In vitro antimicrobial activity of doripenem, a new carbapenem

The doripenem MICs at which 90% of the tested strains were inhibited ranged from 0.03 to 1 microg/ml for 10 species of Enterobacteriaceae (n = 351), from 0.03 to 0.12 microg/ml for oxacillin-susceptible staphylococci (n = 119), from 4 to 32 microg/ml for oxacillin-resistant staphylococci (n = 64), from < or =0.008 to 0.06 microg/ml for penicillin-susceptible streptococci (n = 132), and from 1 to 4 microg/ml for penicillin-resistant streptococci (n = 51). Overall, doripenem demonstrated in vitro activity similar to that of meropenem against gram-negative pathogens and to that of imipenem against gram-positive pathogens.

Prevention of the selection of resistant Staphylococcus aureus by moxifloxacin plus doxycycline in an in vitro dynamic model: an additive effect of the combination

Twenty-four hour ratios of area under the curve (AUC(24)) to MIC of 200-240 h providing quinolone concentrations above the mutant prevention concentration (MPC) protected from enrichment of resistant Staphylococcus aureus in our recent study that simulated the pharmacokinetics of moxifloxacin, gatifloxacin, levofloxacin and ciprofloxacin. These protective AUC(24)/MICs might also be achieved by using antibiotic combinations, assuming additive effects of two anti-staphylococcal agents. To test this hypothesis, changes in S. aureus susceptibility were examined in a dynamic model that simulates 5-day treatment with moxifloxacin and doxycycline, alone and in combination at sub-optimal AUC(24)/MICs of each agent. Significant increases in MIC were observed with monotherapy where moxifloxacin or doxycycline concentrations fell into the mutant selection window (MSW) for more than 80% of the dosing interval (AUC(24)/MIC 60 h). Less pronounced changes in MIC occurred when the summed concentrations of moxifloxacin (AUC(24)/MIC 30 and 60 h) and doxycycline (AUC(24)/MIC 30 and 60 h) were inside the MSWs for the individual drugs for 30-50% of the dosing interval. No loss in susceptibility was found at moxifloxacin or doxycycline AUC(24)/MIC 170 h combined with the smaller AUC(24)/MIC (60 h) of the second compound. These data suggest that the total AUC(24)/MIC of 230 h might protect against S. aureus resistance. As this value is very close to that predicted in monotherapy with moxifloxacin (220 h), an additive protective effect of quinolone+doxycycline on the selection of resistant S. aureus is proposed. The use of drug combinations may be useful for restricting the enrichment of resistant mutants with agents whose clinically achievable AUC(24)/MICs do not provide concentrations above the MPC.

In vitro activity of mupirocin and amoxicillin-clavulanate alone and in combination against staphylococci including those resistant to methicillin

Mupirocin and amoxicillin-clavulanate were synergistic against 9 of 49 (18%) strains of methicillin-resistant and methicillin-susceptible Staphylococcus aureus and coagulase-negative staphylococci (CNS). A pattern of enhanced killing was also found using time-kill studies. Time-kill assays were more discriminatory than chequerboard titration assays in demonstrating synergy. These results suggest that combinations of amoxicillin-clavulanate and mupirocin may have therapeutic benefits in prophylaxis against staphylococcal infections.

Effect of antibiotic sequence on combination regimens against Pseudomonas aeruginosa in a multiple-dose, in vitro infection model

The goal of this study was to investigate the effect of antibiotic sequence on combination regimens against Pseudomonas aeruginosa in an in vitro infection model. Ceftazidime plus ciprofloxacin and ceftazidime plus tobramycin were dosed every 12 h for 48 h using simultaneous or staggered administration. Simultaneous dosing and ceftazidime followed by ciprofloxacin or tobramycin were significantly more active at both 24 h (p = 0.03) and 48 h (p < 0.0001) than ciprofloxacin or tobramycin followed by ceftazidime. Final bacterial kill was sixfold greater with the former regimens. This study showed that antibiotic sequence had a significant and class dependent effect on antibacterial response. The clinical relevance of these observations warrants further investigations in animal models.

