Letter: Ampicillin-resistant Shiga bacillus in Bangladesh

Efficacy and potential of phage therapy against multidrug resistant Shigella spp

Shigella-infected bacillary dysentery or commonly known as Shigellosis is a leading cause of morbidity and mortality worldwide. The gradual emergence of multidrug resistant Shigella spp. has triggered the search for alternatives to conventional antibiotics. Phage therapy could be one such suitable alternative, given its proven long term safety profile as well as the rapid expansion of phage therapy research. To be successful, phage therapy will need an adequate regulatory framework, effective strategies, the proper selection of appropriate phages, early solutions to overcome phage therapy limitations, the implementation of safety protocols, and finally improved public awareness. To achieve all these criteria and successfully apply phage therapy against multidrug resistant shigellosis, a comprehensive study is required. In fact, a variety of phage-based approaches and products including single phages, phage cocktails, mutated phages, genetically engineered phages, and combinations of phages with antibiotics have already been carried out to test the applications of phage therapy against multidrug resistant Shigella. This review provides a broad survey of phage treatments from past to present, focusing on the history, applications, limitations and effective solutions related to, as well as the prospects for, the use of phage therapy against multidrug resistant Shigella spp. and other multidrug resistant bacterial pathogens.

Neonatal Escherichia coli infections in domestic mammals: transmissibility of pathogenic characteristics

Apart from the fact that different serotypes are involved, natural and experimental Escherichia coli infection in domestic mammals closely resembles natural E. coli infection in human beings. Some of the important characteristics of E. coli strains that cause disease in domestic mammals are determined by transmissible plasmids. These include enterotoxin, haemolysin and K88 antigen in piglet enteropathogenic strains and enterotoxin and K99 antigen production in calf and lamb enteropathogenic strains; most strains that cause generalized infections in young domestic mammals, i.e. invasive strains, also produce plasmid-determined colicine V. These are all good reasons for employing young domestic mammals as the animal model for studying certain aspects of E. coli infection in human beings. Exploiting the fact that plasmids can be introduced into bacterial cells by conjugation and can be removed from them by "curing", bacterial strains were created that differed from each other, as far as could be determined, only by the presence or absence of one or more of these plasmid-determined properties. These strains, or cell-free preparations of them, were then given by mouth to piglets, calves, lambs and baby rabbits. The results showed that the K88 antigen, probably on account of its adhesive properties, permitted pig enteropathogenic strains of E. coli to proliferate in the small intestine of piglets; the K99 antigen performed a similar function in calf and lamb enteropathogenic strains. The enterotoxin produced by the proliferating organisms was then chiefly responsible for the subsequent movement of fluid from the body into the small intestine and the consequent diarrhoea. Possession of the Col V plasmid contributed significantly to the virulence of invasive strains of E. coli by enabling them to resist more successfully the defence mechanisms of the host.

Fluoroquinolone resistance linked to both gyrA and parC mutations in the quinolone resistance-determining region of Shigella dysenteriae type 1

We examined the quinolone resistance-determining region (QRDR) of gyrA, gyrB, and parC of recently isolated fluoroquinolone-resistant S. dysenteriae type 1 strains from south Asia and compared data with fluoroquinolone-susceptible strains associated with previous epidemics of 1978, 1984, and 1994. In fluoroquinolone-resistant strains, double mutations (Ser83-->Leu, Asp87-->Asn or Gly) and a single mutation (Ser80-->Ile) were detected in the QRDRs of gyrA and parC, respectively.

Genetic relatedness of ciprofloxacin-resistant Shigella dysenteriae type 1 strains isolated in south Asia

OBJECTIVES

The aim of the present study was to determine the clonal relationships of ciprofloxacin-resistant Shigella dysenteriae type 1 strains isolated from south Asia, and S. dysenteriae 1 strains associated with epidemics in 1978, 1984 and 1994.

METHODS

The antimicrobial susceptibilities were examined by NCCLS methods. Molecular epidemiological characterization was performed by plasmid profiling, pulsed-field gel electrophoresis (PFGE) and mutation analysis of the quinolone resistance-determining region (QRDR) of gyrA by sequencing.

