Imipenem-cilastatin in the treatment of methicillin-sensitive and methicillin-resistant Staphylococcus aureus infections

Clonal Diversity and Epidemiological Characteristics of ST239-MRSA Strains

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen associated with severe morbidity and mortality and poses a significant threat to public health worldwide. The genetic diversity based on sequence types of MRSA strains was illustrated in previous studies; meanwhile, the diversity along with the predominant sequence type, especially in Egypt, remains unknown. The purpose of the current study was to determine the diversity of the predominant MRSA clone ST239-MRSA (n = 50) isolated from different hosts and clinical samples and to illustrate the correlation between the resistance patterns, toxin genes, and the genetic background in Port-said and El-Sharkia Governorates, Egypt. The ST239-MRSA clone was analyzed by phenotypic antibiotyping and various genotypic assays comprising SCCmec, agr, spa, coa, and coa-RFLP in addition to toxin gene profiles. Most of the analyzed strains (40/50, 80%) were multidrug resistant (MDR), belonged to SCCmec-III, agr-I, and coa genotype I, and harbored sea and pvl genes. A negative correlation between the toxin gene profiles and antimicrobial resistance was recorded. Meanwhile, the correlation between the toxin gene profiles and the genetic background was not observed in this study. Although ST239-MRSA strains belonged to a single sequence type, they exhibited a high degree of phenotypic and genotypic diversity, indicating weak clonality and adaptability. With such diversity, it is assumed that these strains may have undergone different evolutionary processes during transmission events among and/or within a single host or tissue niche.

Imipenem–cilastatin-induced thrombocytosis: A probable rare case report

Drug-induced thrombocytosis is difficult to identify and is rarely reported. Here, we report a probable rare case of imipenem–cilastatin-induced thrombocytosis in a 51-year-old female. The patient received imipenem–cilastatin treatment because of an intra-abdominal infection, following which the platelet count increased to a peak value of 1058×109 cells/L in 14 days. When imipenem–cilastatin was replaced by levofloxacin and amikacin, the platelet count decreased progressively and remained within the normal range until the 6-month follow-up. Moreover, platelet counts were independent of the infection. Thrombocytosis was probably attributable to imipenem–cilastatin with a Naranjo score of seven. This is a probable rare case in which the thrombocytosis was likely an adverse reaction induced by imipenem–cilastatin. We suggest that clinicians need to be vigilant concerning the impact of imipenem–cilastatin on platelet count in patients with thrombocytosis.

Antibacterial activity of hydroxychalcone against methicillin-resistant Staphylococcus aureus

Anti-candidal hydroxychalcone, 2,4,2'-trihydroxy-5'-methylchalcone (THMC), was investigated for its antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). THMC showed the minimum inhibitory concentrations of 25.0-50.0 mug/ml against tested 20 strains, at which the effect was based on a bacteriostatic action. THMC of 25.0 mug/ml completely inhibited the incorporation of radio-labelled thymidine and uridine into MRSA cells. In combination with antibiotics, the fractional inhibitory concentration indices were 0.47 for gentamicin and 0.79 for vancomycin, indicating that THMC acts synergistically with these agents. THMC would be a potent therapeutic agent for MRSA infections.

Synergistic effects of mupirocin and an isoflavanone isolated from Erythrina variegata on growth and recovery of methicillin-resistant Staphylococcus aureus

