Bacterial clearance of biologic grafts used in hernia repair: an experimental study

BACKGROUND

Biologic grafts used in ventral hernia repair are derived from various sources and undergo different post-tissue-harvesting processing, handling, and sterilization techniques. It is unclear how these various characteristics impact graft response in the setting of contamination. We evaluated four materials in an infected hernia repair animal model using fluorescence imaging and quantitative culture studies.

METHODS

One hundred seven rats underwent creation of a chronic hernia. They were then repaired with one synthetic polyester control material (n = 12) and four different biologic grafts (n = 24 per material). Biologic grafts evaluated included Surgisis (porcine small intestinal submucosa), Permacol (crosslinked porcine dermis), Xenmatrix (noncrosslinked porcine dermis), and Strattice (noncrosslinked porcine dermis). Half of the repairs in each group were inoculated with Staphylococcus aureus at 10(4) CFU/ml and survived for 30 days without systemic antibiotics. Animals then underwent fluorescence imaging and quantitative bacterial studies.

RESULTS

All clean repairs remained sterile. Rates of bacterial clearance were as follows: polyester synthetic 0%, Surgisis 58%, Permacol 67%, Xenmatrix 75%, and Strattice 92% (P=0.003). Quantitative bacterial counts had a similar trend in bacterial clearance: polyester synthetic 1×10(6) CFU/g, Surgisis 4.3×10(5) CFU/g, Permacol 1.7×10(3) CFU/g, Xenmatrix 46 CFU/g, and Strattice 31 CFU/g (P=0.001). Fluorescence imaging was unable to detect low bacterial fluorescence counts observed on bacterial studies.

CONCLUSION

Biologic grafts, in comparison to synthetic material, are able to clear a Staphylococcus aureus contamination; however, they are able to do so at different rates. Bacterial clearance correlated to the level of residual bacterial burden observed in our study. Post-tissue-harvesting processing, handling, and sterilization techniques may contribute to this observed difference in ability to clear bacteria.

Characterization of Penicillin Intermediate Serotypes ofStreptococcus pneumoniaeCarried by Human Immunodeficiency Virus-Infected Adults and Healthy Children in Uganda

There are little data on the genetic relatedness between antibiotic-resistant pneumococcal isolates colonizing the Ugandan population. Penicillin-intermediate pneumococci of serogroups or serotypes rarely or not previously reported as being penicillin nonsusceptible were selected out of 166 isolates representing 26 capsular serogroups or serotypes isolated from Ugandan children in 1995 and human immunodeficiency virus (HIV) infected Ugandan adults in 2004-2005. Pairs of penicillin-intermediate pneumococci of the same serogroup or serotype present in both patient populations were characterized further by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Seven such pairs of isolates were found and included serogroups 7, 11, 15B/C, and 16 as well as serotypes 13, 21, and 35B. PFGE of these seven pairs showed no clonality between serogroups or serotypes, and clonality only within serogroup 11 and serotype 13. MLST of the 14 individual isolates revealed 13 different sequence types (STs), 11 of which had not previously been recorded. Comparisons with all known STs revealed that most of these strains were related only to strains of the same serotype in other countries, with these related strains frequently also being penicillin intermediate. These findings suggest that penicillin nonsusceptibility in Uganda is likely due to the introduction of antibiotic-resistant pneumococcal clones into Uganda rather than development of resistance within the country.

Alterations of penicillin-binding proteins 1A, 2X, and 2B in Streptococcus pneumoniae isolates for which amoxicillin MICs are higher than penicillin MICs

Penicillin-binding proteins (PBPs) of 15 selected penicillin- and amoxicillin-resistant Streptococcus pneumoniae isolates (MICs of 2 to 8 and 8 to 16 microg/ml, respectively) were studied. In addition to typical changes in PBPs 1A and 2X, these strains had 10 unique changes in PBP 2B, including a (618)A-G substitution, which may be the key alteration associated with amoxicillin resistance.

Macrolide resistance phenotypes in Streptococcus pneumoniae in Santiago, Chile

The mechanism of resistance was investigated in 39 macrolide-resistant clinical isolates of Streptococcus pneumoniae isolated from January 1997 to July 1999 in Santiago, Chile. Our results showed that 22 (56.5%) were macrolide-resistant, clindamycin-susceptible isolates (M phenotype) and 17 (43.5%) were macrolide and clindamycin resistant (MLS(B) phenotype). mefE gene was detected in all M phenotype, while ermB gene was detected in all MLS(B)-phenotype strains. Serotype 14 was the most frequent serotype among M-phenotype strains, and serotypes 19 and 23F were the most frequent serotypes in MLS(B) strains. These results demonstrate that both phenotypes of macrolide-resistant S. pneumoniae are found in Santiago, Chile, with the M phenotype predominating.

