Bacteremia due to Pseudomonas aeruginosa: results from a 3-year national study in the Slovak Republic

Risk factors, mortality and antimicrobial susceptibility of Pseudomonas aeruginosa bacteremias isolated from 148 patients from all University Hospitals in Slovakia were analyzed. Only 1.2% of 169 strains of P. aeruginosa were resistant to meropenem, 4.1% to piperacillin/tazobactam, 7.7% to ceftazidime as well as cefepime and 12% to amikacin. More than 30% of P. aeruginosa were resistant to ciprofloxacin. Our analysis of risk factors for antimicrobial resistance to the particular antimicrobials, indicated no difference in risk factors and outcome in cases infected with P. aeruginosa bacteremias resistant to amikacin, piperacillin/tazobactam or ceftazidime in comparison to episodes caused by P. aeruginosa due to susceptible isolates. When comparing risk factors for P. aeruginosa bacteremia in children vs. adults, cancer vs. non-cancer patients, several differences in risk factors were observed. Neither antimicrobial resistance to amikacin, ceftazidime or piperacillin/tazobactam, nor appropriateness of therapy according to two separate analyses were associated with better outcome.     

In Vitro Activity of Meropenem against Ciprofloxacin-Resistant Enterobacteriaceae and Pseudomonas aeruginosa

Abstract

The in-vitro susceptibilities of a total of 174 ciprofloxacin-resistant Enterobacteriaceae and Pseudomonas aeruginosa were determined. According to the BSAC and NCCLS breakpoints, meropenem, aztreonam, ceftibuten, ceftazidime, imipenem and cefotaxime were the most active (>90%) antimicrobial agents tested against Enterobacteriaceae. Susceptibility of these strains to piperacillin/tazobactam, cefpodoxime and cefixime (84.96%) was higher than that to tobramycin, gentamicin and fosfomycin (50-75%). More than 90% of P. aeruginosa were susceptible to meropenem when both interpretative susceptibility breakpoint criteria were used. Piperacillin, piperacillin/tazobactam and ceftazidime were active against 50-75% of the same strains. Meropenem was the most active antimicrobial tested against all ciprofloxacin-resistant clinical isolates assayed.     

Widespread detection of VEB-1-type extended-spectrum beta-lactamases among nosocomial ceftazidime-resistant Pseudomonas aeruginosa isolates in Sofia, Bulgaria

A total of 132 ceftazidime-resistant clinical isolates of Pseudomonas aeruginosa were collected during 2001-2005 from 5 university hospitals in Sofia, Bulgaria to assess the current levels of antimicrobial susceptibility and to evaluate resistance mechanisms to beta-lactams. Antimicrobial susceptibilities were detected by a disk diffusion method and E-test. Polymerase chain reaction amplification and sequencing of bla(VEB-1 )and bla(PER-1 )were performed. The antibiotic resistance rates were: to piperacillin 90.2%, piperacillin/tazobactam 52.3%, ceftazidime 94.7%, cefepime 88.6%, cefpirome 98.5%, aztreonam 85.6%, imipenem 66.6%, meropenem 63.6%, amikacin 81.1%, gentamicin 84.8%, tobramycin 89.4%, netilmicin 57.6%, ciprofloxacin 83.4%. Structural genes for VEB-1 extended-spectrum beta -lactamases (ESBLs) were found in 75 (56.8%) of the isolates. PER-1 ESBLs were not detected. The VEB-1-producing strains were more resistant than VEB-1 non-producers to amikacin, gentamicin, tobramycin and ciprofloxacin ( P<0.001). VEB-1 appears to have a significant presence among ceftazidime-resistant P. aeruginosa isolates from Sofia.     

