Analysis of plasmid and chromosomal DNA of multidrug-resistant Salmonella enterica serovar typhi from Asia

Molecular analysis of chromosomal DNA from 193 multidrug-resistant (MDR) Salmonella enterica serovar Typhi isolates from 1990 to 1995 from Pakistan, Kuwait, Malaysia, Bangladesh, and India produced a total of five major different pulsed-field gel electrophoresis (PFGE) patterns. Even within a particular country MDR S. enterica serovar Typhi DNA was found to be in different PFGE groups. Similar self-transferable 98-MDa plasmids belonging to either incompatibility group incHI1 or incHI1/FIIA were implicated in the MDR phenotype in S. enterica serovar Typhi isolates from all the locations except Quetta, Pakistan, where the majority were of incFIA. A total of five different PFGE genotypes with six different plasmids, based on incompatibility and restriction endonuclease analysis groups, were found among these MDR S. enterica serovar Typhi isolates.

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.

Genotypic analysis of multidrug-resistant Salmonella enterica Serovar typhi, Kenya

We report the emergence in Kenya during 1997-1999 of typhoid fever due to Salmonella enterica serovar Typhi resistant to ampicillin, tetracycline, chloramphenicol, streptomycin, and cotrimoxazole. Genotyping by pulsed-field gel electrophoresis of XbaI-digested chromosomal DNA yielded a single cluster. The multidrug-resistant S. Typhi were related to earlier drug- susceptible isolates but were unrelated to multidrug-resistant isolates from Asia.

Analysis of Salmonella enterica serotype Typhimurium by phage typing, antimicrobial susceptibility and pulsed-field gel electrophoresis

Three typing methods commonly used for bacteria--phage typing, antimicrobial susceptibility and pulsed-field gel electrophoresis (PFGE)- were used to characterise 64 Salmonella enterica serotype Typhimurium isolates from individual adult patients from Nairobi, Kenya. The isolates encompassed 11 definitive phage types (DTs), which fell into eight PFGE clusters; 31.3% of isolates were either untypable or reacted nonspecifically with the phages used for typing and 26.6% were of DT 56. Plasmids of c. 100 kb were responsible for self-transferable multiresistance among the isolates. Analysis by PFGE and phage type demonstrated that multiresistant Typhimurium strains causing diarrhoea and invasive disease were multiclonal.

Typing of Salmonella enterica serotype paratyphi C isolates from various countries by plasmid profiles and pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) of 61 Salmonella enterica serotype Paratyphi C isolates from six countries gave five distinct clusters. Twenty-four isolates from five countries were susceptible to 10 antimicrobials tested and gave similar restriction endonuclease digest patterns of the 38-MDa plasmid. In contrast, plasmid and PFGE profiles of 37 multidrug-resistant isolates from Zaire were different from those from other countries.

Genotype analysis of Escherichia coli strains isolated from children and chickens living in close contact

Escherichia coli isolates from rectal swabs from 62 chickens and stools from 42 children living in close contact with chickens on the same farms in Kiambu district, Kenya, were compared for their genetic relatedness. Antibiotic susceptibility profiles broadly categorized isolates from the children and from the chickens into two separate clusters: the majority (144; 85.5%) of the E. coli isolates from children were multidrug resistant, while the majority (216; 87.1%) of the E. coli isolates from chickens were either fully susceptible or resistant only to tetracycline. Sixty- and 100- to 110-MDA plasmids were found to encode the transferable resistance to co-trimoxazole and tetracycline. HindIII restriction endonuclease digestion of the 60- and 100- to 110-MDA plasmids produced four distinct patterns for isolates from children and three distinct patterns for isolates from chickens. XbaI digestion of genomic DNA followed by pulsed-field gel electrophoresis (PFGE) analysis produced 14 distinct clusters. There were six distinct PFGE clusters among the isolates from children, while among the isolates from chickens there were seven distinct clusters. Only one PFGE cluster contained isolates from both children and chickens, with the isolates displaying an approximately 60% coefficient of similarity. This study showed that although several different genotypes of E. coli were isolated from children and chickens from the same farms, the E. coli strains from these two sources were distinct.