Surveillance of susceptibility patterns in 1297 European and US anaerobic and capnophilic isolates to co-amoxiclav and five other antimicrobial agents

In vitro susceptibility data were collected for co-amoxiclav and other antimicrobial agents against 1297 recent anaerobe isolates collected in Europe and the USA. The co-amoxiclav (amoxicillin/clavulanic acid) MIC(50/90)s (amoxicillin/clavulanic acid concentration in a ratio of 2:1, expressed in terms of amoxicillin concentration in mg/L) were 0.5/4 for Bacteroides fragilis, </=0.125/1 for Prevotella species, </=0.125/0.25 for Fusobacterium nucleatum, 0.5/1 for Eikenella corrodens, 0.25/8 for Peptostreptococcus anaerobius, </=0.125/0.5 for Micromonas (Peptostreptococcus) micros, </=0.25/0.5 for Fingoldia (Peptostreptococcus) magna, and </=0.125/0.125 for Porphyromonas species. The co-amoxiclav susceptibility rate for B. fragilis was 94.6%, for P. anaerobius 84.3% and for all other species tested 100%. These data indicate that co-amoxiclav remains an effective drug for the antimicrobial treatment and prophylaxis of many anaerobic infections. Among the comparator drugs, metronidazole was very active against all bacterial species (>96% susceptible) except E. corrodens (MIC(50/90) of >32/>64 mg/L), which is a capnophilic organism. Imipenem was also highly active against all species (>98% susceptible). Levofloxacin and clindamycin were the least potent agents tested, particularly against Bacteroides, Prevotella and Peptostreptococcus (levofloxacin susceptibility rates: Bacteroides 72.7%, Prevotella 71.5%, F. magna 72.4%; clindamycin susceptibility rates: Bacteroides 79.5%, Prevotella 92.1%, F. magna 84.7%).

In vitro and in vivo activities of antimicrobials against Nocardia brasiliensis

In Mexico mycetomas are mostly produced by Nocardia brasiliensis, which can be isolated from about 86% of cases. In the present work, we determined the sensitivities of 30 N. brasiliensis strains isolated from patients with mycetoma to several groups of antimicrobials. As a first screening step we carried out disk diffusion assays with 44 antimicrobials, including aminoglycosides, cephalosporins, penicillins, quinolones, macrolides, and some others. In these assays we observed that some antimicrobials have an effect on more than 66% of the strains: linezolid, amikacin, gentamicin, isepamicin, netilmicin, tobramycin, minocycline, amoxicillin-clavulanic acid, piperacillin-tazobactam, nitroxolin, and spiramycin. Drug activity was confirmed quantitatively by the broth microdilution method. Amoxicillin-clavulanic acid, linezolid, and amikacin, which have been used to treat patients, were tested in an experimental model of mycetoma in BALB/c mice in order to validate the in vitro results. Linezolid showed the highest activity in vivo, followed by the combination amoxicillin-clavulanic acid and amikacin.

Inhibition of Resistance Plasmid Transfer in Escherichia coli by Ionophores, Chlortetracycline, Bacitracin, and Ionophore/Antimicrobial Combinations

Medicinal feed additives bacitracin, chlortetracycline (CTC), laidlomycin, lasalocid, and salinomycin inhibited the transfer of multiresistance-conferring plasmid pBR325 (Tet(r) Amp(r) Cp(r), 6.0 kb) into selected gram-negative strains with the use of an in vitro model. High concentrations of ampicillin-sensitive competence-pretreated Escherichia coli HB 101 cells were exposed to 10% (v/v) of 1:10 dimethyl sulfoxide/agent : water containing test mixtures for 0.5 hr prior to plasmid addition and transforming conditions. Transformation was inhibited for all antimicrobials and showed a positive association wich higher concentration. Additional testing of ionophore compounds separately and in combination with bacitracin, chlortetracycline, lincomycin, roxarsone, tylosin, and virginiamycin at representative feed concentrations demonstrated 80.6% to >99.9% inhibition (P < 0.001) of resistance transfer. Bacitracin alone inhibited transformation within the range of 50-500 ppm. No increase in resistance transfer was observed when poultry-derived and reference gram-negative isolates having low or no transformation efficiency were additionally tested. The results suggest that these compounds, at relevant concentrations used in animal feed, may interfere with cell envelope-associated DNA uptake channels or other transformation competence mechanisms. Through these mechanisms, ionophores and cell membrane-interactive feed agents such as CTC and bacitracin may act to inhibit resistance transfer mechanisms within poultry and livestock.

