Development of specific and rapid detection of bacterial pathogens in dairy products by PCR

Virulence Factor Genes and Cytotoxicity of Streptococcus agalactiae Isolated from Bovine Mastitis in Poland

Streptococcus agalactiae can produce a wide variety of virulence factors, including toxins and proteins which facilitate adhesion to and colonization and invasion of the host cells. There are few reports on the characteristics of field isolates from bovine mastitis in Poland. Thus, the aim of this study was to determine the occurrence of types of hemolysis on blood agar, virulence factor genes, and cytotoxicity of S. agalactiae isolates derived from cows with mastitis across Poland. The study included 68 isolates. Virulence genes were tested using standard PCR, and cytotoxicity was determined using methylthiazol tetrazolium (MTT) and lactate dehydrogenase (LDH) tests. Among the tested isolates, 89.7% were β-hemolytic, 8.8% γ-hemolytic, and 1.5% alpha-hemolytic. The only genes detected in all isolates were the cfb, cspA, hylB, and sip genes. Cytotoxicity assessment based on the LDH test revealed that isolates were cytotoxic only to Vero cells. However, according to the results obtained from the MTT test, more than half of the isolates exhibited low cytotoxicity to both SK and Vero cells, whereas the other isolates showed moderate or no cytotoxicity to both cell lines. Our research confirms the prevalence of various virulence genes in S. agalactiae isolated from Polish dairy herds, which have previously been found in isolates recovered from human and animal infections. For the first time, the presence of bac- and scpB-positive isolates of S. agalactiae was determined in Polish dairy cattle, and the cytotoxicity of bovine isolates was assessed. IMPORTANCE We believe that this manuscript is one of the few reports on the characteristics of field S. agalactiae isolates derived from cases of bovine mastitis in cows in Poland in terms of the occurrence of virulence genes and cytotoxicity. For the first time, the presence of bac- and scpB-positive isolates of S. agalactiae was determined in Polish dairy cattle, and the cytotoxicity of bovine isolates was assessed.

Effect of prophylactic vitamin C administration on the efficiency of florfenicol or sulfadiazine-trimethoprim antimicrobial therapy in chickens with staphylococcal arthritis

Septic arthritis (SA) in chickens shows improper response to antibacterial therapy. This study evaluates the effect of prophylactic vitamin C administration on the efficiency of sulfadiazine-trimethoprim (SDT) or florfenicol (FF) in broilers with experimental SA. Broilers (210) were randomly allocated into 7 equal groups: (I) negative control (NC) (normal birds); (II) positive control (PC) arthritic birds by injection of Staphylococcus aureus in tibiotarsal joint at the age of 35 days; (III) vehicle control (injected with sterile medium); (IV) arthritic FF-treated (20 mg/kg/day); (V) arthritic vitamin C + FF-treated (as above + vitamin C at 15 g/100L of D.W. from day 25 of age); (VI) arthritic SDT-treated (35 mg/kg/day); (VII) arthritic vitamin C + SDT-treated. Antibacterial therapy started at day 39 of age and lasted for 5 days. Samplings were performed at the age of 44 and 54 days. A long lasting SA with severe fibrinoheterophilic synovitis and reduced body weights developed in PC broilers as compared to NC group (p < 0.05). Oxidative stress was present at sampling 1. Arthritis was not reflected in IL-6 levels of synovial fluid of PC group. None of the antibacterials resulted in completely successful treatment. Vitamin C did not appreciably improve lameness and arthritis scores, although it decreased lipid peroxidation and improved weights of FF treated-arthritic birds. For SDT-treated birds, vitamin C only ameliorated histopathological changes. In conclusion, except for improving body weight in FF-treated birds, prophylactic administration of vitamin C is not associated with improvements in clinical outcome of antimicrobial therapy of broilers with SA, although it ameliorates oxidative stress and some histopathological changes.

Characterization of Clinical and Carrier Streptococcus agalactiae and Prophage Contribution to the Strain Variability

Streptococcus agalactiae (group B Streptococcus, GBS) represents a leading cause of invasive bacterial infections in newborns and is also responsible for diseases in older and immunocompromised adults. Prophages represent an important factor contributing to the genome plasticity and evolution of new strains. In the present study, prophage content was analyzed in human GBS isolates. Thirty-seven prophages were identified in genomes of 20 representative sequenced strains. On the basis of the sequence comparison, we divided the prophages into eight groups named A–H. This division also corresponded to the clustering of phage integrase, even though several different integration sites were observed in some relative prophages. Next, PCR method was used for detection of the prophages in 123 GBS strains from adult hospitalized patients and from pregnancy screening. At least one prophage was present in 105 isolates (85%). The highest prevalence was observed for prophage group A (71%) and satellite prophage group B (62%). Other groups were detected infrequently (1–6%). Prophage distribution did not differ between clinical and screening strains, but it was unevenly distributed in MLST (multi locus sequence typing) sequence types. High content of full-length and satellite prophages detected in present study implies that prophages could be beneficial for the host bacterium and could contribute to evolution of more adapted strains.

