Ninety-six clinical isolates of Stenotrophomonas maltophilia were examined with the agar dilution method for susceptibility to 19 antimicrobial drugs. Doxycycline, cotrimoxazole, timentin, ofloxacin, fosfomycin, and piperacillin + tazobactam, in that order, inhibited the majority of strains. All isolates were resistant to nitrofurantoin. Concurrent disk susceptibility (Bauer-Kirby method) testing, using currently valid NCCLS interpretative criteria for Pseudomonas aeruginosa, uncovered a significant incidence of very major (category I), major (category II), and minor (categories III and IV) discrepancies for aminoglycosides, cephalosporins, chloramphenicol, and piperacillin + tazobactam and ticarcillin + clavulanic acid. Therefore, new interpretative criteria indicative of intermediate (I) susceptibility of S. maltophilia to these various antibiotics were proposed. In addition, new intermediate susceptibility criteria were proposed for the two beta-lactam-beta-lactamase inhibitor combinations. It was recommended to exclude ciprofloxacin from test batteries against this microorganism due to the wide scatter of minimal inhibitory concentration values and diameters of inhibition zones; the same was true for polymyxin B. It is hoped that the proposed modified, species-specific criteria will improve the clinical utility of laboratory-generated disk antibiograms with respect to the inherently multiple antibiotic-resistant, opportunistic pathogen S. maltophilia.

Anti-Bacterial Agents↗

PubMedDate not supplied

Antibiotic susceptibility testing (agar disk diffusion and agar dilution) of clinical isolates of Corynebacterium jeikeium.

Thirty-three clinical isolates of Corynebacterium jeikeium were examined for susceptibility to 27 antimicrobial drugs with the agar dilution test. Sheep-blood-supplemented Mueller-Hinton agar performed better than Wilkins-Chalgren agar. Disk susceptibility (Bauer-Kirby) tests were carried out in parallel with 24 of the chemotherapeutic agents. All isolates were susceptible to teicoplanin and vancomycin. All isolates resisted fosfomycin, mupirocin, and trimethoprim-sulfamethoxazole. The isolates varied in susceptibility to ciprofloxacin, doxycycline, fusidic acid, ofloxacin, and tetracycline; most were susceptible to rifampin. Surprisingly few discrepancies between agar dilution and disk diffusion tests were encountered when utilizing NCCLS interpretive criteria currently valid for enterococcal isolates.

Agar↗

PubMedDate not supplied

Surveillance of Pseudomonas aeruginosa in intensive care units: clusters of nosocomial cross-infection and encounter of a multiple-antibiotic resistant strain.

Serogrouping (determination of O antigens) and bacteriocin typing (based on susceptibility to one or more of 18 bacteriocins) were employed to survey 210 isolates of Pseudomonas aeruginosa from 201 patients in 8 intensive care units (ICU) during an observation period of 18 months. Eighty-eight isolates (41.9%) were nonserogroupable (NT); most common were serogroups O1, O9, O11, and O3. All except 5 isolates (97.6%) were bacteriocin-typable. However, phenotypic variation of bacteriocin susceptibility, in particular the receptor for bacteriocin No. 13, rendered this typing method presumptive as well. Bacteriocin susceptibility profiles were not predictive of serogroup and vice versa. Workup of 19 isolates from 9 patients disclosed phenotypic variation of antibiotic susceptibility in 3 patients, superinfection by a different strain in 4 patients, and persistence (3 months) of the same strain in 2 patients, respectively. Serotyping and bacteriocin susceptibility test data revealed 15 clusters of putative cross-infection of 2 patients each, 8 clusters involving 3 patients each, one outbreak (serogroup NT, bacteriocin profile 777736) involving 4 patients in the pediatric ICU, one outbreak due to a multiple-antibiotic resistant (MAR) strain in the surgical ICU (4 patients, serogroup O12, bacteriocin profile 30400), and two putative outbreaks in the pneumonology ICU involving 6 patients (serogroup NT, bacteriocin profile 777726) and 9 patients (serogroup NT, bacteriocin profile 777736). Pulsed-field gel electrophoresis (PFGE) macrorestriction analysis (SpeI, XbaI) confirmed the pediatric and surgical ICU strains as singular strains. However, the two putative outbreaks in the pneumonology ICU were due to one particular strain which had infected 13 of the 15 patients as determined with the PFGE genotypic method. Isolates comprising the MAR strain of P. aeruginosa were susceptible only to amikacin, fosfomycin, and polymyxin B; the isolates varied in susceptibility to aztreonam and ceftazidime. This MAR strain was susceptible to the bactericidal activity of 65 vol% of fresh defibrinated human blood from donors B, L, and T. Either amikacin (16 micrograms/ ml) or fosfomycin (8 micrograms/ml) plus blood and amikacin (8 micrograms/ml) combined with fosfomycin (8 micrograms/ml) with and without blood consistently killed isolates of the MAR strain, which thus was amenable to antibiotic therapy.

