Antibacterial activity of extracts from five medicinal plants and their formula against bacteria that cause chronic wound infection

BACKGROUND

Chronic wound is caused by various factors such as chemotherapy, gene damage, treatment with steroids, diabetes mellitus, renal failure, blood pressure, infection and nutritional factors. One of the most common causes is bacterial infection. Antibacterial activity of several herbal plants has been reported. Thai medicinal plants which possess biological activities are potential to develop an alternative treatment of bacterial infection.

OBJECTIVE

To study efficiency of extracts from medicinal plants and their formula against bacteria that cause chronic wound infection.

MATERIAL AND METHOD

Extraction of Thai medicinal plants including Curcuma longa Linn, Rhinacanthus nasutus Linn, Garcinia mangostana Linn, Caesalpinia sappan Linn and Centellia asiatica Linn was performed by maceration with 95% ethanol and decoction followed by freeze dry. Formulation was conducted by varying the ratio of each components. Antibacterial activity were determined disk diffusion and broth dilution against Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Acinetobacter baumanii, Escherichia coli and Klebsiella pneumoniae.

RESULTS

Ethanolic extracts exhibited better antibacterial activity against tested strains than water extracts. Antibacterial activity of Caesalpinia sappan Linn. against S. aureus and MRSA showed the most effective with MIC value of 0.625 mg/ml. One of the five different formulas which contained two times proportion of C. sappan revealed that this formula was able to inhibit all tested strains with the MIC ranging between 0.156 mg/ml and 10 mg/ml.

CONCLUSION

C. sappan is the most effective herbal plant. The formula with two times proportion of C. sappan is potentially best formula for development of medicinal product of chronic wound infection. The potential active compound of C. sappan is suggested for further investigation of antimicrobial activity and other biological properties.

[Quinolone resistance in Gram negative rods in Iceland and association with antibiotic use]

OBJECTIVE

Fluoroquinolones are bacteriocidal drugs that are widely used to treat severe urinary and respiratory tract infections. Studies show that resistance to fluoroquinolones is continuously increasing both in Europe and the United States. The purpose of this study was to measure the frequency of fluoroquinolone resistance in the most prevalent Gram negative rods and look at the correlation with fluoroquinolone use over the last 8 years.

MATERIALS AND METHODS

All strains of Escherichia coli, Klebsiella sp., Proteus sp. and Pseudomonas aeruginosa identified from clinical specimens at the Department of Clinical Microbiology at the Landspitali University Hospital (LUH) during the time period 1.11.2006 to 31.1.2007. Antibiotic susceptibility testing was performed by disc diffusion tests and all strains were tested for ciprofloxacin susceptibility. Antibiotic resistance data for the last years were collected from the reports of the Department of Clinical Microbiology, but ciprofloxacin susceptibility was usually only tested for specimens from hospitalised patients and when there was resistance to two or more antimicrobial agents. Data on antibiotic use/sales was obtained from the State Epidemiologist at the Directorate of Health.

RESULTS

Of the 1861 strains tested, 104 fluoroquinolone resistant strains were identified during the study period, including 91 E. coli (87%), 8 Klebsiella sp. (8%) and 5 P. aeruginosa (5%). No fluoroquinolone resistant Proteus sp. was identified. There was a significant positive correlation between fluoroquinolone use and the frequency of resistant strains of E. coli and Enterobacteriaceae. The frequency of resistant E. coli strains was 6% and it differed significantly between age groups (p >0.001) and sex, 6% for females and 11% for males (p = 0.015). The ratio of fluoroquinolone resistant E. coli was highest in the LUH and homes for the elderly.

CONCLUSION

The frequency of fluoroquinolone resistance is increasing fast in Iceland but is still one of the lowest compared to the other European countries. The frequency is highest in the oldest age groups where the use of the quinolones is the greatest and there was a significant correlation between the quinolone use and the frequency of resistance in E. coli and Enterobacteriaceae. The results highlight the importance of prudent fluoroquinolone use and the need to monitor fluoroquinolone use and resistance.

Effect of xylitol on an in vitro model of oral biofilm

PURPOSE

The aim of the present study was to examine whether xylitol, at different concentrations, inhibits the formation of an experimental model of oral biofilm.

MATERIALS AND METHODS

Biofilms of six bacterial species (Streptococcus mutans, Streptococcus sobrinus, Lactobacillus rhamnosus, Actinomyces viscosus, Porphyromonas gingivalis and Fusobacterium nucleatum) were prepared on hydroxyapatite (HA) discs according to the Zürich Biofilm Model. Xylitol was tested at two concentrations, 1% and 3%. At the end of their designated incubation times, some HA discs were destined for confocal laser scanning microscopy (CLSM) and the others were harvested using a sterile surgical instrument. Aliquots of harvested biofilms were diluted and plated onto specific media. After a 48-h anaerobic incubation at 37 degrees C, the colony-forming units (CFUs) were counted.

RESULTS

CLSM images showed that only a small amount of isolated bacteria was observed on the surface of HA discs. Culture of harvested biofilms showed an inhibition in the growth of different species included in the biofilms.

CONCLUSIONS

Xylitol has a clear inhibitory effect on the formation of the experimental biofilms. This study shows that xylitol is not only efficient in inhibiting the acid production of cariogenic bacteria, but also in preventing the formation of a multispecies biofilm; it confirms the relevance of the use of this polyol for the prevention of oral diseases caused by dental plaque.

[Assessment of the susceptibility of the gram-negative rods isolated from hospitalized patients to cefoperazone/sulbactam]

The susceptibility to cefoperazone/sulbactam of 197 strains of Gram-negative rods demonstrating an ESBL-positive phenotype was determined. The assortment of the investigated strains was as follows (numbers of strains are given in the brackets): E. cloacae (63), S. marcescens (46), K. pneumoniae (21), P. mirabilis (17), E. coli (9), P. vulgaris (8), P. aeruginosa (20) and A. baumanni (13). 83 strains from 197 were susceptible (42.1%). The MIC values were determined and the disc-diffusion method was performed. The susceptibilities among particular species were as follows (the order of data in the brackets is: % of the susceptible strains/MIC50/MIC90): E. cloacae (54.0/16/64), S. marcescens (23.9/64/> or = 128), K. pneumoniae (38.1/32/64), P. mirabilis (41.2/32/64), E. coli (44.4/32/32), P. vulgaris (75.0/8/32), P. aeruginosa (35.0/32/64), A. baumannii (46.2/32/64). Using disc-diffusion method, for 184 strains the difference between diameter of the inhibition zone around the disc with cefoperazone and the disc with cefoperazone/sulbactam was calculated. This difference amounted 5 mm or more in the case of 76.6% of the investigated strains. The results indicate that the comparison of the inhibition zones around cefoperazone and cefoperazone/sulbactam discs may be an additional method useful for phenotypic detection of ESBL producing organisms. These results highly correlated with results obtained by using analogous test with cefpirome and cefpirome/clavulanic acid (85.6% of concordance).

