The prevalence and clinical features of multi-drug resistant Salmonella typhi infections in Baluchistan, Pakistan

How multidrug resistance in typhoid fever affects treatment options

Salmonella enterica serotype Typhi (S. Typhi) is an enteric pathogen that causes typhoid fever. The infection can be severe, with significant morbidity and mortality, requiring antimicrobial therapy. Cases of S. Typhi infection in the United States and other developed countries are often associated with travel to endemic regions. The empirical use of first-line drugs for therapy, including ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole, has resulted in transmissible multidrug resistance. With the global increase in multidrug-resistant S. Typhi, use of ciprofloxacin, with excellent oral absorption, few side effects, and cost-effectiveness, has become popular for treatment. However, decreased ciprofloxacin susceptibility due to point mutations in the S. Typhi genes gyrA and/or parC has caused treatment failures, necessitating alternative therapeutic options. S. Typhi is typically genetically homogenous, with phylogenetic and epidemiological studies showing that identical clones and diverse S. Typhi types often coexist in the same geographic region. Studies investigating point mutations have demonstrated that selective pressure from empirical use of first-line drugs and fluoroquinolones has led to the global emergence of haplotype H-58. Antibiotic resistance is subject to high selective pressure in S. Typhi and thus demands careful use of antimicrobials.

In vitro phytochemical, antibacterial, and antifungal activities of leaf, stem, and root extracts of Adiantum capillus veneris

Adiantum capillus veneris is a medicinally essential plant used for the treatment of diverse infectious diseases. The study of phytochemical and antimicrobial activities of the plant extracts against multidrug-resistant (MDR) bacteria and medically important fungi is of immense significance. Extracts from the leaves, stems, and roots of Adiantum capillus veneris were extracted with water, methanol, ethanol, ethyl acetate, and hexane and screened for their antimicrobial activity against ten MDR bacterial strains and five fungal strains isolated from clinical and water samples. Ash, moisture, and extractive values were determined according to standard protocols. FTIR (Fourier transform infrared Spectroscopy) studies were performed on different phytochemicals isolated from the extracts of Adiantum capillus Veneris. Phytochemical analysis showed the presence of flavonoids, alkaloids, tannins, saponins, cardiac glycosides, terpenoids, steroids, and reducing sugars. Water, methanol, and ethanol extracts of leaves, stems, and roots showed significant antibacterial and antifungal activities against most of the MDR bacterial and fungal strains. This study concluded that extracts of Adiantum capillus veneris have valuable phytochemicals and significant activities against most of the MDR bacterial strains and medically important fungal strains.

Increasing antimicrobial resistance and narrowing therapeutics in typhoidal salmonellae

Multidrug-resistant typhoid fever (MDRTF) is a major public health problem in developing countries and is an emerging problem in the developed world. Because of the difficulties in preventing typhoid by public health measures or immunization in developing countries, great reliance is placed on antimicrobial chemotherapy. The treatment should commence as soon as the clinical diagnosis is made rather than after the results of antimicrobial susceptibility tests but the existence of MDRTF poses a serious clinical dilemma in the selection of empiric antimicrobial therapy. With the widespread emergence and spread of strains resistant to chloramphenicol, ampicillin and trimethoprim, ciprofloxacin became the drug of choice for the treatment of typhoid fever. However, of late the efficacy of fluoroquinolones too has been questioned, mainly due to increasing reports of increasing defervescence time and poor patient response. This indicates that the organism has begun to develop resistance to fluoroquinolones, and is corroborated by a steady increase in Minimum Inhibitory Concentration (MIC) of ciprofloxacin. The therapeutics of ciprofloxacin-resistant enteric fever narrows down to third- and fourth-generation cephalosporins and azithromycin. However, the emergence of extended-spectrum b-lactamases (ESBLs) in typhoidal Salmonellae poses a new challenge and would greatly limit the therapeutic options leaving only tigecycline and carbepenems as secondary antimicrobial drugs. This increasing resistance is alarming and emphasizes the need of effective preventive measures to control typhoid and to limit the unnecessary use of antibiotics.