Clinically significant concentrations of local anesthetics inhibit Staphylococcus aureus in vitro

This study explores which concentrations of local anesthetics might be expected to inhibit the growth of Staphylococcus aureus. Serial dilutions were made of 0.5% and 0.75% bupivacaine, 2% and 5% lidocaine, 2% and 3% chloroprocaine, and 0.2% and 1% ropivacaine. To each concentration of local anesthetic solution, Mueller Hinton broth medium and Staphylococcus aureus were added. The resulting solutions were incubated and then observed for growth 24 and 48 h later. The minimum concentrations of the local anesthetics that could inhibit growth of Staphylococcus aureus were 0.25% bupivacaine, 1.25% lidocaine and 0.75% chloroprocaine. The inhibitory concentration of ropivacaine could not be determined because the more concentrated solutions precipitated in the Mueller Hinton broth. Local anesthetics may help protect against epidural abscess formation if they are used in sufficiently high concentrations. This effect may help explain the very low reported incidence of epidural abscess.

Pneumococcal conjugate vaccine serotypes of Streptococcus pneumoniae isolates and the antimicrobial susceptibility of such isolates in children with otitis media

The ability of the recently licensed 7-valent pneumococcal conjugate vaccine to cover isolates that cause otitis media, especially drug-resistant ones, was assessed using 500 recently obtained US isolates. Of these isolates, 418 (84%) belonged to vaccine-related serogroups, whereas 82 (16%) belonged to non-vaccine-related serogroups. Serotype 3 accounted for 48 (59%) of the non-vaccine-related serogroups. In addition, 93% of the isolates from patients < or =3 years of age belonged to serotypes that were included in or related to the heptavalent vaccine, compared with 49% of the isolates from older patients (P=.001). Most of the isolates (98%-100%) that were resistant to the antimicrobial agents tested were covered by the heptavalent vaccine, including 95.1% of the isolates from patients <2 years of age. The 7-valent pneumococcal conjugate vaccine could therefore potentially provide protection against all but 1 (type 3) of the common otitis media-associated pneumococcal serogroups identified in this study as well as against 98% of antibiotic-resistant isolates.

High prevalence of carriage of antibiotic-resistant Streptococcus pneumoniae in children in Kampala Uganda

There are few data on antibiotic-resistant Streptococcus pneumoniae in Uganda. A total of 191 healthy children in Kampala, Uganda were screened for nasopharyngeal carriage of S. pneumoniae; 118 (62%) of the children were carriers. Antimicrobial susceptibility and serotype of 115 strains was determined. Ninety-six (83.5%) of the isolates were of intermediate resistance to penicillin and 19 (16.5%) were susceptible. All strains were susceptible to cefotaxime. The rates of resistance to other drugs were trimethoprim-sulphamethoxazole (83.5%), tetracycline (28.7%) and chloramphenicol (10.4%). All strains were susceptible to rifampicin, erythromycin and clindamycin. Serogroups 6, 9, 14, 19 and 23 accounted for 80% of the isolates. These data show that the rate of carriage of antibiotic-resistant pneumococci by children is high in Kampala, Uganda.

Susceptibilities of Haemophilus influenzae and Moraxella catarrhalis to ABT-773 compared to their susceptibilities to 11 other agents

The activity of the ketolide ABT-773 against Haemophilus and Moraxella was compared to those of 11 other agents. Against 210 Haemophilus influenzae strains (39.0% beta-lactamase positive), microbroth dilution tests showed that azithromycin and ABT-773 had the lowest MICs (0.5 to 4.0 and 1.0 to 8.0 microg/ml, respectively), followed by clarithromycin and roxithromycin (4.0 to >32.0 microg/ml). Of the beta-lactams, ceftriaxone had the lowest MICs (</=0.004 to 0.016 microg/ml), followed by cefixime and cefpodoxime (0.008 to 0.125 and </=0.125 to 0.25 microg/ml, respectively), amoxicillin-clavulanate (0.125 to 4.0 microg/ml), and cefuroxime (0. 25 to 8.0 microg/ml). Amoxicillin was only active against beta-lactamase-negative strains, and cefprozil had the highest MICs of all oral cephalosporins tested (0.5 to >32.0 microg/ml). Against 50 Moraxella catarrhalis strains, all of the compounds except amoxicillin and cefprozil were active. Time-kill studies against 10 H. influenzae strains showed that ABT-773, at two times the MIC, was bactericidal against 9 of 10 strains, with 99% killing of all strains at the MIC after 24 h; at 12 h, ABT-773 gave 90% killing of all strains at two times the MIC. At 3 and 6 h, killing by ABT-773 was slower, with 99.9% killing of four strains at two times the MIC after 6 h. Similar results were found for azithromycin, with slightly slower killing by erythromycin, clarithromycin, and roxithromycin, especially at earlier times. beta-Lactams were bactericidal against 8 to 10 strains at two times the MIC after 24 h, with slower killing at earlier time periods. Most compounds gave good killing of five M. catarrhalis strains, with beta-lactams killing more rapidly than other drugs. ABT-773 and azithromycin gave the longest postantibiotic effects (PAEs) of the ketolide-macrolide-azalide group tested (4.4 to >8.0 h), followed by clarithromycin, erythromycin, and roxithromycin. beta-Lactam PAEs were similar and shorter than those of the ketolide-macrolide-azalide group for all strains tested.