Protothecosis successfully treated with amikacin combined with tetracyclines. Fallbericht. Protothecose erfolgreich mit Amikacin plus Tetracyclinen behandelt

Summary We report a case of protothecosis in an 18-year-old female student caused by Prototheca zopfii successfully treated with amikacin combined with tetracyclines. Zusammenfassung Es wird über eine Protothecose, verursacht durch Prototheca zopfii, bei einer 18-jährigen Studentin berichtet, die erfolgreich mit Amikacin in Kombination mit Tetracyclinen behandelt wurde.

Combining Quinupristin/Dalfopristin with Other Agents for Resistant Infections

OBJECTIVE

To review the resistance mechanisms of Enterococcus and Staphylococcus spp. and summarize quinupristin/dalfopristin's (QD's) effects on these resistant organisms when combined with other antibiotics via review of the literature and unpublished data.

DATA SOURCES

Data were identified by a PubMed search (1996—May 2003) using the search terms quinupristin/dalfopristin, synergy, in vitro, in vivo, vancomycin-resistant Enterococcus faecium (VREF), methicillin-resistant Staphylococcus aureus (MRSA), and individual antibiotic names. Bibliographies of the resultant PubMed searches were reviewed and included if applicable.

STUDY SELECTION AND DATA EXTRACTION

All studies reviewed were analyzed; specific drug data were included only if clinically pertinent. In vitro data from studies with adequate design were discussed, whereas all case reports and clinical trials were utilized.

DATA SYNTHESIS

In the treatment of VREF, available information seems conflicting, although some clear differences have become apparent. QD—ampicillin and QD—doxycycline combinations have demonstrated beneficial activity, usually displaying synergistic or additive effects even in macrolide-, lincosamine-, and streptogramin-resistant (MLSB) isolates. Vancomycin and chloramphenicol have shown some efficacy, but antagonistic or null results also have been observed. Regarding MRSA, results from many studies of QD combinations have been ambiguous. More common combinations displayed synergy or additive effects against MRSA, but only QD—rifampin showed consistent beneficial activity against MRSA and MLSB isolates. Most other combinations displayed antagonism when tested in vitro.

CONCLUSIONS

Data supporting the use of various QD—antibiotic combinations against VREF and MRSA are increasing, but further in vitro and in vivo data are needed to confirm the findings.

Post-antibiotic and post- -lactamase inhibitor effects of ceftazidime plus sulbactam on extended-spectrum -lactamase-producing Gram-negative bacteria

OBJECTIVES

To measure the in vitro post-antibiotic effect (PAE) and post-beta-lactamase inhibitor effect (PLIE) of a ceftazidime-sulbactam combination on bacteria producing extended-spectrum beta-lactamases (ESBLs).

METHODS

PAE and PLIE were studied for ESBL-producing strains of Escherichia coli and Klebsiella pneumoniae. Two ATCC beta-lactamase-negative strains of E. coli and K. pneumoniae were used as controls. The MICs of a ceftazidime-sulbactam combination were determined with a fixed concentration of sulbactam (8 mg/L). The organisms were exposed to the antibiotics at twice the MIC for 2 h before removal of the antibiotics by filtration of the culture. Bacteria on the filter were resuspended in drug-free medium to determine the PAE and in medium containing ceftazidime, at the same concentration as originally present, to determine the PLIE.

RESULTS

The PAE of ceftazidime was similar for bacteria producing the same ESBL except for E. coli producing CTX-M-1. PLIE values varied according to the type of beta-lactamase but similar results were observed for the strains producing the same ESBLs. PLIEs were longer than PAEs and were longer when the MICs of ceftazidime were lower.

CONCLUSIONS

To the best of our knowledge, we describe here for the first time an in vitro PLIE for a ceftazidime-sulbactam combination on different bacteria producing different ESBLs. These findings indicate that suicide inhibitors may be used in combination with third-generation cephalosporins.

Activity of natural antimicrobial compounds against Escherichia coli and Salmonella enterica serovar Typhimurium

AIMS

The objective of this study was to evaluate the inhibitory activity of several natural organic compounds alone or in combination with nisin against Escherichia coli and Salmonella Typhimurium.