In vitro antibacterial activities of tigecycline and comparative agents by time-kill kinetic studies in fresh Mueller-Hinton broth

Time-kill kinetics performed with tigecycline, in fresh MHB, demonstrated a consistent 1 to 2 log(10) CFU/ml reduction in bacterial counts against the majority of clinically relevant pathogens tested. Although classified as a bacteriostatic agent, tigecycline shows bactericidal activity against select isolates associated with serious infection. In general, vancomycin and imipenem demonstrated bactericidal activity.

Agrichemical impact on growth and survival of non-target apple phyllosphere microorganisms

The impact of conventional agrichemicals commonly used in New Zealand apple production on non-target, culturable phyllosphere microbial populations was studied in the laboratory (agar, leaf, and seedling assays) and field (apple orchard). Morphologically distinct bacteria (three), yeasts (five), and filamentous microfungi (two) were used as indicator species. The agar assay showed that agrichemical toxicity to microorganisms was dependent on product type, product rate, and organism studied. While the fungicides metiram and captan stopped or severely reduced growth of nearly all microorganisms studied, the insecticides tebufenozide and lufenuron and the fungicide nitrothal-isopropyl showed the least amount of microbial toxicity, each affecting 2 of the 10 indicator organisms studied. In the leaf assay a single agrichemical application at field rate either reduced or increased microbial population counts, again depending on product and microorganism. Repeated agrichemical applications, however, reduced microbial population numbers from 10- to 10,000-fold in planta. Further field research validated these findings, although differences in microbial numbers before and after agrichemical applications were less dramatic. In the orchard, total organism numbers recovered within 2-6 days, but species richness (sum of recognizable taxonomic units) declined. Agrichemicals clearly affected non-target, culturable surface microorganisms. The importance of diversity and stability of microbial populations for disease control still needs to be established.

Comparison of Etest, Vitek and agar dilution for susceptibility testing of colistin

In total, 172 isolates of Enterobacteriaceae, Acinetobacter spp., Pseudomonas aeruginosa and Stenotrophomonas maltophilia were tested for susceptibility to colistin by agar dilution, Etest and the Vitek 2 system. Isolates with a colistin MIC < or =2 mg/L were considered to be susceptible. Fifty-four (31%) Gram-negative isolates were resistant to colistin. Categorical agreement between agar dilution and Etest was 87%, and between agar dilution and Vitek 2 was 82%. Based on the data obtained, the Vitek 2 system was unreliable for detecting colistin resistance, and results obtained by Etest may require confirmation by a standard MIC susceptibility testing method.

Reevaluation of current susceptibility breakpoints for Gram-negative rods based on pharmacodynamic assessment

Although pharmacodynamic (PD) modeling is now being considered for decision support for susceptibility breakpoint determination against Gram-negative bacteria, these PD-derived breakpoints should be verified using a clinically applicable population of organisms. In this analysis, a 5000-patient Monte Carlo simulation was used to determine PD breakpoints, the highest 2-fold MIC in which the probability of bactericidal target attainment (PTA) remained > or = 90%. Percent susceptibilities for 639 Pseudomonas aeruginosa, 103 Acinetobacter baumannii, 705 Escherichia coli, and 418 Klebsiella spp. collected during the 2004 Meropenem Yearly Susceptibility Test Information Collection surveillance study were then defined according to the PD-derived breakpoint (%S(PD)) and compared with the current Clinical Laboratory Standards Institute (CLSI)-defined breakpoints (%S(CLSI)). %S(PD) and %S(CLSI) were compared with the bactericidal PTA for each pathogen population to determine the degree of agreement. Resulting PD breakpoints were drug and dose dependent; moreover, values were commonly 2 to 4 MIC dilutions lower than CLSI breakpoints. Overall, %S(PD) more closely agreed with the PTA for the tested beta-lactam and fluoroquinolone dosing regimens. In contrast, %S(CLSI) overestimated PTA for many dosing regimens, especially against Pseudomonas: piperacillin/tazobactam 4.5 g qid (+9.7%), ciprofloxacin 0.4 g bid (+13.7%) and 0.4 g tid (+9.3%), and levofloxacin 0.5 g every 24 h (+22.4%) and 0.75 g every 24 h (+9.9%). Differences were most pronounced against the nonfermenting Gram-negative bacteria and were not observed among the Enterobacteriaceae. As a result, a new method of breakpoint classification is proposed, which is dosing regimen and pathogen specific, and is designed to denote isolates as susceptible only if target bactericidal exposures are achievable with the dosing regimen selected.

Antibiotic regimens and intestinal colonization with antibiotic-resistant gram-negative bacilli

The intestinal tract provides an important reservoir for antibiotic-resistant gram-negative bacilli, including Enterobacteriaceae species, Pseudomonas aeruginosa, and Acinetobacter baumannii. Selective pressure exerted by antibiotics plays a crucial role in the emergence and dissemination of these pathogens. Many classes of antibiotics may promote intestinal colonization by health care-associated gram-negative bacilli, because the organisms are often multidrug resistant. Antibiotics may inhibit colonization by gram-negative pathogens that remain susceptible, but the benefits of this effect are often limited because of the emergence of resistance. Antibiotic formulary alterations and standard infection control measures have been effective in controlling outbreaks of colonization and infection with antibiotic-resistant gram-negative pathogens. Additional research is needed to clarify the role of strategies such as selective decontamination of the digestive tract and decontamination of environmental surfaces and of patients' skin and wounds.

Resistance in nonfermenting gram-negative bacteria: multidrug resistance to the maximum

Nonfermenting gram-negative bacteria pose a particular difficulty for the healthcare community because they represent the problem of multidrug resistance to the maximum. Important members of the group in the United States include Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia, and Burkholderia cepacia. These organisms are niche pathogens that primarily cause opportunistic healthcare-associated infections in patients who are critically ill or immunocompromised. Multidrug resistance is common and increasing among gram-negative nonfermenters, and a number of strains have now been identified that exhibit resistance to essentially all commonly used antibiotics, including antipseudomonal penicillins and cephalosporins, aminoglycosides, tetracyclines, fluoroquinolones, trimethoprim-sulfamethoxazole, and carbapenems. Polymyxins are the remaining antibiotic drug class with fairly consistent activity against multidrug-resistant strains of P aeruginosa, Acinetobacter spp, and S maltophilia. However, most multidrug-resistant B cepacia are not susceptible to polymyxins, and systemic polymyxins carry the risk of nephrotoxicity for all patients treated with these agents, the elderly in particular. A variety of resistance mechanisms have been identified in P aeruginosa and other gram-negative nonfermenters, including enzyme production, overexpression of efflux pumps, porin deficiencies, and target-site alterations. Multiple resistance genes frequently coexist in the same organism. Multidrug resistance in gram-negative nonfermenters makes treatment of infections caused by these pathogens both difficult and expensive. Improved methods for susceptibility testing are needed when dealing with these organisms, including emerging strains expressing metallo-beta-lactamases. Improved antibiotic stewardship and infection-control measures will be needed to prevent or slow the emergence and spread of multidrug-resistant, nonfermenting gram-negative bacilli in the healthcare setting.