Comparative antimicrobial potency of meropenem tested against Gram-negative bacilli: report from the MYSTIC surveillance program in the United States (2004)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program is a longitudinal resistance surveillance network of more than 100 medical centers worldwide monitoring the susceptibility of bacterial pathogens to carbapenems and other broad-spectrum agents. In 2004 (year six), the antimicrobial activity of 12 broad-spectrum agents was assessed against 2,799 Gram-negative bacterial isolates submitted from 15 United States (USA) medical centers using Clinical and Laboratory Standards Institute (CLSI; formerly NCCLS) recommended methods. Meropenem continued to demonstrate a high potency with MIC90 values 4- to 32-fold lower than imipenem against the Enterobacteriaceae. The wide spectrum of activity for meropenem against all Gram-negative isolates was demonstrated by the overall rank order of percentage susceptibility at CLSI breakpoints: amikacin (96.5%) > meropenem (96.0%) > imipenem (95.8%) > piperacillin/tazobactam (91.5%) > tobramycin (91.4%) > cefepime (91.2%) > ceftazidime (89.0%) > gentamicin (88.0%) > aztreonam (81.5%) > levofloxacin (80.5%) > ciprofloxacin (80.2%) > ceftriaxone (69.1%). Only the aminoglycosides (84.5%) and carbapenems (76.1-83.8%) exhibited acceptable levels of susceptibility against the Acinetobacter spp. isolates as this species group became more resistant to all antimicrobial classes. A continued increase in the resistance rate for both ciprofloxacin and levofloxacin over the six years was observed, most alarming among Escherichia coli (20.2-20.7%) and indole-positive Proteus species (34.4-42.2%) isolates, some documented as clonal. Continued surveillance of these broad-spectrum antimicrobial agents appears warranted to monitor the potency and spectrum of activity against Gram-negative pathogens causing serious infections and the emergence of new or novel resistance mechanisms that could compromise carbapenem therapy.     

Antimicrobial use and resistance among Gram-negative bacilli in an Italian intensive care unit (ICU)

Gram-negative bacilli antimicrobial resistance remains a significant problem for patients in the intensive care unit (ICU). We performed a retrospective analysis of microbiological data and antibiotic consumption over a 4-year period (2000-2003) in an Italian ICU. Pseudomonas aeruginosa and Klebsiella pneumoniae represented approximately 40% of all isolates. The most significant trend in antimicrobial use was an increase in use of 3(rd )generation cephalosporins, imipenem, and ciprofloxacin. A significant trend toward an increase in resistance rates to piperacillin, 3( rd )generation cephalosporins and ciprofloxacin was observed for K. pneumoniae and a positive correlation between resistance and drug-usage was evident for K. pneumoniae and piperacillin, cefotaxime, ceftazidime, cefepime, and ciprofloxacin, but not for piperacillin/tazobactam. No statistically significant correlations were evidenced for P. aeruginosa. Trends in resistances were studied also for Serratia spp and Proteus spp. Isolation rates of extended-spectrum beta-lactamase (ESBL)-producing strains in pathogens studied were high, especially for K. pneumoniae (72%, 160/222) and Proteus spp (41%, 18/43). In conclusion, the study showed high resistance among Gram-negative organisms isolated in the ICU and significant ESBL production. A significant correlation between antibiotic consumption and increasing resistance was evident for K. pneumoniae.     

Bacteremia Due to Pseudomonas aeruginosa: Results from a 3-Year National Study in the Slovak Republic

Abstract

Risk factors, mortality and antimicrobial susceptibility of Pseudomonas aeruginosa bacteremias isolated from 148 patients from all University Hospitals in Slovakia were analyzed. Only 1.2% of 169 strains of P. aeruginosa were resistant to meropenem, 4.1% to piperacillin/tazobactam, 7.7% to ceftazidime as well as cefepime and 12% to amikacin. More than 30% of P. aeruginosa were resistant to ciprofloxacin.

Our analysis of risk factors for antimicrobial resistance to the particular antimicrobials, indicated no difference in risk factors and outcome in cases infected with P. aeruginosa bacteremias resistant to amikacin, piperacillin/tazobactam or ceftazidime in comparison to episodes caused by P. aeruginosa due to susceptible isolates. When comparing risk factors for P. aeruginosa bacteremia in children vs. adults, cancer vs. non-cancer patients, several differences in risk factors were observed.