The phytochemical 2',4'-dihydroxy-8-gamma,gamma-dimethylallyl-2",2"-dimethylpyrano[5",6":6,7]isoflavanone (bidwillon B) was isolated from Erythrina variegata and its antibacterial properties against methicillin-resistant Staphylococcus aureus (MRSA) were investigated. Bidwillon B inhibited the growth of 12 MRSA strains at minimum inhibitory concentrations (MICs) of 3.13-6.25mg/l, while MICs of mupirocin were 0.20-3.13 mg/l. The minimum bactericidal concentration (MBC) for bidwillon B and mupirocin against MRSA were 6.25-25mg/l (MBC(90): 12.5mg/l) and 3.13-25mg/l (MBC(90): 25mg/l), respectively. When bidwillon B and mupirocin were combined, synergistic effects were observed for 11 strains of MRSA (fractional inhibitory concentration indices, 0.5-0.75). The MBCs of mupirocin in the presence of bidwillon B (3.13 mg/l) were reduced to 0.05-1.56 mg/l. Bidwillon B at MIC values strongly inhibited incorporation of radio-labelled thymidine, uridine, glucose and isoleucine into MRSA cells. Mupirocin showed lower inhibitory effects than bidwillon B on thymidine, uridine and glucose incorporation, but incorporation of isoleucine was completely blocked with this antibiotic. These results indicate that bidwillon B possesses sufficient anti-MRSA activity for inhibiting growth and recovery, and that the compound acts synergistically with mupirocin. The results also suggest that both compounds act on MRSA via different mechanisms. Bidwillon B may prove to be a potent phytotherapeutic and/or combination agent with mupirocin in the elimination of nasal and skin carriage of MRSA.

Imipenem and meropenem activity against mecA-positive homogeneously and heterogeneously oxacillin-resistant and mecA-negative oxacillin-borderline-susceptible staphylococci

Microbroth dilution and disk-diffusion testing of imipenem and meropenem was performed at 35 and 30 degrees C against 61 phenotypic expression class 3,4 and 9 phenotypic expression class 1,2 oxacillin-resistant isolates of Staphylococcus aureus (ORSA), 51 oxacillin-borderline-susceptible isolates of S. aureus (BORSA), and 37 phenotypic expression class 3,4 and 9 phenotypic expression class 1,2 isolates of Staphylococcus epidermidis (ORSE). Imipenem MIC ranges at 35 degree C were 0.6 to > 64 micrograms/ml for class 3,4 ORSA, 0.03 to 0.25 micrograms/ml for class 1,2 ORSA, 0.015 to 0.12 micrograms/ml for BORSA, 0.03 to 64 micrograms/ml for class 3,4 ORSE, and 0.12 to 8 micrograms/ml for class 1,2 ORSE. Corresponding values for meropenem were 0.5 to 64 micrograms/ml, 0.12 to 4 micrograms/ml, 0.06 to 1 microgram/ml, 0.5 to 64 micrograms/ml, and 1 to 8 microgram/ml. MIC ranges at 30 degrees C did not differ by more than 1 log2 dilution from those at 35 degrees C. After 24 h incubation of disk-diffusion tests at 35 degrees C, 44% of class 3,4 and 100% of class 1,2 ORSA isolates were imipenem-susceptible; after an additional 24 h at 25 degrees C, 39 and 100% of these isolates, respectively, remained susceptible to imipenem. Similar values were obtained with 24 h incubation at 30 degrees C followed by 24 h at 25 degrees C. All BORSA isolates were susceptible to imipenem. Of the ORSE isolates, 22 and 78% of isolates in classes 3,4 and 1,2, respectively, were susceptible at 24 h with little change after an additional 24 h at 25 degrees C. Similar trends were observed with meropenem. In parallel disk-diffusion studies with oxacillin, false-susceptibility rates of 5% of class 3,4 and 44% class 1,2 ORSA isolates after 24 h of incubation at 35 degrees C were reduced to 3 and 0%, respectively, after an additional 24 h of incubation at 25 degrees C. Imipenem- and meropenem-resistant subpopulations of oxacillin-resistant staphylococci did not seem to be detected by altered susceptibility testing conditions.

A prospective, randomized study of pefloxacin versus teicoplanin in the treatment of gram-positive coccal infections in cancer patients: early termination due to emergence of resistance to fluoroquinolones

A randomized prospective study comparing pefloxacin to teicoplanin in the treatment of gram-positive infections in cancer patients was prematurely terminated because of the emergence of pefloxacin resistance associated with oxacillin resistance in Staphylococcus aureus and coagulase-negative staphylococci. Among 56 patients evaluated for efficacy (26 pefloxacin and 30 teicoplanin) and infected with bacteria susceptible to both antibiotics, the clinical cure and eradication rates were similar for pefloxacin (80.5% and 77.3% respectively) and teicoplanin (66.6% and 52.2% respectively). The relapse rates (15% and 10% for pefloxacin and teicoplanin respectively) and the overall mortalities within 1 month (42% and 31%) were similar.