Characterization of antibiotic resistance plasmids from Bordetella bronchiseptica

Of 52 antibiotic-resistant Bordetella bronchiseptica isolates from cats, ten carried plasmids. Only two of these plasmids, pLV1400 and pLV1401, were self-transmissible to Escherichia coli K12; both plasmids encoded resistance to ampicillin, tetracycline, sulphonamides, streptomycin and mercuric chloride, and were of incompatibility group P (IncP). Transferable tetracycline resistance has not been reported in B. bronchiseptica previously. The plasmids were identical in size (c.51 kb), restriction endonuclease digestion pattern and gene sequences (trfA and korA) within the IncP replicon. The trfA and korA sequences differed from those of the archetypal IncP plasmids RP4 and R751. Although the two B. bronchiseptica isolates were from epidemiologically and geographically separated cats, pulsed-field gel electrophoresis of their XbaI- or DraI-digested chromosomal DNA indicated that they were genotypically identical. The plasmid-encoded ampicillin resistance was mediated by a penicillinase of molecular weight 49,000, and pI 8.45 which was inhibited by clavulanate (IC50 = 0.1 mg/L) and tazobactam (IC50 = 0.42 mg/L) but not by parachloromercuribenzoate or EDTA. The high-level tetracycline resistance was mediated by a class C efflux mechanism that has not been described previously in this genus. The presence of transferable multi-drug resistance on a promiscuous plasmid may limit options for therapy of respiratory tract infection in companion and farm animals.

Plasmid diversity of multi-drug-resistant Escherichia coli isolated from children with diarrhoea in a poultry-farming area in Kenya

Biotin-labelled DNA probes and restriction-endonuclease digestion (RED) with HindIII were used to study the diversity of resistance plasmids (R-plasmids) from 414 Escherichia coli isolates: 168 from children living in close contact with antibiotic-fed poultry and 246 from the chickens. Full sensitivity to all 10 antimicrobials tested was more common in the isolates from poultry than in those from the children (36.2% v. 9.5%; P < 0.001). Multi-drug resistance, to at least two of the antimicrobials, was relatively common in the isolates from the children (85.5% v. 26.00%; P < 0.001). Overall, 31% of the poultry isolates were resistant to tetracycline alone. Resistance to amoxycillin was due to production of TEM-1 (89%) and TEM-2 (11%). In > 71% of the isolates from children and 79% of those from poultry, resistance was encoded on a 100-110-kb transferable plasmid belonging to incompatibility group FII. However, RED patterns of R-plasmids from the two groups of isolates were highly diverse and not indicative of any close relatedness. This difference in patterns and in the levels of multi-drug resistance indicate that the isolates from the children and those from the poultry represent two distinct pools of resistance plasmids.

Molecular typing of multi-drug resistant Shigella dysenteriae type 1 by plasmid analysis and pulsed-field gel electrophoresis

Recently, an outbreak of dysentery due to multi-drug resistant Shigella dysenteriae type 1 strains was reported along the coastal area of Kenya and shortly thereafter another outbreak appeared in the outskirts of Nairobi. We analysed 22 multi-drug resistant S. Dysenteriae type 1 strains isolated from cases in the latter outbreak using plasmid deoxyribonucleic acid (DNA) profiles and pulse-field gel electrophoresis of genomic DNA. All isolates were resistant to commonly available drugs including ampicillin, trimethoprim, sulphamethoxazole, chloramphenicol, tetracycline and streptomycin with minimum inhibitory concentrations > 64 micrograms/mL, but were fully sensitive to gentamicin. Only 2 strains were resistant to nalidixic acid. Analysis of plasmid DNA and genomic DNA revealed that all 22 strains were clonally related. It is likely that the present outbreak was related to that on the coast, as suggested by the similarity in drug susceptibility data. The drug susceptibility and molecular epidemiological data provide a useful baseline for future monitoring of epidemic and endemic S. dysenteriae activity in East Africa.

Multi-drug resistant non-typhi salmonellae in Kenya

Two methods of plasmid characterization, restriction digest patterns and incompatibility grouping, were used to study self-transmissible multi-drug resistance among non-typhi salmonellae (NTS). Resistance to ampicillin and other commonly applied beta-lactams was evaluated by iso-electric focusing and disc inactivation. Of the NTS isolated from blood, 75% were Salmonella typhimurium but those included several different phage types. Over 47% of isolates were resistant to three or more of the readily available drugs including ampicillin, cefuroxime, chloramphenicol, co-trimoxazole, streptomycin and tetracycline. Self-transferable resistance plasmids (c. 100 kb) were essentially of incompatibility group incFIIA, but their restriction fragment patterns revealed a diversity in relatedness. More than half of parent strains and their transconjugants produced beta-lactamases which co-electrophoresed with TEM-1 and OXA-1. This study has observed a disturbingly high prevalence of transmissible multi-drug resistance among NTS which are an important cause of morbidity in HIV-1 seropositive individuals.

