Association between cyclohexane resistance in Salmonella of different serovars and increased resistance to multiple antibiotics, disinfectants and dyes

A panel of 388 salmonellas of animal and human origin, comprising 35 serotypes, was tested for resistance to cyclohexane and to a range of antibiotics, disinfectants and dyes. Cyclohexane resistance was detected in 41 isolates (10.6%): these comprised members of the serovars Binza (1 of 15), Dublin (1 of 24), Enteritidis (1 of 61), Fischerkietz (4 of 5), Livingstone (9 of 11), Montevideo (1 of 32), Newport (4 of 23), Saint-paul (1 of 3), Senftenberg (10 of 24) and Typhimurium (9 of 93). Most (39 of 41) of the cyclohexane-resistant isolates were from poultry. Statistical analysis showed that the cyclohexane-resistant strains were significantly more resistant than the cyclohexane-susceptible strains to ampicillin, chloramphenicol, ciprofloxacin, erythromycin, nalidixic acid, tetracycline, trimethoprim, cetrimide and triclosan. The multiresistance patterns seen were typical of those caused by efflux pumps, such as AcrAB. The emergence of such resistance may play an important role in the overall antibiotic resistance picture of Salmonella, with particular effect on ciprofloxacin.     

Cloacal Lactobacillus isolates from broilers show high prevalence of resistance towards macrolide and lincosamide antibiotics.

Eighty-seven Lactobacillus strains isolated from cloacal swabs of broiler chickens derived from 20 different farms in Belgium were identified to species level and tested for susceptibility to macrolide and lincosamide antibiotics. Five different Lactobacillus species were identified as being predominantly present in the cloacae of broilers: Lactobacillus crispatus, Lactobacillus salivarius subsp. salivarius, Lactobacillus amylovorus, Lactobacillus gallinarum and Lactobacillu sreuteri. Acquired resistance prevalence to macrolides and lincosamides was very high in the investigated lactobacilli: 89% of the strains were resistant to either or both lincosamide and macrolide class antibiotics. The vast majority of these resistant strains (96%) displayed constitutive resistance. More than one-half of the macrolide and/or lincosamide resistant strains carried an erm(B), erm(C), mef(A), lnu(A) gene or a combination of these genes.     

Lymphocyte resistance to cold anabiosis of different degree

We studied the resistance of human blood T and B lymphocytes to cold anabiosis (−20°C, −40°C, and −80°C) of different duration. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 8, pp. 142–144, August, 2006     

Natural resistance to Salmonella typhimurium in different inbred mouse strains.

The mechanisms of natural resistance to intravenous challenge with Salmonella typhimurium C5 are complex. LD50 determinations showed inbred mouse strains of low, intermediate and high natural resistance, with BALB/c and B10 strains the most susceptible, A/J the most resistant. Delayed (footpad) hypersensitivity was not by itself a measure of natural resistance. Resistant mouse strains sensitized either s.c. or i.v. with an attenuated salmonella strain showed positive 48 h footpad reactions when tested 8 days later with a salmonella extract, but three very susceptible strains also showed positive reactions. Determinations of the in vivo net growth rate of salmonellae in the liver and spleen during the first phase of the infection (up to day 4) arrange the different mouse strains into two categories of fast and slow net growth rate. All fast net growth rate strains are susceptible, but not all slow net growth rate strains are resistant. Besides slow net growth rate, resistance requires the participation of other factors appearing in the second phase of the infection (towards the end of the first week) probably involving the cellular immune response, which halts further bacterial growth. Not all slow net growth rate strains are equally capable of suppressing bacterial growth in this second phase. The host mechanism determining slow net growth rate is inherited as a dominant trait, and appears to be operating before the main cellular immune response. The influence of this mechanism on net growth rate is reflected in the time to death following a given dose of salmonellae. The present results suggest that overall resistance to salmonellae is polygenic, but that the mechanism responsible for the differences in early net growth rate is less complex.     

Pneumococcal resistance to antibiotics.

The geographic distribution of pneumococci resistant to one or more of the antibiotics penicillin, erythromycin, trimethoprim-sulfamethoxazole, and tetracycline appears to be expanding, and there exist foci of resistance to chloramphenicol and rifampin. Multiply resistant pneumococci are being encountered more commonly and are more often community acquired. Factors associated with infection caused by resistant pneumococci include young age, duration of hospitalization, infection with a pneumococcus of serogroup 6, 19, or 23 or serotype 14, and exposure to antibiotics to which the strain is resistant. At present, the most useful drugs for the management of resistant pneumococcal infections are cefotaxime, ceftriaxone, vancomycin, and rifampin. If the strains are susceptible, chloramphenicol may be useful as an alternative, less expensive agent. Appropriate interventions for the control of resistant pneumococcal outbreaks include investigation of the prevalence of resistant strains, isolation of patients, possible treatment of carriers, and reduction of usage of antibiotics to which the strain is resistant. The molecular mechanisms of penicillin resistance are related to the structure and function of penicillin-binding proteins, and the mechanisms of resistance to other agents involved in multiple resistance are being elucidated. Recognition is increasing of the standard screening procedure for penicillin resistance, using a 1-microgram oxacillin disk.     