Neither antimicrobial resistance to amikacin, ceftazidime or piperacillin/tazobactam, nor appropriateness of therapy according to two separate analyses were associated with better outcome.     

Resistance surveillance in Italy: four-year results from the MYSTIC program

The MYSTIC program is an international, multicenter surveillance study that compares the activity of meropenem, in centers that are prescribers, with that of imipenem, ceftazidime, piperacillin/tazobactam, ciprofloxacin and gentamicin. These Italian data are from 3 centers (neutropenia, cystic fibrosis and intensive care units). A total of 2,072 (238 Gram-positive and 1,834 Gram-negative) aerobic microorganisms were collected during the study. Pseudomonas aeruginosa (33.4%) was the most isolated species followed by Escherichia coli (14.4%). All except one Enterobacteriaceae strain isolated were fully susceptible to meropenem. Moreover, the activity of meropenem against Enterobacteriaceae was about eight-fold greater than that of imipenem and four- to eight-fold more active than that of ceftazidime. Meropenem was highly active against non-fermentative Gram-negative microorganisms, exceeding the activity of most of the other antimicrobial agents tested. Moreover, meropenem showed increasing activity during the 4 years of study (starting from 86.2% in 1997 to 94.0% in 2000). In conclusion, our results indicate that meropenem has excellent potency and spectrum of activity despite being prescribed for the treatment of seriously ill patients, and appears to be a reliable option for the initial empirical treatment of serious nosocomial infections.     

Gram-Negative Non-Fermenting Bacteria from Food-Producing Animals are Low Risk for Hospital-Acquired Infections

Abstract

The aim of this study was to investigate possible indications of epidemiological relationships between Pseudomonas aeruginosa and Acinetobacter baumannii isolated from food-producing animals and those of clinical origin. Screening for P. aeruginosa and A. baumannii isolates from food-producing animals was carried out on 1381 samples. usceptibility testing and PCR amplification of resistance genes were determined. Isolate clonal relatedness was established by PFGE. Forty-one P. aeruginosa and 16 A. baumannii were detected. All P. aeruginosa isolates were sensitive to ciprofloxacin, ceftazidime and piperacillin/tazobactam and seven isolates had low-level imipenem resistance. All A. baumannii isolates were sensitive to imipenem, meropenem, ciprofloxacin and piperacillin/tazobactam but were resistant to ceftazidime. The imipenem-resistant P. aeruginosa and ceftazidime-resistant A. baumannii had different PFGE patterns compared to those of human origin. Based on the findings presented here, animal isolates were not multidrug resistant and they do belong to a different pool from those of humans.     

Susceptibility of bacterial isolates from Turkey--a report from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program

The study monitored the susceptibility of nosocomial pathogens to meropenem and comparator antimicrobial agents isolated as part of the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program from Turkish university hospitals. In terms of minimum inhibitory concentration 90% (MIC(90)) values, meropenem was two- and eight-fold more active than imipenem against Escherichia coli and Klebsiella pneumoniae, respectively. 40.5% of K. pneumoniae, 23.1% of Klebsiella oxytoca and 15.3% of E. coli isolates were extended-spectrum beta-lactamase (ESBL) producers. Piperacillin/tazobactam was the most active agent against isolates of Pseudomonas aeruginosa, followed by meropenem and imipenem. Against Acinetobacter baumannii isolates, meropenem and imipenem were the most active agents. Continued surveillance by the MYSTIC Program appears to be prudent to help focus on effective empiric treatment regimens.     

Clonal spread of imipenem-resistant Pseudomonas aeruginosa in the intensive care unit of a Turkish hospital.