Prevalence and mechanisms of macrolide resistance in Streptococcus pyogenes in Santiago, Chile

Thirty-two macrolide-resistant Streptococcus pyogenes isolates were found among 594 clinical isolates collected from 1990 to 1998 in Santiago, Chile, for an overall prevalence of 7.2%. Among the 32 resistant isolates, 28 (87.5%) presented the M phenotype and 4 (12. 5%) presented the MLS(B) phenotype. Serotyping and pulsed-field gel electrophoresis analysis showed genetic diversity among the resistant isolates.

Evaluation of Etest for susceptibility testing of Mycobacterium tuberculosis

The Etest method for susceptibility testing of Mycobacterium tuberculosis was compared to the agar proportion method using four first-line agents and two fluoroquinolones. Catergorical agreement between the methods was 100% for rifampin, ethambutol, streptomycin, and ofloxacin and 98% for isoniazid. Results were obtained in 6 to 10 days by Etest. The Etest method is suitable for testing the agents evaluated against M. tuberculosis.

Activities and postantibiotic effects of gemifloxacin compared to those of 11 other agents against Haemophilus influenzae and Moraxella catarrhalis

The activity of gemifloxacin against Haemophilus influenzae and Moraxella catarrhalis was compared to those of 11 other agents. All quinolones were very active (MICs, </=0.125 microgram/ml) against 248 quinolone-susceptible H. influenzae isolates (40.7% of which were beta-lactamase positive); cefixime (MICs, </=0.125 microgram/ml) and amoxicillin-clavulanate (MICs </=4.0 microgram/ml) were active, followed by cefuroxime (MICs, </=16.0 microgram/ml); azithromycin MICs were </=4.0 microg/ml. For nine H. influenzae isolates with reduced quinolone susceptibilities, the MICs at which 50% of isolates are inhibited (MIC(50)s) were 0.25 microgram/ml for gemifloxacin and 1.0 microgram/ml for the other quinolones tested. All strains had mutations in GyrA (Ser84, Asp88); most also had mutations in ParC (Asp83, Ser84, Glu88) and ParE (Asp420, Ser458), and only one had a mutation in GyrB (Gln468). All quinolones tested were equally active (MICs, </=0.06 microgram/ml) against 50 M. catarrhalis strains; amoxicillin-clavulanate, cefixime, cefuroxime, and azithromycin were very active. Against 10 H. influenzae strains gemifloxacin, levofloxacin, sparfloxacin, and trovafloxacin at 2x the MIC and ciprofloxacin at 4x the MIC were uniformly bactericidal after 24 h, and against 9 of 10 strains grepafloxacin at 2x the MIC was bactericidal after 24 h. After 24 h bactericidal activity was seen with amoxicillin-clavulanate at 2x the MIC for all strains, cefixime at 2x the MIC for 9 of 10 strains, cefuroxime at 4x the MIC for all strains, and azithromycin at 2x the MIC for all strains. All quinolones except grepafloxacin (which was bactericidal against four of five strains) and all ss-lactams at 2x to 4x the MIC were bactericidal against five M. catarrhalis strains after 24 h; azithromycin at the MIC was bactericidal against all strains after 24 h. The postantibiotic effects (PAEs) against four quinolone-susceptible H. influenzae strains were as follows: gemifloxacin, 0.3 to 2.3 h; ciprofloxacin, 1.3 to 4.2 h; levofloxacin, 2.8 to 6.2 h; sparfloxacin, 0.6 to 3.0 h; grepafloxacin, 0 to 2.1 h; trovafloxacin, 0.8 to 2.8 h. At 10x the MIC, no quinolone PAEs were found against the strain for which quinolone MICs were increased. Azithromycin PAEs were 3.7 to 7.3 h.

Determination of drug susceptibility and DNA fingerprint patterns of clinical isolates of Mycobacterium tuberculosis from Kampala, Uganda

OBJECTIVE

To ascertain the rate of initial drug resistance and transmission patterns of Mycobacterium tuberculosis in Kampala, Uganda.

SETTING

National Tuberculosis (TB) Treatment Centre, Mulago Hospital, Kampala, Uganda and Case Western Reserve University, Cleveland, Ohio, USA and McClellan Memorial Veterans Hospital, Little Rock, Arkansas, USA.

METHODS

Using a radiometric BACTEC 460 TB system, susceptibility of 215 M. tuberculosis isolates from previously untreated patients from Kampala, Uganda (age range, 17-48 years, mean, 28 years; 56% males and 69% human immunodeficiency virus (HIV)-seropositive) was determined for isoniazid, rifampin, streptomycin and ethambutol. Isolates from 73 patients, selected on the basis of geographical location, were tested for strain diversity or relatedness using the IS6110 DNA fingerprinting technique.

RESULTS

Resistance rates were as follows: isoniazid, 7.9% streptomycin, 6.1% rifampin, 1.4% and ethambutol 0.9%. Twelve per cent of the strains were resistant to at least one of the first line drugs tested and 4.7% were multiply resistant. There were no significant differences in resistance rates between patients with and without HIV infection. Using the number and size of DNA fragments containing IS6110, only three clusters of isolates with identical RFLP patterns were found out of the 73 isolates tested (8.2%). Each cluster contained two isolates. Three (4.1%) isolates had less than seven copies of IS6110.