Comparison of imipenem versus cefuroxime plus tobramycin as empirical therapy for febrile granulocytopenic patients and efficacy of vancomycin and aztreonam in case of failure

143 aplastic episodes with fever in 91 haematological patients with granulocytopenia were treated empirically in a randomized prospective study using either imipenem (Imi) or a combination of tobramycin and cefuroxime (T/C). Response after 72 h was significantly better in patients receiving Imi (44/75 vs 27/68, p < 0.05). This was seen especially in patients with bacteriologically proven infections where the isolated staphylococci and streptococci were more susceptible to Imi. In both groups, patients who failed to respond to the initial antibiotic therapy were given vancomycin and aztreonam (V/A). The response rate after another 72 h, measured using the same criteria as after the first 72 h, did not differ statistically between the groups. One patient in each study group died from the bacterial infection, both from Gram-positive bacteraemia. Duration of fever was significantly shorter in the Imi group (4 days vs 7 days, p < 0.04). Serum peak and trough concentrations of the antibiotics were comparable. Both regimens were well tolerated. Our results show that monotherapy with imipenem is superior to the combination of tobramycin and cefuroxime during the first 72 h of therapy and can be safely administered to neutropenic patients with predominantly Gram-positive infections. A combination of vancomycin and aztreonam, given when initial imipenem treatment has failed, was effective in only a few patients. Adjuvant glycopeptide therapy from the outset in the treatment of febrile granulocytopenic patients did not seem worthwhile.

The rapid emergence of fluoroquinolone-methicillin-resistant Staphylococcus aureus infections in a community hospital. An in vitro look at alternative antimicrobial agents

The introduction of ciprofloxacin on an unrestricted basis into a 900-bed community hospital resulted in the emergence of high-level fluoroquinolone resistance among methicillin-resistant Staphylococcus aureus (MRSA) during the subsequent 18 months. Susceptibility testing revealed several old and new compounds to which all the S. aureus strains were susceptible. When an MRSA strain became resistant to ciprofloxacin it also exhibited high-level resistance to ofloxacin, fleroxacin, norfloxacin, and enoxacin. Two new experimental fluoroquinolones, WIN 57273 and CI-960, exhibited good activity against all test strains. Among the glycopeptide compounds, mupirocin and teicoplanin were approximately fourfold more active than vancomycin and ramoplanin. Rifampin and trimethoprim-sulfamethoxazole (TMP/SMZ) showed good activity against most strains as did imipenem. For clindamycin, gentamicin, and tetracycline susceptibilities exhibited a bimodal distribution with at least 10% of strains having resistant MIC values. Surprisingly, the addition of sulbactam potentiated the activity of ampicillin against the ciprofloxacin-resistant MRSA strains, however, sulbactam had little effect on cefoperazone activity against these same strains. Time-kill kinetic studies of selected antimicrobials against ciprofloxacin-resistant strains indicated good killing by vancomycin, ampicillin-sulbactam, and TMP/SMZ. Teicoplanin was less bactericidal than vancomycin while these same strains rapidly developed resistance to rifampin even at concentrations 8 x MIC. These data indicate certain alternative compounds within our study warrant further investigation, especially in vivo, against multiply-resistant staphylococci.