Identification of T and B cell epitopes recognized by humans in the C-terminal 42-kDa domain of the Plasmodium falciparum merozoite surface protein (MSP)-1

The 42-kDa, C-terminal region of the merozoite surface protein-1 (MSP-1) of Plasmodium falciparum is a putative malaria vaccine candidate Ag. Nine synthetic peptides corresponding to predicted T cell sites of MSP-1 in blocks 15 and 16 and eight overlapping peptides representing the conserved block 17 were used to identify naturally immunogenic epitopes. These peptides were tested for their ability to induce proliferation of PBMC from residents in western Kenya, where malaria transmission is holoendemic. Six peptides (PL145, PL146, PL147, PL148, PL149, and PL150) from blocks 15 and 16 induced a positive proliferative response in &gt; 30% of the individuals tested, and three peptides (PL151, PL152, and PL153) induced a proliferative response in &lt; 25% of the donors. Among these peptides, PL146 was from the highly conserved region, PL150 was from a polymorphic region, and all other peptides were from a dimorphic region of blocks 15 and 16. In block 17, only three peptides, PL99, PL100, and PL103, induced proliferation in 30 to 37% of the volunteers. The rest of the peptides induced a proliferative response in approximately 13 to 25% of the donors. The plasma from these donors widely reacted with different allelic forms of 19-kDa recombinant proteins representing block 17 and recognized at least two linear B epitopes, PL104 and PL97. In summary, this study revealed that a majority of immunodominant T and B epitopes are localized in the conserved or dimorphic regions that are nonpolymorphic in the 42-kDa protein of MSP-1. This study suggests that incorporation of T epitopes from the dimorphic blocks 15 and 16 in a vaccine construct may be useful to ensure Ag-specific memory responses.

Identification of T and B cell epitopes recognized by humans in the C-terminal 42-kDa domain of the Plasmodium falciparum merozoite surface protein (MSP)-1

The 42-kDa, C-terminal region of the merozoite surface protein-1 (MSP-1) of Plasmodium falciparum is a putative malaria vaccine candidate Ag. Nine synthetic peptides corresponding to predicted T cell sites of MSP-1 in blocks 15 and 16 and eight overlapping peptides representing the conserved block 17 were used to identify naturally immunogenic epitopes. These peptides were tested for their ability to induce proliferation of PBMC from residents in western Kenya, where malaria transmission is holoendemic. Six peptides (PL145, PL146, PL147, PL148, PL149, and PL150) from blocks 15 and 16 induced a positive proliferative response in > 30% of the individuals tested, and three peptides (PL151, PL152, and PL153) induced a proliferative response in < 25% of the donors. Among these peptides, PL146 was from the highly conserved region, PL150 was from a polymorphic region, and all other peptides were from a dimorphic region of blocks 15 and 16. In block 17, only three peptides, PL99, PL100, and PL103, induced proliferation in 30 to 37% of the volunteers. The rest of the peptides induced a proliferative response in approximately 13 to 25% of the donors. The plasma from these donors widely reacted with different allelic forms of 19-kDa recombinant proteins representing block 17 and recognized at least two linear B epitopes, PL104 and PL97. In summary, this study revealed that a majority of immunodominant T and B epitopes are localized in the conserved or dimorphic regions that are nonpolymorphic in the 42-kDa protein of MSP-1. This study suggests that incorporation of T epitopes from the dimorphic blocks 15 and 16 in a vaccine construct may be useful to ensure Ag-specific memory responses.

Nasopharyngeal carriage of Staphylococcus aureus and carriage of tetracycline-resistant strains associated with HIV-seropositivity

The aim of this prospective study was to investigate the relationship between carriage of antibiotic-resistant Staphylococcus aureus and infection with the human immunodeficiency virus (HIV). A total of 554 pernasal swabs was taken during a six-month period from 554 adult patients attending three outpatient clinics and from inpatients from a hospital in Nairobi, Kenya. Overall, 121 swabs (22%) yielded Staphylococcus aureus, there being significantly higher carriage in HIV-positive patients (71/264, 27%) than in HIV-negative patients (50/290, 17%); p = 0.008. Antimicrobial resistance rates were determined for 110 isolates and were high for penicillin (91%) and tetracycline (72%) and low for erythromycin (8%), methicillin (3%), gentamicin (5%) and chloramphenicol (0%). Genetic analysis showed plasmids in the range of 24-42 MDa to be associated with beta-lactamase production and plasmids in the range of 3-5 MDa to be associated with resistance to tetracycline, erythromycin and trimethoprim. All nine erythromycin-resistant strains were from HIV-positive patients (p = 0.02). There was a significant association of tetracycline resistance with HIV seropositivity (p = 0.002). The association of HIV seropositivity with Staphylococcus aureus carriage and carriage of antibiotic-resistant strains against the background of the HIV epidemic are of relevance in individual patient care and raise concern for public health.