CONCLUSION

This study shows that in Uganda initial drug resistance rates to anti-tuberculosis agents are low and similar to other sub-Saharan African countries and that multiple strains of M. tuberculosis have been transmitted within the community.

Postantibiotic effects of grepafloxacin compared to those of five other agents against 12 gram-positive and -negative bacteria

The postantibiotic effect (PAE) (10x the MIC) and the postantibiotic sub-MIC effects (0.125, 0.25, and 0.5x the MIC) were determined for six compounds against 12 strains. Measurable PAEs ranged between 0 and 1.8 h for grepafloxacin, 0 and 2.2 h for ciprofloxacin, 0 and 3. 1 h for levofloxacin, 0 and 2.2 h for sparfloxacin, 0 and 2.4 h for amoxicillin-clavulanate and 0 and 4.8 h for clarithromycin. Reexposure to subinhibitory concentrations increased the PAEs against some strains.

Prevalence of mefE, erm and tet(M) genes in Streptococcus pneumoniae strains from Central Italy

One hundred and seventy-three Streptococcus pneumoniae strains isolated from surveillance studies conducted in daycare centres were studied. The mefE, erm and tet(M) genes were detected in 16.2, 45.1 and 47.4% of isolates respectively. Agreement between PCR results and antibiotic susceptibility patterns was 100%. Macrolide resistance was due to the presence of erm in 73.6% of strains and to the presence of mefE in the remaining 26.4%. All tetracycline resistant strains carried the tet(M) gene. erm was associated with tet(M) in 98.7% of strains, whereas no isolate carrying mefE carried tet(M). A significant association was found between mefE and serogroup 6 (P < 0.0005) and between erm and tet(M) and serogroup 19 (P < 0.00001).

Susceptibilities of Streptococcus pneumoniae and Haemophilus influenzae to 10 oral antimicrobial agents based on pharmacodynamic parameters: 1997 U.S. Surveillance study

The susceptibilities of Streptococcus pneumoniae (1,476 strains) and untypeable Haemophilus influenzae (1,676 strains) to various oral beta-lactam, macrolide-azalide, and fluoroquinolone antimicrobial agents were determined by broth microdilution. Organisms were isolated from specimens obtained from outpatients in six geographic regions of the United States. MIC data were interpreted according to pharmacodynamically derived breakpoints applicable to the oral agents tested. Among H. influenzae strains, 41.6% were beta-lactamase positive. Virtually all H. influenzae strains were susceptible to amoxicillin-clavulanate (98%), cefixime (100%), and ciprofloxacin (100%), while 78% were susceptible to cefuroxime, 57% were susceptible to amoxicillin, 14% were susceptible to cefprozil, 9% were susceptible to loracarbef, 2% were susceptible to cefaclor, and 0% were susceptible to azithromycin and clarithromycin. Among S. pneumoniae isolates, 49.6% were penicillin susceptible, 17.9% were intermediate, and 32.5% were penicillin resistant, with penicillin MICs for 50 and 90% of the isolates tested of 0.12 and 4 microg/ml, respectively. Overall, 94% of S. pneumoniae isolates were susceptible to amoxicillin and amoxicillin-clavulanate, 69% were susceptible to azithromycin and clarithromycin, 63% were susceptible to cefprozil and cefuroxime, 52% were susceptible to cefixime, 22% were susceptible to cefaclor, and 11% were susceptible to loracarbef. Although ciprofloxacin has marginal activity against S. pneumoniae, no high-level fluoroquinolone-resistant strains were found. Significant cross-resistance was found between penicillin and macrolides-azalides among S. pneumoniae isolates, with 5% of the penicillin-susceptible strains being macrolide-azalide resistant, compared with 37% of the intermediate isolates and 66% of the resistant isolates. Resistance was highest in S. pneumoniae isolates from patients younger than 10 years of age, middle ear and paranasal sinus specimens, and the southern half of the United States. With the continuing rise in resistance, judicious use of oral antimicrobial agents is necessary in all age groups.

Resistance patterns of Streptococcus pneumoniae from children in central Italy

Nasopharyngeal swabs were collected from children aged 3-5 years in central Italy who were attending day-care centres or hospital outpatient clinics. One hundred and twenty-one strains of Streptococcus pneumoniae isolated were tested for susceptibility to penicillin, cefotaxime, erythromycin, clindamycin, tetracycline, chloramphenicol and cotrimoxazole. A high prevalence of penicillin-resistant (14%), erythromycin-resistant (60%) and multiply resistant strains (53%) were found. An unusual finding was that 49 of the 64 (76.6%) multiply resistant strains were penicillin-susceptible, 28 serogroup 6 strains also being resistant to the other antibiotics tested. Such strains have not previously been reported from Italy but have the same features as strains recently found in child carriers in the eastern Mediterranean area.

Activity of HMR 3647 compared to those of five agents against Haemophilus influenzae and moraxella catarrhalis by MIC determination and time-kill assay

The microdilution MICs of HMR 3647, erythromycin A, azithromycin, clarithromycin, roxithromycin, and pristinamycin against 50/90% of 249 Haemophilus influenzae and 50 Moraxella catarrhalis isolates were 2/4, 0.06/0.125; 8/16, 0.25/0.25; 2/4, 0.06/0.125; 16/16, 0.25/0.25; 32/>32, 1/2; and 2/4, 0.5/0.5 microg/ml. Azithromycin was bactericidal against all 10 H. influenzae and 3 of 5 M. catarrhalis isolates and HMR 3647, erythromycin A, clarithromycin, roxithromycin, and pristinamycin were bacteriostatic, against all 15 strains after 24 h at the MIC.