Genetic control of resistance to Salmonella typhimurium infection in high and low antibody responder mice.

Mice selected by Biozzi for high and low responses to sheep erythrocytes were investigated for resistance to subcutaneous Salmonella typhimurium infection. The resistance was measured by LD50 values, viable bacterial counts in liver and spleen at 10 days, and the kinetics of infection over 4 weeks. High responder mice were susceptible to S. typhimurium injected subcutaneously (LD50 less than 10) and low line resistant (LD50 3 x 10(6)). Control of natural resistance to S. typhimurium in inbred mice is primarily by a single gene. Ity, on chromosome 1. Results with hybrid generations of Biozzi mice with either BALB/c (sensitive) or CBA (resistant) inbred mice indicated additional genetic control of resistance in Biozzi mice. Analysis of resistance data of backcrosses of (high x low)F1 with either parental strain showed this genetic control to be at least one other gene in the Biozzi mice, not linked to Ity. The antibody responses in the hybrid generations and inbred and Biozzi parental strains were tested by haemagglutination assays and ELISA. After specific stimulation of the mice there was an inverse relationship between resistance to S. typhimurium and antibody levels.     

Innate resistance of mice to Salmonella typhi infection.

The basis for the natural resistance of mice to Salmonella typhi was examined. In contrast to Salmonella typhimurium, the virulence of S. typhi for mice was independent of the mouse strain and was not affected by inactivation of murine macrophages with silica. However, mice were more susceptible to S. typhi when given iron alone or iron and an iron chelator. The results suggest that the failure of S. typhi to undergo net growth in murine tissues reflects an inability of the bacterium to multiply rather than rapid killing by resident macrophages.     

Dioxidine induces bacterial resistance to antibiotics

The capability of the dioxidine drug to cause bacterial resistance to antibiotics was studied. The study was performed with the use of a bioluminescent test and the recombinant E. coli strains MG 1655 (pSoxS-lux), MG1655 (pKatG-lux), MG1655 (pRecA-lux), and MG1655 (pColD-lux). The strains harbored plasmids with the operon luxCDABE from the photobacteria Photorhabdus luminescens under control of the corresponding E. coli stress-inducible promoters. The mutation frequency of the stable mutants was found by conventional methods for nonpathogenic and opportunistic strains of E. coli, Bacillus amyloliquefaciens, and Klebsiella pneumoniae. Dioxidine was shown to induce the promoters PrecA and Pcda in E. coli MG1655, which suggests the induction of the SOS-response in bacterial cells. The Pcda induction was higher than with PrecA. The value of the induction coefficient was highest if the dioxidine concentration was 2.25 × 10^–5 M. Moreover, this drug enhanced the induction of the SoxS and KatG promoters responding to the superoxide anion radical and hydrogen peroxide, which suggests possible participation of oxidative mechanisms in dioxidine DNA damage. The maximal value of the induction coefficient was also observed under conditions of 2.25 × 10^–5 M. Dioxidine can induce mutations leading to antibiotic resistance in all bacterial strains studied. An increase in mutation frequency was observed for rifampicin (twofold), ciprofloxacin (sixfold), and azithromycin (fourfold). These data show the necessity for an antibiogram for every patient who is taking or has taken dioxidine.     

Dielectrophoretic assay of bacterial resistance to antibiotics

The dielectrophoretic collection spectra of antibiotic-sensitive and antibiotic-resistant strains of Staphylococcus epidermidis have been determined. These indicate that in the absence of antibiotic treatment there is a strong similarity between the dielectric properties of sensitive and resistant strains, and that there is a significant difference between the sensitive strains before and after treatment with the antibiotic streptomycin after 24 h exposure. This method offers possibilities for the assessment of bacterial resistance to antibiotics.     

Current aspects of bacterial resistance to antibiotics

New aspects of the evolution of bacterial antibiotic resistance are discussed. Dissemination of antibiotic resistance appears to be unlimited since resistance genes from Gram-positive cocci have been detected in Gram negative bacteria. This suggests the occurrence of heterogramic genetic transfers between these phylogenetically distinct organisms. New characters of resistance to beta-lactam antibiotics in enterobacteria result from the apparition of mutant of the TEM-1 and TEM-2 penicillinases. Mutations that confer the capacity to hydrolyze the third generation cephalosporins are located in the active site of the enzymes.     