Antimicrobial susceptibility and presence of extrachromosomal deoxyribonucleic acid in Salmonella and Shigella isolates from patients with AIDS

The development of multi-drug resistance by enteric bacteria is an increasing problem in the developing countries. There is need to monitor antimicrobial susceptibility of these organisms in order to ensure appropriate treatment and control of infections. Antimicrobial susceptibility patterns, plasmid DNA content and restriction enzyme digests of plasmid deoxyribonucleic acid (DNA) were used to study 175 Salmonella and Shigella species isolated from predominantly HIV-seropositive adult patients in Nairobi, Kenya. All the isolates were sensitive to ciprofloxacin. A significantly higher proportion of Shigella species were resistant to chloramphenicol, cotrimoxazole, streptomycin and tetracycline compared to Salmonella species (p-value < 0.001). Multi-resistant Salmonella typhimurium isolates had 60, 40 and 5 MDa plasmids, the 5 MDa plasmid was absent in gentamicin sensitive isolates. In addition to 2-10 MDa range of plasmids, multi-resistant Shigella species had a heavy 100-105 MDa plasmid. Restriction enzyme digests were similar for the 60 and 40 MDa plasmid DNA bands from Salmonella typhimurium isolates but did not show any consistency among Shigella spp. Plasmid-encoded multi-drug resistance plays a major role in the spread of resistance among enteric bacteria. It is vital to use drugs rationally in order to control the emergence and spread of multi-drug resistance.

Acquired tetracycline resistance genes in nosocomial Salmonella typhimurium infection in a Kenyan hospital

Tetracyclines have been among the most widely used antibiotics worldwide. Plasmid-mediated tetracycline resistance among hospital strains of bacteria has continued to rise and of major concern has been the transfer of resistance to pathogenic organisms. Bacteraemia due to hospital acquired S. typhimurium has been a major cause of morbidity at Kenyatta National Hospital (KNH), hence the need to study drug susceptibility pattern of this organism. This study also characterized the tetracycline resistance genes using oligonucleotide probes. Ninety seven S. typhimurium strains isolated from patients at KNH were used. Agar dilution method was used to determine minimum inhibitory concentration (MIC). Plasmids were isolated from each strain and the different plasmid profiles were grouped by their molecular weights into 6 patterns. Out of 97, 87 (88%) strains were resistant. MIC ranged from 1 microgram/ml to 128 micrograms/ml. Genes encoding for tetracycline resistance were located on plasmids of molecular weights 65 MDa, 5.2 or both. Plasmid-encoded antimicrobial resistance is likely to spread to other pathogenic organisms, reduce our ability to treat the infection and increase the cost and duration of treatment.

Tetracycline resistance genes in Kenyan hospital isolates of Salmonella typhimurium

All 97 strains of Salmonella typhimurium isolated from patients at a hospital in Nairobi, Kenya, during 1988-90 were resistant to tetracycline. The minimum inhibitory concentration (MIC) showed a large distribution range from 1 microgram/ml to 128 micrograms/ml. The strains were heterogeneous with respect to plasmid content, but initially all strains possessed, in addition to other plasmids, a large 60-, 63- or 65-MDa plasmid. The tetracycline resistance genes were characterized using oligonucleotide probes, and 20% of the resistant strains possessed tetracycline type A (tetr A), 6% tetr B, and 4% tetrC genes. Three strains possessed both type A and B tetracycline resistance determinants, which were shown to be located on the large 65-MDa plasmid. There was no correlation between strains isolated from stools, blood, cerebrospinal or epidural fluids, pus, or urine, with respect to the tetracycline genotypes, MIC values or plasmid content.

Multiresistant Shigella species from African AIDS patients: antibacterial resistance patterns and application of the E-test for determination of minimum inhibitory concentration

The antibacterial resistance pattern and minimum inhibitory concentrations (MIC) of 25 Shigella flexneri, 5 S. boydii, 8 S. sonnei, and 3 strains of S. dysenteriae type 2 isolated from Kenyan prostitutes with bacillary dysentery and AIDS were determined, and the applicability of the E-test for MIC determination evaluated. All strains were resistant to > or = 3 of 9 different antibacterial agents tested. All strains were resistant to tetracycline and erythromycin, 95% to trimethoprim/sulfonamide, 93% to streptomycin, 54% to ampicillin, 39% to chloramphenicol, 2% to nalidixic acid and none to gentamicin and ciprofloxacin. Six different resistance patterns were observed. The most common pattern was resistance to tetracycline, erythromycin, trimethoprim/sulfa and streptomycin (39%). The E-test was shown to be well-suited for susceptibility testing of multiresistant Shigella spp.; the reproducibility was excellent and the correlation with the microtiter dilution method and the disk diffusion method were 98% in both instances. The MIC measured with E-test and the microdilution method were within +/- 1 dilution step for 94.4% of the combinations tested.