Potentially multidrug-resistant non-fermentative Gram-negative pathogens causing nosocomial pneumonia

Owing to its high morbidity and mortality, nosocomial pneumonia represents a particularly serious illness and one of the most frequent complications in ventilated patients admitted to the Intensive Care Unit. Gram-negative microorganisms, such as Pseudomonas aeruginosa, Acinetobacter baumannii and Stenotrophomonas maltophilia, are the most relevant pathogens responsible for particularly difficult-to-treat nosocomial pneumonia. The intrinsic resistance of these bacteria to many antimicrobial agents and, in addition, the variety of their increasingly recognised acquired resistance mechanisms make their management in the hospital setting problematic. Antimicrobials that retain the best activity against P. aeruginosa include carbapenems, piperacillin, cefepime, ceftazidime, ciprofloxacin and certain aminoglycosides, whilst carbapenems and sulphamethoxazole/trimethoprim remain the most active agents against A. baumannii and S. maltophilia, respectively. However, the growing emergence among these microorganisms of multidrug-resistant (MDR) isolates and the severity of associated infections call for potential alternative drugs. Sulbactam alone or in combination with ampicillin may represent an acceptable option for MDR A. baumannii as well as colistin, which also covers MDR P. aeruginosa. Newer fluoroquinolones and some tetracyclines may be alternative drugs both for MDR S. maltophilia and A. baumannii. However, large-scale controlled clinical trials are needed to confirm these promising therapeutic options.

[Effects of high-pressure argon-containing gaseous compositions on operators' rhinopharynx and external ear microflora and its reactivity to antibiotics]

Earlier investigations revealed an important microbiological feature of the human in hyperbaric environment--linear progressive unbalance in the opportunistic and commensal ratio within the main biotopes. Change in the gaseous environment may influence the activity of infectious agents. Purpose of our investigation was to study effects of argon-containing gaseous compositions on the rhinopharynx and external ear microflora in operators, and its reactivity to antibiotics. Attempted was quantification of the operators' aerobic microflora exposed for 6, 7 and 18 days to argon-containing gaseous compositions (normoxic and hypoxic) under an elevated pressure (0.15-0.5 MPa). Evaluated was also susceptibility of the human microflora to antibiotics of the basic chemical classes under these conditions. The argon-containing gaseous compositions in the above pressure range did not have any specific effects on the ratio of aerobic gram-negative bacilli and staphylococci; neither they created selective advantages to any of the groups of microorganisms under study. It was found additionally that long-duration exposure in the argon-containing gaseous environment (6, 7 and 18 days) gave rise to cultures with the signs of hospitalism (e.g., high index of multiple drug resistance). Potentiality of infection development in dwelling modules with argon-containing gaseous environment and proliferation of polyresistant strains point to the necessity to design a respective preventive system.

[Activities of antimicrobial agents against 8,474 clinical isolates obtained from 37 medical institutions during 2000 in Japan]

A survey was conducted to determine the antimicrobial activity of fluoroquinolones and other antimicrobial agents against 8,474 clinical isolates obtained from 37 Japanese medical institutions in 2000. A total of 25 antimicrobial agents were used, comprising 4 fluoroquinolones, 13 beta-lactams, minocycline, chloramphenicol, clarithromycin, azithromycin, gentamicin, amikacin, sulfamethoxazole-trimethoprim, and vancomycin. A high resistance rate of over 85% against fluoroquinolones was exhibited by methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecium. Isolates showing resistance to fluoroquinolones among methicillin-resistant coagulase-negative Staphylococci, Enterococcus faecalis, and Pseudomonas aeruginosa from UTI accounted for 30-60%. However, many of the common pathogens were still susceptible to fluoroquinolones, such as Streptococcus pneumoniae (including penicillin-resistant isolates), Streptococcus pyogenes, methicillin-susceptible S. aureus (MSSA), methicillin-susceptible coagulase-negative Staphylococci, Moraxella catarrhalis, the Enterobacteriaceae family, and Haemophilus influenzae (including ampicillin-resistant isolates). About 85% of P. aeruginosa isolated from RTI were susceptible to fluoroquinolones. In conclusion, this survey of sensitivity to antimicrobial agents clearly indicated trend for increasing resistance to fluoroquinolones among MRSA, Enterococci, and P. aeruginosa isolated from UTI, although fluoroquinolones are still effective against other organisms and P. aeruginosa from RTI as has been demonstrated in previous studies.

In vitro and in vivo antibacterial activities of telithromycin

BACKGROUND

Telithromycin is one of the ketolides, characterised by a 3-keto group instead of L-cladinose and a C(11)-C(12) carbamate link by an alkyl chain to a pyridinum and imidazolium ring side chain. We evaluated in vitro and in vivo antibacterial activities of telithromycin against gynaecological pathogens.

METHODS

In the vitro study, the antibacterial activity of telithromycin against 180 isolates (isolated in the year 2000) of Streptococcus agalactiae (n = 33), Enterococcus faecalis (n = 22), Neisseria gonorrhoeae (n = 30), Peptostreptococcus anaerobius (n = 20), Finegoldia magna (n = 20), Bacteroides fragilis (n = 25) and Prevotella bivia (n = 30) was compared with that of erythromycin A, clarithromycin, azithromycin, ampicillin and levofloxacin. In the in vivo study, the efficacy of telithromycin was evaluated using experimental intra-abdominal abscesses in mice caused by B. fragilis (minimum inhibitory concentration of telithromycin 0.5 mg/l).

RESULTS

In the in vitro study, telithromycin inhibited more than 50% of clinical isolates of S. agalactiae, E. faecalis, N. gonorrhoeae, P. anaerobius, F. magna, B. fragilis and P. bivia at concentrations of 0.016, 0.063, 0.063, 0.032, 0.032, 0.5 and 0.25 mg/l, respectively. Telithromycin inhibited more than 90% of these clinical isolates at concentrations of 0.016, 4, 0.125, 0.063, 0.063, 4 and 1 mg/l, respectively. In the in vivo study, telithromycin inhibited abscess formation and significantly decreased viable cell counts in abscesses in comparison with the untreated group.

CONCLUSIONS

These in vitro and in vivo antibacterial activities suggest that telithromycin could be a potential candidate for the treatment of bacterial infections complicated by chlamydial infection.

Use of Etests with carbapenems for Gram-negative rods producing beta-lactamases

The in vitro activity of imipenem and meropenem on strains of Gram-negative rods producing extended-spectrum beta-lactamase (ESBL) and inducible beta-lactamase (IBL) was studied using the Etest. In all, 185 strains from the surgical intensive care units of four different hospitals were looked at over 2 years. Of these, 94 were ESBL producers and 91 were IBL positive. The in vitro sensitivities of imipenem and meropenem were 89.7 and 95.1%, respectively, against all strains. The imipenem and meropenem sensitivities of Klebsiella spp. were 98.4 and 100%, respectively, but imipenem resistance (21.6%) in Pseudomonas aeruginosa strains was higher than that of meropenem (10.8%).

