuent in the CNS strains studied in our hospital. Daptomycin shows a high efficacy against CNS, and it could be useful for the treatment of primary bacteremia or catheter associated bacteremia. The massive and continuous use of linezolid has led to the appearance of resistance. 

 
Rev Esp Quimioter 2011:24(2):74-78 [pdf]

Phenotypes and mechanisms of resistance to macrolides and lincosamides in Streptococcus agalactiae isolates with clinical significance in an eight-year period (2002-2010)                

F. ARTILES, A. CAÑAS, I. ÁLAMO, B. LAFARGA                               

 

Introduction. Streptococcus agalactiae is the most prevalent agent of invasive disease in the newborn (sepsis, pneumonia, and meningitis), as well as an important cause of puerperal fever, urinary tract infection and surgical site infection. The aim of our study was to know the evolution of macrolide and lincosamide resistance in this microorganism.
Methods. Resistance phenotypes were established according to the erythromycin-clindamycin induction test: M (efflux pump) or MLS_B (methylase). Genetic mechanisms were detected by PCR for the following genes: ermB, ermA, ermTR, and mefA/E. Molecular typing was based on chromosomal DNA macrorestriction and detection of fragments using pulsed-field gel electrophoresis.
Results. During 8 years, 300 isolates of S. agalactiae were recovered. Seventy-eight (26%) were resistant to macrolides, and seventy (23%) were resistant to lincosamides. Constitutive MLS_B was observed in 21% of the isolates (all but one carrying the ermB gene), with a erythromycin MIC₉₀ ≥ 256 mg/L. Inducible MLS_B was observed in 2.3% of the isolates (all carrying the ermTR gene), with a MIC₉₀ of 6 mg/L. M phenotype was observed in 2.7% of the isolates (all carrying the mefA/E gene), with a MIC₉₀ of 6 mg/L. Molecular typing revealed the presence of two major clones (A and B) comprising 56.6% of the isolates. Most of the isolates (90.5%) belonging to clon A carried the ermB gene.
Conclusions. Macrolide resistance in our area is similar to that observed in the rest of Spain, but there has been no increase in the incidence rate along the study period. 

 
Rev Esp Quimioter 2012:25(1):42-46 [pdf]

Evaluation of pharmacodynamic target attainment with vancomycin treatment of bacteremia due to Staphylococcus aureus methicillin resistant

J. A. LEPE, M. V. GIL-NAVARRO, M. D. SANTOS-RUBIO, J. BAUTISTA, J. AZNAR

 

Objective: The objective of the study is to evaluate the ability of standard vancomycin dosing strategies actually recommended to attain the pharmacodynamic target of an area under the curve of vancomycin serum concentration versus time from 0 to 24 hours (AUC24h) to minimum inhibitory concentration (MIC) ratio greater than 400:1 for patients with a suspected or documented methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia by individual analysis and Monte Carlo simulation.
Material and methods: The study included all patients admitted with suspected or proven MRSA infection during the years 2007-2008, and who were initially treated with vancomycin at a dose of 30 mg/kg/day, and underwent pharmacokinetic monitoring. The area under the curve of vancomycin serum concentration versus time from 0 to 24 hours (AUC24h) was calculated as daily dose/clearance total (D24h/CL). Additionally, we studied 45 isolates of MRSA obtained from blood cultures in the period 2007-2008. The MIC to vancomycin was determined using Epsilon-test®. The PK-PD parameter calculated was AUC24h/MIC. Microsoft
Excel was used to perform a 10.000 subject Monte Carlo simulation. An AUC24h/MIC ≥ 400 was assumed as the target attainment.
Results: In the individual study, the percentage of patients with AUC24h/MIC50/90 ≥ 400 was 50%. The probability (%) of attaining AUC24h/MIC ratio values ≥ 400 by Monte Carlo simulation was of 66%. The vancomycin MIC value from which the scenario would have to wait a suboptimal treatment (target <90%) was >1 mg/L.
Discussion: This study shows that in the population studied to achieve a vancomycin AUC24h/MIC ≥ 400 is not always attained with the standard dose. Therefore, one would expect a high probability of suboptimal vancomycin AUC24h/MIC ratios for patients infected with organisms with vancomycin MICs of >1 mg/L treated with doses of 30 mg/kg/day.

 
Rev Esp Quimioter 2010:23(1):43-47 [pdf]