Part I. Analysis of data gaps pertaining to Salmonella enterica serotype Typhi infections in low and medium human development index countries, 1984-2005

There are only 10 contemporary, population-based studies of typhoid fever that evaluate disease incidence using blood culture for confirmation of cases. Reported incidence ranged from 13 to 976/100 000 persons per year. These studies are likely to have been done preferentially in high- incidence sites which makes generalization of data difficult. Only five of these studies reported mortality. Of these the median (range) mortality was 0% (0-1.8%). Since study conditions usually involved enhanced clinical management of patients and the studies were not designed to evaluate mortality as an outcome, their usefulness for generalizing case-fatality rates is uncertain. No contemporary population-based studies reported rates of complications. Hospital-based typhoid fever studies reported median (range) complication rates of 2.8% (0.6-4.9%) for intestinal perforation and case-fatality rates of 2.0% (0-14.8%). Rates of complications other than intestinal perforation were not reported in contemporary hospital-based studies. Hospital-based studies capture information on the most severe illnesses among persons who have access to health-care services limiting their generalizability. Only two studies have informed the current understanding of typhoid fever age distribution curves. Extrapolation from population-based studies suggests that most typhoid fever occurs among young children in Asia. To reduce gaps in the current understanding of typhoid fever incidence, complications, and case-fatality rate, large population-based studies using blood culture confirmation of cases are needed in representative sites, especially in low and medium human development index countries outside Asia.

Multidrug-resistant Salmonella enterica serovar paratyphi A harbors IncHI1 plasmids similar to those found in serovar typhi

Salmonella enterica serovars Typhi and Paratyphi A cause systemic infections in humans which are referred to as enteric fever. Multidrug-resistant (MDR) serovar Typhi isolates emerged in the 1980s, and in recent years MDR serovar Paratyphi A infections have become established as a significant problem across Asia. MDR in serovar Typhi is almost invariably associated with IncHI1 plasmids, but the genetic basis of MDR in serovar Paratyphi A has remained predominantly undefined. The DNA sequence of an IncHI1 plasmid, pAKU_1, encoding MDR in a serovar Paratyphi A strain has been determined. Significantly, this plasmid shares a common IncHI1-associated DNA backbone with the serovar Typhi plasmid pHCM1 and an S. enterica serovar Typhimurium plasmid pR27. Plasmids pAKU_1 and pHCM1 share 14 antibiotic resistance genes encoded within similar mobile elements, which appear to form a 24-kb composite transposon that has transferred as a single unit into different positions into their IncHI1 backbones. Thus, these plasmids have acquired similar antibiotic resistance genes independently via the horizontal transfer of mobile DNA elements. Furthermore, two IncHI1 plasmids from a Vietnamese isolate of serovar Typhi were found to contain features of the backbone sequence of pAKU_1 rather than pHCM1, with the composite transposon inserted in the same location as in the pAKU_1 sequence. Our data show that these serovar Typhi and Paratyphi A IncHI1 plasmids share highly conserved core DNA and have acquired similar mobile elements encoding antibiotic resistance genes in past decades.

Antibiogram pattern and seasonality of Salmonella serotypes in a North Indian tertiary care hospital

The antibiogram pattern and seasonal distribution of Salmonella serotypes were analysed retrospectively over a 6-year period from January 1999 to December 2004. Blood cultures received in the Bacteriology Laboratory were processed by standard procedures and the Salmonella spp. isolates were identified with specific antisera and standard biochemical tests. Antimicrobial susceptibility testing was carried out by a standard disc diffusion method and the minimum inhibitory concentration (MIC) of ciprofloxacin for 332 representative Salmonella isolates was determined by E test. Salmonella Typhi (75.7%) was the predominant serotype among 830 Salmonella spp. isolated during the study period followed by S. Paratyphi A (23.8%). The maximum number of enteric fever cases occurred during April-June (dry season) followed by July-September (monsoon season). There was a decrease in multidrug-resistant (MDR) S. Typhi, but MDR S. Paratyphi A isolates increased. There was also a dramatic increase in nalidixic acid-resistant isolates. All isolates were susceptible to third-generation cephalosporins and ciprofloxacin except one S. Typhi strain which demonstrated high-level ciprofloxacin resistance with a MIC of 16 mug/ml. A knowledge of the seasonal distribution and antibiotic resistance pattern of Salmonella in a particular geographical region is helpful in the delineation of appropriate control measures required for prevention of enteric fever.