Limit of detection of genomic DNA by conventional PCR for estimating the load of Staphylococcus aureus and Escherichia coli associated with bovine mastitis

Detection of mastitis-associated bacteria can be accomplished by culturing or by molecular techniques. On the other hand, rapid and inexpensive methods to enumerate bacterial load without culturing can be better achieved by molecular methods. Staphylococcus aureus and Escherichia coli are the predominant bacterial pathogens associated with bovine mastitis. Here, we describe the application of conventional PCR for the limit of detection (LOD) of genomic DNA of S. aureus and E. coli based on single-copy genes. The selected genes were thermonuclease (nuc), aureolysin (aur), and staphopain A (scpA) for S. aureus and β-D-glucuronidase A (uidA), cytochrome d oxidase (cyd), and rodA (a gene affecting cell shape and methicillin sensitivity) for E. coli. The LOD was 5.3, 15.9, and 143 pg for aur, nuc, and scpA genes, corresponding to S. aureus genomic copies of 1.75 × 10(3), 5.16 × 10(3), and 4.71 × 10(4), respectively. The LOD was 0.45, 12.3 and 109 pg for uidA, rodA and cyd genes, corresponding to E. coli genome copies of 8.91 × 10(1), 2.43 × 10(3), and 2.16 × 10(4), respectively. Application of uidA and aur PCRs to field strains revealed that as low as approximately 100 genome copies of E. coli and 1000-10,000 copies of S. aureus could be detected. This study is the first to report LOD of genomic DNA using conventional PCR for aur and scpA genes of S. aureus, and rodA and cyd genes of E. coli. The results should be useful for developing assays to assess bacterial load in milk and to determine the load that contributes to subclinical or clinical mastitis.

Characterization of the microbial community in a lotic environment to assess the effect of pollution on nitrifying and potentially pathogenic bacteria

This study aimed to investigate microbes involved in the nitrogen cycle and potentially pathogenic bacteria from urban and rural sites of the São Pedro stream. Water samples were collected from two sites. A seasonal survey of bacterial abundance was conducted. The dissolved nutrient content was analysed. PCR and FISH analysis were performed to identify and quantify microbes involved in the nitrogen cycle and potentially pathogenic bacteria. The seasonal survey revealed that the bacterial abundance was similar along the year on the rural area but varied on the urban site. Higher concentration of dissolved nutrients in the urban area indicated a eutrophic system. Considering the nitrifying microbes, the genus Nitrobacter was found, especially in the urban area, and may act as the principal bacteria in converting nitrite into nitrate at this site. The molecular markers napA, amoA, and nfrA were more accumulated at the urban site, justifying the higher content of nutrients metabolised by these enzymes. Finally, high intensity of amplicons from Enterococcus, Streptococcus, Bacteroides/Prevotella/Porphyromonas, Salmonella, S. aureus, P. aeruginosa and the diarrheagenic lineages of E. coli were observed at the urban site. These results indicate a change in the structure of the microbial community imposed by anthrophic actions. The incidence of pathogenic bacteria in aquatic environments is of particular importance to public health, emphasising the need for sewage treatment to minimise the environmental impacts associated with urbanisation.

Incidence of staphylococci and streptococci during winter in mastitic milk of sahiwal cow and murrah buffaloes