METHODS AND RESULTS

The minimum inhibitory concentration (MIC) of five natural organic compounds were determined, and the effect of their combinations with nisin was evaluated by the checkerboard assay using the Bioscreen C. As expected, nisin by itself showed no inhibition against either of the Gram-negative bacteria. Thymol was found to be the most effective with the lowest MIC values of 1.0 and 1.2 mmol 1-1 against Salm. Typhimurium and E. coli, respectively. After thymol, the antimicrobial order of the natural organic compounds was carvacrol > eugenol > cinnamic acid > diacetyl. However, the combination of nisin with the natural organic compounds did not result in the enhancement of their antimicrobial activities. On the contrary, combination of nisin with diacetyl against Salm. Typhimurium resulted in an antagonism of diacetyl activity.

CONCLUSIONS

While the individual natural organic compounds showed inhibitory activity against the two Gram-negatives, their combinations with nisin showed no improvement of antimicrobial activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows the potential of the natural organic compounds to control E. coli and Salm. Typhimurium.

Bactericidal activities of daptomycin, quinupristin-dalfopristin, and linezolid against vancomycin-resistant Staphylococcus aureus in an in vitro pharmacodynamic model with simulated endocardial vegetations

In search of treatment alternatives against vancomycin-resistant S. aureus (VRSA), an in vitro pharmacodynamic model with simulated endocardial vegetations incorporating protein and a high inoculum was used to simulate daptomycin, linezolid, quinupristin-dalfopristin, and vancomycin against the Michigan VRSA strain. Daptomycin and quinupristin-dalfopristin exhibited the greatest bacterial reductions, and all tested agents except vancomycin exhibited bactericidal activity against the VRSA.

Contemporary in vitro synergy rates for aztreonam combined with newer fluoroquinolones and beta-lactams tested against gram-negative bacilli

Aztreonam has been commonly used in various combinations to enhance antimicrobial spectrum of co-drugs and produce potential synergistic activity. Although well studied in vitro over 10 years ago, aztreonam combination testing has been poorly documented with newer or commonly used agents against contemporary isolates. All MIC tests (alone or in combination) used in this experiment were reference broth microdilution methods in checkerboard tray designs. Aztreonam was combined with ciprofloxacin, gatifloxacin, levofloxacin, cefepime, ceftazidime and imipenem at clinically relevant concentrations. Interaction categories were defined by established criteria. Forty strains each of Pseudomonas aeruginosa and Enterobacteriaceae (12 species; aztreonam MIC, 1-16 microg/ml) were tested for each antimicrobial combination (480 total determinations). No antagonism or indeterminate interactions were identified. The overall rates of synergy or partial synergy for aztreonam with fluoroquinolone combinations was 63.4% versus P. aeruginosa, greatest for aztreonam with gatifloxacin (67.5%). Interaction categories varied greatly among aztreonam with beta-lactam combinations. Aztreonam with ceftazidime or cefepime versus P. aeruginosa had 75.0 - 85.0% partial or complete synergy rates, but aztreonam with imipenem showed dominant indifference (65.0%). In contrast, aztreonam with imipenem was more likely to exhibit synergy (32.5%) when tested against Enterobacteriaceae. Aztreonam, often used as an aminoglycoside substitute in antimicrobial combinations, continues to demonstrate enhanced, but variable drug activity interactions for contemporary antimicrobial combinations when tested against recent (2002) clinical isolates.

[Alternative schemes of eradication therapy and ways of overcoming acquired resistance of Helicobacter pylori to the treatment]

The author believes that eradication of Helicobacter pylori (HP) should be strictly justified and confined to cases with confirmed diagnosis of HP. Ineffective HP eradication leads to acquired resistance of HP to anti-chelicobacter therapy. How to overcome this resistance is shown.

Antimicrobial susceptibility and synergy studies of Stenotrophomonas maltophilia isolates from patients with cystic fibrosis