Anti-Bacterial Agents↗

PubMedDate not supplied

Stenotrophomonas (Xanthomonas) maltophilia: in vitro susceptibility to selected antimicrobial drugs, single and combined, with and without defibrinated human blood.

Sixteen selected isolates of Stenotrophomonas maltophilia varied in susceptibility to the combined phagocytic/serum bactericidal activity of fresh defibrinated human blood (65 vol%). Four representative isolates (X1, X11, X25, and X50), which differed in susceptibility to cefepime, ceftazidime, rifampin, and timentin, were subjected to checkerboard microtiter broth dilution tests involving combinations of cefepime plus timentin, ceftazidime plus ofloxacin, cotrimoxazole plus timentin, rifampin plus polymyxin B, and rifampin plus polymyxin B nonapeptide; all combinations yielded additive or synergistic effects against all four strains. Unexpectedly, the combination of cefepime plus timentin was bactericidally active against the two cefepime-resistant isolates. This finding was substantiated by blood/broth plus combined antimicrobial drug assays. Cefepime plus timentin effectively killed all four test strains. Ofloxacin combined with ceftazidime was bactericidally active against the test strains, including two isolates (X11, X50) with intermediate ofloxacin sensitivity. Cotrimoxazole plus timentin in blood, but not in broth, was bactericidal for the timentin-resistant isolate X25. As expected, various triple combinations of chemotherapeutic agents in blood and broth revealed polymyxin B plus rifampin, regardless of the third combination partner, to exert bactericidal activity against all test strains. Similarly, rifampin combined with ofloxacin and ceftazidime was bactericidally active in blood and broth. The observation that timentin combined with cefepime was effective against cefepime-resistant strains of S. maltophilia might prove of clinical relevance with regard to chemotherapy of nosocomial infections due to multiple-antibiotic resistant strains of this opportunistic pathogen.

Anti-Bacterial Agents↗

PubMedDate not supplied

A cluster of nosocomial cross-infection due to multiple antibiotic-resistant Acinetobacter baumannii: Characterization of the strain and antibiotic susceptibility studies.

