Characterization of self-transmissible plasmids determining lactose fermentation and multiple antibiotic resistance in clinical strains of Klebsiella pneumoniae

Plasmid profiling and incompatibility grouping of multidrug resistant Salmonella enterica serovar Typhi isolates in Nairobi, Kenya

OBJECTIVES

Plasmids harbour antibiotic resistance genes which contribute to the emergence of multidrug resistant pathogens. We detected the presence of plasmids in multidrug resistant Salmonella enterica serovar Typhi (S. Typhi) isolates from our previous study and consequently determined their incompatibility groups and possibility of conjugation transmission. Plasmids were extracted from 98 multidrug resistant S. Typhi isolates based on alkaline lysis technique. Plasmid incompatibility grouping was established by PCR replicon typing using 18 pairs of primers to amplify FIA, FIB, FIC, HI1, HI2, I1-Iγ, L/M, N, P, W, T, A/C, K, B/O, X, Y, F and FIIA replicons. Antibiotic resistance phenotypes were conjugally transferred from S. Typhi isolates with plasmids to Escherichia coli K12F strain devoid of plasmids.

RESULTS

Approximately 79.6% of the MDR S. Typhi isolates were related to the existence of plasmids. We detected 93.6% of plasmids belonging to incompatibility (Inc) group HI1. The other incompatibility groups identified included IncFIC (16.7%), IncP (1.3%), and IncI1 (1.3%) which appeared together with Inc HI1. MDR S. Typhi isolated carried a homologous plasmid of incompatibility group HI1 most of which transferred the resistance phenotypes of ampicillin, tetracycline and chloramphenicol to the transconjugants.

Salmonella bongori provides insights into the evolution of the Salmonellae

The genus Salmonella contains two species, S. bongori and S. enterica. Compared to the well-studied S. enterica there is a marked lack of information regarding the genetic makeup and diversity of S. bongori. S. bongori has been found predominantly associated with cold-blooded animals, but it can infect humans. To define the phylogeny of this species, and compare it to S. enterica, we have sequenced 28 isolates representing most of the known diversity of S. bongori. This cross-species analysis allowed us to confidently differentiate ancestral functions from those acquired following speciation, which include both metabolic and virulence-associated capacities. We show that, although S. bongori inherited a basic set of Salmonella common virulence functions, it has subsequently elaborated on this in a different direction to S. enterica. It is an established feature of S. enterica evolution that the acquisition of the type III secretion systems (T3SS-1 and T3SS-2) has been followed by the sequential acquisition of genes encoding secreted targets, termed effectors proteins. We show that this is also true of S. bongori, which has acquired an array of novel effector proteins (sboA-L). All but two of these effectors have no significant S. enterica homologues and instead are highly similar to those found in enteropathogenic Escherichia coli (EPEC). Remarkably, SboH is found to be a chimeric effector protein, encoded by a fusion of the T3SS-1 effector gene sopA and a gene highly similar to the EPEC effector nleH from enteropathogenic E. coli. We demonstrate that representatives of these new effectors are translocated and that SboH, similarly to NleH, blocks intrinsic apoptotic pathways while being targeted to the mitochondria by the SopA part of the fusion. This work suggests that S. bongori has inherited the ancestral Salmonella virulence gene set, but has adapted by incorporating virulence determinants that resemble those employed by EPEC.

Pathogenic Escherichia coli and food handlers in luxury hotels in Nairobi, Kenya

BACKGROUND

The epidemiology and virulence properties of pathogenic Escherichia coli among food handlers in tourist destination hotels in Kenya are largely uncharacterized.

METHOD

This cross-sectional study among consenting 885 food handlers working in nine luxurious tourist hotels in Nairobi, Kenya determined the epidemiology, virulence properties, antibiotics susceptibility profiles and conjugation abilities of pathogenic Escherichia coli.