[Mechanisms behind the development of antibiotic resistant bacteria]

BACKGROUND

Bacterial resistance to antibiotics is an increasing threat to the successful treatment of hospital and community-acquired infections.

MATERIAL AND METHODS

Based on relevant literature, this article focuses on some of the essential resistance problems caused by pathogens such as pneumococci, staphylocci, enterococci and gram-negative rods, and provides a review of the genetic and molecular basis of bacterial resistance, as well as of the global trends in bacterial resistance.

RESULTS

Mechanisms of resistance continue to evolve and disseminate among gram-negative as well as gram-positive pathogens. New problems are developing, such as glycopeptide resistance in Staphylococcus aureus. Bacteria have become resistant to antibiotics as a result of chromosomal changes or the exchange of genetic material via plasmids and transposons. The emergence of multiresistant bacteria e.g. S. aureus, enterococci and Mycobacterium tuberculosis, has made many currently available antibiotics ineffective.

INTERPRETATION

The introduction of new antibiotics has always been followed by development of resistance.

Evaluation of the VITEK 2 system for the identification and susceptibility testing of three species of nonfermenting gram-negative rods frequently isolated from clinical samples

VITEK 2 is a new automatic system for the identification and susceptibility testing of the most clinically important bacteria. In the present study 198 clinical isolates, including Pseudomonas aeruginosa (n = 146), Acinetobacter baumannii (n = 25), and Stenotrophomonas maltophilia (n = 27) were evaluated. Reference susceptibility testing of cefepime, cefotaxime, ceftazidime, ciprofloxacin, gentamicin, imipenem, meropenem, piperacillin, tobramycin, levofloxacin (only for P. aeruginosa), co-trimoxazole (only for S. maltophilia), and ampicillin-sulbactam and tetracycline (only for A. baumannii) was performed by microdilution (NCCLS guidelines). The VITEK 2 system correctly identified 91.6, 100, and 76% of P. aeruginosa, S. maltophilia, and A. baumannii isolates, respectively, within 3 h. The respective percentages of essential agreement (to within 1 twofold dilution) for P. aeruginosa and A. baumannii were 89.0 and 88.0% (cefepime), 91.1 and 100% (cefotaxime), 95.2 and 96.0% (ceftazidime), 98.6 and 100% (ciprofloxacin), 88.4 and 100% (gentamicin), 87.0 and 92.0% (imipenem), 85.0 and 88.0% (meropenem), 84.2 and 96.0% (piperacillin), and 97.3 and 80% (tobramycin). The essential agreement for levofloxacin against P. aeruginosa was 86.3%. The percentages of essential agreement for ampicillin-sulbactam and tetracycline against A. baumannii were 88.0 and 100%, respectively. Very major errors for P. aeruginosa (resistant by the reference method, susceptible with the VITEK 2 system [resistant to susceptible]) were noted for cefepime (0.7%), cefotaxime (0.7%), gentamicin (0.7%), imipenem (1.4%), levofloxacin (2.7%), and piperacillin (2.7%) and, for one strain of A. baumannii, for imipenem. Major errors (susceptible to resistant) were noted only for P. aeruginosa and cefepime (2.0%), ceftazidime (0.7%), and piperacillin (3.4%). Minor errors ranged from 0.0% for piperacillin to 22.6% for cefotaxime against P. aeruginosa and from 0.0% for piperacillin and ciprofloxacin to 20.0% for cefepime against A. baumannii. The VITEK 2 system provided co-trimoxazole MICs only for S. maltophilia; no very major or major errors were obtained for co-trimoxazole against this species. It is concluded that the VITEK 2 system allows the rapid identification of S. maltophilia and most P. aeruginosa and A. baumannii isolates. The VITEK 2 system can perform reliable susceptibility testing of many of the antimicrobial agents used against P. aeruginosa and A. baumannii. It would be desirable if new versions of the VITEK 2 software were able to determine MICs and the corresponding clinical categories of agents active against S. maltophilia.

Characterisation of some Ornithobacterium rhinotracheale strains and examination of their transmission via eggs

The biochemical characteristics and antibiotic susceptibility of 12 Ornithobacterium rhinotracheale strains isolated from chickens and turkeys suffering from respiratory clinical signs and the survival of some isolates on egg-shell and within chicken eggs during hatching were examined. All O. rhinotracheale strains showed typical biochemical characteristics. Among the 16 drugs examined, penicillin G, ampicillin (MICs ranging from < or = 0.06 microgram/ml to 1 microgram/ml), ceftazidim (with MICs from < or = 0.06 microgram/ml to 0.12 microgram/ml), erythromycin, tylosin, tilmicosin (with some exceptions MICs ranged from < or = 0.06 microgram/ml to 1 microgram/ml) and tiamulin (MICs varied from < or = 0.06 microgram/ml to 2 micrograms/ml) were the most effective. Lincomycin, oxytetracycline and enrofloxacin also gave good inhibitions, but with most strains in a higher concentration (MICs ranged in most cases from 2 micrograms/ml to 8 micrograms/ml). The other antibiotics inhibited the growth of O. rhinotracheale only in very high concentrations (colistin) or not at all (apramycin, spectinomycin, polymyxin B). At 37 degrees C, O. rhinotracheale did not survive on egg-shell for more than 24 hours, while upon inoculation into embryonated chicken eggs it killed embryos by the ninth day, and from the 14th day post-inoculation no O. rhinotracheale could be cultured from the eggs at all. These results suggest that O. rhinotracheale is not transmitted via eggs during hatching.

Antibiotic resistance among Gram-negative non-fermentative bacteria at a teaching hospital in Saudi Arabia

The incidence and antimicrobial resistance of Gram-negative non-fermentative bacteria isolated over 1 year at King Abdulaziz University Hospital, Jeddah, Saudi Arabia were investigated. A total of 499 of these microorganisms were collected and account for 16% of all Gram-negative bacteria isolated. The most common species were Pseudomonas aeruginosa 291 (56%), Acinetobacter baumannii 170 (34%), and Stenotrophomonas maltophilia 35 (7%). 168 (34%) of these microorganisms were isolated from Intensive Care Unit (ICU), 147 (30%) from General Medicine, and 24 (25%) from Surgery wards. ICU was the main site of isolation of P. aeruginosa and S. maltophilia, while A. baumannii was more frequently isolated from medicine and surgery units. The vast majority of the isolates were resistant to many antibiotics tested. The antimicrobial resistance patterns of P. aeruginosa showed lowest resistance to imipenem (13%), amikacin (17%), and ciprofloxacin (18%). Imipenem was also the most active antimicrobial agent against A. baumannii (15%) resistance. S. maltophilia exhibited multi-drug resistance, and was susceptible only to sulfonamide (6%).

