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The occurrence of the trehalose fermenting, tetracycline and polymyxin resistant phenotype among the Enterobacteriaceae.

In Proteus morganii, P. mirabilis, and Providencia stuartii the ability to ferment trehalose and resistance to tetracycline were associated in 90%-97% of the strains. The same was true of at least 78% of the strains of Serratia marcescens. Proteus vulgaris showed a more quantitative association of the two traits. As the characters occur independently in 3-10% of the strains, the association is considered to be due to simultaneous selection in some natural niche. The trehalose fermenting, tetracycline and polymyxin resistant species ferment few other carbohydrates, fewer than the remainder of the Serratia species.

Drug Resistance, Microbial↗

Prevalence and genetic analysis of plasmid-mediated quinolone resistance determinants QnrA and QnrS in Enterobacteriaceae isolates from a French university hospital.

The spread of plasmid-mediated quinolone resistance determinants QnrA and QnrS was evaluated in a collection of 186 extended-spectrum beta-lactamase (ESBL)-positive enterobacterial isolates from 2002 to 2005 and 185 nalidixic acid-resistant strains isolated during the first 6 months of 2005 at the Bicêtre hospital, France. Out of these 186 ESBL-positive isolates, 2.2 and 1.6% carried a QnrA1 and a QnrS1 determinant, respectively. The ESBLs associated with QnrA1 were VEB-1, SHV-12, and CTX-M-1, whereas those associated with QnrS1 were TEM-52, SHV-12, and CTX-M-1. Among the 185 nalidixic acid-resistant strains isolated in 2005, 0.5 and 2.7% had a QnrA1 determinant and a QnrS1 determinant, respectively. The genetic environments of the qnrA1 gene differed but were always associated with sul1 type integrons. In contrast, qnrS1 genes were not embedded in class 1 integrons but located often (but not systematically) downstream of the insertion sequence ISEcl2 on plasmids that often carried a novel beta-lactamase gene, bla(LAP-1). This is the first study identifying the QnrS resistance determinant in Europe and indicating that this determinant might also be widespread.

Anti-Bacterial Agents↗

Emergence and dissemination of Enterobacteriaceae isolates producing CTX-M-1-like enzymes in Spain are associated with IncFII (CTX-M-15) and broad-host-range (CTX-M-1, -3, and -32) plasmids.

The spread of CTX-M-1-like enzymes in Spain is associated with particular plasmids of broad-host-range IncN (blaCTX-M-32, blaCTX-M-1), IncL/M (blaCTX-M-1), and IncA/C2 (blaCTX-M-3) or narrow-host-range IncFII (blaCTX-M-15). The identical genetic surroundings of blaCTX-M-32 and blaCTX-M-1 and their locations on related 40-kb IncN plasmids indicate the in vivo evolution of this element.

Drug Resistance, Bacterial↗

Spontaneous implantation of antibiotic-resistant Enterobacteriaceae in the digestive tract of chickens in the absence of selective pressure.

In the absence of selective pressure by antibiotics, resistant enterobacteria implanted rapidly in the intestinal tract of chickens, where these organisms subsequently persisted in high numbers. Food could be an important source of this contamination: resistant Escherichia coli present in small numbers in the diet became rapidly and persistently established in the gut. The human caretaker played a passive role in the spread of antibiotic-resistant bacteria between separate groups of chickens. Resistant enteric organisms colonized the gut of animals, with different population sizes. Some strains were able to reach high numbers (10(7) to 10(9)/g), and other strains established themselves at a lower level (10(3) to 10(5)/g), whereas a third type seemed to be only transient inhabitants, unable to persist.

Animals↗

Susceptibility of the anaerobic bacteria, group D streptococci, Enterobacteriaceae, and Pseudomonas to semisynthetic penicillins: carbenicillin, piperacillin, and ticarcillin.

