Objective: To find out the spatial autocorrelation of antibiotic resistance of S. pneumonia and test the significance of distance as a risk factor. Methods: Descriptions of penicillin and macrolide resistance in EARS-Net countries from 2006 to 2010 were given. Global moran’s I and Anselin moran’s I were used to assess the spatial autocorrelation and gravity model was used to test the significance of distance and other socio – economic factors. Results: The trend of resistance in Europe was stable. Positive spatial autocorrelation existed from 2006 to 2010 for penicillin (Z(I): 0.16-0.2) and 2009 to 2010 for macrolide (Z(I): 0.11 -0.13). Some clusters (hotspots) were identified; they were Cyprus (2006-2010 for penicillin and 2009 to 2010 for macrolide), Spain (2006 for penicillin), France (2006 for penicillin), Romania (2009 for penicillin and macrolide) and Bulgaria (2009 for penicillin and macrolide). The result of gravity model showed that only parameters of population in 2007 for penicillin (p<0.05) and parameter of distance in 2009 for penicillin (p<0.05) in Cyprus were statistically significant. Conclusion: Distance was not a risk factor of high prevalence of antibiotic resistance of S. pneumoniae although there was a positive spatial autocorrelation. Improvement in surveillance system and appropriate public action were recommended for controlling the spread of resistant strain of S. pneumoniae. / published_or_final_version / Public Health / Master / Master of Public Health

The diminishing choice of effective antibiotics against resistant pathogens has forced clinicians to revive the use of old antibiotics. Hence, fosfomycin has been frequently suggested for alternative therapies given its track record of low resistance rates despite extensive use. However, there have been recent reports of plasmid-mediated fosfomycin resistance among animals and healthy humans in Asia. Accordingly, comparison of shared fosfomycin resistance mechanisms between animals and humans will shed light on the spread of resistance and guide future use of antimicrobials. This study aimed to investigate plasmid-mediated fosfomycin resistance in E. coli isolates collected from patients and animals in Hong Kong. Non-duplicate E. coli isolates were cultured from 1711 urinary isolates and 167 blood clinical samples collected from multiple centres during 1996-2008 and from fecal samples of 210 cattle, 214 pigs, 460 chickens, 398 stray cats, 368 stray dogs and 456 wild rodents during 2008-2010. A total of 2106 animal samples yielded 1693 E. coli isolates of which 831 were ESBL-producers. Fosfomycin-resistant isolates were more likely than fosfomycin-susceptible isolates to be ESBL-producers and multidrug resistant (≥3 antimicrobial classes). Of the 101 fosfomycin-resistant isolates, 97 (96.0%) were fosA3 positive and 94 (93.1%) were blaCTX-M positive. Of the 1878 clinical isolates, 18 were fosfomycin-resistant of which six were fosA3-positive and two were positive for another fosA variant (designated fosKP96). All but one fos-carrying clinical isolate was ESBL-producing. The majority of the fos-carrying E. coli strains belonged to diverse clones under two main clonal complexes CC58 accounting for 38 (36.2%) strains and CC10 for 32 (30.5%) strains. PCR mapping showed that all fosA3-containing regions were followed by a downstream IS26. In all clinical isolates and 81 (83.5%) of animal isolates, an IS26 was also found upstream. In 14 (14.4%) of animal isolates, the fosA3 gene was preceded by an upstream blaCTX-M-14-containing transposon-like structure (ΔISEcp1-blaCTX-M-14-ΔIS903 or ISEcp1-IS10-blaCTX-M-14-ΔIS903). For the remaining two animal isolates, the upstream region could not be defined. In a random subset of 18 animal isolates, fosA3 was carried on transferable plasmids with sizes of 50–200 kb and the following replicons: F2:A-:B- (n = 3), F16:A1:B- (n = 2), F24:A-B- (n = 1), IncHI2 (n = 3), IncN (n = 2), IncI1 (n = 1), B/O (n = 1) and untypeable (n = 5). Among six fosA3-carrying clinical isolates, the distributions were: F2:A-:B- (n = 2), IncN (n = 1), multi-replicon F-:A-:B1/IncN (n = 1) and untypeable (n = 2). Both fosKP96-carrying plasmids belonged to IncN. Restriction fragment length polymorphism analysis showed that the four F2:A-:B- plasmids carrying fosA3 and blaCTX-M-3 genes from a pig, dog and two patients shared an almost identical pattern. The complete plasmid sequences further demonstrated their homology. This study demonstrated the emergence of fosA3-mediated fosfomycin resistance among E. coli isolates from multiple sources. Highly similar IncFII plasmids and IS26 transposon-like structures appear to be the main vehicles for dissemination. This study also highlighted occurrence of plasmids carrying fosKP96 that may have been overlooked by others as this variant could not be detected by established PCR markers. / published_or_final_version / Microbiology / Master / Master of Philosophy