Pseudomonas aeruginosa may cause life-threatening infections, especially in nosocomial settings. Although carbapenems are considered as one of the most effective alternatives in antipseudomonal therapy, resistance to the carbapenem group of antibacterials is a growing problem. In the first 6 months of 1997, P. aeruginosa isolates that were resistant to almost all antipseudomonal agents including imipenem were recovered from various specimens from intensive, care unit (ICU) patients. Isolates with the same antibiogram profile caused a small outbreak in May 1997. A retrospective case-control study revealed that the major risk factors for infection/colonization with multiresistant P. aeruginosa were prolonged stay in the ICU (p<0.001), previous and lengthy imipenem usage (p<0.001 and p<0.0001, respectively), and mechanical ventilation (p<0.001). Analytical isoelectric focusing of the sonicates prepared from the isolates showed that each isolate produced 1-5 beta-lactamases, enzymes with isoelectric points (pIs) of 5.1, 6.4, 8.5-8.7 being the most prevalent. DNA macrorestriction patterns of imipenem-resistant isolates were distinct from those of the imipenem-sensitive isolates recovered from ICU patients during the same interval and from the environmental isolates (controls). Thus, our results indicate that colonized patients appear to be the major source for cross-contamination of other patients and if imipenem is selected for empirical therapy, emergence of resistant strains should be anticipated and appropriate precautions taken.     

An observational study on the epidemiology of respiratory tract bacterial pathogens and their susceptibility to four injectable beta-lactam antibiotics: piperacillin, piperacillin/tazobactam, ceftazidime and ceftriaxone

Bacterial infections of the respiratory tract account for a large proportion of total medical consultations in general practice. In recent years, antibiotic resistance has increased alarmingly in a number of bacterial species that are common causes of these infections. The aim of this observational study was to determine the antibiotic resistance of microbial agents isolated from patients with acute or acutely exacerbated respiratory infections. Subjects recruited as potential sources of bacteria were either outpatients seen in a number of specialized clinics and hospital practices, or hospitalized patients. Overall, 648 consecutive patients (67% male, mean age 48.1+/-27.0 years) with infection of the upper or lower respiratory tract were observed during a 13-month period. A total of 551 pathogenic microbial strains were isolated and tested for their in vitro susceptibility to piperacillin, piperacillin/tazobactam, ceftazidime, and ceftriaxone. Among all isolates, the four most frequent pathogens were Pseudomonas aeruginosa (132 isolates, 24%), Streptococcus pyogenes (99 isolates, 18%), Staphylococcus aureus (93 isolates, 17%), and Klebsiella pneumoniae (46 isolates, 8%). The susceptibility of gram-positive isolates ranged from 97.5% to 95.1%, and no remarkable difference was found in the antibacterial activity of tested b-lactam antibiotics. The susceptibility of gram-negative isolates to piperacillin and piperacillin/tazobactam was also similar: 96.5% and 97.1%, respectively. In contrast, differences were found between piperacillin (or piperacillin/tazobactam) and either ceftazidime (p=0.003) or ceftriaxone (p<0.0003) in gram-negative isolates. We conclude that, despite the extensive use of beta-lactam antibiotics (piperacillin, ceftazidime, and ceftriaxone) in medical practice during the past three decades, the susceptibility of the most common pathogens involved in the etiology of upper and lower respiratory tract infections to these antibiotics is still high. In particular, bacterial resistance developed by gram-positive organisms against piperacillin is negligible and not alarming.     