Imipenem versus gentamicin combined with either cefuroxime or cephalothin as initial therapy for febrile neutropenic patients

A prospective randomized study was conducted to determine the efficacy of imipenem-cilastatin (hereafter referred to as imipenem) (500 mg four times daily) versus combination therapy for febrile neutropenic patients receiving either no prophylaxis or ciprofloxacin for prevention of infections. Combination therapy consisted of gentamicin (80 mg every 8 h) plus either cefuroxime (1,500 mg every 8 h) or cephalothin (1,000 mg every 4 h) for suspected catheter-related infections. Ninety-four neutropenic fever episodes in 87 patients were evaluable for efficacy. The overall clinical rate of response to imipenem was significantly higher than that to combination therapy (91 versus 74%; P = 0.05). The difference in efficacy was most pronounced in patients with microbiologically documented infections (89 versus 53%; P = 0.025), which were predominantly caused by gram-positive bacteria. Differences in susceptibility may have caused the better rate of response to imipenem. Two of 29 gram-positive bacteria were imipenem resistant, whereas 10 were resistant to cephalothin and cefuroxime and 12 were resistant to gentamicin. No causative gram-negative bacterium and 24 gram-positive bacteria were isolated in 61 fever episodes with ciprofloxacin prophylaxis (oral). In contrast, nine causative gram-negative and five gram-positive bacteria were isolated in 33 episodes without prophylaxis. The difference in distribution proved to be statistically significant for gram-negative (P = 0.0001) as well as gram-positive (P = 0.025) bacteria, indicating that ciprofloxacin effectively prevented the occurrence of gram-negative bacteria and may have contributed to the relatively large number of gram-positive bacteria isolated. Empirical initial therapy with imipenem may be a valuable alternative to combination therapy for neutropenic fever episodes.

Failure of routine susceptibility tests to detect imipenem resistance among strains of methicillin-resistant Staphylococcus aureus

We tested 75 methicillin-resistant Staphylococcus aureus strains for susceptibility to imipenem by using disk diffusion tests and broth microdilution tests with standard and heavy inocula. Population analysis was performed on isolates that appeared to be susceptible by these methods. All of the strains contained subpopulations of cells that are phenotypically resistant to imipenem.

Ceftazidime versus imipenem-cilastatin as initial monotherapy for febrile neutropenic patients

One hundred febrile episodes in 89 neutropenic patients after cytotoxic chemotherapy were randomized to be treated with either ceftazidime or imipenem as initial monotherapy. The clinical characteristics of the two groups of patients were comparable. The response of the fever in patients who received imipenem was significantly better than that in those who received ceftazidime (77 versus 56%, respectively; P = 0.04), especially in those with microbiologically documented infection (81 versus 33%, respectively; P = 0.02). The in vitro susceptibilities and the clinical responses suggested that, with the possible exception of Pseudomonas spp., imipenem was more effective than ceftazidime in treating neutropenic infections caused by both gram-positive and -negative organisms. An additional 23 and 21% of the patients in the ceftazidime and imipenem groups, respectively, responded to the addition of cloxacillin and amikacin following failure of monotherapy. The majority of the treatment failures, relapses, and superinfections were related to resistant infective organisms such as methicillin-resistant Staphylococcus spp. and Pseudomonas spp. or disseminated fungal infections.

Antimicrobial use in hospital-acquired infections

The appropriate use of antibiotics in nosocomial infections has been a goal of infectious disease practitioners and hospital epidemiologists since the emergence of resistant staphylococci more than 30 years ago. This challenge has assumed new proportions in the 1980s for many reasons. First, resistant gram-positive and gram-negative bacteria are increasingly common. Thus many traditional drugs or combinations of drugs lack efficacy. Second, there are so many new antibiotics available that it is difficult for any but the most knowledgeable to use each of them appropriately. Third, economic reality has forced hospitals and physicians to alter their activities and focus more on cost considerations than was ever necessary before. Last, infectious disease as a subspecialty in internal medicine is profoundly different in the 1980s; many infections must be controlled for life rather than cured because of underlying infection with human immunodeficiency virus, which suppresses immunity. The use of antibiotics is now rapidly changing and the state of the art in 1989 is likely to be outdated very soon as new pathogens emerge and new drugs are developed. The appropriate use of the quinolones is a great challenge that we now face. Can we preserve this valuable class of drugs, or will resistance develop quickly because of widespread, indiscriminate, and inappropriate use? To what extent can we phase out aminoglycoside use without compromising efficacy and without promoting the development of resistance? Do the monobactams have a real role to play in combination therapy? How should formularies approach the diverse cephalosporins that now inundate the market? These are only a few of the fundamental questions that must be addressed as this decade ends.