A multiple antibiotic-resistant (MAR) strain of Acinetobacter baumannii caused nosocomial cross-infection among 3 patients of a surgical intensive care unit. The isolates were of identical biochemical profile (77776 S-U-) and serotype (serovar 36) and identical in terms of pulsed-field gel electrophoresis macrorestriction (SmaI, ApaI) analysis. This MAR strain was susceptible only to netilmicin, tobramycin, imipenem, meropenem, polymyxin B, and trovafloxacin. The minimal bactericidal concentrations of imipenem and meropenem were markedly higher than the corresponding minimal inhibitory concentrations against this strain. Combined fresh defibrinated human blood (65 vol%) and antimicrobial drug assays yielded the following results: polymyxin was the most rapidly bactericidally effective antibiotic in the presence of blood and in broth. Tobramycin and netilmicin were efficacious in 65 vol% blood. Imipenem was slightly more effective than meropenem in broth, whereas both carbapenems sterilized blood-containing assay tube contents. Trovafloxacin failed to achieve bactericidal activity (to 99.9% kill) in the presence of blood, presumably because this strain was resistant to ciprofloxacin and borderline susceptible to ofloxacin. Trovafloxacin combined with either imipenem or meropenem yielded an indifferent effect. However, the combination of trovafloxacin (2 microg/ml) plus tobramycin (1 microg/ml) achieved sterilization of tube contents in the presence of blood within 4 h after exposure and in broth following extended (overnight) incubation. This MAR strain of A. baumannii was high-level resistant to rifampin; thus the combination of polymyxin B plus rifampin proved indifferent.

Acinetobacter↗

PubMedDate not supplied

Nosocomial outbreak of cross-infection due to multiple-antibiotic-resistant Klebsiella pneumoniae: characterization of the strain and antibiotic susceptibility studies.

A multiple-antibiotic-resistant (MAR) strain of Klebsiella pneumoniae was introduced into a pediatric ward and subsequently colonized neonates of two wards with several cases of systemic infection. This strain produced an extended-spectrum beta-lactamase and was resistant to cefotaxime, ceftazidime, and, among others, all aminoglycosides including amikacin. The majority of representative isolates examined with macrorestriction analysis of genomic DNA (pulsed-field gel electrophoresis) were identical. The strain was susceptible to the innate antibacterial systems operative in fresh defibrinated blood from two adults. Combined human blood/antimicrobial drug assays documented the in vitro bactericidal activity of carbapenems (meropenem was slightly more effective than imipenem), fluoroquinolones (ciprofloxacin and trovafloxacin), and polymyxin B against this MAR strain of K. pneumoniae.

Adult↗

PubMedDate not supplied

Surveillance of nosocomial cross-infections due to three Acinetobacter genospecies (Acinetobacter baumannii, genospecies 3 and genospecies 13) during a 10-Year Observation period: serotyping, macrorestriction analysis of Genomic DNA and antibiotic susceptibilities.

During a 10-year surveillance period, a total of 2,359 isolates comprising the genus Acinetobacter were recovered and identified presumptively with phenotypic tests. Genospecies 3 was the most common (n = 1,053), followed by genospecies 13 (n = 352), Acinetobacter baumannii (n = 335), Acinetobacter Iwoffi (n = 162), and genospecies 14 (n = 97); 100 isolates (4.2%) were categorized as questionable Acinetobacter. There were 34 clusters of putative nosocomial cross-infection due either to genospecies 3 (n = 16), A. baumannii (n = 10) or genospecies 13 (n = 8). Apart from 3 clusters due to two multiple-antibiotic-resistant strains of genospecies 13 and one strain of A. baumannii, respectively, there was no significant increase of antibiotic resistance discernible during the decade-long period of Acinetobacter surveillance.

Acinetobacter↗

PubMedDate not supplied

Enterococcus faecalis: in vitro activity of antimicrobial drugs, singly and combined, with and without defibrinated human blood, against high-level-gentamicin-resistant isolates.

Teicoplanin (4 micrograms/ml) combined with 4 micrograms/ml of ampicillin, mezlocillin, and piperacillin, respectively, proved more efficacious than vancomycin (4 micrograms/ml) combined with the three beta-lactam antibiotics against three representative clinical isolates of Enterococcus faecalis that showed high-level-gentamicin resistance (HLGR). In the presence of 65% (v/v) of fresh defibrinated human blood, teicoplanin (4 micrograms/ml) alone afforded significant bactericidal activity, but failed to completely sterilize assay tube contents, whereas teicoplanin combined with any of the three beta-lactam antibiotics consistently and completely killed HLGR E. faecalis inocula.

