- Volume 60, Issue 5, 2011

Heritable hypermutation in bacteria is mainly due to alterations in the methyl-directed mismatch repair (MMR) system. MMR-deficient strains have been described from several bacterial species, and all of the strains exhibit increased mutation frequency and recombination, which are important mechanisms for acquired drug resistance in bacteria. Antibiotics select for drug-resistant strains and refine resistance determinants on plasmids, thus stimulating DNA recombination via the MMR system. Antibiotics can also act as indirect promoters of antibiotic resistance by inducing the SOS system and certain error-prone DNA polymerases. These alterations have clinical consequences in that efficacious treatment of bacterial infections requires high doses of antibiotics and/or a combination of different classes of antimicrobial agents. There are currently few new drugs with low endogenous resistance potential, and the development of such drugs merits further research.

We investigated the population structures of faecal Escherichia coli in 30 healthy young adults (13 males and 17 females) aged between 20 and 45 years and 29 elderly adults (14 females and 15 males) aged between 65 and 77 years. In all, 1566 strains were typed with the PhPlate system and grouped into biochemical phenotypes (BPTs). Strains with shared BPTs were further typed using randomly amplified polymorphic DNA analysis. Forty-four per cent of the strains were shared between two or more age and gender groups. Elders had a significantly higher (P<0.001) number of BPTs (mean±standard error 3.3±0.27) than younger groups (1.82±0.27). Phylogenetic affiliation and virulence-associated genes (VAGs) of the strains showed that more than 80 % of the strains belonging to dominant types belonged to phylogroups B2 and D. Amongst dominant BPTs, phylogenetic group A was significantly associated with females (P<0.0001), and elders were more likely to carry group D (P<0.0124). Elderly males had a higher prevalence of VAGs than young males (P<0.0001) and young females (P<0.0005). We conclude that there is a lower prevalence of E. coli with uropathogenic properties in healthy young adults than in elders.

PPE37 is a member of the Mycobacterium tuberculosis proline-proline-glutamic acid (PPE) multigene family. Its expression is upregulated in bacteria that are phagocytosed by macrophages and is enhanced even more in bacteria isolated from the lungs of infected mice. This raises the possibility that PPE37 may play a role in the virulence of M. tuberculosis and led to this investigation of the function of PPE37. Recombinant bacterial strains, one expressing the M. tuberculosis PPE37 protein (Ms_ppe37) and another harbouring the vector alone (Ms_vec) were generated from the non-pathogenic Mycobacterium smegmatis. These bacterial strains were used to infect peritoneal exudate and bone marrow-derived macrophages. It was found that, despite the comparable intracellular survival between the two recombinant M. smegmatis strains, Ms_ppe37 induced a significantly lower level of tumour necrosis factor alpha and interleukin 6 in the infected macrophages compared with Ms_vec. Western blot analyses revealed that the activation levels of nuclear factor kappa B, mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase and MAPK/p38 were lower in macrophages infected with Ms_ppe37 than in macrophages infected with Ms_vec. These results suggest that PPE37 may have a potential role in interfering with the pro-inflammatory cytokine response of infected macrophages.

Transfusion-associated bacterial sepsis is the most common microbiological risk of transfusion and is caused mostly by platelet concentrates (PCs). The most frequently identified bacterial contaminants of PCs are coagulase-negative staphylococci (CNS). In order to learn more about the distribution, source and risk of the CNS that are involved in bacterial contamination of PCs, CNS strains isolated during platelet screening were collected and characterized to the species level with three different methods: 16S rRNA and sodA gene sequencing, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and amplified fragment length polymorphism (AFLP) analysis. AFLP analysis was also used for the typing of the CNS strains. A total of 83 CNS strains were analysed by sequencing and 8 different CNS species were identified, with Staphylococcus epidermidis being the predominant species. MALDI-TOF MS and AFLP analysis confirmed these results to a large extent. However, MALDI_TOF MS could not identify all strains to the species level and AFLP analysis revealed an additional, likely novel, CNS species. The species identified are mainly recognized as being part of the normal skin flora. Typing of the CNS strains by AFLP analysis showed that there was not a unique strain which is significantly more often present during bacterial contamination of PCs.