RESULTS

Plasmid patterns of the current ciprofloxacin-resistant strains from India, Nepal and Bangladesh were very similar to those of the 1978, 1984 and 1994 epidemic isolates of S. dysenteriae 1, except for the presence of a new plasmid of approximately 2.6 MDa, which was found in one recent ciprofloxacin-resistant strain isolated in Bangladesh. PFGE analysis showed that the ciprofloxacin-resistant strains isolated in Bangladesh, India and Nepal belonged to a PFGE type (type A), which was possibly related to that of the 1984 and 1994 clone of S. dysenteriae 1, but different from 1978 epidemic strains. The current ciprofloxacin-resistant strains belong to five subtypes (A3-A7), all of which were found in India, but in Bangladesh and Nepal, only A3 existed. Mutation analysis of the QRDR of gyrA revealed that amino acid substitutions at positions 83 and 87 of ciprofloxacin-resistant strains isolated in Bangladesh were similar to those of the strains isolated in Nepal, but different (at position 87) from ciprofloxacin-resistant strains isolated in India.

CONCLUSIONS

PFGE and mutation analysis of gyrA showed differences between the current ciprofloxacin-resistant S. dysenteriae 1 strains isolated in south Asia and those associated with epidemics in 1978, 1984 and 1994.

Multi-gene amplification: simultaneous detection of three virulence genes in diarrhoeal stool

Enterotoxigenic Escherichia coli (ETEC) and Shigella account for a substantial proportion of acute diarrhoeal illnesses among Third-World children. Rapid detection of these infectious agents in faeces followed by the prompt implementation of public health measures could help reduce their spread during the early phase of epidemics. Towards this end, three pairs of synthetic oligonucleotide primers were prepared and shown to hybridize specifically to the genes encoding the heat-stable (ST) and the heat-labile (LT) enterotoxins of ETEC and to invasion-associated loci (ial) of the large Shigella virulence plasmid. When the three primer pairs were used together in the polymerase chain reaction (PCR), the three corresponding genetic loci could be simultaneously amplified using DNA extracted directly from stool; the amplified products were readily detected by ST-, LT- and ial-specific, alkaline phosphatase-labelled oligonucleotide probes (AP probes). The performance of this system was evaluated in a Mayan community in southeastern Mexico, where diarrhoeal illnesses are a common cause of childhood morbidity and mortality. Using only simple and inexpensive laboratory equipment, multigene amplification with these primers and probes led to the identification of ETEC and/or Shigella in the stools of 20 out of 71 children with diarrhoea; the procedure could be completed in seven hours and was more sensitive than conventional diagnostic tests or DNA probes used without amplification.

Shigellosis in Zaria, northern Nigeria

368 strains of Shigella were recovered from stool specimens in the Department of Medical Microbiology, Ahmadu Bello University Teaching Hospital, Zaria, during the period January 1980 to December 1984. S. flexneri was found to be the most common (60%) followed by S. boydii (20.7%), S. dysenteriae (14.1%) and S. sonnei (5.2%). Males were more frequently infected (61.4%) than females (38.6%). Maximum cases were seen in the 21-to 40-year age group (48.9%). Almost two-thirds of the cases of shigellosis (64.4%) were recorded during the rainy season. Antimicrobial resistance to four or more drugs was recorded in (38%) of the isolates.

Comparative efficacies of single intravenous doses of ceftriaxone and ampicillin for shigellosis in a placebo-controlled trial

To evaluate ceftriaxone for the treatment of shigellosis, 94 adult males with acute dysentery were randomly assigned to receive ceftriaxone (1 g), ampicillin (4 g), or saline placebo intravenously in single doses in a double-blind design. Stool cultures were positive for Shigella dysenteriae in 52 patients, S. flexneri in 38 patients, and other species in 4 patients. Both ceftriaxone and ampicillin caused reductions in the mean duration of fever and the means of daily stool frequency 2 to 4 days after therapy versus placebo (P less than 0.05). The ability of ceftriaxone to reduce stool frequency during 6 days after treatment was significant in patients with S. flexneri infections (P less than 0.05), whereas S. dysenteriae infections were relatively refractory to improvement by both antibiotics. Neither drug had a significant effect on overall duration of diarrhea, blood in stool, or tenesmus. Ampicillin reduced the mean duration of positive stool cultures after treatment from 2.6 days in the placebo group to 1.1 days (P less than 0.05), whereas ceftriaxone did not affect the duration of Shigella sp. excretion. These results indicate that single intravenous doses of ceftriaxone and ampicillin caused some clinical improvement in acute shigellosis but only ampicillin exerted a bacteriological effect on Shigella sp. excretion.