Emergence of imipenem-resistant Pseudomonas aeruginosa during treatment of intra-abdominal infection in a patient with ovarian carcinoma

A 59-year-old woman was admitted to the hospital with ovarian carcinoma. After cytoreductive surgery, the patient developed intra-abdominal sepsis. After 17 days of intravenous imipenem, the patient's sputum culture grew imipenem-resistant Pseudomonas aeruginosa. On the 21st day of treatment with imipenem, her peritoneal culture also grew imipenem-resistant Pseudomonas aeruginosa.

Salt-supplemented medium for testing methicillin-resistant staphylococci with newer beta-lactams

The addition of 2% NaCl to cation-supplemented Mueller-Hinton broth (CSMHB) was evaluated for microdilution testing of the susceptibility of staphylococci to five cephalosporins, imipenem, amoxicillin-clavulanate, and ticarcillin-clavulanate. With Staphylococcus aureus, NaCl improved the recognition of methicillin (oxacillin) resistance to cefamandole, imipenem, or ticarcillin-clavulanate. Resistance to amoxicillin-clavulanate was readily determined, irrespective of the presence of added salt. The addition of 2% NaCl to CSMHB did not significantly improve detection of resistance to any of the beta-lactams among coagulase-negative staphylococci. Since the addition of NaCl did not have significant adverse effects on tests with coagulase-negative staphylococci, the routine addition of 2% NaCl to oxacillin or methicillin tests with staphylococci may be justifiable on the basis of convenience or standardization. However, addition of NaCl to susceptibility tests of other beta-lactams does not consistently improve recognition of resistance among staphylococci and thus cannot be recommended for routine use.

Methicillin-resistant Staphylococcus aureus: pediatric perspective

Methicillin-resistant S. aureus has emerged as a nosocomial pathogen of major importance in pediatric patients. Infection occurs most often in hospitalized individuals with underlying predisposing medical conditions. Any body site may be involved, and bacteremia frequently occurs concomitantly. Vancomycin is the antibiotic of choice for serious MRSA infections; PRPs and cephalosporins generally are not effective. The likelihood of an adverse outcome of infection increases with the severity of an underlying condition and delay in institution of appropriate therapy. Infection control measures have met with only limited success in eradicating MRSA from the hospital environment. Methicillin-resistant S. aureus is likely to remain of considerable clinical significance to physicians caring for seriously ill children.

Methicillin-resistant staphylococci

Strains of staphylococci resistant to methicillin were identified immediately after introduction of this drug. Methicillin-resistant strains have unusual properties, the most notable of which is extreme variability in expression of the resistance trait. The conditions associated with this heterogeneous expression of resistance are described. Methicillin resistance is associated with production of a unique penicillin-binding protein (PBP), 2a, which is bound and inactivated only at high concentrations of beta-lactam antibiotics. PBP2a appears to be encoded by the mec determinant, which also is unique to methicillin-resistant strains. The relationships between PBP2a and expression of resistance and implications for the mechanism of resistance are discussed. The heterogeneous expression of methicillin resistance by staphylococci poses problems in the detection of resistant strains. Experience with several susceptibility test methods is reviewed and guidelines for performance of these tests are given. Treatment of infections caused by methicillin-resistant staphylococci is discussed. Vancomycin is the treatment of choice. Alternatives have been few because methicillin-resistant strains often are resistant to multiple antibiotics in addition to beta-lactam antibiotics. New agents which are active against methicillin-resistant staphylococci are becoming available, and their potential role in treatment is discussed.