Emerging antimicrobial resistances among Proteus mirabilis in Europe: report from the MYSTIC Program (1997-2001). Meropenem Yearly Susceptibility Test Information Collection

Resistance patterns that are currently problematic in Europe can vary greatly within the same species over time, among various patient populations and among geographic regions on the same continent. The results from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program, which monitors carbapenem resistance rates in institutions using meropenem, were used to determine resistance differences among Proteus mirabilis. MIC results from 688 P. mirabilis strains were classified into 4 patient care groups: ICU (n=426), neutropenia patients (NP; n=145), general wards (n=97) and cystic fibrosis patients (CF; n=20). A total of 40 centers from 12 European countries have participated since 1997, divided into 3 geographic regions (East, North, South). All testing was performed by NCCLS reference methods and interpretive criteria, including screening of extended-spectrum beta-lactamase (ESBL) phenotypes. Over the monitored interval the resistance rates varied for each agent without a clear trend toward a greater rate. Rank order of susceptibility was: meropenem (99%) > piperacillin/tazobactam (TAZ; 96%) > cefepime (95%) > ceftazidime (CAZ; 94%) > imipenem (IPM; 92%). Ciprofloxacin (CIP) was the least active agent tested (MIC90 4 microg/ml; 86% susceptible). Unexpectedly, 3.6% of P. mirabilis were imipenem-resistant (MIC, > or = 16 microg/ml). Greater rates of resistance were found for strains from NP and CF patients, and from eastern or southern European sites, usually associated with epidemic clusters. Generally susceptible species such as P. mirabilis have recently emerged as therapeutic problems in European medical centers following mutations that compromise CIP, CAZ and aminoglycoside use. Imipenem also showed decreased susceptibility of greater than 7% compared to less than 1% for meropenem. Continued surveillance by the MYSTIC Program appears to be a prudent practice to focus effective empiric treatment regimens.     

A pharmacodynamic simulation to assess tigecycline efficacy for hospital-acquired pneumonia compared with other common intravenous antibiotics

A pharmacodynamic model was used to generate supportive data comparing tigecycline with other broad-spectrum agents against pathogens implicated in hospital-acquired pneumonia (HAP). A 5000 patient Monte Carlo simulation determined the probability of target attainment (PTA) of tigecycline (+/- ceftazidime) compared with imipenem, levofloxacin, and piperacillin/tazobactam (+/- vancomycin). PTA was calculated over MICs of current Gram-positive and Gram-negative bacteria collected from worldwide surveillance and weighted by the expected prevalence of these pathogens causing HAP. For monotherapy, the weighted PTA was imipenem (78.2%), piperacillin/tazobactam (73.3%), tigecycline (62.9%), and levofloxacin (62.5%). By pathogen PTA was greatest for tigecycline against Gram-positives, and ceftazidime or imipenem against Gram-negatives. Combination therapy increased PTA to 88.6%, 85.5%, 80.6%, and 69.8% for tigecycline, imipenem, piperacillin/tazobactam, and levofloxacin, respectively. Based on contemporary resistance data, tigecycline plus ceftazidime is predicted to achieve its pharmacodynamic targets similarly to combination therapy with imipenem plus vancomycin for the treatment of patients with HAP.     

Antimicrobial resistance in gram-negative isolates from European intensive care units: data from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) programme

Susceptibility data were collected for 6243 gram-negative isolates from 29 European ICUs participating in the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Programme (1997-2000). The most commonly isolated bacteria were Pseudomonas aeruginosa (22.5%), Escherichia coli (19.8%), Klebsiella pneumoniae (10.4%), and Enterobacter cloacae (7.7%). The incidence of extended-spectrum beta-lactamase-producers was higher in Turkish, Russian and Italian ICUs (27.9-39.6%) than in other countries (2.5-10.8%). The frequency of AmpC-cephalosporin hyper-producers was 16.8-55.4%. Meropenem was more active against Proteus mirabilis than imipenem (99.0% versus 88.8% susceptibility, respectively). Against Acinetobacter baumannii, meropenem (79.6% susceptible) and imipenem (82.2%) were more active than comparators (34.3-51.6%). Meropenem and imipenem exhibited good activity against P. aeruginosa (76.1% and 68.2%, respectively; but with inter-country variation). Ciprofloxacin resistance in E. coli and K. pneumoniae increased and needs close monitoring. Meropenem (98.2-99.8% susceptibility) and imipenem (88.8-99.4%) remained potent against important species of gram-negative bacteria from European ICUs actively using meropenem.     