Sodium piperacillin T-1220, a new semisynthetic penicillin, was tested in vitro against 297 clinical isolates of anaerobic bacteria and 669 aerobic bacteria by the conventional agar dilution method and compared with carbenicillin and ticarcillin. At a 100-mug/ml concentration the three drugs showed comparable effectiveness against the anaerobes tested. However, at 20 mug/ml, piperacillin was the most effective drug against Bacteroides fragilis, peptostreptococci, and group D streptococci. At this drug concentration only 48% of the B. fragilis strains exhibited susceptibility to carbenicillin only, 64% exhibited susceptibility to ticarcillin but 90% exhibited susceptibility to piperacillin. Similar findings were observed with peptostreptococci and group D streptococci. On a weight basis piperacillin was statistically shown to be the most effective antibiotic of the three tested against these anaerobes. At 20 mug/ml, piperacillin exhibited a statistically significant difference (P < 0.01) over carbenicillin and ticarcillin for Serratia marcescens, Escherichia coli, Klebsiella species, Klebsiella pneumoniae, Pseudomonas isolates, and Citrobacter diversus. At both 20- and 100-mug/ml concentrations, piperacillin appeared to be the most effective (calculated P < 0.01) upon Klebsiella species, K. pneumoniae, S. marcescens, and C. freundii in activity over ticarcillin and carbenicillin.

Aerobiosis↗

In vitro activity of piperacillin compared with that of carbenicillin, ticarcillin, ampicillin, cephalothin, and cefamandole against Pseudomonas aeruginosa and Enterobacteriaceae.

Piperacillin (T-1220), a semisynthetic derivative of aminobenzylpenicillin, was more active than either carbenicillin or ticarcillin against Pseudomonas aeruginosa; over 60% of isolates were inhibited at a concentration of 6.3 mug/ml. Piperacillin was bactericidal for 84% of Pseudomonas strains at 100 mug/ml, carbenicillin killed 60%, and ticarcillin killed 68% at that concentration. Piperacillin was also more active than the other penicillins against isolates of Escherichia coli, Enterobacter, and Proteus mirabilis. The combination of piperacillin and tobramycin, demonstrating synergistic inhibition of 87% of strains of P. aeruginosa, was the most active of the penicillin-aminoglycoside combinations tested for synergism.

Ampicillin↗

Heterogeneity of 6'-N-acetyltransferases of type 4 conferring resistance to amikacin and related aminoglycosides in members of the family Enterobacteriaceae.

DNA-DNA hybridization and immunoblotting were used to assess the relatedness between the 6'-N-acetyltransferases of type 4 encoded by plasmid pAZ007 from a clinical isolate of Serratia marcescens and those encoded by NR79 and R5. The absence of detectable DNA-DNA homology and of immunological cross-reactivity suggests the existence of at least two distinct 6'-N-acetyltransferase type 4 genes that mediate amikacin resistance in gram-negative bacilli.

Acetyltransferases↗

In vitro activity of amifloxacin against outer membrane mutants of the family Enterobacteriaceae and frequency of spontaneous resistance.

Amifloxacin showed potent inhibitory activity against DNA gyrase of Escherichia coli. The difference in the susceptibilities of lipopolysaccharide-deficient Salmonella typhimurium mutants and their parent strain was less than twofold, and the difference in the susceptibilities of porin-deficient E. coli mutants and their parent strain was less than twofold. There was cross resistance among the quinolone group of agents; however, the decrease in MIC for norB mutants was slightly lower than that of other fluoroquinolones. Cell lysis was induced with combined treatment of amifloxacin and sodium dodecyl sulfate in E. coli. The frequency of mutants spontaneously resistant to amifloxacin was extremely low in all species tested.

Anti-Bacterial Agents↗

Ticarcillin and ticarcillin-clavulanic acid susceptibility tests: error rates for disk tests with consecutively isolated members of the family Enterobacteriaceae.