Stenotrophomonas maltophilia is a newly emerging pathogen being detected with increasing frequency in patients with cystic fibrosis (CF). The impact of this multidrug-resistant organism on lung function is uncertain. The optimal treatment for S. maltophilia in CF patients is unknown. We studied the in vitro activity of ten antimicrobial agents, and conducted synergy studies by using checkerboard dilutions of eight pairs of antimicrobial agents against strains isolated from 673 CF patients from 1996 to 2001. This represents approximately 7 to 23% of the CF patients in the United States who harbor S. maltophilia annually. Doxycycline was the most active agent and inhibited 80% of 673 initial patient isolates, while trimethoprim-sulfamethoxazole inhibited only 16%. High concentrations of colistin proved more active than high concentrations of tobramycin and gentamicin. Serial isolates (n = 151) from individual patients over time (median, 290 days) showed minimal changes in resistance. Synergistic or additive activity was demonstrated by trimethoprim-sulfamethoxazole paired with ticarcillin-clavulanate (65% of strains), ciprofloxacin paired with ticarcillin-clavulanate (64% of strains), ciprofloxacin paired with piperacillin-tazobactam (59% of strains), trimethoprim-sulfamethoxazole paired with piperacillin-tazobactam (55% of strains), and doxycycline paired with ticarcillin-clavulanate (49% of strains). In all, 522 (78%) isolates were multidrug resistant (i.e., resistant to all agents in two or more antimicrobial classes) but 473 (91%) of these were inhibited by at least one antimicrobial combination (median, four; range, one to eight). To determine appropriate treatment for patients with CF, it is important to monitor the prevalence, antimicrobial susceptibility, and clinical impact of S. maltophilia in this patient population.

[Case report: Otitis due to Vibrio alginolyticus]

Infections caused by Vibrio alginolyticus is generally disregarded because of the fact that it is an unusual pathogen for humans. In this report, a 57 years old male patient with otitis media has been presented. Intense and pure isolation of V. alginolyticus was achieved from the ear discharge sample. According to the history, it was detected that he was on vacation at Mediterranean coast three weeks ago, thus the transmission of the bacteria is possibly via seawater. The isolate was found sensitive to all of the tested antibiotics, and the patient was treated successfully with the combination of ciprofloxacin and amoxicillin-clavulanate. This case was presented to withdraw attention to V. alginolyticus infections which are very rarely seen, but should be taken into consideration in related cases.

[Interaction of neomycin with other antibiotics on selected bacterial strains]

Antimicrobial combinations are used most frequently to provide broad-spectrum empirical coverage in the treatment of bacterial infections. However, combination of two antibiotics may not influence their activity, may lead to synergy or antagonism in the activity. Neomycin may be combined with one of the following antibiotics: ampicillin, procaine penicillin, gramicidin, bacitracin, polymyxin B, lincomycin, oxytetracycline, and erythromycin in some human and veterinary multiantibiotic drugs distributed in Poland. The checkerboard method has been one of the traditional assays for the measurement of antibiotic interactions. The aim of this study was to analyse the activity interaction of neomycin with second antibiotic in multiantibiotic drugs distributed in Poland on standards and clinical bacterial strains. Checkerboard results for all strains demonstrated synergism for 2.5% of combinations, only for standards strains. In one case Salmonella Enteritidis, in combination of neomycin with bacitracin, inhibition effect was observed. Additive effects were predominant--49%. In 18% neutral effects were shown, but in 26% of combinations FIC indexes were not possible to calculate, because of the resistance of clinical strains to the highest concentration of at least one antibiotic. In combination of aminoglycoside (neomycin) with beta-lactams antibiotics (ampicillin, procaine penicillin) in vitro, no synergy was observed for all examined strains. The best results were achieved for combinations of neomycin with peptide antibiotics (polymyxin, gramicidin and bacitracin)--5 for all 6 synergy effect observed.

Elements of design: the knowledge on which we build

The time the free drug serum concentration of antibiotic remains above the pathogen MIC (T > MIC) determines bacteriological efficacy and emergence or selection of resistance for penicillin and amoxicillin with or without clavulanate. Multiple studies in animal and in-vitro models now support this conclusion. The size of the T > MIC (the pharmacokinetic/-dynamic target) is > 40-50% to maximise antibacterial effect and pathogen eradication for Streptococcus pneumoniae and probably also Haemophilus influenzae. The size of the T > MIC for optimal antibacterial effect is changed by host immune status but not by bacterial inoculum or mechanism of resistance. There is good animal evidence to support the prediction that, as long as the target T > MIC is achieved, strains of S. pneumoniae with amoxicillin MICs of 0.016 mg/L will respond to amoxicillin in the same way as those with MICs of 1-2 mg/L. Emergence of resistance to amoxicillin/clavulanate in S. pneumoniae is related to low T > MIC (< 20%) and also to the degree of population heterogeneity to amoxicillin. Selection of resistant strains of S. pneumoniae is also related to T > MIC. Monte Carlo simulations based on the pharmacokinetics of amoxicillin with or without clavulanate in humans are needed to best predict the likely efficacy of different amoxicillin dosing regimens. This approach adequately allows the considerable pharmacokinetic variability in amoxicillin handling by infected patients to be accounted for as well as differences in pathogen beta-lactam susceptibility.