Ampicillin↗

PubMedDate not supplied

Enterococcus faecium: in vitro activity of antimicrobial drugs, singly and combined, with and without defibrinated human blood, against multiple-antibiotic-resistant strains.

The minimal inhibitory (MICs) and bactericidal concentrations of 14 antimicrobial drugs were determined against 17 clinical isolates of Enterococcus faecium, including 4 glycopeptide-resistant strains. Both teicoplanin and vancomycin lacked bactericidal activity against all 13 susceptible isolates. Time-kill experiments served to test various antibiotic combinations chiefly against glycopeptide-resistant strains in Mueller-Hinton broth (MHB) and in MHB supplemented with 65% (v/v) fresh defibrinated human blood. Co-trimoxazole, fusidic acid, and novobiocin yielded bacteriostatic effects. Rifampin was bactericidally active against rifampin-susceptible strains (MICs = 0.125 micrograms/ml), but less so against low-level-rifampin-resistant (MICs = 2-8 micrograms/ml) strains in MHB. However, in the presence of human blood, rifampin (2 micrograms/ml) combined with co-trimoxazole (0.25/4.75 micrograms/ml) killed rifampin-susceptible and low-level-rifampin-resistant, but not moderate-level-rifampin-resistant (MICs = 16-32 micrograms/ml) strains of E. faecium. Of two topical drugs examined, mupirocin merely inhibited strains of E. faecium; conversely, taurolidine at 2,000 micrograms/ml was efficacious against all strains examined, although the kinetics of bactericidal activity were retarded somewhat in the presence of 65 vol% human blood.

Anti-Bacterial Agents↗

PubMedDate not supplied

Taurolidine: in vitro activity against multiple-antibiotic-resistant, nosocomially significant clinical isolates of Staphylococcus aureus, Enterococcus faecium, and diverse Enterobacteriaceae.

Taurolidine at < or = 1,250 micrograms/ml killed all 37 isolates of multiple-antibiotic-resistant Staphylococcus aureus (n = 9), Enterococcus faecium (n = 17), and Enterobacteriaceae (n = 11). Time-kill experiments disclosed that bovine serum (65% v/v) only marginally retarded the bactericidal activity of 2,000 and 1,000 micrograms/ml of taurolidine against the various strains. Taurolidine at 2,000 micrograms/ml did not antagonize the bactericidal activity of 50% (v/v) fresh human serum against promptly and delayed serum-sensitive test strains of Escherichia coli and Serratia marcescens. In the presence of 65% (v/v) of fresh defibrinated human blood from two donors, however, the bactericidal activity of this antimicrobial compound was delayed, i.e., manifested only following extended (overnight) incubation, against staphylococcal and enterococcal isolates, though less so in the case of Enterobacteriaceae. Taurolidine at 2,000 micrograms/ml killed ingested, i.e., intraphagocytic bacteria of human-serum-resistant S. marcescens strains CDC 06:H3 and P016:H-.

Anti-Bacterial Agents↗

PubMedDate not supplied

Exposure of clinical isolates of Acinetobacter baumannii and genospecies 3 to defibrinated human blood with and without added human 'natural' or (patient) immune antibodies.

Fresh defibrinated blood (65% v/v) from 2 human donors failed to completely kill strains of Acinetobacter baumannii and genospecies 3, representing four serovars each. Although colony counts were reduced > or = 90%, there invariably occurred rebound growth following extended incubation. Neither selected serovar-specific or isolate-homologous (following experimental bacteremia) rabbit immune sera nor three intravenously applicable IgG preparations augmented the bactericidal activity of human blood against six selected strains of A. baumannii and genospecies 3, despite documented antibody contents of all sera and IgG preparations employed. The majority of the sera from 22 patients who were early reconvalescent from systemic infection due to A. baumannii or genospecies 3, showed raised IgM antibody titers, and all sera demonstrated markedly elevated IgG antibody titers as determined with an enzyme-linked immunoassay. Defibrinated blood from donors B and T failed to completely kill the bacteria inocula of these 22 Acinetobacter isolates. Only one patient serum enhanced the bactericidal activity of human blood in the absence of antimicrobial drug(s), and only 1 patient serum with large amounts of detectable antimicrobial drug(s) effected complete killing of the homologous bacterial inoculum.