A five-laboratory coordinated study was undertaken to determine whether ticarcillin and ticarcillin-clavulanic acid disk susceptibility tests could accurately detect resistance among enteric bacilli. Each facility performed disk tests and broth microdilution susceptibility tests with reagents distributed from a common source, and appropriate controls were included in order to ensure methodologic uniformity. Each institution tested 500 consecutively isolated enteric bacilli against ticarcillin and ticarcillin-clavulanic acid. The prevalence of discrepancies between disk tests and dilution tests with 2,435 unselected enteric bacilli provided a valid estimate of the true error rate for tests with the two disks. The current interpretive criteria for susceptibility tests with ticarcillin and ticarcillin-clavulanic acid disks were found to be reliable; i.e., there were major or very major discrepancies between MIC categories and disk test results for less than 1% of all strains and minor discrepancies for only 5 to 10%. Even lower error rates would occur if the zone size-interpretive criteria were modified, but at this time it is difficult to determine whether the practical problems created by making such changes can be justified by the magnitude of the problem that is being resolved.

Clavulanic Acids↗

Detection of extended-spectrum beta-lactamases in members of the family Enterobacteriaceae: comparison of the double-disk and three-dimensional tests.

The three-dimensional and clavulanate double-disk potentiation tests were compared as procedures for the detection of extended-spectrum beta-lactamase production in 32 strains of Escherichia coli and Klebsiella pneumoniae, 31 of which produced TEM-1, TEM-2, TEM-3, TEM-4, TEM-5, TEM-7, TEM-8, TEM-9, TEM-10, TEM-12, TEM-101, SHV-1, SHV-2, SHV-3, SHV-4, SHV-5, CAZ-2, MIR-1, or an unidentified extended-spectrum beta-lactamase with a pI of 5.95, with some strains producing multiple beta-lactamases. The three-dimensional test, which was performed in conjunction with a routine disk diffusion test, detected extended-spectrum beta-lactamase production in 26 of 28 (93%) of the strains that produced extended-spectrum beta-lactamases. The clavulanate double-disk potentiation test detected extended-spectrum beta-lactamases in only 22 of the 28 strains (79%) when it was performed as currently recommended. The three-dimensional test, when performed in conjunction with the disk diffusion test, offered the advantages of providing simultaneous information about both antibiotic susceptibility and extended-spectrum beta-lactamase production, coupled with a greater sensitivity and earlier detection of extended-spectrum beta-lactamases.

Anti-Bacterial Agents↗

Cefepime, piperacillin-tazobactam, and the inoculum effect in tests with extended-spectrum beta-lactamase-producing Enterobacteriaceae.

There is little information about the clinical effectiveness of cefepime and piperacillin-tazobactam in the treatment of infections caused by extended-spectrum beta-lactamase (ESBL)-producing pathogens. Some inferences have been drawn from laboratory studies, which have usually involved only one or a few strains of ESBL-producing Klebsiella pneumoniae or Escherichia coli that produced only a limited range of ESBLs. Such studies are indirect, sometimes conflicting, indicators of efficacy. To extend previous laboratory findings, a study was designed to investigate organism-drug interactions by determining the in vitro activities of eight parenteral beta-lactam agents against 82 clinical and laboratory strains of Klebsiella, Escherichia, Enterobacter, Citrobacter, Serratia, Morganella, and Proteus species that produced 22 different ESBLs, alone or in combination with other beta-lactamases. Activities were determined in broth microdilution MIC tests using standard and 100-fold-higher inocula. An inoculum effect, defined as an eightfold or greater MIC increase on testing with the higher inoculum, was most consistently detected with cefepime, cefotaxime, and ceftriaxone and least frequently detected with meropenem and cefoteten. Piperacillin-tazobactam was intermediate between these two groups of agents. Although the inoculum effect is an in vitro laboratory phenomenon, if it has any predictive value in identifying increased risk of therapeutic failure in serious infections, these results support suggestions that cefepime may be a less-than-reliable agent for therapy of infections caused by ESBL-producing strains.

Anti-Bacterial Agents↗