[Epidemiological, clinical and biological profile of resistant or recurrent pulmonary tuberculosis in Abidjan]

From August to December 1998, over a period of 5 months, a cross-sectional study had been carried out in Abidjan in order to analyze the epidemiological and microbiological features of BAAR+ TB patients in situation of failure or relapse after specific treatment. We investigated 79 patients enrolled in the departments of pulmonary disease of two general hospitals in Abidjan (CHU of Cocody and Treichville) and a TB outpatients' clinic. From 45 strains of Mycobacterium obtained by culture, 33 antibiograms were performed. The rate of multi-drug-resistance (MDR-TB) was 79%. Among MDR--TB patients, those aged of 20-40 years were the most concerned age group (72%) with a clear male predominant rate (sex ratio: 3). Among them 49/79 (62%) had an educational level lower or equal to primary school standarts and most of them lived in dwellings with common yard (67%). In their medical history only 40% had tuberculosis and 2 cases of self-medication were reported. MDR--TB prevailed among patients having at first a positive bacilloscopy. No link between HIV infection and MDR--TB was found.

[Comparison of checkerboard and time-kill methods for the analysis of two antibiotics combined]

Activity interaction analysis of two antibiotics by two methods: checkerboard and "time-kill" was compared during this study. Combinations of procaine penicillin, polymyxin B and bacitracin with neomycin and procaine penicillin with dihydrostreptomycin were examined. Checkerboard method is the most widely used technique for antimicrobials interactions analyses. The "time-kill" method, performed by the broth macrodilution technique, provides a dynamic picture of antimicrobial action and interaction over time (based on serial colony counts). Differences of "time-kill" method and the checkerboard technique, allow single visual examination (after 16 to 24 hours of incubation). Additive and inhibition effects were observed in combinations of neomycin with beta-lactam antibiotic (procaine penicillin) and peptide antibiotics (bacitracin and polymyxin B) on clinical strain S. Enteritidis IL 35 "Time-kill" method also confirmed observations mentioned above. In combinations of procaine penicillin with dihydrostreptomycin on strains E. coli IL 531 and E. coli IL 256 synergy effects on checkerboard technique were noticed. Such observation was not confirmed by the "time-kill" method. The methodologies and definitions of synergism are variable and not standardized. This situation should be improved, because comparison of the results obtained by different methods becomes a very difficult task.

A model for the efficacy of combined inhibitors

AIMS

The method of the sum of the fractional inhibitory concentrations (SigmaFIC) is used ubiquitously in the investigation of antimicrobial combinations. The inherent assumption of this simple equation is that in a mixture all antimicrobials have identical dose responses. The aim of this work was to analyse the outcome of removing this assumption.

METHODS AND RESULTS

A model to describe the efficacy of combined inhibitors was produced which removed the assumption of identical dose responses. The results of several checkerboard experiments showed that the new model, termed the facomb was a more general form of the SigmaFIC method, but the features described by the SigmaFIC as either synergy or antagonism could be attributed to differences in the dose responses of antimicrobials in combination. Where the model failed to adequately describe experimental data it was suggested that these might be cases of true antagonism or synergy.

CONCLUSIONS

The SigmaFIC methodology used to describe the effect of antimicrobial combinations (preservatives and antibiotics) is valid only when it is demonstrated that individual components of the mixture have identical dose responses. Otherwise the SigmaFIC method is invalid. Descriptions of antimicrobial synergy may simply be due to the mixing of antimicrobials with differing dose responses.

SIGNIFICANCE AND IMPACT OF THE STUDY

Studies aimed at producing synergistic mixtures of antimicrobials, which ignore the dose response of the individual antimicrobials, may waste valuable research effort looking for a physiological explanation for an apparent synergy, where none, in-fact, exists. Conversely, mixing antimicrobials with very different dose responses might lead to mixtures with an 'apparent' synergy which may themselves be very useful therapeutically.

Characterization of small bowel resection and intestinal adaptation in germ-free rats

BACKGROUND

After massive small bowel resection (SBR), the remnant bowel adapts by increasing enterocyte proliferation and apoptosis. The purpose of this study was to investigate the relevance of luminal bacteria on postresection intestinal cell turnover.