RESULT

Pathogenic Escherichia coli was detected among 39 (4.4%) subjects, including 1.8% enteroaggregative Escherichia coli (EAEC) harboring aggR genes, 1.2% enterotoxigenic Escherichia coli (ETEC) expressing both LT and STp toxins, 1.1% enteropathogenic Escherichia coli (EPEC) and 0.2% Shiga-like Escherichia coli (EHEC) both harboring eaeA and stx2 genes respectively. All the pathotypes had increased surface hydrophobicity. Using multivariate analyses, food handlers with loose stools were more likely to be infected with pathogenic Escherichia coli. Majority 53.8% of the pathotypes were resistant to tetracycline with 40.2% being multi-drug resistant. About 85.7% pathotypes trans-conjugated with Escherichia coli K12 F(-) NA(r) LA.

CONCLUSION

The carriage of multi-drug resistant, toxin expressing pathogenic Escherichia coli by this population is of public health concern because exposure to low doses can result in infection. Screening food handlers and implementing public awareness programs is recommended as an intervention to control transmission of enteric pathogens.

Self-transmissible antibiotic resistance to ampicillin, streptomycin, and tetracyclin found in Escherichia coli isolates from contaminated drinking water

Presence and survival of cultivable bacteria in drinking water can act as a vehicle to disseminate virulence genes (adherence, enterotoxigenic and antibiotic resistance) to other bacteria. This can result in high morbidity and mortality, and the failure of the treatment of life threatening bacterial infections in humans and animals. In this study, antibiotic resistance (ABR) patterns and transferability of the ABR markers was investigated in Escherichia coli isolates obtained from drinking water and human urine samples. The ABR in E. coli isolates was determined against 15 antibiotics commonly used in human and veterinary medicine. A high frequency of ABR to carbenicillin (56%), tetracycline (53%) and streptomycin (49%) and a low frequency of cefizoxime (5%), amikacin (8%), cefazidine, (5%), chloramphenicol (9%), and kanamycin (18%) was found in the tested E. coli isolates. ABR to kanamycin (0% vs. 35%) and moxalactam (4% vs. 30%) was higher in drinking water isolates whereas resistance to streptomycin (92% vs. 15%), ampicillin (24% vs. 10%), and nalidixic acid (12% vs. 0%) was higher in human urine isolates. A large number of E. coli isolates (93%) exhibited resistance to two or more antibiotics. Two of E. coli isolates from drinking water showed resistances to six (Cb Cm Cx Ip Mx Tc and An Cb Km Mx Sm Tc) and one was resistant to seven antibiotics (Am An Cb Km Mx Sm Tc). A majority of the multiple antibiotic resistant E. coli isolates contained one or more plasmids (size ranged approximately 1.4 Kb to approximately 40 Kb). The ABR traits (Am and Tc) were transferable to other bacteria via conjugation. These data raise an important question about the impact of E. coli containing self-transmissible R-plasmids as a potential reservoir of virulence genes in drinking water.

Molecular characterization of a novel plasmid-encoded cefotaximase (CTX-M-12) found in clinical Klebsiella pneumoniae isolates from Kenya

Nine Klebsiella pneumoniae isolates, six from blood and three from cerebrospinal fluid of newborn babies at Kenyatta National Hospital, Nairobi, Kenya, were analyzed for the mechanism of cephalosporin resistance. By using pulsed-field gel electrophoresis of XbaI-digested chromosomal DNA, all the nine isolates were found to be clonal. PCR and direct sequencing revealed a novel extended-spectrum beta-lactamase, which we designated CTX-M-12. It has a more potent hydrolytic activity against cefotaxime than against ceftazidime and a pI of 9.0 and is encoded on a large self-transferable ca. 160-kbp plasmid.

Antibiotic susceptibility and genotypes of non-typhi Salmonella isolates from children in Kilifi on the Kenya coast