Molecular typing demonstrating transmission of gram-negative rods in a neonatal intensive care unit in the absence of a recognized epidemic

Molecular typing techniques have been used in outbreak investigations. In this study, molecular typing techniques were used to track the spread of gram-negative rods (GNRs) in a neonatal intensive care unit (NICU) in the absence of an outbreak. Stool or rectal swab cultures for GNRs were obtained from all infants on admission, weekly, and on discharge. GNRs were tested for gentamicin susceptibility and were typed by contour-clamped homogeneous electric field electrophoresis. Transmission of identical strains of GNRs among infants was noted. Shared strains were more gentamicin resistant compared with unique strains (53% vs. 10%; P=.0001). Infants first colonized when they were >1 week of age had more total days of antibiotic treatment and had a higher rate of acquiring a shared and gentamicin-resistant strain, compared with infants colonized earlier. Antibiotic use increases colonization of infants in the NICU with resistant and shared strains of GNRs.

Degradation of various chlorophenols under alkaline conditions by gram-negative bacteria closely related to Ochrobactrum anthropi

From concrete debris of a demolished herbicide production plant several Gram-negative bacterial strains were isolated, which exhibit metabolic capabilities for the degradation of 2,4-dichlorophenol (DCP)l), 4-chloro-2-methylphenol (MCP) and 4-chlorophenol (4-CP), while 2-chlorophenol (2-CP) was degraded at a slower rate. Degradative activity was inducible and was impeded by adding of 100 mg/l of chloramphenicol to growing cultures. The strains displayed alkaliphilic properties with optimum DCP/MCP degradation at pH values around 8.5-9.5; activity was observed up to pH values of 11. Degradation was most likely complete according to chlorine balances; formation of intermediary products was observed with MCP some time. Specific activity of up to 380 mumol/h.g dry mass was found within the concentration range of 10-20 mg/l DCP; higher concentrations retarded the activity with complete inhibition at 200-400 mg/l. Some of the strains carry plasmids whose presence was not unambiguously correlated to the degradative properties. Ribotyping revealed a high degree of relationship between the strains. Preliminary taxonomic investigations showed close relationship to Ochrobactrum anthropi.

Brucella abortus and its closest phylogenetic relative, Ochrobactrum spp., differ in outer membrane permeability and cationic peptide resistance

The outer membrane (OM) of the intracellular parasite Brucella abortus is permeable to hydrophobic probes and resistant to destabilization by polycationic peptides and EDTA. The significance of these unusual properties was investigated in a comparative study with the opportunistic pathogens of the genus Ochrobactrum, the closest known Brucella relative. Ochrobactrum spp. OMs were impermeable to hydrophobic probes and sensitive to polymyxin B but resistant to EDTA. These properties were traced to lipopolysaccharide (LPS) because (i) insertion of B. abortus LPS, but not of Escherichia coli LPS, into Ochrobactrum OM increased its permeability; (ii) permeability and polymyxin B binding measured with LPS aggregates paralleled the results with live bacteria; and (iii) the predicted intermediate results were obtained with B. abortus-Ochrobactrum anthropi and E. coli-O. anthropi LPS hybrid aggregates. Although Ochrobactrum was sensitive to polymyxin, self-promoted uptake and bacterial lysis occurred without OM morphological changes, suggesting an unusual OM structural rigidity. Ochrobactrum and B. abortus LPSs showed no differences in phosphate, qualitative fatty acid composition, or acyl chain fluidity. However, Ochrobactrum LPS, but not B. abortus LPS, contained galacturonic acid. B. abortus and Ochrobactrum smooth LPS aggregates had similar size and zeta potential (-12 to -15 mV). Upon saturation with polymyxin, zeta potential became positive (1 mV) for Ochrobactrum smooth LPS while remaining negative (-5 mV) for B. abortus smooth LPS, suggesting hindered access to inner targets. These results show that although Ochrobactrum and Brucella share a basic OM pattern, subtle modifications in LPS core cause markedly different OM properties, possibly reflecting the adaptive evolution of B. abortus to pathogenicity.

Antibacterial agents that target lipid A biosynthesis in gram-negative bacteria. Inhibition of diverse UDP-3-O-(r-3-hydroxymyristoyl)-n-acetylglucosamine deacetylases by substrate analogs containing zinc binding motifs

UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) catalyzes the second step in the biosynthesis of lipid A, a unique amphiphilic molecule found in the outer membranes of virtually all Gram-negative bacteria. Since lipid A biosynthesis is required for bacterial growth, inhibitors of LpxC have potential utility as antibiotics. The enzymes of lipid A biosynthesis, including LpxC, are encoded by single copy genes in all sequenced Gram-negative genomes. We have now cloned, overexpressed, and purified LpxC from the hyperthermophile Aquifex aeolicus. This heat-stable LpxC variant (the most divergent of all known LpxCs) displays 32% identity and 51% similarity over 277 amino acid residues out of the 305 in Escherichia coli LpxC. Although A. aeolicus LpxC deacetylates the substrate UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine at a rate comparable with E. coli LpxC, a phenyloxazoline-based hydroxamate that inhibits E. coli LpxC with K(i) of approximately 50 nM (Onishi, H. R., Pelak, B. A., Gerckens, L. S., Silver, L. L., Kahan, F. M., Chen, M. H., Patchett, A. A., Galloway, S. M., Hyland, S. A., Anderson, M. S., and Raetz, C. R. H. (1996) Science 274, 980-982) does not inhibit A. aeolicus LpxC. To determine whether or not broad-spectrum deacetylase inhibitors can be found, we have designed a new class of hydroxamate-containing inhibitors of LpxC, starting with the structure of the physiological substrate. Several of these compounds inhibit both E. coli and A. aeolicus LpxC at similar concentrations. We have also identified a phosphinate-containing substrate analog that inhibits both E. coli and A. aeolicus LpxC, suggesting that the LpxC reaction proceeds by a mechanism similar to that described for other zinc metalloamidases, like carboxypeptidase A and thermolysin. The differences between the phenyloxazoline and the substrate-based LpxC inhibitors might be exploited for developing novel antibiotics targeted either against some or all Gram-negative strains. We suggest that LpxC inhibitors with antibacterial activity be termed "deacetylins."

Heavy metal-resistant bacteria as extremophiles: molecular physiology and biotechnological use of Ralstonia sp. CH34

In contrast to thermophilic or psychrophilic organisms, heavy metal-resistant bacteria do not supply enzymes that are active under harsh conditions, but are themselves tools for the evaluation and remediation of heavy metal-contaminated environments. Ralstonia sp. CH34 is a gram-negative bacterium with a remarkable set of resistance determinants, allowing this bacterium to live in extreme environments that are heavily contaminated with toxic metal ions. These heavy metal ions are mostly detoxified by inducible ion efflux systems that reduce the intracellular concentration of a given ion by active export. Because all metal resistance determinants in this bacterium are inducible, their regulatory systems can be used to develop biosensors that measure the biologically important concentrations of heavy metals in an environment. Resistance based on metal ion efflux detoxifies only the cytoplasm of the respective cell. Therefore, this resistance mechanism cannot be used directly to develop biotechnological procedures; however, metal ion efflux can protect a cell in a metal-contaminated environment. Thus, the cell can be enabled to mediate biochemical reactions such as precipitation of heavy metals with the carbon dioxide produced during growth or degradation of xenobiotics.