Determination of penicillin MICs for Streptococcus pneumoniae by using a two- or three-disk diffusion procedure

The potential for the use of the disk diffusion method to accurately predict penicillin MICs for Streptococcus pneumoniae was investigated with penicillin (6 microg), methicillin (5 microg), and oxacillin (1 microg) disks. A total of 183 S. pneumoniae isolates were tested by three MIC procedures (agar dilution, microdilution, and E-test). Regression analyses of the geometric mean of the three MIC results against (i) the sum of the zone diameters for methicillin, penicillin, and oxacillin disks; (ii) the sum of the zone diameters for methicillin and penicillin disks; and (iii) each of the three individual zone diameters were performed. Calculated MICs were determined from each of these regression analyses and compared to the mean reference MICs. A high level of correlation was obtained with both the two- and the three-disk procedures (r = 0.97), with essential agreement rates (+/-1 doubling dilution) between MICs calculated by the three-disk procedure and the two-disk procedure and the mean reference MICs of 98.4 and 98.9%, respectively. No major or very major errors were obtained with the two- or three-disk procedures. The accuracy of the disks used individually was lower (r = 0.84 to 0.93). However, oxacillin and methicillin disk testing remain excellent for screening strains, with all penicillin-susceptible strains having zones of >21 and >22 mm, respectively. The combination disk procedure, which involves the use of three disks (methicillin, oxacillin, and penicillin) or two disks (methicillin and penicillin) for testing S. pneumoniae, can provide accurate penicillin MICs and qualitative category results that are comparable to results obtained by the E-test, agar, and microdilution MIC methods.

Synergistic activity of trovafloxacin with other agents against gram-positive and -negative organisms

The synergistic activity of trovafloxacin with other agents against 55 Gram-positive and -negative bacteria was determined by checkerboard titration. Synergistic fractional inhibitory concentration (FIC) indices (< or = 0.5) were seen in two methicillin-susceptible and one methicillin-resistant Staphyloccocus aureus with teicoplanin, one of each of the latter two with vancomycin; one methicillin-resistant coagulase-negative Staphylococcus with rifampin and one with fusidic acid; five Stenotrophomonas maltophilia with cefoperazone; three Pseudomonas aeruginosa with ticarcillin/clavulanate, four with aztreonam, two with ceftazidime, one with tobramycin, one with cefoperazone, and one with ceftriaxone; one pneumococcus with ceftriaxone; one Enterococcus faecalis with ceftriaxone, and one with vancomycin; two Bacteroides fragilis with metronidazole, two with clindamycin, and one with cefoxitin; and one Clostridium perfringens with metronidazole and one with clindamycin. All other FIC indices were additive/indifferent (0.51-2.0), and no antagonistic FIC indices (> 4.0) were observed.

Resistance patterns of streptococcus pneumoniae from carriers attending day-care centers in southwestern Greece

The resistance to beta-lactam and non-beta-lactam antibiotics of 133 nasopharyngeal isolates of Streptococcus pneumoniae recovered from December 1995 to February 1996 from children attending seven day-care centers in southwestern Greece was studied. Reduced susceptibility to one or more anti-microbial agents was found in 70 isolates (53%), as follows: penicillin, 17% intermediate, 12% resistant; cefotaxime, 10.5% intermediate, 1.5% resistant; trimethoprim-sulfamethoxazole, 8% intermediate, 35% resistant; chloramphenicol, 27% resistant; tetracycline, 29% resistant; and erythromycin/clindamycin, 19% resistant. Eighty-seven percent of penicillin-intermediate or -resistant strains belonged to serogroups/serotypes 19, 21, and 23. Fifty-six percent of the antibiotic-resistant pneumococci were multiply resistant, including serogroup 6 strains that were penicillin-susceptible but resistant to all non-beta-lactam drugs tested, as well as serogroup 23 strains resistant to penicillin, chloramphenicol, tetracycline, and trimethoprim-sulfamethoxazole. The high incidence of antibiotic-resistant pneumococci and the divergent and unique resistance patterns found in this study underline the need for global surveillance of S. pneumoniae to document the evolution and spread of resistant strains and to guide therapy.

