An evaluation of the potential of the multiple antibiotic resistance operon (mar) and the multidrug efflux pump acrAB to moderate resistance towards ciprofloxacin in Escherichia coli biofilms. (25/261)

The chromosomal multiple antibiotic resistance operon, mar, is widely represented amongst Gram-negative bacteria and has been implicated in resistance towards oxidative stress agents, organic solvents and a large number of structurally unrelated antimicrobial agents. The major mechanism associated with such increased resistance is an upregulation of the efflux pump acrAB. Growth as a biofilm is often associated with similar generalized reductions in susceptibility to inimical agents. Escherichia coli K12 (AG100), an isogenic mutant of AG100 constitutive for mar expression (AG102) and an isolate deleted of the mar locus (MCH164) were grown as biofilms in cellulose-fibre depth filters and perfused with a simple salts, minimal medium (CDM) over 120 h. Biofilms were exposed to various concentrations of ciprofloxacin (0.004, 0.015 and 0.1 mg/L) for 42 h. The numbers of viable cells within the perfusate and within the biofilm were estimated throughout. Whereas no differences were seen between the wild-type and mar-deleted isolates, that constitutive for mar displayed reduced susceptibility to ciprofloxacin at concentrations of 0.004 mg/L (MIC for AG100 was 0.0052 mg/L). Similar antibiotic perfusion experiments were conducted using isolates in which the efflux pump acrAB was either deleted (AG100-A) or constitutively expressed (AG100-B). Exposure of AG100-A biofilms to ciprofloxacin at 0.004 and 0.1 mg/L showed similar susceptibilities to those seen in the wild-type (AG100) and mar-deleted (MCH164) isolates and suggested that acrAB was not induced within the attached population. On the other hand, constitutive expression of acrAB (AG100-B) protected biofilms against the lower concentration of ciprofloxacin used (0.004 mg/L). This protection was again lost at concentrations of 0.1 mg/L. Overall, these results show that ciprofloxacin resistance in biofilms is not mediated by the upregulation of the mar or acrAB operons.  (+info)

Presence of ROB-1 beta-lactamase correlates with cefaclor resistance among recent isolates of Haemophilus influenzae. (26/261)

beta-Lactamase production in Canadian isolates of Haemophilus influenzae has remained relatively constant (25-35%) over the last decade despite increasing cefaclor resistance (MIC >/= 32 mg/L). TEM (294/324, 90.7%) and ROB-1 (30/324, 9.3%) prevalence rates among 324 isolates of H. influenzae obtained from across Canada in 1997-1998 were similar (P > 0.05) to previously published reports. However, 66. 7% (26/39) of cefaclor-resistant isolates were ROB-1-positive (P < 0. 001) and the remaining four ROB-1-positive isolates were cefaclor-intermediate (MIC 16 mg/L). Susceptibilities to loracarbef (P < 0.001) and cefprozil were also reduced in the presence of ROB-1 while the activities of cefuroxime, cefotaxime, cefixime and imipenem were similar in both TEM- and ROB-1-positive solates.  (+info)

A novel CTX-M beta-lactamase (CTX-M-8) in cefotaxime-resistant Enterobacteriaceae isolated in Brazil. (27/261)

To estimate the diversity of extended-spectrum beta-lactamases in Brazil, 18 strains from different species of the family Enterobacteriaceae exhibiting a positive double-disk synergy test were collected by a clinical laboratory from several hospitals in Rio de Janeiro, Brazil, in 1996 and 1997. Four strains (Proteus mirabilis, Enterobacter cloacae, Enterobacter aerogenes, and Citrobacter amalonaticus) hybridized with a 550-bp CTX-M probe. The P. mirabilis strain produced a CTX-M-2 enzyme. The E. cloacae, E. aerogenes, and C. amalonaticus isolates harbored a bla gene which was identified by cloning and sequencing as a bla(CTX-M) gene. E. coli HB101 transconjugants and the E. coli DH5alpha transformant harboring a recombinant plasmid produced a CTX-M beta-lactamase with an isoelectric point of 7.6 conferring a resistance phenotype characterized by a higher level of resistance to cefotaxime than to ceftazidime, as observed with the other CTX-M enzymes. The deduced protein sequence showed a novel Ambler class A CTX-M enzyme, named CTX-M-8, which had 83 to 88% identity with the previously described CTX-M enzymes. The phylogenic study of the CTX-M family including CTX-M-8 revealed four CTX-M types, CTX-M-8 being the first member of a new phylum of CTX-M enzymes. The evolutionary distances between the four types of CTX-M were large, suggesting that the four clusters branched off early from a distant unknown enzyme and that intermediate enzymes probably existed.  (+info)

Cross-resistance patterns among clinical isolates of Klebsiella pneumoniae with decreased susceptibility to cefuroxime. (28/261)