Acinetobacter↗

PubMedDate not supplied

Gentamicin- and methicillin-resistant Staphylococcus aureus: phenotypic and genotypic characterization of three putative nosocomial outbreak strains.

Nineteen representative isolates of gentamicin- and methicillin-resistant Staphylococcus aureus (MRSA) were found to comprise three phenotypes; these differed with regard to hydrolysis of nitrocefin and production of staphylococcal enterotoxin A or/and toxic shock syndrome toxin-1. All MRSA isolates produced a capsule and were susceptible to coumermycin, nitrofurantoin, novobiocin, trimethoprim, trimethoprim-sulfamethoxazole, teicoplanin and vancomycin. All MRSA isolates were resistant to co-amoxiclav, ciprofloxacin, clarithromycin, gentamicin, methicillin, norfloxacin, ofloxacin, oxacillin and polymyxin B.

Anti-Bacterial Agents↗

PubMedDate not supplied

Immunobiology of methicillin-resistant Staphylococcus aureus: immune response of rabbits and patients to systemic infection.

Teichoic acid (TA) and peptidoglycan (PG) extracted from Staphylococcus aureus strains ATCC 25923 and Lafferty as well as formalinized cells of these two strains and several clinical methicillin-resistant S. aureus (MRSA) isolates were immunogenic for New Zealand White rabbits. Rabbits which had recovered from experimental bacteremia due to MRSA seroconverted, i.e. demonstrated raised titers of antibodies against TA and PG of the S. aureus strain Lafferty and against whole cells (WC) and ultrasound cell lysates (UCL) of MRSA isolates No. 1 and 2 (representative of nosocomial MRSA strain I), as determined with enzyme-linked immunosorbent assays. Furthermore, sera from 2 long-term survivor rabbits recognized four polypeptides (apparent molecular weight = 38.9, 33.9, 30.9, and 28.2 kDa) shared by UCL extracts from MRSA isolates No. 1 and 2, as determined with immunoblots. Neither normal nor immune rabbit sera augmented the bactericidal activity of fresh defibrinated human blood (65% v/v) against selected MRSA isolates and S. aureus strain ATCC 25923. Sera from 12 patients with documented systemic infection due to MRSA outbreak strain I were examined for IgM and IgG antibodies against TA, WC, and UCL antigens. Three patient sera exhibited raised IgM antibodies against TA; 7 of 12 patient sera showed increased IgG anti-TA titers. Only 1 patient had a markedly raised IgM anti-WC titer, whereas 4 and 10 of the patients had increased IgG titers against WC from MRSA isolates No. 1 and 2, respectively. However, all 12 patients had raised IgG titers against UCL from MRSA isolate No.2 versus 4 of 12 patients with elevated IgG titers against UCL from MRSA isolate No.1. Immunoblots with 3 selected patient sera revealed IgG antibodies to be more multifaceted than IgM antibodies. Sera from 11 of the 12 patients contained antimicrobial drug(s); yet only 5 of these 11 sera (used at 10% v/v in broth) killed inocula of MRSA isolate No. 43. None of the 12 patient sera (10% v/v) enhanced the bactericidal activity of human blood against selected MRSA isolates. Neither three commercial intravenously applicable IgG preparations nor an IgG anti-alpha-hemolysin formulation (employed at 10% v/v) augmented the bactericidal activity of fresh defibrinated human blood against selected MRSA isolates comprising MRSA outbreak strain I.

Animals↗