Mastitis is a serious problem in dairy sector and among various aetiological agents, the incidence of staphylococci and streptococci remains high in milking animal. The present study was focused on detection of staphylococci and streptococci in winter season. Milk samples (117) of mastitic animals were tested for presence of staphylococci and streptococci using biochemical and PCR based assays. The testing revealed majority of animals (90.6%) were infected with more than one causative agent. Amongst 117 sample, 109 and 90 comprised of staphylococci and 90 streptococci, respectively. Distribution proportion of S. aureus, S. epidermidis, S. agalactiae, S. uberis and S. dysgalactiae among the mastitic cases was found as 64.9, 7.7, 5.1, 1.7, 48.7, 65.8 and 0.8%, respectively. Streptococci and staphylococci were observed in different combinations and the frequent were S. aureus/S. agalactiae/S. uberis, S. aureus/S. uberis, S. aureus/S. agalactiae and S. agalactiae/S. uberis which were accounted for 23.9, 19.7, 5.9 and 2.6%, respectively. Approximately half of the (52.1%) cases were observed for reoccurrence of mastitis. Reoccurrence of mastitis in winter season among these cases was significantly low as compared to summer (cattle-5 cases; buffaloes-2 cases). In addition, prevalence of S. aureus, S. agalactiae, S. uberis, and S. epidermidis in reoccurring mastitic cases was 73.7, 63.9, 45.9 and 6.6%, respectively. The observations revealed mastitis causing pathogens remains in hidden phase in winter season; however, cannot be neglected. The observation might be helpful in culling or segregation of cows for mastitis reduction programmes.

Detection of Group B Streptococcus in Brazilian pregnant women and antimicrobial susceptibility patterns

Group B Streptococcus (GBS) is still not routinely screened during pregnancy in Brazil, being prophylaxis and empirical treatment based on identification of risk groups. This study aimed to investigate GBS prevalence in Brazilian pregnant women by culture or polymerase chain reaction (PCR) associated to the enrichment culture, and to determine the antimicrobial susceptibility patterns of isolated bacteria, so as to support public health policies and empirical prophylaxis. After an epidemiological survey, vaginal and anorectal specimens were collected from 221 consenting laboring women. Each sample was submitted to enrichment culture and sheep blood agar was used to isolate suggestive GBS. Alternatively, specific PCR was performed from enrichment cultures. Antimicrobial susceptibility patterns were determined for isolated bacteria by agar diffusion method. No risk groups were identified. Considering the culture-based methodology, GBS was detected in 9.5% of the donors. Twenty five bacterial strains were isolated and identified. Through the culture-PCR methodology, GBS was detected in 32.6% specimens. Bacterial resistance was not detected against ampicillin, cephazolin, vancomycin and ciprofloxacin, whereas 22.7% were resistant to erythromycin and 50% were resistant to clindamycin. GBS detection may be improved by the association of PCR and enrichment culture. Considering that colony selection in agar plates may be laboring and technician-dependent, it may not reflect the real prevalence of streptococci. As in Brazil prevention strategies to reduce the GBS associated diseases have not been adopted, prospective studies are needed to anchor public health policies especially considering the regional GBS antimicrobial susceptibility patterns.

Diarrheagenic Escherichia coli strains recovered from urban pigeons (Columba livia) in Brazil and their antimicrobial susceptibility patterns

Urban pigeons (Columba livia) come into close contact with humans and animals, and may contribute to the spread of infectious agents. These may include human pathogens such as diarrheagenic Escherichia coli strains, which are able to survive in pigeon feces, thus creating potential for human exposure and infection. Our objectives were to determine the occurrence of diarrheagenic E. coli strains in fresh feces from urban pigeons and their drug susceptibility patterns. E. coli strains were isolated from 100 fresh feces samples and presumptive phenotypic species identification was carried out, confirmed by amplification of specific 16S ribosomal RNA encoding DNA. Multiplex PCR was performed to characterize pathogenic strains. Drug susceptibility patterns were determined by the agar dilution method. Enteroinvasive E. coli, Shiga toxin-producing E. coli, enteropathogenic E. coli, and enterotoxigenic E. coli were detected at an overall rate of 12.1%. Among the isolated E. coli strains, 62.1% were susceptible to all tested drugs, whereas 37.9% were resistant to at least one of the antimicrobials tested. Amikacin was the less effective drug (36.8% resistance), followed by ampicillin (7.8%). No resistance was detected to gentamicin, ceftriaxone, and ceftazidime and almost all the isolates were susceptible to ampicillin-sulbactam (98.4%), levofloxacin (97.8%), and trimethoprim-sulfamethoxazole (96.1%). Since these pigeons may harbor multidrug-resistant pathogens, their presence in an urban environment could be an important component of infection spread, with impact on public health.

Postnatal development of bacterial population in the gastrointestinal tract of calves

Bacterial 16S rDNA from fecal samples of two calves were amplified by PCR and analyzed by denaturing gradient gel electrophoresis; selected bands were sequenced. Escherichia coli and Bifidobacterium animalis were the initial colonizers, followed by species closely related to the genera Bacteroides, Clostridium and Faecalibacterium. Change of diet was connected with shifts of bacterial population and with the occurrence of many bacterial species that have not been cultured up to now. The diet change corresponded with an alteration in a volatile-fatty-acid concentration in fecal samples.