A 4-year retrospective study was undertaken at the Kilifi District Hospital on the coast of Kenya to determine the antibiotic-susceptibility patterns and genotypes of non-typhi Salmonella (NTS) isolates from children. Overall, during the period 1994-97, positive cultures were obtained from 543 (14%) of 3885 blood samples, 364 (30%) of 1210 stool samples and 143 (11%) of 1283 cerebrospinal fluid (CSF) samples. NTS were isolated from 151 (27.8%), 72 (19.8%), and 11 (7.7%) of these positive cultures, respectively. The total 234 NTS isolates were serotyped: the most frequent were Salmonella enterica serotype Enteritidis (41%) and S. enterica serotype Typhimurium (38%). Antibiotic sensitivity testing was done using ampicillin (amp), chloramphenicol (chl), gentamicin (cn), co-trimoxazole (s-t), cefuroxime (cxm), ciprofloxacin (cip), cefotaxime (ctx), amoxicillin-clavulanic acid 20 micrograms-10 micrograms (amc), and tobramycin (tob). Of the 234 isolates, 43 were sensitive to all antibiotics tested and 133 were multiple drug resistant (MDR). The most common resistance type seen was amp, cn, cxm, s-t, ctx, amc, tob (36/234). Our results indicate a high proportion of MDR amongst the isolates from Kilifi. We conclude that 2 major serotypes of salmonella, i.e., S. enterica serotype Typhimurium and S. enterica serotype Enteritidis, of micro-epidemic nature that have been previously unrecognized in Kilifi are responsible for infection in Kilifi district on the coast of Kenya and that over half (56.8%) of total NTS isolates are MDR.

Diagnostic and public health dilemma of lactose-fermenting Salmonella enterica serotype Typhimurium in cattle in the Northeastern United States

The presence of lactose-fermenting Salmonella strains in clinical case materials presented to microbiology laboratories presents problems in detection and identification. Failure to detect these strains also presents a public health problem. The laboratory methods used in detecting lactose-fermenting Salmonella enterica serotype Typhimurium from six outbreaks of salmonellosis in veal calves are described. Each outbreak was caused by a multiply-resistant and lactose-fermenting strain of S. enterica serotype Typhimurium. The use of Levine eosin-methylene blue agar in combination with screening of suspect colonies for C8 esterase enzyme and inoculation of colonies into sulfide-indole-motility medium for hydrogen sulfide production was particularly effective for their detection. A hypothesis for the creation of lactose-fermenting salmonellae in the environment is presented. It is proposed that the environment and husbandry practices of veal-raising barns provide a unique niche in which lactose-fermenting salmonellae may arise.

Characterization of the drug resistance plasmid R2418: restriction map and role of insertion and deletion in its evolution

Escherichia coli 2418 strain is resistant to beta-lactam antibiotics (ampicillin, carbenicillin, and cephalothin), streptomycin, tetracycline, kanamycin, and chloramphenicol. This strain contains at least two conjugative plasmids (R2418 and R2418S) encoding resistance to beta lactam antibiotics and resistance to both beta-lactam antibiotics and streptomycin, respectively. Restriction endonuclease mapping of plasmid DNAs indicates that the plasmid R2418S has evolved from R2418 DNA by the insertion of 2.5-kb DNA between BamHI and PvuII sites, and deletion of 0.5-kb DNA within the EcoRI-EcoRV region. The 2.5-kb DNA insert is responsible for streptomycin resistance. This evolution is also associated with a reduction in the efficiency of conjugal transfer for the plasmid R2418S. The conjugal transfer of streptomycin resistance occurs only through the coresidence of the conjugative plasmid R2418 or R2418S in the donor cell. In accordance with the hypothesis that the Smr determinant is due to a putative transposon, plasmid-free transconjugants resistant to streptomycin only were isolated. Southern blot analysis of HindIII chromosomal digests extracted from these transconjugants shows that the Smr determinant is inserted into different sites in chromosomal DNA.

Epidemiological fingerprinting of Klebsiella pneumoniae by small-fragment-restriction-endonuclease-analysis (SF-REA)

Epidemiological fingerprinting of Klebsiella pneumoniae was performed by restriction endonuclease analysis (REA) of whole cell DNA. 11 isolates from 4 patients in an intensive care unit and 80 unrelated strains were examined in this study. DNA was cleaved with restriction endonuclease EcoR I, electrophoresed on 10% polyacrylamide gels, and restriction fragment patterns were visualized by silver staining. The analysis of small fragments within the cleavage patterns (SF-REA) yielded sufficient information for reliable strain identification. The gel patterns of unrelated strains exhibited marked differences by direct visual comparison. In contrast, the isolates from the ICU could only be subdivided into 2 types, supporting our suspicion of nosocomial infections in some of these patients. SF-REA was evaluated with regard to interstrain discriminatory ability, reproducibility, and practicability. Our results indicate that SF-REA may be used as a rapid, precise and reliable technique in typing K. pneumoniae strains.