[Ornithobacterium rhinotracheale infections in poultry: a review]

O. rhinotracheale is a relatively new bacterium. It is found in commercial fowl and wild birds throughout the world. O. rhinotracheale causes respiratory disease, presenting as pneumonia and air sacculitis. It is transmitted horizontally as well as vertically. O. rhinotracheale is difficult to isolate. Serologically, twelve serotypes can be distinguished, of which serotype A is the most prevalent. Treatment can be difficult, because acquired resistance against the regular antibiotics is common in O. rhinotracheale isolates. An inactivated vaccine for broiler breeders has been developed and for turkeys an inactivated autovaccine can be made.

Mechanism of antibacterial and degradation behavior of a chlorinated isoxazolylnaphthoquinone

The chemical stability of 3-chloro-2-hydroxy-(3, 4-dimethyl-5-isoxazolyl)-1,4-naphthoquinon-4-imine (ClQ(1)), a new potential antimicrobial agent was analyzed at different pH values by first-derivative spectroscopy. The degradation of ClQ(1) followed a pseudo-first-order kinetics in aqueous media at different pH values. The interaction of antibiotics with respiratory chain of Staphylococcus aureus generates superoxide anion, an oxygen radical capable of producing damage to the bacteria. The performed assays have demonstrated that ClQ(1) presents higher activity and toxic oxidant generation at pH 5.0 than at pH 7.5. In addition, the antibacterial activity of other halogenated isoxazolylnaphthoquinones was also studied in different collection and clinical strains which presented the following decreasing activity, ClQ(1) > BrQ(1) > DClQ(1) whereas DBrQ(1) did not show inhibition properties. The antibacterial and stability properties evidenced by ClQ(1) are so important that must be taken into account when new alternative treatments against beta-lactamase-positive S. aureus strains are investigated.

Interactions between cationic liposomes and bacteria: the physical-chemistry of the bactericidal action

The bactericidal effect of dioctadecyldimethylammonium bromide (DODAB), a liposome forming synthetic amphiphile, is further evaluated for Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, and Staphylococcus aureus in order to establish susceptibilities of different bacteria species towards DODAB at a fixed viable bacteria concentration (2.5 x 10(7) viable bacteria/mL). For the four species, susceptibility towards DODAB increases from E. coli to S. aureus in the order above. Typically, cell viability decreases to 5% over 1 h of interaction time at DODAB concentrations equal to 50 and 5 microm for E. coli and S. aureus, respectively. At charge neutralization of the bacterial cell, bacteria flocculation by DODAB vesicles is shown to be a diffusion-controlled process. Bacteria flocculation does not yield underestimated counts of colony forming units possibly because dilution procedures done before plating cause deflocculation. The effect of vesicle size on cell viability demonstrates that large vesicles, due to their higher affinity constant for the bacteria (45.20 m(-)) relative to the small vesicles (0.14 m(-)), kill E. coli at smaller DODAB concentrations. For E. coli and S. aureus, simultaneous determination of cell viability and electrophoretic mobility as a function of DODAB concentration yields a very good correlation between cell surface charge and cell viability. Negatively charged cells are 100% viable whereas positively charged cells do not survive. The results show a clear correlation between simple adsorption of entire vesicles generating a positive charge on the cell surfaces and cell death.

Beta-lactamases and outer membrane investigations in beta-lactam-resistant Comamonas acidovorans strains

Imipenem-induced beta-lactamase (level of expression, specific activity and kinetic parameters (Vmax and Km) in response to nitrocefin) and outer membrane proteins (OMPs) (hydrophobicity, permeability and electrophoretic pattern) were characterized in, one beta-lactam sensitive (PAC-9), one resistant (PAC-1) and two resistant laboratory mutants (PAC-9M, PAC-9M2) of Comamonas acidovorans strains. Beta-lactamases from both mutant strains showed different Vmax values compared to the parental strains. Beta-lactam resistance was found to be associated in PAC-1 with inducible beta-lactamase production and OMP alteration by the appearance of a 102-KDa protein. Moreover, PAC-1 was less permeable to nitrocefin than PAC-9. These data indicate that C. acidovorans resistance to beta-lactam resulted from synergy between beta-lactamase and OMP alterations.

[A consideration on the results of nationwide surveillance of antimicrobial susceptibilities--gram-positive cocci and gram-negative cocci]

The results of the semi-annual nationwide surveillance of antimicrobial susceptibilities, conducted by the Japanese Ministry of Health and Welfare during the period of January 1993 to July 1995, were analyzed for typical Gram-positive cocci and Gram-negative cocci in the purpose of provision of an index for antimicrobial selection. During these 3 years, Streptococcus pyogenes (group A) and Streptococcus agalactiae (group B) showed slightly increasing tendency in susceptibility to ofloxacin (OFLX) and sulfamethoxazole/trimethoprim (ST), while Streptococcus pneumoniae and Moraxella (Branhamella) catarrhalis showed slightly decreasing tendency to cefaclor (CCL). However, these annual changes were almost negligible. Generally, these microorganisms showed relatively good susceptibilities, every year, to the principal antimicrobial agents being approved for use against Gram-positive and -negative cocci. However, Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis showed tendencies of decreased susceptibility to some of the antimicrobial agents. On the other hand, cefmetazole (CMZ), vancomycin (VCM), latamoxef (LMOX), ST and minocycline (MINO) showed good activities against some of the Gram-positive and -negative cocci to which no indication are approved. In conclusion, beside the identification of the causative microorganisms and the performance of antimicrobial susceptibility testing, such analyses (graphics of susceptibility tendency of clinical isolates to variety of antimicrobial agents) could be used as an index for selection of antimicrobial agents, when emergent and urgent selection of an antimicrobial agent is necessary.

Unusual clinical presentation of infection due to Flavimonas oryzihabitans

Six cases of Flavimonas oryzihabitans infection are presented, four of which were community-acquired pneumonia and two of which were nosocomially acquired bacteremia. All four cases of pneumonia occurred in immunosuppressed hosts, three of whom were HIV-positive individuals and one of whom was a young man affected by chronic myeloid leukemia. Flavimonas oryzihabitans is recognized with increasing frequency as a cause of opportunistic infection, but the present cases of community-acquired pneumonia due to this organism are believed to be the first four reported in the English literature. The findings emphasize that Flavimonas oryzihabitans should be included in the list of pathogens that cause community-acquired infections in the immunocompromised host.

Advances in the macrolides and quinolones

The widespread, frequent clinical use of the macrolides and quinolones has led to resistance in several species. With the prevailing increase of resistance, new developmental compounds with improved spectra, pharmacokinetics, and reduced adverse effects are required, coupled with logical use of the current armamentarium.