Acinetobacter baumannii is an important nosocomial pathogen worldwide because of its remarkable ability to acquire antibiotic resistance. The global emergences of multidrug-resistant A. baumannii (MDR-AB) clones are predominated by a number of widely disseminated clones, namely clonal complex (CC) 1, CC2, and CC3. In early 2010, we reported two major clones of MDR-AB, designated HKU1 and HKU2 belong to sequence types (ST) 96 and ST92, widely disseminating in our hospitals. ST92 is a predominant clone that is prevalent in more than 30 countries, whereas ST96 has been identified recently and is geographically confined to certain parts of China. Our previous study only investigated the isolates collected in the year 2005-2006. We therefore extended our investigation over a six-year period (2005-2010) to generate a more complete picture of the molecular epidemiology and resistance mechanisms in A. baumannii. Firstly, we performed the susceptibility test on various antimicrobial agents and employed molecular methods to characterize the epidemiology of the target A. baumannii isolates. For the entire study period, increased resistance rates were noted for the seven antimicrobial agents, namely imipenem, piperacillin-tazobactam, cefoperazone, ticarcillin-clavulanate, ciprofloxacin, gentamicin and amikacin (P <0.01). Worryingly, an increased trend was also observed for the pandrug-resistant rate, from 0.2% in the year 2005-2006, to 1.9-2.9% in the year 2007-2008 and up to 6.0-8.1% in the year 2009-2010 (chi square for trend, P <0.001). Pulsed-field gel electrophoresis and multilocus sequence typing (PFGE/MLST) categorized 100 out of 108 (92.6%) isolates into four clones (PFGE/MLST), namely HKU2/ST92 (n = 14), HKU3/ST254 (n = 73), HKU4/ST137 (n = 5), and HKU5/ST362 (n = 8), respectively. PCR showed that 88.9% (96/108) of the amikacin-resistant isolates were armA positive and all isolates were found to harbour at least one of the OXA-type carbapenemases with frequencies as follows: OXA-51-like (98/108, 90.7%), OXA-23-like (85/108, 78.7%), OXA-58-like (9/108, 8.3%) and OXA-24-like (8/108, 7.4%). Secondly, we compared the biological fitness of the circulating clones by performing the doubling time and adhesion experiment. The results demonstrated that HKU3/ST254 has a higher capability for replication and adherence to human bronchial epithelial cells. Together with the higher antibiotic resistance rate, the selective advantages in terms of biological fitness may facilitate the clonal expansion and wide dissemination of this lineage. Finally, whole genome sequence data showed a high amount of resistance genes intermixed with various insertion sequence (IS) elements, integrons and transponsons clustering inside the resistance islands. The presence of a second genomic resistance island conferring aminoglycoside and sulphonamide resistance, additional loci outside the resistance islands harbouring resistance genes and the high amount of antibiotic efflux pumps in various A. baumannii genomes demonstrated that resistance islands contribute a significant part to the multidrug-resistant phenotype in A. baumannii but are not the only factor. The correlation analysis further demonstrated the significance of IS elements in the dissemination of antibiotic resistance genes in the A. baumannii genomes. As a whole, whole genome sequence data may provide an informative and efficient approach to generating a more comprehensive picture to study the resistance mechanism of the epidemic strains. / published_or_final_version / Microbiology / Doctoral / Doctor of Philosophy