The incidence of carbapenem-resistant Acinetobacter baumannii infection is increasing, which might be associated with high morbidity and mortality among critically ill patients with limited therapeutic options. This study was conducted to evaluate the clinical and microbiological features of carbapenem-resistant A. baumannii bacteraemia. The medical records of 28 adult patients with this bacteraemia admitted to Korea University Guro Hospital, from January 2005 through December 2010, were reviewed. Using the 28 bloodstream isolates, we intended to detect genes encoding carbapenemases, and investigate the inoculum effect on each of the antimicrobial agents rifampicin, imipenem, colistin and tigecycline. With one blood isolate from a patient with pneumonia, rifampicin-inducible resistance was examined using the experimental mouse pneumonia model. Out of 28 carbapenem-resistant A. baumannii bloodstream infections (BIs), the most common primary focus was the central venous catheter (35.7 %) and then the lung (32.1 %). The 30 day overall mortality was 53.6 %; in most cases (80 %) the patients died within 10 days after the onset of the bacteraemia. By univariate analysis, inappropriate antimicrobial therapy (73.3 vs 30.8 %, P = 0.02), mechanical ventilation (53.3 vs 15.4 %, P = 0.04) and a high Pitt bacteraemia score (4.9±1.9 vs 2.2±1.2, P<0.01) were statistically significant risk factors for mortality, while only a high Pitt bacteraemia score (odds ratio 2.6; 95 % confidence interval 1.1–6.5) was independently associated with 30 day mortality by multivariate analysis. All 28 isolates had the bla OXA-51-like gene with upstream ISAbaI, 2 of which additionally had the bla OXA-58-like gene and the bla OXA-23-like gene. Inoculum effect and rifampicin inducible resistance were not detected. Considering the rapid progression to death in carbapenem-resistant A. baumannii BIs, early empirical antibiotic therapy would be warranted based on the local microbiological data in each hospital.

A retrospective study was performed on case reports of Pneumocystis pneumonia (PCP) from 1959 to 2009 in mainland China. The epidemiological characteristics of PCP over half a century were investigated over two time spans. The first was from 1959, when the first incidence of PCP was reported, to 1984, before the emergence of AIDS in mainland China. The second was from 1985, when the first AIDS case was reported in mainland China, to the end of 2009. A total of 2351 PCP cases were reported during these two time spans, covering a 51-year period. Only seven PCP cases were reported during the first time span. Six were diagnosed by autopsy, accordingly without treatment, whilst the other was diagnosed by open lung biopsy in a living patient who eventually recovered following treatment with sulfadiazine and pyrimethamine. The other 2344 PCP cases were reported during the second time span (1985–2009) from 21 provinces, four municipalities and three autonomous regions. Among the 2344 PCP cases, 70.22 % (1646/2344) were identified together with human immunodeficiency virus (HIV) infection or were in AIDS patients. The remaining 698 non-HIV-infected patients had undergone organ transplantation, had other underlying diseases such as malignancy or hypoimmunity, or had undetermined diagnosis. The results of statistical analysis indicated that AIDS was the most common underlying disease of PCP for patients <1 year and >14 years. For patients aged between 1 and 14 years, haematological malignancy was the most common underlying disease. The trend of the underlying diseases changed with time, showing that the number of PCP patients afflicted by HIV/AIDS increased dramatically, reaching almost threefold during the most recent 5 years compared with the level of the previous 10 years. The number of patients undergoing organ transplantation or with other underlying diseases rose constantly, but the number of malignancies tended to decline from 1995–2004 to 2005–2009. During the second time span (1995–2009), most of the patients (97.61 %) were diagnosed alive and only 56 cases (2.39 %) were identified by autopsy. The mortality of PCP patients treated with anti-Pneumocystis drugs was 14.61 % for those with HIV/AIDS and 15.84 % for those without HIV/AIDS. For the PCP patients without anti-Pneumocystis treatment, all (100 %) of the HIV/AIDS-associated PCP patients died, whilst 13.79 % (4/29) of non-HIV-infected PCP patients survived. These data from epidemiological investigation of PCP in China over a period of half a century may provide useful information for prevention and the development of treatment of PCP.