Mechanism of therapeutic effectiveness of cefixime against typhoid fever

beta-Lactams have been considered ineffective against organisms growing inside mammalian cells because of their poor penetration into cells. However, cefixime has been shown to be clinically effective against typhoid fever. The probable mechanism of therapeutic effectiveness of cefixime against typhoid fever was investigated using Salmonella enterica serovar Typhimurium instead of S. enterica serovar Typhi both in a cellular and in a mouse infection model. Cefixime was able to inhibit the growth of serovar Typhimurium inhabiting monocyte-derived THP-1 cells. Elongation of serovar Typhimurium in THP-1 cells was observed microscopically. Apparent morphological changes of serovar Typhimurium in THP-1 cells were also observed by electron microscopy. The concentration of cefixime inside THP-1 cells was almost half (46 to 48%) of the concentration outside the cells when serovar Typhimurium coexisted in the solution. The length of time after oral dosing (8 mg/kg) that cefixime was present-calculated from levels in serum-at a concentration above the MIC at which 90% of the serovar Typhi organisms inside human cells were inhibited was presumed to be more than 12 h. Cefixime also showed excellent activity in the mouse systemic and oral infection models based on infections caused by serovar Typhimurium. It is concluded that a fair amount of cefixime can enter mammalian cells and inhibit the growth of bacteria inside cells when the bacteria are sensitive enough to cefixime, as are serovars Typhimurium and Typhi.

Clinical and bacteriological profiles of patients with typhoid fever treated during 1975-1998 in the Tokyo Metropolitan Komagome Hospital

Patients with typhoid fever presenting to the Tokyo Metropolitan Komagome Hospital during the period 1975-1998 were retrospectively investigated. All cases were diagnosed by a positive culture for Salmonella typhi in either of their clinical specimens. Of the total number of 130 patients, 57% contracted the disease abroad; this population increased in later years as the total numbers of cases decreased. The period from disease onset to diagnosis averaged 14 days with 20% of the cases requiring over three weeks to establish a diagnosis. As for symptomatology relative bradycardia was seen in less than half of the cases, and rose spots or splenomegaly in less than one third. A positive blood culture was the most frequent test establishing the diagnosis followed by a positive stool culture. Intestinal bleeding was recognized in as many as 35 cases (27%) and even intestinal perforation occurred in two cases (1.5%). Chloramphenicol was most commonly employed during the early study period, however, during the late period it was replaced by fluoroquinolones. The clinical cure rate was 98% with regimens that include fluoroquinolones/quinolone; however it was 87% with the other antimicrobial regimens. Bacteriological relapse occurred in 25% of the non-fluoroquinolone group while only in 2.0% in the fluoroquinolone/quinolone group. Four strains of Salmonella typhi that were multi-resistant to chloramphenicol, ampicillin and cotrimoxazole were isolated in travelers from Asia. Early diagnosis by appropriate bacteriological examination regardless of classical symptomatology should be stressed and the use of fluoroquinolones is warranted in the treatment of typhoid fever.

Antibacterial activity of cefixime against Salmonella typhi and applicability of Etest

Recent clinical studies have shown the excellent efficacy of cefixime for the treatment of typhoid fever. In this study, the in vitro antibacterial activity of various antibiotics including cefixime against 73 clinical isolates of Salmonella typhi from a variety of sources was evaluated by the conventional agar-dilution method and Etest. Eighteen strains of these 73 isolates were chloramphenicol- and cotrimoxazole- (sulfamethoxazole-trimethoprim) resistant, and 12 of these 18 strains were also resistant to amoxicillin because of beta-lactamase production. Cefixime showed excellent activity against all 73 strains with an MIC90 value of 0.25 &mgr;g/ml. Reflecting its high beta-lactamase stability, cefixime also had excellent activity against beta-lactamase-producing amoxicillin-resistant strains. Antibacterial activity of cefixime was comparable to ceftriaxone, ofloxacin, and ciprofloxacin, which are often used for the treatment of typhoid fever. The MIC values obtained from the Etest correlated well with the results of the conventional agar-dilution method, suggesting the usefulness of the Etest as a new easy MIC determination method. The microbiological results supplement the previous clinical data, which showed that oral cefixime provides a safe and effective alternative for the treatment of typhoid fever, even in cases of multidrug-resistant S. typhi.