Comparative efficacies of pivmecillinam and ampicillin in acute shigellosis

The clinical efficacies of pivmecillinam and ampicillin were compared in a randomized double-blind trial in the treatment of acute shigellosis. Of 44 adult male patients, all culture positive for Shigella strains, 22 patients received 400 mg of pivmecillinam and 22 patients received 500 mg of ampicillin every 6 h. Both drugs were administered orally for 5 days. Four patients receiving ampicillin were infected with Shigella strains that were resistant to ampicillin but susceptible to pivmecillinam, and two patients receiving pivmecillinam were infected with Shigella strains resistant to both ampicillin and pivmecillinam. The mean duration of diarrhea in all patients receiving pivmecillinam was 3.3 days compared with 4.5 days in patients receiving ampicillin (P less than 0.05). When patients infected with the resistant strains were excluded, the mean duration of diarrhea in patients receiving pivmecillinam was 3.2 days compared with 4.1 days in patients receiving ampicillin. The patients infected with strains susceptible to both antibiotics had mean durations of fecal excretion of Shigella strains of 1.2 days for those treated with pivmecillinam and 1.4 days for those treated with ampicillin. The patients infected with organisms resistant to both drugs had longer durations of diarrhea and fecal excretion of Shigella strains. The results suggest that pivmecillinam is as effective as ampicillin and can be a useful drug for the treatment of shigellosis.

Drug resistance in Shigella dysenteriae, S flexneri and S boydii in England and Wales: increasing incidence of resistance to trimethoprim

A total of 2753 strains of shigella belonging to subgroups A, B, and C that were isolated from patients in England and Wales during the period from 1979 to mid-1983 were studied. Of these, 1690 (61%) were from patients recently returned from abroad or in contact with recent travellers, and 760 (45%) of these affected travellers from the Indian subcontinent. The number of strains resistant to sulphonamides and streptomycin remained at a high level throughout (average 76% and 72% respectively). Resistance to tetracyclines, ampicillin, and chloramphenicol rose, reaching 63%, 51%, and 48%, respectively, in 1982. Strains resistant to trimethoprim were seen in substantial numbers for the first time and increased from 1.3% of all strains in 1979 to 9.9% in 1982 and 16.8% in the first half of 1983. The proportion of patients with recent foreign contact was notably smaller among those with strains resistant to trimethoprim than among those with strains sensitive to trimethoprim. The increase in resistance to trimethoprim might partly result from the use in Britain of compounds containing trimethoprim for the treatment of shigellosis.

Interruption of shigellosis by hand washing

High attack rates, increasing resistance to antibiotics and high mortality make shigellosis a serious problem. As Shigella is associated with poor hygiene we examined the effectiveness of a simple intervention, washing hands with soap and water, in checking the spread of the disease. The study population was comprised of confirmed cases of shigellosis. These and matched controls were followed up for 10 days. Several pieces of soap and earthenware pitchers for storing water were provided to the study families and they were advised to wash their hands with soap and water after defaecation and before meals. Compliance was monitored daily by observing the size of the soap and residual water. Rectal swabs of contacts of both the groups were obtained for culture. The secondary infection rate was 10.1% in the study group and 32.4% in the control group. The secondary case (symptomatic) rate was 2.2% in the study group and 14.2% in the control group. These results suggest that hand-washing has a positive interrupting effect, even in unsanitary environments.

Plasmid characterisation in the investigation of an epidemic caused by multiply resistant Shigella dysenteriae type 1 in Central Africa

A strain of Shigella dysenteriae type 1 resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, and tetracyclines has caused an epidemic of shiga dysentery in northeast Zaire. Since November 1979, it has caused many deaths in an extensive area which now includes neighbouring Rwanda. The strain carries a resistance plasmid of compatibility group X, indistinguishable from the plasmid previously found in strains from Somalia. This contrasts with multiply resistant strains of Sh. dystenteriae type 1 from Central America and South-East Asia in which resistance is determined by plasmids of compatibility group B.

Microbial development of drug resistance: mechanisms and clinical significance

Bacteria have demonstrated a disconcerting ability to develop resistance to antimicrobial agents nearly as quickly as new compounds become available. During the past two decades the molecular bases of several types of resistance have been elucidated. Mechanisms of resistance include the transference of genetic material either through conjugation (involving direct contact between microorganisms), or indirectly through transduction (involving bacteriophages). In addition to this "infectious" drug resistance, genetic mutations which permit the utilization of new metabolic pathways, and the production of enzymes which can inactivate the antimicrobic have been described. One particularly complex problem has been the ability of many Enterobacteriaceae to develop resistance to multiple antimicrobials simultaneously. The possible effect of such an occurrence is illustrated by the recent epidemic of multiply resistant Salmonella typhi in Mexico. Because the typhoid bacilli shared an identical resistance pattern to an epidemic Shigella dysenteriae type 1 the in vivo interspecies transmission of resistance has been postulated. Understanding the various mechanisms of resistance development should allow more rational use of antimicrobial agents.