To determine the association of clinical characteristics with Cryptosporidium types and subtypes, faecal specimens from 2548 children with diarrhoea were screened by microscopy for Cryptosporidium spp., and positive specimens were genotyped and subtyped by PCR-RFLP. A total of 87 of the 2548 children (3.4 %) had cryptosporidial diarrhoea by microscopy and the majority (41.4 %) of the infected children were in the 4–8-year-old age group. Molecular characterization of the 83 children studied further (4 had mixed infections and were not subtyped) showed that Cryptosporidium parvum was the most commonly identified species (73.5 %) and consisted of three subtypes: IIa and IId were the most common (80.3 %), followed by IIc. Twenty-two (26.5 %) of the children had Cryptosporidium hominis and showed three subtypes: Id was the most common (54.5 %), followed by Ia (36.4 %) and Ie. Associated clinical manifestations varied between C. parvum and C. hominis. Diarrhoea associated with subtype Id, the most commonly identified C. hominis subtype, was more severe than that associated with other subtypes. In conclusion, this study confirmed a very different Cryptosporidium genotype and subtype distribution compared with other tropical countries among Kuwaiti children with diarrhoea, with a predominance of C. parvum IIa and IId. In addition, subtype Id of C. hominis was associated with more diverse and severe clinical manifestations in infected children, suggesting that parasite genetics may play an important role in the clinical manifestations of human cryptosporidiosis.

Sheep have been proposed as a source of human verocytotoxigenic Escherichia coli infection on a number of occasions but few prevalence studies have focused on identifying rates of carriage of these pathogens in this species. The purpose of this work was to establish the frequency of excretion of E. coli of serogroups O157, O26, O103, O111 and O145 in sheep presented for slaughter in Scotland and to examine their carriage of known virulence determinants. The study involved microbiological isolation of E. coli from 1082 sheep presented for slaughter in four Scottish abattoirs between July 2005 and June 2006. Using faecal enrichment and immunomagnetic separation, the isolation rate from these samples was 3.4 % for E. coli serogroup O157, 5.2 % for E. coli serogroup O26, 2.3 % for E. coli serogroup O103 and 0.1 % for E. coli serogroup O145. E. coli O111 was not isolated. In the last month of testing, which coincided with sorbitol-fermenting E. coli O157 (SFO157) cases in children in Scotland, all 83 recta received were screened and tested negative for SFO157 strains. The study found no verocytotoxin-positive strains amongst the E. coli serogroup O103 or O145 isolates. Verocytotoxin-positive strains were identified amongst isolates of E. coli serotypes O157 : H7 and O26 : H11. E. coli O157 : H7 was not isolated from samples collected between January and March, a statistically significant drop (P<0.001) in mean shedding relative to other months. There was evidence (P = 0.003) of higher shedding of O157 in adults and hoggs than in lambs. E. coli O26 : H11 was isolated throughout the year, with a statistically significant peak in shedding in the third quarter (P = 0.003). The results showed that sheep presented for slaughter in Scotland may carry strains of E. coli, particularly of serogroups O157 and O26, which can be presumed to have potential to cause human infection. They did not support a hypothesis that human cases of E. coli O157 : H7 are higher in any particular Scottish region as a direct consequence of a higher rate of faecal carriage in sheep in that region.

Larvae of Galleria mellonella (Greater Wax Moth) have been shown to be susceptible to Campylobacter jejuni infection and our study characterizes this infection model. Following infection with C. jejuni human isolates, bacteria were visible in the haemocoel and gut of challenged larvae, and there was extensive damage to the gut. Bacteria were found in the extracellular and cell-associated fraction in the haemocoel, and it was shown that C. jejuni can survive in insect cells. Finally, we have used the model to screen a further 67 C. jejuni isolates belonging to different MLST types. Isolates belonging to ST257 were the most virulent in the Galleria model, whereas those belonging to ST21 were the least virulent.

Herein, we report a case of endogenous endophthalmitis caused by Enterococcus casseliflavus. The organism was sensitive to gentamicin, vancomycin and chloramphenicol and resistant to cefazolin, ofloxacin, gatifloxacin and ciprofloxacin. The patient was successfully treated with vitrectomy and sensitivity-based intravitreal vancomycin.