Background A pandemic clone, Escherichia coli sequence type 131 (ST131), has been disseminated worldwide and represents an important cause of antimicrobial resistant infections. The spread of this resistant clone has become a great public health concern. Objectives The aims of this study were to investigate the prevalence of ST131 in Escherichia coli isolates from human urinary cultures in Hong Kong and study the antimicrobial phenotypes of ST131. Methodology This study included 340 E. coli clinical urinary isolates obtained from patients in four district hospitals between May 2013 and July 2013 in Hong Kong. Antimicrobial susceptibilities were assessed by disk diffusion method with reference to CLSI. The isolates were investigated by phylogroup-specific and ST131-specific PCR assays. ST131 strains were further assessed for subclone distribution, antimicrobial resistance and extended-spectrum β-lactamase (ESBL) type. Results A total of 18.5% (63/340) of the E. coli population was identified as ST131. ST131 isolates were significantly more likely than non-ST131 isolates to be ciprofloxacin resistant (69.8%, 44/63 versus 31.0%, 86/277; P <0.001), gentamicin resistant (38.1%, 24/63 versus 24.9%, 69/277; P=0.03) and ESBL producers (41.3%, 26/63 versus 18.8%, 52/277; P <0.001). Among the ST131 E. coli isolates, 68.3% (43/63) belonged to the H30 subclone. Most H30 isolates were ST131-O25b (97.7%, 42/43). Also, the ST131-H30 E. coli subclone was statistically associated with ciprofloxacin resistance compared with the non-H30 ST131 isolates (P <0.001). Additionally, strains which were co-resistant to ciprofloxacin, co-trimoxazole and gentamicin were overwhelmingly associated with the H30 subclone than non-H30 (23.3%, 10/43 versus 0%, 0/20; P=0.02). Conclusion This study showed that ST131 isolates were widespread among human E. coli urinary isolates in Hong Kong. The increase in antimicrobial resistance phenotypes are highlighted with ST131, especially the H30 subclone isolates. The dissemination of the ST131 resistant clonal group has aroused clinical attention and limited the choice of empirical treatment. / published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.

The characteristics and expression of laboratory derived chloramphenicol (CM) resistance in P. aeruginosa were examined. Resistant strains exhibiting single cell resistance of 1.5 to 2 mg/mL were readily isolated following one passage in CM at 150 to 1000 (mu)g/mL. Isogenic strains, selected on CM at 150 and 500 (mu)g/mL were chosen for detailed study. Resistance was not a consequence of drug detoxification or altered sensitivity of the target site. The resistant strains exhibited unusual phenotypic properties including pronounced variations in growth rate, CM susceptibility and cell morphology as a function of the composition of the growth medium. Growth in CM also resulted in significant alterations in amino acid transport and respiratory capacity, the extent of which varied with the strain, the growth medium and the concentration of CM. These drug and medium-dependent alterations were determined to reside in an increased and highly specific requirement for Ca('2+), Mg('2+), Mn('2+) or Sr('2+). Manipulation of the divalent cation concentration of a variety of growth media resulted in dramatic alterations in growth rate, resistance and amino acid transport. Ca('2+) was significantly more effective than the latter three ions. The expression of native and plasmid-mediated CM resistance was also modified by the external concentration of divalent cations. In view of the nature and specificity of the cation requirement, it was concluded that (1) divalent cation-mediated alterations of outer membrane permeability are fundamental to the expression of native and acquired CM resistance in P. aeruginosa; (2) laboratory-derived CM resistance involves envelope changes, such that interaction with divalent cations promotes more effective exclusion of CM. The latter conclusion is supported by other divalent cation-dependent alterations in envelope function in the resistant strains.

The characteristics of the effects of chloramphenicol on Pseudomonas aeruginosa were examined. Resistant strains were easily isolated following a single passage in chloramphenicol at 150 $ mu$g/ml to 500 $ mu$g/ml. Drug detoxification or altered sensitivity of the target site could not be the mechanism of resistance. This resistance to chloramphenicol was correlated with the addition of an outer membrane protein with a molecular weight of 49 kDa and the loss of two outer membrane proteins, one with the molecular weight of 19 kDa and the other of about 10 kDa. The highly specific requirement of the resistant strains for Ca$ sp{2+}$, Mg$ sp{2+}$, Mn$ sp{2+}$ or Sr$ sp{2+}$ described by Irvin and Ingram (1982) was confirmed by the observation that the outer membrane of the resistant cells contained twice as much Mg$ sp{2+}$ cation as the sensitive cells. Many other experiments designed to observe the effects of chloramphenicol on the outer membrane of P. aeruginosa failed. It was concluded that the observations made in this study strongly suggested a "re-structuring" of the outer membrane of P. aeruginosa, rendering the resistant cells more impermeable to chloramphenicol.

