RESUMO
INTRODUCTION: Bloodstream infections with multidrug-resistant (MDR) Gram-negative bacteria (GNB) are among the most frequent complications in immunocompromised cancer patients because of their considerable morbidity and mortality. Several guidelines on antimicrobial therapy have addressed empirical treatment for such serious infections; however, the emergence of microbial resistance has become a significant problem worldwide. MATERIALS AND METHODS: In this study, starting from November 2015 to October 2016, a total of 529 blood specimens were collected from febrile neutropenic cancer patients at a tertiary care cancer hospital in Egypt. RESULTS: On examination for positive bacterial growth, it was found that 334 specimens showed no growth, while 195 were positive. Out of the 195 positive culture specimens, 102 (102/195, 52.3%) were Gram-negative and 93 (93/195, 47.7%) were Gram-positive. Out of the 102 GNB, 70 (70/102, 68.6%) were MDR, including Escherichia coli (27/70, 38.6%), Klebsiella pneumoniae (24/70, 34.3%), Acinetobacter baumannii (9/70, 12.8%), Enterobacter cloacae (4/70, 5.7%), Pseudomonas aeruginosa (2/70, 2.8%), Klebsiella oxytoca (2/70, 2.8%), and Klebsiella ornithinolytica (2/70, 2.8%). All MDR GNB showed high resistance to ampicillin, cefepime, ceftriaxone, and cephradine (minimum inhibitory concentration at which 50% of the isolates were inhibited [MIC50] >512 µg/mL for each). However, they showed good susceptibility to colistin (MIC50 <1 µg/mL). The most common extended-spectrum ß-lactamases (ESBLs) genes detected were ctx-m (39/70, 55.7%), shv (31/70, 44.3%), and tem (22/70, 31.4%). The most common aminoglycoside-resistant gene detected was aac(6')-Ib (42/70, 60%) followed by the plasmid-mediated quinolone resistance determinants; qnrA (2/70, 2.8%), qnrB (9/70, 12.8%), and qnrS (19/70, 27.1%). ESBL determinants were significantly associated with resistance to ciprofloxacin, levofloxacin, amikacin, and carbapenems (P-value <0.005). The fractional inhibitory concentration index for ampicillin/sulbactam plus ceftriaxone, ampicillin/sulbactam plus amikacin, and amikacin plus levofloxacin showed synergism against 29 (29/70, 41.4%), 19 (19/70, 27.1%), and 11 (11/70, 15.7%) isolates of the tested MDR GNB isolates, respectively. CONCLUSION: Accordingly, new empirical antibiotics should be administered including the use of colistin or meropenem alone or both against the MDR GNB in neutropenic cancer patients.
RESUMO
Acyl homoserine lactones (AHLs) are the most common class of quorum sensing signal molecules (autoinducers) that have been reported to be essential for virulence of many relevant pathogenic bacteria such as Pseudomonas aeruginosa. New approach for controlling infections of such bacteria is through quorum quenching. In this study, the acyl homoserine lactone inhibitory activity of the crude enzyme from a Bacillus weihenstephanensis-isolate P65 was characterized. The crude enzyme was found to have relatively high thermal stability and was stable in pH range 6 to 9. The crude enzyme extract was found to have lactonase activity of 36.3 U/mg total protein. Maximum enzyme activity was achieved within a range of 28-50°C and pH 6-9. None of the metals used enhanced the activity neither did EDTA inhibit it. However, a concentration of 10 mM Fe(+2) reduced the activity to 73.8%. Catalytic activity and kinetic constants were determined using hexanoyl homoserine lactone as a substrate. Studying enzyme substrate specificity using synthetic standard signals displayed broad spectrum of activity. The enzyme was found to be constitutive. Isolation and complete nucleotide sequence of the respective lactonase gene were done and submitted to the Genbank database under accession code KC823046.