Bacterial susceptibilities to piperacillin/tazobactam in a tertiary care hospital: 5-year review

Several factors influence the speed of development of antibacterial resistance, among which is the amount of antibiotic consumption. During the 3-year period 1998-2000, the consumption of piperacillin/tazobactam (pip/tazo) increased by 85% in our hospital. Five years ago we conducted a comparative in vitro study to evaluate susceptibilities of microorganisms to pip/tazo. The objective of the present study was to re-evaluate in vitro susceptibilities to pip/tazo, compared to other beta-lactams, and the potential impact its increased consumption might have on its susceptibility patterns. The study was performed between November 2000 and April 2001. As in 1996, of the beta-lactams studied, pip/tazo and imipenem had the highest susceptibility rates against selected pathogens (>90% susceptibility rates). P. aeruginosa susceptibilities to both imipenem and pip/tazo were high (97% for both). P. aeruginosa susceptibilities to cefepime were lower. Despite its increased use, pip/tazo retained its initially observed high susceptibility rates for the study pathogens.     

Antimicrobial Resistance in Gram-Negative Hospital Isolates: Results of the Turkish HITIT-2 Surveillance Study of 2007

Abstract

Resistance rates to amikacin, ciprofloxacin, ceftazidime, cefepime, imipenem, cefoperazone/sulbactam and piperacillin/tazobactam in Escherichia coli (n= 438)Klebsiella pneumoniae (n= 444)Pseudomonas aeruginosa (n= 210) and Acinetobacterbaumanni (n=200) were determined with e-test in a multicenter surveillance study (HITIT-2) in 2007. ESBL production in Escherichia coli and K. pneumoniae was investigated following the CLSI guidelines. Overall 42.0% of E.coli and 41.4% of K. pneumoniae were ESBL producers. In E. coli, resistance to imipenem was not observed, resistance to ciprofloxacin and amikacin was 58.0% and 5.5% respectively. In K. pneumoniae resistance to imipenem, ciprofloxacin and amikacin was 3.1%, 17.8% 12.4% respectively. In P. aeruginosa the lowest rate of resistance was observed with piperacillin/tazobactam (18.1%). A. baumanni isolates were highly resistant to all the antimicrobial agents, the lowest level of resistance was observed against cefoperazone/sulbactam (52.0%) followed by imipenem (55.5%). This study showed that resistance rates to antimicrobials are high in nosocomial isolates and show variations among the centers.     

In vitro interaction of colistin and rifampin on multidrug-resistant Pseudomonas aeruginosa

The administration of colistin is considered as the last alternative for infections by multidrug-resistant isolates of Pseudomonas aeruginosa; however its use is limited due to its considerable toxicity and poor pharmacokinetics. In order to define the in vitro activity of colistin combined with rifampin, 28 isolates resistant to piperacillin, ceftazidime, imipenem, meropenem, ciprofloxacin, amikacin, rifampin and colistin were tested. Seventeen of them that were found by PFGE to be genetically distinct were over time exposed to 2 microg/ml of colistin, to 2 microg/ml of rifampin and to their combination. Applied concentrations were selected to correspond to the mean serum level of the tested antimicrobials. Synergy between colistin and rifampin was found in four (23.5%), six (35.3%), seven (41.7%) and two (11.8%) isolates after 2, 4, 6 and 24 hours of growth, respectively. Bacterial re-growth was detected after 24 hours of exposure to the tested interaction. It is concluded that colistin and rifampin express a considerable in vitro synergistic effect on multidrug-resistant P. aeruginosa. The reported interaction should be tested in animal studies before introduction in clinical practice.     