The frequency of decreased susceptibility to cefuroxime and quinolones and the correlation between these drug resistance traits was investigated in clinical isolates of Klebsiella pneumoniae from two Danish counties. Eighty-three randomly selected clinical isolates of K. pneumoniae with decreased susceptibility to cefuroxime were examined for cross-resistance patterns and the production of beta-lactamases. The frequency of resistance to cefuroxime and ciprofloxacin has increased from <5% in 1990 to 15% and 7% in 1998, respectively. Two of the 83 isolates were multiply resistant and seemed to produce extended-spectrum beta-lactamases. However, cross-resistance to ciprofloxacin and other classes of drug in 68% of the remaining isolates indicates that other resistance mechanisms, such as penetration barriers, had probably been selected in these Danish isolates. The susceptibility to ciprofloxacin decreased successively with decreasing susceptibility to cefuroxime for K. pneumoniae. This did not occur in cefuroxime-resistant Escherichia coli.  (+info)

Animal and human multidrug-resistant, cephalosporin-resistant salmonella isolates expressing a plasmid-mediated CMY-2 AmpC beta-lactamase. (29/261)

Salmonella spp. are important food-borne pathogens that are demonstrating increasing antimicrobial resistance rates in isolates obtained from food animals and humans. In this study, 10 multidrug-resistant, cephalosporin-resistant Salmonella isolates from bovine, porcine, and human sources from a single geographic region were identified. All isolates demonstrated resistance to cephamycins and extended-spectrum cephalosporins as well as tetracycline, chloramphenicol, streptomycin, and sulfisoxazole. Molecular epidemiological analyses revealed eight distinct chromosomal DNA patterns, suggesting that clonal spread could not entirely explain the distribution of this antimicrobial resistance phenotype. However, all isolates encoded an AmpC-like beta-lactamase, CMY-2. Eight isolates contained a large nonconjugative plasmid that could transform Escherichia coli. Transformants coexpressed cephalosporin, tetracycline, chloramphenicol, streptomycin, and sulfisoxazole resistances. Plasmid DNA revealed highly related restriction fragments though plasmids appeared to have undergone some evolution over time. Multidrug-resistant, cephalosporin-resistant Salmonella spp. present significant therapeutic problems in animal and human health care and raise further questions about the association between antimicrobial resistance, antibiotic use in animals, and transfer of multidrug-resistant Salmonella spp. between animals and man.  (+info)

Multiple-antibiotic resistance mediated by structurally related IncL/M plasmids carrying an extended-spectrum beta-lactamase gene and a class 1 integron. (30/261)

A conjugative IncL/M plasmid (pSEM) conferring resistance to gentamicin, amikacin, kanamycin, sulfonamides, and expanded-spectrum cephalosporins was found in pathogenic strains of Salmonella enterica serotype Typhimurium. Resistance to aminoglycosides was encoded by a sul1-type class 1 integron (In-t3). An extended-spectrum beta-lactamase gene, bla(SHV-5), was identified 3. 5 kb downstream of the integrase (intI1) gene of In-t3. Nucleotide sequence analysis of the 5.3-kb bla(SHV-5)-In-t3 region of pSEM highlighted striking similarities with IncL/M plasmids isolated from nosocomial gram-negative pathogens, conferring resistance to expanded-spectrum cephalosporins and aminoglycosides.  (+info)

Evaluation of current activities of fluoroquinolones against gram-negative bacilli using centralized in vitro testing and electronic surveillance. (31/261)

Given the propensity for Enterobacteriaceae and clinically significant nonfermentative gram-negative bacilli to acquire antimicrobial resistance, consistent surveillance of the activities of agents commonly prescribed to treat infections arising from these organisms is imperative. This study determined the activities of two fluoroquinolones, levofloxacin and ciprofloxacin, and seven comparative agents against recent clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia using two surveillance strategies: 1) centralized in vitro susceptibility testing of isolates collected from 27 hospital laboratories across the United States and 2) analysis of data from The Surveillance Network Database-USA, an electronic surveillance network comprising more than 200 laboratories nationwide. Regardless of the surveillance method, Enterobacteriaceae, P. aeruginosa, and A. baumannii demonstrated similar rates of susceptibility to levofloxacin and ciprofloxacin. Susceptibilities to the fluoroquinolones approached or exceeded 90% for all Enterobacteriaceae except Providencia spp. (+info)

High rates of resistance to cephalosporins among viridans-group streptococci causing bacteraemia in neutropenic cancer patients. (32/261)

The prevalence of resistance to cephalosporins among viridans-group streptococci causing 88 (18%) cases among 485 bacteraemias in neutropenic cancer patients was studied. Rates of resistance to ceftriaxone, ceftazidime, cefpirome and cefepime were 22, 53, 14 and 34%, respectively. Previous administration of beta-lactam therapy was the only factor significantly associated with bacteraemia due to cephalosporin-resistant strains; only 11 (16%) of 68 patients infected with cephalosporin-susceptible bacteria had received these antibiotics compared with 10 (50%) of 20 patients infected with cephalosporin-resistant bacteria (P = 0.0052).  (+info)