Increasing prevalence of antimicrobial resistance in Streptococcus pneumoniae in Kuwait: implications for therapy

From 2001 to 2004, 824 consecutive Streptococcus pneumoniae isolates obtained from all the teaching hospitals and primary-care centers serving all of Kuwait were studied for their susceptibility to a number of antibiotics. Of these, 514 (63%) were resistant to penicillin, 55% of which were of intermediate resistance, with a minimum inhibitory concentration (MIC) of 0.16-1 microg/ml, and 8% were of full resistance (MIC > or =2 microg/ml). The prevalence of penicillin resistance was significantly higher among the eye isolates than the rest of the isolates combined. Resistance across all classes of antibiotics was more common with the isolates from blood and cerebrospinal fluid (CSF). Decreased susceptibility to ceftriaxone, cefotaxime, imipenem, meropenem, erythromycin, and cotrimoxazole was observed in 15%, 12.8%, 10.2%, 8.6%, 42%, and 69% of isolates, respectively. Multidrug-resistant S. pneumoniae was isolated mostly from invasive diseases. There has been a remarkable increase in the prevalence of drug-resistant S. pneumoniae isolates in Kuwait over the past 20 years, and Kuwait has thus joined the league of hyperendemic countries for penicillin-resistant S. pneumoniae (PRSP). It is also conceivable that Kuwait, with a large expatriate population of workers, may serve as a focal point for further dissemination of resistant clones to the rest of the world. These data are unique because they are representative of the whole Kuwaiti population.     

High prevalence of azithromycin resistance to Treponema pallidum in geographically different areas in China

Treatment with effective antibiotics is one important strategy for syphilis control in China. This study aimed to evaluate the prevalence of azithromycin resistance to T. pallidum in China. A cross-sectional study was conducted among 391 patients with early syphilis recruited from STD clinics in eight cities during October 2008 and October 2011. The swabs were obtained from the moist lesions of the participating patients. A touchdown/nested PCR of the 23S ribosomal RNA (rRNA) gene was performed on DNA samples extracted from these specimens. The presence or absence of the A2058G point mutation, conferring resistance to azithromycin, was determined by restriction enzyme digestion analysis of the PCR amplicon by MboII. Two hundred and eleven patients with primary or secondary syphilis were found to have T. pallidum DNA in their moist lesions by PCR assays. The A2058G mutation was present in 91.9% (194/211, 95% CI, 87.2–95.1%) of these patients, with no significant differences noted between patients from the eastern part (93.8%), southern part (88.6%) and northern part (95.2%) of China (v² = 2.303, p 0.316). Compared with patients who had not taken macrolides in previous years before study entry, the patients who had taken the antibiotics had a significantly higher prevalence of azithromycin resistance (97.0% vs. 62.5%), with an odds ratio of 19.65 (95% CI, 5.77–66.93). It can be concluded that prevalence of azithromycin resistance is substantial in China and consequently that the macrolides should not be used as a treatment option for early or incubating syphilis in China.     

Increasing tinea capitis prevalence in Stockholm reflects immigration.

The aim was to describe the mycological and clinical data in children diagnosed with tinea capitis in a hospital setting in Stockholm. Information concerning demography, symptoms, mycology and treatment were obtained, retrospectively, from medical records of all children up to 15 years of age diagnosed with tinea capitis during two 3-year periods, 1989--1991 and 1999--2001, at the Pediatric Dermatology Unit of the Karolinska Hospital in Stockholm. Between 1989 and 1991, five children were diagnosed with tinea capitis. Between 1999 and 2001, there were 92 children, the vast majority (86%) being of foreign extraction, mostly African (83%). Trichophyton violaceum was the most prevalent pathogen, affecting 68% of the children. Of the anthropophilic infections, 62% were linked to relatives. In 71% of all positive cultures, microscopy was positive. The most common clinical findings were scaling of the scalp (80%), itching (54%) and patches of alopecia (52%). The treatment consisted of the oral antimycotics terbinafine (n = 48) or griseofulvin (n = 49). During the last decade there has been an increase in tinea capitis in Stockholm, most commonly caused by Trichophyton violaceum, corresponding with the increased immigration from Africa. Spread within the family seems to be of importance, and family members are preferably screened in an effort to prevent continued transmission. It is important to bear the diagnosis of tinea capitis in mind, especially as, untreated, some cases can develop permanent alopecia and may also cause further spreading of this infection.     

Spurious sulfamethoxazole-trimethoprim resistance of Salmonella typhi.

Several studies have identified thymidine excess in susceptibility test media as the cause of spurious resistance of various bacteria to sulfamethoxazole-trimethoprim. We document the phenomenon in Salmonella typhi and Salmonella paratyphi-A and demonstrate its occurrence in 3 of 17 (18%) lots of Mueller-Hinton agars now in use in major medical laboratories in Lima, Peru. The findings are particularly significant because sulfamethoxazole-trimethoprim is an important alternative to chloramphenicol or ampicillin for the treatment of typhoid and paratyphoid fevers.     

Mechanisms of resistance of enterococci to beta-lactam antibiotics

Two mechanisms are responsible for resistance of enterococci to beta-lactam antibiotics: alterations of penicillin-binding proteins and production of a beta-lactamase. The latter has been found in a few clinical isolates ofEnterococcus faecalis, whereas the former appears to account for resistance in most strains. A correlation has been established between the amount of a particular penicillin-binding protein which has a low affinity for penicillin and the level of resistance. The higher activity of some penicillins, as compared to cephalosporins, has been related to the relatively higher affinity for these penicillins of the penicillin-binding protein involved in the mechanism of resistance. Alterations in the autolytic enzyme pattern have been associated with the paradoxical response to bactericidal activity of penicillin often exhibited byEnterococcus faecalis clinical isolates.