Comparative activity of trovafloxacin, alone and in combination with other agents, against gram-negative nonfermentative rods

In the first part of this study, agar dilution MICs were used to test the activities of trovafloxacin, ciprofloxacin, ofloxacin, levofloxacin, sparfloxacin, clinafloxacin, ceftazidime, and imipenem against 458 gram-negative nonfermenters. The overall respective MICs at which 50% of isolates are inhibited (MIC50s) and MIC90s were as follows: trovafloxacin, 1.0 and 16.0 microg/ml; ciprofloxacin, 2.0 and 16.0 microg/ml; ofloxacin, 2.0 and 32.0 microg/ml; levofloxacin, 1.0 and 16.0 microg/ml; sparfloxacin, 1.0 and 16.0 microg/ml; clinafloxacin, 0.5 and 4.0 microg/ml; ceftazidime, 8.0 and 128.0 microg/ml; imipenem, 2.0 and 256.0 microg/ml. Clinafloxacin was the most active of all the quinolones tested. The MIC90s of trovafloxacin were < or = 4.0 microg/ml for Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Flavobacterium odoratum, and Chryseobacterium meningosepticum; trovafloxacin MIC90s were < or = 2.0 microg/ml for Moraxella spp., Pseudomonas stutzeri, and Chryseobacterium indologenes-C. gleum. Of the other quinolones tested, the MICs of sparfloxacin and levofloxacin were lower than those of ciprofloxacin and ofloxacin. High ceftazidime MICs (> or = 32.0 microg/ml) were observed for all nonfermentative species tested. Although for the majority of strains tested imipenem MICs were < or = 8.0 microg/ml, high imipenem MICs were observed for many species, especially S. maltophilia, Burkholderia cepacia, F. odoratum, and Chryseobacterium meningosepticum. For Alcaligenes xylosoxidans strains, the MICs of all compounds were generally a few dilutions lower than those for Alcaligenes faecalis-A. odorans. Time-kill studies with five strains revealed that trovafloxacin and all quinolones yielded more rapid time-kill kinetics than ceftazidime and imipenem. Synergy testing by checkerboard titrations of 286 strains with trovafloxacin combined with ceftazidime, amikacin, and imipenem revealed fractional inhibitory concentration (FIC) indices in the range indicating synergism (< or = 0.5) for 81, 41, and 40 strains, respectively, and FIC indices indicating additivity or indifference (> 0.5 to 4.0) for 205, 245, and 246 strains, respectively. No FIC indices indicating antagonism (> 4.0) were observed. Synergy between trovafloxacin and ceftazidime was found for 32 of 36 S. maltophilia strains. Time-kill studies with 20 strains showed that for most strains for which FIC indices were in the range indicating additivity or indifference, FIC indices indicated synergy by the time-kill method. Synergy was particularly noticeable for S. maltophilia strains with combinations of ceftazidime and trovafloxacin.

Evaluation of Haemophilus influenzae isolates with elevated MICs to amoxicillin/clavulanic acid

A 1994 to 1995 national Haemophilus influenzae surveillance study of 1910 strains showed that 13 strains (0.7%) were resistant to amoxicillin/clavulanic acid (MIC, > or = 8/4 micrograms/ml). These and other selected strains were investigated further in this study. Susceptibility of the surveillance study strains was determined with the commercial microdilution trays used in the original study and in triplicate with reference broth microdilution trays prepared by the investigators, as well as by Etest and disk diffusion. Amoxicillin/clavulanic acid resistance was confirmed for only one of the surveillance study strains. This strain produced double zones of growth with Etest and disk-diffusion methods, with the double zone containing spheroplasts. When the amoxicillin/clavulanic acid MICs of all beta-lactamase positive strains were compared, MIC results obtained with surveillance study trays and the Etest were one to two dilutions higher than MICs obtained with reference trays. The distribution and modal amoxicillin/clavulanic acid MICs of beta-lactamase-positive and -negative strains was essentially the same for a comparison group of strains using reference trays, in contrast to a fourfold higher modal MIC for beta-lactamase-positive strains using surveillance study reagents and strains. These differences in MICs could be attributed to variations in inoculum, the presence of spheroplasts, and/or a difference in potency of amoxicillin and/or clavulanic acid in the tray and Etest reagents used. Methods for assessing the adequacy of the clavulanic acid content are not adequate, amoxicillin control values and a beta-lactamase-positive H. influenzae control strain are required.

Activities of levofloxacin, ofloxacin, and ciprofloxacin, alone and in combination with amikacin, against acinetobacters as determined by checkerboard and time-kill studies

A total of 101 Acinetobacter genospecies (77 Acinetobacter baumannii strains and 24 non-A. baumannii strains) were tested for their susceptibilities to levofloxacin, ofloxacin, and ciprofloxacin and for synergy between the quinolones and amikacin by checkerboard titration and time-kill analyses. The MICs at which 50% of the isolates are inhibited (MIC50)/MIC90s for the 101 strains were as follows (in micrograms per milliliter): levofloxacin, 0.25/16.0; ofloxacin, 0.5/32.0; ciprofloxacin, 0.25/> 64.0; and amikacin, 1.0/> 32.0. At empiric breakpoints of < or = 2.0 microg/ml, 61% of the strains were susceptible to all three quinolones. At a breakpoint of < or = 16.0 microg/ml, 84% of the strains were susceptible to amikacin. Checkerboard titrations yielded synergistic fractional inhibitory concentration (FIC) indices (< or = 0.5) for one strain with levofloxacin and amikacin and for two strains with ofloxacin and amikacin. Indices of > 0.5 to 1.0 were seen for 57, 54, and 55 strains with levofloxacin plus amikacin, ofloxacin plus amikacin, and ciprofloxacin plus amikacin, respectively, and indices of > 1.0 in 43, 45, and 46 strains, respectively, were found with the above three combinations. No strains yielded antagonistic FIC indices (> 4.0). Most FIC results of > 1.0 occurred in strains for which the quinolone MICs were > 2.0 microg/ml and for which the amikacin MICs were > or = 32.0 microg/ml. By contrast, synergy (defined as > or = 2 log10 decrease compared to the more active compound alone by time-kill analysis) was found in all seven strains tested for which the quinolone MICs were < or = 2.0 microg/ml. For eight other strains for which the quinolone MICs were > 2.0 microg/ml as determined by time-kill analysis, quinolone and amikacin concentrations in combination were usually too high to permit clinical use. Time-kill analysis was found to be more sensitive in detecting synergy than was the checkerboard method.