Clinical problems posed by multiresistant nonfermenting gram-negative pathogens

In this review I will briefly survey the role of Pseudomonas aeruginosa, Acinetobacter baumanii, Stenotrophomonas maltophilia, and Burkholderia cepacia as opportunistic pathogens. A common feature of these organisms is intrinsic resistance to multiple antibiotics. All of these organisms can be recovered from the environment, commonly cause device-related infections, are often resistant to disinfectants, and have the potential to spread from patient to patient via fomites or the hands of medical personnel. Newer clinical syndromes will be emphasized, including the increasing importance of P. aeruginosa infections in patients with AIDS, as well as the role of carbapenems in selecting for A. baumanii and S. maltophilia and the unique niche of B. cepacia in patients with cystic fibrosis.

[Evaluation of antibacterial activities of various antibiotics against glucose non-fermentative gram-negative rods other than Pseudomonas aeruginosa]

MICs of piperacillin, sulbactam/cefoperazone, minocycline (MINO), gentamicin, amikacin, flomoxef, ceftazidime, cefozopran, cefsulodin and imipenem were determined, against 189 clinical isolated strains of glucose non-fermentative Gram-negative Rods (NFGNR; Acinetobacter baumannii (44), Alcaligenes faecalis (5), Alcaligenes xylosoxidans (25), Burkholderia cepacia (12), Chryseobacterium indologenes (23), Chryseobacterium meningosepticum (9), Pseudomonas fluorescens (8), Pseudomonas putida (12), Stenotrophomonas maltophilia (51). Most species of these NFGNR show resistance to many antibiotics tested. Among the antibiotics used in this study, the only antibiotic effective against all species of NFGNR tested is MINO. The spectrums of antibacterial activities of various antibiotics determined by MICs may be useful in preliminary test for identification of these NFGNR.

Extended-spectrum beta-lactamases: an actual problem of hospital microbiology (a review)

Although there is a variety of mechanisms of bacterial resistance to beta-lactam antibiotics, the most important one is production of beta-lactamases inactivating penicillins and cephalosporins. The classification of beta-lactamases is based on biochemical, enzymological (i.e. molecular structure, inhibitory property, substrate-profile, relative rate of hydrolysis) and immunological characters. Extended-spectrum beta-lactamases (ESBLs) can be derived from TEM or SHV enzymes. These enzymes have now been sequenced and it has been found that relatively few point mutations have occurred in the gene of the TEM and SHV type enzymes. These point mutations clustered in five areas of the gene. The amino acid mutations can alter the conformation, the active site and change the hydrance of beta-lactamase-cephalosporin binding capacity. So the enzyme is able to bind and hydrolyse the third generation cephalosporins. Successive mutation interacted radically increasing the binding capacity of enzymes and confer resistance to newer cephalosporins. The use of these drugs provides a strong selective pressure to develop these mutations. Sporadic nosocomial outbreaks due to strains producing an ESBL led to an epidemic problem in some hospitals resulting in a concurrent dissemination of genes, plasmids or strains. Clinical epidemiological importance and role of ESBLs and emergence of multiply resistance of bacteria of nosocomial importance are discussed in this brief.

Construction and characterization of an NaCl-sensitive mutant of Halomonas elongata impaired in ectoine biosynthesis

Using transposon mutagenesis we generated a salt-sensitive mutant of the halophilic eubacterium Halomonas elongata impaired in the biosynthesis of the compatible solute ectoine. HPLC determinations of the cytoplasmic solute content showed the accumulation of a biosynthetic precursor of ectoine, L-2,4-diaminobutyric acid. Ectoine and hydroxyectoine were not detectable. This mutant failed to grow in minimal medium with NaCl concentrations exceeding 4%. However, when supplemented with organic osmolytes, the ability to grow in high-salinity medium (15% and higher) was regained. We cloned and sequenced the regions flanking the transposon insertion in the H. elongata chromosome. Sequence comparisons with known proteins revealed significant similarity of the mutated gene to the L-2,4-diaminobutyric acid acetyltransferase from the ectoine biosynthetic pathway in Marinococcus halophilus. Analysis of a PCR product demonstrated that the ectoine biosynthetic genes (ectABC) follow the same order as in M. halophilus.

Regulation of poly(beta-hydroxybutyrate) synthesis in Methylobacterium rhodesianum MB 126 growing on methanol or fructose

The intracellular concentration of CoA metabolites and nucleotides was determined in batch cultures of Methylobacterium rhodesianum grown on methanol and shifted to growth on fructose. The intracellular concentration of CoA decreased from a high value of 0.6 nmol/mg poly(beta-hydroxybutyrate)-free bacterial dry mass during growth on methanol to a low value of 0.03 nmol/mg poly(beta-hydroxybutyrate)-free bacterial dry mass after a shift to fructose as a carbon source. The levels of NADH, NADPH, and acetyl-CoA were also lower. Under these conditions, acetyl-CoA was metabolized by both citrate synthase and beta-ketothiolase, and poly(beta-hydroxybutyrate) synthesis and growth occurred simultaneously during growth on fructose. Moreover, the level of ATP was approximately 50% lower during growth on fructose, supporting the hypothesis of a bottleneck in the energy supply during the growth of M. rhodesianum with fructose.

Biomineralization of carbonates by Halomonas eurihalina in solid and liquid media with different salinities: crystal formation sequence

Carbonate precipitation by 20 strains of the moderately halophilic species Halomonas eurihalina in both solid and liquid media was studied. The influence of salinity and temperature on the quantity and type of crystals precipitated was also investigated. Some strains of H. eurihalina formed crystals in all conditions tested. The mineral phases precipitated were magnesium calcite, aragonite and monohydrocalcite in variable proportions depending on various factors such as the type of growth medium employed and its salinity. Scanning electron microscopy and X-ray dispersive energy microanalysis were used to investigate the crystal formation sequence. The process of biolith formation was sequential. It started with chains or filaments of bacteria, giving way to discs which finally produced spherical forms of approximately 50 microns in diameter. We suggest a mechanism of carbonate crystal formation by H. eurihalina.

[Ecological consequences of radioactive pollution for soil bacteria within the 10-km region around the Chernobyl Atomic Energy Station]

The diversity of aerobic chemoorganotrophic (capable of growing on nutrient agar) bacteria in radioactive soil (0.3-17.0 microCi/kg soil) sampled in the 10-km zone around the Chernobyl Nuclear Power Plant (CNPP) was found to be lower than that observed in control, uncontaminated soil with a radioactivity of 0.002-0.006 microCi/kg soil. All the radioactive soil samples contained the bacteria Bacillus cereus and Methylobacterium extorquens or M. mesophillicum, which exhibited a high tolerance to 0.3-1.0 M hydrogen peroxide, whose action can to a certain extent simulate the effect of ionizing radiation. Some of the contaminated soil samples contained other species of chemoorganotrophic bacteria with a low tolerance to H2O2. The survival of bacteria in the Chernobyl accident zone is probably due to the functioning of mechanisms efficiently neutralizing peroxide compounds and repairing radiation-damaged DNA. The population of cellulolytic, nitrifying, and sulfate-reducing bacteria in contaminated soil was found to be 1-2 orders of magnitude less than in control soil, indicating the unfavorable effect of anthropogenic radiation on the abundance and diversity of soil bacteria.