Efficacy of coumermycin, ofloxacin and vancomycin against methicillin-resistant Staphylococcus aureus in vitro and in experimental infections of mice

In vitro, coumermycin (a bis-hydroxicoumarin gyrase inhibitor) proved significantly more active than ofloxacin and vancomycin against 100 strains of methicillin-resistant Staphylococcus aureus (MRSA). The MIC90 was 0.5 microgram/ml, whereas the corresponding figures for the other antimicrobials were 2.0 and 4.0 micrograms/ml. In vivo, an otherwise lethal septicemia, induced by intraperitoneal administration of a MRSA in mice, was "successfully treated" in 50% of the animals (ED50) with the following dosages (microgram/g b. wt.): coumermycin 0.9, ofloxacin 10.8, vancomycin 22.4. The ED50 of coumermycin was significantly (2 p less than 0.01) different from those of the other drugs. Renal infection as produced in mice by transcutaneous inoculation of the same MRSA was treated with either of the antimicrobials at different dosages (single doses of 0.0 or 1.6 or 6.3 or 25.0 micrograms/g b. wt., twice daily) during 6 days. The largest reductions of viable counts in the kidneys at each dosage as compared to the bacterial counts of untreated animals were achieved with coumermycin (3.4 or 5.5 or 7.7 log10). These reductions are significantly (2 p less than 0.01) different from those achieved with the comparable dosages of ofloxacin and vancomycin which were 0.1 or 1.8 or 2.8 and 0.4 or 1.4 or 3.0 log10 respectively. After a single subcutaneous injection of 250 micrograms mean concentrations in serum of mice for coumermycin were 6.2-5.0 micrograms/ml for 8 h, for ofloxacin 2.0-0.5 micrograms/ml for 2 h, and for vancomycin 14.7-2.5 micrograms/ml for 2 h. Coumermycin and ofloxacin could be alternatives to vancomycin in the therapy of human infections due to MRSA.

Comparative in vitro activity of CGP 31608, a new penem antibiotic

The in vitro activity of a new penem antimicrobial agent, CGP 31608, was compared with those of imipenem, SCH 34343, and several other antimicrobial agents against approximately 600 bacterial isolates. CGP 31608 was active against gram-positive organisms, including methicillin-susceptible Staphylococcus aureus (MIC for 90% of the isolates [MIC90], 0.25 microgram/ml) and penicillin-susceptible streptococci (MIC90s, less than or equal to 2 micrograms/ml). Penicillin-resistant streptococci (including enterococci) and methicillin-resistant S. aureus were more resistant to the penem. Activities of CGP 31608 against members of the family Enterobacteriaceae were remarkably uniform, with MIC90s of 8 to 16 micrograms/ml. CGP 31608 was at least as active as imipenem and ceftazidime and more active than piperacillin against Pseudomonas aeruginosa. Drug activity was not influenced by the presence of any of 10 plasmid-mediated beta-lactamases. Against strains of Serratia marcescens, Enterobacter cloacae, and P. aeruginosa with derepressible chromosomally mediated beta-lactamases, the presence of cefoxitin did not induce increased resistance to CGP 31608. The new drug was also active against anaerobes (MIC90s, 0.25 to 8 micrograms/ml), Haemophilus influenzae (MIC90s, 0.5 to 1.0 micrograms/ml), and Legionella spp. (MIC90, 2 micrograms/ml). CGP 31608 showed an antibacterial spectrum similar to those of imipenem and SCH 34343 (except that the latter is not active against P. aeruginosa) but was generally less potent than these drugs. However, CGP 31608 demonstrated more activity (MIC90) than imipenem against P. aeruginosa, Pseudomonas cepacia, and methicillin-resistant Staphylococcus epidermidis and S. aureus.

Imipenem/cilastatin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic efficacy

Imipenem is the first available semisynthetic thienamycin and is administered intravenously in combination with cilastatin, a renal dipeptidase inhibitor that increases urinary excretion of active drug. In vitro studies have demonstrated that imipenem has an extremely wide spectrum of antibacterial activity against Gram-negative and Gram-positive aerobic and anaerobic bacteria, even against many multiresistant strains of bacteria. It is very potent against species which elaborate beta-lactamases. Imipenem in combination with equal doses of cilastatin has been shown to be generally well tolerated and an effective antimicrobial for the treatment of infections of various body systems. It is likely to be most valuable as empirical treatment of mixed aerobic and anaerobic infections, bacteraemia in non-neutropenic patients and serious hospital-acquired infections.