Variation in erythromycin and clindamycin susceptibilities of Streptococcus pneumoniae by four test methods

Susceptibilities of 124 strains of Streptococcus pneumoniae to erythromycin and clindamycin were determined by the National Committee for the Clinical Laboratory Standards (NCCLS) broth microdilution method, with incubation for 20 to 24 h in ambient air and with modifications of this method by incubation for up to 48 h in air and CO2. Strains were also tested by agar dilution, E-test, and disk diffusion; good correlation was obtained with these methods, with clear separation into bimodal populations of susceptible and resistant stains. The broth microdilution method, however, using incubation in air for 24 h (NCCLS method), misclassified 4 of 92 erythromycin-resistant strains (1 as susceptible and 3 as intermediate) and 25 of 58 clindamycin-resistant strains (all as susceptible). With the exception of one strain with clindamycin, susceptible and resistant strains were correctly classified by the microdilution method with incubation in CO2 for 24 h or in ambient air for 48 h. Disk diffusion, agar dilution, and E-test methods with incubation in 5% CO2 are therefore reliable methods for susceptibility testing of pneumococci against these agents. However, the NCCLS microdilution method, which specifies incubation for 20 to 24 h in ambient air, produced significant very major errors (43%) clindamycin. Modification of the microdilution method by incubation in 5% CO2 or by extension of incubation time in ambient air to 48 h corrected these errors. Disk diffusion, however, was shown to be a simple, convenient, and reliable method for susceptibility testing of pneumococci to erythromycin and clindamycin and is suggested as the method of choice for these agents.

Comparative activities of LY 333328, a new glycopeptide, against penicillin-susceptible and -resistant pneumococci

Microdilution MIC testing was used to test the susceptibility of 202 pneumococci to LY 333328 and six other agents. LY 333328 was the most active glycopeptide (MIC at which 90% of the pneumococci were inhibited [MIC90], 0.008 microgram/ml), followed by teicoplanin (MIC90, 0.06 microgram/ml) and vancomycin (MIC90, 0.5 microgram/ml). Rifampin resistance was seen in some penicillin-resistant strains. The MICs of imipenem and ceftriaxone rose with those of penicillin. Time-kill testing confirmed the excellent antipneumococcal activity of LY 333328.

Antipneumococcal activities of cefpirome and cefotaxime, alone and in combination with vancomycin and teicoplanin, determined by checkerboard and time-kill methods

The checkerboard titration method was used to test the synergy of cefpirome and cefotaxime with teicoplanin or vancomycin against 35 penicillin-susceptible, 34 penicillin-intermediate, and 31 penicillin-resistant pneumococci. The MICs at which 50 and 90% of isolates are inhibited (MIC50s and MIC90s, respectively) of both cefpirome and cefotaxime were 0.016 and 0.06 microgram/ml, respectively, for penicillin-susceptible strains and 0.125 and 0.5 microgram/ml, respectively, for penicillin-intermediate strains. The MIC50s and MIC90s of cefotaxime for penicillin-resistant strains were 1.0 and 2.0 micrograms/ml, respectively, and those of cefpirome were 0.5 and 1.0 microgram/ml, respectively. All pneumococci were inhibited by cefpirome at MICs of < or = 1.0 microgram/ml. The MIC50s and MIC90s of vancomycin and teicoplanin (0.25 and 0.25 microgram/ml and 0.03 and 0.03 microgram/ml, respectively) did not differ for the three groups. Checkerboard synergy studies showed that cefpirome and vancomycin showed synergy for 31 strains (fractional inhibitory concentration [FIC] indices, < or = 0.5) cefpirome and teicoplanin showed synergy for 18 strains, cefotaxime and vancomycin showed synergy for 51 strains, and cefotaxime and teicoplanin showed synergy for 27 strains. Cefpirome and vancomycin had FIC indices indicating indifference (2.0) for two strains, and cefotaxime and vancomycin had FIC indices indicating indifference for one strain. All other FIC indices indicating indifference or additivity were > 0.5 to 1.0. No FIC indices indicating antagonism (> 4.0) were found. Synergy between beta-lactams and glycopeptides for three susceptible, three intermediate, and three resistant strains were tested by the time-kill assay, and all combinations were synergistic by this method. Synergy between cephalosporins and glycopeptides can be demonstrated and may be useful for the treatment of pneumococcal infections, especially meningitis.