Cloning of bacterial genes specifying degradation of 4-chlorobiphenyl from Pseudomonas putida OU83

Genes capable of 4-chlorobiphenyl (4-CBP) degradation were cloned from 4-CBP-degrading Pseudomonas putida OU83 by using a genomic library which was constructed in the broad-host-range cosmid vector pCP13. P. putida AC812 containing chimeric cosmid-expressing enzymes involved in the 4-CBP degradation pathway were identified by detecting 3-phenylcatechol dioxygenase activity (3-PDA). Chimeric cosmid clones pOH83, pOH84, pOH85, pOH87, and pOH88 positive for 3-PDA grew in synthetic basal medium containing 4-CBP (5 mM) as a carbon source. Restriction digestion analysis of recombinant cosmids showed DNA inserts ranging from 6 to 30 kilobase pairs. Southern hybridization data revealed that the cloned DNA inserts originated from strain OU83. Gas chromatography-mass spectrometry analysis of the metabolites of P. putida AC812(pOH88) incubated with 4-CBP and 4'-chloro-3-phenylcatechol showed the formation of 4-chlorobenzoic acid and benzoic acid. These results demonstrate that the cloned DNA fragments contain genes encoding for chlorobiphenyl dioxygenase (cbpA), dihydrodiol dehydrogenase (cbpB), 4'-chloro-3-phenylcatechol dioxygenase (cbpC), a meta-cleavage compound (a chloro derivative of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate) hydrolase (cbpD), and a new dechlorinating activity (dcpE). The location of the cbpC gene specifying 3-PDA was determined by subcloning an EcoRI DNA fragment (9.8 kilobase pairs) of pOH88 in plasmid vector pUC19. The cloned gene encoding 3-PDA was expressed in Escherichia coli HB101 and had substrate specificity only for 3-phenylcatechol and 4'-chloro-3-phenylcatechol.

Molecular cloning of 3-phenylcatechol dioxygenase involved in the catabolic pathway of chlorinated biphenyl from Pseudomonas putida and its expression in Escherichia coli

Genes encoding 3-phenylcatechol dioxygenases were cloned from the chlorobiphenyl-degrading Pseudomonas putida strain OU83, using broad-host-range cosmid vector pCP13. Restriction enzyme analysis of DNA from 2,3-dioxygenase-positive chimeric cosmids showed DNA inserts ranging in size from 6.0 to 30 kilobases. The origin of the DNA insert in hybrid clones was established by using 32P-labeled hybrid clones (pOH101 and pOH810). A 2.3-kilobase HindIII fragment was common to two clones. The 2,3-dioxygenase from the parent P. putida strain, OU83, and the recombinant clones (pOH101 and pOH8101) showed similar characteristics as determined by isoelectric focusing and polyacrylamide gel electrophoresis. The 2,3-dioxygenase from the Escherichia coli recombinant cosmid showed a pI of 5.0, a Km of 14 microM, and broad substrate activity with catechol, 4-chlorocatechol, 4-methylcatechol, and 2,3-dihydroxybiphenyl.

Plasmid profiles and klebocin types in epidemiologic studies of infections by Klebsiella pneumoniae

The epidemiological methods of klebocin typing, antibiogram and plasmid DNA profile were evaluated using organisms isolated from a suspected epidemic of gentamicin-resistant Klebsiella pneumoniae and unrelated strains from different geographical areas as controls. The electrophoretic analysis of plasmid DNAs from Klebsiella pneumoniae showed the presence of at least one and up to as many as seven plasmids in each strain. The molecular weight of plasmid DNAs ranged from 1 to greater than 70 mega daltons. While none of the control Klebsiella pneumoniae strains showed identical plasmid profiles, 63% of the epidemic-related Klebsiella pneumoniae strains did. Klebocin typing and plasmid DNA profile gave different results for the same strains. Plasmid DNA profile was found to be a more valuable method than klebocin typing alone or klebocin typing in combination with antibiogram for differentiating epidemiologically related from unrelated isolates. Both plasmid DNA profile and klebocin typing methods were superior to antibiogram.