METHODS

Male germ-free (GF) and normally colonized control rats underwent either a 75% mid-SBR or sham operation. In other experiments, normally colonized control rats were given antibiotics in the drinking water. After 7 days, the remnant ileum was harvested and adaptation verified by alterations in wet weight, crypt depth, and villus height. Proliferation and apoptosis were measured in crypts as the percent of crypt cells staining for Ki-67 or the number of apoptotic bodies per crypt.

RESULTS

Both GF and control rats demonstrated significant increases in all adaptive parameters. Proliferation was increased after SBR in both groups, but significantly greater in the GF animals over control. This response could not be recapitulated after antibiotic treatment. Apoptosis increased equally after SBR in all groups.

CONCLUSION

Resection-induced intestinal adaptation occurs normally in GF animals. Epithelial-microbial interactions are probably not involved in the activation of enterocyte apoptosis. The germ-free studies offer the possibility that luminal bacteria may attenuate the proliferative response of the enterocyte to massive small bowel resection.

In VitroActivities of Daptomycin, Linezolid, and Quinupristin-Dalfopristin against a Challenge Panel of Staphylococci and Enterococci, Including Vancomycin-IntermediateStaphylococcus aureusand Vancomycin-ResistantEnterococcus faecium

We assessed the in vitro activities of daptomycin, linezolid, and quinupristin-dalfopristin (QD) against a contemporary challenge panel of 88 staphylococcal and 90 enterococcal isolates. The staphylococci selected included vancomycin-intermediate Staphylococcus aureus (VISA), methicillin-resistant S. aureus, and coagulasenegative staphylococci. Enterococcal isolates included vancomycin-resistant Enterococcus faecium (VREF) containing either vanA, vanB1, or vanD. The MICs of daptomycin, linezolid, and QD were determined using commercial broth microdilution panels. All three VISA isolates were susceptible to daptomycin, linezolid, and QD. QD was the most active agent against staphylococcal isolates (MIC50 < or = 0.5 microg/ml and MIC90 = 1 microg/ml), including those with decreased susceptibility to vancomycin. QD was also the most active agent against VREF (MIC90 < or = 0.5 microg/ml). No differences were seen for susceptibility of vanA, vanB1, and vanD VREF strains for daptomycin, linezolid, or QD. Daptomycin was the most effective against E. faecalis. On the basis of manufacturer-suggested interpretive criteria, 92% of isolates were susceptible (MIC90 = 4 microg/ml). All isolates tested were susceptible to at least one antimicrobial agent for which interpretive criteria have been defined. Population analysis of three S. aureus isolates for which the daptomycin MICs were 8 microg/ml showed a pattern of homogeneous resistance.

In vivo effects of fluoroquinolones on rabbit corneas

PURPOSE

The use of topical fluoroquinolones to treat microbial keratitis is associated with an increased incidence of corneal perforation compared to other standard treatments. This study examined the effects of topical fluoro-quinolones on corneal collagen and keratocytes in intact rabbit corneas and corneas with an epithelial defect.

METHODS

Studies consisted of one group of intact corneas and one group of corneas where a 6-mm epithelial defect was created with a surgical scrape. Within each group, eyes were randomly assigned to one of four topical medications (0.3% ciprofloxacin, 0.3% ofloxacin, fortified antibiotics (1.36% tobramycin, 5% cefrazolin) or Tears Naturale (Alcon Laboratories, Frenchs Forest, NSW, Australia). Two drops were instilled hourly for 48 h and then 2-hourly for an additional 48 h. At 96 h the corneas were removed and processed for light microscopy, immunohistology for collagen IV, V and VI, and apoptosis staining.

RESULTS

In intact rabbit corneas there was no demonstrable difference between treatment groups. In corneas with an epithelial defect, both fluoroquinolones delayed epithelial healing when compared to fortified antibiotics or tears. Keratocyte loss was seen in all groups and was greatest in the ofloxacin group. Median stromal thickness with keratocyte loss were: ofloxacin 30%; ciprofloxacin 10%; fortified antibiotics 7.5%; and tears 15% (ofloxacin vs tears, Mann-Whitney = 16.0, P = 0.09). Keratocyte loss did not correlate with the amount of demonstrable apoptosis. Collagens IV, V and VI showed no differences between treatments.

CONCLUSIONS

These results suggest that ofloxacin is potentially cytotoxic to corneal keratocytes. Such an effect could lead to the observed increased incidence of corneal perforation in microbial keratitis.