In vitro anti-Mycobacterium avium activities of quinolones: predicted active structures and mechanistic considerations

The relationship between the structures of quinolones and their anti-Mycobacterium avium activities has been previously derived by using the Multiple Computer-Automated Structure Evaluation program. A number of substructural constraints required to overcome the resistance of most of the strains have been identified. Nineteen new quinolones which qualify under these substructural requirements were identified by the program and subsequently tested. The results show that the substructural attributes identified by the program produced a successful a priori prediction of the anti-M. avium activities of the new quinolones. All 19 quinolones were found to be active, and 4 of them are as active or better than ciprofloxacin. With these new quinolones, the updated multiple computer-automated structure evaluation program structure-activity relationship analysis has helped to uncover additional information about the nature of the substituents at the C5 and C7 positions needed for optimal inhibitory activity. A possible explanation of drug resistance based on the observation of suicide inactivation of bacterial cytochrome P-450 by the cyclopropylamine moiety has also been proposed and is discussed in this report. Furthermore, we confirm the view that the amount of the uncharged form present in a neutral pH solution plays a crucial role in the drug's penetration ability.

Anti-Mycobacterium avium activity of quinolones: in vitro activities

The MICs of 88 quinolones against 14 selected reference and clinical strains of Mycobacterium avium-M. intracellular complex were determined. Agents tested included ciprofloxacin, sparfloxacin (PD 131501), and 86 other experimental quinolones. Test strains were selected to represent various susceptibilities to ciprofloxacin and other drug resistance profiles. MICs were determined by the microdilution method in 7HSF broth, with incubation for 14 days at 35 degrees C. The results showed 25 of the quinolones to be active against the strains, with MICs for 90% of the strains (MIC90s) of 2 to 32 micrograms/ml. Ten of these compounds had activities equivalent to or greater than that of ciprofloxacin. The most active compound was PD 125354, with an MIC50 of 0.5 micrograms/ml and an MIC90 of 2 micrograms/ml; comparable values for ciprofloxacin were 4 and 8 micrograms/ml, respectively. The next most active compounds, with MIC90s of 4 micrograms/ml, were sparfloxacin (PD 131501), PD 123982, PD 135144, and PD 119421. MIC90s of PD 131575, PD 126889, PD 122642, PD 139586, and PD 143289 were 8 micrograms/ml. Further evaluation of the most active agents is warranted, as is assessment of structure-activity relationships of active and inactive agents to elucidate the active portions of the compounds and to lead to the development of compounds with enhanced activity.

Evaluation of the E-Test for susceptibility testing of pneumococci

The E-Test (AB Biodisk, Sweden) is an antibiotic gradient strip that is applied to an inoculated agar plate and results in an elliptical zone of inhibition that intercepts the graded strip, producing a quantitative (microgram per milliliter) result. Pneumococci (100) were used in this study, 38 penicillin-susceptible [minimal inhibitory concentrations (MICs), less than or equal to 0.12 micrograms/ml], 42 intermediately resistant (MICs, 0.12-1.0 micrograms/ml), and 20 resistant (MICs, greater than 1 microgram/ml). E-Test strips were evaluated on Mueller-Hinton agar plates with 5% sheep blood. Agar dilution MICs were determined by the National Committee for Clinical Laboratory Standards (NCCLS) method. Penicillin MICs for the E-Test tended to be slightly lower (one log2 dilution) than reference MICs due to the continuous scale from which E-Test MICs were read. All but two penicillin-susceptible isolates were correctly categorized by the E-Test method. Of the 62 penicillin-resistant strains, 59 had E-Test MICs of greater than or equal to 0.12 micrograms/ml, with 88% of these strains having E-Test MICs within one doubling dilution of the reference MICs. However, using the current NCCLS breakpoint MICs, many of the penicillin-resistant strains with reference MICs of 2 micrograms/ml were categorized as intermediate by the E-Test, with MICs of 0.38-1 microgram/ml. For chloramphenicol, erythromycin, and tetracycline, correlation of the two methods was excellent. E-Test chloramphenicol MICs provided clearer separation of susceptible and resistant strains than did the reference method. We conclude that the E-Test is a reliable method for determination of MICs of the antibiotics evaluated for pneumococci.

Purification and characterization of an extracellular protease from Pseudomonas cepacia

An extracellular proteinase (PSCP) produced by Pseudomonas cepacia was purified from culture supernatants by ammonium sulfate precipitation, anion exchange chromatography on DEAE-Sephacel, and G200 gel filtration chromatography. The protease has an apparent Mr of 34,000 by electrophoresis. Substrates cleaved by the protease include gelatin, hide powder, and collagen but not human immunoglobulin G (IgG), IgM, secretory IgA, or IgA. The enzyme had the characteristics of a metalloprotease, a pH optimum of 6, and a temperature optimum of 45 degrees C. Intratracheal instillation of purified PSCP into rat lungs produced a bronchopneumonia characterized by polymorphonuclear cell infiltration and proteinaceous exudation into large airways. Rats responded immunologically to active immunization with PSCP, but this response was not protective against subsequent lung infection with P. cepacia. PSCP was shown to have antigenic similarity with Pseudomonas aeruginosa elastase by an immunoblotting technique. Sera from 10 cystic fibrosis patients, with and without a previous history of P. cepacia colonization, were shown to possess antibody reactive against PSCP.