The increase in carbapenem use and emergence of Stenotrophomonas maltophilia as an important nosocomial pathogen

Carbapenems, being the broadest spectrum antibiotics, may allow those organisms intrinsically resistant to these drugs to be involved more frequently in nosocomial infections. Imipenem was introduced to the specialized hospital units in Kuwait in October, 1992 and meropenem in late 1996. The main objective of this study was to observe prospectively whether, under similar laboratory conditions for microbial isolation/identification while these drugs are in use in the hospital, there is any proportional increase over time in the recovery of Stenotrophomonas maltophilia in relation to the number of yearly admissions and drug use. In addition, we also looked for categories of patients infected by S. maltophilia, type of infection and antibiotic susceptibility. There was an increase in the number of S. maltophilia isolates from 1993 to 1997 significantly correlated with the increase in year-wise consumption of carbapenems (p<0.004). No correlation was observed between yearly number of admissions and both the consumption of carbapenems (p>0.51) and isolation of the organism (p>0.59). Most isolates were from cancer, burns and cardiac patients. The commonest types of infection were wound and septicemia. The organisms were susceptible mostly to ciprofloxacin and co-trimoxazole. The study thus indicates that carbapenem use in a hospital environment may result in emergence of nosocomial infections due to multiresistant S. maltophilia in high risk patients with very limited choice of antibiotics for therapy.     

Relationship of antibiotic resistance phenotype to the R-pyocin susceptibility pattern in clinical isolates of Pseudomonas aeruginosa

One hundred sixteen clinical isolates of Pseudomonas aeruginosa were collected from 7 hospitals in Athens. All strains were studied for their susceptibility to cefotaxime, ceftazidime, carbenicillin, aztreonam, imipenem, nalidixic acid, ciprofloxacin, gentamicin, and chloramphenicol. In addition, the R-pyocin susceptibility pattern was determined and the strains were O-serotyped and tested for their agglutination in acriflavine. The isolates included 53 strains resistant to both gentamicin and carbenicillin, 13 to carbenicillin only, 20 to gentamicin only, and 30 sensitive to gentamicin and carbenicillin. The multiresistant isolates displayed relatively higher resistance to all other antibiotics except aztreonam and cefotaxime. Remarkably 30 out of 53 multiresistant isolates reacted with one pyocin only, namely pyocin R2. This R-pyocin response was not encountered in any other strains of the other antibiotic resistance phenotypes. These isolates belonged to the 0-12 serogroup. The 0-12 serogroup was represented only in a minority of strains giving other R-pyocin reactions. It is interesting that strains reacting with pyocin R5 only were mostly susceptible to antibiotics. The results clearly indicate lipopolysaccharide-core mutations in multiresistant clinical isolates of P. aeruginosa. Despite the fact that the R-pyocin resistance pattern can not define the precise possible defect, the multiple and high level resistance associated with R2-pyocin reaction seems to be an interesting trait.     

Resistance Surveillance in Italy: Four-Year Results from the MYSTIC Program

Abstract

The MYSTIC program is an international, multicenter surveillance study that compares the activity of meropenem, in centers that are prescribers, with that of imipenem, ceftazidime, piperacillin/tazobactam, ciprofloxacin and gentamicin. These Italian data are from 3 centers (neutropenia, cystic fibrosis and intensive care units). A total of 2,072 (238 Gram-positive and 1,834 Gramnegative) aerobic microorganisms were collected during the study. Pseudomonas aeruginosa (33.4%) was the most isolated species followed by Escherichia coli (14.4%). All except one Enterobacteriaceae strain isolated were fully susceptible to meropenem. Moreover, the activity of meropenem against Enterobacteriaceae was about eight-fold greater than that of imipenem and four- to eight-fold more active than that of ceftazidime. Meropenem was highly active against non-fermentative Gram-negative microorganisms, exceeding the activity of most of the other antimicrobial agents tested. Moreover, meropenem showed increasing activity during the 4 years of study (starting from 86.2% in 1997 to 94.0% in 2000). In conclusion, our results indicate that meropenem has excellent potency and spectrum of activity despite being prescribed for the treatment of seriously ill patients, and appears to be a reliable option for the initial empirical treatment of serious nosocomial infections.