Antimicrobial activity and spectrum investigation of eight broad-spectrum beta-lactam drugs: a 1997 surveillance trial in 102 medical centers in the United States. Cefepime Study Group

Because antimicrobial agents become less effective after the emergence of resistance mechanisms in clinically prevalent pathogens, physicians must utilize local, regional, and national antimicrobial susceptibility surveillance data to assist in choices of appropriate agents. An investigation of the spectrum and potency of eight broad-spectrum beta-lactam drugs (cefepime, cefotaxime, ceftazidime, ceftriaxone, imipenem, piperacillin with or without tazobactam, and ticarcillin/clavulanic acid) was performed using a common protocol and method (Etest; AB BIODISK, Solna, Sweden) in 102 clinical microbiology laboratories in the United States. A total of 9777 strains of Gram-negative bacilli were tested from late 1996 through April 1997. Quality assurance measures using three control strains observed quality control failures in 13 laboratories (usually ticarcillin/clavulanic acid or piperacillin), but only 2% of results required deletion. A total of 33.4% of Enterobacter spp. (1977 strains) were either resistant or intermediately susceptible to ceftazidime. Only imipenem (99.6% susceptible) and cefepime (99.1%) remained highly active against strains of Enterobacter, as well as Citrobacter freundii, indole-positive Proteae, and Serratia spp. Ceftazidime-resistant Escherichia coli and Klebsiella pneumoniae were detected at rates of 10.3% and 23.8%, respectively. Although these were participant-selected strains, only imipenem and cefepime had broad-spectrum coverage (> or = 97.1%) against these extended-spectrum beta-lactamase phenotypes. A dominant number of these extended-spectrum beta-lactamase phenotypes were reported from medical centers in the Northeast, but a nationwide distribution was observed. Among the nonenteric Gram-negative bacilli (4057 strains), the rank order of susceptibility (percent inhibited at published breakpoint concentrations) was: imipenem (86.1%) > piperacillin/tazobactam (80.1%) > cefepime (77.1%) > ceftazidime = piperacillin (74.9%) > ticarcillin/clavulanic acid (61.6%) > cefotaxime (18.2%) > ceftriaxone (12.9%). The cephalosporins, cefepime and ceftazidime, had rates of resistance for the 3005 Pseudomonas aeruginosa isolates of 10.1% and 14.4%, respectively. For all Gram-negative strains tested, only two contemporary beta-lactam antimicrobials exhibited > 90% inhibition of strains, imipenem at 93.6% and cefepime at 90.2%. These drugs were superior to the other tested compounds (48.8-84.3%). Ticarcillin/clavulanic acid had the narrowest spectrum of activity (48.8% of isolates susceptible). These results indicate that carbapenems and a new fourth-generation cephalosporin, cefepime, possess usable in vitro potencies against current clinical strains of Gram-negative bacilli, many of which harbored resistance to other antimicrobial agents.

Multicenter evaluation of the in vitro activity of six broad-spectrum beta-lactam antimicrobial agents in Puerto Rico. The Puerto Rico Antimicrobial Resistance Study Group

The minimum inhibitory concentrations of 6 broad-spectrum beta-lactam antimicrobial agents were determined by use of the Etest versus a total of 569 bacteria in 7 Puerto Rican hospital laboratories. These included 342 recent clinical isolates of Enterobacteriaceae, 63 Pseudomonas aeruginosa, 54 Acinetobacter species, and 110 oxacillin-susceptible staphylococci. Extended spectrum beta-lactamase production was noted among 11% of Klebsiella pneumoniae isolates. Hyperproduction of Amp C cephalosporinase was observed with > 20% of isolates of Enterobacter spp., Serratia spp., and Citrobacter freundii. The overall rank order of activity of the six beta-lactams examined in this study versus all clinical isolates was imipenem (95.8% susceptible) > cefepime (91.1%) > piperacillin/ tazobactam (82.3%) > cefotaxime (77.6%) > piperacillin (72.5%) > ceftazidime (67.0%).

Multicenter evaluation of the antimicrobial activity for six broad-spectrum beta-lactams in Venezuela using the Etest method. The Venezuelan Antimicrobial Resistance Study Group

In early 1997, a 15-laboratory surveillance project was initiated in Venezuela to monitor the potency and spectrum of 6 broad-spectrum antimicrobial agents (cefepime, cefotaxime, ceftazidime, piperacillin, piperacillin/tazobactam, and imipenem) tested against approximately 100 organisms per participant center (1297 strains). Ten groups of organisms were tested by the Etest method (AB BIODISK, Solna, Sweden) with results validated by concurrent quality control strain analysis. Results from all centers were tabulated and 96.3% of quality assurance tests were within ranges recommended by the National Committee for Clinical Laboratory Standards. Among the six beta-lactam class drugs tested, imipenem and cefepime were the most active against all isolates tested. Overall, the rank order of susceptibility of the six agents was imipenem (97.2%, susceptible; MIC90 2 micrograms/ml) > cefepime (92.8%; MIC90 6 micrograms/mL) > piperacillin/tazobactam (77.2-83.0%; MIC90 > 256 micrograms/mL) > cefotaxime (72.2%; MIC90 > 256 micrograms/mL) > piperacillin (56.8-65.8%; MIC90 > 256 micrograms/mL) > ceftazidime (64.66%; MIC90 128 micrograms/mL). Both cefepime and imipenem were active against ceftazidime-resistant strains of Enterobactericaeae as well as against Pseudomonas aeruginosa and oxacillin-susceptible staphylococci. Resistance phenotypes consistent with extended spectrum beta-lactamases (ESBLs) and stably derepressed Bush group 1 cephalosporinases were documented in strains of Klebsiella spp. and Enterobacters, respectively. These data should be used to guide empiric therapy with beta-lactams in Venezuela, and additionally will provide a reference statistical baseline to which future studies in this nation can be compared.

Meningitis due to Ochrobactrum anthropi: an emerging nosocomial pathogen. A report of 3 cases

We describe 3 cases of Ochrobactrum anthropi meningitis following the implantation of pericardial allograft tissue to cover dural defects following craniotomy. Following an extensive epidemiologic investigation, the tissue allograft was found to have been contaminated with this unusual organism during the harvesting and processing of the tissue in the tissue bank. This organism was only susceptible to imipenem, tetracycline, gentamicin, and ciprofloxacin. The clinical presentation of these patients was subacute. Two of the patients developed osteomyelitis of the bone flap; while another developed a relapse of infection along a former ventriculoperitoneal shunt track 6 months after the initial infection. Appropriate clinical outcome was only observed after removal of tissue allograft implants, debridement of devitalized tissue and bone, removal of shunt devices, and prolonged courses of antibiotics. No deaths were observed.