Plasmodium falciparum is a protozoan parasite that causes malaria, a disease that is widely spread in the tropical world. Chloroquine has been very effective against malaria since it was introduced into the field until the emergence of chloroquine resistant malaria. Chloroquine resistant malaria has become widely spread in the endemic area. In addition, cross resistance to other antimalarial drugs that are different in structure and function has been reported, even though some of these drugs had not been previously used in that particular region. The objective of this study was to determine the molecular mechanism of this resistance. Actinomycin D resistant Plasmodium falciparum was selected in vitro from the drug sensitive parental clone, 3D7. Interestingly, we found that the selected strain is resistant to chloroquine, mefloquine, antimalarial drugs, and Rhodamine 123. Comparison between 3D7 parental and 3D7R/act-D2 resistant P. falciparum did not show a difference in the level of expression of pfmdr1 previously implicated in the drug resistance. In addition we found that the level of accumulation of two drugs actinomycin D is reduced in the resistant parasite as compared with the sensitive one. Further studies indicated that the reduction in the drug accumulation was due to the increase in drug efflux. Furthermore, to identify if other P-glycoprotein homologues are involved in the resistance, oligonucleotide primers to conserved sequences in ABC domains have been used. An ABC protein homologous to subunit 4 of the 26S proteasome complex has been cloned. In vitro transcription, translation and immunoprecipitation analysis were done using reticulocytes lysate and polyclonal antibodies generated against peptide sequence in the P. falciparum S4 subunit. Surprisingly a decrease in the expression of this gene was found in the resistant clone, 3D7R/act-D2, compared to its parental cell line as determined by Northern blot analysis. Studies are in progress to determine

Bacteriological survey of the fish pathogens in Greek mariculture between 1994- 1997 was followed by analysis of prevalence in sea bass, sea bream, sharpsnout bream and common Dentex and discussion of the impact of various fish pathogens. In addition antibiotic resistance profiles and frequencies were studied using quantitative antibiogram and MIC analysis for the two most commonly used antibiotics Oxolinic acid and Oxytetracycline and clinically relevant MIC breakpoints were extrapolated for different fish species and main fish pathogens. The kinetics of the above antimicrobials were analysed in eight experiments where two fish species namely sea bass and sea bream as well as two water temperatures were employed. Muscle, liver, serum, skin samples were analysed by two HPLC methods and two bioassay methods were developed. The relative importance and significance of these findings was evaluated in the general context of pharmacokinetic studies in fish. Kinetic data were compared to clinical data and practical implications were evaluated. Issues like antibiotic resistance and its implications, the implications of residues and resistance in human health and the environment were analysed in order to put this study in context. Conclusions tackled important aspects of antimicrobial chemotherapy and future work was suggested.

Plasmodium falciparum is a protozoan parasite and the causative agent of the most lethal form of malaria, a major disease in the tropical world. Chloroquine has been very effective in treatment of this disease, however the emergence of chloroquine-resistant strains in most geographical regions where malaria is endemic has made difficult the control of malaria. In addition, resistance to other antimalarials has been observed in these regions. The objective of this study was to determine the molecular mechanisms of multidrug resistance in P. falciparum. We have selected in vitro a P. falciparum strain resistant to actinomycin D from a parental drug sensitive clone, 3D7. Interestingly, we found that the actinomycin D resistant clone is less sensitive to chloroquine and mefloquine (antimalarial drugs) and rhodamine123. Comparison between parental 3D7 and resistant P. falciparum did not show differences in the copy number or level of expression of pfmdr1 previously implicated in chloroquine or mefloquine resistance. Furthermore, to identify if other P-glycoprotein homologues are involved in resistance, we used oligonucleotide primers to conserved sequences in ABC domains. An ABC protein, a homologue to the subunit 4, of the 26S proteasome complex has been cloned. To determine if this gene was involved in resistance to actinomycin D, a Northern blot was done. Surprisingly it was found a decreased in the expression of this gene in the resistant cell line, 3D7R/actD2, in comparison with its parental cell line, 3D7. Studies are in progress to determine the role of the PFS4 subunit in the resistance phenotype of 3D7R/actD2.